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Sample records for semi-insulating gaas doped

  1. Effect of the V{sub As}V{sub Ga} complex defect doping on properties of the semi-insulating GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Deming, E-mail: xautmdm@163.com; Qiao, Hongbo; Shi, Wei; Li, Enling [Department of Applied Physics, Xi' an University of Technology, Xi' an 710054 (China)

    2014-04-21

    The different position V{sub As}V{sub Ga} cluster defect doping in semi-insulating (SI) GaAs has been studied by first-principles calculation based on hybrid density functional theory. Our calculated results show that EL6 level is formed due to the V{sub As}V{sub Ga} complex defect, which is very close to the experimental result. It provides the explanation of the absorption of laser with the wavelength beyond in semi-insulating GaAs. The formation energy of V{sub As}V{sub Ga} complex defect is found to decrease from surface to interior gradually. The conduction band minima and valence band maxima of GaAs (001) surface with the V{sub As}V{sub Ga} complex defect are all located at Γ point, and some defect levels are produced in the forbidden band. In contrast, the conduction band minima and valence band maxima of GaAs with the interior V{sub As}V{sub Ga} complex defect are not located at the same k-point, so it might involve the change of momentum in the electron transition process. The research will help strengthen the understanding of photoelectronic properties and effectively guide the preparation of the SI-GaAs materials.

  2. Electron paramagnetic resonance of isolated Assub(Ga)+ antisite defect in neutron-transmutation doped semi-insulating GaAs

    International Nuclear Information System (INIS)

    Manasreh, M.O.; McDonald, P.F.; Kivlighn, S.A.; Minton, J.T.; Covington, B.C.

    1988-01-01

    The isolated Assub(Ga) antisite defect produced by the neutron-transmutation doping in semi-insulating GaAs was studied using the electron paramagnetic resonance technique. The results show that the optically induced quenching of the isolated Assub(Ga) + antisite defect is quite different from that of the EL2 center. Illumination with white light seems to always reduce the electron paramagnetic resonance spectrum suggesting that depopulation of the EL2 center does not introduce a noticeable change in the Assub(Ga) + antisite concentration. (author)

  3. Semi-insulating GaAs detectors of fast neutrons

    International Nuclear Information System (INIS)

    Sagatova, A.; Sedlackova, K.; Necas, V.; Zatko, B.; Dubecky, F.; Bohacek, P.

    2012-01-01

    The present work deals with the technology of HDPE neutron conversion layer application on the surface of semi-insulating (SI) GaAs detectors via developed polypropylene (PP) based glue. The influence of glue deposition on the electric properties of the detectors was studied as well as the ability of the detectors to register the fast neutrons from "2"3"9Pu-Be neutron source. (authors)

  4. Influence of substrate on the performances of semi-insulating GaAs detectors

    CERN Document Server

    Baldini, R; Nava, F; Canali, C; Lanzieri, C

    2000-01-01

    A study of the carrier transport mechanism, the charge collection efficiency and the energy resolution has been carried out on semi-insulating GaAs X-ray detectors realised on substrates with concentrations of acceptor dopants N sub a , varying from 10 sup 1 sup 4 to 10 sup 1 sup 7 cm sup - sup 3. The electron collection efficiency (ECE) and the reverse current were found to decrease with increasing N sub a , while the resistivity of the material was found to increase. At room temperature, the best collection efficiency (95%) and the best energy resolution (13.7 keV FWHM) for 59.5 keV X-rays of the sup 2 sup 4 sup 1 Am source, have been achieved with the less doped detectors (N sub a approx 10 sup 1 sup 4 cm sup - sup 3). The concentrations of ionised EL2 sup + , determined by optical measurements in IR regions, was shown to increase with N sub a and to be quasi-inversely proportional to the ECE values. This behaviour strongly supports the hypothesis that the EL2 defects play a main role in the compensation o...

  5. Lateral n-p-n bipolar transistors by ion implantation into semi-insulating GaAs

    International Nuclear Information System (INIS)

    Canfield, P.; Forbes, L.

    1988-01-01

    GaAs bipolar transistors have not seen the major development effort that GaAs MESFETs have due primarily to the short minority carrier lifetimes in GaAs. The short minority carrier lifetimes require that the base region be very thin which, if done by implantation, requires that the doping be high to obtain a well defined base profile. These requirements are very difficult to achieve in GaAs and typically, if high current gain and high speed are desired for a bipolar technology, then heterostructure bipolars are the appropriate technology, although the cost of heterostructure devices will be prohibitive for some time to come. For applications requiring low current gain, more modest fabrication rules can be followed. Lateral bipolars are particularly attractive since they would be easier to fabricate than a planar bipolar or a heterojunction bipolar. Lateral bipolars do not require steps or deep contacts to make contact with the subcollector or highly doped very thin epilayers for the base region and they can draw upon the semi-insulating properties of the GaAs substrates for device isolation. Bipolar transistors are described and shown to work successfully. (author)

  6. Terahertz emission from semi-insulating GaAs with octadecanthiol-passivated surface

    International Nuclear Information System (INIS)

    Wu, Xiaojun; Xu, Xinlong; Lu, Xinchao; Wang, Li

    2013-01-01

    Terahertz (THz) emission from octadecanthiol (ODT) passivated (1 0 0) surface of the semi-insulating GaAs was measured, and compared with those from the native oxidized and the fresh surfaces. It was shown that the self-assembled ODT monolayer can stabilize the GaAs (1 0 0) surface, and maintain a THz surface emission 1.4 times as efficient as the native oxidized surface under equal conditions. Surface passivation can reduce the built-in electric field in the depletion region of the GaAs (1 0 0), resulting in the suppression of the THz radiation to a different extent. Oxidation of GaAs surface reduces the THz amplitude mainly in the low-frequency region. These results indicate that GaAs can be made a more effective THz source by choosing molecular passivation technique. Conversely, the THz emission features such as polarity, amplitude, and phase from molecule-passivated surfaces may be used to characterize the attached molecules.

  7. Light controlled prebreakdown characteristics of a semi-insulating GaAs photoconductive switch

    International Nuclear Information System (INIS)

    Ma Xiangrong; Shi Wei; Ji Weili; Xue Hong

    2011-01-01

    A 4 mm gap semi-insulating (SI) GaAs photoconductive switch (PCSS) was triggered by a pulse laser with a wavelength of 1064 nm and a pulse energy of 0.5 mJ. In the experiment, when the bias field was 4 kV, the switch did not induce self-maintained discharge but worked in nonlinear (lock-on) mode. The phenomenon is analyzed as follows: an exciton effect contributes to photoconduction in the generation and dissociation of excitons. Collision ionization, avalanche multiplication and the exciton effect can supply carrier concentration and energy when an outside light source was removed. Under the combined influence of these factors, the SI-GaAs PCSS develops into self-maintained discharge rather than just in the light-controlled prebreakdown status. The characteristics of the filament affect the degree of damage to the switch. (semiconductor devices)

  8. Light controlled prebreakdown characteristics of a semi-insulating GaAs photoconductive switch

    Science.gov (United States)

    Xiangrong, Ma; Wei, Shi; Weili, Ji; Hong, Xue

    2011-12-01

    A 4 mm gap semi-insulating (SI) GaAs photoconductive switch (PCSS) was triggered by a pulse laser with a wavelength of 1064 nm and a pulse energy of 0.5 mJ. In the experiment, when the bias field was 4 kV, the switch did not induce self-maintained discharge but worked in nonlinear (lock-on) mode. The phenomenon is analyzed as follows: an exciton effect contributes to photoconduction in the generation and dissociation of excitons. Collision ionization, avalanche multiplication and the exciton effect can supply carrier concentration and energy when an outside light source was removed. Under the combined influence of these factors, the SI-GaAs PCSS develops into self-maintained discharge rather than just in the light-controlled prebreakdown status. The characteristics of the filament affect the degree of damage to the switch.

  9. Muon track induced current measurements in semi-insulating GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Eshchenko, D.G., E-mail: dimitry.eshchenko@psi.c [Physik-Institut der Universitaet Zuerich, CH-8057 Zuerich (Switzerland); Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen (Switzerland); Storchak, V.G. [Russian Research Centre ' Kurchatov Institute' , Kurchatov Sq. 1, Moscow 123182 (Russian Federation); Cottrell, S.P. [ISIS Facility, Rutherford Appleton Laboratory, Oxfordshire OX11 OQX (United Kingdom)

    2009-04-15

    We report on preliminary muon-track-induced current measurements in semi-insulating (SI-) GaAs. At T=70K, after simultaneous treatment of the sample by muon irradiation and a strong electric field (a square wave with |E|>10kV/cm and the polarity changed every 1/(50) s) for approximately 2 h, the sample is transferred to a metastable-like state which is characterized by increased life-times for non-equilibrium electrons and holes. The sample can be returned to the original state by heating up to 250 K. Our results for SI-GaAs suggest a muon-track-induced electric-field-assisted neutralization process for the deep traps.

