Symposium : B
Semiconducting oxides
| start at | Subject | Num. |
|---|---|---|
| 14:00 | Introductory Remarks | |
| Defects, electronic states and spectroscopy : C. R. A. Catlow | ||
| 14:10 | Deep acceptors in ZnO Authors : Filip Tuomisto Department of Applied Physics, Aalto University Resume : The quest for mass-production-ready p-type ZnO has continued for more than a decade, and various candidates for shallow acceptors have been studied. The focus has been on two main groups, namely substitutional impurities from group I (Li, Na, substituting for Zn) and group V (N, P, As, Sb, substituting for O). Many reports of p-type conductivity have been published in the past years, and at least as many reports, based on both experimental and theoretical considerations, explaining why so many attempts to obtain p-type ZnO have failed – it turns out that the acceptor-like impurities tend to create deep states in the gap and compensate the residual, quite probably H-induced, n-type conductivity of ZnO.
I will present a compilation of the most recent results and interpretations obtained with positron annihilation spectroscopy on ZnO where either intrinsic or extrinsic acceptors have been introduced either during growth or by post-growth processing. Positrons are particularly sensitive to open volume defects, making them a perfect tool for studying vacancies – in high-purity ZnO the Zn vacancies have been identified as the dominant acceptor-like defects. Positrons can also be used to study negatively charged defects with no open volume, such as ionized acceptors. I will discuss the behaviour of these (deep) acceptors in various processing conditions and their possible interactions with hydrogen and other defects in the lattice. | 1 1 |
| 14:55 | Studies of Electron Trapping in ZnO semiconductor Authors : Leonid Chernyak, University of Central Florida, Physics Department, 4000 Central Florida Blvd., Orlando, FL 32816-2385, USA Resume : It has been recently discovered that electron injection into ZnO semiconductor doped with phosphorus, lithium, antimony or nitrogen using either electron beam of a Scanning Electron Microscope or a forward bias application to p-n junction or Schottky barrier, leads to a multiple-fold increase of minority carrier diffusion length, L, and lifetime. It has also been demonstrated that forward biasing a ZnO-based photovoltaic detector results in a several-fold long-lasting responsivity enhancement due to a longer minority carrier diffusion length in the detector’s antimony-doped p-region as a result of electron injection. The observed electron injection effects were attributed to the charging of the deep meta-stable centers associated with the above-referenced impurities.
The systematic optical and electrical studies were carried out on the representative range of ZnO samples to determine the activation energy for the effects of electron injection. For example, the activation energy for ZnO doped with antimony (ZnO:Sb) is about 220 meV, which is in agreement with the activation energy for a SbZn-2VZn acceptor complex.
L reaches its maximum of ~ 2.5 micron after 50 min of continuous exposure to the electron beam. Further monitoring revealed that irradiation-induced increase persists for at least one week. Annealing the sample at 175 C for 30 minutes resulted in L decrease to ~ 1micron. This behavior further supports the involvement of deep traps in the phenomenon of interest. | 1 2 |
| 15:15 | Deep Level Defects in Electron Irradiated ZnO Single Crystal Studied by Deep Level Transient Spectroscopy Authors : X. H. Lu, C. C. Ling, Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, P.R.China. Z. Q. Zhong, School of Microelectronics and Solid-State Electronics, University of Electronic Science and Technology of China, Chengdu, Sichuan, P.R.China. Resume : Undoped melt grown n-type ZnO single crystal (n~1016cm-3) was irradiated by 1.7-MeV electrons with fluence of 1014 cm-2 followed by post-irradiation annealing. Au Schottky contacts were thermally evaporated onto the samples with hydrogen peroxide pre-treatment. Deep level transient spectroscopy measurement was used to investigate the deep traps induced by the electron irradiation. The dominant trap in the as-grown ZnO single crystal has the activation energy of 0.28eV. The electron irradiation introduced an extra trap having the activation energy of 0.16eV. Thermal annealing study was also performed to study the thermal evolution of these deep level defects. | 1 3 |
| 15:30 | Coffee break | |
| 15:50 | Point defects in transparent semiconducting oxides: An embedded cluster perspective Authors : Alexey A. Sokol, University College London, Department of Chemistry, Materials Chemistry, 3rd Floor, Kathleen Lonsdale Building, Gower Street, London WC1E 6BT, UK Resume : Transparent semiconducting oxides are very important class of versatile advanced functional materials comprising copper, zinc, indium and tin oxides, all of which can be co-doped or alloyed to form more complex, multicomponent systems. Moreover they are complemented by closely related titanium based oxides including titania and strontium titanate, etc. Point defects in these materials are the major source of their optoelectronic and catalytic properties, for which these materials are valued. However, the nature of the defect states in the majority of cases remains unclear and is the matter of ongoing debate. A hybrid QM/MM embedded cluster approach proves to be an indispensable tool for treating defects in these materials, for which popular models using periodic boundary conditions fail to provide definitive answers. This approach is naturally suited for consideration of the charged species, allows one to use relevant quantum mechanical methods and provides defect energy levels from many-electron wave functions and densities rather than one-electron levels. Results of embedded cluster calculations can be further verified against or used for prediction of spectroscopic signatures of defects of interest. | 1 4 |
