Symposium : A
Advanced Silicon Materials Research for Electronic and Photovoltaic Applications III
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| Electronic Device Technology : B. Cheng and E. Simoen | ||
| 08:30 | Subsecond thermal processing for advanced electronics and photovoltaics Authors : Wolfgang Skorupa Affiliations : Institute of Ion Beam Physics & Materials Research Helmholtz-Zentrum Dresden-Rossendorf, Germany Resume : This talk reviews the advances that subsecond thermal processing using flash lamps and lasers brings to the processing of the most advanced semiconductor materials, thus enabling the fabrication of novel electronic structures and materials. It will be demonstrated how such developments can translate into important practical applications leading to a wide range of technological benefits.
Recently we could demonstrate that germanium and silicon exhibit superconductivity at ambient pressure. Techniques of the state-of-the-art semiconductor processing as ion implantation and FLA were used to fabricate such material based on a highly doped Ga-rich layer at the surface. Moreover we demonstrated that carrier-mediated ferromagnetism can be reached in manganese-implanted and Laser-annealed Ge.
Regarding photovoltaic applications, we dealt with two aspects: (i) the thermal processing of so-called dirty silicon demonstrating a distinct improvement of the metal diffusion suppression compared to RTP and furnace treatments, and (ii), for the annealing of CIGS layers millisecond annealing leads to better optical output and lower degradation
Whereas all these examples base on solid phase processing the more sophisticated approach of subsecond thermal processing regards on working with the liquid phase at the surface of solid substrates. A very recent example is the controlled formation of III-V nanocrystals (InAs, GaAs) in silicon after ion beam synthesis (Nano Lett. 11 (2011) 2814). | 14 1 |
| 09:00 | Boron pile-up in implanted silicon induced by submicrosecond laser annealing Authors : G. Fisicaro1, K. Huet2, R. Negru2, J. Venturini2, M. Hackenberg3, P. Pichler3-4, and A. La Magna1 Affiliations : 1- CNR IMM, Z.I VIII Strada 5 I -95121 Catania, Italy 2- Excico 13-21 Quai des Gresillons, 92230 Gennevilliers, France 3- Fraunhofer Institute for Integrated Systems and Device Technology, Schottkystrasse 10, 91058 Erlangen, Germany 4- Chair of Electron Devices, University of Erlangen-Nuremberg, Cauerstrasse 6, 91058 Erlangen, Germany Resume : Dopant pile-up mechanism in melting silicon during excimer laser irradiations has been studied. Boron implanted silicon samples have been annealed by means of sub-microsecond laser processes in the melting regime. In the process conditions chosen (in single and multi-pulse configurations) the maximum melt depth is much larger than the implanted B ions projected range. Varying the laser fluence (i.e. the maximum melt depth), dopant redistributed profiles delineated three different regimes: against-gradient, pile-up and no-pile-up regimes. In view of the anomalous silicon properties in liquid phase in a tight temperature range above the melting point, we have developed a model which considers the possibility of two different states governing the dopant diffusion in a tight temperature range around the melting temperature. Therefore B atoms can reside in two different states, one characterized by larger diffusivity than the other, where the temperature in the molten region rules the corresponding concentrations. Atoms in the weakly diffusing state resides in regions where the temperature field lies just above the melting point of Si (~9 K higher that the silicon melting point), whilst atoms in the large diffusivity state are in the remaining liquid regions. The model accurately reproduces boron redistribution and its accumulation at the maximum melt depth, elucidating the dopant evolution mechanism in the silicon melting phase. | 14 2 |
| 09:15 | Defect Engineering for Modern Power Devices Authors : Reinhart Job 1), Johannes Laven 2), Franz-Josef Niedernostheide 2), Hans-Joachim Schulze 2), Holger Schulze 3), Werner Schustereder 3) Affiliations : 1) Muenster University of Applied Sciences, Department of Electrical Engineering, 48565 Steinfurt, Germany 2) Infineon Technologies AG, 81726 München, Germany 3) Infineon Technologies Austria AG, 9500 Villach, Austria Resume : The presentation summarizes our recent investigations concerning hydrogen-related electrically active defect states in high-resistive n-type float-zone (FZ) silicon wafers provided as substrates for high-power devices. Radiation damage was caused by light-ion implantation (H, He). In addition, hydrogen was introduced during post-implantation hydrogen plasma treatments at moderate temperatures. The formation and evolution of hydrogen-related donor states was studied after successively annealing at low thermal budgets. For comparison, just hydrogen implanted and annealed FZ Si was analyzed, too. Hydrogen implantation and subsequent H-plasma exposure causes the formation of excessive donor states in the wafer regions down to the projected ion range Rp of the implanted ions. After 15-min H-plasma exposures, for example, the n-type doping profiles exhibit a maximum at the projected ion range Rp, which can be attributed to the formation of vacancy-hydrogen complexes. Close to the surface, acceptor-like states can be observed, too. In hydrogen implanted samples no acceptor-like states could be observed around Rp, but in helium implanted samples this could happen under certain process conditions. Based on our experimental investigations the formation mechanisms of donor- and acceptor-like defect states and the conversion efficiency of radiation damage into hydrogen related donors will be discussed. | 14 3 |
| 09:45 | Reduction of Phosphorus Diffusion in Germanium by Fluorine Implantation Authors : H. A. W. El Mubarek Affiliations : Royal Academy of Engineering and EPSRC Research Fellow, Microelectronics and Nanostructures Group, School of Electrical and Electronic Engineering, Sackville Street Building University of Manchester Sackville Street Manchester M13 9PL Resume : Recently, there has been a renewed interest in the use of germanium for post CMOS devices due to its high carrier mobility [1]. Phosphorus is the most promising n type dopant for Ge MOS devices as it has the highest activation levels in Ge in comparison to As and Sb [2]. However, the extrinsic diffusion of phosphorus in Ge is very high and the activation levels are still not high enough, both of which are a hindrance to the processing of future ultra shallow junction MOS devices in Ge [1]. Our previous work was the first to report a study of the effect of fluorine co-implantation on phosphorus diffusion in germanium [3]. We observed a reduction in phosphorus diffusion in germanium by fluorine implantation but an increase in sheet resistance which was attributed to the excess damage caused by the fluorine implantation [3]. Recently Impellizzeri et al have reported a study showing that F+ co implantation suppresses arsenic diffusion in Ge [4]. In this work a detailed study of the effect of fluorine co-implantation on phosphorus diffusion and activation in germanium is shown. Phosphorus and fluorine were implanted at variable energies and doses into (100) p type germanium wafers. The samples were then annealed in N2 at variable temperatures and for variable durations. Phosphorus and fluorine profiles were characterized by Secondary Ion Mass Spectroscopy. The electrical activity of the phosphorus was measured using sheet resistance measurements. The ion implantation damage was also investigated using Transmission Electron Microscopy. For the first time in literature, it is shown that fluorine suppresses phosphorus diffusion and enhances the electrical activity of phosphorus in germanium. These exciting and novel results which open the way to the realization of Ge MOS devices will be presented at the conference.
[1] D. P. Brunco, B. De Jaeger,G. Eneman, J. Mitard, G. Hellings, A. Satta, V. Terzieva, L. Souriau, F. E. Leys, G. Pourtois, M. Houssa, G. Winderickx, E. Vrancken, S. Sioncke, K. Opsomer,G. Nicholas, M. Caymax, A. Stesmans, J. Van Steenbergen, P. W. Mertens, M. Meuris and M. M. Heynsa, “Germanium MOSFET Devices: Advances in Materials Understanding, Process Development, and Electrical Performance”, Journal of The Electrochemical Society, 155 _7_ H552-H561, (2008)
[2] P. Tsouroutas,D. Tsoukalas,I. Zergioti,N. Cherkashin, and A. Claverie “Modeling and experiments on diffusion and activation of phosphorus in Germanium” Journal of Applied Physics, 105, 094910 (2009)
[3] H. A. W. El Mubarek, A. S. Gandy and M. Alaraimi, “A study of the Effect of Fluorine Implantation on Phosphorus Diffusion in Germanium”, presented at the EMRS Spring 2011 Conference in Nice, France, May 2011
[4] G. Impellizzeri, S. Boninelli, F. Priolo, E. Napolitani, C. Spinella, A. Chroneos,
and H. Bracht, “Fluorine effect on As diffusion in Ge”, Journal of Applied Physics, 109, 113527 (2011). | 14 4 |
| 10:00 | Coffee break | |
| Thin layers in Silicon Device Technology : R. Job and W. Skorupa | ||
| 10:30 | Growth of high-quality GeSn alloys for high-speed electronic devices Authors : Buwen Cheng (1), Shaojian Su (1), Chunlai Xue (1), Guangze Zhang (1), Qiming Wang (1), Genquan Han (2), Lanxiang Wang (2), Wei Wang (2), Yee-Chia Yeo (2) Affiliations : (1) State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences. (2) Department of Electrical and Computer Engineering, National University of Singapore. Resume : GeSn alloy is a viable candidate as a high mobility material for high-speed electronic devices. Having larger lattice parameter than Ge, it is also a promising stressor material for strained Ge channel MOSFETs. In this paper, growth and some applications of GeSn alloys will be introduced. Ge1-xSnx alloys (x≤0.155) were grown by solid source MBE on Si, Ge/Si, and Ge substrates. The high-quality was confirmed by HRXRD, TEM, and RBS measurements. The thermal stability was studied by annealing the Ge1-xSnx alloys at various temperatures. It was found that the Ge1-xSnx could be stable at 500℃ as the x value was about 0.03. However, the thermal stability became worse as x increases. GeSn p-i-n photodetectors and GeSn channel pMOSFETs have been successfully fabricated with good performance. The GeSn photodetectors extended the responsivity wavelength to 1800nm. The GeSn pMOSFETs exhibited a hole mobility of 430 cm2/Vs, which was 66% higher compared to that of Ge control pMOSFETs. Compared with the Ge control pMOSFETs, the GeSn pMOSFETs had a 64% reduced S/D resistance due to the smaller Schottky barrier height at interface between NiGeSn S/D and GeSn channel. | 15 1 |
| 11:00 | Oxidation rates for sub-100nm films of SiGe Authors : Ethan Long, Augustinas Galeckas, Andrej Yu Kuznetsov Affiliations : Department of Physics/Centre for Materials Science and Nanotechnology, University of Oslo, P.O. Box 1048 Blindern, N-0316 Oslo, Norway Resume : Oxidation rates for sub-100nm films of SiGe are examined and compared to previous reports and established models for Si oxidation. This comparative analysis is performed with a focus on oxidation of epitaxial thin films of Si1-XGeX in dry O2 at 1atm at 1000ºC, 950ºC, 900ºC, 850ºC, and 800ºC. The experimental results presented here indicate that oxidation rates for SiGe closely match those of Si and provide evidence that the presence of Ge in very thin films of SiGe does not lead to enhanced or retarded oxidation rates as compared to Si. It is also demonstrated that established models for oxidation of Si also provide a good estimation of oxidation of thin films of SiGe. | 15 2 |
| 11:15 | Epitaxial Si, SiGe and Ge on binary and ternary rare earth oxide buffers for electronic and photonic applications Authors : R. Dargis, E. Arkun, R. Roucka, R. Smith, D. Williams, A. Clark, M. Lebby Affiliations : Translucent Inc., 952 Commercial St., CA94303 USA Resume : The growth of semiconductor layers on an insulator attracts a lot of attention in industry because of the possible cost reductions by using these kind of structures as a virtual substrate for electronics (high carrier mobility channel devices), photovoltaic (multi junction solar cells) and solid state lighting applications. Here we demonstrate some results of the development of epitaxial heterostructures with group IV semiconductors (Si, SiGe and Ge) on rare earth oxide buffer layers grown on Si(111). Lattice engineering of binary (Gd2O3, Er2O3, Nd2O3, La2O3) and ternary (Me1xMe21-x)2O3 rare earth oxide layers makes it possible to accommodate the lattice mismatch between the silicon substrate and the grown semiconductor layer leading to a reduction of the defect density. It also opens the opportunity for stress engineering and the avoidance of the formation of structural defects and mechanical damage caused by different thermal-mechanical properties of the substrate and the layers. We demonstrate a crack free 1 µm thick epitaxial single crystal Ge layer grown on a pseudomorphic cubic La2O3 layer. In addition to this, results of our study reveal that the thermal conductivity of the rare earth oxides is a factor of 5 higher than silicon dioxide and this is a further motivation for their application as buried layer for semiconductor on insulator structures. | 15 3 |
| 11:30 | A new approach to grow very thin, smooth and relaxed SiGe epilayers on a Si(100) substrate Authors : M. Myronov, J. Halpin, H.A.A. Alabdulali, D.R. Leadley Affiliations : Department of Physics, The University of Warwick, Coventry CV4 7AL, UK Resume : There is a great demand for development of a technique for epitaxial growth of thin, smooth, relaxed and low-defect density high Ge content SiGe buffers by industrial type Chemical Vapour Deposition (CVD) on a Si(100) substrate. Such buffer layers are used as a global strain tuning platform for subsequent epitaxial growth of strained Si, Ge or III-V semiconductors heterostructures, which has already found applications as parts of various optoelectronic, photovoltaic and electronic devices. In particular, strained Si and Ge quantum wells heterostructures grown on relaxed SiGe buffers exhibited extremely high room-temperature 2DHG and 2DEG mobilities. [1, 2]
In this work we propose a new approach to grow very thin (~300 nm thick) and relaxed high Ge content SiGe buffers on the Si(100) substrate. The epitaxial growth was carried out in an industrial class Reduced Pressure CVD reactor. The SiGe buffers exhibit very smooth surface morphology with RMS surface roughness below 2 nm and relatively low threading dislocations densities. Both parameters vary with variation of Ge content from 0.7 up to 0.95 in the SiGe epilayers.
[1] M. Myronov, K. Sawano, Y. Shiraki, T. Mouri and K. M. Itoh, Appl. Phys. Lett. 91, 082108 (2007).
[2] M. Myronov, K. Sawano, K. M. Itoh and Y. Shiraki , Applied Physics Express 1, 021402 (2008). | 15 4 |
| 11:45 | Properties Ultra- thin SiGe- on- insulator Materials prepared by Ge condensation method Authors : Cheng Li, Shihao Huang, Weifang Lu, Jianfang Xu, Wei Huang, Hongkai Lai, Songyan Cheng Affiliations : Department of Physics, Semiconductor photonics research center, Xiamen University, Xiamen Fujian 361005, China Resume : SiGe- on- insulator (SGOI and GOI) is considered one of the promising materials for partially replacement of Si to manufacture high performance electronic devices. Several methods invented for fabrication of SOI wafers have been used to fabricate SGOI and GOI, such as oxygen ions implantation, bonding and Smartcut@ techniques. In 2001, Tezuka et al. proposed a simple approach, so called Ge condensation, to fabricate SGOI and GOI by thermal oxidation of SiGe layer on SOI substrate due to the selectively oxidation of Si in SiGe layer, condensing Ge between the two Si oxide layers.
In this work, ultra-thin SiGe-on-insulator (SGOI and GOI）materials with various Ge concentrations were fabricated by oxidation of SiGe on SOI, in which Si was oxidized and Ge was confined between the two oxide layers. Si1-xGex epilayers with various Ge concentration were firstly grown on Si and SOI substrate in an ultra- high vacuum chemical vapor deposition with a base pressure of 3x10-10 Torr. 180- nm- thick Si0.88Ge0.12 epilayer was grown on Si substrate at 650oC for investigation of the oxidation behavior of SiGe alloy. 70- nm- thick Si0.81Ge0.19 epilayer was grown at 550oC on SOI substrate with a 6 nm Si cap layer to fabricate SGOI and GOI materials. All of the samples were diced and oxidized in a conventional furnace. The Ge profile, strain status, and morphology of the oxidized SiGe were characterized by X-ray diffraction (XRD), Raman Spectroscopy, Auger electron energy spectroscopy (AES), atomic force microscopy (AFM) and photoluminescence. The crystal structure of GOI was measured by high resolution transmission electron microscopy (HRTEM).
Si0.88Ge0.12 epilayers on Si substrate were oxidized at 950, 1000 and 1050oC for various durations. The oxide thickness on SiGe and Si for comparison as a function of oxidation time is studied. At the beginning, the oxide rate of SiGe is much higher than that of Si at the same temperature. The oxide thickness vs. oxidation time can be described by the parabolic law (Deal-Grove model), which has been generally used to predict the oxidation of Si. However, when the oxide thickness reaches a critical value, the oxide rate of SiGe becomes slow, much smaller than that of Si. It seems that oxygen can not arrive at the interface after the oxide thickness reaches several hundred nanometers. Ge concentration increases at the beginning of oxidation and then decreases with oxidation time. The maximum of Ge concentration varies with oxide temperature and Ge profile is determined by accumulation and diffusion of Ge in SiGe layer during oxidation.
With the oxidation data of SiGe on Si substrate, we optimized the parameters to oxide Si0.81Ge0.19 on SOI substrate. The different on SOI substrate is that Ge diffusion can be blocked by the buried oxide. The samples were pre- oxidized at 900oC to transform Si cap layer to a thin SiO2 layer for preventing Ge loss in the subsequent processes. Then increasing temperature to 1150oC, SiGe is selectively oxidized to SiO2. When thickness of SiO2 was about 250nm, the oxide rate becomes slow. SiO2 was partially removed for accelerating oxide rate. When Ge concentration is about 0.4, the melting point of SiGe alloy is reduced and the oxidation temperature is set up at 900oC. Cycle thermal oxidation and annealing are carried out to obtain uniform SiGe or Ge layer on insulator. Ge profile in the SiGe layer is quit uniform.
Ge concentration, degree of strain relaxation, and thickness of SiGe layer were measured by Raman spectra and XRD rocking curves. With increase of oxidation time, Ge concentration continues increasing with the continuously decrease of thickness of SiGe layer. What interesting is that the degree of strain relaxation changes nonlinearly. Carefully evaluation of the relationship among strain, Ge concentration and SiGe thickness, we find that the strain status of SiGe is dominated by the critical thickness of SiGe layer, as reported on SiGe epilayer on Si substrate.
Ulta-thin GOI materials were prepared by oxidation of SiGe on SOI substrate. HRTEM images shows that the GOI is uniform and the interface between Ge and SiO2 is clear and sharp. Room temperature photoluminescence from direct band transition of the ultra- thin Ge layer is observed, which suggests that Ge layer fabricated by oxidation and annealing have good crystal quality. | 15 5 |
| 12:00 | Solid phase epitaxy in Si and Ge Authors : B. C. Johnson1,2), T. Ohshima1) and J. C. McCallum2) Affiliations : 1) Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, Gunma 370-1292, JAPAN 2) School of Physics, University of Melbourne, Parkville, VIC, AUSTRALIA Resume : Solid phase epitaxy (SPE) is an important process used to activate dopants on a low thermal budget in Si and Ge device fabrication. The enhancement of the SPE rate by the presence of dopants is well described by a Fermi level effect as encapsulated by the generalized Fermi level shifting (GFLS) model. Dopant dependent deviations from the model have recently been attributed to dopant-induced lattice strain in the plane of growth. Here, data is presented over a broad range of dopant concentrations and SPE anneal temperatures in both Si and Ge including new results in Sb doped Ge. Although an active Sb concentration above the solubility limit is achieved a significant portion of the implanted atoms are not. Theoretical predictions using a simple form of the generalized Fermi level shifting model which incorporates both dopant and dopant-induced stress effects is shown to agree well with all data. A single set of two parameters are determined which describe the dopant enhanced SPE data well independent of dopant species and concentration. | 15 6 |
| 12:15 | Lunch break | |
| Solar Cell Technology : M. Kittler and J. Murphy | ||
| 14:00 | Review on PECVD Al2O3 for the surface passivation of c-Si solar cells Authors : Pierre Saint-Cast, Saskia Kühnhold, Marc Hofmann, Jochen Rentsch and Ralf Preu Affiliations : Fraunhofer Institute for Solar Energy Systems Resume : State-of-the-art silicon solar cells are made out of p-type silicon and feature an aluminum back surface field (Al-BSF) on the rear surface. This technology now arrived to maturation with an energy conversion efficiency n of around 18 % for Czochralski-grown silicon (Cz-Si). In order to allow the transition of the present technologies to a rear-passivated structure with higher efficiencies, industrially feasible surface passivation processes are needed. So far the best candidate seems to be Al2O3 passivation layers.
In spite of this technological improvement, the solar cell efficiency will be still limited around n = 20 % by the recombination mechanism inherent in boron-doped p-type material (oxygen-boron-complex traps).
In order to overcome this limitation the solar cells have to be processed from special p-type material (Ga-doped, magnetically casted or float-zone p-type Si) or from n-type silicon. A major issue to implement the n-type wafer technology is the passivation of the emitter surface with an industrially feasible process. Here again Al2O3 layers have shown to provide the highest passivation quality.
The implementation of future c-Si solar cells technologies can highly benefit from recently developed Al2O3 passivation layers. In this presentation, we will review the development of industrially compatible high quality PECVD Al2O3 layers which was performed during the last four years. | 16 1 |
| 14:15 | Phosphorus diffusion through Silicon Nitride thin films for selective emitter application Authors : L.Crampette (1,2), G.Poullain (3), Y.Cuminal (2), Y.Pellegrin (4), B.Semmache (1) Affiliations : (1) Irysolar, 395 rue Louis Lépine 34000 Montpellier France (2) Centre d'Electronique et de Micro-optoélectronique de Montpellier, CEM2, UMR-CNRS 5507, Université Montpellier 2 - Sciences et Techniques du Languedoc, CC 067, Place Eugène Bataillon, 34095 Montpellier cedex 5, France (3) Université de Lyon; Institut des Nanotechnologies de Lyon INL-UMR5270, CNRS, INSA de Lyon, Villeurbanne, F-69621, France (4) Semco Engineering, 625 rue de la Croix Verte,Parc Euromédecine 34196 Montpellier Cedex 5 France Resume : In this paper we present a new concept of phosphorus diffusion through silicon nitride films to realize selective emitters. The most common ways for selective emitter are using laser processing after a previous phosphorus thermal diffusion step. In this study, we propose to deposit a silicon nitride film before the phosphorus diffusion process. The idea is first to open the fingers area by laser ablation and then perform one diffusion step both trough the silicon nitride film and directly on the ablated pattern. This way, selective emitter structures with various sheet resistance couples (Low, High) could be obtained. Usually, silicon nitride films are used as masking layers against the phosphorus diffusion. However, the SiNx layer could be oxidized during the POCl3 diffusion process. This oxidation phenomenon was already mentioned elsewhere and is explained by the role of POCl3 catalysis. The formation of the PSG (P2O5, SiO2) phase into the modified SiNx layer is responsible of the phosphorus diffusion into the silicon substrate. This P-diffusion mechanism depends on different parameters: SiNx thickness, diffusion thermal budget (temperature, dwell time). We observed two interesting process conditions to obtain appropriate sheet resistance couples (Low, High). The first one is obtained at constant diffusion thermal budget (875°C – 30 min) and a silicon nitride thickness in a range of 13-20nm. For the second one, we increased the diffusion temperature (900°C) and reduced the diffusion time and the silicon nitride thickness. Finally, we obtained several interesting couples (40/60 ohms/sq; 40/80Ohms/sq) which can used for selective emitters applications. The sheet resistance was measured by means of 4-point probe system. Phosphorus profiles were characterized by Secondary ion spectrometry (SIMS). | 16 2 |
| 14:30 | Efficient Crystalline Si/Poly(ethylene dioxythiophene):Poly(styrene sulfonate)(PEDOT:PSS):Graphene Oxide(GO) Composite Heterojunction Solar Cells Authors : Qiming Liu, Masaharu Ono, Keiji Ueno, Tomohisa Ino, and Hajime Shirai Affiliations : Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan Resume : Now, crystalline silicon(c-Si)/amorphous silicon (a-Si:H) heterojunction solar cells have been extensively studied and the power-conversion efficiency η have been achieved over 22%. Most of deposition studies on a-Si:H films have been performed using low-pressure plasma-enhanced chemical vapor deposition (PE-CVD) method. On the other hand, recent research on organic thin-film solar cells (OSCs) has extended dramatically because of low-lost and easy methods, i.e., spin-coating, ink-jet, and spray coating. However, the efficiency is still limited to be 3-5%.
In this study, efficient c-Si heterojunction solar cells with conductive poly(ethylene dioxythiophene)(PEDOT):poly(styrene sulfonate)(PSS) and graphene oxide (GO) composite are presented using a structure of Ag/PEDOT:PSS/PEDOT:PSS:GO composite/c-Si (100)(ρ: 3-5 Ω·cm)/Al. The power-conversion efficiency η enhanced up to 9.7% under illumination of AM1.5 100 mW/cm2 simulated solar light by adjusting the PEDOT:PSS and GO mixing concentration ratio, after the subsequent thermal annealing at 200˚C for 1h. The fundamental band gap energy in PEDOT:PSS increase with GO mixing concentration, which suppress electron recombination and/or impede hole current at the anode. The 12.5% GO added PEDOT:PSS cell showed en efficiency of 9.7%. These findings originate from that building potential is enhanced up to 1.1 eV, which suppress the electron-hole recombination near the anode. In addition, the PEDOT:PSS films were spin-coated on textured c-Si for improving the light trapping effect. The short circuit current is enhanced to 33mA/cm2 with an efficiency of 7.6%. | 16 3 |
| 14:45 | Fabrication And Characterization Of Thin C-Si Solar Cells By Low Cost Methods Authors : E. Ochoa-Martínez(1), C. Vázquez(2), I. Hoces(3), M. Gabás(1), B. Hartiti(4), Jimeno, J. C.(3), J.R. Ramos-Barrado(1) Affiliations : 1)Dpto. de Física Aplicada I, Lab. de Materiales y Superficies Universidad de Málaga 29071, Málaga, Spain 2)Isofotón S.A., c/Severo Ochoa 50, 29590 Málaga, Spain 3)Instituto de Tecnología Microelectrónica (TiM) UPV/EHU, Alda, Urquijo s/n 48013 Bilbao, Spain. 4)Laboratoire LPMAER, FST de Mohammédia, Université Hassan II, BP 146, 20800 Mohammédia. Morocco Resume : More than half of the cost of a c-Si solar cell has its origin in the production and purification of silicon, consequently photovoltaic industry is slowly decreasing the thickness of the semiconductor substrate. One of the processes that wafers must pass prior to become a solar cell is the pn junction formation or emitter diffusion. In this work an alternative low cost method for phosphorus diffusion suitable for extremely thin (<100um) c-Si solar cells is proposed. The results shown are the product of industrially feasible techniques like spray coating, open furnace diffusion and screen printing. Several structures have been tested with different dopant sources, dopant levels and antireflective coatings. The I-V curve on solar simulator, Suns-Voc, spectral response and contact resistance scanning (CORESCAN) are the most important characterization techniques used to determine the overall performance of the resulting cells.