  10. A comparative study of Mg and Pt contacts on semi-insulating GaAs: electrical and XPS characterization

    Czech Academy of Sciences Publication Activity Database

    Dubecký, F.; Kindl, Dobroslav; Hubík, Pavel; Mičušík, M.; Dubecký, M.; Boháček, P.; Vanko, G.; Gombia, E.; Nečas, V.; Mudroň, J.

    2017-01-01

    Roč. 395, Feb (2017), s. 131-135 ISSN 0169-4332 Institutional support: RVO:68378271 Keywords : semi-insulating GaAs * metal -semiconductor contact * interface * work function * electron transport * XPS Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 3.387, year: 2016

  11. Photocurrent spectra of semi-insulating GaAs M-S-M diodes: role of the contacts

    Czech Academy of Sciences Publication Activity Database

    Dubecký, F.; Oswald, Jiří; Kindl, Dobroslav; Hubík, Pavel; Dubecký, M.; Gombia, E.; Šagátová, A.; Boháček, P.; Sekáčová, M.; Nečas, V.

    2016-01-01

    Roč. 118, Apr (2016), 30-35 ISSN 0038-1101 Institutional support: RVO:68378271 Keywords : photocurrent spectroscopy * semi-insulating GaAs * detectors * contacts Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.580, year: 2016

  12. Imaging performance of a Timepix detector based on semi-insulating GaAs

    Science.gov (United States)

    Zaťko, B.; Zápražný, Z.; Jakůbek, J.; Šagátová, A.; Boháček, P.; Sekáčová, M.; Korytár, D.; Nečas, V.; Žemlička, J.; Mora, Y.; Pichotka, M.

    2018-01-01

    This work focused on a Timepix chip [1] coupled with a bulk semi-insulating GaAs sensor. The sensor consisted of a matrix of 256 × 256 pixels with a pitch of 55 μm bump-bonded to a Timepix ASIC. The sensor was processed on a 350 μm-thick SI GaAs wafer. We carried out detector adjustment to optimize its performance. This included threshold equalization with setting up parameters of the Timepix chip, such as Ikrum, Pream, Vfbk, and so on. The energy calibration of the GaAs Timepix detector was realized using a 241Am radioisotope in two Timepix detector modes: time-over-threshold and threshold scan. An energy resolution of 4.4 keV in FWHM (Full Width at Half Maximum) was observed for 59.5 keV γ-photons using threshold scan mode. The X-ray imaging quality of the GaAs Timepix detector was tested using various samples irradiated by an X-ray source with a focal spot size smaller than 8 μm and accelerating voltage up to 80 kV. A 700 μm × 700 μm gold testing object (X-500-200-16Au with Siemens star) fabricated with high precision was used for the spatial resolution testing at different values of X-ray image magnification (up to 45). The measured spatial resolution of our X-ray imaging system was about 4 μm.

  13. On the modelling of semi-insulating GaAs including surface tension and bulk stresses

    Energy Technology Data Exchange (ETDEWEB)

    Dreyer, W.; Duderstadt, F.

    2004-07-01

    Necessary heat treatment of single crystal semi-insulating Gallium Arsenide (GaAs), which is deployed in micro- and opto- electronic devices, generate undesirable liquid precipitates in the solid phase. The appearance of precipitates is influenced by surface tension at the liquid/solid interface and deviatoric stresses in the solid. The central quantity for the description of the various aspects of phase transitions is the chemical potential, which can be additively decomposed into a chemical and a mechanical part. In particular the calculation of the mechanical part of the chemical potential is of crucial importance. We determine the chemical potential in the framework of the St. Venant-Kirchhoff law which gives an appropriate stress/strain relation for many solids in the small strain regime. We establish criteria, which allow the correct replacement of the St. Venant-Kirchhoff law by the simpler Hooke law. The main objectives of this study are: (i) We develop a thermo-mechanical model that describes diffusion and interface motion, which both are strongly influenced by surface tension effects and deviatoric stresses. (ii) We give an overview and outlook on problems that can be posed and solved within the framework of the model. (iii) We calculate non-standard phase diagrams, i.e. those that take into account surface tension and non-deviatoric stresses, for GaAs above 786 C, and we compare the results with classical phase diagrams without these phenomena. (orig.)

  14. Growth of semi-insulating InP through nuclear doping

    International Nuclear Information System (INIS)

    Aliyev, M.I; Rashidova, Sh.Sh; Huseynli, M.A.

    2012-01-01

    Full text : Semi-insulating semiconductors are widely used in so-called dielectronics. Dielectric devices have quick response, good frequency characteristics, a low noise level, low sensitivity to temperature changes, etc. One of the most promising semiconductor materials is InP. At present annealing and doping are commonly used techniques to grow semi-insulating InP. The aim of this work was to grow semi-insulating InP through nuclear doping (by irradiation with gamma-quanta). InP single crystals were obtained by Czochralski method. Specimens were irradiated with doses of 10kGr at room temperature. Electrical conductivity and Hall effect were measured before and after irradiation in the temperature range 77 to 320K. After irradiation reduction in electrical conductivity was observed. This fact can be associated with formation of M-centers in positively threefold charged states of vacancy and antisite defects. Under irradiation first Ini interstitial atoms and phosphorus vacancies form. Further, the Ini atoms occupy the phosphorus vacancies. As a result there appear InP antiste defects, which along with indium vacancies form V I nI n p + In p + + complexes of the acceptor type. These complexes turn out to be traps for charge carriers and electrical conductivity of irradiated InP are sharply reduced to semi-insulating specimens

  15. Temperature Dependency and Alpha Response of Semi-Insulating GaAs Schottky Radiation Detector at Low Bias Voltage

    International Nuclear Information System (INIS)

    Kang, Sang Mook; Ha, Jang Ho; Park, Se Hwan; Kim, Han Soo; Kim, Yong Kyun

    2009-01-01

    The last decade has seen a growing interest in semiconductor radiation detectors operated at room or nearly room temperature. Great efforts have been invested in the development of radiation detectors based on semi-insulating (SI) GaAs. The main reasons are as follows: (i) high resistance against radiation damage; (ii) it possesses a good energy resolution, which relates to its active volume; (iii) such a detector also exhibits fast signal rise times, which results from a high mobility and drift velocity of charge carriers; (iv) its large band gap energy allows a SI GaAs detector to operate at room temperature. Other important features are a good technology base and low production and operating costs. An alpha particle monitoring method for the detection of Pu-238 and U-235 is becoming important in homeland security. Alpha measurement in a vacuum is known to provide a good resolution sufficient to separate an isotope abundance in nuclear materials. However, in order to apply it to a high radiation field like a spent fuel treatment facility, a nuclear material loading and unloading process in a vacuum is one of the great disadvantages. Therefore, the main technical issue is to develop a detector for alpha detection at air condition and low power operation for integration type device. In this study we fabricated GaAs Schottky detector by using semi-insulating (SI) wafer and measured current-voltage characteristic curve and alpha response with 5.5 MeV Am-241 source

  16. Experimental investigation of limit space charge accumulation mode operation in a semi-insulating GaAs photoconductive semiconductor switch

    International Nuclear Information System (INIS)

    Ma Xiangrong; Shi Wei; Xiang Mei

    2013-01-01

    Experiments with the limited space-charge accumulation (LSA) mode of oscillation in a large gap semi-insulating (SI) GaAs photoconductive semiconductor switch (PCSS) are discussed. It has been observed that growth and drift of a photo-activated charge domain (PACD) are quenched only when the bias voltage is more than twice the threshold voltage. The original negative resistance characteristics are directly utilized in the LSA mode; during LSA operation the spatial average of the electric field varies over a large portion of the negative differential mobility region of the velocity—electric field characteristic. The work efficiency of an SI GaAs PCSS is remarkably enhanced by electric field excursions into the positive resistance region when the total electric field is only below the threshold part of the time. The LSA mode can only operate in the certain conditions that satisfy the quenching of the accumulation layer and the smaller initial domain voltage. (semiconductor devices)

  17. Sulfur passivation of semi-insulating GaAs: Transition from Coulomb blockade to weak localization regime

    Energy Technology Data Exchange (ETDEWEB)