| 16:35 | Prospects for p-type conductivity in ZnO Authors : John L. Lyons, Anderson Janotti, and Chris G. Van de Walle Materials Department, University of California-Santa Barbara Resume : ZnO is regarded as a highly promising material for LEDs and lasers. It features a direct band gap, the ability to form heterostructures with ZnMgO and ZnCdO, a large exciton binding energy, and the availability of single-crystal substrates. The most significant barrier to realizing ZnO-based optoelectronics is the difficulty in producing p-type material. Among the possible acceptors, N has been considered the most promising; however, in spite of many published reports, reproducibility and stability are still major issues, and devices based on p-n homojunctions have remained elusive. We have studied the electronic and structural properties of the N acceptor in ZnO using state-of-the-art first-principles calculations based on the Heyd-Scuseria-Ernzernhof hybrid functional. We find that N has an exceedingly high ionization energy of 1.3 eV, meaning that N cannot lead to hole conductivity in ZnO. We have also analyzed the optical transitions (absorption and luminescence) and charge distribution associated with the N impurity, which offer characteristic signatures that can be compared to experimental photoluminescence and EPR results. Our results enable us to critically reexamine prior experimental results on N doping in ZnO. We also address more broadly whether there is still any chance of obtaining p-type ZnO. Our investigations indicate that substitutional dopants will not yield shallow acceptors, but interstitial dopants such as fluorine still offer hope. | 1 5 |
| 16:55 | Ab initio exploration of the properties of a novel polymorph of ZnO: how multi-centre bonding can lead to efficient atomic hydrogen transport and p-doping Authors : Daniele Stradi (1), Frances Illas (1), Stefan T. Bromley* (1,2) 1. Institut de Qu?ca Te?a i Computacional (IQTCUB), Universitat de Barcelona, Barcelona, Spain 2. Instituciátalana de Recerca i Estudis Avan?s (ICREA), 08010 Barcelona, Spain Resume : Zinc oxide (ZnO) has attracted much attention due to its potential role as a cheap biocompatible material for optoelectronics, transparent electronics and spintronics. One key challenge to be overcome in order for this promise to be realised is the control of acceptor dopants in the in the material, which lead to negative charge carriers (i.e. n-doping). Recently, it has been found that the main cause of this unintentional n-doping is due to the intimate multi-centre interaction between atomic hydrogen at oxygen defect sites with Zn centres [1,2]. The ubiquitous nature of hydrogen makes it very difficult to avoid and the production of p-doped ZnO remains a highly sought after goal for practical applications.
A possible alternative strategy to control the doping in ZnO is not to to induce modifications to the wurtzite crystal structure (wz-ZnO, the ground state polymorph under standard conditions) but to attempt to change the polymorphic form. ZnO can exist in the zincblende structure, undergoes a transition to the rocksalt phase at ~9GPa and has been prepared as the h-BN structure in thin films [3]. Recently we have predicted that the polymorphism is ZnO is likely to be much more wide-ranging [4], potentially allowing one to choose the properties of interest by changes in the crystal structure. Of all the new stable low density ZnO polymorphs predicted one in particular is calculated to be thermodynamically stable under mild negative pressure conditions [5]. The structure of this form of ZnO is found to be nanoporous, with a structure analogous to the silicate zeolite sodalite (SOD-ZnO) [6].
Employing density functional calculations (both pure GGA and HSE with screened exchange [7]) the atomic H transport properties of SOD-ZnO were probed using (i) ab initio molecular dynamics and, (ii) climbing image nudged elastic band transition state searches. Although the electronic structure of SOD-ZnO differs little with respect to wz-ZnO, the nanoporous crystal structure allows for quite distinct H-ZnO interactions. Firstly, we find that atomic H is surprisingly stable as an atomic species within the nanocages of SOD-ZnO. Further, atomic H can hop between cages with a very small energy barrier [8] and, during the transit, SOD-ZnO becomes p-doped. These latter properties are linked with a new type of multi-centre interaction which we compare with the picture of the known H multi centre bonding in wz-ZnO [8]. The relevance of our results to hydrogen purification membranes and atomic trapping and control is discussed.
[1] A. Janotti, C. G. Van de Walle, Nature Mater. 6, 44 (2007).
[2] E. V. Lavrov, et al., Phys. Rev. B 79, 165210 (2009).
[3] C. Tusche, H. L. Meyerheim, J. Kirschner, Phys. Rev. Lett. 99, 026102 (2007)
[4] M. A. Zwijnenburg, F. Illas, S. T. Bromley, Phys. Rev. Lett., 104, 175503 (2010).
[5] W. Sangthong, J. Limtrakul, F. Illas, S. T. Bromley, Phys. Chem. Chem. Phys., 2010 (in press).
[6] J. Carrasco, F. Illas, S. T. Bromley, Phys. Rev. Lett., 99, 235502 (2007).
[7] J. Heyd, G. E. Scuseria, M. Ernzerhof, J. Chem. Phys. 118, 8207 (2003).