There have been obtained cells with efficiencies of up to 11.2% which is a promising figure considering that there has not been any major optimization on texturization or the metallization processes. The use of a simple water dilution of phosphoric acid has resulted in satisfactory results, which in addition to a cost reduction, implies a potential decrease in the amount of solvents and surfactants. In particular the homemade "Precursor C" showed an outstanding performance under the conditions of the present study. | 16 4 |
| 15:00 | Large-area crystalline silicon nanodome arrays on nanoimprinted glass for photovoltaic and photonic applications Authors : C. Becker (1), T. Sontheimer (1), D. Lockau (1), V. Preidel (1), E. Rudigier-Voigt (2), M. Bockmeyer (2), F. Schmidt (3), B. Rech (1) Affiliations : 1 Helmholtz-Zentrum Berlin für Materialien und Energie, Institut Silizium-Photovoltaik, Kekuléstr. 5, 12489 Berlin, Germany 2 SCHOTT AG, Hattenbergstr. 10, 55122 Mainz, Germany 3 Zuse Institute Berlin, Takustraße 7, 14195 Berlin, Germany Resume : By high-rate electron-beam evaporation of silicon on nanoimprint textured glass substrates large-area two-dimensionally periodic crystalline silicon nanodome arrays with lattice constants between 300nm and 2µm were prepared [1]. All processing steps - silicon deposition, solid phase crystallization and selective wet-chemical etching - have very little technological intricacy, are scalable to several hundred square centimeters and thus hold the potential for low-cost production of advanced photovoltaic devices or large-area photonic crystals. The formation of periodic free standing crystalline silicon nanodomes is based on the distinctive growth properties of silicon on flat and oblique surfaces. The structures exhibit a promising absorption enhancement and diffuse scattering in the near infrared wavelength region compared to respective planar silicon films enabling the development of highly effective light trapping architectures for polycrystalline silicon thin-film solar cells. Photonic band structure effects could be identified by angular resolved reflection measurements agreeing well with the outcome of three-dimensional optical finite element simulations inspiring the formation of large-area two-dimensional photonic band-gap materials. The extreme versatility, scalability and simplicity of the fabrication method allow for systematic tailoring of silicon-based photonic structures for photovoltaic devices.
[1] T. Sontheimer et al., Phys. Stat. Sol. RRL 5, 376 (2011) | 16 5 |
| 15:15 | Recombination in Solar Cells: Impact on the Carrier Transport Authors : Yu. G. Gurevich, J.E. Vel?uez-P?z Affiliations : Departamento de F?ca, CINVESTAV-IPN, Av. IPN 2508, Apartado Postal 14-740, M?co D.F., 07000, M?co; Departamento F?ca Aplicada, Universidad de Salamanca, Plaza de la Merced, E-37008 Salamanca, Spain. Resume : Charge carrier transport underlies the electrical behaviour of any semiconductor device and, in particular, of solar cells. Despite the efforts made to correctly model such transport in semiconductors over the years, many questions still remain open. One of these open questions is how to model carrier recombination. The mathematical expression routinely used to model the recombination rate [1] is basically incorrect since it has recently been demonstrated that it violates Maxwell’s equations, and hence a new corrected model must be developed [2]. This problem was partly addressed in previous works, [3]. Recombination is a key feature when describing carrier transport in semiconductors because it strongly affects the electrical response of the semiconductor at all levels of external excitation. This phenomenon is not limited to pure electrical problems but is very general, since the nonequilibrium charge carriers created by several physical sources (photo-generation, for instance) will lead to similar situations that need to be described using the same model [4–8]. The last remark that must be made about the need for a correct modelling of recombination is that in devices operating under a strong excitation regime (the operation of solar cells lies in this regime) the importance of a correct formulation of the recombination terms is even more important.
In the present contribution we will discuss the importance of recombination in monocrystalline and amorphous solar cells in the framework of a general transport model in 1D [9]. Our results show that the new formulation corrects the inconsistencies found in the Shockely model that is the basic one used in solar diodes modelling. Furthermore, recombination plays the key role to eliminate those inconsistencies in this model.
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[7] A. Konin, Semicond. Sci. Technol. 18 (2003) L17.
[8] M. Krcmar, W. Saslow, Phys. Rev. B 65 (2002) 233313.
[9] Yu.G. Gurevich, G. N. Logvinov, J. E. Velaquezc, O. Titov, “Transport and recombination in solar cells: New perspectives”, Solar Energy Materials & Solar Cells 91 (2007) 1408–1411 | 16 6 |
| 15:30 | Anti-Reflection Etching of Silicon Surfaces Catalyzed with Ionic Metal Solutions Authors : Vernon E. Yost, Dr. Howard Branz Affiliations : NREL (Alliance for Sustainable Energy, Golden, CO ) Resume : A method for etching a silicon surface which includes positioning a substrate (of either mono or multi-crystalline silicon) into a Teflon vessel which is filled with a volume of dilute (<0.4mM) noble metal (Au, Ag or Pt) solution so as to cover the surface. The etching solution consists of a equal volume of a 1:5:2 solution of HF: 30% H2O2:H2O and is subjected to ultrasonication for 3-4 minutes at room temperature or 60 seconds at 40*C.
The Hydrogen peroxide provides a means of producing 1-5nm nanoparticle metals which perform the etching as well as producing extra SiO2 surfaces for further tunneling. This goes on until the tunnel reach a depth of ~500nm.
This results in a "Black Silicon" which exhibits <0.5% reflectivity across the usable 350-1160nm solar spectrum and results in wafers that currently exhibit 18% efficiency without the need for Si3N4 or ITO deposition layers following p-n junction formation (with POCl3) and Pd, Pt, Ag grid deposition.
IPC8 Class: AC03C2568FI; USPC CLass 21699 (International). | 16 7 |
| 15:45 | Coffee break | |
| Modeling and Ab Initio Calculation : V. Borodin and A. Carvalho | ||
| 16:15 | Hydrogen in C-rich Si and the diffusion of vacancy-hydrogen complexes Authors : Stefan K. Estreicher [1], Michael Stavola [2] Affiliations : [1] Physics Department, Texas Tech University, Lubbock TX 79409-1051; [2] Physics Department, Lehigh University, Bethlehem PA 18015 Resume : Carbon-rich cast-Si material is often used for single-junction Si photovoltaics. Most of the carbon impurities are at substitutional sites. The hydrogenation of this material leads to the formation of a number of H-containing complexes, some of which are typically seen only in irradiated material. In particular, the H2*(C) (C-Hbc•••Si-Hab and Si-Hbc•••C-Hab) and C2H2 (C-H H-C) defects dominate the IR spectrum. The fully-saturated vacancy (VH4) also forms. VH4 normally anneals out at 650oC. However, in C-rich Si, it begins to anneal around 550oC while a new complex labeled VH3CH appears. There, C replaces one of the four Si nearest-neighbors to the vacancy. Since substitutional C is not mobile up to much higher temperatures, this observation implies that VH4 begins to hop around at 550oC and then traps at C. This in turn implies that all four VHn complexes (n = 1, 2, 3, 4) are mobile at moderate temperatures. In this talk, I will summarized the key experimental and theoretical results about H interactions in C-rich Si, and discuss the results of nudged-elastic-band calculations showing the migration paths and activation energies of the four VHn complexes. | 17 1 |
| 16:45 | First-principles and empirical potential simulation study of intrinsic and carbon-related defects in silicon Authors : F. Zirkelbach, B. stritzker, K. Nordlund, W. G. Schmidt, E. Rauls, J. K. N. Lindner Affiliations : Experimentalphysik IV, Institut für Physik, Universität Augsburg, Universitätsstr. 1, D-86135 Augsburg, Germany; Experimentalphysik IV, Institut für Physik, Universität Augsburg, Universitätsstr. 1, D-86135 Augsburg, Germany; Department of Physics, University of Helsinki, Pietari Kalmink. 2, 00014 Helsinki, Finland; Department Physik, Universiät Paderborn, Warburger Straße 100, 33098 Paderborn, Germany; Department Physik, Universiät Paderborn, Warburger Straße 100, 33098 Paderborn, Germany; Department Physik, Universiät Paderborn, Warburger Straße 100, 33098 Paderborn, Germany Resume : Results of atomistic simulations aimed at understanding precipitation of silicon carbide in silicon are presented.
The study involves a systematic investigation of intrinsic and carbon-related defects as well as defect combinations and defect migration by both, quantum-mechanical first-principles as well as empirical potential methods.
Comparing formation and activation energies, ground-state structures of defects and defect combinations as well as energetically favorable agglomeration of defects are predicted.
Moreover, the highly accurate ab initio calculations unveil limitations of the analytical method based on a Tersoff-like bond order potential.
A work-around is proposed in order to subsequently apply the highly efficient technique on large structures not accessible by first-principles methods.
The outcome of both types of simulation provides a basic microscopic understanding of defect formation and structural evolution particularly at non-equilibrium conditions strongly deviated from the ground state as commonly found in SiC growth processes.
A possible precipitation mechanism, which conforms well to experimental findings clarifying contradictory views present in the literature is outlined. | 17 2 |
| 17:00 | Vacancy-Mediated Diffusion in Biaxially Strained Si: a theoretical study. Authors : P. Pochet, D. Caliste, K. Z Rushchanskii Affiliations : Laboratoire de Simulation Atomistique (L_Sim), SP2M, INAC, CEA-UJF, 17 Av. des Martyrs, 38054 Grenoble, France Resume : Understanding the influence of stress on diffusivity in Si based alloys is a key challenge in modern semiconductor technology. For layered materials, like SiGe alloys used in electronic, the lattice mismatch between Si and Ge, makes the connection between inter-diffusion and stress of particular importance. In recent years, it has been shown that external strain can enhance or retard diffusion of impurities as well as self-diffusion of the alloys components [1-3]. The parameter which describes the effect of strain on the diffusivity is denoted Q' as the strain derivative of the activation energy Q. Experimentally, two measurement methods have been used in the literature [1, 2].
In this paper, we will summarize the different approaches to Q' calculation and clarify its analytical formulation. This new analysis of published experiments of silicon self-diffusion in SiGe layers under stress will highlight that Q' is different between tensile and compressive environments. While current experimental values are scattered between 10 and 100, we will show that our new analysis makes all these results consistent. We will also propose an approach of the strain dependency of Q' based on our DFT calculations [4, 5]. It relies on the strong non-linear behavior of the vacancy barrier, as represented by the split vacancy. We also consider the entropic contribution of the other paths describing the vacancy jump. We attribute [6] the Q'-strain dependency mainly to an electronic effect in the pairing around the split vacancy .
[1] N. E. B. Cowern et al., PRL 72, 2585 (1994).
[2] A. Y. Kuznetsov et al., PRB 59, 7274 (1999).
[3] N. R. Zangenberg, et al, PRL 87, 125901 (2001).
[4] D. Caliste and P. Pochet, PRL 97 135901 (2006)
[5] K. Z. Rushchanskii, P. Pochet and F. Lançon APL 92, 152110 (2008)
[6] D. Caliste, K. Rushchanskii, P. Pochet APL 98, 031908 (2011) | 17 3 |
| 17:15 | Density functional theory study of the effect of pressure on formation and activation enthalpies of intrinsic point defects in single crystal Si Authors : Koji Sueoka, Eiji Kamiyama, Hiroaki Kariyazaki, Jan Vanhellemont Affiliations : Okayama Prefectural University ; Ghent University Resume : In 1982, Voronkov1 presented a model describing point defect behavior during the growth of single Si crystal from a melt and derived a criterion to predict if the crystal was vacancy- or self-interstitial-rich. According to the Voronkov criterion, a crystal that is pulled with the ratio Z0 of pulling speed v over temperature gradient G0 at the melt/solid interface, larger than a critical value Z0crit, is vacancy-rich while when Z0 is smaller than the critical value, the crystal is interstitial-rich. Recently, one of the authors claimed that one should take into account the impact of stress introduced by the thermal gradient on the critical value Z0crit by considering the hydrostatic pressure dependence of the formation enthalpy of point defects2. To evaluate the impact of stress more correctly, the pressure dependence of both the formation enthalpy (Hf) and the activation enthalpy (Hm) of the intrinsic point defects should be taken into account.
The purpose of this study is to quantify the dependence of Hf and Hm of the self-interstitial I and the vacancy V on the pressure P, or in other words, the pressure dependence of the formation energy (Ef) and the relaxation volume (vf), by density functional theory (DFT) calculations. There has been a lot of ab initio calculations of the properties of intrinsic point defects in Si crystals3. However, the calculations for the point defect properties in Si crystals under pressure are rather scarce. For self-interstitials I, to our knowledge, the only relaxation volumes calculated for I come from Centoni et al.4, besides an older calculation by Antonelli and Bernholc5. However, the pressure dependence of Ef and vf for I, i.e., the pressure dependences of Hf and Hm were not reported. For vacancies V, the reported pressure dependences of Hf are inconsistent. Initially Antonelli and Bernholc5 obtained an increase of Hf of V under pressure while later Antonelli et al.6 and Centoni et al.4 found a decrease, while Ganchenkova et al.7 concluded an increase of Hf under the pressure. One of the goals of the present study is therefor also to clarify this issue. In the present work, DFT calculations were performed within the generalized gradient approximation (GGA) for electron exchange and correlation, using the CASTEP code8. The Kohn-Sham equation9 was solved self-consistently to obtain the ground state of the system for given atomic configurations. The wave functions were expanded with the plane waves, and the ultra-soft pseudo-potential method10 was used to reduce the number of plane waves. The cutoff energy was 340 eV. The expression proposed by Perdew et al.11 was used for the exchange-correlation energy in the GGA. The density mixing method12 and BFGS geometry optimization method13 were used to optimize the electronic structure and atomic configurations, respectively. Periodic boundary conditions were used with cubic supercells of 216 atoms for calculations of perfect and defect-containing Si crystals. k-point sampling was performed at 2×2×2 special points in a Monkhorst-Pack grid14. The value of the cutoff energy and the mesh of k-point sampling were sufficient to obtain converged results for 216 Si-atoms supercells.
The reference point in this study was the perfect Si crystal. The pressure P in cubic cells with different volumes was determined by fitting the total energy for different volumes to a Birch-Murnaghan equation of state15. In our calculations, the equilibrium atomic volume is 20.39 Å3. The bulk modulus at P = 0 was 87.7 GPa and its pressure derivative was 4.02. The pressures P in cubic cells with different volumes were also obtained analytically with the method by Nielsen and Martin16. The analytically obtained pressures P agreed well with those obtained by fitting to the Birch-Murnaghan equation of state.
Similar calculations were performed with cubic supercells containing point defects. In single crystal Si , the thermal equilibrium concentrations of self-interstitials I and vacancies V even near melt temperature, are well below 5×1015 cm-3. For such low concentration, the calculation cells should be surrounded by perfect cells. These perfect Si crystals should deform isotropically under the hydrostatic pressure. Therefore, we imposed the cubic shape for the defect-involving calculation cell. In each case, the supercells were set at a particular cubic volume and the ionic coordinates were fully relaxed to build up a list of energy-pressure-volume data points by using the analytically obtained P. In the present study only neutral point defects were considered.
For the self-interstitial, the two lowest energy configurations, i.e. the [110] dumbbell (D) and the tetrahedral (T) sites were calculated. It is well known that, for neutral I, the [110] D-site is the lowest-energy configuration while the T-site is the transition state3,17. A vacancy was introduced by eliminating one Si atom located around the center of each supercell. Further details of the point defect configurations considered in this study will be commented on later. The energy-pressure-volume data of perfect and defect-involving cubic cells were used to find the relationship between pressure P and (1) formation energy Ef, (2) relaxation volume vf, and (3) formation enthalpy Hf.
For self-interstitials I, it was found that Ef is almost constant for pressures up to 1 GPa. The formation energies are 3.425 eV for the D-site and 4.406 eV for the T-site at P = 0. That is, the activation energy of I at P = 0 is 0.981 eV. The relaxation volumes of I at the D-site and the T-site are also independent of pressure. The (relaxation/formation) volumes are (11.292 / -9.100) Å3 for the D-site and (5.242 / -15.150) Å3 for the T-site at P = 0. Centoni et al.4 obtained formation volumes of -6.5 Å3 for the D-site and -12.8 Å3 for the T-site at P = 0. However, the pressure dependence of Ef and vf for self-interstitials were not reported.
The formation enthalpies of I decrease linearly with increasing pressure P. The calculations show that the formation enthalpy HfI of the neutral I at the D-site and the activation enthalpy HmI of the neutral I are given by
HfI = 3.4251 – 0.0571×P (eV), HmI = 0.9811 – 0.0384×P (eV) (1)
with P given in GPa. This result indicates that hydrostatic pressure leads to an increase of the equilibrium concentration and diffusion of self-interstitials.
For vacancies V, the neighboring atoms will tend to re-bond in ways that make the defect less symmetric, particularly in a covalently bonded crystal like Si. If the atoms are forced to maintain a Td symmetry, the four neighbors draw in toward the center, pulling the rest of the lattice with them. However, the ground state involves a Td to D2d symmetry-breaking relaxation by Jahn–Teller distortion. In this study, two type distortions were observed. In the first distortion labeled h-JT of the ground state, the distance between the atoms in each pair is 2.993 Å, and the distance between atoms belonging to different pairs is 3.508 Å at P = 0. In the second distortion labeled l-JT, the distance between the atoms in each pair is 3.609 Å, and the distance between atoms belonging to different pairs is 3.428 Å at P = 0.
Ef of V is almost constant under for pressures up to 1 GPa. The Jahn–Teller distortion of h-JT reduces the formation energy by about 0.229 eV from Td symmetry at P = 0. The distortion of l-JT gives slightly lower energy of about 0.024 eV compared to Td symmetry at P = 0. The activation energy of V (h-JT is the ground state, and split-V is the transition state) is 0.249 eV at P = 0.
In contrast to I, the relaxation volumes VfV of V decrease with increasing P. It is interesting that the formation volume becomes negative for h-JT and split-V from P = 0 to 1 GPa. The (relaxation/formation) volumes are (-24.105 / -3.713) Å3 of h-JT, (-17.299 / 3.093) Å3 of l-JT, (-17.299 / 3.093) Å3 of Td symmetry, and (-28.062 / -7.671) Å3 of split-V, at P = 0. Several negative values of formation volumes for V with Jahn–Teller distortion were reported as -0.4 Å3 (Centoni et al.), -2.0 Å3 (Windl et al.), -1.7 Å3 (Antonelli et al.), -1.15 Å3 (Ramanarayanan et al.), -6.7 Å3 (Sugino and Oshiyama) 3.
The formation enthalpy of h-JT (most stable) and split-V decrease with the square of the pressure P increase. The calculations indeed lead to HfV of neutral V and HmV of neutral V dependencies on P given by
HfV = 3.5425 – 0.0206×P2 – 0.0185×P (eV), HmV = 0.2491 + 0.0172×P2 – 0.0373×P (eV) (2)
with P given in GPa. These results indicate that hydrostatic pressure leads to a slight increase of the equilibrium concentration and diffusion of vacancies but this increase is considerably smaller than that of self-interstitials. Taking into account recombination between vacancies and self-interstitials, pressure thus makes a Si crystal more interstitial-rich.
The impact of pressure on the critical value Γ0crit will be discussed on the basis of the results of the DFT calculations.
REFERENCES
[1] V. Voronkov, J. Cryst. Growth 59, 625 (1982).
[2] J. Vanhellemont, J. Appl. Phys. 110, 063519 (2011).
[3] B. Puchala, PhD Thesis, The University of Michigan (2009) and references therein.
[4] S. Centoni et al., Phys. Rev. B72, 195206 (2005).
[5] A. Antonelli and J. Bernholc, Phys. Rev. B 40, 10643 (1989).
[6] A. Antonelli et al., Phys. Rev. B 81, 2088 (1998).
[7] M. Ganchenkova et al., Nucl. Inst. Meth. Phys. Rev. B 202, 107 (2003).
[8] The CASTEP code is available from Accelrys Software Inc.
[9] W. Kohn and L. Sham, Phys. Rev. 140, A1133 (1965).
[10] D.Vanderbilt, Phys. Rev. B41, 7892 (1990).
[11] J. Perdew et al., Phys. Rev. Lett. 77, 3865 (1996).
[12] G. Kresse and J. Furthmüller, Phys. Rev. B54, 11169 (1996).
[13] T. Fischer and J. Almlof, J. Phys. Chem. 96, 9768 (1992).
[14] H. Monkhorst and J. Pack, Phys. Rev. B13, 5188 (1976).
[15] J. Poirier: Introduction to the Physics of the Earth’s Interior, 2nd ed., Cambridge University Press, New York, (2000).
[16] O. Nielsen and R. Martin, Phys. Rev. B32, 3792 (1985).
[17] W. Windl, ECS Transactions 3, 171-182 (2006) | 17 4 |
| 17:30 | Kinetic Monte Carlo simulations of the epitaxial growth of silicon nanofilms on the Si(100)2×1 surface from silane Authors : Vivien Guenther (1), Christiane Schlawitschek (2), Christian Klauer (3), Fabian Mauss (4) Affiliations : (1-4) Brandenburg University of Technology (BTU Cottbus) – Chair of Thermodynamics and Thermal Process Engineering, Siemens-Halske-Ring 8, 03046 Cottbus, Germany Resume : Technological applications of epitaxial structures such as silicon films for microelectronics or solar panels require a high degree of geometric uniformity. Modelling and simulation may contribute insights to control the fabrication of these materials at an atomic level. We present Kinetic Monte Carlo (KMC) simulations carried out on silicon chemical vapour deposition (CVD) of Si(100)2×1 surfaces as a function of surface temperature and silane partial pressure.
The present KMC method includes not only adsorption, abstraction, desorption, and incorporation reactions on the silicon surface but also numerous migration processes and surface reconstruction playing a major role during the epitaxial growth of silicon. The rates and probabilities of the kinetic surface processes are taken from experimental and calculated data from the literature. Different values of the Arrhenius parameters of a surface process according to of the nature of adjacent surface sites and of the process direction - parallel and perpendicular to the silicon dimer rows - are taken into account.
Silicon films of up to 15 layers are grown in the simulations and all the surface processes, e.g. the adsorption of silane, the dimer opening, or the formation of new dimers, are visualized in detail. The simulations provide short-time microscopic mechanisms and predict the macroscopic phenomena such as growth rate, surface roughness and hydrogen desorption rate in agreement with experimental results. | 17 5 |
| 17:45 | Density functional study on the formation energy of vacancy in Si, Ge, and Si1-xGex Authors : Hiroaki KARIYAZAKI, Koji SUEOKA Affiliations : Okayama Prefectural University Resume : Recently much attention has been paid to MOS channel materials with higher mobility than Si. The technology trend has re-opened the door for Ge, several applications as channel engineering have been proposed and demonstrated such as SiGe-on-insulator (SGOI), Ge-on-insulator (GOI) and so on. Ge is therefore the key-material for future LSI devices and it is important to control the crystal quality.
This study aims to characterize systematically the dependence of the formation energy of the neutral vacancy V on Ge concentration in Si1-xGex crystals from x = 0 (pure Si) to x = 1 (pure Ge). The vacancy formation energy Ef(V), in pure Si, pure Ge, and Si1-xGex was quantified by ab-initio calculation based on the density functional theory (DFT) with 64-atoms cubic supercells. The Si1-xGex model with each Ge concentration was constructed by replacing the corresponding number of Si atoms to Ge atoms in 64 Si atoms cell. A vacancy was introduced at the center of the supercell by eliminating one atom in the fully relaxed supercell, and the stable structure was calculated by geometry optimization.