    Bagraev, N. T., E-mail: Bagraev@mail.ioffe.ru [Ioffe Institute (Russian Federation); Chaikina, E. I. [Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, Division de Fisica Aplicada (Mexico); Danilovskii, E. Yu.; Gets, D. S.; Klyachkin, L. E.; L’vova, T. V.; Malyarenko, A. M. [Ioffe Institute (Russian Federation)

    2016-04-15

    The sulfur passivation of the semi-insulating GaAs bulk (SI GaAs) grown in an excess phase of arsenic is used to observe the transition from the Coulomb blockade to the weak localization regime at room temperature. The I–V characteristics of the SI GaAs device reveal nonlinear behavior that appears to be evidence of the Coulomb blockade process as well as the Coulomb oscillations. The sulfur passivation of the SI GaAs device surface results in enormous transformation of the I–V characteristics that demonstrate the strong increase of the resistance and Coulomb blockade regime is replaced by the electron tunneling processes. The results obtained are analyzed within frameworks of disordering SI GaAs surface that is caused by inhomogeneous distribution of the donor and acceptor anti-site defects which affects the conditions of quantum- mechanical tunneling. Weak localization processes caused by the preservation of the Fermi level pinning are demonstrated by measuring the negative magnetoresistance in weak magnetic fields at room temperature. Finally, the studies of the magnetoresistance at higher magnetic fields reveal the h/2e Aharonov–Altshuler–Spivak oscillations with the complicated behavior due to possible statistical mismatch of the interference paths in the presence of different microdefects.

  18. Growth and characterization of semi-insulating carbon-doped/undoped GaN multiple-layer buffer

    International Nuclear Information System (INIS)

    Kim, Dong-Seok; Won, Chul-Ho; Kang, Hee-Sung; Kim, Young-Jo; Kang, In Man; Lee, Jung-Hee; Kim, Yong Tae

    2015-01-01

    We have proposed a new semi-insulating GaN buffer layer, which consists of multiple carbon-doped and undoped GaN layer. The buffer layer showed sufficiently good semi-insulating characteristics, attributed to the depletion effect between the carbon-doped GaN and the undoped GaN layers, even though the thickness of the carbon-doped GaN layer in the periodic structure was designed to be very thin to minimize the total carbon incorporation into the buffer layer. The AlGaN/AlN/GaN heterostructure grown on the proposed buffer exhibited much better electrical and structural properties than that grown on the conventional thick carbon-doped semi-insulating GaN buffer layer, confirmed by Hall measurement, x-ray diffraction, and secondary ion mass spectrometry. The fabricated device also showed excellent buffer breakdown characteristics. (paper)

  19. A comparative study of Mg and Pt contacts on semi-insulating GaAs: Electrical and XPS characterization

    Energy Technology Data Exchange (ETDEWEB)

    Dubecký, F., E-mail: elekfdub@savba.sk [Institute of Electrical Engineering, SAS, Dúbravská cesta 9, Bratislava, SK-84104 (Slovakia); Kindl, D.; Hubík, P. [Institute of Physics CAS, v.v.i., Cukrovarnická 10, CZ-16200 Prague (Czech Republic); Mičušík, M. [Polymer Institute, SAS, Dúbravská cesta 9, Bratislava, SK-84541 (Slovakia); Dubecký, M. [Department of Physics, Faculty of Science, University of Ostrava, 30. dubna 22, CZ-70103 Ostrava 1 (Czech Republic); Boháček, P.; Vanko, G. [Institute of Electrical Engineering, SAS, Dúbravská cesta 9, Bratislava, SK-84104 (Slovakia); Gombia, E. [IMEM-CNR, Parco area delle Scienze 37/A, Parma, I-43010 (Italy); Nečas, V. [Faculty of Electrical Engineering and Information Technology, SUT, Ilkovičova 3, Bratislava, SK-81219 (Slovakia); Mudroň, J. [Department of Electronics, Academy of Armed Forces, Demänová 393, Liptovský Mikuláš, SK-03106 (Slovakia)

    2017-02-15

    Highlights: • Explored were diodes with full-area low/high work function metal contacts on semi-insulating GaAs (S). • The Mg-S-Mg diode is promising for radiation detectors for its low high-field current. • The XPS analysis of Mg-S interface shows presence of MgO instead of Mg metal. - Abstract: We present a comparative study of the symmetric metal-SI GaAs-metal (M-S-M) diodes with full-area contacts on both device sides, in order to demonstrate the effect of contact metal work function in a straightforward way. We compare the conventional high work function Pt contact versus the less explored low work function Mg contact. The Pt-S-Pt, Mg-S-Mg and mixed Mg-S-Pt structures are characterized by the current-voltage measurements, and individual Pt-S and Mg-S contacts are investigated by the X-ray photoelectron spectroscopy (XPS). The transport measurements of Mg-S-Pt structure show a significant current decrease at low bias while the Mg-S-Mg structure shows saturation current at high voltages more than an order of magnitude lower with respect to the Pt-S-Pt reference. The phenomena observed in Mg-containing samples are explained by the presence of insulating MgO layer at the M-S interface, instead of the elementary Mg, as confirmed by the XPS analysis. Alternative explanations of the influence of MgO layer on the effective resistance of the structures are presented. The reported findings have potential applications in M-S-M sensors and radiation detectors based on SI GaAs.

  20. Effect of H{sup +} implantation on the optical properties of semi-insulating GaAs crystals in the IR spectral region

    Energy Technology Data Exchange (ETDEWEB)

    Klyui, N. I.; Lozinskii, V. B., E-mail: lvb@isp.kiev.ua [Jilin University, College of Physics (China); Liptuga, A. I.; Dikusha, V. N. [National Academy of Sciences of Ukraine, Lashkaryov Institute of Semiconductor Physics (Ukraine); Oksanych, A. P.; Kogdas’, M. G.; Perekhrest, A. L.; Pritchin, S. E. [Kremenchug National University (Ukraine)

    2017-03-15

    The optical properties of semi-insulating GaAs crystals subjected to multienergy hydrogen-ion implantation and treatment in a high-frequency electromagnetic field are studied in the infrared spectral region. It is established that such combined treatment provides a means for substantially increasing the transmittance of GaAs crystals to values characteristic of crystals of high optical quality. On the basis of analysis of the infrared transmittance and reflectance data, Raman spectroscopy data, and atomic-force microscopy data on the surface morphology of the crystals, a physical model is proposed to interpret the effects experimentally observed in the crystals. The model takes into account the interaction of radiation defects with the initial structural defects in the crystals as well as the effect of compensation of defect centers by hydrogen during high-frequency treatment.

  1. Effect of H+ implantation on the optical properties of semi-insulating GaAs crystals in the IR spectral region

    International Nuclear Information System (INIS)

    Klyui, N. I.; Lozinskii, V. B.; Liptuga, A. I.; Dikusha, V. N.; Oksanych, A. P.; Kogdas’, M. G.; Perekhrest, A. L.; Pritchin, S. E.

    2017-01-01

    The optical properties of semi-insulating GaAs crystals subjected to multienergy hydrogen-ion implantation and treatment in a high-frequency electromagnetic field are studied in the infrared spectral region. It is established that such combined treatment provides a means for substantially increasing the transmittance of GaAs crystals to values characteristic of crystals of high optical quality. On the basis of analysis of the infrared transmittance and reflectance data, Raman spectroscopy data, and atomic-force microscopy data on the surface morphology of the crystals, a physical model is proposed to interpret the effects experimentally observed in the crystals. The model takes into account the interaction of radiation defects with the initial structural defects in the crystals as well as the effect of compensation of defect centers by hydrogen during high-frequency treatment.

  2. Surface barrier analysis of semi-insulating and n{sup +}-type GaAs(0 0 1) following passivation with n-alkanethiol SAMs

    Energy Technology Data Exchange (ETDEWEB)

    Marshall, Gregory M. [Laboratory for Quantum Semiconductors and Photon-Based BioNanotechnology, Department of Electrical and Computer Engineering, Universite de Sherbrooke, Sherbrooke, Quebec, J1K 2R1 (Canada); Institute for Chemical Process and Environmental Technology, National Research Council of Canada, Ottawa, Ontario, K1A 0R6 (Canada); Bensebaa, Farid [Institute for Chemical Process and Environmental Technology, National Research Council of Canada, Ottawa, Ontario, K1A 0R6 (Canada); Dubowski, Jan J., E-mail: jan.j.dubowski@usherbrooke.ca [Laboratory for Quantum Semiconductors and Photon-Based BioNanotechnology, Department of Electrical and Computer Engineering, Universite de Sherbrooke, Sherbrooke, Quebec, J1K 2R1 (Canada)

    2011-02-15

    The surface Fermi level of semi-insulating and n{sup +}-type GaAs(0 0 1) was determined before and after passivation with n-alkanethiol self-assembled monolayers (SAMs) by X-ray photoelectron spectroscopy. Fermi level positioning was achieved using Au calibration pads integrated directly onto the GaAs surface, prior to SAM deposition, in order to provide a surface equipotential binding energy reference. Fermi level pinning within 50 meV and surface barrier characteristics according to the Advanced Unified Defect Model were observed. Our results demonstrate the effectiveness of the Au integration technique for the determination of band-edge referenced Fermi level positions and are relevant to an understanding of emerging technologies based on the molecular-semiconductor junction.