[8] D. Stradi, F. Illas, S. T. Bromley, submitted 2010. | 1 6 |
| Poster Session I: Defects, electronic states and spectroscopy : D. J. Payne | ||
| 17:30 | Electrical characteristics of as-grown and H plasma treated n-type ZnO grown by different techniques Authors : Vl. Kolkovsky, L. Wolff, E. V. Lavrov, J. Weber Technische Universität Dresden, 01062 Dresden, Germany Resume : In the present study single-crystalline ZnO grown from the vapor phase, melt, and high-temperature aqueous solution (hydrothermal growth) have been investigated by means of capacitance-voltage, deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS before and after hydrogen plasma treatments. We demonstrate that in good agreement with previous results H acts as a shallow donor in all these materials. However, in hydrothermally grown ZnO H can also interact with acceptors leading to their complete passivation. In DLTS studies dominant peaks appear in the range of 120-170 K in all materials studied. The properties of the DLTS lines are different and depend on the growth procedure of ZnO. The origin of these lines is discussed in the present work. | 2 1 |
| 17:30 | Irradiation induced defects in n-type ZnO Authors : Vl. Kolkovsky, J. Weber Technische Universität Dresden, 01062 Dresden, Germany A. N. Larsen Institute of Physics and Astronomy, University of Aarhus, DK 8000 Aarhus C, Denmark S. B. Lastovskii NAS Belarus, Sci Pract Mat Res Ctr, Minsk 220072, Belarus Resume : In the present study low temperature electron-irradiated single-crystalline ZnO grown from the vapor phase were investigated in-situ with electrical measurements such as capacitance-voltage (CV), deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS. From the CV measurements we demonstrate that a big part of radiation-induced donor defects anneals below room temperature. Similar defects were also observed using helium or hydrogen implantation in n-type ZnO. The origin of these defects will be addressed in this study. On the other hand, no additional dominant lines in comparison with as-grown n-type ZnO appear in the DLTS spectrum after the electron- and light ion irradiations. In these studies two dominant peaks were observed in the DLTS spectrum in the temperature range from 40K to 300K. The electrical characteristics of these lines, their annealing behaviour and possible origin will be discussed. | 2 2 |
| 17:30 | Photoluminescence properties of spray pyrolysis deposited ZnO nanorods Authors : E.K?er, T.Raadik, T.Dedova, J.Krustok*, A.Mere, M.Krunks Department of Materials Science, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia. *Corresponding author. Tel: (372) 6203364; fax: (372) 6203367; E-mail: krustok@staff.ttu.ee (J?Krustok). Resume : Photoluminescence (PL) properties of highly structured ZnO layers comprising well-shaped hexagonal rods, is presented. The ZnO rods (length 500-1000 nm, diameter 100-300 nm) were deposited in air onto the preheated glass substrates by low cost chemical spray pyrolysis (CSP) method using zinc chloride solutions and growth temperatures in the temperature range of 450-550 °C. Spray deposited ZnO nanostructured layers with high internal surface area have been used as window material for extremely thin absorber layer (ETA) solar cells showing energy conversion efficiency of 4%. The aim of this work is to study the effect of the variation in deposition parameters (substrate temperature, solution concentration, spray rate) on PL of the spray deposited ZnO nanorods. At room temperature we observed very low intensity of SA (self-activated) emission. At T=10K five narrow PL peaks were distinguished in the exciton spectral region: a free exciton peak around 3.378 eV; acceptor bound exciton at 3.359 eV; two donor bound excitons at 3.363 eV and 3.368 eV; two electron transition (TET) at 3.334 eV. Temperature and excitation intensity dependence of PL emission was used to study a physical nature of these excitons. It was found that the substrate temperature is the most sensitive deposition parameter affecting the excitonic PL in ZnO nanorods. The possible reason of this effect, as well as the possible impact on thin film solar cell performance, is discussed. | 2 3 |
| 17:30 | Advances in computational studies of energy materials Authors : C. R. A. Catlow, M. Miskuvova, A. G. H. Smith, A. A. Sokol, A. Walsh AND S. M. Woodley Resume : We review recent developments and applications of computational modelling techniques from our group in the field of materials for energy technologies, including hydrogen production, energy storage and conversion, and light absorption and emission. Materials studied include Sn2TiO4, SrTiO3, GaN, ZnO, Ag2O and Cu2O. Special attention is paid to the modelling of nanostructured systems, including ceria (CeO2 and Ce2O3) and group 13 sesquioxides. We consider applications based on both interatomic potential and electronic structure methodologies.