The obtained Ef(V) in pure Si and in pure Ge was 3.58 eV and 2.33 eV, respectively, while Si0.5Ge0.5 was 4.22 eV (Si vacancy) and 5.02 eV (Ge vacancy). It is interesting that the Ef(V) has a hat-shaped dependence on the Ge concentration. This is contrasting to the lattice constant, which obeys to Vegard’s low in Si1-xGex system. | 17 6 |
| Postersession II : J. Kang and S. Pizzini | ||
| 18:00 | The use of two-dimensional nanorod arrays with slanted ITO film to enhance optical absorption for photovoltaic applications Authors : Yung-Chi Yao, Li-Wei She, Chun-Mao Cheng, Yi-Ching Chen, and Ya-Ju Lee Affiliations : Institute of Electro-Optical Science and Technology, National Taiwan Normal University, Taipei 116, Taiwan Resume : Two-dimensional (2D) Si-nanorod arrays offer a promising architecture that has been widely recognized as attractive devices for photovoltaic applications. To further reduce the Fresnel reflection that occurs at the interface between the air and the 2D Si-nanorod array because of the large difference in their effective refractive indices, we propose and adopt a slanted ITO film as an intermediate layer by using oblique-angle sputtering deposition. The nearly continuous surface of the slanted ITO film is lossless and has high electrical conductivity; therefore, it could serve as an electrode layer for solar cells. As a result, the combination of the above-mentioned nanostructures exhibits high optical absorption over a broad range of wavelengths and incident angles, along with a calculated short-circuit current density of Jsc =32.81 mA/cm2 and a power generation efficiency of η=22.70%, which corresponds to an improvement of approximately 42% over that of its bare single-crystalline Si counterpart. | 17 7 |
| 18:00 | Influence of UV irradiation on micro-structural and optical properties of nanocrystalline silicon thin films Authors : Atif Mossad Ali1,2, H. Kobayashi3, T. Inokuma4, and A. Al-Hajry5 Affiliations : 1Department of Physics, Faculty of Science, King Khalid University, Abha, P. O. Box 9004, Saudi Arabia. 2Department of Physics, Faculty of Science, Assiut University, Assiut, Egypt. 3Institute of Scientific and Industrial Research, Osaka University, and CREST, Japan Science and Technology Organization, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan. 4Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-Machi, Kanazawa, Ishikawa 920-1192, Japan. 5Department of Physics, College of Science and Arts, Najran University, Najran, P.O. Box 1988, Saudi Arabia. Resume : Nowadays, nanocrystalline silicon (nc-Si) thin films have attracted considerable interest due to their potential applications in optoelectronic devices such as Si MOSFETs, single electron transistors and single hole transistors, solar cells and thin film transistors. In addition, nc-Si is expected to exhibit quantum size effects and has the potential for application to ultra large-scale integrated circuit. In order to contribute such devices, nc-Si films were deposited on Si (100), glass (Corning 7059) and fused quartz substrates by plasma-enhanced chemical vapor deposition. The feed gases were SiF4/SiH4/H2 with the flow rates of [SiF4] = 0.2 sccm, [SiH4] was varied and [H2] = 15 sccm. The deposition temperature and rf power during the film deposition were maintained at 200 oC and 30 W, respectively. The structural properties were investigated by measurements of X-ray diffraction, transmission electron microscopy, and Raman scattering. The morphology of the films was investigated by atomic force microscopy. The vibrational spectra were measured by Fourier transform infrared spectrometer. The optical properties of the films were evaluated by measurements of the optical absorption and photoluminescence (PL). The PL spectra showed few peaks at room temperature. These peaks and Raman peak position of Si are strongly depended on UV illumination. | 17 8 |
| 18:00 | Enhancement of IR light emission from beta-FeSi2 nanocrystals embedded in Si Authors : Yoshihito Maeda1,2, Kentaro Nishimura1, Takahito Nakajima1, Kazumasa Narumi2, Seiji Sakai2 Affiliations : 1 Department of Energy Science and Technology, Kyoto University, Sakyo-ku, Kyoto, 606-8501, Japan, 2 Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan Resume : Beta-FeSi2 is one of important light emitting materials which can be synthesized on Si substrates. We report synthesis of beta-FeSi2 nanocrystals embedded in a Si matrix and enhancement of IR light emission at 1544 nm (corresponding to the A band at 0.803eV). High purity synthesis of the nanocrystal can be realized by iron ion-beam implantation into Si substrates and post thermal anneal. We found the fact that the intensity of light emission was affected by a thermal annealing process. A double step process of both preannealing at 400 or 500oC and postannealing at 800oC was very effective to enhacement of the A-band light emission. Observations using Rutherford backscattering spectrometry (RBS), IR absorption spectroscopy and Scaning Electron Microscope (SEM) teach us that the enhacement of light emission from beta-FeSi2 nanocrystals surely originate from increase in nucleation density of nanocrystals. | 17 9 |
| 18:00 | Photoluminescence property of carbon-doped beta FeSi2 nanocrystals Authors : Yoshihito Maeda1,2, Kentaro Nishimura1, Takahito Nakajima1, Bui Matsukura1, Kazumasa Narumi2, Seiji Sakai2 Affiliations : 1 Department of Energy Science and Technology, Kyoto University, Sakyo-ku, Kyoto, 606-8501, Japan, 2 Advanced Science Reseach Center, Japan Atomic Energy Agency, Tokai, Ibaraki, 319-1195, Japan Resume : We report enahncement of photoluminescence (PL) intensity by doping of carbon atoms into beta-FeSi2 nanocrystals. Carbon atoms were doped into the nanocrystals by implantation of C60 cluster ions. The most appropriate condition of implantation dose at the energy of 60 keV was investigated by PL measurements. At the best doping condition, we found enhacement of the intrinsic (A band) PL intensity by 230% in comparison with non-doped samples. A model of bound excitons at doped carbon atoms in nanocrystals was discussed as one of possible models to undestand the observed PL enhancement. | 17 10 |
| 18:00 | Optical and optoelectronic properties of porous silicon and silicon nanowires for photovoltaic application Authors : M. Karyaoui*, M. Ben Rabha, W. Dimassi, M. Amlouk, J.C. Harmand and R. Chtourou Affiliations : Laboratoire de photovolta?e, Centre de Recherches et des Technologies de l’?ergie, Technopole de Borj-C?ia BP 95, 2050 Hammam-Lif, Tunisia Resume : This paper deals with the preparation and the surface modification of porous silicon (PS) and silicon nanowires (SiNWs) obtained by chemical etching method. The optical properties of PS and SiNWs were studied by means of LAMBDA 950 UV/Vis/NIR Spectrophotometer equipped with an integrating sphere. The morphological and optoelectronic properties were studied using scanning electron microscope (SEM), and Laser-beam-induced current (LBIC) technique respectively. The results show that the chemical etching of the silicon surface drops the total reflectivity of the order of 2 % in 400-1100 nm wavelength range for SiNWs. Moreover, the minority carrier diffusion length is found equal to 180 µm of PS samples. | 17 11 |
| 18:00 | Deep-level studies in high-temperature annealed silicon wafers for layer transfer in thin-film solar cells Authors : E. Simoen, V. Depauw, I. Gordon and J. Poortmans Affiliations : Imec, Kapeldreef 75, B-3001 Leuven, Belgium Resume : Introduction. There is currently strong research interest in the development of silicon thin-film solar cells on a transparent substrate [1]. One of the major requirements is the low-cost fabrication of a thin silicon layer. A method which satisfies this requirement relies on layer-transfer, which starts from a silicon wafer, where cavities have been formed by anodic or dry etching [2-4]. This is followed by a high-temperature anneal in hydrogen or argon. Due to the surface migration of silicon atoms, a buried layer of cavities is formed at a certain depth of the substrate, which forms a continuous macropore for sufficiently long annealing times. This enables then the detachment and transfer of a thin silicon film to a glass substrate [4]. The interesting aspect of this approach is that the parent Si wafer can be reused for subsequent layer transfers, provided that the lifetime and crystalline properties are not too much degraded. It has been observed, however, that after three layer transfers the recombination lifetime of the starting wafer is degraded by one decade [5]. This raises the question of the origin of the high-temperature-treatment induced recombination centers. An initial assessment by deep-level transient spectroscopy (DLTS) on p-type Cz substrates revealed some hole traps, which turned out to be most likely created by the sputtering of the Al Schottky barrier [5]. The purpose of the present work is to report on the DLTS observations of two series of samples, which have thermally evaporated Al Schottky barriers. This should avoid the issue of radiation damage during contact formation.
Experimental. Two sets of wafers have been processed: with or without macropores. In the first case, an oxide mask and deep-UV lithography was applied to p-type CZ (100) Si with a resistivity of around 10 cm, followed by plasma etching (more detailed information can be found in [6]). This resulted in 3 m deep cylindrical pores, spaced 800 nm from each other and 550 nm in diameter [4]. Annealing at 1150 oC in H2 was performed for 20 min, so that a regular array of buried voids or pores was formed. A second set of wafers underwent the same high-temperature annealing without pore formation. Both n- and p-type Si wafers, with different resistivities have been included in the study. In all cases, a 2 mm diameter Al Schottky barrier was evaporated. Fourier-transform DLTS has been carried out, as outlined elsewhere in more detail [4,7].
Results and Discussion. It will be shown that in the p-type Cz annealed wafers no deep levels have been observed, demonstrating that the previous observations were indeed related to radiation-induced centers [5]. On the other hand, in the p-Si Schottky barriers with voids, several hole traps have been discovered [7], whereby deep levels at 0.19 eV and 0.41 eV could be related to metal contamination and may be responsible for the observed lifetime degradation after annealing. Finally, in the n-type CZ material, a strong increase in the doping concentration has been found, compared with the starting material and a deep level at EC-0.43 eV has been consistently found, which may be related with a P-V or V-V center. These results will be compared with the spectra on annealed high-resistivity n-type Float-Zone wafers.
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[4] V. Depauw, O. Richard, H. Bender, I. Gordon, G. Beaucarne, J. Poortmans, R. Mertens, and J.-P. Celis, Thin Solid Films 516, 6934 (2008).
[5] V. Depauw, E. Simoen, I. Gordon, and J. Poortmans, Phys. Stat. Sol. A 208, 600 (2011).
[6] V. Depauw, Y. Qui, K. Van Nieuwenhuysen, I. Gordon, and J. Poortmans, Prog. Photovolt: Res. Appl. 19, 844 (2010).
[7] E. Simoen, V. Depauw, I. Gordon, and J. Poortmans, Semicond. Sci. Technol. 27, 015013 (2012). | 17 12 |
| 18:00 | Electrical behaviour of Ge nanoparticles network embedded in SiO2 matrix Authors : Ionel Stavarache, Ana-Maria Lepadatu, Adrian V. Maraloiu, Catalin Palade,Valentin S. Teodorescu, and Magdalena Lidia Ciurea Affiliations : National Institute of Materials Physics, 105 bis Atomistilor Street, Magurele 077125, Romania Resume : Structure and electrical investigations were performed in order to investigate films containing Ge nanoparticles embedded in SiO2 matrix. These films were deposited by RF magnetron sputtering and subsequently thermally annealed in H2 at 2 atm and 500 oC [1].
The structure is investigated by transmission electron microscopy (TEM) and high resolution TEM. Two kinds of features are revealed: a low density of big Ge nanoparticles (20-50 nm) and a network of small amorphous Ge nanoparticles (5 nm) with high density, both embedded in the amorphous SiO2 matrix.
The electrical behaviour of films is studied by measuring current-temperature (I–T) and current-voltage characteristics. The electrical transport takes place through the network of amorphous Ge nanoregions. The I–T characteristics have different temperature dependences at low and high temperatures. At low temperature, the T-1/4 dependence of the logarithm of the current is evidenced, while at high temperature, the T-1 Arrhenius dependence is found. The behavior at low temperature is explained by the hopping mechanism on localized states located in a band near the Fermi energy [2], while at high temperature by the charge excitation to the extended states. At both low and high temperatures, the conductivity is nearly constant, supporting the proposed mechanisms [3].
1. I Stavarache et al., J. Nanopart. Res. 13, 221 (2011)
2. M Pollak et al., Phys. Rev. Lett. 30, 856 (1973)
3. M Fujii et al., J. Appl. Phys. 83, 1507 (1998) | 17 13 |
| 18:00 | Accelerated Degradation of a-Si:H Solar Cell with Full Spectrum Ultra High Irradiance Authors : Sang Hyun Park, Jun-Sik Cho, Jae Ho Yun and Kyung Hoon Yoon Affiliations : Korean Institute of Energy Research (KIER), 102 Yuseong-gu, Taejeon, South Korea Resume : Following global growth in photovoltaic energy generation facilities, long – term reliability more than 25 years of PV module gains significant importance. For the practical and reasonable estimation of long-term reliability, detailed understanding on each degradation factors is essential. Besides long-term continuous degradation in converted electrical power, a-Si:H solar cell especially shows severe early stage degradation from light irradiance. Despite considerable efforts for the past 25 years, this complex nature of light induced degradation effect is still not fully understood. Due to this distinct characteristic of a-Si:H thin film, development of evaluation method for long-term degradation is very important.
Usually, the degradation of a-Si:H solar cell has been tested under general simulated light-soaking environment similar to the IEC 61646 standard test method. This test utilizes light intensity of 1 sun (1kW/ m2). Although this test gives some understanding of solar cell degradation, it does not give enough information on practical characteristics of total long term degradation more than 25 years. For one example, the efficiency stabilization point of a-Si:H solar cell which takes around 3~6 months outfield irradiance can hardly be estimated with previous method because it demands more than 2 or 3 continuous week light soaking for one test set.
In this work, we utilize ultra-high irradiance chamber which can generate higher than 1 sun intensity up to 7 suns full spectrum irradiance. Although there have been several previous works to evaluate high irradiance test to shorten the test time, almost all tests utilized UV wavelength range irradiance only due to the lack of proper full spectrum equipment. This works will evaluate up to 7 suns full spectrum continuous light-soaking test sets and results.
The test cell has been prepared utilizing Korean commercial a-Si:H solar cell fabrication line for uniform characteristics before light-soaking degradation. Each test cell has been fabricated and cut out from original panel size glass following customized active area laser isolation for this light soaking test. Preliminary light soaking test results under 3 suns intensity clearly indicates that high irradiance gives intensive degradation results. This result showed significantly accelerated degradation of a-Si:H solar cell compared to the 1 sun test.
In our presentation, more detailed results of a-Si:H thin film light–soaking test with high irradiance up to 7 suns will be presented. The effectiveness of ultra-high irradiance in analyzing long term reliability of a-Si:H thin film will be discussed in detail. | 17 14 |
| 18:00 | Enhanced formation and sensitization of Si nanocrystals in Al2O3:Er/Si:Er multilayers Authors : J.Z.Wang,1 * X.L Zhang,1 S.L Yang,1 M.Z Yang,2 Y.D Zheng,1 F. Lu,2 and Y. Shi Affiliations : 1School of Electronic Science and Engineering, and Key Laboratory of Photonic and Electronic Materials, Nanjing University, Nanjing 210093, China 2Department of Physics, Fudan University, Shanghai 200433, China Resume : The Er-doped materials are of great research interests in optical communications technology1,2, due to their strong intra-4f Er3+ emission at 1.54 μm wavelength, the standard fiber telecommunication wavelength. Er doped Silicon-rich Alumina shows excellent luminescence properties and very promising to realize Si-based photo-electronic device where Si nanoclusters (Si-NCs) have been used as sensitizers to improve the luminescence of Er3+ ions where the excitation of Si-NCs can be transferred to nearby Er3+ centers for enhanced luminescence performance. 3,4
An enhanced crystallization of Si nanocrystals (Si-NCs) is achieved in Al2O3:Er/Si:Er multilayers fabricated by pulsed laser deposition and subsequent rapid thermal annealing. From the HRTEM and Raman analyses, Implanted Er atoms introduce additional strains in the initial amorphous Si layers and serve as nucleation centers that enhance Si crystallization at low annealing temperatures. And the average size of Si-NCs is controlled well by adjusting the thickness of the Si layers. Furthermore, Angle resolved x-ray photoelectron spectroscopy (ARXPS) results show that thanks to the formation of Si-NCs and the favored chemical environment of Er3+ through annealing treatment at 600 ˚C, an optimized 1.54 μm photoluminescence is obtained. Our result stresses the importance of controlling the formation of Si-NCs to improve the performance of Er3+ luminescence.
[1] J.Z Wang et.al Appl. Phys. Lett. 91, 191115 (2007);
[2] J.Z Wang et.al Appl. Phys. A 94 399 (2009);
[3] S. Núñez-Sánchez, et. al Appl. Phys. Lett. 98, 151109 (2011);
[4] J.Z Wang et.al Chinese Physics Letter 06 4243 (2009). | 17 15 |
| 18:00 | Light-emitting Si nanodots formed by swift heavy ions in Si/SiO2 multilayers Authors : G.A. Kachurin1, S.G. Cherkova1, D.V. Marin1,2, A.H. Antonenko1, V.A. Volodin1,2, A.G. Cherkov1,2 and V.A. Skuratov3 Affiliations : 1A.V. Rzhanov Institute of Semiconductor Physics SB RAS, 630090 Novosibirsk, Russia; 2Novosibirsk State University, 630090 Novosibirsk, Russia; 3Joint Institute for Nuclear Research, 141980 Dubna, Russia. Resume : Properties of Si nanodots are extensively investigated because of their potential applications for Si-based optoelectronics. Usually they are prepared by the high-temperature annealing of Si-rich SiOx. However, this method results in a relatively broad size distribution of the light-emitting Si nanocrystals. Moreover, their size and density cannot be controlled independently. To narrow the size distribution the layer-by-layer deposition of the nanometer-scale amorphous Si and SiO2 multilayers with subsequent annealing has been proposed recently. Unfortunately, the smaller is a nanoparticle the higher temperatures are needed for its crystallization. We attempted to influence the formation of Si nanodots by irradiation of the ultrathin Si/SiO2 multilayers with swift heavy ions (SHI). The structural transformations in their tracks might be stimulated either by ionization or by heat. Six pairs of the 7-8 nm-thick amorphous Si and 10-15 nm-thick SiO2 layers have been deposited on the Si substrates. The layers were irradiated with 167 MeV Xe ions to the doses of 1012-1014 cm-2. Photoluminescence, FTIR absorption, Raman scattering and HREM were used for the characterizations. It was found, that irradiation made the Si-SiO2 borders less distinct and the FTIR spectra revealed a decrease in quantity of Si-O bonds. PL band centered at 500-600 nm has appeared which intensity grew with the ion dose. Such emission is traditionally ascribed to the Si nanoinclusions in SiO2. HREM supported that idea, revealing an appearance of 3-5 nm size dark spots. After annealing at 800-1100 oC the SiO2 network restored and Raman spectroscopy evidenced disappearance of the amorphous Si phase. The photoluminescence strongly increased with a shift of maximum intensity to ~800 nm, typical of Si nanocrystals. Its post-annealing intensity still remained proportional to the SHI dose. The effects observed are discussed. | 17 16 |
| 18:00 | Structural and optical properties study of nanocrystalline Si (nc-Si) thin films deposited on porous aluminum by PECVD Authors : Skander Ktifa, Monther Ghrib, Faycel saadalla, Nouredine Yacoubi Affiliations : Photothermal Laboratory,IPEI Nabeul, University of CarthageTunisia Resume : Porous anodic alumina films are an interesting material [1] for nanotechnology applications because of its unusual properties compared to the bulk counterparts. A lot of works have been devoted to the anodisation of bulk aluminum in order to get a porous film on its surface [2–3]. Different methods of film growth on the surface of the porous matrix layer were used, as for example reactive sputtering [4] and low pressure metal-organic chemical vapor deposition [5]. In this work we demonstrate the capability to grow porous aluminum layers by a simple electrochemical anodisation method, The anodizing process was done by varying the anodizing voltage between 200 to 400 mV. A crystalline silicone films are deposited on the porous aluminum layer by a PECVD technique.
Photothermal deflection spectroscopy (PDS) is used to determine the optical absorption spectrum so the gap energy by comparing the experimental amplitude of the photothermal signal to the corresponding theoretical one. The aim of this work is to investigate the influence of anodisation current on the optical properties of the porous aluminum silicon layers.
The morphology characterization studied by atomic force microscopy (AFM) technique has shown that the grain size of (nc-Si) increases with the anodisation current. However a bang gap shift of the energy gap was observed by both Photoluminescence and Photothermal deflection spectroscopy. | 17 17 |
| 18:00 | Optimization of a SiCxN1-x solar cell Authors : M. Anani, Z. Chama and C. Mathieu Affiliations : Djillali Liabes University. Sidi Bel Abbes. Algeria; University of Artois. Lens. France Resume : This present work investigates the efficiency calculations of a SiCN semiconductor alloy as a solar cell. The presence of a bowing parameter influences the general efficiency of such a structure. This material allies the well mastered Silicon technology added with the idea of a nitrogen insertion in the original SiC material. Calculations concerning the electrical parameters of such solar cell have been conducted in order to improve the global production of electricity using mathematical models taking in considerations the particularities of this singular alloy. | 17 18 |
| 18:00 | Chemical Mist Deposition of Graphene Oxide (GO) and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)(PEDOT:PSS) films for Crystalline Si Thin-Film Solar Cells Authors : Taiga Hiate, Masahiro Imamura, Ryo Ishikawa, Takeshi Fukuda, Keiji Ueno, and Hajime Shirai Affiliations : Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan Resume : Now, crystalline silicon(c-Si)/amorphous silicon (a-Si:H) heterojunction solar cells have been extensively studied and the power-conversion efficiency η have been achieved over 22%. Most of deposition studies on a-Si:H films have been performed using low-pressure plasma-enhanced chemical vapor deposition (PE-CVD) method. On the other hand, recent research on organic thin-film solar cells (OSCs) has extended dramatically because of low-lost and easy methods, i.e., spin-coating, ink-jet, and spray coating. However, the efficiency is still limited to be 3-5%.
In this study, Electrospray deposition (ESD) and Chemical Mist Deposition (CMD) techniques are proposed for uniform deposition of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid)(PEDOT:PSS) and graphene oxide (GO) films on crystalline silicon(c-Si) wafer. In general, the uniform deposition of PEDOT:PSS and GO films on hydrophobic RCA-cleaned c-Si wafer by spin-coating method is crucial for efficient c-Si solar cells and the products condense preferentially. To overcome this difficulty, the ESD and CMD techniques are used for the uniform deposition of conjugated polymer films for efficient c-Si solar cell devices. The initial growth stage of PEDOT:PSS and GO films by the ESD and CMD methods was investigated by through the real-time spectroscopic ellipsometric characterization. The c-Si/PEDOT:PSS:GO solar cells exhibited an efficiency of 9.7%. The CMD method is also available for the large-area and uniform deposition of conjugated polymer thin films. These methods are promising for the uniform deposition of PEDOT:PSS conjugated polymer thin-film for c-Si thin-film solar cells. | 17 19 |
| 18:00 | Electrospray deposition of poly(3-hexylthiophene)(P3HT) films for crystalline Si thin-film solar cells Authors : Tomohisa Ino, Taiga Hiate, Takeshi Fukuda, Keiji Ueno, and Hajime Shirai Affiliations : Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan Resume : Electrospray deposition (ESD) of poly(3-hexylthiophene)(P3HT) films was investigated with conjugated with real-time monitoring by spectroscopic ellipsometry for crystalline silicon thin-film solar cells. The ESD made possible the uniform deposition of P3HT on c-Si and subsequent PEDOT:PSS layer. On the contrary, the spin-coated product condenses preferentially on hydrophobic c-Si wafer using conventional spin-coating method. The SE study revealed the initial growth stage of P3HT films proceeded homogenously with as a solvent. The poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)(PEDOT:PSS)/P3HT/(n-type)/c-Si heterojunction solar cells These findings suggest that the ESD technique is a promising suppress the uniform deposition and the transport of deposition precursors. | 17 20 |
| 18:00 | Carrier transport in conductive Poly(ethylene dioxythiophene):Poly(styrene sulfonate)(PEDOT:PSS)/c-Si heterojunctions Authors : Zeguo Tang, Taiga Hiate, Tomohisa Ino, Keiji Ueno, and Hajime Shirai Affiliations : Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan Resume : We investigated conductive PEDOT:PSS with and without graphene oxide (GO) additions/crystalline silicon heterojuntion devices with carrier transport and capacitance measurement techniques. The devices consist of spin-coated PEDOT:PSS with different GO additions on n-type crystalline silicon wafers. In conjugation with numerical simulations indicate a large band offset at the interface between the two materials. The ideal factor and junction build-in potential deduced from current-voltage and capacitance-voltage plots are .1.8-2 and 0.8~1.02 eV for GO added PEDOT:PSS devices, respectively. From the illuminated IV characteristics, the open circuit voltages were in the range from 0.48 to 0.53 V with increasing GO concentration up to 14% in PEDOT:PSS. Temperature-dependent dark I-V measurements suggest that the carrier transport in the devices is controlled by recombination in the space-charge region. These findings indicate the silicon/conjugated polymer junction can be good candidate for c-Si solar cells. | 17 21 |
| 18:00 | Halogen Lamp Heating for the Fabrication of Selective Emitter Silicon Solar Cells Authors : Kyu-Min Him1,2, Mi-ju Park1, Hi-deok Lee2, Jin-su yoo3 Affiliations : 1DMS CO., LTD 2 Dept. of Electronic Eng, Chungnam National University 3Korea Institute of Energy Research Resume : Fabrication of selective emitter silicon solar cell was discussed on this paper. Recombination of minority carriers were reduced with heavily doped emitter under metal grid. For the process of potential barrier, lamp heating was used instead of conventional laser processing.