  3. Dielectric properties of semi-insulating Fe-doped InP in the terahertz spectral region.

    Science.gov (United States)

    Alyabyeva, L N; Zhukova, E S; Belkin, M A; Gorshunov, B P

    2017-08-04

    We report the values and the spectral dependence of the real and imaginary parts of the dielectric permittivity of semi-insulating Fe-doped InP crystalline wafers in the 2-700 cm -1 (0.06-21 THz) spectral region at room temperature. The data shows a number of absorption bands that are assigned to one- and two-phonon and impurity-related absorption processes. Unlike the previous studies of undoped or low-doped InP material, our data unveil the dielectric properties of InP that are not screened by strong free-carrier absorption and will be useful for designing a wide variety of InP-based electronic and photonic devices operating in the terahertz spectral range.

  4. A study on carbon incorporation in semi-insulating GaAs crystals grown by the vapor pressure controlled Czochralski technique (VCz). Pt. I. Experiments and Results

    Energy Technology Data Exchange (ETDEWEB)

    Jacob, K.; Frank, C.; Neubert, M.; Rudolph, P. [Institut fuer Kristallzuechtung im Forschungsverbund Berlin e.V. (IKZ) (Germany); Ulrici, W. [Institut fuer Kristallzuechtung im Forschungsverbund Berlin e.V. (IKZ) (Germany); Paul-Drude-Inst. fuer Festkoerperelektronik, Berlin (Germany); Jurisch, M. [Institut fuer Kristallzuechtung im Forschungsverbund Berlin e.V. (IKZ) (Germany); Freiberger Compound Materials GmbH, Freiberg (Germany); Korb, J. [Institut fuer Kristallzuechtung im Forschungsverbund Berlin e.V. (IKZ) (Germany); GTT Technologies, Freiberg (Germany)

    2000-07-01

    In the past it has been demonstrated that the carbon concentration of large semi-insulating (SI) GaAs single crystals grown by the conventional liquid encapsulation Czochralski (LEC) technique can be controlled by several methods including variations of growth parameters. It was the aim of the present paper to clarify which of the relationships of LEC growth could be used for a carbon control in the VCz-method characterized by the application of an inner chamber made from graphite to avoid selective As evaporation. In detail this comprised a study of the influence of several growth parameters like the water content of the boric oxide, the composition of the working atmosphere, the gas flow, a titanium gettering and additions of gallium oxide. As a result, for the first time carbon concentrations down to {approx} 10{sup 14} cm{sup -3} were obtained in 3{sup ''} (75 mm) diameter VCz crystals. (orig.)

  5. Investigation of semi-insulating InP co-doped with Ti and various acceptors for use in X-ray detection

    International Nuclear Information System (INIS)

    Zdansky, K.; Gorodynskyy, V.; Kozak, H.; Pekarek, L.

    2005-01-01

    Semi-insulating InP single crystals co-doped with Zn and Ti and co-doped with Ti and Mn were grown by Czochralski technique. Wafers of these crystals were annealed for a long time at a high temperature and cooled slowly. The samples were characterized by temperature dependent resistivity and Hall coefficient measurements. The binding energies of Ti in semi-insulating InP co-doped with Ti and Zn and co-doped with Ti and Mn were found to differ which shows that Ti may occupy different sites in InP. The curves of Hall coefficient vs. reciprocal temperature deviate from straight lines at low temperatures due to electron and hole mixed conductance. The value of resistivity of the annealed semi-insulating InP co-doped with Ti and Mn reaches high resistivity at a reduced temperature easily achievable by thermo-electric devices which could make this material useable in X-ray detection. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  6. Formation of a quasi-neutral region in Schottky diodes based on semi-insulating GaAs and the influence of the compensation mechanism on the particle detector performance

    CERN Document Server

    Rogalla, M

    1999-01-01

    A model for the electric field distribution beneath the Schottky contact in semi-insulating (SI) GaAs particle detectors is developed. The model is based on a field-enhanced electron capture of the EL2-defect. The influence of the compensation mechanism in SI-GaAs on the field distribution, leakage current density and charge collection properties of the detectors will be discussed. The detailed understanding allows then a device optimization. (author)

  7. Semi-insulating GaAs and Au Schottky barrier photodetectors for near-infrared detection (1280 nm)

    Science.gov (United States)

    Nusir, A. I.; Makableh, Y. F.; Manasreh, O.

    2015-08-01

    Schottky barriers formed between metal (Au) and semiconductor (GaAs) can be used to detect photons with energy lower than the bandgap of the semiconductor. In this study, photodetectors based on Schottky barriers were fabricated and characterized for the detection of light at wavelength of 1280 nm. The device structure consists of three gold fingers with 1.75 mm long and separated by 0.95 mm, creating an E shape while the middle finger is disconnected from the outer frame. When the device is biased, electric field is stretched between the middle finger and the two outermost electrodes. The device was characterized by measuring the current-voltage (I-V) curve at room temperature. This showed low dark current on the order of 10-10 A, while the photocurrent was higher than the dark current by four orders of magnitude. The detectivity of the device at room temperature was extracted from the I-V curve and estimated to be on the order of 5.3x1010 cm.Hz0.5/W at 5 V. The step response of the device was measured from time-resolved photocurrent curve at 5 V bias with multiple on/off cycles. From which the average recovery time was estimated to be 0.63 second when the photocurrent decreases by four orders of magnitude, and the average rise time was measured to be 0.897 second. Furthermore, the spectral response spectrum of the device exhibits a strong peak close to the optical communication wavelength (~1.3 μm), which is attributed to the internal photoemission of electrons above the Schottky barrier formed between Au and GaAs.

  8. LO-phonon and plasmon coupling in neutron-transmutation-doped GaAs

    International Nuclear Information System (INIS)

    Kuriyama, K.; Sakai, K.; Okada, M.

    1996-01-01

    Coupling between the longitudinal-optic (LO) phonon mode and the longitudinal plasma mode in neutron-transmutation-doped (NTD) semi-insulating GaAs was studied using Raman-scattering spectroscopy and a Fourier-transform infrared spectrometer. When the electron concentration due to the activation of NTD impurities (Ge Ga and Se As ) approaches ∼8x10 16 cm -3 , the LO-phonon endash plasmon coupling is observed. This behavior is consistent with the free-electron absorption due to the activation of NTD impurities in samples annealed above 600 degree C. copyright 1996 The American Physical Society

  9. A contribution for the detection of deep defects in semi-insulating GaAs by means of PICTS; Ein Beitrag zum Nachweis tiefer Stoerstellen in halbisolierendem GaAs mittels PICTS

    Energy Technology Data Exchange (ETDEWEB)

    Zychowitz, G.

    2006-02-03

    The PICTS procedure is one of the most frequently applied methods for the characterization of semi-insulating semiconductors. The methodical progresses in the determination of defect parameters by this proceudure are presented in this thesis. as practicable method for the detection of a temperature-dependent change of the occupation ratio of a trap the normation of the PICTS spectra on the emission rate of the electrons is introduced. It is shown that peaks, in which this normation fails, must not applied for the determination of the defect parameters. The studies prove that for the complete charge-alteration of the defects a suitable excitation intensity must be applied. By PICTS measurements on copper-doped samples a systematic dependence of the peak heights of copper-correlated peaks on the copper content of the samples is detected. By the studies it is proved that copper can be detected by means of PICTS up to a minimal AES copper concentration of [Cu{sub min}]approx5.10{sup 14} cm{sup -3}.

  10. Room-temperature particle detectors with guard rings based on semi-insulating InP co-doped with Ti and Zn

    International Nuclear Information System (INIS)

    Yatskiv, R.; Zdansky, K.; Pekarek, L.