1. Philosophical Transactions of the Royal Society A 368, 3379 (2010). | 2 4 |
| 17:30 | Persistent Photoconductivity in ZnO-based Schottky Diodes Authors : D. H. -S. Kim and M. W. Allen. The MacDiarmid Institute for Advanced Materials and Nanotechnology, Department of Electrical and Computer Engineering , University of Canterbury, Christchurch 8140, New Zealand. Resume : The origin of persistent photoconductivity (PPC) in ZnO-based materials is divided into two categories, both of which are somewhat controversial. Some authors [1,2] have linked the PPC effect to intrinsic and/or extrinsic bulk point defects that exhibit meta-stable charged states. On the other hand, others [3,4], relate the PPC effect to the capture of photo-generated holes by surface states, which varies with ambient conditions. Most authors [5-7] have evaluated the PPC effect in individual ZnO nanowires or nanodevices, which have a high surface-to-volume ratio to exclude other influences and simplify the analysis. Here, we have used low ideality factor iridium oxide and silver oxide based ZnO Schottky photodiodes, fabricated using reactive eclipse pulsed laser deposition, on a range of different bulk ZnO substrates to investigate the PPC effect. These photodiodes are very sensitive to UVA illumination, exhibiting more than 5 orders of magnitude increase in reverse current on illumination with 365 nm light. It was observed that PPC recovery contains both fast and slow processes which vary with surface polarity and material composition. Dielectric passivation of the photodiode surface [8] using organic layers, MgO, Si3N4, and CHfO3 was also performed and the results used to assess the relative roles of surface versus bulk contributions to the PPC effect in ZnO.
References :
1. S. Lany, and A. Zunger,. Phys. Rev. B. 72, 035215 (2005).
2. A. Janotti, and C. G. Van de Walle,. Appl. Phys. Lett. 82, 122102 (2005).
3. B. Claflin, D. C. Look, and D. R. Norton., J. Elect. Mater. 36, 442 (2007).
4. S. A. Studenikin, N. Golego, and M. Cocivera. J. Appl. Phys. 87, 2413 (2000).
5. Z. Fan et al., Appl. Phys. Lett. 85, 5923 (2004).
6. W. I. Park et al., Appl. Phys. Lett. 85, 5052 (2004).
7. S. Hullavarad et al., Nanoscale. Res. Lett. 12, 1421 (2009).
8. H. von Wenckstern et al., J. Elect. Mater. 39, 559 (2010). | 2 5 |
| 17:30 | Mechanism of ZnO thermal emission Authors : V.I. Kushnirenko 1, I.V. Markevich 1, B.M. Bulakh 1, T.V. Zashivailo 2 1 V. Lashkarev Institute of Semiconductor Physics, NAS of Ukraine, Pr. Nauky 45, Kiev, 03028, Ukraine 2 National Technical University of Ukraine “КРI”, Pr. Pobedy 37, Kiev, 03056, Ukraine Resume : Earlier, the possibility of application of wide-band-gap semiconductor thermal emission in visible-light-source development has been theoretically considered [1]. It was supposed that such an emission should be caused by band-to-band recombination of thermally generated electron-hole pairs [1]. However, the mechanism of thermal emission in wide-band-gap semiconductors has not been studied experimentally.
In the present work, thermal emission in ZnO crystals was observed and investigated. Undoped needle-shaped ZnO single crystals were grown by a vapor-phase technique. Indium electrodes were melted on both crystal ends and d.c. or a.c. voltage was applied to the sample. Essential heating of the crystal occurred at current value of about 0.01 A and light emission began at about 800oC. The emission had initially green color and shifted toward longer wavelength with temperature. Emission and transmission spectra were measured at different crystal temperatures. It was found that the emission is not due to band-to-band transitions but resulted from recombination of thermally generated carriers through some defect centers.
[1] Yu.N. Nikolaev, M.V.Fock, Tr. Fiz. Inst. im. P.N. Lebedeva, Akad. Nauk SSSR, 50 (1970) 106. | 2 6 |
| 17:30 | Nanoparticle-dispersed high-k organic-inorganic hybrid dielectrics for solution-processable Zinc Oxide Thin Film Transistors Authors : Yangho Jung, Flexible and low-temperature fabrication electronics Resume : In recent, the various electronic devices are expected to satisfy multi functionalites including light weight, low power consumption, optical transparency, flexibility, and low-temperature fabrication. The thin film transistors (TFTs) are the essential component for the various electronic devices.
In this study, we fabricated Solution-Processable thin gate dielectrics for Solution-Processable Zinc Oxide Thin Film Transistors using a photosensitive organic-inorganic hybrid material based on organosiloxane synthesized by a sol-gel reaction, followed by heat treatment at low temperature of 180oC. A sol-gel reaction between 3-methacryloxypropyltrimethoxysilane and zirconium propoxide led to the formation of solution-processable hybrid materials. The electrical characteristics of hybrid dielectrics were controlled by adjusting the zirconium alkoxide concentration. We added Melamin system cross linker (full methoxy methylated melamin) for the improvement of film density at the low process temperature. In addition, we confirmed the effect of melamin system cross linker by using Fourier Transform infrared spectrometer (FT-IR). The chemical structure of organic-inorganic hybrid dielectrics is observed by X-ray Photoelectron Spectroscopy(XPS), Atomic force microscopic (AFM), and high resolution transmittance electron microscopy (HRTEM). We have analyzed optical transmittance of the film with UV/Vis spectroscopy.
