Symposium : T
Physics and Applications of Novel gain materials based on Nitrogen and Bismuth Containing III-V Compounds
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| New Materials : Chair to be confirmed | ||
| 08:30 | Growth and optical properties of Ga(In)NSb for long wavelength applications Authors : M. J. Ashwin, J. J. Bomphrey, and T. S. Jones (1) D. Walker and P. A. Thomas (2) T. D. Veal (3) Affiliations : (1) Department of Chemistry, University of Warwick, Coventry, UK (2) Department of Physics, University of Warwick, Coventry, UK (3) Stephenson Institute for Renewable Energy and Department of Physics, University of Liverpool, Liverpool, UK Resume : Dilute nitride antimonides of varying composition have a range of potential applications, including improving the efficiency of thermophotovoltaics based on GaSb by harvesting the 2-4 μm photons and as an alternative to HgCdTe for long wavelength infrared sources and detectors operating in the 8-14 μm atmospheric transmission window. The incorporation of N in molecular-beam epitaxy of GaNxSb1−x alloys with x ≤ 0.022 has been investigated as a function of temperature (325–400°C) and growth rate 0.25–1.6 μmh-1. At fixed growth rate, the incorporated N fraction increases as the temperature is reduced until a maximum N content for the particular growth rate reached. At each temperature, there is a range of growth rates over which the N content is inversely proportional to the growth rate; the results are understood in terms of a kinetic model. This systematic growth rate- and temperature-dependence enables the N content and resulting band gap to be controlled. Fourier transform infrared absorption spectroscopy and modelling has been used to investigate the optical properties of the films. The inclusion of N pairs in the model was found to be vital to reproduce the composition-dependence of the absorption onsets. | 3 1 |
| 09:00 | Effects of hydrogen irradiation on the optical and electronic properties of site-controlled InGaAsN V-groove quantum wires Authors : Marco Felici 1-2, Antonio Polimeni 1, Giovanna Lavenuta 1, Elena Tartaglini 1, Mario Capizzi 1, Romain Carron 2, Dan Fekete 2-3, Pascal Gallo 2, Benjamin Dwir 2, Alok Rudra 2, Eli Kapon 2, Giorgio Pettinari 4-5, Peter C. M. Christianen 4, Jan C. Maan 4, Affiliations : 1 Dipartimento di Fisica, Sapienza Università di Roma, P.le A. Moro 2, 00185 Roma, Italy; 2 Laboratory of Physics of Nanostructures, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland; 3 Department of Physics, Technion-Israel Institute of Technology, Haifa 32000, Israel; 4 High Field Magnet Laboratory, Institute for Molecules and Materials, Radboud University Nijmegen, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands; 5 School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom; Resume : Epitaxial deposition of InGaAs on a GaAs substrate patterned with V-grooves is a proven method for the fabrication of site-controlled quantum wires, QWRs. Recently, this method was paired to the large band-gap bowing typical of dilute nitrides to grow high-quality InGaAsN QWRs emitting at ~1.3 μm at RT.
The properties of such QWRs are assessed here by polarization-dependent photoluminescence (PL) and micro-magneto-PL. Both the strong polarization anisotropy of the QWR emission and the dependence of the diamagnetic shift on the orientation of the applied magnetic field confirm the 1D nature of the QWR excitons. Further, the possibility of passivating N impurities by H irradiation is used to turn off the effects of N incorporation, and to estimate the N content (x) in the QWRs. Both the H-induced blueshift of the QWR emission (70meV) and the measured value of the electron effective mass are consistent with x~1%.
Nitrogen is also found to enhance the In intake in the QWR, possibly due to the strain reduction associated with N introduction in the lattice. A significant N-induced strain reduction is indeed pointed out by the observation that the polarization degree (PD) of the InGaAsN QWR emission decays quickly with increasing temperature, indicating a small splitting between the QWR valence-band levels. In fully hydrogenated samples, conversely, the PD is roughly constant up to 250K, suggesting the recovery of a larger separation between the QWR hole states upon N passivation. | 3 2 |
| 09:15 | Independent tuning of electron and hole confinement in InAs/GaAs quantum dots through a thin GaAsSbN capping layer Authors : J. M. Ulloa1, D. F. Reyes2, M. Montes1, D.L. Sales2, D. González2, A. Guzman1, A. Hierro1 Affiliations : 1 ISOM, Universidad Politécnica de Madrid,Ciudad Universitaria s/n, 28040 Madrid, Spain; 2 Departamento de Ciencia de los Materiales e IM y QI, Universidad de Cádiz, 11510 Puerto Real (Cádiz), Spain Resume : The possibility of engineering the electronic structure of semiconductor quantum dots (QD) is crucial for many applications: a fine control of the confined electron levels is required to tune the intraband transitions in quantum dot infrared photodetectors, devices like QD solar cells or QD memories require also an accurate control of the QD-barrier band offset energies, etc. All these ap-plications would strongly benefit from an independent control of the electron and hole confinement potentials in the QD. It is well known that adding Sb mainly modifies the valence band (VB) of GaAs, whereas N is known to change only the conduction band (CB) of GaAs. Therefore, we study in this work the possibility of using a thin GaAsSbN capping layer (CL) to independently modify the electron and hole confinement energies in MBE-grown InAs/GaAs QDs through the N and Sb contents, respectively. We show that the QD-CL band structure can be broadly tuned through the CL composition, and converted from type-II in the VB, to type I, and to type-II in the CB. Nevertheless, N is found to enhance the temperature-induced quenching of the photoluminescence (PL), and the simultaneous presence of Sb and N degrades the PL even at low temperature. Different growth strat-egies trying to avoid this problem are tested. The influence of the Sb and N content on the QD opti-cal properties is discussed in correlation with an analysis of the structural properties performed by transmission electron microscopy. | 3 3 |
| 09:30 | Impact of N on the structural properties of GaAsSbN-capped InAs QDs studied by advanced transmission electron microscopy techniques Authors : D. F. Reyes1, D. L. Sales1, J.M. Ulloa2, A. Guzman2, A.Hierro2, A. Mayoral3 and D. González1 Affiliations : 1 Dpto. de Ciencia de los Materiales e I. M. y Q. I., Facultad de Ciencias, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain 2 Dpto. de Ingeniería Electrónica, Instituto de Sistemas Optoelectrónicos y Microtecnología (ISOM), E.T.S.I. Telecomunicación, Universidad Politécnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain 3 Laboratorio de Microscopías Avanzadas (LMA), Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, Zaragoza, Spain Resume : A promising alternative to design semiconductor laser devices in the last years is the use of a thin GaAs layer with Sb or N to cover InAs QDs. However, the incorporation of high Sb contents shrinks strongly the valence band, changing the QD effective bandgap from direct to indirect, and high nitrogen content increases the defect density. The result is in both cases a degradation of the optical properties. One possible solution is the simultaneous incorporation of reduced Sb and N contents. In this work, we analyze the effect of nitrogen addition in QDs inside quantum wells (DW) of InAs/GaAs0.9Sb0.1, grown by molecular beam epitaxy, and studied by advanced transmission electron microscopy (TEM) and photoluminescence (PL) techniques.