    2009-01-01

    Particle detectors made with a guard-ring (GR) electrode, operating at room temperature, have been studied. The detectors were fabricated on a semi-insulating InP crystal co-doped with Ti and Zn, grown using the Liquid-Encapsulated Czochralski technique. The detection performance of the particle detectors was evaluated using alpha particles emitted from a 241 Am source. Good detector performance has been achieved with measured charge-collection efficiencies of 99.9% and 98.2% and FWHM energy resolutions of 0.9% and 2.1%. The measurements were carried out at 230 K for negative and positive bias voltages of the irradiated electrode. The good performance is due to the SI properties of the material which has been achieved by doping with suitable Ti atoms and co-doping with a low concentration of Zn acceptors, sufficient to fully compensate shallow donors. Electron and hole charge-collection efficiencies (CCEs) were measured at various temperatures. At room temperature, unlike at low temperature (T<250 K), the hole CCE was better than the electron CCE, which can be explained by the presence of electron-trapping centres in InP with a temperature-dependent capture rate.

  11. Effect of Fe doping on optical properties of freestanding semi-insulating HVPE GaN:Fe

    Czech Academy of Sciences Publication Activity Database

    Gladkov, Petar; Humlíček, J.; Hulicius, Eduard; Šimeček, Tomislav; Paskova, T.; Evans, K.

    2010-01-01

    Roč. 312, č. 8 (2010), s. 1205-1209 ISSN 0022-0248 R&D Projects: GA AV ČR IAA100100719; GA MŠk(CZ) LC06040 Institutional research plan: CEZ:AV0Z20670512; CEZ:AV0Z10100521 Keywords : Fe-doping * Optical characterization * Hybride vapor phase epitaxy * Nitrides Subject RIV: JB - Sensors, Measurment, Regulation Impact factor: 1.737, year: 2010

  12. Performance study of radiation detectors based on semi-insulating GaAs with P+homo- and heterojunction blocking electrode

    Czech Academy of Sciences Publication Activity Database

    Dubecky, F.; Hulicius, Eduard; Frigeri, P.; Perd´ochová-Šagátová, A.; Zat´ko, B.; Hubík, Pavel; Gombia, E.; Boháček, P.; Pangrác, Jiří; Franchi, S.; Nečas, V.

    2006-01-01

    Roč. 563, - (2006), s. 159-162 ISSN 0168-9002 R&D Projects: GA AV ČR(CZ) IAA1010404 Grant - others:Slovak Grant Agency for Science(SK) 2/4151/24 Institutional research plan: CEZ:AV0Z10100521 Keywords : GaAs radiation detector * blocking electrode * P + -N homojunction and heterojunction * gamma irradiation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.185, year: 2006

  13. Doping assessment in GaAs nanowires

    DEFF Research Database (Denmark)

    Goktas, N. Isik; Fiordaliso, Elisabetta Maria; LaPierre, R. R.

    2018-01-01

    Semiconductor nanowires (NWs) are a candidate technology for future optoelectronic devices. One of the critical issues in NWs is the control of impurity doping for the formation of p-n junctions. In this study, beryllium (p-type dopant) and tellurium (n-type dopant) in self-assisted GaAs NWs...

  14. Anomalous diffusion of Ga and As from semi-insulating GaAs substrate into MOCVD grown ZnO films as a function of annealing temperature and its effect on charge compensation

    Directory of Open Access Journals (Sweden)

    Pranab Biswas

    2014-05-01

    Full Text Available The diffusion behavior of arsenic (As and gallium (Ga atoms from semi-insulating GaAs (SI-GaAs into ZnO films upon post-growth annealing vis-à-vis the resulting charge compensation was investigated with the help of x-ray photoelectron spectroscopy (XPS and secondary ion mass spectroscopy. The films, annealed at 600 ºC and 700 ºC showed p-type conductivity with a hole concentration of 1.1 × 1018 cm−3 and 2.8 × 1019 cm−3 respectively, whereas those annealed at 800 ºC showed n-type conductivity with a carrier concentration of 6.5 × 1016 cm−3. It is observed that at lower temperatures, large fraction of As atoms diffused from the SI-GaAs substrates into ZnO and formed acceptor related complex, (AsZn–2VZn, by substituting Zn atoms (AsZn and thereby creating two zinc vacancies (VZn. Thus as-grown ZnO which was supposed to be n-type due to nonstoichiometric nature showed p-type behavior. On further increasing the annealing temperature to 800 ºC, Ga atoms diffused more than As atoms and substitute Zn atoms thereby forming shallow donor complex, GaZn. Electrons from donor levels then compensate the p-type carriers and the material reverts back to n-type. Thus the conversion of carrier type took place due to charge compensation between the donors and acceptors in ZnO and this compensation is the possible origin of anomalous conduction in wide band gap materials.

  15. Stability and diffusion of interstitital and substitutional Mn in GaAs of different doping types

    CERN Document Server

    Pereira, LMC; Decoster, S; Correia, JG; Amorim, LM; da Silva, MR; Araújo, JP; Vantomme, A

    2012-01-01

    We report on the lattice location of Mn impurities (< 0.05%) in undoped (semi-insulating) and heavily $n$-type doped GaAs, by means of $\\beta^{-}$-emission channeling from the decay of $^{56}$Mn produced at ISOLDE/CERN. In addition to the majority substituting for Ga, we locate up to 30% of the Mn impurites on tetrahedral interstitial sites with As nearest neighbors. In line with the recently reported high thermal stability of interstitial Mn in heavily $p$-type doped GaAs [L. M. C. Pereira et al., Appl. Phys. Lett. 98, 201905 (2011)], the interstitial fraction is found to be stable up to 400$^{\\circ}$C, with an activation energy for diffusion of 1.7–2.3 eV. By varying the concentration of potentially trapping defects, without a measurable effect on the migration energy of the interstitial impurities, we conclude that the observed high thermal stability is characteristic of isolated interstitial Mn. Being difficult to reconcile with the general belief that interstitial Mn is the donor defect that out-dif...

  16. Characterization of semi-insulating materials by photoinduced current transient spectroscopy: Fe doped INP for micro-optoelectronics and CdZnTe for nuclear detection

    International Nuclear Information System (INIS)

    Cherkaoui, K.

    1998-01-01

    The need of semi-insulating materials, of great quality, concerns various application domains. For instance, the very resistive substrates InP and CdZnTe are respectively adapted to the micro-optoelectronic circuits and to nuclear detectors. These two materials have been characterized by the thermal photoinduced current transient spectroscopy. The first part of this thesis is the defects analysis of annealing InP substrates, to understand the compensation process of this material. Two activation energy levels around 0,2 to 0,4 eV resulting from the thermal treatment have been detected. The iron omnipresence in the substrates, even undoped, has been noticed. It is then necessary to take into account the iron presence to understand the compensation process in these InP annealing substrates. the second part presents the study of the CdZnTe material, elaborated by the Bridgman method, to emphasize the defects leading to the decrease of the detector performances. The presence of three deep levels, near the forbidden band middle, is in relation with the detectors performances. (A.L.B.)

  17. Detectors of Gamma Rays and Alpha Particles Based on Ta-Doped InP Converted to the Semi-Insulating State by Annealing

    Czech Academy of Sciences Publication Activity Database

    Žďánský, Karel; Gorodynskyy, Vladyslav; Pekárek, Ladislav

    2009-01-01

    Roč. 56, č. 5 (2009), s. 2997-3001 ISSN 0018-9499 R&D Projects: GA AV ČR KAN400670651; GA AV ČR(CZ) KAN401220801; GA AV ČR IBS2067354 Institutional research plan: CEZ:AV0Z20670512; CEZ:AV0Z10100520 Keywords : radiation detection * semiconductor doping * crystal growth Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.591, year: 2009

  18. Substrate and Mg doping effects in GaAs nanowires

    Directory of Open Access Journals (Sweden)

    Perumal Kannappan

    2017-10-01

    Full Text Available Mg doping of GaAs nanowires has been established as a viable alternative to Be doping in order to achieve p-type electrical conductivity. Although reports on the optical properties are available, few reports exist about the physical properties of intermediate-to-high Mg doping in GaAs nanowires grown by molecular beam epitaxy (MBE on GaAs(111B and Si(111 substrates. In this work, we address this topic and present further understanding on the fundamental aspects. As the Mg doping was increased, structural and optical investigations revealed: i a lower influence of the polytypic nature of the GaAs nanowires on their electronic structure; ii a considerable reduction of the density of vertical nanowires, which is almost null for growth on Si(111; iii the occurrence of a higher WZ phase fraction, in particular for growth on Si(111; iv an increase of the activation energy to release the less bound carrier in the radiative state from nanowires grown on GaAs(111B; and v a higher influence of defects on the activation of nonradiative de-excitation channels in the case of nanowires only grown on Si(111. Back-gate field effect transistors were fabricated with individual nanowires and the p-type electrical conductivity was measured with free hole concentration ranging from 2.7 × 1016 cm−3 to 1.4 × 1017 cm−3. The estimated electrical mobility was in the range ≈0.3–39 cm2/Vs and the dominant scattering mechanism is ascribed to the WZ/ZB interfaces. Electrical and optical measurements showed a lower influence of the polytypic structure of the nanowires on their electronic structure. The involvement of Mg in one of the radiative transitions observed for growth on the Si(111 substrate is suggested.