We expect that solution processable thin gate dielectrics could be a breakthrough to realize the transparent, flexible and low-temperature fabrication electronics. | 2 7 |
| 17:30 | The effects of oxygen partial pressure on the electrical properties of the IGZO TFTs by using IPVD method. Authors : Jun-Yong Bak1,2, Woo-Seok Cheong1,*, Mi-Hee Lee1, Sung Mook Chung1 and Hong-Seung Kim2. 1Oxide Electronics Research Team, ETRI, 138, Gajeongno, Yuseong-Gu, Daejeon, 305-700, Korea. 2Department of Nano Semiconductor Engineering, Korea Maritime University, Busan, 606-791, Korea. Resume : abstract
RF magnetron sputtering is a well-known deposition method for oxide semiconductors, due to a good thin film uniformity and electrical property, so that this method has been applied to active layers for thin film transistors (TFTs). RF magnetron sputtering can easily control the conductivity of thin films by adjusting various process conditions [1], where, especially, the control of oxygen partial pressure is a crucial factor. Up to now, there have been no reports on oxide semiconductors made by other sputter systems, for example, advanced sputtering. In this study, ionized physical vapor deposition (IPVD) will be used for the deposition of In2O3-Ga2O3-ZnO (IGZO) semiconductors. IPVD with inductively coupled plasma (ICP) can enhance the plasma density for a high ionization rate. [2] We will investigate how the IPVD affects electrical properties of TFTs, as functions of oxygen partial pressure and ICP power, compared with conventional magnetron sputtering.
Reference
[1] P. Barquinha, G. Goncalves, L. Pereira, R. Martins, E. Fortunato. Thin. Solid. Films., 515, 8450, 2008.
[2] Jeon G Han, J. Phys. D: Appl. Phys. 42, 2009, 043001 | 2 8 |
| 17:30 | ZnO NANOFIBERS FIELD EFFECT TRANSISTORS FOR SENSING AND BIOSENSING Authors : A. Baranowska – Korczyc*, K. Fronc, B. Sikora, A. Reszka, K. Sobczak, I. Fijałkowska, J. Bujak, K. Dybko, W. Paszkowicz, P. Dłużewski, B.J. Kowalski, D. Elbaum Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46 Warsaw, Poland (+48 22 843 6601) *) e-mail: akorczyc@ifpan.edu.pl Resume : The Field Effect Transistors (FETs) are very promising, fast and real-time detection sensors. We constructed FET detector taking advantage of the electric conduction properties of ZnO nanofibers and obtained these one-dimensional (1D) nanostructures by electrospinning followed the calcinations [1]. The nanofibers were calcined at air in 500º C for 4 h. They are effective gating materials for a transistor channel. Our FET is a light (UV-325nm) sensor and shows the resistivity decrease after immersion of the nanofibers in water or ethanol. These 1D structures can be applied to construct a family of bio-sensors based on FETs [2]. We intend to explore ZnO nanofibers as bio-detectors.
REFERENCES
[1] J.Y. Park, S.S. Kim Journal Am. Ceram. Soc., 92 [8] (2009) 1691–1694 [2] V. Pachauri ,A. Vlandas ,K. Kern,K. Balasubramaninn, Small, 2009, DOI: 10.1002/smll.200900876
The research was partially supported by the European Union within European Regional Development Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08), and by the Ministry of Science and Higher Education (Poland) through Grant No. N N518 424036. | 2 9 |
| 17:30 | Synthesis and characterization ZnO and ZnO/MgO core/shell nanocrystals and application in biology Authors : B. Sikora, K. Fronc, A. Baranowska – Korczyc, A. Nowicka [1], W. Paszkowicz, K. Sobczak, P. Dłużewski, A. Reszka, B. J. Kowalski, I. Fijałkowska, A. Szczepankiewicz [2], D. Elbaum Institute of Physics Polish Academy of Science, al. Lotników 32/46, Warsaw, Poland; [1] Warsaw University of Life Sciences – SGGW, Nowoursynowska 166 ST.Warsawa, Poland; [2] Nencki Institute of Experimental Biology, Pasteur 3, 02-093, Warsaw, Poland Resume : Semiconductor nanocrystals with nanoscale size lead to the quantum confinement effect, which result in interesting optical and electronic properties. The unique photophysical properties of nanocrystals provides a new class of biological labels that could overcome the limitations of organic fluorophores. Stability against photobleaching [1], high quantum yield [2], and large surface – to – volume ratios make nanocrystals superior to organic fluorophores in detection sensivity as well as in long – term tracking of biological processes.
Our aim was to synthesize and characterize a uniform and stable ZnO/MgO core/shell nanocrystals for biosensory applications for example FRET measurements.
ZnO/MgO core/shell nanocrystals were analyzed using luminescence and absorbance spectrophotometer, Atomic Force Microscopy, X-Ray diffraction and Transmission Electron Microscopy. Size obtained from these methods were from 4 to 10 nm depending on conditions of reaction. ZnO/MgO nanocrystals have wurtzite structure. MgO shell prevented aggregation of ZnO and enhanced luminescence from ZnO core.
We applied ZnO/MgO nanocrystals in C. elegans. Fluorescence Microscopy images of C. elegans showed nanoparticles internalized by worms. C. elegans was alive for several days with nanoparticles inside, what may indicate on non – toxic nanocrystals.
[1] X. Wu et al, Nat. Biotechnol., 21 (1), (2003), 41, [2] W. C. Chan et al., Science, 281, (1998), 2016.