Heating temperature, which depends on concentration of light intensity and sheet resistance were analyzed for the proper fabrication of selective emitter solar cells. | 17 22 |
| 18:00 | Modification of High Efficiency Crystalline Silicon Solar cell on Conventional Process using Photoresist as Mask Authors : Kyu-Min Him1,2, Jaekyeong Lee1, Hi-Deok Lee2, Jin-Soo Yoo3 Affiliations : 1DMS CO., LTD. 2Dept. of Electronic Eng, Chungnam National University 3Korea Institute of Energy Research Resume : For the fabrication of high efficiency silicon solar cell, diffusion of phosphorous chloride oxide(POCl3) takes itself an important role. Etch-back processed selective emitter was then fabricated to analyze phosphorous diffused layer. Following of photoresist mask was adapted after POCl3 diffusion with novel method screen printing instead of spin coating and UV exposure as usual. Measured grid finger width of photoresist were 120㎛ and rest of diffused surface were etched with HF : HNO3 : DI solution for different surface doping concentration Ns. Resulting conversion efficiency were recorded 17.7% and following electrical parameters were 76.8% for fill factor and 625mV for open circuit voltage. | 17 23 |
| 18:00 | Optoelectronic properties improvement of monocrystalline silicon using Al2O3 surface passivation and Authors : M. Ben Rabha1*, M. Salem1, M. A. El Khakani2 B. Bessais1, M. Gaidi1 Affiliations : 1Laboratoire de Photovoltaïque, Centre de Recherches et des Technologies de l’Energie, Technopole de Borj-Cédria, BP 95, 2050 Hammam-Lif, Tunisia 2 Institut National de la Recherche Scientifique, INRS-Énergie, Matériaux et Télécommunications, 1650, Blvd. Lionel-Boulet, Varennes, Québec, Canada J3X 1S2 Resume : In this paper, we report the effect of Al2O3 (before and after UV irradiation) on the monocrystalline silicon (c-Si) surface passivation. Al2O3 films with a thickness of about 20 nm are deposited by pulsed laser deposition technique (PLD) on c-Si substrate. it was demonstrated that Al2O3 coating is a very interesting low temperature solution for surface passivation. After UV irradiation, Al2O3 treatment induce an increase up to 30% of the minority carrier lifetime. In this work we will demonstrate that this novel combined Al2O3/UV treatment leads to an excellent level of monocrystalline silicon surface passivation quality as required for high efficiency solar cells.
Keywords : Monocrystalline Silicon ; Al2O3Surface passivation ; lifetime ; UV irradition. | 17 24 |
| 18:00 | MONOCRYSTALLINE SILICON SURFACE PASSIVATION BY POROUS SILICON/Al2O3 COMBINED TREATMENT Authors : M. Ben Rabha1*, M. Salem1, W.Dimassi1, M. A. El Khakani2 B. Bessais1, M. Gaidi1 Affiliations : 1Laboratoire de Photovoltaïque, Centre de Recherches et des Technologies de l’Energie, Technopole de Borj-Cédria, BP 95, 2050 Hammam-Lif, Tunisia 2 Institut National de la Recherche Scientifique, INRS-Énergie, Matériaux et Télécommunications, 1650, Blvd. Lionel-Boulet, Varennes, Québec, Canada J3X 1S2 Resume : In this paper, we report on the effect of porous silicon/Al2O3 combined treatment on the surface passivation of monocristalline Si (c-Si). Al2O3 films with a thickness of 30 nm are deposited by pulsed laser deposition (PLD) are tested for its surface passivation properties on porous Si/p-type monocrystalline silicon wafers. The level of surface passivation is determined by techniques based on photoconductance and Laser Beam Induced Current. As a results, the effective minority carrier lifetime increase from 1µs to 6 µs at ∆n=1015cm-3 and the reflectivity reduce from 40% to about 3% after Al2O3/PS coating.
Keywords : Monocrystalline Silicon ; Porous silicon ; Al2O3Surface passivation ; Reflectivity ; LBIC | 17 25 |
| 18:00 | Nanocavity Generation by Plasma Immersion Ion Implantation in mono and multicristalline Silicon Authors : El Amin Kouadri Boudjelthia, Caroline Andreazza, Hasnaa Etienne, Michel Thomas, Marie-France Barthe, Gabrielle Regula, Esidor Ntsoenzok Affiliations : CEMHTI; CRMD; IBS; IBS; CEMHTI; IM2NP; CEMHTI Resume : Creation of nanocativies in silicon has numerous potentialities for microelectronics, optoelectronics and photovoltaics. Indeed, nanocavities can getter detrimental transient metal impurities, they are used to smartly exfoliate thin slides of wafers used for silicon on insulator technology and eventually, nanocavities in pseudo substrate can control the relaxation of Si1-xGex/Si layers for stress engineering. Thus, it is of great importance to be able to grow nanocavities with a low cost process as Plasma Immersion Ion Implantation. The formation of cavities by immersion plasma is different because the implantation profile is a plateau due to multi-energetic implantation unlike the conventional monoenergetic implantation given by a Gaussian profile with a well defined Rp. In this work we successfully determine the right plasma immersion ion implantation and annealing parameters to obtain shallow nanocavities of nanometric scale. We used n type multicristalline (with 2 to 5 mm grain size) and monocristalline silicon 2×2cm2 in size. They were hydrogen plasma treated at 20kV with doses of either 2×1016 cm-2 or 5×1016 cm-2. Then, they were annealed at temperatures ranging from 800°C to 1000°C. The wafers were then investigated by positron annihilation spectroscopy and transmission electron microscopy. The results show the presence of nanocavities in the area implanted with various geometries which depend on the crystal orientation of the grain in multicrystalline silicon. | 17 26 |
| 18:00 | Electrical properties enhancement of multicrystalline silicon solar cells purified under O2 atmosphere Authors : L. Derbali * and H. Ezzaouia Affiliations : Photovoltaïc laboratory, Research and Technology Center of Energy, Technopôle de Borj-Cédria. BP 95 Hammam-Lif 2050, Tunisia Resume : In this work, a porous silicon-based gettering technique was applied to multicrystalline silicon (mc-Si) wafers. Porous silicon (PS) was formed by the stain-etching technique and was used as a sacrificial layer for efficient external purification technique. The gettering procedure consists of achieving a PS/mc-Si/PS structure that undergoes a heat treatment at temperature ranging between 700 °C and 950 °C for 90 min in an infrared furnace under an O2 ambient. After removing the PS layers, mc-Si solar cells were realized. This process enables to concentrate unwanted impurities in an active region (i.e. the PS layer) close to the surface and to remove them by dissolving the PS layer. The effect of the gettering procedure was evaluated by means of the dark current–voltage (I–V) characteristic to measure the defect density at a selected grain boundary (GB), before and after treatment, and it is also evaluated by the relative increase of the minority carrier diffusion length L, measured by the light beam induced current (LBIC) technique. The serial resistance and the shunt resistance carried out from the dark (I–V) curves confirm this gettering-related solar cell improvement. The current-voltage characteristic at AM 1.5 shows a significant improvement of the electrical properties of mc-Si solar cells subjected to this treatment. | 17 27 |
| 18:00 | Effects of Hydrogenation and Phosphorous incorporation in Silicon Quantum Dot Superlattices Investigated by Electron Spin Resonance Authors : Brian J. Simonds 1, Ivan Perez-Wurfl 2, Yong Heng-So 2, P. Craig Taylor 1 Affiliations : 1 Colorado School of Mines, Golden, Colorado, USA 80401; 2 The University of New South Wales, Sydney, NSW, Australia, 2052 Resume : The ability of bandgap engineering and the natural abundance of silicon have made silicon quantum dots an appealing material system for next generation photovoltaics. In particular, a superlattice geometry allows for the creation of dots in a SiO2 matrix where dot size and spacing can be reasonably controlled. In our investigation we study the effects of passivation with hydrogen on various size dots with different lateral and vertical dot spacings. Electron paramagnetic resonance (EPR) is employed as it is extremely sensitive to the changes in defect concentration which occur with passivation. These measurements show that there are two main defects: a Pb-center defect associated with the dot surfaces and a defect native to the SiO2. In addition, it is found that the effect of hydrogen is sharply dependent on size and is fairly efficient for dots larger in diameter than about 4.5nm but has an almost negligible effect for sizes below this. Photoluminescence experiments also confirm this finding. Also studied with EPR was the effect of phosphorous (P) doping. The incorporation of P showed that upon annealing, the Pb-center defect density gradually disappears. Absent in the P doped samples, however, is the appearance of well-known EPR signatures that show P is incorporated in the dot. One likely explanation for this is that the P dopants make their way to the surface where they act as a passivant but do not substitutionally dope the dot. | 17 28 |
| 18:00 | Electron Transfer and Recombination at Ultrafast Times in Hydrogenated Nanocrystalline Silicon Authors : Brian J. Simonds 1, Matthew R. Bergren 1 3, Baojie Yan 2, Guozhen Yue 2, Matthew C. Beard 3, Tom E. Furtak 1, Richard Ahrenkiel 1, P. Craig Taylor 1, Reuben Collins 1 Affiliations : 1 Colorado School of Mines, Golden, Colorado, USA 80401; 2 United Solar Ovonic LLC, Troy, Michigan USA 48084; 3 National Renewable Energy Laboratory, Golden, Colorado, USA 80401 Resume : Nanocrystalline silicon (nc-Si) combines the higher absorption coefficient of amorphous silicon (a-Si) with the higher mobility of crystal silicon (c-Si) while lacking the light-induced degradation seen in pure a-Si. The nc-Si studied here is comprised of monodisperse silicon crystallites and is generally free of the agglomerated conical features prevalent in other nc-Si:H materials. Here the decay of photoexcited carriers is studied utilizing transient THz spectroscopy for the picosecond (ps) to nanosecond (ns) times scales and an RF technique for times beyond 1 ns. A range of nc-Si volume fractions (Xc) is studied from 0% (a-Si) to 80%. In the shortest times measured we find that all samples exhibit a behavior similar to a-Si. At intermediate times, between 3 and 300 ps, a rise in the THz signal is observed that is ascribed to electrons being transferred from interface defect states to the nanocrystals. This transfer is dependent on Xc. Temperature and wavelength dependent data further support the electron transfer conclusion. At longer times, carriers decay in a manner consistent with multiple trapping. This suggests that even though excited carriers have reached the crystallite, interface defects still dominate transport. Furthermore, our results suggest that carriers generated in a-Si transfer to the c-Si before they completely thermalize, which provides a potential route for hot-carrier extraction within a suitably designed amorphous-nanocrystalline material. | 17 29 |
| 18:00 | Minority carrier Lifetime enhancement in multicrystalline silicon by combining Cr doped TiO2and porous silicon treatment Authors : A. Hajjaji1, 2, M. Ben Rabha2, N. Janene2, M. Gaidi2, B. Bessais2 and M. A. El Khakani1 Affiliations : 1 Institut National de la Recherche Scientifique, INRS-?ergie, Mat?aux et T?communications, 1650, Blvd. Lionel-Boulet, Varennes, Qu?c, Canada J3X 1S2 2Laboratoire de Photovolta?e, Centre de Recherches et des Technologies de l’Energie, Technopole de Borj-C?ia, BP 95, 2050 Hammam-Lif, Tunisia Resume : In this paper a new passivation method is proposed for multicrystalline Silicon wafers for the purpose of solar cell application. The new method combines the use of double treatment based on Cr doped TiO2 and porous silicon. The obtained nanocomposit is investigated for its passivation and antireflection properties. The TiO2 and Cr mixture are deposited by RF-magnetron co-sputtering technique. The Cr doping concentration is optimised by controlling the power applied to the Cr target and varies from 0 to 17 at.%. We demonstrate that, in the 350 - 700 nm wavelength range, the total reflectivity decreases from 41% for untreated mc-Si to about 17% after treatment. The TiO2/porous Si treated sample present a high photoluminescence intensity and an enhancement of the optoelectronic properties. This improvement is amplified by Cr doping. As a result the effective minority carrier lifetime shows an enhancement from 2 µs for uncoated mc-Si to about 733 µs for Cr-TiO2-2 at. % /PS treated ones. Atomic Force Microscopy (SEM) analysis shows a clear correaltion between surface morphology evolution changes after each process and the minority carrier liftime improvement. This improvement is attributed to the passivation effect of Cr-TiO2/ PS nanocomposit on the surface, grain boundaries and bulk of the mc-Si. | 17 30 |
| 18:00 | Analysis of nanocrystallite silicon (nc-Si) growth on anodic alumina layer using chemical deposition Authors : N.Khedher, M. Ghrib, R.Ouertani , H. Ezzaouia Affiliations : Laboratoire de Photovoltaïque (LPV), Technopôle de Borj-Cédria B.P. 95, 2050 Hammam-Lif, Tunisia. Resume : Porous anodic alumina is an extensively studied material due to its unique, self-organized structure that resembles a honeycomb. In this paper, we present results on the fabrication of porous alumina following by growth of the nanocrystalline silicon (nc-Si) by plasma enhanced chemical deposition (PECVD). The porous aluminum layer is fabricated using anodization technical in diluted sulfuric acid solution (70% H2SO4 and 30% H2O2) for the aluminum foil during 28min and for different anodized current varied from 200-400mA. We demonstrate that structure and properties of the (nc-Si) films depend strongly on the currents anodization. The microstructure of anodizing sample before and after deposed nc-Si has been observed using atomic force microscope (AFM), X-ray diffraction and Raman spectroscopy analysis. We show that the sizes of the pores increase from 15 to 28nm. although the sizes of the nanocrystallite silicon reach 55nm when the anodized current reaches 350mA. Also, the photoluminescence spectra of the nc-Si films were very intense compared to the porous alumina sample. These indicate the presence on it the surface and in the pores walls of the Porous alumina films. For alumina layer PL present one spectral peak noted () is at constant wavelength at 1.18ev the other noted () peak shifts also to longer wavelengths. But for nc-Si:H films PL shown one large peak. These indicate exhibited a large radiative transition in the photon energy ranges of 1.86–2.4 eV. The obtained results will be discussed in detail.
Keywords: Alumina, Anodization, Nanocrystalline silicon, Raman spectroscopy, Photoluminescence. | 17 31 |
| 18:00 | Theoretical limit of the down-converters contribution to quantum efficiency of silicon solar cells Authors : A. Zerga, H. Hachemi, K. Benyelles Affiliations : Materials and Renewable Energies research Unity URMER, Faculty of Sciences University Abou Bekr Belkaïd – Tlemcen BP:119 Tlemcen 13000 Algeria Resume : The crystalline silicon solar cells have the major inconvenient of weak absorption in the blue photons region of a solar spectrum. Indeed, these photons are absorbed only in the cell surface where a high recombination dominates due to the heavy doping emitter. However, many authors have shown that silicon at a nanometer scale, has a remarkable property of converting blue photons into visible and near infrared ones that can be absorbed by the silicon in bulk. Also, they proposed different techniques to confine the silicon nanocrystals in the antireflection layers of the standard solar cells.
In this study, we present an analytical method for determining the theoretical limit of the down-converters contribution to quantum efficiency of silicon solar cells. This method is based on calculating the area of the different domains of the spectral irradiance as a function of photon energy. Our results showed that it is possible to achieve 16.7% quantum efficiency improvement if the blue photons are converted into visible ones. Finally, a test example has been invested by this analytical method. This is the case of a solar cell with SiNx: H antireflection layer where silicon nanocrystals are formed by thermal annealing. The estimated contribution is about 0.2% in the considered case of a monochromatic excitation of 3,16eV. | 17 32 |
| 18:00 | On the nature of annealing induced defects in SiC/SiOx hetero-superlattices Authors : Kaining Ding , Urs Aeberhard, Oleksandr Astakhov, Wolfhard Beyer, Friedhelm Finger, Reinhard Carius, Uwe Rau Affiliations : IEK-5 Photovoltaik, Forschungszentrum Jülich, D-52425 Jülich, Germany Resume : The growth of silicon quantum dots (Si-QDs) in SiC/SiOx hetero-superlattices (HSL) represents a promising approach to overcome the competing nature of quantum confinement and carrier transport in nanostructured solar absorbers. Recently, we reported on the successful fabrication of SiC/SiOx HSL with embedded Si-QDs. However, the post deposition annealing treatment required for the formation of Si-QDs also promotes the generation of additional defects. These defects give rise to increased sub-band gap absorption, high densities of paramagnetic centers and decreased PL intensity, but the nature of the defects was so far unclear. Understanding the nature of these defects may help to optimize the processing steps and to develop passivation methods for the reduction of annealing induced defects. In the present work, we deposited SiC, SiO1.2 single layer references and SiC/SiO1.2 HSL samples, which were subsequently annealed at different temperatures. The evolution of structural, optical and electrical properties upon annealing shows that the rise of additional defects correlates with hydrogen effusion and not with formation of crystallites, element inter-diffusion or phase separation. Thus, we assume that these additional defects are mainly dangling bonds arising from the effusion of hydrogen. We also report on results of application of different hydrogen passivation methods confirming that reincorporated hydrogen reduces the defect density due to passivation of dangling bonds. | 17 33 |
| 18:00 | Influence of porous silicon passive layer and TiO2 coating on the optoelectronic properties of multicrystaline Si substrate Authors : N. Janene1, A. Hajjaji1,2, M. Ben Rabha1, My. Ali El Khakani2, B. Bessais1 and M. Gaidi1 Affiliations : 1Laboratoire de Photovolta?e, Centre de Recherches et des Technologies de l’Energie, Technopole de Borj-C?ia, BP 95, 2050 Hammam-Lif, Tunisie 2 Institut National de la Recherche Scientifique, INRS-?ergie, Mat?aux et T?communications, 1650, Blvd. Lionel-Boulet, Varennes, Qu?c, Canada J3X 1S2 Resume : In this work, a novel passivation technique is proposed for multicrystalline silicon wafers for the purpose of solar cell application. The new method combines the use of double treatment based on porous Si and TiO2 passivation. Porous silicon (PS) were prepared by electrochemical anodization of multi crystalline substrates under different conditions of current density (The current density used is between 20 and 100 mA/cm2). It was demonstrated that the porosity increases with increasing current density from 27, 66% to 81%.TiO2 nanoparticles with different nanometric sizes were incorportaed inside pores by the way of the pulsed laser deposition (PLD) technique. .The deposited layers have been characterized by Fourier transform infrared spectroscopy (FTIR) analysis and Atomic force microscopy (AFM).The energy band gap The binary structure of TiO2/SP minimize the average reflectivity from 30% for bare multi crystalline silicon to around 6% for treated substrate, in the 350 – 700 nm wavelength. The TiO2/porous Si treated sample present a high photoluminescence intensity and an enhancement of the optoelectronic properties. As a result the effective minority carrier lifetime shows a strong enhancement after the combined treatment. Atomic force microscopy (AFM) analysis shows a clear correlation between surface morphology evolution changes after each process and the optoelectronic properties improvement. | 17 34 |
| 18:00 | Germanium VLS Nanowire Elaboration Authors : Quentin BENOIT A LA GUILLAUME, Vincent CALVO, Amit SOLANKI, Nicolas PAUC, Pascal GENTILE, Noël MAGNEA Affiliations : SP2M, UMR-E CEA/UJF-Grenoble 1, INAC, MINATEC, 17 rue des Martyrs, F-38054 Grenoble Cedex, France Resume : Germanium and Silicon/Germanium micro and nanostructure are generating a growing interest due to the higher mobility in germanium and to the fact that a suitable doping level associated to tensile strain can lead to a pseudo-direct bandgap material as it has been recently demonstrated. This property seems to be the most promising way to achieve goup IV CMOS compatible Laser whose working wavelength would lies within the telecommunication L band. In that perspective, core-shell nanowire structures can provide a way of shaping, doping and stressing this kind of device.
In this presentation, we will show the elaboration of doped and strained core-shell Germanium nanowire. We managed to grow Germanium nanowire and Silicon/Germanium heterostructures using a catalysed VLS mechanism in a CVD apparatus. Firstly Gold catalysts have been used and give a good nanowire shape, but since gold is a deep level impurity in Germanium, other catalysts will be explored. Doping levels of few 1019cm-3 have been reached using phosphorous atoms via insitu incorporation. In order to apply stress to the core Germanium, we have deposited shells with mismatched thermal expansion coefficient. Strain value can then be tailored through temperature variation. A finite element model of thermal expansion mismatch induced strain has been build to calculate strain values. | 17 35 |
| 18:00 | Growth and characterization of nanostructured silicon-carbon films prepared by PECVD Authors : U. Coscia1, G. Ambrosone2, D.K. Basa3, S. Ferrero4, V. Rigato5, L. Mercaldo6 Affiliations : 1Dipartimento di Scienze Fisiche,Università di Napoli "Federico II"&CNISM Unita’ di Napoli, Complesso Universitario MSA, via Cintia, I-80126, Napoli, Italy 2Dipartimento di Scienze Fisiche,Università di Napoli "Federico II"&CNR-SPIN, Complesso Universitario MSA, via Cintia, I-80126 Napoli, Italy 2x, Complesso Universitario MSA, Via Cintia, I-80126 Napoli, Italy 3Department of Physics, Utkal University, Bhubaneswar- 751004, India 4Dipartimento di Scienza dei Materiali ed Ingegneria Chimica, Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Torino, Italy 5 INFN-Laboratori Nazionali Legnaro, Legnaro, Italy 6 ENEA-Portici Research Center, p.le E. fermi, 80055 Portici, Napoli, Italy Resume : Nanostructured silicon-carbon films composed of Si nanocrystallites embedded in an amorphous silicon-carbon matrix are very interesting advanced materials for studying quantum confinement effects in semiconductors as well as for device applications as intrinsic layer for UV photodetectors, solar cells and visible light emitting devices. In this work nanostructured silicon carbon films were grown in a RF PECVD system from silane and methane gas mixtures highly diluted in hydrogen by varying rf power and keeping constant the other deposition parameters. Samples were deposited on 7059 Corning glass and c-Si(100) substrates for different characterizations. Rutherford back scattering and elastic recoil detection analysis were carried out to determine the elemental composition of films, while UV-VIS-NIR, FTIR, Raman spectroscopies were performed to obtain optical and structural properties. The steady state photoconductivity was measured under white light illumination of 100 mW/cm2 in AM1 condition. Raman and FTIR techniques are shown to be sensitive probes to investigate the structural properties of nanostructured silicon carbon films and the optical properties are observed to correspond to material with crystalline-amorphous mixed phases. The study demonstrates that with increasing carbon content in the films Si crystallite size as well as crystalline fraction decrease approximately from 10 to 3 nm and from 70 to 15% respectively, while the photosensitivity increases by two order of magnitude. | 17 36 |
| 18:00 | Controlling the size of the silicon quantum dots in silicon carbide host matrix by post deposition sequential annealing in vacuum and air Authors : Partha Chaudhuri; Arindam Kole Affiliations : Energy Research Unit, Indian Association for the Cultivation of Science, Kolkata – 700032 Resume : Tuning of the band gap of the silicon nanocrystals by controlling their sizes below their excitonic Bohr radius (called the Si quantum dot) is an effective way to develop all silicon third generation multijunction solar cells. We have tried a “top down” technique to control the size of the silicon nanocrystals embedded in a amorphous silicon carbide (a-SiC:H) host matrix deposited by a plasma enhanced chemical vapour deposition (PECVD) process. Initially, a few sets of samples of a-SiC:H were deposited by PECVD method from mixtures of silane (SiH4) and methane (CH4) highly diluted in Ar by varying the deposition parameters. The samples were first annealed in vacuum upto 600C to grow silicon nanocrystallites of sizes greater than 20nm within the a-SiC:H host. In the next step the samples were annealed in ambient air sequentially at higher temperatures. It was observed that a core shell structure was formed with the Si nanocrystallites as the core and an oxide layer as the shell. The changes in the crystalline Si volume fraction and the size of the nanocrystallites were determined by raman and xrd Debye - Sherrer method. The size of the core gradually decreased in size and the oxide shell layer became thicker with increased annealing temperature in air. The bandgap of the Si nanocrystallites was found to vary between 1.9eV to 2.6 eV following an inverse power law of the size of the nanocrystallites. Effect of a thin Al layer on this sequential oxidation in vacuum and in air ambient was also studied. | 17 37 |
| 18:00 | Local Structural Characterization of Ni Silicide Thin-Films Using EXAFS Authors : M. Alper Sahiner1, P. Y. Hung2, P.S. Lysaght2, J. C. Woicik3, D. Guerrero1 Affiliations : 1Seton Hall University, Physics Department, South Orange, New Jersey 07079, USA; 2International SEMATECH, Austin, TX 78741, USA; 3National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA Resume : The local structural characterization of novel contact materials (nickel silicides) on N2+ implanted Si(100) substrates have been performed using Extended X-ray-Absorption Fine-Structure Spectroscopy (EXAFS) at the National Synchrotron Light Source. The crystal phases of nickel silicides that are stabilized on Si (100) substrates (NiSi or NiSi2) upon varying implant doses and post deposition annealing conditions were identified. The questions addressed are whether the final stabilized crystal phases of the nickel silicide layers could be identified and the fraction of the various crystal symmetries could be determined in nickel silicide layers with multi crystal phase components. The identification of the stabilized crystal phases after modifications in the nickel silicide formation process is crucial, as it was shown that a Si rich Ni silicide layer at the NiSix/Si interface causes a significant reduction in the electron Schottky barrier height (SBH). EXAFS analyses using experimental and theoretical references were performed on nickel slicide thin films on silicon substrates exposed to different N2+ ion doses prior to nickel deposition and silicidation processes. Specifically, using EXAFS analyses, the stabilized phases (e.g. NiSi vs NiSi2 etc) and their ratios were determined. EXAFS was proved to be sensitive to the subtle modifications of the crystal structures introduced by these modifications in the processing conditions. EXAFS analysis of the experimental references materials and detailed EXAFS simulations with calculated theoretical reference EXAFS functions, the crystal structures in nickel silicide films were identified and correlated with the N2+ ion implantation dose. | 17 38 |
| 18:00 | Blue Emitting Silicon Nanocrystals: Origin of Luminescence and the Factors Influencing it Authors : Mita Dasog, Jonathan G. C. Veinot Affiliations : Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada, T6G 2G2 Resume : Semiconductor nanoparticles (or quantum dots) have received immense attention because of their size dependent luminescence. Among them, silicon (Si) nanocrystals are gaining popularity because of their bio-inert nature and material abundance. Unfortunately, silicon is not compatible with traditional colloid chemistry and solution-based reactions used to prepare many quantum dots, innovative solution-, gas-, and solid-phase methods yielding silicon nanocrystals (Si-NCs) have been established. While these procedures afford seemingly identical NCs the optical properties of these quantum dots are unpredictable and two general groupings exist – “size dependent-emitters” and “blue-emitters”. While some scientists argue the luminescence originates from the defects or the NC interface; others believe the NCs are quantum confined and luminescence arises from band gap transitions. This presentation will highlight and explain the origin of blue emission in Si nanocrystals of varying sizes and synthetic methods. | 17 39 |
| 18:00 | Impurity-dependent photoluminescence behaviors from Si/SiO2 multilayers Authors : Weiwei Mu, Hongcheng Sun, Wei Xu, Jie Xu, Jun Xu, Wei Li, Ling Xu, Kunji Chen Affiliations : Nanjing National Laboratory of Microstructures, School of Electronic Science and Engineering and School of Physics, Nanjing University, Nanjing 210093 Resume : Si nanostructure, such as Si quantum dots, embedded in SiO2 host matrix is one of the promising materials for realizing Si-based light source used in optoelectronics and biology. So far, many literatures have been published to do with the luminescence from Si nanostructures. In order to further increase the flexibility of device design and improve the device performance, introducing impurity to obtain p-type and n-type Si nanostructures is still an open question and the study on the influence of impurities on the luminescence behaviors is necessary. In this work, we prepared phosphorus (P) doped Si/SiO2 multilayers in PECVD system by controlling the P-doping concentrations. The as-grown samples were subsequently annealed in 800℃, 900℃ and 1000℃, respectively. As revealed by Raman spectra, the Si sub-layers keep the amorphous structures after 800℃ annealing and start to crystallize at 900℃. After 1000℃ annealing, the formation of Si quantum dots can be clearly identified in cross-sectional TEM image and the size is about 2.5nm. The photoluminescence (PL) behaviors from Si/SiO2 multilayers were systematically investigated as functions of P-doping concentrations and annealing temperatures. For 800℃ annealed sample, no luminescence signals can be detected in the visible range. However, one near infrared luminescence band can be found, whose intensity is gradually increased with increasing the P-doping concentrations. After 900℃ annealing, the PL spectra of multilayers contain two luminescence bands centered at 900nm and 1300nm, respectively. Both luminescence intensities are weak. Further increasing the annealing temperature to 1000℃ causes the disappearance of near infrared luminescence band. However, the band around 900nm is significantly enhanced. With increasing the P-doping concentrations, the visible luminescence signals become weaker while the peak energy is almost unchanged. The introducing of phosphorus may induce the defect states in the Si/SiO2 interfaces and enhance the Auger recombination effect which results in the change of luminescence behaviors. This work was supported by NSF of China (No.61036001) and NSF of Jiangsu Province (BK2010010). | 17 40 |
| 18:00 | Reduction of surface reflectivity in multi-crystalline silicon solar cells by wet nano-texturing Authors : Hyo Sik Chang, Young Joon Cho Affiliations : Graduate School of Green Energy Technology, Chungnam National University, 305-764, Korea Resume : The effect of electroless wet treatment on the multicrystalline silicon solar cells was investigated. We have prepared the nanostructure on multi-crystalline silicon surface so that less light is reflected by wet nano-texturing like reactive ion etching. The nanotexturization can reduce the average reflectance to about 4.1% in the wavelength of 300~900nm. We have also obtained effective reflectance 2.5% with Al2O3/SiNx:H coating. It was found that wet nano-texturing led to a lower reflectance which is lower than in the case of conventional acid texturization. Thus, we can expect the further increase of efficiency of silicon solar cells with the nanotexturization by wet chemical process. | 17 41 |
| 18:00 | Hydrogenated amorphous silicon carbide (a-SiCx:H) for the passivation of thin-film solar cells Authors : A.Gaufrès, F. Husser, E. Fourmond, M. Lemiti Affiliations : INL, Université de Lyon, INSA, UMR - CNRS 5270, Bât Blaise Pascal, 7 avenue Jean Capelle, 69621 Villeurbanne Cedex, France Resume : We investigate the use of amorphous hydrogenated silicon carbide (a-SiCx:H) as a material for the passivation of thin-film solar cells. The current industrial process is based on silicon nitride but a-SiCx:H can be an alternative. The deposition is made by PECVD technique at low temperature (400 °C) with silane and methane. Deposition parameters are optimized to find the most favorable configuration for minimizing the surface recombination velocity.