The addition of nitrogen in GaAsSb DW produces a strong redshift in the PL emission peak, together with an important loss of intensity. Nevertheless, TEM images show that the incorporation of N does not induce significant changes in QD morphology or in the extended defect density. Moreover, the average content of Sb and N estimated in the capping layer region far away from QDs by TEM deformation analysis is in good agreement with nominal values (10% and 2.6% respectively).However, high resolution Z-contrast studies evidence an accumulation of Sb around QDs in the nitride sample that does not occur in the sample without N. The huge changes in the atomic distribution around the QDs by the addition of N and its effect in the PL spectra are discusse. | 3 4 |
| 09:45 | Incorporation of Dilute Concentrations of Nitrogen in GaSb, and GaAs as a Function of Substrate Temperature During Molecular Beam Epitaxy Authors : Stefan P. Svensson, Wendy L. Sarney Affiliations : US Army Research Laboratory, 2800 Powder Mill Road, Adelphi, MD 20783 Resume : The incorporation of dilute concentrations of nitrogen in GaSb and GaAs has been studied as a function of substrate temperature during molecular beam epitaxy. We observe the presence of new crystalline phases that may be the source of previously reported conflicting N-concentrations measured by x-ray and other chemical analysis techniques such as SIMS. Past reports show that the N incorporation rate in GaSb was found to be strongly dependent on the substrate temperature. In contrast, N-incorporation in GaAs in a similar temperature range is nearly independent of substrate temperature up to about 500 C where the onset of a monotonic decrease is seen. These observations were based on the epi-substrate peak separations determined from (004) x-ray rocking curves, assuming substitutional incorporation of N on Sb or As sites in a zincblende lattice. Models have been put forth that explains this in terms of re-evaporation during growth of the atomic N at elevated temperatures, but these conflict with SIMS data. By performing ultra-wide 2 theta-omega scans we have found new crystalline phases that are not due to spinodal decomposition. We observe a direct relationship between the peak intensity of these phases and the amount of apparently missing N. At the lowest growth temperatures the XRD-determined N-content in GaSbN and GaAsN is the same and the spurious phases disappear, indicating that it is only possible to produce single crystalline, cubic GaSbN under these growth conditions. | 3 5 |
| 10:00 | Carrier Lifetime Measurements for 1.3-μm InGaNAs Quantum Dot Lasers Using Impedance Matching Authors : Kevin Paker Affiliations : the university of birmingham Resume : Semiconductor Quantum Well(QD) lasers have shown some superior performance characteristics
compared to Quantum Well (QW) lasers over the last few years.InGaNAs QD material system
allows emission at 1.3 μm wavelength, which is suitable for optical fibre data communication. The
importance of carrier loss mechanisms in these lasers has not been studied in much detail. In
particular the role of Auger loss and mono-molecular losses with p-doping need analysis
This work presents experimental results of carrier lifetime studies in QD lasers using an impedance
matching measurement technique. The carrier lifetime analysis can be related to the usual loss
coefficients associated with monomolecular (A), radiative recombination (B) and Auger (C) loss
processes. The lifetime is measured in the frequency range 0.045-2GHz and for various
temperatures around room temperature. We have used an InGaNAs QD laser with a threshold
current Ith=48 mA at 298K and an emitting wavelength temperature dependence of 0.395 nm/K. The
laser emission spectrum is 3 nm wide at FWHM with gain of 2 cm-1 at 298K at the threshold current. | 3 6 |
| 10:15 | Time-resolved photoluminescence and optical gain in Ga(NAsP) heterostructures pseudomorphically grown on silicon Authors : N.C. Gerhardt 1, N. Koukourakis 1, M. Klimasch 1, M.R. Hofmann 1, S. Liebich 2, M. Zimprich 2, K. Volz 2, W. Stolz 2, B. Kunert 3 Affiliations : 1 Photonics and Terahertz Technology, Ruhr-University Bochum, Universitaetsstr. 150, 44780 Bochum, Germany; 2 Structure and Technology Research Laboratory and Faculty of Physics, Philipps-University Marburg, Hans-Meerwein-Str., 35032 Marburg, Germany; 3 NAsP III/V GmbH, Am Knechtacker 19, 35041 Marburg, Germany Resume : The development of optoelectronic integrated circuits (OEICs) on silicon using the advanced complementary metal oxide semiconductor technology is one of the most important challenges in photonics today. However the integration of an electrically pumped semiconductor laser on silicon as a key component for this technology remains a huge challenge. The novel dilute nitride material Ga(NAsP) is a very promising candidate to fill this gap. Because of its direct nature and its capability for pseudomorphical growth on exactly oriented (001) silicon substrate, Ga(NAsP) is perfectly qualified as an active material for lasers on silicon. Here we investigate the optical properties of Ga(NAsP)/BGaP heterostructures grown lattice matched on (001) silicon substrate using time-resolved photoluminescence (PL) and optical gain spectroscopy. The results show an s-shape behaviour for the temperature dependent PL peak energy and a strong non-exponential behaviour for the PL transients. Both indicate a significant impact of disorder-induced localization effects in the novel material system. The impact of the localization effects depends strongly on the material composition and growth conditions. Surprisingly, samples with higher N content show less pronounced localization effects. In order to identify the ideal material composition for electrically pumped lasers, the impact of localization effects on the PL as well as on the optical gain will be discussed in detail during this talk. | 3 7 |
| 10:30 | Coffee break | |
| Bismuths : Chair to be confirmed | ||
| 10:45 | Growth and Properties of High Bismuth Content GaAsBi Alloys Authors : R. B. Lewis, M. Masnadi-Shirazi, V. Bahrami, T. Tiedje Affiliations : Department of Electrical and Computer Engineering, University of Victoria, Victoria, BC, Canada, P. Mooney, Department of Physics, Simon Fraser University, Burnaby, BC, Canada Resume : Progress on Bi-containing III-V semiconductor alloys has been held back by difficulties with incorporation of Bi by usual growth methods. In molecular beam epitaxy, Bi has a strong tendency to surface segregate with excess Bi remaining on the surface in the form of metallic droplets. These problems can be overcome in MBE by growing at low temperatures and at an As:Ga ratio close to unity where a (2x1) reconstruction is observed. Even a small Arsenic overpressure causes the Bi concentration to decrease rapidly. As a highly mismatched alloy system, GaAsBi is unusual in that the photoluminescence intensity increases with Bi concentration up to x~5%. A Bi concentration as high as 21.5% has been achieved at a growth temperature of 195C in high crystal quality films on GaAs substrates, with a predicted theoretical bandgap of 3 m. In many samples, we find the Cu-Pt ordering of Bi on (111) planes in x-ray rocking curve measurements of the normally forbidden (½½½) peak. Capacitance measurements on junction structures show that the density of deep levels in low temperature grown Bi-alloys is much lower than for GaAs samples grown at comparable temperatures, presumably because of the surfactant properties of Bi. Similar to the results of G. Pettinari et al [1], but extending to higher Bi concentrations, we find that the hole mobility increases with increasing Bi concentration above x~8%.
1. G. Pettinari, A. Patane, A. Polimeni, Xianfeng Lu, T. Tiedje, Appl. Phys. Lett. (accepted for publication, 2012) | 4 1 |
| 11:15 | Light emission from InGaAs/GaAs quantum wells at 1.3 µm using Bi as surfactant Authors : Hong Ye (a), Yuxin Song (a), Yi Gu (b) and Shumin Wang (a,*) Affiliations : a) Department of Microtechnology and Nanoscience, Chalmers University of Technology, Gothenburg, Sweden b) Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, China * Corresponding author. E-mail address: shumin@chalmers.se Resume : Uncooled telecom (1.3 or 1.55 m) laser diodes have attracted much attention recently with potentials of replacing commercial telecom lasers made of InGaAsP. Bismuth-containing III-V alloys have been considered as an emerging material due to temperature-insensitive band-gap and strong band-gap bowing effect1. Previous investigations of Bi in InGaAs growth reveal two different behaviors: incorporation and surfactant, depending on the growth temperature with a boundary of around 450 C (typical for InGaAs/InP). Increasing the growth temperature leads to the rapid decrease in the incorporated Bi, and accumulated Bi atoms on the surface behave as surface surfactant2. In this work we focus on investigating the Bi surfactant effect on the optical properties of highly strained InGaAs QWs grown on GaAs substrates to achieve 1.3 µm light emission at room temperature. Photoluminescence (PL) is used for the material characterization. Our results show that using Bi as surfactant on InGaAs QWs has potential to extend InGaAs QW lasers to the important telecom wavelength of 1.3 µm.
[1] V. M. Ustinov and A.E. Zhukov, Semiconductor Science and Technology 15, R41-R54 (2000).
[2] G. Feng, K. Oe and M. Yoshimoto, Journal of Crystal Growth 301-302, 121-124 (2007).
[3] M.R. Pillai, Seong-Soo Kim, S.T. Ho and S.A. Barnett, Journal of Vacuum and Science Technology B 18, 1232-1236 (2000).
[4] S. Tixier, M. Adamcyk, E.C. Young and T. Tiedje, Journal of Crystal Growth 251, 449-454 (2003). | 4 2 |
| 11:30 | MOVPE growth of Ga(AsBi)/GaAs quantum well structures Authors : P. Ludewig, N. Knaub, W. Stolz, K. Volz Affiliations : Department of Physics and Material Sciences Center, Philipps-University Marburg Resume : Bismuth (Bi)-containing III/V semiconductors are interesting from the application as well as from the fundamental point of view. Bi increases the spin-orbit splitting in conventional III/V semiconductors and hence certain Auger loss processes could be suppressed in future laser devices using these materials as active layers. High Bi-fractions are needed to achieve the required band-alignment for this application. These high Bi-fractions are very challenging to achieve experimentally, as the dilute Bi-material system is highly metastable and hence needs to be grown under extreme non-equilibrium conditions.
In this work we present recent results of the epitaxial growth of Ga(AsBi) multi quantum well structures (MQW) by metal organic vapour phase epitaxy (MOVPE). Ga(AsBi) bulk and MQW samples were grown on (001) GaAs substrates at low temperatures using TMGa, TBAs and TMBi as metal-organic precursors. The Bi fraction of the samples was determined by high resolution x-ray diffraction (HRXRD), the structural quality was furthermore investigated by transmission electron microscopy.