Acknowledgements: The research was partially supported by the European Union within European Regional Development Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08) and was partially supported by the Ministry of Science and Higher Education (Poland) through Grant No. N515 015 32/0997 begin_of_the_skype_highlighting 015 32/0997 end_of_the_skype_highlighting and No. N N518 424036. | 2 10 |
| 17:30 | Effect of the annealing environment on the optical properties of ZnO/GaAs grown by MOCVD Authors : J. K. Dangbégnon, K. Talla, J. R. Botha Department of Physics, PO Box 77000, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa Resume : The activity of p-type dopants in ZnO remains a controversial subject. In this paper, the optical properties of ZnO grown on GaAs substrate using metalorganic chemical vapor deposition (MOCVD) is investigated by photoluminescence. Post-growth annealing in nitrogen and oxygen was performed for different times and at different temperatures in order to incoporate As from the substrate into the ZnO thin films. Low temperature photoluminescence (PL) of the samples annealed in the different ambients shows more pronounced changes when the annealing is performed in oxygen at 550C. A transition at ~ 3.35 eV is observed after annealing at this temperature. A further increase in the annealing temperature leads to the disappearance of this line. An increase in intensity of this new transition is accompanied by an enhancement in radiative recombination involving structural defects, such as the stacking fault related transition at 3.31 eV (1) and the Y-line (2). Temperature dependent PL demonstrates the excitonic nature of the transition at ~ 3.35eV, which is assigned to an arsenic-related acceptor bound exciton recombination, with an activation energy for the acceptor of 100 meV. Furthermore, the enhancement of the radiative centers related to structural defects is ascribed to colatteral damage arising from the incorporation of the much larger As-atoms into the ZnO lattice.
(1) M. Schirra et al., Phys. Rev. B 77, 125215 (2008)
(2) B. K. Meyer et al., phys. stat. sol. (b) 241, 231– 260 (2004) | 2 11 |
| 17:30 | Growth, optical and magneto-optical properties of Ni-doped ZnO thin films Authors : A.I. Savchuk, I.D. Stolyarchuk, G.I. Kleto, V.V. Makoviy, M.M. Smolinsky, Department of Physics of Semiconductors and Nanostructures, Chernivtsi National University, 2 Kotsyubynsky Street., 58012 Chernivtsi, Ukraine Resume : Among diluted magnetic semiconductor (DMS) materials, ZnO-based systems doped with transition metals belong to the most attractive, since there is possibility to control independently the concentration of the charge and spin of the carriers. However, the experimental confirmation of ferromagnetism in ZnO-based DMS is controversial, and the mechanisms of such an ordering are unclear. Our previous works were devoted to studies of the Mn single doped ZnO bulk crystals and thin films. In this work, we focus main attention on growth and characterization of Zn1-xNixO thin films. The preparation of this material meets some difficulties due to large driving force for phase segregation into NiO and ZnO.
Zn1-xNixO thin films were deposited by pulsed laser deposition (PLD) method and RF-diode sputtering technique with planar cathode and 1.76 MHz power source in argon-oxygen mixture. Targets for both techniques were prepared by solid state reaction using of ZnO (99.99 %) and Ni (99.5 %) powders in stoichiometric ratios. Content of Ni was varied in range of 0 | 2 12 |
| 17:30 | Comparative study on fabrication methods of ZnO thin films Authors : Dedong Han1, Yi Wang1, Shengdong Zhang1, Ruqi Han1, Satoru Matsumoto2 and Ino yuuso2 1 Institute of Microelectronics, Peking University, Beijing 100871, China, 2 Department of electrical engineering, Keio University, Japan Resume : 1. Introduction
In recent years, ZnO has been researched as a potential transparent oxide semiconductor material very much[1-5]. ZnO has attracted significant attention due to its extensive applications in varied fields. They can are used in photodetectors, light-emitting diodes, solar cells, thin film transistors, FPD, flexible display, OLED devices etc[6-13], because ZnO has good piezoelectric, conductive and optical properties. It has been considered as an alternative to GaN due to its superior properties, such as a large exciton binding energy (∽60 meV) and band gap energy (∽3.37 eV). Many growth process ways of ZnO have been studied such as sol–gel process, electrochemical growth, chemical vapor deposition, and sputtering. The sputtering process is good way to make highly quality ZnO films because that is very compatible with conventional IC and TFT processing. We have fabricated ZnO films using three different methods, respectively. The structural, and electrical properties of ZnO thin films were comparatively studied in this paper.
2. Experimentation
The first method is annealing oxide method that pure Zn thin films were sputtered on glass substrates by radio frequency (rf) sputtering at room temperature, then they were annealed at 350oC in O2 ambient for an hour. The sample is signed as sample 1#. The second method is reactive sputtering method that Zn was sputtered by radio frequency (rf) sputtering in O2 ambient at room temperature, ZnO thin film was reactive formed on glass substrate. The sample is signed as sample 2#. The third method is direct sputtering method that pure ZnO was directly sputtered on glass substrate. The sample is signed as sample 3#.