We have made ellipsometry measurements of the optical indexes n and k on the deposited film in order to study the variation of the optical paramaters with the flow rates of the precursor gases. The surface passivation abilities of a-SiCx:H are characterised by minority carrier lifetime measurements by QSSPC method. C-V measurements are carried on to quantify the fixed charges density and interface states of the deposited film responsible of the passivation. The chemical composition and the nature of the bonds within the layers is studied by FTIR.
First results tell us that the passivation improves with silane proportion until about 600 µs. The a-SiCx:H can be used as a passivating layer. Moreover, this material can passivate the p-type silicon substrate as well as the n-type one depending on film stoichiometry. This is related to the ellipsometry results and permit us to find, for the front and back side of the solar cell, which is the best chemical composition to increase the conversion efficiency. | 17 42 |
| 18:00 | Thermally activated phase transformation in nanostructured SiOx/SiO2 layers Authors : M. Roussel1, E. Talbot1, R. Pratibha Nalini2, F. Gourbilleau2, P. Pareige1. Affiliations : 1 Groupe de Physique des Matériaux, Université et INSA de Rouen, UMR CNRS 6634 - Av. de l’université, BP 12, 76801 Saint Etienne du Rouvray, France, EU ; 2 Centre de Recherche sur les Ions, les Matériaux et la Photonique (CIMAP), CEA/CNRS/ENSICAEN/UCBN, 6 Bd. Maréchal Juin, 14050 Caen Cedex 4, France, EU Resume : Due to their optical and electric properties, silicon nanoclusters embedded in silica have been deeply studied as serious candidates for new generations of photovoltaic cells, memory devices, waveguide amplifiers… These materials exhibit light emission and carrier storage properties which are strongly dependent on their microstructure. As a matter of fact, nanoclusters size distribution, number density, interface, as well as the host oxide composition are key parameters which govern the wavelength of the light emission, the number density of trapped charges…
Size control of silicon nanoclusters is commonly achieved by thermal annealing of SiOx/SiO2 multilayered structures. We studied the influence of the annealing time, annealing temperature, SiOx layer thickness, and SiO2 layer thickness on growth kinetics and Si diffusion in SiOx. Atom probe tomography, which provides a 3D chemical mapping of the analyzed material at atomic scale has been used to investigate the phase separation in such arrays of Si-nc.
The first part of this work is dedicated to the diffusion of Si in suboxide matrix. It demonstrates that diffusion in SiOx is highly dependent on the silicon supersaturation. The second part of this work is focused on decomposition between Si and SiO2 for different thicknesses of SiOx and SiO2 layers. It has been observed that the thickness of the layers drastically change the decomposition process, sometime from spinodal-like decomposition to classical growth of particles. | 17 43 |
| 18:00 | MODELLING, SIMULATION AND OPTIMIZATION OF N-P-N-P SILICON MULTILAYER SOLAR CELLS Authors : A. BOUZIDI, A.S. BOUAZZI, M. AMLOUK Affiliations : Unit?e Physique des Dispositifs ?emi-conducteurs Resume : We simulate the conception parameters of a model of a silicon multilayer solar cell. The cell is composed by four layers of opposite conductivities forming three junctions inside the cell. The electric contacts are tailored vertically to collect the minority carrier generated under illumination.
We developed the equations giving the output power, the fill factor and the efficiency of the cell, taking into account the series resistances of each layer. We optimized, using Matlab software, the thicknesses of the layers, the impurity concentration level and the distance between the electric contacts.
We showed that the optimized photovoltaic structure, with the silicon properties published at the Ioffe institute website, gives an efficiency of 20.66 %. The n-p-n-p silicon cell deliver a short circuit current Icc = 45.3 mA/cm², an open circuit voltage Voc = 0.746 V and an output power of 28.5 mW/cm². The corresponding fill factor is FF = 84.29 %. | 17 44 |
| 18:00 | SIZE-DEPENDENT STRUCTURAL PROPERTIES OF QUASI-ONE-DIMENSIONAL SILICON CLUSTERS Authors : F. T. UMAROVA*, A. B. NORMURODOV*, B. L. OKSENGENDLER**, N. N. TURAEVA** Affiliations : *Institute of Nuclear Physics, Academy of Sciences, Uzbekistan **Institute of Polymer Chemistry and Physics, Academy of Sciences, Uzbekistan Resume : The family of pristine quasi-one-dimensional silicon clusters with the layer number n=25 is investigated by the new quantum-chemical tight-binding method. The structural properties of these clusters are studied as function of cluster sizes. To investigate hollow clusters we have chosen isomer of Si12 of regular hexagonal prism form. Such cluster consisted of two hexagons was shown to be stable (A. Kuzubov et al., 2006). Contributions in the bonds, which are perpendicular to hexagon’s planes, have been brought by all the p-orbitals. The distinctive feature of the investigated clusters is presence of three-coordinated atoms on the top and bottom layers. The optimized geometries of clusters show that the middle layers widen with increasing sizes, whereas the top and bottom layer’s bond lengths decrease, and clusters have trended to the fullerene-like form. The relaxed structure of cluster with 30 atoms loses its hollow structure. Analysis of the obtained results of quantum-chemical calculations has been conducted in framework of the correlative approach of Wigner (1938) and virial theorem (March, 1958). Electron energies are studied separately for each layer. It has been shown to exist a distinction in radial pressing (stretching) forces in different layers, and dependence of the distinction values from the layer number (i.e. from cluster size). As a result, the cluster assumes the barrel-like form. On the whole, the approach under consideration allowed us to throw light upon particularity of formation of fullerene-like structures during growth of hexagonal clusters. | 17 45 |
| 18:00 | Identification of efficient core emission from chemically synthesized Si quantum dots Authors : K. Dohnalova1, H. Zuilhof2, T. Gregorkiewicz1 Affiliations : 1 Van der Waals-Zeeman Institute, University of Amsterdam, Science Park 904, NL- 1098 XH Amsterdam, The Netherlands; 2 Laboratory of Organic Chemistry, Wageningen University, Dreijenplein 8, 6703 HB Wageningen, The Netherlands Resume : Emission from Si quantum dots (SiQDs) is fully determined by the core properties for H-terminated SiQDs and by the surface states for small O-terminated SiQDs. A tailored semi-phenomenological model for the O-terminated SiQDs has been suggested by Wolkin et al. in 1999. Since then, SiQDs with other terminations have been studied, as N- or C-linked organic molecules. Observed PL, however, could not be explained by the existing SiQD models. In particular, the blue-shifted PL with nanosecond decay frequently reported for SiQDs prepared by wet chemistry is totally unexpected and raised doubts about its origin. At the same time, these materials deserve a lot of attention, as the preparation procedure is relatively simple and cheap, yielding large amounts of SiQDs. Moreover studies suggest their non-toxicity for biological systems.
In our work we show beyond reasonable doubt, that this extraordinary emission does indeed originate from SiQDs. This is concluded from a comprehensive study , using combination of the experimental results on ensemble and single dots optical spectroscopy with theoretical modeling. We provide conclusive evidence that the PL in these materials appears as a result of the phonon-less radiative recombination with size-dependent wavelength, which is enabled by energy structure modification induced by the C-linked molecules at the surface of the SiQDs. | 17 46 |
| 18:00 | Optical properties of Tb3+ doped silicon oxynitride films for frequency conversion Authors : Y-T. An, C. Labbé, M. Morales, P. Marie, F. Gourbilleau Affiliations : CIMAP UMR CNRS/CEA/Ensicaen/UCBN 6 Boulevard Maréchal Juin, 14050 Caen Cedex 4, France Resume : The quantum cutting process, in which an energetic photon is converted into two low-energy photons, has great interest to obtain high efficiency solar cell. This process has already been reported in Tb3+-Yb3+ glasses matrix from which a Tb3+ ion is able to excite two Yb3+ ions. But for photovoltaic applications, Si-based thin film is more suitable due to Complementary Metal Oxide Semicondutor integration. However, Tb3+ and Yb3+ co-doped system suffers from the low absorption cross-section in glasses. Our first objective is to achieve an efficient sensitization of Tb3+ ion at high energy via the use of an appropriate matrix to get a high quantum yield in the Tb3+-Yb3+ system.
In this work, silicon oxynitride layers doped by Tb3+ ions were fabricated by reactive magnetron co-sputtering of a Si target topped with Tb4O7 chips under plasma of pure nitrogen. X-Ray diffraction and FTIR were carried out to characterize the sample composition. The photoluminescence (PL) properties were studied as a function of deposition conditions such as plasma pressure, RF target power density, annealing treatment. We determined the best deposition parameters allowing optimizing the Tb3+ PL intensity. Moreover, this emission was enhanced after an annealing treatment at low temperature (600ºC for 1 h). An energy transfer to the Tb3+ has been demonstrated via a non-resonant excitation of the Tb3 PL excitation study. The possibility to achieve a QC effect in Tb-Yb system is thus further studied. | 17 47 |
| 18:00 | Size of Si ncs and energy band alignment in SiO2 Authors : Gabriele Seguini (1), Michele Perego (1), Celia Castro (2), Sylvie Schamm-Chardon (2), Paolo Pellegrino (3). Affiliations : (1) Laboratorio MDM, IMM-CNR, Via C. Olivetti 2, 20846 Agrate Brianza (MB), Italy (2) CEMES-CNRS and Université de Toulouse, nMat group, BP94345, 31055 Toulouse, Cedex 4, France (3) Universitat de Barcelona, MIND, IN2UB, E-08028 Barcelona, Catalunya, Spain Resume : Si nanocrystals (ncs) embedded in oxide host are intensively studied both to investigate the properties of the matter at nanometric scale and for nanoelectronic, optoelectronic, and photovoltaic applications. Among these wide characterization efforts the direct measurement of the Si ncs energy alignment in the SiO2 host is still lacking. The synthesis of 2-dimensional arrays of Si ncs in SiO2 matrix has been achieved by e-beam deposition of SiO2/SiO/SiO2 multilayer structures followed by high temperature (1050°C) thermal treatment in N2 atmosphere. The Si ncs band gap increases with the reduction of the size that is controlled by means of the thickness of the SiO layer. The experimental determination of the energy band alignment of Si ncs in a SiO2 matrix is achieved through the measurement of their conduction band and valence band energy positions in the SiO2 host compared to the bulk Si/SiO2 interface energy barriers. The determination of the energy band alignment between the Si ncs and the SiO2 matrix is achieved by means of photo-ionization/-neutralization and capacitance spectroscopy. [1] The correlation between all the experimental data collected provides a realistic picture of the evolution of the band energy alignment for Si ncs as a function of their size.
This research activity has been funded by the ERANET PLUS “NanoSci-E+” consortium through the NANO-BLOCK project.
[1] G. Seguini et al., Appl. Phys. Lett., 99, 082107 (2011). | 17 48 |
| 18:00 | Evolution of SiHx hydrides during the phase transition from amorphous to nanocrystalline Authors : C. Garozzo1, R.A. Puglisi1, C. Bongiorno1, C. Spinella1, S. Mirabella2, R. Reitano3, S. Di Marco4, M. Foti4, S. Lombardo1. Affiliations : 1 Consiglio Nazionale delle Ricerche – Istituto per la Microelettronica e Microsistemi, Ottava Strada 5, Zona Industriale, 95121 Catania, Italy; 2 MATIS-IMM-CNR, Via Santa Sofia 64, Catania, Italy; 3 Università di Catania, Dipartimento di Fisica, Via Santa Sofia 64, Catania, Italy; 4 STMicroelectronics, Str.le Primosole 50 95121 Catania, Italy. Resume : We present a study on the morphological evolution of hydrogenated amorphous silicon layers obtained by plasma enhanced chemical vapor deposition at different H dilutions in the regime close to the formation of the nanocrystalline (nc-Si) phase. The role of hydrogen in the transition from the amorphous to the crystalline phase is investigated by accurate structural and chemical characterisation, from the early stages of nucleation, where the nuclei present size slightly larger than the critical nucleus, i.e. about 0.8 nm in radius, up to the formation of crystalline grains larger than 30 nm in radius. H is found to have a crucial role in the transition from a-Si:H to nc-Si:H, because it forms an intermediate bond-centred Si–H–Si configuration, and when the H moves away from the bond-centred location, the strained Si–Si bonds either break or relax, undergoing local structural rearrangements closer to those of c-Si. During this phase transition a part of H bonds at its grain boundaries. A correlation between the structural characteristics of the crystalline phase and the bonding mechanism of Si with H through multiple hydrides, such as Si-H2 and Si-H3 is found. Particularly the SiH3 are found to be directly correlated to the shape and the size of the nanocrystallites present in the films. The multiple hydrides are found to play a role also in the electrical characteristics of p-i-n a-Si:H solar cells whose intrinsic layer is realised in the above H dilution conditions. | 17 49 |
| 18:00 | Pumping intensity dependence of photoluminescence spectra of SiGe quantum islands grown on prepatterned Si substrates: evidence of carrier interaction and biexcitonic transition Authors : Petr Klenovský, Moritz Brehm, Vlastimil Křápek, Elizabeth Lausecker, Florian Hackl, Thomas Fromherz, Günter Bauer, Josef Humlíček Affiliations : Department of Condensed Matter Physics, Faculty of Science, Masaryk University, Kotlářská 2, 61137 Brno, Czech Republic, CEITEC - Central European Institute of Technology, Masaryk University, Kamenice 753/5, 62500 Brno, Czech Republic; Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, 4040 Linz, Austria; Department of Condensed Matter Physics, Faculty of Science, Masaryk University, Kotlářská 2, 61137 Brno, Czech Republic, Institute of Physics, Academy of Sciences of the Czech republic, Cukrovarnická 10, Praha 6, 162 53, Czech Republic; Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, 4040 Linz; Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, 4040 Linz; Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, 4040 Linz; Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, 4040 Linz; Department of Condensed Matter Physics, Faculty of Science, Masaryk University, Kotlářská 2, 61137 Brno, Czech Republic, CEITEC - Central European Institute of Technology, Masaryk University, Kamenice 753/5, 62500 Brno, Czech Republic Resume : The pumping intensity (I) dependence of the photoluminescence (PL)
spectra of SiGe quantum dots grown on prepatterned Si(001) substrates
was studied. Their analysis revealed up to seven spectral lines
attributed to phonon-assisted recombinations, no-phonon recombinations
of the ground and excited states of excitons, all showing linear
dependencies of the peak intensity on I. At large values of I, additional
lines with a quadratic dependence on I appear in he PL spectra
that are assigned to biexciton transition. The experimentally obtained
energies of the no-phonon transitions are in good agreement with the
exciton and biexciton energies calculated within the framework of a k.p𝑝 theory. To the best of our knowledge this is the first clear evidence of the carrier interaction and biexcitonic transition in SiGe/Si QDs. | 17 50 |
| 18:00 | On the impact of the interfacial SiOx-layer on the passivation properties of PECVD synthesized Aluminum oxide Authors : Abdelazize Laades1, Mario Bähr1, Hans-Peter, Sperlich2, Michael Blech1, A. Lawerenz1 Affiliations : 1CiS Forschungsinstitut für Mikrosensorik und Photovoltaik GmbH, Konrad-Zuse-Str. 14, 99099 Erfurt, Germany; 2 Roth & Rau AG, An der Baumschule 6-8, 09337 Hohenstein-Ernstthal, Germany Resume : Due to its unique feature of containing a negative charge, aluminum oxide (a-AlOx) is favorable for the passivation of lowly and heavily doped p-type silicon surfaces. A main issue is the presence of an interfacial silicon sub-oxide layer, which forms independently of the deposition method and strongly controls the passivation properties. In this work, the interface passivation of a-AlOx/a-SiNx:H stacks deposited on p-type (100) mono-crystalline silicon by plasma enhanced chemical vapor deposition (PECVD) is investigated by means of charge carrier lifetime and capacitance voltage (CV) measurements. To control the quality of the interface, we performed different surface preparation steps prior to a-AlOx deposition resulting in a thermally oxidized surface with variable oxide thickness, a wet chemically grown oxide and a native oxide. Our investigation is focussing on the interface passivation mechanisms upon firing as applied in the silicon solar cell industry. From the flat band voltage shift monitored by CV measurements, we found that the effective charge density decreases when increasing oxide thickness and even switching from negative to positive polarity for very thick interlayers. The passivation has been activated by a firing step due to an increase of the negative charge. With thermal oxides thinner than 4 nm and native oxide, a good passivation is achieved. However, an excellent passivation level is attained using an ultrathin high-quality wet chemical oxide. | 17 51 |
| 18:00 | Detailed investigation of the structural and passivation properties of silicon oxynitrides for silicon solar cells Authors : Abdelazize Laades1, Michael Blech1, Maurizio Roczen2, Alexander Lawerenz1 Affiliations : 1CiS Forschungsinstitut für Mikrosensorik und Photovoltaik GmbH, Konrad-Zuse-Straße 14, 99099 Erfurt, Germany; 2Helmholtz-Zentrum Berlin (HZB), Institute for Silicon Photovoltaics, Kekuléstrasse 5, 12489 Berlin, Germany Resume : We investigated the structural and passivation properties of hydrogenated amorphous silicon oxynitrides (a-SiOxNy:H) prepared by plasma enhanced chemical vapor deposition controlling the gas flow ratio N2O/SiH4. To analyze the thermal stability, test samples were subjected to high temperature firing in the range 850 to 950 °C.
Using energy dispersive X-ray analysis and X-ray photoelectron spectroscopy, we determined the stoichiometry x = [O]/[Si] in the whole range from 0 to 2. Charge carrier lifetime measurements revealed that Si-rich a-SiOxNy:H features excellent surface passivation on p- and n-type CZ silicon in the as-deposited state. After firing, a SiOx/a-SiNy:H stacks with near-stoichiometric a SiOx showed an outstanding thermal stability. Surface recombination velocities below 22 cm/s and 10 cm /s for p- und n-type CZ silicon have been reproducibly reached. A fine tracing of the density and spectral position of the Si-O-Si stretching vibration by means of the Fourier transform infrared spectroscopy revealed valuable information on the incorporation of oxygen atoms. Accordingly, we found that a high density and frequency of Si-O-Si bonds approaching the characteristic frequencies of thermal SiO2 and silica (1075 to 1080 cm–1) is clearly correlated to the interface passivation quality. Combined with the hydrogen migration from an a-SiNy:H cap layer induced by firing, the a SiO2/a-SiNy:H system features passivation properties close to thermally grown silicon oxide. | 17 52 |
| 18:00 | High density core-shell silicon nanowire array for the realization of low cost solar cells Authors : L. Dupré, T. Gorisse, D. Buttard, P. Gentile, A. Solanki, N. Pauc Affiliations : SiNaPS/SP2M, UMR-E CEA/ UJF-Grenoble 1, INAC, 38054 Grenoble, FRANCE Université Joseph Fourier, Grenoble-1, 38000 Grenoble FRANCE Resume : The future use of nanostructures such as silicon nanowires in solar cells will occur only if their growth is self-organized, with high density and controlled in terms of dimensions and localization in space. We demonstrated the growth of silicon nanowire arrays of high density using anodic alumina template on silicon wafer [1]. Currently most of the studies and characterizations are performed on single nanowire devices showing an axial P-N junction and resulting in promising photovoltaic capabilities.
In this work we develop and study the performance of arrays of nanowires functionalized as solar cells using a radial P-N or P-i-N junction thanks to a core shell structure. The core of the structure is made of a P-doped nanowire grown by Chemical Vapor Deposition (CVD) using the Vapor-Liquid-Solid method, and the shell is created by a 2D deposition of intrinsic and/or N-doped silicon layer by CVD. The resulting device is then a dense array of vertically aligned and functionalized silicon nanowires that presents interesting photovoltaic capabilities.
The use of porous alumina membranes enables to grow wires on universal substrates (effective growth direction different from the preferential growth direction) with a good regularity. This property will be a crucial point for developing silicon nanowire arrays on low-cost substrates such as glass or polymer for low-cost photovoltaics.