We will discuss the Bi-incorporation mechanisms in GaAs by varying several growth parameters as temperature, V/III- and V/V ratios.
The MQW samples exhibit pendellösung fringes in HRXRD, pointing towards a good structural quality. In addition room-temperature photoluminescence at the expected wavelengths has been observed. | 4 3 |
| 11:45 | The influence of annealing on the properties of GaAsBi grown at different temperatures Authors : J. Puustinen (1), A. Schramm (1), P. Laukkanen (2), L. Juhola (1), M. Guina (1) Affiliations : 1) Optoelectronics Research Centre, Tampere University of Technology, FI-33101 Tampere, Finland; 2) Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland Resume : Despite of a recent surge of results concerning GaAsBi alloys, the synthesis and understanding of this material system is far from enabling practical applications. The large size of the Bi atom makes it difficult to incorporate Bi within the GaAs lattice leading to a complicated optimization process of the growth parameters. One particular development area that needs to be addressed is the interplay between the growth conditions and thermal annealing (RTA), and their combined effect on adjusting the characteristics of GaAsBi films. The purpose of this paper is to investigate the effect of different post-growth RTA treatments on the properties of GaAsBi layers grown at different temperatures. GaAsBi films with a thickness of 300 nm were grown by solid-source molecular beam epitaxy on GaAs(001) substrates. The growth temperature was varied between 300°C and 400°C and the As/Ga ratio was close to one. The temperature was monitored with a thermocouple. The annealing temperature was varied between 500°C and 800°C. The samples exhibited clear XRD features that indicated Bi concentrations of about 1.2% to 1.5%. The lattice constant of low temperature GaAsBi layers was found to decrease with increasing RTA temperature. On the other hand, the films grown at around 400°C did not show significant change in the structural properties after annealing. AFM pictures revealed high quality surfaces with a roughness in the range of 0.2-1.1 nm that did not change much during annealing. | 4 4 |
| 12:00 | Long wavelength (~3 µm) emission from InGaAsBi layers grown by molecular beam epitaxy Authors : Jan Devenson, Vaidas Pačebutas, Renata Butkutė, Bronislovas Čechavičius, and Arūnas Krotkus Affiliations : Department of Optoelectronics, Center for Physical Sciences and Technology, 01108, Vilnius, Lithuania Resume : Bismuth-containing III-V semiconductors have attracted much attention because of the strong their band-gap dependence on Bi-content and prospect for the new long-wavelength optoelectronic devices. We have grown Bismuth-containing InGaAs layers by molecular beam epitaxy on InP:Fe (100) substrates. Incorporation of Bismuth above 7% has been confirmed by X-ray diffraction measurements. Bismuth distribution in the layers has been studied by secondary ion mass spectroscopy. Photoluminescence signals at wavelengths as long as 3 µm have been observed at liquid nitrogen temperature. Optical properties of these samples were studied by photoreflectance (PR) and contactless electrical reflectance (CER) measurements. The band-gap temperature dependence was shown to be significantly weaker in Bi-containing InGaAs layers than that in InGaAs buffer layers. InGaAsBi grown by a more mature InP technology could be considered as a material alternative to antimonide-based compounds for mid-infrared optoelectronic devices. | 4 5 |
| 12:15 | Growth and characterisation of GaAsBi p-i-n diodes Authors : F. Bastiman1, C. J. Hunter1, A. R. Mohmad1,2, R. Richards1, J. S. Ng1, S. J. Sweeney3, and J. P. R. David1 Affiliations : 1Department of Electronic and Electrical Engineering, University of Sheffield, Sir Frederick Mappin Building, Mappin Street, Sheffield S1 3JD, United Kingdom 2Institute of Microengineering and Nanoelectronics, Universiti Kebangsaan Malaysia (UKM), 43000 Bangi, Selangor, Malaysia 3Advanced Technology Institute and Department of Physics, University of Surrey, Guildford, Surrey GU2 7XH, United Kingdom Resume : The bismuth alloy GaAs1-xBix has a number of interesting properties, namely large reductions in the band gap and large spin orbital splitting. The narrow band gap offered by such an alloy is particularly well suited to the fabrication of infrared emitters and photodetectors however, difficulties in the molecular beam epitaxy (MBE) growth process have limited the impact of this alloy so far.
In this work it is shown that by using As4, conventional non-stoichiometric MBE growth conditions can be used for growing GaAsBi with [Bi] of up to 6% at a nominal substrate temperature of 370 °C. The same incorporation is achieved using As2 at the same temperature but the Ga:As:Bi flux ratios need to be much more rigidly controlled.
The optical and structural properties of both bulk and quantum well (QW) GaAsBi layers are investigated via photoluminescence (PL) and high resolution x-ray diffraction (HR-XRD) measurements respectively. The epitaxially grown layers show excellent optical properties with room temperature peak PL wavelengths in the 1000- 1300 nm range.
In order to further characterise this material, p-i-n diodes with doped GaAs cladding layers were grown and fabricated with a nominal [Bi] of 6%. The absorption properties have been systematically investigated by measuring the photocurrent spectra in these structures. The GaAs0.94Bi0.06 layers varied in thickness from 50 nm to 350 nm and showed a photo-response in the near-infrared up to almost 1300nm. The absorption coefficients of the layers obtained from responsivity data were of the order of 104 cm-1 at energies ~200 meV above the band gap. Below the band gap, the absorption coefficients showed an exponential dependence on the photon energy (Urbach tailing) | 4 6 |
| 12:30 | Band engineering of dilute bismide and nitride alloys for efficient near- and mid-infrared semiconductor lasers Authors : E. P. O’Reilly1,2, M. Usman1 and C. A. Broderick1,2 Affiliations : 1 Tyndall National Institute, Lee Maltings, Cork, Ireland 2 Department of Physics, University College Cork, Ireland Resume : Although important in optical communications, InP-based lasers in the 1.3-1.6 micron range have large threshold currents and temperature sensitivities, requiring energy-demanding temperature control. Past work has shown that Auger recombination involving carrier excitation to the spin-split-off (SO) band dominates the threshold current of such lasers near room temperature. The SO splitting is less than the band gap at telecomm wavelengths in conventional alloys. Replacing As by Bi in GaBiAs leads to a rapid increase in SO splitting and reduction in the band gap. Photoreflectance measurements show that the SO splitting exceeds the band gap for Bi composition x > 10%. Incorporation of Bi in GaAs is predicted to lead to a band-anticrossing (BAC) effect in the valence band (VB). We present tight-binding calculations which confirm that the observed variation of the band gap and SO energy with x are well described by a BAC interaction between the extended states of the GaAs VB edge and localized Bi impurity states in the VB. We extend these calculations to consider GaBiNAs alloys. We show that Bi and N largely act independently of each other, as Bi principally influences the VB, and N the conduction band (CB). III-V Bi-N alloys then offer significant opportunity for engineering the CB and VB offsets, the band gap and SO splitting, with wide scope for the design of photonic devices, including loss-free lasers in the telecomm band with potential as efficient, uncooled sources. | 4 7 |
| 13:00 | Lunch | |
| Transport : Chair to be confirmed | ||
| 14:30 | Effect of Bi alloying on the transport properties of the dilute bismide alloy, GaAsBi Authors : R.N. Kini, B. Fluegel, A. J. Ptak, R. France, and A. Mascarenhas Affiliations : Indian Institute of Science Education and Research Thiruvananthapuram, CET Campus, Thiruvananthapuram 695016, Kerala, India; National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401, USA; National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401, USA;National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401, USA;National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401, USA Resume : We studied the effect of Bi incorporation on the carrier mobilities & electron effective mass in the dilute Bismide alloy, GaAsBi using electrical transport and PL techniques. We observed no significant degradation in the electron Hall mobility with Bi incorporation in GaAs, up to a concentration of 1.2%. At higher Bi concentration (≥1.6%) some degradation of the electron mobility was observed, although there is no apparent trend. Our measurements show that the hole Hall mobility decreases with increasing Bi concentration. Analysis of the temperature dependant Hall transport data of p-type GaAsBi epilayers along with low-temperature PL measurements of p-doped and undoped epilayers suggests that Bi incorporation results in the formation of several trap levels above the valence band which we attribute to Bi-Bi pair states. The decrease in hole mobility with increasing Bi concentration can be explained as being caused by scattering at the isolated Bi and the Bi-Bi pair states. Magnetic field and temperature dependent resistivity measurements on n-type GaAsBi showed clear Shubnikov de Haas oscillations up to a concentration of 0.88%. The measured electron effective mass exhibits a gradual increase upto a concentration of 0.4% Bi and then a gradual decrease. Accounting for the giant bandgap & spin orbit bowing, the measured changes in the effective mass are in qualitative agreement with perturbation theory applied to these band changes, confirming that Bi perturbs the valence band. | 5 1 |
| 15:00 | Electron Transport in GaAsN and InAsN Authors : N. Vogiatzis, J.M. Rorison Affiliations : University of Bristol, Dpt Electrical and Electronic Engineering, Merchant Venturers Building, Woodland Road, Bristol, BS8 1UB , UK Resume : GaAsN and InAsN are highly non-miscible systems. Their common characteristic is that when nitrogen atom substitutes the isoelectronic arsenic atom in GaAs and InAs it does not alloy properly, but forms a highly localized nitrogen state above the conduction band (CB) of the host materials. The difference between the two is that in GaAsN the localised nitrogen state lies considerably closer to the bottom of the host CB than in InAsN. This results in the perturbation of the CB and in the localisation phenomena being significantly stronger in GaAsN than in InAsN. Therefore, the altered shape of the resulting CB will in turn affect differently the electron transport in each of these systems.