3. Results and discussion
3.1. Crystallinity and orientation
The X-ray diffraction (XRD) spectrum of ZnO thin films is showed in the Fig. 1(a)(b)(c), respectively. The XRD pattern of ZnO thin film sample 1# indicates three reflection peaks of hexagonal wurtzite structure, (100), (002), and (101), at 2θ=31.77°, 34.42°, and 36.25°. These peaks are in good accordance with the JCPDS Card No. 36-1451 with lattice constants of a=3.25 Å and c=5.21 Å. Some weak peaks such as (102),(110), (103) and (112) have also been observed but with small intensities. The sharp diffraction peak (002) indicates that the ZnO thin film has grown along the c-axis. In addition, the figure also shows that the intensity of the (002) diffraction peak is smaller than that of the (100) and (101) diffraction peaks. Therefore, it was suggested that the ZnO thin films are not perpendicular to the substrate surface. XRD spectrums of sample 2# and 3# presents intense peak of (002) orientation of the wurtzite structure. The dominant peak of XRD pattern of ZnO thin film is located at 2θ = 34.42°. The diffraction peak of metallic Zn was not detected by XRD for the samples. The XRD pattern indicates highly oriented crystallographic growth of ZnO films with c-axis perpendicular on glass. The surface free energy is the smallest on the (002) surface of ZnO and hence the thin films tend to grow along it.
3.2. Morphological properties
Fig. 2(a)(b)(c) show the field emission scanning electron microscopy (SEM) pictures of the three ZnO thin film samples. It can be seen that the sample 1# had uneven surface with inconspicuous grains, which indicated the low crystal quality of ZnO thin film. In contrast, sample 3# is composed of densely packed uniform ZnO nanocrystals, and sample 2# had a gray smooth and dense plane. Therefore, sample 2# has the best crystal quality of ZnO thin film in three samples.
The two-dimensional (2D) and three-dimensional (3D) views of the surface morphology of ZnO thin film are shown in Figs. 3(a)-(c), respectively. It is observed that the grains grow uniformly with homogenous distribution. The AFM (atomic force microscopy) images of the sample 2# also show that the best quality homogenous film in three samples.
3.3. Electronic properties
Electronic properties of ZnO thin films were investigated by Hall effect measurements. Hall effect measurements in the van der Pauw techniques were used to determine the mobility and carrier concentration of the ZnO thin films. From Hall effect measurement of the ZnO thin films , the values of resistivity, carrier concentration and mobility were obtained. The results are showed in the table 1. From these results, we can see that the resistivity of sample 1# is the lowest and the resistivity of sample 2# is the highest. Mobility of sample 2# is the highest than that of the others.
4. Conclusions
In summary, we have fabricated ZnO thin films on glass substrates by three different methods. The structural characterization of ZnO thin films were studied by X-ray diffraction (XRD), the surface morphology of ZnO thin film were investigated by field emission scanning electron microscopy (SEM) and atomic force microscopy (AFM), and electronic properties of ZnO thin films were investigated by Hall effect measurements. The results show that the thin films had high crystalline quality. Comparative study on three fabrication methods of ZnO thin films, we can see that reactive sputtering method is very good method because the thin film fabricated by this method has good crystalline quality, surface morphology, and electronic properties. Besides, this method is very compatible with conventional IC and TFT processing. | 2 13 |
| 17:30 | DEFORMATON CHARACTERISTICS OBTAINED BY NANOINDENTATION ON ZnO FILMS Authors : Roberts Zabels1, Faina Muktepavela1, Edmunds Tamanis2 1Institute of Solid State Physics, University of Latvia, 2 University of Daugavpils, Latvia e-mail: rzabels@gmail.com Resume : The production and practical use of functional materials in devices is often connected with contact-induced processes that influence mechanical stability of the device. Nanoindentation is a well suited method for testing the deformation behavior and mechanical properties of materials because it is associated with the contact-induced deformation.
In this work ZnO films on Si, SiO2 and glass were investigated by means of nanoindentation. For comparison a ZnO single crystal was analyzed as well. Thin films were obtained by a very simple mechanoactivated oxidation method (MAOM) [1]. Results showed that the ZnO single crystal is relatively soft material with hardness of 2.0 GPa and Young’s modulus of 160 GPa on the prismatic plane. Indentation induced plastic deformation in this crystal is connected with the mechanism of dislocation sliding.
Nanostructured ZnO films on glass when compared to single crystal are characterized by increased hardness – up to 9 GPa and decreased modulus – up to 120 GPa. This is due the phase-structure factor. During indentation no dislocation sliding or formation of micro-cracks were observed. ZnO/glass contact interface was stabile and exhibited high adhesion: at load Pmax>2N no signs of delamination were detected. However in systems ZnO/Si and ZnO/SiO2 contact interface adhesion is weak (cracks and delamination at Pmax<1N) and depends on the development of mechanoactivated topochemical reactions. The obtained results demonstrate the dependence of ZnO deformation behavior on structure factor and adhesion processes on contact interfaces.