[1] D. Buttard, T. David P. Gentile, F. Dhalluin, T. Baron, Phys. Stat. Sol. RRL 1, 19 (2009). | 17 53 |
| 18:00 | A new route to silicon QDs fabrication in a silicate matrix Authors : Alessandro Antonaia, Anna Castaldo, Maria Luisa Addonizio, Emilia Gambale Affiliations : ENEA (Italian National Agency for new technologies, Energy and Sustainable Economic Development) Resume : Silicon nanocrystals (Si-NCs) embedded in a dielectric matrix can be successfully employed in the field of silicon optoelectronics and third-generation photovoltaic. Depending on nanocrystal size, the bandgap energy of Si-NCs can be tuned. On the other hand, electronic coupling can be obtained by proper choice of Si-NCs grain size and dielectric matrix material. A great deal of work has been done on growth and characterization of Si quantum dots embedded in dielectric matrices such as silicon oxide, nitride and carbide. There are many methods to produce Si-NCs but they usually need a very high temperature annealing step to promote crystallization that can be unsuitable to insert Si-NCs layer in a device. We propose an innovative process to fabricate Si nanostructures dispersed in an insulating matrix by means of a cheap and scalable method. This fabrication process is composed of two steps: starting from ZnO and Si targets, a magnetron deposition in co-sputtering mode has been carried out, followed by an annealing cycle under vacuum that did not exceed 560 °C. The sputtered materials consist of multiple alternate layers of a-Si and ZnO. The resulting materials after annealing consist of Si-NCs dispersed in an insulating zinc silicate matrix. A so low crystallization temperature can be considered an important goal for an appropriate employment of Si-NCs materials. A convenient process window has been selected in order to promote a reaction between ZnO and Si, giving homogeneously dispersed Si-NCs without any residual amount of a-Si. Nanocrystal size and related bandgap have been tuned by varying the power ratio between Si and ZnO cathodes in the sputtering process. The layers have been characterized by TEM, X-ray diffraction, UV-VIS-NIR, micro-RAMAN, FTIR and PL techniques. | 17 54 |
| 18:00 | Mechanisms of the formation of gold droplet ensembles on Si substrates during thermal anneals Authors : A. Sarikov, A. Pastushenko, A. Klimovskaya Affiliations : V. Lashkarev Institute of Semiconductor Physics NAS Ukraine 41 Nauki avenue, 03028, Kiev, Ukraine Resume : Formation of the patterns of catalytically active metal droplets on substrates is an important stage for the growing Si wire-like crystals because this stage predetermines the main wire characteristics. Understanding physical mechanisms of droplet evolution during thermal processing and determination of associated parameters are the clue to the controlled formation of droplet ensembles and thus to the predicted growing Si wire-like crystals.
In this work, self-organization evolution of the size distribution of gold droplets on the surface of Si substrate during thermal anneals is studied theoretically. A kinetic model of droplet evolution that takes into account the combined action of two evolution mechanisms, namely the droplet coalescence and the Ostwald ripening, is proposed. The coalescence is dominant for relatively small and mobile droplets and leads to the formation of logarithmic normal droplet size distribution. At low droplet mobility (e. g. large droplets, rough surface, low temperature etc.) Oswald ripening becomes prevailing and the Lifshitz-Slyozov size distribution of droplets forms. From the comparison of theoretical results with the experimental data, the characteristics of both mentioned mechanisms for droplet evolution as well as the conditions for the transition from coalescence to Ostwald ripening are determined depending on the substrate type, initial droplet distribution, and treatment temperature. | 17 55 |
| 18:00 | Defect engineering during the contact co-firing step in an industrial belt furnace. Authors : A. Peral, J-F. Lelièvre, F. Recart, C. del Cañizo Affiliations : Instituto de Energía Solar - Universidad Politécnica de Madrid Resume : In a typical industrial multicrystalline solar cell production line there are two high temperature steps after the crystallization process. The first one is the Phosphorus Diffusion Gettering, which has been widely investigated in order to achieve lower metal concentrations and higher charge carrier lifetimes. The second one is the contact co-firing step, which has been less studied although it can reduce significantly the final solar cell efficiency.
In this work, the effects of the contact co-firing step in the concentration and distribution of metal impurities are studied by means of both simulations and experiments in an industrial belt furnace. The results confirm the dissolution of iron precipitates and the phosphorous gettering of interstitial iron during the rapid thermal annealing process if carried at 800-900 ºC.
Moreover, the performance of the rapid thermal annealing depends heavily on the original position of the wafer in the ingot. The effects of different time-temperature profiles of the contact co-firing step have been simulated for a wide range of as-grown material using the Impurity to Efficiency (I2E) simulation tool that has been developed in a collaboration IES-MIT. The distinct materials are characterized by the total as-grown iron concentration and the as-grown precipitate radius. According to these two characteristics, two distinct types of material can be distinguished inside of the typical cast multicrystalline silicon ingots: center region material (material A) has a low density of big radius iron precipitates; material from the border and towards the top region (material B) has a higher density of small radius iron precipitates. The as-grown material range of the simulations includes both material types: the total as-grown iron concentration varies between 〖10〗^13 and 〖10〗^16 cm^(-3), while the as-grown precipitate radius varies in quite a wide range (15-50 nm). In addition, the as-grown interstitial iron concentration is assumed to be 5•〖10〗^11 cm^(-3) for all the cases.
The results of the simulations are reported below. The post-processed interstitial iron concentration after a standard phosphorous diffusion gettering at 850 ºC lays below 〖10〗^12 cm^(-3) for all the simulated as-grown values. After a standard rapid thermal annealing at 900 ºC the interstitial iron concentration remains constant or increases, depending on the as-grown iron concentration and precipitate radius. In this case, an increase will arise if the dissolution of iron precipitates is presumably higher than the external gettering of interstitial iron. However, after a standard rapid thermal annealing at 800 ºC, the concentration does not change with the annealing. In this case, the dissolution is compensated by the external gettering. Another time-temperature profile, which is named ‘extended’, has been simulated for 800 and 900 ºC. For a peak temperature of 800 ºC, for material A, the extended annealing leads to poorer results than the standard one, showing higher interstitial iron concentrations. Material B responses better to the extended annealing, decreasing interstitial iron concentration. When 900 ºC are used, the standard co-firing, in general, does not modify or increase the interstitial iron concentration, while the extended co-firing increases it. Only for some determined radii and total as-grown iron concentration the interstitial iron can be lower using the extended co-firing (instead of the standard one).
The conclusion of the simulations is that the final interstitial iron concentration can be reduced during this final fabrication step of multicrystalline silicon solar cells if an optimized time-temperature profile is used for the contact co-firing step. The optimum profile has to be designed according to the ingot position and can result in using just a small additional process time in the furnace (<2’).
In the experimental work, the different time-temperature profiles were implemented for a set of 40 multicrystalline silicon wafers from the same ingot. First, the wafers were phosphorous diffused. Second, they were SiNx PECVD deposited on both sides. Later, they were annealed in an industrial belt furnace. All the experiments confirm the dissolution of iron in the absence of phosphorous emitter whereas, when present, the phosphorous gettering limits the dissolution. In this material, the as-grown interstitial iron concentration is typically 5•〖10〗^11 cm^(-3). After standard phosphorous diffusion it is in the range of 8•〖10〗^10 cm^(-3), an order of magnitude below the as-grown value. After rapid thermal annealing, the interstitial iron concentration lies in the same order of magnitude than after phosphorous diffusion for all time-temperature profiles, but a clear tendency can be observed. At 800 ºC, an increased interstitial iron concentration is observed for the standard co-firing, whereas the concentration decreases for the extended co-firing. At 900 ºC, the opposite phenomenon is observed: the standard co-firing does not modify the interstitial iron concentration, but the extended co-firing increases it.
Furthermore, some solar cells have been fabricated with both the standard and the extended contact co-firing steps at 800 and 900 ºC. The efficacy of the optimized co-firing step has been proven in these solar cells.
In conclusion, this work has shown through both simulations and experiments in an industrial belt furnace the need to optimize the time-temperature profile used for the contact co-firing step according to the as-grown iron concentration and distribution. The design of defect engineering processes leads to a reduction of the final interstitial iron concentration and to an increase of the solar cell efficiency. The I2E simulation tool has allowed to estimate the optimum diffusion and firing conditions tailored for different silicon materials. All the experimental results are consistent with the simulation reported above. | 17 56 |
| 18:00 | Oxidation of the hydrogen and hydrocarbon covered nanosilicon Authors : A.P. Mukhtarov, A.B.Normurodov, M.T. Swihart Affiliations : A.P. Mukhtarov; A.B.Normurodov; Institute of Nuclear Physics AN RUz, 100214 Tashkent, Uzbekistan; M.T. Swihart University at Buffalo, State University of New York, Buffalo, New York 14260-4200, USA Resume : Silicon nanoparticles have attracted great interest due to their luminescence properties and use as light emitters in displays or general illumination. The origin and characteristics of the luminescence are associated with the nanoparticle size, its shape and the nature of its surface. But Si nanoparticles oxidized easily on air that lead to red-shifted emission. Si nanoparticles with organic monolayer on the surface were found to be quite resistant to oxidation.
Here the oxidation phenomena of the hydrogen terminated nanoparticles upon heating or under 254 nm UV radiation and the stability of the hydrocarbon covered particles has been researched by non-conventional tight-binding method.
We considered clusters with oxygen atoms bonded to silicon atoms of the surface. Oxygen bonded to one Si of the bare cluster made the (-) charged cluster more stable than the neutral one. The same oxygen bonded to Si29H24 made the neutral cluster more favorable than other charge states. Carbonyl (-CH=O) and carboxyl (-COOH) groups appeared to be unstable on the Si29H24 surface, losing H atoms. The oxidation of H-terminated nanoparticles upon heating or under 254 nm UV radiation in experiment, and the stability of the hydrocarbon covered particles, can be easily explained by breaking surface Si-H bonds, which requires ~3.75 eV, initiating subsequent oxidation. The Si-CH3 binding energy is ~5.5 eV and therefore these bonds are stable against UV irradiation or moderate heating. | 17 57 |
| 18:00 | The structure-induced changes in electrophysical properties of SiGe submicron wires Authors : A. Druzhinin (1,3), I. Ostrovskii (1,3), A. Dolgolenko (2), Yu. Khoverko (1,3), S. Nichkalo (1), Iu. Kogut (1), R. Koretskii (1) Affiliations : (1) Scientific-Research Center “Crystal”, Lviv Polytechnic National University, 1 Kotlyarevskii Str., Lviv, 79013, Ukraine (2) Kiev Institute for Nuclear Research of National Academy of Sciences of Ukraine, 47 Nauky Ave., Kiev, 03680, Ukraine (3) International Laboratory of High Magnetic Fields and Low Temperatures, 95 Gajowicka Str., 53-421, Wroclaw, Poland Resume : Considering the application of semiconductor whiskers in electronics one should take into account their specific structure that may affect the mechanical and electrophysical properties of crystals. In particular, CVD grown submicron Si and SiGe whiskers represent a kind of heterostructure consisting of single-crystalline core covered with nanoporous shell. In this report we show that charge carriers transport and quasi-particles scattering in p-SiGe whiskers substantially differs from that of bulk crystals. In particular, in contrast to the expected increasing, the ∆E2 activation energy of conductivity at cryogenic temperatures decreased and the hole mobility was found to be 1,5 times higher than that of bulk p-SiGe. It was found that in whisker samples the value of collisions integral was higher than in bulk p-SiGe, which infers the decreased scattering of charge carriers by phonons and the enhanced phonon drag effect in whiskers. The latter has been confirmed by the shift of Seebeck coefficient maximum towards higher values of temperature on S(T) dependencies of whiskers. The assumption that the observed changes in electrophysical properties of p-SiGe whiskers are caused by the interface tension due to the lattice mismatch between the crystalline core and nanoporous shell was made. | 17 58 |
| 18:00 | Modelling the splitting of thin silicon films from porosified crystalline silicon upon high temperature annealing in hydrogen Authors : Moustafa Y. Ghannam, Yaser Abdulraheem, Abdul Azeez Alomar, Jef Poortmans Affiliations : Kuwait University-Kuwait; Kuwait University-Kuwait; Kuwait University-Kuwait; IMEC Leuven-Belgium Resume : Splitting a thin silicon film upon high temperature annealing of porosified crystalline silicon goes first through spheroidization of the vertical pores into spherical micro-cavities. If the initial pores are close enough to each other, the cavities coalesce followed by rapid surface diffusion and flat plate splitting. It has been demonstrated that splitting is more successfull when the annealing is carried out in hydrogen. In the present work a study on the specific role of hydrogen in the splitting process is carried out. During high temperature annealing in hydrogen gas at T > 1100oC in-diffusing hydrogen molecules dissociate and isolated atomic hydrogen migrate and segregate at the surface of the cavities forming low energy Si-H complexes thereby lowering the cohesive strength (surface energy). Upon gradual cooling atomic hydrogen is liberated from Si-H bonds and form hydrogen molecules inside the cavity which help building up a differential internal pressure on its wall. An analytical model based on ideal gas law, mass transfer, energy balance based on thermodynamics and thermal elasticity principles is proposed to determine the pressure and its impact on cavity expansion and de-cohesion of Si-Si bonds. Comparing analytical results with reported experimental observations it appears that while splitting is successful in samples showing immediate coalescence of closely packed pores, hydrogen helps building up the pressure needed for remote micro-cavity expansion and coalescence. The pressure in the cavity, however, seems not reaching the level needed for cracking. | 17 59 |
| 18:00 | Strain distribution in GaAs/Si Quantum Wires Authors : T. Tchelidze , A. Davydok Affiliations : Tbilisi State University, Faculty of Exact and Natural Sciences, Department of Physics. 3 Chavchavadze Ave 0179 Tbilisi Georgia, 3University of Siegen, Department of Physics, Walter-Flex-Str. 3 57068 Siegen, Gemany Resume : Semiconductor nano wires are subject of continuously growing interest, which is connected to wide range of potential application for advanced electronic, photonic, sensing. Because unique properties their investigation have also fundamental importance. One of the interesting issue is nanowires elastic properties. Different from planar hetero structures nanowire can relief strain energy via lateral relaxation and one can expect this one dimensional structure can be grow defect free more easily than planar structures. That is why evaluation of strain distribution along nanowire and strain energy distribution is crucial for growth optimization.
We calculated displacement and stress field , and elastic energy for GaAs nanowires grown on Si substrate. For calculations variational method was used. For radial coordinate dependence polynomial dependence (with linear and quadratic terms) and for vertical coordinate dependence exponential functions are taken inside the wire region. Radial and vertical displacements decreases as 1/r with increasing radial coordinate in substrate outside the wire region. For 30 nm wire size calculated total strain energy is 10^6 eV. The most of it is accumulated in substrate. Energy accommodated in wire 7 *10^4 eV. Strain energy was calculated as a function of nanowire diameter. On the base of obtained results we estimated maximum radius of nanowire bellow which dislocation free growth takes place. | 17 60 |
| 18:00 | Investigation of Si nanowires from VLS growth Authors : Ulrich Herr, Benjamin Riedmueller, Mike Haddad, Khaleel AbuShgair, Manfred Madel, Klaus Thonke Affiliations : Ulm University, 89081 Ulm, Germany Resume : Si nanowires are of interest for photovoltaics and sensors. We report about the growth of Si nanowires using a vapor-liquid-solid (VLS) growth process at atmospheric pressure. At elevated growth temperatures, singe crystalline wires with clear facets are obtained. The orientation of the wires has been studied by EBSD. Contacts have been applied to the wired using metal deposition in a FIB microsope. Electrical characterization under illumination shows the presence of a significant photoconductivity. Further functionalization of the Si nanowires by combining them with luminescent nanoparticles is presently under investigation. | 17 61 |
| 18:00 | Hospital lighting photovoltaic system-grid interconnected Authors : Viveros Ramirez, Delgadillo Angelica, Hernandez Hugo Affiliations : pyrotechnical metropolitan university of Hidalgo MX, autonomy university of Mexico Resume : Hospital lighting photovoltaic system-grid interconnected
Secure energy supply is vital in a hospital, ensure that energy is available to ensure patient safety, reduce accidents and avoid financial penalties related to the lack of electricity. Besides the maintenance policy is key to ensuring the performance of energy and avoids unnecessary costs due to lack of it. Cost constraints: hospitals are under enormous cost pressures, because the cost of emergency care is increasing rapidly. With a PV system interconnected to the network, offer integrated solutions for the entire infrastructure of the building, in terms of lighting with savings of up to 25% of capital expenditure costs of electricity, in full compliance with safety standards and required by the laws and regulations that are required. A complete electrical distribution architecture that maximizes uptime. Energy efficiency and maintenance optimization, saving up to 30% in operating costs. Service teams to help improve hospital performance throughout its life cycle. | 17 62 |
| 18:00 | Optical modeling of front surface enhances absorption by sol-gel and wet-etching process for solar cell applications Authors : S.J Lee;M.G Hurb;T.S Kimc; D.H Yoon Affiliations : School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 440-746, Republic of Korea; School of Interdisciplinary Program in Photovoltaic System Engineering, Sungkyunkwan University, Suwon 440-746, Republic of Korea; Symphony energy31613~1614 samhung bldg.705-9 yeoksam-dong, gangnam-gu,seoul 135-711, Republic of Korea; School of Advanced Materials Science and Engineering, SKKU Advanced Institute of Nanotechnology(SAINT), Sungkyunkwan University, Suwon 440-746, Republic of Korea Resume : Plasma-enhanced chemical vapor deposition (PECVD)silicon nitride(SiNx) film is widely used as an antireflection coating (ARC) and passivation layer for commercial high efficiency silicon solar cells. However, (PECVD) SiNx processes are very expensive and complex, so the process are not suitable for low-cost and high efficiency silicon solar cells.
In this study, multi-crystalline silicon (MC-Si) solar cell apply to use silicon dioxide sol-gel coating process and wet etching process for ARC and passivation with low-cost. This researches are silicon dioxide sol-gel coating and silicon dioxide wet etching processes. This experiment conditions have spraying coated silicon dioxide layer treatment temperature and different component of etchant volume ratios (HF:HNO3:H2O). The conditions were determined by mathematic calculation based on the acid etching theory and experimental data. SiO2 layer etching ratio and thickness were determined treatment temperature and spraying deposition conditions. After SiO2 sol-gel coated MC-Si wafer samples were etched with the different acids. The samples were measured by UV-IR. Samples were etched with 1:3:8, 1:4:10 (HF: HNO3: 3rd D.I water) are closer to low reflectance (3~7%) in 500~600nm wavelength. The wafers' surface was textured because particles have certain shape as porous layer. This etching process can replace (PECVD) SiNx processes and texturing. And also, those wafers show improving short-circuit current by passivation effect and enhanced ARC. On the whole, we combined surface texturing, passivation and ARC process into only two process by silicon dioxide sol-gel coated wafer wet etching process.
In conclusion, It is believed to change simple manufacturing process and low production cost by using this spraying deposited SiO2 sol-gel ARC and chemical texturing processes. | 17 63 |
| 18:00 | Reduced Process Step for Local Back Contact in Crystalline Silicon Solar Cell by a Dot of Fine Pattern Screen Printing Method Authors : Jonghwan Lee, Vinh Ai Dao, Youn-Jung Lee, Minkyu Ju, Cheolmin Park, Kyungyul Ryu, Kyuho Choi, Bongi Kim, Junsin Yi Affiliations : School of Information and Communication Engineering, Sungkyunkwan University, Suwon, 440-746, Korea Resume : We presented a detailed study on a Local Back Contact (LBC) formation of rear-surface-passivated silicon solar cells, where both the LBC opening and also metallization are realized by one-step of alloying of a dot of fine pattern screen-printed aluminum paste with silicon substrate. Base on Energy Dispersive X-ray (EDX) and Scanning Electron Microscopy (SEM) characterization, we suggest that the distribution of the aluminum and the silicon concentration determine the Local-Back-Surface-Field (Al-p+) layer thickness, resistivity of the Al-p+ and hence the quality of the Al-p+ formation. The highest penetration of silicon concentration of 78.17% in aluminum resulting in longer Al-p+ layer thickness of 5 um, then minimum LBC resistivity of 0.92 x 10-6 Ω cm2 was obtained. The degradation of the rear-surface passivation due to high temperature of LBC formation process can be fully recovered by forming gas annealing (FGA) at temperature and hydrogen content of 450 0C and 15%, respectively. The application of the optimized LBC of rear-surface-passivated by a dot of the fine pattern screen printing aluminum paste results in efficiency of up to 19.98 % with a Voc = 649 mV on 10.24 cm2 p-type Cz silicon wafers. With assisting of FGA for rear-surface passivated recovering, efficiencies up to 20.35 % with a Voc of 662 mV, FF of 82%, Jsc of 37.5 mA/cm2 are demonstrated. | 17 64 |
| 18:00 | Improved performance of n-i-p silicon thin-film solar cells via nanotextured Ag/Al:Si back reflectors Authors : Jun-Sik Cho†, Byungyeol Jang, Ji Eun Lee, Sang-Hyun Park, Jinsu Yoo, Joo Hyung Park, Kyung Hoon Yoon Affiliations : Korea Institute of Energy Research Resume : Highly textured Ag/Al:Si back reflectors for flexible n-i-p silicon thin-film solar cells were prepared on flexible stainless steel substrates by dc magnetron sputtering, and their light scattering properties were investigated systematically.
Silicon thin-film solar cells on flexible substrates are considered the most promising candidates for low-cost solar cells because roll-to-roll processing on flexible substrates allows a higher throughput, and the production equipment requires less floor space. Compared to silicon thin-film solar cells on glass substrates, flexible silicon thin-film solar cells have many advantages, including flexible and unbreakable characteristics, cheap substrates and ease of handling and transportation, which opens new possibilities for the application of photovoltaics, such as easier deployment and better integration into buildings. Substrate structures with the n-i-p configuration of silicon thin- films are usually used for flexible silicon thin-film solar cells, in which metal layers with high reflectance are used as the back reflector. For amorphous and microcrystalline silicon thin-film solar cells, light trapping is crucial to obtain a high current density because the light absorption of the silicon thin-film absorbers is relatively low. In the n-i-p substrate structure, one of most efficient methods to enhance light trapping is to make the back reflector surface rough. The textured surfaces of back-reflectors increase the optical path length due to the light scattering on the textured surface at oblique angles and the enhanced internal total reflection at the interface within the cells.
In this study, the surface texturing of dc sputtered Ag/Al:Si bilayers were carried out by changing the surface features of Al:Si films. The surface morphology of the sputtered Al:Si films was controlled precisely by varying the deposition parameters. The optical properties, such as total and diffuse reflectance, were investigated for the back reflectors with different surface features. The influence of the highly textured Ag/Al:Si back reflectors on the performance of flexible silicon thin-film solar cells will be also explained in detail. | 17 65 |
| 18:00 | Magnetron sputtered amorphous silicon films with closed porosity: microstructure and optical properties Authors : V.Godinho (1), D. Jamon (2), T.C. Rojas (1), J.Garcia-Lopéz (3), A. Fernandez (1) Affiliations : (1) 1Instituto de Ciencia de Materiales de Sevilla CSIC-US Avenida Américo Vespucio 49, 41092 Sevilla, Spain; (2) Laboratoire Dispositifs et Instrumentation en Optoélectronique et Microondes Université Jean Monnet 21, rue Paul Michelon 42023 Saint-Etienne; (3) CNA-Centro Nacional de Aceleradores, Tomas Alva Edison s/n, 41092 Sevilla, Spain Resume : Over the recent years, porous silicon has attracted considerable attention due to possible applications such as solar cells [1], optoelectronics [2] and photonic devices [3]. Being fully compatible with the established microelectronic technology, one of the most attracting features of porous silicon is its “made to order” refractive index.
Recently we reported on the formation of porous silicon oxynitride coatings by magnetron sputtering with controlled refractive index depending on their deposition conditions [4,5]. The closed porosity formed allowed to keep the good mechanical properties characteristic of these coatings.
Porous silicon has been produced by a variety of approaches, but it is most commonly prepared by electrochemical etching in HF based solutions. In this work we present for the first time the possibility to produce porous silicon coatings by magnetron sputtering.
The microstructure of the coatings was evaluated by SEM and TEM, which showed clearly well defined closed pores ranging from 10 to 50 nm. The presence of deposition gas inside the pores was proved by RBS measurements confirming that the pores are closed and the chemical bonding state of silicon was investigated by XPS and EELS. Spectroscopic ellipsometry measurements showed a considerable decrease on the coatings refraction index when compared with dense coatings deposited in similar conditions.
References
[1] A. Ramizy, Z. Hassan, K. Omar. Y. Al-Domi, M.A. Mahdi, Applied Surface Science, 257, 6112 (2011)
[2] D. Abidi, S.Romdhane, A. Brunet-Burneau, J.L. Fave, European Physical Journal Applied Physics, 45, 10601(2009)
[3] R.S. Dubey, D.K. Gautam, Optik, 122, 494 (2011)
[4] V.Godinho, M.C. Jiménez de Haro, J. García-López, V. Goossens, H. Terryn, M.P. Delplancke- Ogletree, A. Fernandez, Applied Surface Science, 256, 4548 (2010)
[5] V. Godinho , T.C. Rojas, A. Fernandez, Microporous and Mesoporous Materials, 149, 142 (2012) | 17 66 |
| 18:00 | Efficiency improvement of crystalline silicon solar cells by controlling the doping profile of POCl3 diffusion Authors : H. Ghembaza, A. Zerga, R. Saim Affiliations : Materials and Renewable Energies research Unity URMER, Faculty of Sciences University Abou Bekr Belka?– Tlemcen BP:119 Tlemcen 13000 Algeria Resume : The emitter formation process is known that is a crucial step in the manufacturing of the crystalline silicon solar cells. Several techniques are used in the photovoltaic industry and the most widespread one is based on the POCl3 diffusion in cylindrical quartz tube. Despite the effectiveness of this technique to be reproducible and simple, it presents the major disadvantage to have a heavily doped “dead” zone near the surface where a high minority carrier recombination is imposed. Our proposed modeling of phosphorus diffusion profiles can be summarized in the presence of an erfc distribution near to the surface and other Gaussian distribution in bulk region of emitter.