We expand our previous work to use a single and an ensemble Monte Carlo model in GaAsN and InAsN, to investigate respectively the steady and dynamic behavior of electron transport from low to high fields. We compare our theoretical results with experimental studies which indicate a different behavior in the two alloys; namely a characteristic negative differential velocity behavior in GaAsN which is important for high frequency electronics and a sharp increase of the conductivity in InAsN indicative of impact ionization. Details of the models will be jointly provided and the role of the band structure and of the concentration of N will be assessed. Understanding how the electron dynamics can be tailored in these systems, can be useful in the in the design of novel optoelectronic devices. | 5 2 |
| 15:15 | Current oscillations in p-i-n GaInNAs/GaAs MQW structures Authors : H. M. Khalil1, S. Mazzucato1, B. Royall1, N. Balkan1 and J. Puustinen2, V. M. Korpijärvi2, M. Guina2 Affiliations : 1 School of Computer Science and Electronic Engineering, University of Essex, CO4 3SQ, Colchester, UK. 2 Optoelectronics Research Centre, Tampere University of Technology, Korkeakoulunkatu 10, FI-33720, Tampere, Finland Resume : In this paper we present the studies of current oscillations with applied reverse bias in GaInNAs/GaAs multiple quantum well (MQW) p-i-n structures. We investigated the oscillations as a function of temperature, light intensity and wavelength. The results are analised in terms of the sweep out of the photogenerated holes from the intrinsic region and the consequent tunnelling and thermionic emission of non-euilibrium electrons from the quantum wells. | 5 3 |
| 15:30 | Effects of Bi incorporation on the electronic properties of GaAs: carrier effective mass, mobility, and Bi-induced acceptor states Authors : G. Pettinari (1,2,3), A. Polimeni (2), M. Capizzi (2), H. Engelkamp (3), P.C.M. Christianen (3), J.C. Maan (3), A. Patanè (1), and T. Tiedje (4) Affiliations : (1) School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, UK; (2) CNISM-Dipartimento di Fisica, Sapienza Università di Roma, P.le A. Moro 2, 00185 Roma, Italy; (3) High Field Magnet Laboratory, Institute for Molecules and Materials, Radboud University Nijmegen, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands; (4) Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T IZ4, Canada Resume : We review our recent studies [PRB 81, 235211 (2010); PRB 83, 201201R (2011)] and report new results on the effects of Bi incorporation on the electronic properties of GaAs. Ga(AsBi) is a highly mismatched III–V semiconductor alloy that exhibits unique electronic properties and an uncommon dependence on composition of fundamental band structure parameters (i.e., band-gap energy and carrier effective mass) that are boosting several exciting new lines of research in Materials Science.
In particular, we report on the anomalous compositional dependence of the exciton reduced mass in Ga(AsBi) (0% ≤ [Bi] ≤ 10.6%): first, the exciton reduced mass increases with increasing Bi-concentration up to [Bi] < 6%; then, for [Bi] > 8% it decreases to values smaller than in GaAs. These results indicate the existence of Bi-concentration intervals in which the strength of the hybridization between GaAs continuum-states and Bi-related localized levels is markedly different. Furthermore, far infrared absorption spectroscopy at high magnetic fields (B up to 30 T) and Hall measurements (B up to 14 T) in nominally undoped Ga(AsBi) provide direct evidence of Bi-induced acceptor states, whose concentration increases with [Bi] up to values of 10^17 cm^-3 for [Bi] = 10.6% at room temperature. This increase is paralleled by a decrease of the hole mobility. An analysis of the free-hole concentration as a function of Bi-concentration suggests high-order Bi-complexes to be the origin of the acceptor levels. | 5 4 |
| 16:00 | Coffee break | |
| Poster session I : Chair to be confirmed | ||
| 16:00 | Elaboration of ZnO substrates for nitride growth by transmission electron microscopy Authors : M. Korytov 1), T. Markurt 1), Y.J. Cho 2), O. Brandt 2), H. Riechert 2), and M. Albrecht 1) Affiliations : 1 - Leibniz Institute for Crystal Growth (IKZ), Max-Born-Str. 2, 12489 Berlin, Germany 2 - Paul Drude Institut, Hausvogteiplatz 5-7, 10117 Berlin, Germany Resume : (In,Ga)N is promising alloy for optoelectronic devices, due to its ability to emit light in a wide spectral range overlapping the whole visible spectrum. One of the main challenging issues for this material is a lack of available native substrate. Heteroepitaxial growth on common foreign substrates leads to crystalline quality degradation due to the high lattice mismatch.
In this work, we study growth of InN and In-rich (In,Ga)N alloys by plasma-assisted molecular beam epitaxy on Zn- and O-face dislocation-free ZnO substrates. Our investigations by aberration-corrected high-resolution transmission electron microscopy and scanning transmission electron microscopy show that the interfacial chemical reactions, limiting use of ZnO for nitride growth, can be overcome by choosing right growth conditions. Properly grown samples have monocrystalline structure with regular interface between the epilayer and the substrate; the only observed imperfection is polarity inversion.
Based on these achievements, possible strategies for fabrication of lattice-matched (In,Ga)N/ZnO structures will be discussed.