  19. Electric properties of semi-insulating crystals CdTe:Cl

    International Nuclear Information System (INIS)

    Arkadyeva, E.N.; Matveev, O.A.

    1977-01-01

    Hall effect and conductivity measurement were carried out on chlorine doped semi-insulating CdTe crystals, of p and n electric type. In p type crystals the depth of the dominating level was determined (+0.7eV) as well as the concentration of associated centres (10 13 -10 14 cm -3 ). The mobility values are limited by a process of diffusion on heterogeneities

  20. Self-Assembled Monolayers of CdSe Nanocrystals on Doped GaAs Substrates

    DEFF Research Database (Denmark)

    Marx, E.; Ginger, D.S.; Walzer, Karsten

    2002-01-01

    This letter reports the self-assembly and analysis of CdSe nanocrystal monolayers on both p- and a-doped GaAs substrates. The self-assembly was performed using a 1,6-hexanedithiol self-assembled monolayer (SAM) to link CdSe nanocrystals to GaAs substrates. Attenuated total reflection Fourier tran...

  1. Comparative research on the transmission-mode GaAs photocathodes of exponential-doping structures

    International Nuclear Information System (INIS)

    Chen Liang; Qian Yun-Sheng; Zhang Yi-Jun; Chang Ben-Kang

    2012-01-01

    Early research has shown that the varied doping structures of the active layer of GaAs photocathodes have been proven to have a higher quantum efficiency than uniform doping structures. On the basis of our early research on the surface photovoltage of GaAs photocathodes, and comparative research before and after activation of reflection-mode GaAs photocathodes, we further the comparative research on transmission-mode GaAs photocathodes. An exponential doping structure is the typical varied doping structure that can form a uniform electric field in the active layer. By solving the one-dimensional diffusion equation for no equilibrium minority carriers of transmission-mode GaAs photocathodes of the exponential doping structure, we can obtain the equations for the surface photovoltage (SPV) curve before activation and the spectral response curve (SRC) after activation. Through experiments and fitting calculations for the designed material, the body-material parameters can be well fitted by the SPV before activation, and proven by the fitting calculation for SRC after activation. Through the comparative research before and after activation, the average surface escape probability (SEP) can also be well fitted. This comparative research method can measure the body parameters and the value of SEP for the transmission-mode GaAs photocathode more exactly than the early method, which only measures the body parameters by SRC after activation. It can also help us to deeply study and exactly measure the parameters of the varied doping structures for transmission-mode GaAs photocathodes, and optimize the Cs-O activation technique in the future. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

  2. Growth and characteristics of p-type doped GaAs nanowire

    Science.gov (United States)

    Li, Bang; Yan, Xin; Zhang, Xia; Ren, Xiaomin

    2018-05-01

    The growth of p-type GaAs nanowires (NWs) on GaAs (111) B substrates by metal-organic chemical vapor deposition (MOCVD) has been systematically investigated as a function of diethyl zinc (DEZn) flow. The growth rate of GaAs NWs was slightly improved by Zn-doping and kink is observed under high DEZn flow. In addition, the I–V curves of GaAs NWs has been measured and the p-type dope concentration under the II/III ratio of 0.013 and 0.038 approximated to 1019–1020 cm‑3. Project supported by the National Natural Science Foundation of China (Nos. 61376019, 61504010, 61774021) and the Fund of State Key Laboratory of Information Photonics and Optical Communications (Beijing University of Posts and Telecommunications), China (Nos. IPOC2017ZT02, IPOC2017ZZ01).

  3. Microhardness of epitaxial layers of GaAs doped with rare earths

    International Nuclear Information System (INIS)

    Kulish, U.M.; Gamidov, Z.S.; Kuznetsova, I.Yu.; Petkeeva, L.N.; Borlikova, G.V.

    1989-01-01

    Results of the study of microhardness of GaAS layer doped by certain rare earths - Gd, Tb, Dy - are presented. The assumption is made that the higher is the value of the first potential of rare earth impurity ionization (i.e. the higher is the filling of 4f-shell), the lower is the effect of the element on electric and mechanical properties of GaAs epitaxial layers

  4. Photoacoustic study of the effect of doping concentration on the transport properties of GaAs epitaxial layers

    NARCIS (Netherlands)

    George, S.D.; Dilna, S.; Prasanth, R.; Radhakrishnan, P.; Vallabhan, C.P.G.; Nampoori, V.P.N.

    2003-01-01

    We report a photoacoustic (PA) study of the thermal and transport properties of a GaAs epitaxial layer doped with Si at varying doping concentration, grown on GaAs substrate by molecular beam epitaxy. The data are analyzed on the basis of Rosencwaig and Gersho's theory of the PA effect. The

  5. High purity and semi-insulating 4H-SiC crystals grown by physical vapor transport

    Energy Technology Data Exchange (ETDEWEB)

    Augustine, G.; Hobgood, H.McD.; Balakrishna, V.; Dunne, G.T.; Hopkins, R.H.; Thomas, R.N. [Northrop Grumman Corp., Pittsburgh, PA (United States). Science and Technology Center; Doolittle, W.A.; Rohatgi, A. [Georgia Inst. of Tech., Atlanta, GA (United States). School of Electrical and Computer Engineering

    1998-06-01

    High purity undoped and semi-insulating vanadium doped 4H-SiC single crystals with diameters up to 50 mm were grown by the physical vapor transport method. Undoped crystals exhibiting resistivities in the 10{sup 2} to 10{sup 3} {Omega}-cm range and photoconductive decay (PCD) lifetimes in the 2 to 9 {mu}s range, were grown from high purity SiC sublimation sources. The crystals were p-type due to the presence of residual acceptor impurities, mainly boron. The semi-insulating behavior of the vanadium doped crystals is attributed to compensation of residual acceptors by the deep level vanadium donor located near the middle of the band gap. (orig.) 6 refs.

  6. Visible-light electroluminescence in Mn-doped GaAs light-emitting diodes

    International Nuclear Information System (INIS)

    Nam Hai, Pham; Maruo, Daiki; Tanaka, Masaaki

    2014-01-01

    We observed visible-light electroluminescence (EL) due to d-d transitions in light-emitting diodes with Mn-doped GaAs layers (here, referred to as GaAs:Mn). Besides the band-gap emission of GaAs, the EL spectra show two peaks at 1.89 eV and 2.16 eV, which are exactly the same as 4 A 2 ( 4 F) → 4 T 1 ( 4 G) and 4 T 1 ( 4 G) → 6 A 1 ( 6 S) transitions of Mn atoms doped in ZnS. The temperature dependence and the current-density dependence are consistent with the characteristics of d-d transitions. We explain the observed EL spectra by the p-d hybridized orbitals of the Mn d electrons in GaAs

  7. Andreev reflections at interfaces between delta-doped GaAs and superconducting Al films

    DEFF Research Database (Denmark)

    Taboryski, Rafael Jozef; Clausen, Thomas; Hansen, Jørn Bindslev

    1996-01-01

    By placing several Si delta-doped layers close to the surface of a GaAs molecular beam epitaxy-grown crystal, we achieve a compensation of the Schottky barrier and obtain a good Ohmic contact between an in situ deposited (without breaking the vacuum) Al metallization layer and a highly modulation...

  8. Subnanosecond linear GaAs photoconductive switching: Revision 1

    Energy Technology Data Exchange (ETDEWEB)

    Druce, R.L.; Pocha, M.D.; Griffin, K.L.; Hofer, W.W.

    1989-01-01

    We are conducting research in photoconductive switching for the purpose of generating subnanosecond pulses in the 25--50kV range. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as a closing and opening switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). The closing time of a linear GaAs switch is theoretically limited by the characteristics of the laser pulse used to activate the switch (the carrier generation time in GaAs is /approximately/10/sup /minus/14/ sec) while the opening time is theoretically limited by the recombination time of the carriers. The recombination time is several ns for commercially available semi-insulating GaAs. Doping or neutron irradiation can reduce the recombination time to less than 100 ps. We have observed switch closing times of less than 200 ps with a 100 ps duration laser pulse and opening times of less than 400 ps with neutron irradiated GaAs at fields of tens of kV/cm. The illumination source was a Nd:YAG laser operating at 1.06 /mu/m. 4 refs., 11 figs.