However, this work is devoted to study the effects of the temperature, diffusion time, surface concentration and doping profile on the crystalline silicon solar cells performances by using the new modeling. The first results of our numerical modeling carried out via the Silvaco Atlas® simulation package show the possibility of efficiency gain of 2.78%. This result is also confirmed by the IQE calculus which present an evident enhancement in short wavelength region (380-450nm) of about 23%. | 17 67 |
| 18:00 | Double side multicrystalline silicon passivation by one step stain etching-based porous silicon Authors : M. Ben Rabha and B. Bessaïs Affiliations : Laboratoire de Photovoltaïque, Centre de Recherches et des Technologies de l’Energie. BP 95, 2050 Hammam-Lif, Tunisia rabha2222@yahoo.fr Resume : In this paper, we investigate the effect of stain etching-based porous silicon (PS) on the double side (DS) multicrystalline silicon (mc-Si). Special attention is given to the use of the stain etched PS as an antireflection coating as well as for surface passivating capabilities. Stain etching of DS mc-Si leads to the formation of PS nanostructures, that dramatically decrease the surface reflectivity from 40% to about 3% and increase the effective lifetime from 1 µs to 8 µs at a minority carrier density (Δn) of 1015 cm−3. These results let us correlate the rise of the lifetime values to the photoluminescence intensity and to the hydrogen passivation as shown by FTIR analysis. This low-cost PS formation process can be applied in the photovoltaic cell technology as a standard procedure.
Keywords: Stain Etching; multicrystalline silicon; reflectivity; lifetime. | 17 68 |
| 18:00 | Passivation quality and carrier diffusion length improvement of multicrystalline silicon Authors : M. Ben Rabha , W. Dimassi, H. Ezaouia and B. Bessais Affiliations : Laboratoire de Photovolta?e, Centre de Recherches et des Technologies de l’Energie. BP 95, 2050 Hammam-Lif, Tunisia Resume : This paper presents the effect of silicon nitride (SiNx:H) films formed by plasma-enhanced chemical vapor deposition (PECVD) method on multi-crystalline silicon (mc-Si) wafers including the passivation quality and The minority carrier diffusion length improvement after hydrogenation. Furthermore, the effective lifetime of passivated wafers by PECVD and porous silicon is investigated.
Keywords: Multicrystalline silicon; silicon nitride; carrier lifetime; porous silicon. | 17 69 |
| 18:00 | The usage of Si-based tandem and triple cells for water splitting. A new application for multi-solar cells. Authors : Wolfram Calvet, Eswaran Murugasen, Jürgen Ziegler, Quanbao Ma, Dominic Fertig, Bernhard Kaiser, Wolfram Jaegermann Affiliations : Center of Smart Interfaces and Department of Materials Science, Technical University of Darmstadt, Petersenstrasse 32, 64287 Darmstadt, Germany Resume : Silicon as an indirect semiconductor with a band gap of 1.12 eV is a relatively cheap and widely used material in microelectronics. However, it cannot be used for direct photo-assisted splitting of water since the requested voltage of 1.23 V for this reaction is not reached. In order to overcome this, multi-solar cells or tandem/triple structures based on silicon are applicable providing photovoltages over 1.4 V sufficient for the direct production of hydrogen from water.
In this work we report about thin film α-Si/µc-Si tandem cells manufactured by the Forschungszentrum Juelich which were used in an electrochemical setup using 0.1 M sulfuric acid as electrolyte and a white light source with an intensity of 100 mW/cm2.
Two types of similar prepared solar cells are investigated, one with silver back contact as a protection layer and one without any silver layer covering the ZnO buffer layer. Besides the variation of the electrolyte with respect to stability and conversion efficiency the effect of platinum as catalyst which has been deposited electro-chemically is considered. First results with 4.7 % efficiency of the α-Si/µc-Si tandem structure as photoelectrochemical solar cell (PES) are very promising with a high potential for further improvement towards direct water splitting. | 17 70 |
| 18:00 | Formation of dendritic structures in thin silicon films on amorphous substrates by high intensity flash lamp annealing Authors : R. Endler (1), M. Voelskow (1), T. Schumann (1), T. Gebel (2), H. Liepack (2), A. Kolitsch (1), W. Skorupa (1) Affiliations : (1) Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, POB 510119, 01314 Dresden, Germany ; (2) DTF Technology GmbH, Meschwitzstr. 21, 01099 Dresden, Germany Resume : Grain enlargement of the poly silicon is a key process to improve the electronic properties of microelectronic and photovoltaic devices. We report on lateral dendritic crystal growth in thin silicon films during liquid phase crystallization (LPC) induced by high intensity flash lamp irradiation (FLA). In a series of experiments first a 140 nm SiO2 film and then amorphous silicon of 100 nm thickness were deposited on 500µm thick (100) Si wafers. After that the top silicon film was ion implanted with carbon, first, with the aim to improve the wetting properties of the underlying silicon dioxide by the liquid silicon film during the LPC process. Secondly, due its different solubility in solid and liquid silicon, carbon is responsible for the formation of a laterally depending melting temperature inducing a lateral dendritic growth process. To prove in particular this influence of carbon on the wetting and crystallization process, the flash lamp irradiated structures were studied using XTEM analysis. The pulse annealing process was carried out using the commercial flash lamp annealing tool FLA-50RD of DTF-Technology. The installed set of standard Xenon flash lamps guarantees irradiation densities up to 150 J/cm^2 at a pulse length of 20 ms on preheated substrates. As expected, depending on the carbon implantation conditions and the FLA energy densities, the films show, as a result, up to several hundred micrometers extended grains having the characteristic dendritic shape. | 17 71 |
| 18:00 | Deposition of Silicon films on Rigid and Flexible Substrates by High Pressure Spraying of Silicon based liquid Precursor- Cyclopentasilane Authors : H. Hadjiev, H.Frey and H.R. Khan Affiliations : IVT-Institut für Ionenstrahl- und Vakuumverfahrenstechnik e.V. Fritz-Müller-Strasse 137 73730 Esslingen, Germany Resume : Developing simple and high rate deposition techniques for the deposition of silicon films for the applications in microelectronics and solar cells is a challenge to reduce the costs of production. The conventional high vacuum process deposition techniques are expensive. The deposition of the thin films of silicon using a silicon based liquid precursor- cyclopentasilane diluted with toluene(1vol.%) has been reported1. In this paper , we report the deposition of silicon films using pure cyclopentasilane and solutions diluted with toluene. Films are deposited using a specially developed high pressure spraying system with ultraviolet and electron beam sources. Films are deposited on rigid and flexible substrates such as glass, quartz, glass and carbon fibers kept at various temperatures. The structural, morphological and chemical composition of the films deposited under various deposition conditions and using various concentrations of Cyclopentasilane are investigated by techniques such as X-ray diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray Analysis. The photoconductivity of the films is also measured. The films deposited from toluene diluted cyclopentasilane show the presence of carbon impurity which affects the morphology and other properties of the films. The system and the detailed results of the investigations will be presented. Presently we are in the process of n- and p-doping the Si films for flexible solar cells applications.
1.Shimoda et al. | 17 72 |
| 18:00 | Boron Doped Hydrogenated Amorphous Silicon Oxide Films Prepared at High Hydrogen dilution Authors : Jinjoo Park1, S. M. Iftiquar1, Seungman Park1, Youngkuk Kim1, Sunwha Lee1, Kichan Yoon1, Hyeongsik Park1, Chonghoon Shin2, Seungsin Baek1, Younjung Lee1, Junsin Yi1,2* Affiliations : 1 School of Information and Communication Engineering, Sungkyunkwan University 2 Department of Energy Science, Sungkyunkwan University Resume : We have investigated diborane (B2H6) doped wide bandgap hydrogenated amorphous silicon oxide (a-SiO:H) films prepared by using silane (SiH4) hydrogen (H2) and nitrous oxide (N2O) in a radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) system at various hydrogen dilutions. In our study, we report on the defect state reduction of amorphous silicon oxide films. The films prepared with higher hydrogen dilution show lower Urbach energy (Eu), lower defect density (Nd), lower microstructure (R*), lower short and medium range disorder (ωTO, ГTO, ITA/ITO, ILA/ITO), higher dark conductivity (σd) and higher refractive index (n) with higher optical gap (Eg). Defect density (Nd) decreases from 1.0 x 1018 cm-3 to 8.6 x 1016 cm-3, Eu decreases from 248 meV to 153 meV, and R* decreases from 0.46 to 0.26, Raman peak ωTO-TO mode position shifts from 480.24 to 483.28, ГTO-full width half maximum of ωTO decreases from 78.16 to 63.87, ITA/ITO–the ratio of integrated area of TA and TO mode decreases from 0.624 to 0.474, ILA/ITO-the ratio of integrated area of LA and TO mode deceases from 0.272 to 0.151,σd increases from 4.6×10-7S.cm-1 to 1.1×10-6S.cm-1, n increases from 3.70 to 3.86. Reduced Nd, Eu and R* at wide Eg indicates that the films are more useful for solar cell window layer. Applying this layer to a single junction solar cell shows open circuit voltage (Voc) = 0.80 V, short circuit current density (Jsc) = 16.3 mA/cm2, fill factor (FF) = 72%, efficiency (η) = 9.4%. | 17 73 |
| 18:00 | NANOSCALE PLASTICITY REDEFINED: A MYSTERY OF CURRENT SPIKE AND NANOSCALE DECONFINEMENT Authors : R. Nowak, D. Chrobak Affiliations : Nordic Hysitron Laboratory, Department of Materials Sciences, Aalto University School of Science and Technology, 00076 Aalto, Finland Resume : One of the fundamental questions in materials science concerns the nature of deformation of solids. The onset of plasticity is traditionally understood in terms of dislocation nucleation and motion. A recent study of nanoscale deformation has proven that initial displacement transient events occurring in metals are the direct result of dislocation nucleation. Meanwhile, our MD-calculations indicate that in GaAs this initial displacement transient is related rather to a pressure-induced crystal transition. This never before seen nanoindentation-induced phase transformation of GaAs structure, is in consistent agreement with the curious electrical response of GaAs to nanoindentation [1]. The results obtained for GaAs and dramatic impact of crystal imperfections on the functional properties of Si nano-volumes motivated studying the onset of incipient plasticity in Si nano-spheres. Molecular dynamics calculations and supporting experimental results reveal that plasticity onset in Si nano-spheres below 130 nano-meter diameter is governed by dislocation-driven mechanisms, in striking contrast to bulk Si where incipient plasticity is dominated by phase transformations. The transition from phase transformation-driven to dislocation-governed incipient plasticity is determined to be a consequence of the increasing role of nano-scale confinement. This new discoveries call for a major shift in nanoscale plasticity.
1. R. Nowak, D. Chrobak, S. Nagao, D. Vodnick, M. Berg, A. Tukiainen, and M. Pessa: Nature Nanotechnology 4 (2009) 287
2. D. Chrobak, N. Tymiak, A. Beaber, O. Ugurlu, W.W. Gerberich and R. Nowak, Nature Nanotechnology 6 (2011) 480-484 | 17 74 |
| 18:00 | CHEMICAL VAPOR DEPOSITION OF HIGHLY CRYSTALLIZED AND TEXTURED TITANIUM NITRIDE AS BUFFER LAYER FOR SOLAR CONVERSION APPLICATIONS Authors : Rym BENABOUDa, Ouassila GOURMALAa, Guy CHICHIGNOUDa, Elisabeth BLANQUETa, Carmen JIMENEZb, Béatrice DOISNEAUa, Kader ZAIDATa, Michel PONSa Affiliations : a SIMaP, Grenoble INP, UJF, CNRS, 38402 Saint Martin d'Hères, France; b LMGP, Grenoble INP Minatec, CNRS, 3 parvis Louis Néel, 38016 Grenoble, France Resume : A new attractive way to have cheap silicon for solar conversion is to grow a crystalline silicon layer on metallic substrates, such as stainless steel. This structure implies the development of a buffer layer to prevent interdiffusion at medium temperatures (around 1000°C) between the two layers - and thus silicide formation - but also to compensate lattice parameters and thermal expansion coefficients mismatches between metal and silicon, and ideally to transfer some crystalline properties (grain size, texture) from the substrate to the silicon layer. Titanium nitride layer (TiN) was chosen as a buffer layer and grown by CVD. Before TiN growth, substrates are electro polished for texture transfer. Process parameters influence, such as temperature, pressure and gas flows (TiCl4 and NH3) are evaluated for epitaxial growth.The structure and the interfaces stabilities of these silicon/nitride/metal stacks were studied by Electron backscatter diffraction, scanning electron microscopy and X-ray diffraction | 17 75 |
| 18:00 | Large step-free mesas on Si(111) prepared by molecular beam epitaxy Authors : Andreas Fissel1, Jan Krügener2, H. Jörg Osten2 Affiliations : 1Information Technology Laboratory, 2Institute of Electronic Materials and Devices, Leibniz University Hannover Resume : The continuous process of downscaling in silicon semiconductor technology leads to problems related to the atomic arrangement of the used materials for MOS devices, where the gate oxide is only a few monolayers thick. Thickness variations due to atomic steps on the initial Si surface are expected to have a significant impact on the electronic device properties due a local field enhancement. Furthermore, in future quantum-effect based devices, such as resonant tunneling structures, thickness variation due to stepped surfaces will have a strong influence on the tunneling behavior of carriers. Since step-free substrates are not available, the problem could only be overcome by preparation of step-free areas on substrates having lateral dimension to accommodate a typical device area. To realize step-free areas on a desired location on a substrate patterned surfaces with trenches (Mesas) or ridges (Craters) are essential, which can be produced by standard devices processing.
We will present studies of molecular beam epitaxial growth on structured Si(111) to realize mesa surfaces free of steps at temperatures near the (7x7) -“1x1” surface phase transition. Significant changes in mesa surface morphology were found within an only small increase in temperature, which are discussed with regard to the presence of the two surface phases under certain conditions and their specific influence on the growth kinetics. Under optimized conditions step-free mesas with dimensions of 10x10 µm² were obtained. | 17 76 |
| 18:00 | Electrical characterization of Si/PS/ZnO:In solar cell synthesized by rf-magnetron sputtering based on nanopowder target material Authors : H. Belaid1, M. Nouiri1, Z. Ben Ayadi1, K. Djessas(2), L. El Mir(1,3,*) 1 Laboratory of Physics of Materials and Nanomaterials Applied at Environment (LaPhyMNE), Gabes University, Faculty of Sciences in Gabes, Gabes, Tunisia. 2Laboratoire de Mathématiques et Physique des Systèmes (MEPS), Université de Perpignan, 52, avenue Paul Alduy, 66860 Perpignan Cedex, France. 3Al-Imam Muhammad Ibn Saud University, College of H. Belaid1, M. Nouiri1, Z. Ben Ayadi1, K. Djessas(2), L. El Mir(1,3,*) Affiliations : 1 Laboratory of Physics of Materials and Nanomaterials Applied at Environment (LaPhyMNE), Gabes University, Faculty of Sciences in Gabes, Gabes, Tunisia. 2Laboratoire de Mathématiques et Physique des Systèmes (MEPS), Université de Perpignan, 52, avenue Paul Alduy, 66860 Perpignan Cedex, France. 3Al-Imam Muhammad Ibn Saud University, College of Sciences, Department of Physics, Riyadh 11623, Saudi Arabia. Resume : Indium doped zinc oxide (IZO) nanopowder synthesized by sol-gel method has been grown onto p-type porous silicon (PS) substrate by rf-magnetron sputtering at room temperature. The obtained IZO thin films with a thickness of about 400 nm using indium concentration of 3 at %, were polycrystalline with a hexagonal wurtzite structure and preferentially orientation in the (002) crystallographic direction. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to study the films morphology. The obtained IZO films, generally used as TCO in solar cells, have a typical columnar structure and very smooth surface. From electrical characterizations: current-voltage (I-V) on dark and under illumination and capacity-voltage (C-V) at different frequency measurements, we can conclude that we have Schottky electronic behaviors where the depletion-layer is developed principally in p-type silicon region. | 17 77 |
| 18:00 | Modeling of Photo- and Electroluminescence of Hydrogenated Microcrystalline Solar Cells Authors : T. C. M. Müller, B. E. Pieters, T. Kirchartz, R. Carius, and U. Rau Affiliations : IEK5-Photovoltaik Forschungszentrum Jülich, 52425 Jülich, Germany; IEK5-Photovoltaik Forschungszentrum Jülich, 52425 Jülich, Germany;Department of Physics, Imperial College London, South Kensington SW7 2AZ, United Kingdom;IEK5-Photovoltaik Forschungszentrum Jülich, 52425 Jülich;IEK5-Photovoltaik Forschungszentrum Jülich, 52425 Jülich Resume : Recently, photoluminescence (PL) and electroluminescence (EL) have received much attention as characterization techniques for photovoltaic devices. The methods are applied to study e.g. optical band-gap, defect states, or quasi-Fermi level splitting. Spatially resolved EL imaging is used to derive local junction voltage differences making it a fast inline characterization method for solar modules. The usual determination of voltage differences from EL relies on the assumption that the emission follows a diode law with an ideality factor of unity. This assumption is fulfilled for crystalline silicon solar cells but interpretation of EL and PL experiments on μc-Si:H solar cells is not so straight forward. Previous work showed that PL of μc-Si:H is well explained with radiative tail-to-tail transitions, and that the ideality factor for PL depends on the slopes of the band tails This fact hampers the direct determination of local voltage differences. In this work we extend the work on PL to EL experiments. Due to the low mobility in μc-Si:H transport limitations play an important role in EL experiments. To take into account the low mobility of μc-Si:H we combine the simulation of the luminescence of tail-to-tail recombination with transport simulations using the Advanced Semiconductor Analysis program. This way we can consistently explain EL and PL measurements as well as dark and illuminated current/voltage characteristics over a wide temperature range. | 17 78 |
| 18:00 | Low-cost approach to fabricate a local Al-doped back surface field using oxidized porous silicon as a mask and micro groove machining process Authors : Wissem Dimassi, Hatem Ezzaouia Affiliations : Laboratoire de Photovoltaïque, Centre de Recherche et des Technologies de l’Energie, PB : 95, Hammam Lif 2050, Tunisia Resume : The purpose of this work is to develop a back surface field (BSF) for industrial crystalline silicon solar cells. We present a low-cost approach to fabricate a local Al-doped back surface field for high efficiency screen-printed solar cells, using oxidized porous silicon (ox-PS) as a mask. Micro periodic fingers were opened on the porous silicon layer using a micro groove machining process. Fourier transform infrared (FTIR) spectroscopy investigations of the PS layer show the possibility to use PS as an oxide dielectric Layer. The Light Beam Induced Current (LBIC) mapping of the realized device, confirm the presence of a micro periodic back contact structure and explain why the solar cell performance with boron local-BSF diffused at the back side is impacted. As a result we found an improvement of the I-V characteristics in dark conditions and AM illumination. | 17 79 |
| 18:00 | Effect of thermal treatments on the optical, electrical and optoelectronic properties of the silicon nanowires for solar cells application Authors : M. Karyaoui 1,*, M. ben Rabha1, S. Sancho1, W. Dimassi1, J.C. Harmand2, R.Chtourou1 and M. Amlouk3 Affiliations : 1 Laboratoire de photovoltaïque, Centre de Recherches et des Technologies de l’Énergie, Technopole de Borj-Cédria BP 95, 2050 Hammam-Lif, Tunisia 2 Laboratoire de Photonique et de Nanostructures, CNRS Route Nozay 91 460, Marcoussis, France 3 Unité de Physique des dispositifs à Semi-conducteurs UPDS, Faculté des Sciences de Tunis, Tunis El-Manar University 2092 Tunisia Resume : In this paper, we report the effect of thermal oxidation treatment on the optical, electrical and optoelectronic properties of the silicon nanowires (SiNWs) prepared by chemical etching method. As a result, the Scanning Electron Microscope (SEM) shows high density nanowires with average length about of 3.7 µm and the reflectivity measurement shows that the SiNWs have a low rate reflexion about 2%. The SiNWs passivation has been studied in infrared oven under controlled atmosphere at different temperature. The LBIC measurements of the SiNWs revel that the thermal treatments improve the optoelectronic response at 900°C and the effective diffusion length was improved from 150 μm for untreated SiNWS to 235 μm after thermal treatment.
Keywords: silicon nanowires SiNWs, chemical etching, rapid oxidation, current-voltage, LBIC | 17 80 |
| 18:00 | Electrical behaviour of MIS devices based on Si nanocrystal embedded in SiOx-Si-Nd/SiNx-Si Multilayer Authors : E. Jacques(1), L. Pichon(1), L. Khomenkova(2), C. Labbé(2), F. Gourbilleau(2) Affiliations : (1)Groupe Microélectronique, IETR, UMR CNRS 6164, campus de Beaulieu, 35042 Rennes cedex, France (2)Centre de Recherche sur les Ions, les MAtériaux et la Photonique, UMR CEA/CNRS/ENSICAEN/UCBN 6 boulevard du Maréchal Juin, 14050 Caen cedex 4, France Resume : We analyse the electrical properties of multilayer made of silicon rich oxide (SRO) and silicon rich nitride (SRN) doped with Neodymium (Nd) layers integrated in MIS (Metal Insulator Semiconductor) device. The aim of such a study consists in fabricating thin layer for future electroluminescent devices doped with rare earth ions (Nd) which benefit from the efficient sensitizing effect of Si nanoclusters (Sinc) towards the Nd3+ ions. The deposition has been performed by reactive magnetron sputtering, consisting in the formation of alternating SRO/SRN films, with nominal thickness of 3 nm for each layer. The multilayer is then composed with 9 periods of SRO/SRN films, which was subsequently submitted to an optimized annealing treatment.
The multilayer is deposited on p-type (111) oriented silicon substrate with resistivity in the range 0.001-0.005 cm. Next, aluminum was thermally evaporated on active layer. Both aluminum and active layers were patterned by wet etching to define the geometry of the device. A second thermal evaporation of aluminum on the back surface was carried out to ensure the ohmic contact with the p-type crystalline silicon. Finally, the devices were annealed into forming gas (H2:N2, 10%) at 390°C to stabilize the electrical properties of the devices. The conduction mechanisms of the MIS structures were studied by analysing thermal and bias dependences of the carriers transport in relation with the silicon content (9, 11 and 15%) of the SRO layer. | 17 81 |
| 18:00 | THERMAL DEHYDROGENATION OF AMORPHOUS SILICON: EFFECT OF THE SUBSTRATE TEMPERATURE DURING DEPOSITION Authors : A. de Calheiros Velozo(1), G. Lavareda(2,3), C. Nunes de Carvalho(2,4), A. Amaral(1,4) Affiliations : (1) Dep. de Física, Instituto Superior Técnico (UTL), Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal (2) Dep. de Ciência de Materiais, Faculdade de Ciências e Tecnologia (UNL), 2825-114 Caparica, Portugal (3) Centro de Tecnologias e Sistemas, Faculdade de Ciências e Tecnologia (UNL), 2825-114 Caparica, Portugal (4) Inst. Ciência e Engenharia de Materiais e Superfícies, Instituto Superior Técnico (UTL), Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal Resume : Doped hydrogenated amorphous silicon (a-Si:H) can be deposited by PECVD on crystalline silicon as a pre-deposition layer for a subsequent diffusion, in order to form pn junctions. However, when a-Si:H is heated beyond 300ºC, thermal dehydrogenation occurs liberating molecular hydrogen. If the dehydrogenation rate is too high, mechanical stress appears in the films that can lead to pin holes or even to a complete peal-off. The initial hydrogen concentration of the as-deposited films is, then, of major importance as well as the dehydrogenation process time and temperature, for a smooth hydrogen exodiffusion.
In this work, samples of doped and undoped a-Si:H were deposited at temperatures ranging from 100ºC to 350ºC and then submitted to different dehydrogenation temperatures (from 350ºC to 450ºC) and times (from 1h to 10h). Initial and final film parameters were measured in order to determine the a-Si:H characteristics, namely hydrogen content, optical gap, refractive index, growth and etch rates, conductivity and thermal activation energy of conductivity. | 17 82 |
| 18:00 | Polycrystalline Si grain size dependence of film temperature during laser crystallization process. Authors : G. Marcins, J. Butikova, I. Tale, B. Polyakov, A. Muhin, A. Voitkans Affiliations : Institute of solid State Physics, University of Latvia Resume : Polycrystalline silicon (p-Si) film was obtained from amorphous silicon at varied substrate temperatures using laser crystallization process. The film crystallinity and grain size was estimated as a function of crystallization parameters.