Besides, a very new approach of growing InN films on bulk In2O3 substrates will be presented. | p1 1 |
| 16:00 | Ab initio calculation of structural and electronic properties of AlN1-xBix Authors : M. Mbarkia,R. Alayaa, A. Rebeyb aLaboratoire de physique des matériaux et nanomatériaux appliquée à l’environnement, Faculté des Sciences de Gabès, Université de Gabès, 6072 Gabès, Tunisia bUnité de Recherche sur les Hétéro-Epitaxies et Application, Faculté des Sciences de Monastir, Université de Monastir, 5019 Monastir, Tunisia Affiliations : M. Mbarki R. Alaya A. Rebey Resume : In this work we have calculated the structural and electronic properties of AlN1-xBix alloy by using the density functional theory based on the full potential linearised augmented plane wave method (FPLAPW). The calculated lattice parameter of AlN1-xBix alloys shows an increase by increasing the composition x of bismuth (Bi), while significant deviation from Vegard’s law is observed. We have studied the variation of the energy gap and the electron effective masses of the ternary compound with respect to composition x of Bi. | p1 2 |
| 16:00 | Synthesis of bismuth oxide films by thermal oxidation of bismuth nano-droplets deposit on GaAs substrate Authors : H. Fitouri, R. Boussaha, A. Rebey and B. El Jani Affiliations : Université de Monastir, Unité de Recherche sur les Hétéro-Epitaxies et Applications Faculté des Sciences de Monastir, 5000 Monastir, Tunisia Resume : Bismuth oxide has attracted considerable attention due to its interesting characteristics, such as the large values of the energy band gap, high refractive index and dielectric permittivity, besides remarkable photoconductivity and photoluminescence. This oxide material is promising for development of various modern technologies of solid state device. In this work, bismuth oxide films were prepared by dry thermal oxidation of bismuth nano-droplets deposit on GaAs substrate by metalorganic vapor phase epitaxy. The oxidation process of Bi nano-droplets consists of a heating from the room temperature to a different oxidation temperatures (350, 500, 600°C) with a temperature rate of 14°C/min. The annealing duration was fixed to 30 min. The presence of oxygen in the annealed films was confirmed by energy dispersive X-ray measurements using a scanning electron microscope (SEM). The SEM images show that the density of Bi aggregates decreases and their size increases with increasing annealing temperature. The photoluminescence spectra under excitation at 325 nm shows a strong and broad emission centered at around 640-660 nm. The reflectance spectra of the films were studied in spectral domains ranged between 200 nm and 1200 nm. The results show that the thickness of the bismuth oxide increases with increasing annealing temperature. By fitting the reflectivity signal, we extracted the refractive index variation of bismuth oxide films as a function of the wave length. | p1 3 |
| 16:00 | Scattering Mechanisms in GaInNAs/GaAs quantum wells Authors : Engin Tiras and Sukru Ardali Affiliations : Department of Physics, Faculty of Science, Anadolu University, Yunus Emre Campus, Eskisehir 26470, Turkey Resume : We studied momentum scattering mechanisms in n- and p-type doped GaInNAs as a function of composition where the temperature dependence of electron mobility is calculated for major scattering processes using the theoretical expressions available in the literature and compared with the experimental results. In n-type samples, it is found that alloy disorder scattering and the LO phonon scattering are the dominant scattering mechanisms at low and high temperatures, respectively. In p-type sample, it is found that ionized impurity and interface roughness scattering are the dominant scattering mechanisms at low temperatures and the LO phonon scattering is the dominant scattering mechanism at high temperatures. | p1 4 |
| 16:00 | Nitrogen composition dependence of longitudinal optical phonon energy in GaInNAs/GaAs quantum wells Authors : Tulay Tiras, Engin Tiras and Sukru Ardali, Affiliations : Department of Physics, Faculty of Science, Anadolu University, Yunus Emre Campus, Eskisehir 26470, Turkey Resume : The composition dependence of longitudinal optical (LO) phonon energy in n and p type modulation-doped GaInNAs/GaAs quantum wells has been obtained using two techniques: one optical and the other electronic. Raman and Infrared spectroscopy measurements are the optical techniques and temperature dependent Hall Effect measurements is the electronic technique. Optical techniques give the value of LO phonon energy directly from the spectra. To obtain the LO phonon energy from the temperature-dependent Hall Effect measurements, appropriate theoretical expressions for the energy and momentum relaxation rates have to be used. The results obtained from the two independent techniques compare extremely well. | p1 5 |
| 16:00 | Intersubband optical absorptions coefficients and refractive index changes in modulation-doped GaInNAs/GaAs quantum well Authors : F. Ungan1,*, U. Yesilgul1, S. Sakiroglu2, E. Kasapoglu1, H. Sari1 O. Donmez3, A. Erol3, M. C. Arikan3 and I. Sokmen2 Affiliations : 1Cumhuriyet University, Physics Department, 58140 Sivas, Turkey 2Dokuz Eylül University, Physics Department, 35160 Buca, İzmir, Turkey 3İstanbul University, Physics Department, 35160 Vezneciler, İstanbul, Turkey Resume : The effect of nitrogen and indium mole concentration on the intersubband optical absorption coefficients and refractive index changes in a modulation-doped GaInNAs/GaAs quantum well is theoretically calculated within the framework of the effective-mass approximation. Results are obtained for several concentrations of nitrogen and indium. The numerical results show that the intersubband optical absorption coefficients and refractive index changes strongly depend on the nitrogen and indium concentrations. | p1 6 |
| 16:00 | The effect of electric field on the impurity binding energy of shallow donor impurities in a GaInNAs/GaAs quantum well Authors : U.Yesilgul1, F.Ungan1, S.Sakiroglu2, E.Kasapoglu1, H.Sari1, C.A.Duque3, M.E. Mora-Ramos4, I.Sökmen2 Affiliations : 1Cumhuriyet University, Physics Department, 58140 Sivas, Turkey 2Dokuz Eylul University, Physics Department, 35160 Buca, Izmir, Turkey 3Instituto deFı´sica, Universidad de Antioquia, AA 1226 Medellı´n, Colombia 4Facultad de Ciencias,Universidad Auto´noma del Estadode Morelos, Ave. Universidad 1001, CP. 62209 Cuernavaca, Morelos, Mexico Resume : Using a variational approach, we have calculated the impurity position dependence of the binding energy for a hydrogenic donor impurity in a GaInNAs/GaAs quantum well in the presence of the electric field. Our calculations have revealed the dependence of the impurity binding on the applied electric field, and the impurity position. | p1 7 |
| 16:00 | Hybrid-Functional Study of Band-Structures of GaAs$_{1-x}$N$_x$ and GaSb$_{1-x}$N$_x$ Alloys Authors : V. Virkkala, V. Havu, F. Tuomisto, M. J. Puska Affiliations : Department of Applied Physics, Aalto University, P.O. Box 11100, FI-00076 Aalto, Finland Resume : In this work we consider GaAs$_{1-x}$N$_x$ and GaSb$_{1-x}$N$_x$ alloys. We make use of the hybrid functionals in which part of the semilocal exchange-correlation functional is substituted by the Hartree-Fock exchange. Hybrid functionals give band gaps near to the experimental ones and makes it possible to study band structures of GaSb$_{1-x}$N$_x$ alloys ab initio without any parameter fitting.
The main result of our calculations is that nitrogen affects both GaAs and GaSb in a similar way, by creating well-localized states above the band gap, related to the bonding of nitrogen to the surrounding Ga atoms. According to our calculations in the case of a single nitrogen atom in the supercell, the tail in DOS due to the nitrogen induced states hybridize with bulk conduction band states and extends towards the band gap by the same amount in both materials. This is due to similar Ga-N bonds. The tails enter into the bulk band gap regions causing the observed band gap reductions. The reason for the observed stronger band gap reduction in
GaSb$_{1-x}$N$_x$ than in GaAs$_{1-x}$N$_x$ was found to be the positions of bulk band edges relative to the Ga-N bond energy, i.e. the position of the nitrogen induced states. Our findings do not support the common suggestion that the greater electronegativity mismatch between N and Sb compared to that between N
and As should explain the stronger band gap reduction in GaSb$_{1-x}$N$_x$ than in GaAs$_{1-x}$N$_x$. | p1 8 |
| 16:00 | Nitrogen incorporation into GaAsN and InGaAsN layers grown by Liquid-Phase-Epitaxy Authors : M. Milanova1*, P. Vitanov2, P. Terziyska3, G. Popov1, G. Koleva1 Affiliations : 1Central Laboratory of Applied Physics, 59 St. Petersburg Blvd, 4000 Plovdiv, Bulgaria; 2Central Laboratory of Solar Energy and New Energy Sources, 72 Tzarigradsko Chaussee Blvd, 1784 Sofia Bulgaria; 3 Semiconductor Research Laboratory, Department of Electrical Engineering, Lakehead University, 955 Oliver Rd, Thunder Bay, ON, Canada, P7B 5Z5, Canada Resume : This paper presents the comparison of nitrogen incorporation in GaAsN and InGaAsN layers grown on GaAs from Ga- and In-rich solution, respectively, by liquid-phase epitaxy. Polycrystalline GaN has been used as a source of nitrogen in two cases. The initial epitaxy temperature has been varied in the temperature range 650-550 °C. The N concentration of Ga1-xAsNx layers from 0.1 to 0.6% has been measured by X-ray diffractometry (XRD) assuming Vegard’s law. Higher nitrogen incorporation efficiency has been found for InGaAsN layers grown from In- solution. The composition of the epitaxial InxGa1-xAs1-yNy layers has been determined by a combination of X-ray microanalysis and XRD measurements and N concentration in the alloy up to 3% has been registered. Lattice matched InGaAsN layers exhibit high crystalline quality as it has been evaluated by XRD, Atomic Force and Scanning Electron microscopy measurements.