  9. Subnanosecond linear GaAs photoconductive switching, revision 1

    Science.gov (United States)

    Druce, R. L.; Pocha, M. D.; Griffin, K. L.; Hofer, W. W.

    Research was conducted in photoconductive switching for the purpose of generating subnanosecond pulses in the 25 to 50kV range. The very fast recombination rates of Gallium Arsenide (GaAs) was exploited to explore the potential of GaAs as a closing and opening switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). The closing time of a linear GaAs switch is theoretically limited by the characteristics of the laser pulse used to activate the switch (the carrier generation time in GaAs is (approx. 10(-14) sec) while the opening time is theoretically limited by the recombination time of the carriers. The recombination time is several ns for commercially available semi-insulating GaAs. Doping or neutron irradiation can reduce the recombination time to less than 100 ps. Switch closing times of less than 200 ps with a 100 ps duration laser pulse and opening times of less than 400 ps with neutron irradiated GaAs at fields of tens of kV/cm was observed. The illumination source was a Nd:YAG laser operating at 1.06 microns.

  10. Radiation damages and electro-conductive characteristics of Neutron-Transmutation-Doped GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Kuriyama, Kazuo; Sato, Masataka; Sakai, Kiyohiro [Hosei Univ., Koganei, Tokyo (Japan). Coll. of Engineering; Okada, Moritami

    1996-04-01

    Neutron Transmutation Doping (NTD) method made it possible to do homogeneous doping of impurities and to easily control the doping level. Thus, the method has been put into practice for some materials such as silicon. Here, the annealing behavior of anti-site defects generated in neutron-irradiated GaAs was studied. Electric activations of NTD-impurities were started around 550degC in P1 and P2 radiation fields, which were coincident with the beginning of extinction of electron trapping which was caused by anti-site defects due to fast neutron radiation. The electric resistivities of GaAs in neutron radiation fields; P1, P2 and P3 changed depending with the annealing temperature. The electric resistivities of GaAs in P1 and P2 fields indicate the presence of hopping conduction through radiation damages. The resistance of GaAs irradiated in P1 was smaller by nearly 2 orders than that of the untreated control. Further, the electric activation process for NTD-impurities was investigated using ESR and Raman spectroscopy. (M.N.)

  11. Supralinear photoconductivity of copper doped semi-insulating gallium arsenide

    Science.gov (United States)

    Schoenbach, K. H.; Joshi, R. P.; Peterkin, F.; Druce, R. L.

    1995-05-01

    The high gain effect was shown to be a threshold effect and was dependent on the photoactivation energy level. For the studied material, laser energy densities in the order of 10 mJ cm(sup - 2) for a laser pulse duration of 200 ps were needed to switch into the high gain mode. The observed supralinear behavior of the peak photoconductivity and the charge carrier lifetime can be accounted by the shifts in quasi Fermi levels and the occupancy of copper states within the forbidden gap. Numerical simulations were also presented that yielded quantitative values for the trapping cross sections and recombination center densities. From the perspective of applications, the GaAs:Si:Cu material had great potential for high-power repetitive switching and photodetection.

  12. Supralinear photoconductivity of copper doped semi-insulating gallium arsenide

    Energy Technology Data Exchange (ETDEWEB)

    Schoenbach, K.H.; Joshi, R.P.; Peterkin, F. [Physical Electronics Research Institute, Old Dominion University, Norfolk, Virginia 23529 (United States); Druce, R.L. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

    1995-05-15

    We report on the intensity dependent supralinear photoconductivity in GaAs:Si:Cu material. The results of our measurements show that the effective carrier lifetime can change over two orders of magnitude with variations in the intensity of the optical excitation. A threshold intensity level has been observed and can be related to the occupancy of the deep copper level. Numerical simulations have also been carried out to analyze the trapping dynamics. The intensity dependent lifetimes obtained from the simulations match the experimental data very well. Finally, based on the nonlinear intensity dependence of the effective lifetimes, a possible low-energy phototransistor application for the GaAs:Cu material system is presented. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  13. The Mn site in Mn-doped GaAs nanowires: an EXAFS study

    International Nuclear Information System (INIS)

    D’Acapito, F; Rovezzi, M; Boscherini, F; Jabeen, F; Bais, G; Piccin, M; Rubini, S; Martelli, F

    2012-01-01

    We present an EXAFS study of the Mn atomic environment in Mn-doped GaAs nanowires. Mn doping has been obtained either via the diffusion of the Mn used as seed for the nanowire growth or by providing Mn during the growth of Au-induced wires. As a general finding, we observe that Mn forms chemical bonds with As but is not incorporated in a substitutional site. In Mn-induced GaAs wires, Mn is mostly found bonded to As in a rather disordered environment and with a stretched bond length, reminiscent of that exhibited by MnAs phases. In Au-seeded nanowires, along with stretched MnAs coordination, we have found the presence of Mn in a MnAu intermetallic compound. (paper)

  14. Towards low-dimensional hole systems in Be-doped GaAs nanowires

    DEFF Research Database (Denmark)

    Ullah, A. R.; Gluschke, J. G.; Jeppesen, Peter Krogstrup

    2017-01-01

    -gates produced using GaAs nanowires with three different Be-doping densities and various AuBe contact processing recipes. We show that contact annealing only brings small improvements for the moderately doped devices under conditions of lower anneal temperature and short anneal time. We only obtain good......GaAs was central to the development of quantum devices but is rarely used for nanowire-based quantum devices with InAs, InSb and SiGe instead taking the leading role. p-type GaAs nanowires offer a path to studying strongly confined 0D and 1D hole systems with strong spin–orbit effects, motivating...... our development of nanowire transistors featuring Be-doped p-type GaAs nanowires, AuBe alloy contacts and patterned local gate electrodes towards making nanowire-based quantum hole devices. We report on nanowire transistors with traditional substrate back-gates and EBL-defined metal/oxide top...

  15. Photovoltaic Properties of p-Doped GaAs Nanowire Arrays Grown on n-Type GaAs(111)B Substrate

    Science.gov (United States)

    2010-01-01

    We report on the molecular beam epitaxy growth of Au-assisted GaAs p-type-doped NW arrays on the n-type GaAs(111)B substrate and their photovoltaic properties. The samples are grown at different substrate temperature within the range from 520 to 580 °C. It is shown that the dependence of conversion efficiency on the substrate temperature has a maximum at the substrate temperature of 550 °C. For the best sample, the conversion efficiency of 1.65% and the fill factor of 25% are obtained. PMID:20672038

  16. Exciton states in GaAs δ-doped systems under magnetic fields and hydrostatic pressure

    Energy Technology Data Exchange (ETDEWEB)

    Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autónoma del Estado de Morelos, Ave. Universidad 1001, CP 62209 Cuernavaca, Morelos (Mexico); Instituto de Física, Universidad de Antioquia, AA 1226 Medellín (Colombia); Duque, C.A., E-mail: cduque@fisica.udea.edu.co [Instituto de Física, Universidad de Antioquia, AA 1226 Medellín (Colombia)

    2013-04-15

    Excitons in GaAs n-type δ-doped quantum wells are studied taking into account the effects of externally applied magnetic fields as well as of hydrostatic pressure. The one-dimensional potential profile in both the conduction and valence bands is described including Hartree effects via a Thomas–Fermi-based local density approximation. The allowed uncorrelated energy levels are calculated within the effective mass and envelope function approximations by means of an expansion over an orthogonal set of infinite well eigenfunctions and a variational method is used to obtain the exciton states. The results are presented as functions of the two-dimensional doping concentration and the magnetic field strength for zero and finite values of the hydrostatic pressure. In general, it is found that the exciton binding energy is a decreasing function of the doping-density and an increasing function of the magnetic field intensity. A comparison with recent experiments on exciton-related photoluminescence in n-type δ-doped GaAs is made.

  17. Positron deep-level transient spectroscopy in semi-insulating-GaAs using the positron velocity transient method

    International Nuclear Information System (INIS)

    Tsia, M.; Fung, S.; Beling, C.D.

    2001-01-01

    Recently a new semiconductor defect spectroscopy, namely positron deep level transient spectroscopy (PDLTS) has been proposed that combines the energy selectivity of deep level transient spectroscopy with the structural sensitivity of positron annihilation spectroscopy. This paper focuses on one variant of PDLTS, namely positron velocity PDLTS, which has no sensitivity towards vacancy defects but nevertheless is useful in studying deep levels in semi-insulators. In the present study the electric field within the depletion region of semi-insulating GaAs is monitored through the measurement of the small Doppler shift in the annihilation radiation that comes from this region as a result of positron drift. The drift is the result of an increasing electric field produced by space charge building up from ionizing deep level defects. Doppler shift transients are measured between 50-300 K. The EL2 level emission transients are clearly seen at temperatures around 300 K that yield E C -0.78±0.08eV for the energy of EL2. The EL2 electron capture rate is found to have an activation energy of 0.61±0.08eV which most probably arises from freeze out of conduction electrons. We find the surprising result that emission and capture transients can be seen at temperatures below 200 K. Possible reasons for these transients are discussed. (orig.)