References
[1] F. Muktepavela, G. Bakradze, L. Grigorjeva, R. Zabels, E. Tamanis, Thin Solid Films, 518 (2009) 1263 | 2 14 |
| 17:30 | CHARACTERIZATION OF ZnO GROWN BY PLASMA ASSISTED MOLECULAR BEAM EPITAXY ON C-SAPPHIRE AND ON GaN/c-Al2O3 TEMPLATES Authors : D. Dobosz, M. Pietrzyk, M. Stachowicz, E. Przezdziecka, A. Kozanecki, A. Wierzbicka, H. Teisseyre, Z.R. Zytkiewicz, B.J. Kowalski Institute of Physics, PAS, Al. Lotników 32/46, 02-668 Warsaw, Poland Resume : Zinc oxide semiconductor has attracted wide interest as a material promising for applications in optoelectronic devices operating in the blue and ultraviolet spectral ranges. A large free-exciton binding energy of about 60 meV ensures that excitonic emissions are significant at room temperature. Currently many groups put a lot of effort in optimization of growth techniques of ZnO films on different substrates.
In this work we study characteristics of ZnO layers grown using plasma-assisted MBE technology. ZnO layers were deposited on c-Al2O3 and GaN/c-Al2O3 templates at the same growth conditions. The layers were grown on 20-40 nm thick ZnO buffer layers deposited at 450C and then annealed at 600C before the growth. Layers of 700 nm ZnO were grown at 650C under different Zn and O flux conditions. The layers were characterized using luminescence (PL), scanning electron microscopy (SEM), and x-ray diffraction (XRD). In general, ZnO layers grown on sapphire reveal better surface morfology, however, the (0002) and other XRD reflexes are wider than for layers grown on GaN. The PL of ZnO on sapphire is dominated by excitons bound to Al donor, whereas in ZnO on GaN excitons bound to Ga dominate. The FWHM of excitonic lines varies from 2 to 5 meV, with a tendency to smaller width for ZnO on GaN. SEM images reveal a high concentration of threading dislocations estimated to ~109 cm-2. Mapping of emission intensity near dislocations was performed using SEM-CL technique.
Work supported in part by the European Union within European Regional Development Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08). | 2 15 |
| 17:30 | Zinc tin oxide thin film transistors fabricated by ionized physical vapor deposition Authors : 1,2Mi-Hee Lee, 1Woo-Seok Cheong, 1Jun-Yong Bak, 1Sung-Mook Chung, and 2In-Hwan Lee 1Oxide Electronics Research Team, ETRI, 161Gajeong-dong, Yuseong-gu, Daejeon 305-350, Korea Phone: +82-42-860-5372, E-mail: mhlee03@etri.re.kr 2School of Advanced Materials Engineering, Research Center for Advanced Materials Development, Engineering College, Chonbuk National University, Jeonju 561-756, Korea Resume : An ionized physical vapor deposition (IPVD) equipped with inductively coupled plasma (ICP) can activate and ionize sputtering atoms by using a high density plasma, so that this method has several advantages, improvement of the film quality such as density and adhesion, control of the reactivity, and decreasing the deposition temperature [1]. However, there have been few reports on the electrical and optical properties of oxide semiconductors prepared by IPVD.
In this study, using IPVD, ZnO-SnO2 (ZTO) oxide semiconductors were deposited at room temperature. Specially, the effects of ICP power on the electrical performance of the top/bottom gate ZTO-thin film transistors were investigated, where the 20-nm ZTO films were obtained at the ICP power ranging from 100W to 800W, and 180-nm Al2O3 gate insulators and 150-nm ITO electrodes were employed.
References
[1] J T Gudmundsson, J. Phys.: Conf. Ser 100 (2008) 082002. | 2 16 |
| 17:30 | Structural and optical properties of ZnO layers deposited by rf plasma on SiO2/Si and Ti/Si patterned substrates Authors : A. Kozanecki1, F. Cerqueira2, D. Szmigiel3, M. Stachowicz1, B.J. Kowalski1 1Institute of Physics, PAS, Al. Lotników 32/46, 02-668 Warsaw, Poland 2University do Minho, Braga, Portugal, 3Institute of Electron Technology, Piaseczno, Poland. Resume : Due to their excellent physical properties ZnO nanostructures have been widely studied for practical applications to electronics and photonics in UV light sources, sensors and solar cells. Particularly interesting is the possibility of integration of light emitting layers on SOI structures. For this it is desirable to explore low temperature process. This study examines structural and optical properties of ZnO thin films deposited on photolitographically patterned templates of SiO2/Si as well as on Ti/Si templates. The ZnO layers were deposited by reactive magnetron sputtering of Zn target within a mixture of O2 and Ar/H2 gases at a fixed RF sputtering power of 80 W. Substrate temperature during deposition was within the 200-600C range and at each temperature the layers were deposited on both types of templates in one process.
The structural properties of the ZnO layers were characterized using scanning electron microscopy (SEM), SEM-CL, photoluminescence (PL) and micro-Raman spectroscopy. The cross sectional SEM images reveal columnar growh of ZnO on all substrates. The growth rate does not depend on the substrate. SEM data show that morphology of ZnO layers deposited on different substrates differs at low growth temperatures, however, differences disappear for higher growth temperatures. In low temperature PL two bands dominate: at 369 nm which can be related to emission of excitons bound to neutral donors and a much broader emission which probably is due to electron bound to donor – free hole recombination near 400 nm. Micro-Raman spectra reveal that samples grown at 600C are of very good crystallinity.
Work supported in part within European Regional Development Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08). | 2 17 |
| Back | ||
| Une réalisation advisa.fr |  |