Electrical properties of the samples have been characterized by temperature-dependent Hall effect measurements. Nominally undoped GaAsN and InGaAsN are n-type with Hall concentration about one order of magnitude higher in comparison to layers not containing nitrogen. Thermally activated increase in free carrier concentration at temperatures higher than 200 K is observed, suggesting the presence of carrier trapping levels below the alloy conduction band edge. Lattice matched to GaAs thick InGaAsN layers exhibit high values of 2000 cm2/ V.s for the Hall electron mobility. | p1 9 |
| 16:00 | On the study of PAMBE growth of InN by STM Authors : Rui Yang, Tomasz Krzyzewski, Tim Jones Affiliations : university of warwick, UK Resume : The InN (0001) was grown on GaN/sapphire by Plasma Assistant Molecular Beam Epitaxy (PAMBE) with a GaN buffer layer. By controlling the growth rate ratio of In and N, the InN layers were grown in In-rich, N-rich and equivalent regions respectively. The growth of InN was monitored by reflection high energy electron diffraction (RHEED) and characterised by in-situ Scanning tunnelling microscopy (STM. The surface features were studied by ex-situ X-ray diffraction (XRD), Atomic force microscopy (AFM) and Scanning electron microscopy (SEM). A series of InN grown with different growth rates were investigated and the growth mechanism of InN layer was illustrated by the growth profile. | p1 10 |
| 16:00 | Effects of substrate defects on photoluminescence of GaNP and GaNAs epitaxial layers: optically detected magnetic resonance study Authors : D. Dagnelund 1, Y. Puttisong 1, H. Yonezu 2, A. J. Ptak 3, W. M. Chen 1 and I. A Buyanova1 Affiliations : 1 Department of Physics, Chemistry and Biology Link?g University, S-581 83 Link?g, Sweden 2 Department of Electrical and Electronic Engineering, Toyohashi University of Technology, Toyohashi, Aichi, 441-8580, Japan 3 National Renewable Energy Laboratory, Golden, Colorado 80401, USA Resume : Severe nonradiative recombination is a major problem for optical and electrical quality of dilute nitrides. Many studies have been devoted to defect characterization and the role of defects in carrier recombination processes in dilute nitrides. But, but up to now, the effect of the substrate quality on defects in dilute nitride epilayers is unknown. In this study, by means of photoluminescence and optically detected magnetic resonance techniques we show that defects residing in the substrate material prior to the epitaxial growth have effect on radiative recombination of dilute nitrides epilayers. We demonstrate this in two representative cases. Firstly, in GaNP, a phosphorus antisite defect labeled PP3-Yp, (readily observed in GaP substrate), is observed to be detrimental to near band-edge radiative recombination of GaNP. Secondly, in GaNAs, a strongly anisotropic paramagnetic center (present in the substrate prior to growth) related to Cr has been found to quench the near band-edge radiative recombination of GaNAs. The observed effect could be either attributed to the propagation of defect from substrate into the epilayer or influence on the band-edge recombination via decrease in carrier feeding from the substrate. In either case, defects residing in the substrate material prior to the epitaxial growth are shown to degrade the band-to-band recombination in dilute nitrides epilayers. | p1 11 |
| 16:00 | Bismuth incorporation into InAs/GaAs Quantum Dots Authors : D. F. Reyes1, F. Bastiman2, D. L. Sales1, C. Hunter2, M. A. Roldán1, A. Mayoral3, M. Varela4, S.J. Pennycook4, S. I. Molina1 and D. González1 Affiliations : 1 Dpto. de Ciencia de los Materiales e I. M. y Q. I., Facultad de Ciencias, Universidad de Cádiz, 11510, Puerto Real, Cádiz, Spain 2 The University of Sheffield, Department of Electronic and Electrical Engineering, Mappin Street, S1 3JD, UK 3 Laboratorio de Microscopías Avanzadas (LMA), Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, Zaragoza, Spain 4Oak Ridge National Laboratory, Oak Ridge TN 37831 USA. Resume : Recently, III-V semiconductor nanostructures containing diluted quantities of bismuth (Bi) have generated great interest; mainly due the bandgap reduction of up to 88 meV/% Bi. 1. Bismuthides are hence promising candidates for photovoltaic (1.24 µm) and telecommunications (1.3-1.55 µm) devices. The miscibility gap between GaBi and GaAs and a tendency of Bi to surface segregate requires low growth temperatures in order to achieve significant Bi incorporation into GaAs. 2 This work explores use of the rapid atomic agglomeration found during the S K transition in order to incorporate Bi into In(Ga)As QDs. The incorporation of Bi into InAs/GaAs quantum dots grown under different molecular beam epitaxy conditions is evaluated using advanced transmission electron microscopy (TEM) and photoluminescence (PL) techniques.
TEM images show changes in the size distribution of QD as well as an increase in defect density. These facts explain the reduction of the PL efficiency when increasing the incident Bi flux, but they do not explain the appreciable redshift for the higher nominal Bi content sample. The analysis of integrated intensities from resolution Z-contrast images reveals that only this high [Bi] sample shows clear bismuth incorporation into the QDs core, while Bi is regularly distributed into the wetting layer in samples with lower nominal Bi concentration.
1 Z. M. Fang et al., J. of Appl. Phys. 68 (3),1187 (1990);
2 S. Tixier et al., Appl. Phys. Lett. 82 (14), 2245 (2003) | p1 12 |
| 16:00 | Analysis of Line Shape and Modulation Mechanisms on Low Dimensional Dilute Nitride Structures Authors : O. Donmez, A. Erol and M.C. Arıkan Affiliations : Istanbul University Science Faculty Department of Physics, Vezneciler, 34134, Istanbul, Turkey Resume : We present an application of modulation spectroscopy to analyze the optical transition energy levels of undoped and modulation doped GaInNAs/GaAs quantum well device structures with different nitrogen and indium contents at room temperature. The line shape and modulation mechanisms are analyzed experimentally and theoretically. Modulation spectra of undoped quantum well structures show third derivative-like behavior. Therefore, the spectra were analyzed using Lorentzian line shape of third derivative functional form and line broadening was determined as about 25meV which indicates that modulation occurs in low-field regime. The results of modulation spectra of GaInNAs-based devices (Vertical Cavity Surface Emitting Laser- VCSEL and Vertical Cavity Semiconductor Optical Amplifier- VCSOA) have first derivative behavior and line broadenings are determined as about 5meV. We do not observe any modulation signal from modulation doped quantum well structures which can be the result of secreening effect due to high carrier concentration. Photoluminescence measurements are also carried out at room temperature for comparison with the modulation spectra. Conduction band and valance band offsets are also calculated using model-solid theory and compared with experimental data. | p1 13 |
| 16:00 | Structural and Electronic Properties of GaAsxBi1-x Ternary Semiconductor Alloy for Terahertz Applications Authors : M. Aslan, B.Gazi Yalcin, M. Ustundag Affiliations : Sakarya University Art and Science Faculty Physics Department Esentepe 54187 Adapazari-Sakarya / Turkey Resume : We have performed first principles method to investigate structural and electronic properties of GaAsxBi1-x ternary semiconductor alloy using Density Functional Theory (DFT) and pseudopotantial method within the Generalized Gradient Approximations (GGA). The zinc-blende phase is found stable for GaAsBi alloy. In this study we investigate the bowing parameter with changing Bi concentration in GaAsBi alloy. By using the bowing paremeter of GaAsBi alloy, we obtained ideal bandgap energy for various terahertz phonics applications. To determine the optimum lattice parameter on GaAs substrate and band gap energy of the GaAsBi ternary semiconductor alloy we calculate separately the lattice constant and band gap energy of GaAs and GaBi binary semiconductors. For studied materials, lattice parameters and band gap energies are compared with available theoretical and experimental works. | p1 14 |
| 16:00 | Study on low electron mobility in GaAsN Authors : Makoto Inagaki; Kazuma Ikeda; Hiroyuki Kowaki; Yoshio Ohshita; Nobuaki Kojima; Masafumi Yamaguchi Affiliations : Toyota Technological Institute Resume : The origin of low electron mobility has been considered to be due to inhomogeneity of N distribution and N-related lattice defects. In this study, however, we indicate the phonon and alloy scattering are more dominant by investigating the effects of N composition, temperature, and growth conditions of chemical beam epitaxy on electron mobility in GaAsN. The measured electron mobility in GaAsN is lower than the half of expected value which proposed by S. Fahy et al. In their model, the mobility was calculated with physical properties based on the band anti-crossing model and limited by alloy scattering. However, the effective mass determined by the energy shifts of Landau levels was different from the expected value. Hence, we calculated the phonon scattering and alloy scattering with the experimental determined effective mass. The mobility limited by the above scatterings has similar to be the one measured at above ~250 K by Hall effect. Also the N composition dependence of the mobility is expressed by the above scatterings. It should be noted that we obtained the Hall electron mobility which was higher than previously reported value. As a result, the intrinsic limits on electron mobility in GaAsN may be observed. Hence, electron mobility in GaAsN is considered to be mainly limited by phonon and alloy scattering due to large effective mass for electron, not by inhomogeneity of N distribution and N-related defects. | p1 15 |
| 16:00 | Correspondence between N-H Stretch and Wagging Mode in GaAsN Grown by Chemical Beam Epitaxy Authors : Kazuma Ikeda, Makoto Inagaki, Suguru Wada, Nobuaki Kojima, Yoshio Ohshita, Masafumi Yamaguchi Affiliations : Toyota Technological Institute Resume : GaAsN grown by organic sources contains N-H complexes with the density of 10^17 to 10^18 cm^-3. The N-H complexes with such high density can significantly affect the electrical property in GaAsN, which act as both unintentional donor and acceptor depending on their structures. Making correspondences between the stretch and wagging modes enhances the understanding of the structures of N-H complexes. In this work, we obtained the correspondence between the two N-H modes with wavenumbers of around 2952 and 961 cm-1 at 300K. Two-fold rotational symmetries in (001) plane appeared in the IR absorption intensities of those modes. The fluctuations of absorption intensities were ellipsoidal as a function of the polarization direction rotated in (001) plane. The difference absorption intensities in between the long and short axis directions of the ellipsoids were several percent to the original intensities in each mode. In addition, the long axis of the ellipsoids in the two modes were orthogonal to each other. The result suggests the following physical pictures: the population of the N-H bond directions fluctuates ellipsoidally in (001) plane; the amount of the fluctuating population is similar in both modes; the vibration amplitudes of the two modes are orthogonal, that is, the N-H bond directions of the two modes coincide. Therefore, we asserts that the stretch modes at 2952 cm-1 and wagging modes at 961 cm-1 originates from the same N-H bond. | p1 16 |
| 16:00 | Properties of InGaN Films Over the Optical and Terahertz Ranges Authors : A. Gauthier-Brun (1), A. Gokarna (1), W. Liu (2), E. Dumont (3), J. H. Teng (2), E. Dogheche (1), S. J. Chua (2), D. Decoster (1) Affiliations : (1) Institute of Electronics, Microelectronics and Nanotechnology; (2) Institute of Materials Research and Engineering; (3) Faculté Polytechnique de Mons Resume : III-Nitride alloys have been largely studied and are a material of choice for UV to green light-emitting diodes and laser diodes. Their unique properties like the high breakdown field, the large electron saturation velocity or the chemical stability at high temperatures makes them promising candidates for solid-state lighting and high-power electronics for micro and millimeter, especially terahertz waves in which highly efficient emitters and detectors are still a bottleneck. However, designing effective devices requires a precise understanding and knowledge of the optical properties of these materials. There is only little intelligence on the refractive index dispersion of InGaN as a function of the In composition and material quality.