Si wafer was used as a substrate. Its surface was thermally oxidized and 400 nm SiO2 layer was made. On top of it 270 nm thick a-Si layer was deposited by electron beam evaporation. The laser crystallization was performed in vacuum by second and third harmonic Nd:YAG pulse laser (6 ns) at variable energy densities. The x-y stage was used to move the sample and large crystallized areas were obtained by scanning the laser beam over the film surface. Raman spectroscopy measurements were performed to determine crystallinity of the obtained films. Atomic force microscopy measurements were performed to determine crystalline grain size. SECCO etch was used to increase visibility of grain boundaries. | 17 84 |
| 18:00 | Advanced Tunnel-Recombination Junctions for a-Si / µc-Si Tandem Cells Authors : Simon Kirner1, Max J. Klingsporn 2, Sebastian Neubert 1, Matthias Zelt 1, Sonya Calnan 1, Onno Gabriel 1, Bernd Stannowski 1, Affiliations : 1PVcomB, Helmholtz-Zentrum Berlin, Germany, 2IHP Microelectronics GmbH, Germany, Resume : In amorphous-/ microcrystalline silicon (a-Si/µc-Si) tandem cells, the inner n-/p-contact, called tunnel-recombination junction (TRJ), consisting of the top cell (TC) n-layer and the bottom cell (BC) p-layer, has to fulfill three important requirements:(1) forming a low resistance ohmic contact (2) acting as a seed layer for the µc-Si growth of the BC i-layer and (3) absorbing as few light as possible and in case an intermediate reflector (IR) is used reflecting part of the incoming light back into the TC. Microcrystalline silicon oxide (µc-SiOx) is known to be an appropriate material that fulfills these requirements. We systematically investigated combinations of n- and p- type, oxygen- and non oxygen-containing layers in the TRJ within tandem devices as well as n-/p-test structures using transmission electron microscope, Raman-, and reflection- and transmission-spectroscopy, as well as electrical characterizations. We found that the deposition of a very thin µc-Si layer between two oxygen containing layers improves the conductivity of the TRJ significantly and allows for a high fill factor (>73%). Thereby, the oxygen content in the IR can be increased providing a low index of refraction (n<2). We explain this by a better tunnel-recombination process due to a sharper n-/p-junction as well as improved crystallization.This hypothesis is supported by numerical device simulations. The best solar cell with an IR fabricated at the PVcomB so far had an initial efficiency of 10.8%. | 17 85 |
| 18:00 | Photocurrent spectroscopy of silicon quantum dots embedded in multilayer structures Authors : B. Dridi Rezgui (1,3), F. Gourbilleau (2), D. Maestre (3), O. Palais (3), A. Sibai (1), M. Lemiti (1) and G. Brémond (1) Affiliations : ) University of Lyon, Institut des Nanotechnologies de Lyon INL-UMR 5270, CNRS, INSA de Lyon Bât. Blaise Pascal, 7 av. Jean Capelle, Villeurbanne, F-69621, France 2) CIMAP, UMR CEA/CNRS/Ensicaen/University of Caen, 6 Boulevard Maréchal Juin, 14050 Caen Cedex 4, France 3) Aix-Marseille University, IM2NP, Faculté des Sciences de Jérome, F-13397 Marseille France ; CNRS, IM2NP, Faculté des Sciences de Jérome, F-13397 Marseille France Resume : The great interest in silicon nanostructures formed on the basis of Si quantum dots (Si QDs) embedded in SiO2 multilayers is driven by their potentiality as wide gap absorber layer in tandem solar cells. The information about carrier transport in such structures is important from a physical and a practical point of view. This work is devoted to the analysis of photoconductivity mechanisms in Si-rich silicon oxide (SRSO)/SiO2 multilayer (MLs) structures.
SRSO/SiO2 MLs with varying SRSO layer thicknesses were deposited by reactive magnetron sputtering on silicon substrate and were subsequently annealed at 1100° C for 1 h under N2 atmosphere. The measurements of photocurrent (PC) were carried out in the spectral range 0.75 - 3.75 eV using a homemade standard PC experiment with transversal or lateral configuration. Our experiments reveal a PC edge dependence on the size of silicon quantum dots. The observed blueshift of the photocurrent spectra with decreasing the QD size can be interpreted by a quantum confinement effect. Bias voltages and temperature dependence of the photocurrent spectra are also investigated in order to quantify the hopping and tunnelling mechanisms of the electric conduction in our structures.
Finally, the photocurrent density JPh produced by the nanostructured films under AM1.5 illumination is determined using a calibration procedure with a pyroelectric detector. Although the current density extracted from the PC measurements is relatively low, the results obtained in this work could define a route to optimized Si-based tandem solar cells. | 17 86 |
| 18:00 | Formation of shallow front emitters for solar cells by RTP Authors : Hans B. Normann, Edouard V. Monakhov, Bengt G. Svensson Affiliations : Centre for Materials Science and Nanotechnology, University of Oslo, Norway Resume : A proposed improvement to the industry standard solar cell is to reduce the emitter depth
while maintaining low sheet resistance. High absorption coefficient of blue light in silicon
means a shallow emitter will result in an improvement of the blue-light response and hence
increase the solar cell efficiency. In this work we report on formation of shallow front
emitters by phosphorous in-diffusion during rapid thermal processing (RTP).
Filmtronics P509 liquid phosphorus diffusant was deposited on 1 Ωcm p-type mono-Si.
Diffused shallow emitters were processed by annealing the samples at 900°C and 950°C in
the range of 10–40 s in Annealsys AS-Micro furnace. The samples were cleaned in RCA
HF-dip to easily remove the phosphorus glass, and leave the silicon surface hydrofobic. The
chemical depth concentration of phosphorus in the samples was measured by secondary ion
mass spectrometry (SIMS) using a Cameca IMS7f microanalyer and 15 keV Cs primary
ions. Sheet resistance measurements were performed on a Jandel KM3-AR 4-point probe
instrument.
It is found that emitters with the depths in the range 75-200 nm and the maximum doping
concentrations in the range 1020-1021 cm-3 can be formed after the RTP treatments. High
solubility of phosphorus in silicon at elevated temperatures ensures a low sheet resistance
down to 40-80 Ohm/sq. It is shown that the phosphorous in-diffusion during RTP is a viable
method for formation of front emitters for solar cells. | 17 87 |
| 18:00 | Two-step Texturing Using Ag Catalyst for c-Si Solar cell with less reflectivity Authors : Byoung Jin Oh. In Hwan Yeo. Jun Hee Kim. Ju Eok Park. Donggun Lim*. Affiliations : Department of Electronic Engineering, Korea National University of Transportation, 50 Daehak-ro, Chungju, Chungbuk 380-702, Republic of Korea Resume : The silicon surface after saw damage etching is shiny and reflects more than 35% of incident light. The surface texturing can reduce the optical reflectance to less than 10%. In order to get more effective texturing, two-step texturing using Ag catalyst was applied. P-type CZ-silicon wafer had an average thickness of 200 μm and a resistivity of 2.5 Ω-cm. The wafer were first degreased by HCl(10%) for 3min, followed by immersion in HF(10%) for 3min. Then the wafers were first texturing by NaOH solution at 80℃ for on the surface by evaporation system. After this process the samples were etched in HF : H2O2 : H2O = 1 : 5 : 10 at room temperature for 80~240s. Due to the local catalytic of Ag ultra thin film, this treatment results in the nano-scale texturing on the micro-scale texturing. The average reflectance was less than 2% with two-step texturing. | 17 88 |
| 18:00 | plasma enhanced chemical vapor deposition (PE-CVD) hydrogenated silicon (Si:H) thin films The effect of hydrogen dilution on structural, electrical and optical properties Authors : Ben Amor Sana*, Dimassi Wissem, Ezzaouia Hatem Affiliations : doctorante,maitre assistant,professeur Resume : Hydrogenated silicon (Si:H) thin films were deposited from pure silane (SiH4) and hydrogen (H2) gas mixture by conventional plasma enhanced chemical vapor deposition (PE-CVD) method at low temperature (500°C) using high rf power. The structural, optical and electrical properties of these films are carefully and systematically investigated as a function of hydrogen dilution of silane (R). Characterization of these films with low angle X-ray diffraction revealed that the crystallite size in the films tends to decrease and at same time the volume fraction of crystallites increases with increase in R. The Fourier transform infrared (FTIR) spectroscopic analysis showed at low values of R, the hydrogen is predominantly incorporated in the Si:H films in di-hydrogen (Si–H2) and (Si–H2)n complexes. However, with increasing R the hydrogen bonding in Si:H films shifts from di-hydrogen (Si–H2) and (Si–H2)n complexes to the mono-hydrogen (Si–H) bonding configuration. Both hydrogen content in the Si:H films and thiknes of different layers decrease with increase in R. The carrier life time was determined. A correlation between electrical and structural properties has been found. | 17 89 |
| 18:00 | Improving the performance of solars cells using acid treatment in polycristalline silicon grain boundaries Authors : khemir Haikel*, Dimassi Wissem, Ezzaouia Hatem Affiliations : doctorant,maitre assistant,professeur Resume : In this work we study the effect of preferential grooving
on grain boundaries (GB) with chemical etching HF/
HNO3 and its influence on polycristalline silicon cells
performances. This treatment enables to reduce their
area and then their highly recombination effect. Indeed,
we show that grooved GB assure deep penetration
of phosphorus and metallic contacts, which lead to
a P–Al-co-gettering of undesired impurities. Results
demonstrated that the reflectivity is reduced causing
an improvement in absorption as well as LBIC
current. In addition, it was revealed that decrease in
the recombination activity in regions close to the GBs
decreased compared to ungrooved sample investigated
by the two-dimensional Light-Beam-Induced-Current
(LBIC) imaging wich measured the distribution of
current in a cell illuminated with monochromatic laser
beam. For the result, the comparison is made between
samples treated and untreated others. | 17 90 |
| 18:00 | A spectroscopic ellipsometry study of ultra thin amorphous silicon layers deposited on crystalline silicon by PECVD Authors : Yaser Abulraheem, Ivan Gordon, Twan Bearda, Jozef Poortmans Affiliations : Kuwait University, Kuwait ; IMEC, Belgium Resume : A spectroscopic ellipsometry study of ultra thin amorphous silicon layers deposited on crystalline silicon by PECVD
Yaser Abdulraheem(*), Ivan Gordon(**), Twan Bearda(**) and Jozef Poortmans(**)
(*)Electrical Engineering Department, College of Engineering & Petroleum, Kuwait University
P.O. Box 5969, 13060 Safat, Kuwait
yma@eng.kuniv.edu.kw ; ymakuniv@gmail.com
(**) IMEC, Kapeldreef 75, 3001, Leuven, Belgium
An optical study based on spectroscopic ellipsometry, performed on ultrathin amorphous silicon (a-Si) layers, is presented in this work. Ultrathin layers of amorphous silicon have been deposited intrinsically on Float Zone, n-type mono-crystalline silicon (c-Si) wafers by PECVD , using Silane gas at 200oC and 15 Watt plasma source power for 30 seconds. The layer thicknesses along with their optical properties –including their refractive index and optical loss- were characterized by spectroscopic ellipsometry in a wavelength range from 850 nm to 250 nm. Two samples, one including an interfacial silicon dioxide layer in between the a-Si film and the c-Si substrate, and one without, were prepared. The spectroscopic ellipsometry data were fitted to a Tauc-Lorentz (TL) optical model and the fitting parameters were extracted and used to compute the refractive index and optical loss over the above mentioned wavelength range.
Furthermore, the a-Si films for both samples were etched away in a controlled fashion using a TMAH solution prepared at room temperature. The optical properties along with the TL fitting parameters were extracted from the model as the films were thinned down by etching. An etch rate for ultrathin a-Si layers in the TMAH solution (1:4 in DI water) at room temperature was measured and was found to slow down drastically at the c-Si interface.
From the TL parameters, it was found that the a-Si films exhibited properties that evolved with thickness suggesting deposited layers which are non-homogeneous. It was also found that the degree of crystallinity increased for layers closer to the c-Si substrate interface. | 17 91 |
| 18:00 | Effect of Diffusion Time in Spin on Doping for C-Si Solar cell Authors : Byoung Jin Oh. In Hwan Yeo. Ju Eok Park. Jun Hee Kim. Donggun Lim*. Affiliations : Department of Electronic Engineering, Korea National University of Transportation, 50 Daehak-ro, Chungju, Chungbuk 380-702, Republic of Korea Resume : Rapid thermal processing (RTP) drastically decreases the time required to perform solar cell processes. RTP were used to form emitter of crystalline silicon solar cells. The emitter sheet resistance is studied as a function of time and temperature. The objective of this paper is reduction of doping process time with same performance. Emitter diffusion was carried out by using a spin on doping and a RTP. Rapid thermal diffusion was performed in the temperature range of 675-725℃ for 1m30s-15m. Thermal budgets yielded a 50Ω/sq emitter using a P509 source. To reduce process time and get high efficiency, rapid thermal diffusion by IR lamp was employed in air atmosphere at 725℃ for 1m 30s. The efficiency was comparable to a cell diffused at 675℃ for 15m. | 17 92 |
| 18:00 | Optimization of antireflection multilayer for industrially crystalline silicon solar cells Authors : N. Sahouane, A. Zerga Affiliations : Materials and Renewable Energies research Unity URMER, Faculty of Sciences University Abou Bekr Belka?– Tlemcen BP:119 Tlemcen 13000 Algeria Resume : Reflection of the incident photons by the silicon surface is a major source of losses for photovoltaic conversion. However, these losses can be minimized by depositing an antireflection layer, usually silicon nitride SiNx:H, combined to an appropriate texturing. This layer should also provide a good passivation where a real dilemma can be arising. Indeed, the refractive index must be in minimum to reduce the reflectivity and it must be in maximum to improve the passivation. To achieve this, one first approach consists to use a double antireflective layer with two materials of different refractive index n. Among the materials that are appropriate from the standpoint of physics and technology are SiNx:H-rich silicon, oxynitride SiOxNy and silicon oxide SiOx.
To optimize the antireflection multilayers, we have developed a numerical simulation code with Matlab software package where we have used the method of transfer matrix to solve the optical equations. These solutions permit us to plot the optical reflectivity and the absorption versus wavelengths and layer thicknesses. We considered the case of glass encapsulated cells (dg = 3 mm, dEVA = 0.5 mm).
The optical refractive index and thicknesses of considered materials, which allowed us to have the best results of reflection, were used to simulate the electrical properties of the cell with Silvaco software. Thus, our results showed that the average reflectivity of 4.4% is obtained with a first oxide layer (n1= 1.5 and d1=55nm), and a second layer of silicon nitride (n2=2.1 and d2=53nm). However, the cell efficiency can increase by 0.3%. In the case of the triple layer, our optimization has shown that it is possible to increase the yield of 0.7% with the refractive indices (1.48, 2 and 2.4) and thicknesses (80, 5 and 50) nm. | 17 93 |
| 18:00 | Numerical Modelling of selective emitter crystalline silicon solar cells Authors : A. Zerga, N. Benadla, W. Kazi-Tani, A. Slaoui Affiliations : Materials and Renewable Energies research Unity URMER, Faculty of Sciences University Abou Bekr Belkaïd – Tlemcen BP:119 Tlemcen 13000 Algeria Resume : In the PV industry, the standard emitters formed by POCl3 diffusion present a high surface concentration. This is necessary for good quality metallization but it is detrimental to the surface and bulk passivation effects. Therefore, a differential doping between contacted and non-contacted regions is required to improve the performances of the mc-Si solar cells and it can be obtained by different approaches: etch-back, overdoping, self-doping paste, laser overdoping, barrier diffusion,… These approaches can be summarized in numerical simulation in two types of selective emitter: aligned and no aligned surfaces
In this work, we present a comparative study of aligned surface selective emitter and no- aligned surface one by using 2D numerical optimization methods. The simulation code was developed via Athena and Atlas modulus of SILVACO package. The best values of differential doping, width of finger contact, width of heavy doped region, junction depth and surface recombination velocity are investigated. Finally, our obtained results on crystalline silicon solar cells by using selective emitter concept showed a maximum efficiency improvement of about 1.04%. | 17 94 |
| 18:00 | Optical and structural characterization of SiNx:H deposited by PECVD in front face of silicon solar cell, before and after thermal treatment front contact Authors : Rabaa Bousbih *, Wissem Dimassi, Ikbel Haddadi, and Hatem Ezzaouia Affiliations : doc,doc,doc,prof Resume : It is vital for the optical performance of the cell that the behavior of the PECVD SiNx:H upon annealing is known. For this aim, we have studied the effect of thermal treatement on the structural and optical properties of the SiNx :H by varying annealing temperature from
400 °C to 950°C in infrared (IR) heated furnace under nitrogen. A loss of hydrogen has been observed. The thickness of different layers decrease as function of the temperature increase | 17 95 |
| 18:00 | Silver-doped TiO2 thin films– Influence of annealing temperature on structural, optical and photocatalytic properties Authors : J. Ben naceur1, R. Mechiakh2, F. Bousbih1, R. Chtourou1 Affiliations : 1 Laboratoire de Photovolta?e ,Centre de Recherche des Sciences et des Technologies de l’Energie, BP.95, Hammam-Lif 2050, Tunisia. 2 D?rtement de M?cine, Facult?e M?cine, Universit?adj Lakhdar, Batna, Algeria. Resume : Silver doped TiO2 thin film has been successfully prepared onto silicon substrate by using sol-gel spin coating technique. The effects of annealing temperatures on the structural, surface morphology and optical proprieties have been characterized by Raman, atomic force microscopy (AFM) and ellipsometric spectroscopies. Raman spectroscopy shows phase transformation from anatase to rutile phase occurred when the annealing temperatures reaches 1000 °C. For optical proprieties, the refractive index, and the optical band gap (Eg) of the films were determined from spectroscopic ellipsometry measurements. As for band gap energy, there is decreasing in band gap energy when the annealing temperatures increases. The Anatase phase was find to show higher photocatalytic activity than the rutile one. | 17 96 |
| 18:00 | Enhancement of optoelectronic proprieties of monocristallin silicon solar cells by a thin porous silicon with mechanical grooving Authors : Zarroug Ahmed; Dimmassi Wissam; Ezzaouia HATEM Affiliations : Groupe de recherche au Laboratoire de Photovoltaïque, Centre de Recherche et des Technologies de l’Energie, Resume : In this work, we are interested to fabricate a grooved front side field for high efficiency screen-printed solar cells, using oxidized porous silicon (ox-PS) as a mask with a low-cost approach.
In fact, new methods concerning efficient reduction are developed, in this work we display the creating of a rough surface which enhances the absorption of incident light by the solar cell and reduces the reflectivity of monocrystalline silicon (c-Si).
It clearly can be seen that the mechanical grooving enables us to elaborate the texturing of monocrystalline silicon wafer by opening the micro periodic fingers.
Results demonstrated that the application of a PS layer followed by a thermal treatment under O2 ambient is able to getter unwanted impurities from solar grade monocrystalline silicon which enhances the electrical activity of the c-Si wafer.
In addition, the Fourier transform infrared (FTIR) spectroscopy investigations of the PS layer illustrate the possibility to use PS as an oxide dielectric Layer.
This simple and low cost method decreases the total reflectivity and improves the diffusion length of the minority carriers
Keywords: Microgroove, porous silicon, texturization, | 17 97 |
| 18:00 | Optimization of firing temperature profiles on screen printed crystalline silicon solar cell using rapid thermal processing Authors : Byoung Jin Oh. In Hwan Yeo. Ju Eok Park. Jun Hee Kim. Donggun Lim*. Affiliations : Department of Electronic Engineering, Korea National University of Transportation, 50 Daehak-ro, Chungju, Chungbuk 380-702, Republic of Korea Resume : Limiting thermal exposure time using rapid thermal processing (RTP) has emerged as promising simplified process for manufacturing of solar cell in a continuous way. To reduce process time and get well-contacted electrode, RTP was employed in air atmosphere with various temperatures and profiles. This paper reports the optimization of co-firing process by using the RTP. After screen printing, actual temperature profile is a key issue for high-quality metal-semiconductor contact. The plateau time during the firing process were varied at 450℃ for 10∼16sec. Glass frit in Ag paste is important for the Ag/Si contact formation and the performances of crystalline Si solar cell. Glass frits in Ag paste etch anti-reflection layer during plateau time. The peak temperature were varied at 650~750℃. The junction leakage current was observed by high peak temperature or long plateau time. A result, Optimization of fabrication process has achieved 17.14% efficiency at plateau time 12s and peak temperature 680℃. | 17 98 |
| 18:00 | ITO and ZnO:Al effects on ITO/ZnO:Al/c-Si heterojunction solar cell by AMPS-1D Authors : A. Bouloufa1 and F. Khaled1 Affiliations : 1Laboratoire d’Electrochimie et Materiaux (LEM), University Ferhat Abbas de Sétif-Algérie Resume : In this work, we present performances of ITO/ZnO:Al/c-Si solar cells analysed AMPS-1D software. The research activities in the photovoltaic field are related to materials development, which can be obtained at low cost and to improve the conversion efficiency. One of the known ways to increase the conversion efficiency is the reducing of the radiation losses at the front surface of the cell using TCO layers such as IOT and ZnO:Al. ITO and ZnO:Al are still the most commonly used and widely studied transparent conducting oxides. The combination of optical transparency and electrical conductivity is capable of yielding high efficiency. Recently, a current density of about 23mA/cm2 has been obtained for a single silicon solar cell of 500µm thick using ZnO:Al as conductive transparent oxide. Because of unique properties of high transmittance, low resistivity of about 10-4 Ω.cm, wide band gap and antireflective property, a thin layer of ITO has been deposited on ZnO:Al. The performances of such structure have been studied using the device simulator AMPS-1D (Analysis of Microelectronic and Photonic Structures) using experimental data of ITO and ZnO:Al. Results obtained confirm that ITO improve the short circuit current density (JSC), fill (FF) and efficiency. Typical photovoltaic parameters found were 23.53 mA/cm2, 0.835 and 23% respectively. | 17 99 |
| 18:00 | Porosity dependence of magnetoconductance in n-type porous silicon Authors : B. Chouaibi1, M. Raddaoui1, A. Ben Fredj1, S. Romdhane1,2, M. Bouaïcha3 and H. Bouchriha1 Affiliations : 1Laboratoire Matériaux Avancés et Phénomènes Quantiques, Faculté des Sciences de Tunis, Université El-Manar, 2092 Campus universitaire Tunis, Tunisia 2 Faculté des Sciences de Bizerte, 7021 Zarzouna, Bizerte, Université de Carthage, Tunisia 3 Laboratoire de Photovoltaïque, Centre de Recherches et des Technologies de l’Energie, BP 95 Hammam-Lif 2050, Tunisie Resume : Research in magnetotransport of semiconductors without using magnetic materials is a field of ongoing interest. Silicon holds exceptional promise for magnetoelectronics, by virtue of its long spin coherence [1] and compatibility with the current CMOS technology. Within the past decades the influence of the magnetic field on p-type silicon devices has been explored as well. There is intense activity in the field of electronic transport to study original ways of building nanoelectronic devices by measuring the magnetoresistance in silicon at low field [2].One of the most recent structures being developed is semiconductor nanowires, and particularly, silicon nanowires (SiNWs). A new process for growing and contacting silicon nanowires has been studied and observed a positive magnetoconductance behavior, with an increase of its amplitude by decreasing the temperature, which was interpreted as a manifestation of quasi-1D weak localization [3]. Porous silicon (PS), in particular, represents a very interesting nanostructured solid. Thus, simulations about PS have mainly focused on the investigation of silicon quantum wire (QW). The aim of this paper is to report the observation of the magnetoconductance (MC) effect in porous silicon (PS) layers (p-type and n-type PS). The MC has been found to be positive at room temperature in the entire range of the applied magnetic field (under 8000 G).And we study for porosity dependence of MC in n-type PS. The observed positive magnetoconductance was well described in terms of the weak localization theory (WL) in diffusive semiconductors [4]; it is well known that in disordered metallic systems, WL plays a dominant role at higher temperatures and lower fields [5]. Low magnetic field transport measurements measuring the variation in conductance as a function of magnetic field allow us to measure the phase coherence length . The increase beyond the Drude conductivity when an electron gas is subjected to low magnetic field is known as WL and is due to the destruction of the constructive interference between time-reversed trajectories. However, from this model we find excellent agreement with experimental results explains the porosity dependence of magnetoconductance in n-type PS.
References
[1] I. Appelbaum, B. Huang, and D. J. Monsma, Nature (London) 447, 295 (2007)
[2] C. Wan, X. Zhang, X. Gao, J. Wang and X. Tan, Nature 477,304–307 (2011)
[3] J. F. Dayen, A. Rumyantseva, C. Ciornei, T. L. Wade, and J.-E. Wegrowe, Phys. Rev. Lett. 90, 173110 (2007)
[4] D. M. Zumbühl, J. B. Miller, C. M. Marcus, K. Campman, A. and C. Gossard, Phys. Rev. Lett. 89, 276803 (2002)
[5] P. K. Choudhury, M. Jaiswal, and R. Menon, Phys. Rev. B. 76, 235432 (2007) | 17 100 |
| 18:00 | Polycrystalline silicon solar cells from RST ribbon process Authors : F. De Moro1, N. Auriac2, B. Grange2, B. Drevet2, H. Lignier2, A. Focsa3, K. Derbouz3, A. Slaoui3, Affiliations : 1 Solarforce S.A., 1 rue du dauphin 38300 Bourgoin-Jallieu 2 CEA-INES, 50 Avenue du Lac Léman 73370 Le Bourget Du Lac 3 CNRS-InESS, 23 Rue du Lœss 67037 Strasbourg Resume : The growth of the market of PV electricity has taken the module sale price below 1$/Wp. In this context, ribbon technologies, such as the RST (Ribbon on Sacrificial Template) technology of Solarforce, which yields silicon wafers 100µm thick, are a pertinent answer as they offer a drastic reduction of silicon consumption.
This paper presents the results of a study of the PV performances of classical cells made out of p type and n type RST substrates. The first part presents the crystalline texture of the RST ribbons; it is completed by a survey of the content of RST wafers in all types of impurities: metallic, carbon, oxygen and SiC precipitates. The second part is an analysis of the dependence of the bulk lifetime on ribbon growth, the carbon burn-off step and the cell fabrication process. The third part discusses the results of the measurements of the conversion efficiency of cells made on p and n type RST substrates (cells were not textured and the hydrogenation was not optimized).
Cells were made on ca. 100 µm thick p-type RST substrates 5x5 cm2 and 1cm2 in surface area. The best value obtained was 12.8% (pseudo : 13.2%) on 5x5 cm2 cells and 13.6% (pseudo = 14.6%) on 1cm2 cells.
1cm2 cells were made on n-type RST substrates, using ion implantation or spin-on deposition for the emitter fabrication and PECVD SiO2 deposition or thermal oxidation for the passivation of the emitter. The best value was ca. 13.5% (15% SunVoc). It is concluded that the potential of RST material is 15%. | 17 101 |
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