In this poster, we report the optical properties of GaN, InN and InxGa(1-x)N (x < 15%) thin films over two frequency areas of interest: the UV-to-IR domain (between 400 nm and 1.6 µm) and the terahertz range (from 0.3 to 3 THz). The samples are grown by metalorganic chemical vapor deposition on a GaN-on-sapphire template. The structures and compositions are characterized using SEM, TEM, XRD and SIMS, while the optical properties are determined through ellipsometry and terahertz time-domain spectroscopy. | p1 17 |
| 16:00 | Effects of thermal annealing on optical and electronic transport properties in n- and p-type Modulation Doped GaInNAs/GaAs Quantum Wells Authors : F. Sarcan, O. Donmez, M. Gunes, A. Erol, M. C. Arikan, J. Puustinen, M. Guina Affiliations : Istanbul University Science Faculty Department of Physics, Vezneciler, 34134, Istanbul, Turkey, Tampere University of Technology Optoelectronics Research Center, 33101, Tampere, Finland Resume : In this study, effect of thermal annealing on optical and electronic transport properties of p- and n-type modulation-doped Ga0.68In0.32N0.009As0.991/GaAs quantum well structures are presented. Photoluminescence (PL) and Hall Effect measurements are employed in the investigations. Both type of samples are rapid thermal annealed at 700oC for 600s. The mobility of 2D holes in p-type modulation doped sample is found to be higher than that of 2D electrons in n-type modulation doped quantum well at low temperatures. As a result of thermal annealing process, both hole and electron mobilities are enchanced. Analyzing of temperature dependent Hall mobility results, dominant scattering mechanisms are determined and the effect of thermal annealing on scattering mechanisms is investigated. The PL results indicate that the thermal annealing improves the optical quality of the samples and cause a blue-shift. Varshni parameters are determined using temperature dependence of PL peak energies. | p1 18 |
| 16:00 | Photonic Band Gap Waveguide Filters Based on Diluite Nitrides Authors : Giovanna Calò (1), Marco Grande (1), Dimitris Alexandropoulos (2,3), Antonella D’Orazio (1), Vincenzo Petruzzelli (1) Affiliations : 1) Dipartimento di Elettrotecnica ed Elettronica, Politecnico di Bari, Via Re David n.200, 70125 Bari, Italy 2) School of Computer Science and Electronic Engineering, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, UK 3) Department of Materials Science, University of Patras, Patras 26504, Greece Resume : The wavelength filtering characteristic of defective Photonic Band Gap (PBG) waveguides based on dilute nitrides is investigated in this paper. The analysed structures exploits GaInNAs-GaInAs MQW ridge waveguides in which a one-dimensional periodical variation of the geometrical sizes creates a periodic lattice and, therefore, a PBG in the transmission spectrum. The presence of geometrical defects in the periodic lattice can induce a selective transmission of discrete wavelengths in the PBG. In this way, the structure can behave as a wavelength selective filter.
In this paper, we investigate both the passive and the active behaviour of the PBG filters, focusing on the effect induced by the variation of the geometrical and the electrical parameters, on the gain and on the filter performances. The analysis is performed by using proprietary codes, based on the Bidirectional Beam Propagation Method with the Method of Lines (BBPM-MoL), introducing the rate equations. The material gain coefficients, included in the rate equations, are calculated in the context of the free-carrier theory. In this way the bandstructure effects are taken into account rigorously in the electromagnetic simulation. | p1 19 |
| 16:00 | Characterization of optical properties of GaAsBi layers grown by metalorganic vapor phase epitaxy Authors : I. Zaied, H. Fitouri, Z. Chine, A. Rebey and B. El Jani Affiliations : Université de Monastir, Unité de Recherche sur les Hétéro-Epitaxies et Applications Faculté des Sciences de Monastir, 5000 Monastir, Tunisia Resume : The temperature dependence of electro-optical properties of GaAsBi layers grown by metalorganic vapor phase epitaxy on (100)GaAs substrate has been investigated by photoreflectance spectroscopy (PR). Our results show that with increasing Bi content, alloys exhibit a strong thermal stability of the heavy hole (EHH), light hole (ELH) to conduction band transition and spin-orbit splitting energy (ESO). Indeed, for GaAsBi (x = 4.8%), the obtained values for the temperature coefficient of EHH, ELH and ESO was confirmed to be -0.16, -0.12 and -0.10 meV/K in the temperature range 150-300 K. The internal electric field estimated from PR measurements in GaAsBi with low Bi content, show also a high stability in this temperature domain. | p1 20 |
| 16:00 | The influence of Sb on InNAs (Sb) properties investigated by Fourier transform infrared photoluminescence and photoreflectance Authors : M. Latkowska1, R. Kudrawiec 1, F. Janiak1, M. Motyka1, J. Misiewicz1, Q. Zhuang2, A.M.R. Godenir2 and A.Krier2 Affiliations : 1Institute of Physics, Wrocław University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wrocław, Poland; 2 Physics Department, Lancaster University, Lancaster LA1 4YB, United Kingdom Resume : Narrow gap semiconductor alloys are needed as the fundamental material for many optoelectronic devices e.g. lasers and photodetectors operating in the mid infrared (2-5 um) spectral range. One of the material with desired bandgap is InNAs. However, optical quality of this material is far away from perfection. On the other hand it is well known that the introduction of antimony greatly improves the growth morphology and optical efficiency of GaInNAsSb/GaAs quantum wells, due to its reactive surfactant properties.
The aim of our work is investigation of antimony influence on the optical quality of InNAs(Sb) alloys. Two series of 1-um-thick InNAs(Sb) epilayers (with different nitrogen content) with and without Sb, grown on InAs substrate, have been the subject of our study.
The influence of antimony incorporation on InNAs(Sb) properties has been investigated using Fourier transform infrared (FTIR) photoluminescence and photoreflectance (PR).
The dramatically improvement of photoluminescence peak intensity and reduction of PL broadening has been observed for the samples with Sb. Based on PL and PR comparison it has been found that after Sb addition the Stokes shift and S-shape are strongly reduced. The power dependent PL experiment have been performed and delocalized emission is able to be observed only for layers with Sb. Our results suggest that in InNAsSb antimony reduces defects concentration which can be connected with the surfactant properties of antimony. | p1 21 |
| 16:00 | Study of InGaAs/GaAs layers by high resolution X-ray diffraction and in situ monitored by spectral reflectance Authors : T. Mzoughi, H. Fitouri, A. Rebey and B. El Jani Affiliations : Universit?e Monastir, Unit?e Recherche sur les H?ro-Epitaxies et Applications Facult?es Sciences de Monastir, 5000 Monastir, Tunisia Resume : InGaAs layers were grown by atmospheric pressure metalorganic vapor phase epitaxy on (100)GaAs substrate. InGaAs films were elaborated with different V/III ratios and at a growth temperature of 450°C. Spectral reflectance (SR) in the range (200-1200 nm) was employed to in situ monitor epitaxy. SR signal shows that the surface structure changed for a few seconds after trimethylindium supply in to the reactor. The difference between refractive index of InGaAs layers and GaAs substrate results in pronounced easily detected interference oscillations in the reflected beam intensity. The oscillations period provides an accurate and immediate measure of growth rate. In addition, the average value of reflectance presents an estimate of the quality and surface roughness. High resolution X-ray diffraction measurements from (004) and (115) planes were used to investigate the crystalline quality. The results show that the In content depend strongly to the V/III ratio. Detailed HRXRD characterization shows that diffraction peaks splitting represent a crystallographic tilting between the substrate and the epitaxial layer. The value of this tilt is lower compared to the Nagai tilt. The relaxation state of the layers is more achieved at higher In content. | p1 22 |
| 16:00 | A comparative study on electronic transport properties of n-and p- modulation doped Ga0.68In0.32As/GaAs and dilute nitride Ga0.68In0.32N0.012As0.988/GaAs Quantum Well Authors : M. Gunes1*, O. Donmez1, F. Sarcan1, A. Erol1, M. C. Arikan1, J. Puustinen2, M. Guina2 Affiliations : 1 Department of Physics, Science Faculty, Istanbul University, 34134, Istanbul, Turkey 2Tampere University of Technology Optoelectronics Research Center, 33101, Tampere Finland Resume : We compare the electronic transport properties of n- and p-modulation doped Ga0.68In0.32As/GaAs and Ga0.68In0.32N0.012As0.988/GaAs single quantum well structures with nitrogen concentration. The experiments included the spectral photoluminescence (PL) between 77K and 300K and Hall Effect measurements at temperatures between 14 K and 300 K. The PL results show that the addition of small amount of nitrogen reduces the band gap as commonly observed by us and others. The temperature dependence of the PL emission energy is fitted by the Varshni relation and Bose-Einstein expression for all investigated samples. It was shown that at high temperatures, the slope of linear region band gap energy (dE/dt) in GaInNAs is about %20 smaller than that of GaInAs. This may be explained in terms of enhances interaction between N localized state and extended conduction band state. The differences between the transport characteristics of 2D electrons and holes in samples which have the same nitrogen composition have been determined. It was found that 2D holes mobility is much greater than the electrons in the same N content. The high mobility of 2D holes compared to electrons in n-modulation doped GaInNAs is explained in terms of negligible effect of nitrogen on valance band and to the absence of alloy scattering of holes with localized nitrogen complexes. | p1 23 |
| 16:00 | Density of States in GaAsBi Authors : N. Vogiatzis, J.M. Rorison Affiliations : University of Bristol, Dpt Electrical and Electronic Engineering, Merchant Venturers Building, Woodland Road, Bristol, BS8 1UB , UK Resume : GaAsBi is a highly mismatched alloy which has attracted attention because of its unusual physical characteristics and its potential for device applications, such as lasers and semiconductor optical amplifiers at telecom wavelength mainly because of its potential to suppress the non-radiative Auger process. Bi substitutes the isoelectonic As atom forming a localized defect state exactly in the same way that N does in GaAs. This results to an interaction with the extended states of GaAs, which can be explained in the context of a band anti-crossing model. Unlike however N in GaAs, Bi forms a single localised state close to the valence band (VB) edge of GaAs, which is associated with the electronegativity of Bi atom being smaller than that of the As one.
As in GaAsN, in GaAsBi high concentration of Bi results in the formation of additional higher order cluster states which are quasi-resonant with the VB edge of GaAs. The interplay of these localised states with the extended states affect the energy band gap, the hole effective masses and the densities of states (DOS). In this work we model the effect of the localized states on the VBDOS, by using an impurity Anderson model and a Green’s functions approach. This method has been used previously for GaAsN and has provided a good explanation particularly on how the densities of states are modified near the localized states. Knowledge of the modified DOS is important as they are also expected to affect the hole transport properties. | p1 24 |
| 16:00 | Characterization of deep-level defects in dilute GaAsN epitaxial layers grown by APMOVPE Authors : Ł. Gelczuk1, M. Dąbrowska-Szata1, P. Kamyczek2, E. Zielony2, E. Placzek-Popko2, B. Ściana1, D. Pucicki1, D. Radziewicz1, M. Tłaczała1 Affiliations : 1 Faculty of Microsystem Electronics and Photonics, Wroclaw University of Technology, Janiszewskiego 11/17, 50-372 Wroclaw, Poland 2 Institute of Physics, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland Resume : The semiconductors of group III-V diluted with nitride, as GaAsN or InGaAsN alloys, are of great interest due to their unique properties and potential applications in modern optoelectronic devices, especially high efficiently multi-junction solar cells, infrared lasers or HBTs. A scientific interest of this class of materials is connected with facility and elasticity in formation of their electrical and optical properties. The introduction of small amounts of nitrogen into GaAs drastically decreases band gap energy of GaAsN down to about 1eV and simultaneously reduces the lattice parameters of the crystal. Furthermore, incorporation of indium to GaAsN compensates the mechanical strains, which additionally improve crystal quality. Unfortunately, technology limitations of these materials involve generation of many electrically active defects, which can significantly affect deterioration of their properties. Therefore, the fundamental goal is to relate the electrical properties of defects with the properties of III-V-N compounds. In this paper, we report the electrical characterization of deep-level defects in APMOVPE grown GaAsN/GaAs heterostructures, with low nitrogen contents (0.5%-1.5%) using standard and high resolution Laplace DLTS. The DLTS temperature spectra revealed several closely spaced deep traps in the samples. Combination of standard and high resolution DLTS techniques enabled us to specify the fundamental parameters of the traps as well as to identify them. | p1 25 |
| 16:00 | GaAs1-xBix dilute alloys band structure and carrier effective mass calculation using Band Anti-crossing model Authors : A. Ben Nasr, M. M. Habchi, A. Rebey, H. Fitouri, B. El Jani Affiliations : Unité de Recherche sur les Hétéro-Epitaxies et Applications (URHEA) - Faculty of Sciences - University of Monastir - Tunisia. Resume : Thanks to their important optoelectronic properties, the GaAs1-xBix dilute ternary alloys have several applications in device fabrication. The substitution of As by Bi leads to a significant reduction of the band-gap energy accompanied by an increase in the spin-orbit splitting. This behavior was explained using the Valence Band Anti-crossing model (V-BAC). In fact, it is due to the hybridization effects between the isoelectronic states of Bi localized at about 0.4 eV and 1.9 eV below the VB edge in GaAs and the extended valence band states. In this work, the (14x14) V-BAC model was developed and applied to determine the band structure of GaAs1-xBix along the high symmetry k-directions (Δ, Λ and Sigma) at room temperature for different Bi compositions ranging from 0 to 0.05. We have also determined the effective mass changes versus x at Γ point for each sub-band in k-directions. We found that the electron effective mass m*bc and m*so± are isotropic whereas m*hh/lh± are anisotropic. Concerning their evolution as a function of x, m*bc and m*so+ decrease slowly with Bi composition, m*hh+ increases with x and m*lh+ have a maximum at x = 0.016 in the Δ-direction which shifts slightly in the Λ- and Sigma-directions, whereas m*so- and m*hh/lh- decrease for x inferior to 0.03 and a saturation stage appears beyond this value. | p1 26 |
| 16:00 | Characterization of diluted GaAsBi epitaxied on (111)A GaAs substrates Authors : I. Zaied, H. Fitouri, A. Rebey and B. El Jani Affiliations : Université de Monastir- Unité de Recherche sur les Hétéro-Epitaxies et Applications Faculté des Sciences de Monastir 5019, Tunisia. Resume : Dilute GaAsBi layers were grown by atmospheric pressure metalorganic vapor phase epitaxy on (111)A GaAs substrates. High-resolution X-ray diffraction (HRXRD) and photoreflectance (PR) analyses were performed in order to characterize structural and optical properties of the grown material. We find that the HRXRD patterns display pronounced Pendellösung fringes originating from interferences within the GaAsBi layers, indicating smooth and coherent interface. The growth rate is slightly larger in the (111)A epilayers than in (001) epilayers. In a PR signal, a shift to a longer wavelength is observed confirming the Bi incorporation. The temperature dependence of the band gap energy was evaluated by analyzing the PR spectra. | p1 27 |
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