  18. Lifetime studies of self-activated photoluminescence in heavily silicon-doped GaAs

    Science.gov (United States)

    Sauncy, T.; Palsule, C. P.; Holtz, M.; Gangopadhyay, S.; Massie, S.

    1996-01-01

    We report results of a detailed temperature dependence study of photoluminescence lifetime and continuous emission properties in silicon-doped GaAs. The primary focus is on a defect-related emission at 1.269 eV (T=20 K). GaAs crystals were grown using molecular-beam epitaxy with most of the experiments conducted on a sample having a carrier concentration of 4.9×1018 cm-3. The intensity is seen to decrease above 100 K, with no corresponding decrease in the measured lifetime of 9.63+/-0.25 ns. The intensity decrease implies an activation energy of 19+/-2 meV, which is approximately one order of magnitude smaller than what was previously obtained for similar defects in Czochralski-grown GaAs with other dopants. We interpret our results in terms of a configuration coordinate model and obtain a more complete picture of the energy-level structure. The experiments indicate that the upper level in the recombination process is about 20 meV below the conduction-band continuum, with the lower state approximately 300 meV above the valence band. Our results are consistent with the identification of the corresponding defect complex microstructure as being a silicon-at-gallium substitution, weakly interacting with a gallium vacancy second-nearest neighbor, known as the Si-Y defect complex.

  19. Photoluminescence of highly compensated GaAs doped with high concentration of Ge

    Science.gov (United States)

    Watanabe, Masaru; Watanabe, Akira; Suezawa, Masashi

    1999-12-01

    We have studied the photoluminescence (PL) properties of Ge-doped GaAs crystals to confirm the validity of a theory developed by Shklovskii and Efros to explain the donor-acceptor pair (DAP) recombination in potential fluctuation. GaAs crystals doped with Ge of various concentrations were grown by a liquid-encapsulated Czochralski method. They were homogenized by annealing at 1200°C for 20 h under the optimum As vapor pressure. Both quasi-continuous and time-resolved PL spectra were measured at 4.2 K. The quasi-continuous PL spectra showed that the peak position shifted to lower energy as the Ge concentration increased, which was consistent with the Shklovskii and Efros's theory. Under very strong excitation in time-resolved measurements, the exciton peak appeared within short periods after excitation and then the peak shifted to that of DAP recombination. This clearly showed that the potential fluctuation disappeared under strong excitation and then recovered as the recombination proceeded.

  20. Magnetoresistance and Curie temperature of GaAs semiconductor doped with Mn ions

    International Nuclear Information System (INIS)

    Yalishev, V.Sh.

    2006-02-01

    Key words: diluted magnetic semiconductors, magnetoresistance, ferromagnetism, ionic implantation, molecular-beam epitaxy, magnetic clusters, Curie temperature. Subjects of the inquiry: Diluted magnetic semiconductor GaAs:Mn. Aim of the inquiry: determination of the possibility of the increase of Curie temperature in diluted magnetic semiconductors based on GaAs doped with Mn magnetic impurity. Method of inquiry: superconducting quantum interference device (SQUID), Hall effect, magnetoresistance, atomic and magnetic force microscopes. The results achieved and their novelty: 1. The effect of the additional doping of Ga 0,965 Mn 0,035 As magnetic epitaxial layers by nonmagnetic impurity of Be on on the Curie temperature was revealed. 2. The exchange interaction energy in the investigated Ga 0,965 Mn 0,035 As materials was determined by the means of the magnetic impurity dispersion model from the temperature dependence of the resistivity measurements. 3. The effect of magnetic clusters dimensions and illumination on the magnetoresistance of GaAs materials containing nano-dimensional magnetic clusters was studied for the first time. Practical value: Calculated energy of the exchange interaction between local electrons of magnetic ions and free holes in Ga 1-x Mn x As magnetic semiconductors permitted to evaluate the theoretical meaning of Curie temperature depending on concentration of free holes and to compare it with experimental data. Sphere of usage: micro- and nano-electronics, solid state physics, physics of semiconductors, magnetic materials physics, spin-polarized current sources. (author)

  1. X-ray characterization Si-doped InAs nanowires grown on GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Saqib, Muhammad; Biermanns, Andreas; Pietsch, Ullrich [Universitaet Siegen, Festkoerperphysik (Germany); Grap, Thomas; Lepsa, Mihail [Forschungszentrum Juelich, Institut fuer Bio- und Nanosysteme (Germany)

    2011-07-01

    Semiconductor nanowires (NW) are of particular interest due to the ability to synthesize single-crystalline 1D epitaxial structures and heterostructures in the nanometer range. However, many details of the growth mechanism are not well understood. In particular, understanding and control of doping mechanisms during NW growth are important issues for technological applications. In this contribution we present a x-ray diffraction study of the influence of Si-doping in InAs NWs grown on GaAs(111) substrates using In-assisted MBE growth. With the help of coplanar and asymmetric x-ray diffraction, we monitor the evolution of the lattice constants and structure of the InAs NWs as function of doping concentration. We observe that increasing the nominal doping concentration leads to the appearance of additional diffraction maxima corresponding to material whose vertical lattice parameter is 1% smaller than that of the undoped nanowires. Those lattice parameters can be attributed with alloy formation in the form of island like crystallites.

  2. Microinhomogeneities in Semi-Insulating Cd(Zn)Te

    International Nuclear Information System (INIS)

    Fochuk, P.; Nykoniuk, Y.; Zakharuk, Z.; Kopach, O.; Kovalenko, N.

    2017-01-01

    Here, we investigated the temperature dependences (TDs) in the range of 290-423 K for the Hall constant R H and the Hall carrier mobility μn (σ R H ) in semi-insulating Cd 0.9 Zn 0.1 Te:In (CZT) crystals. As-grown, CZT material has nonequilibrium distributions of native and impurity-related defects. Thus, before taking any measurements, the samples were kept inside the test chamber in the dark at 423 K to reach an equilibrium state at T <; 423 K. For all the tested samples, the R H TD could be described by two activation energies. At the transitional point, the TD of the carrier mobility also changes from “normal” at high temperatures to “exponential” at low temperatures. The latter is a result of the collective effect of drift barriers due to microinhomogeneity. Therefore, only the high-temperature activation energies can be assigned to the ionization energies of the compensated deep donors (ε D ). For different samples, the values for ε D 0 (at absolute zero) were found to be in the range of 0.50-0.78 eV, and the degree of donor compensation [D + ]/[D] is between 0.3 and 0.98. The low-temperature region, where there are strong effects of crystal microinhomogeneities, cannot be used to characterize the ionization energy of donors. Therefore, we describe the activation energy as ε 1 = ε D - αε b , where ε b is the drift barrier height found from the TD of the carrier mobility and α takes a value close to unity. Values of ε b for our studied samples lie within (0.05-0.35) eV.

  3. Impact of substrate temperature on the incorporation of carbon-related defects and mechanism for semi-insulating behavior in GaN grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Armstrong, A.; Poblenz, C.; Green, D.S.; Mishra, U.K.; Speck, J.S.; Ringel, S.A.

    2006-01-01

    The electrical conductivity and deep level spectrum of GaN grown by molecular beam epitaxy and codoped with carbon and silicon were investigated for substrate temperatures T s of 650 and 720 deg. C as a function relative carbon and silicon doping levels. With sufficiently high carbon doping, semi-insulating behavior was observed for films grown at both temperatures, and growth at T s =720 deg. C enhanced the carbon compensation ratio. Similar carbon-related band gap states were observed via deep level optical spectroscopy for films grown at both substrate temperatures. Due to the semi-insulating nature of the films, a lighted capacitance-voltage technique was required to determine individual deep level concentrations. Carbon-related band gap states underwent substantial redistribution between deep level and shallow acceptor configurations with change in T s . In light of a T s dependence for the preferential site of carbon incorporation, a model of semi-insulating behavior in terms of carbon impurity state incorporation mediated by substrate temperature is proposed

  4. n-Type Doping and Morphology of GaAs Nanowires in Aerotaxy

    Energy Technology Data Exchange (ETDEWEB)

    Metaferia, Wondwosen [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Sivakumar, Sudhakar [Lund University; Persson, Axel R. [Lund University; Geijselaers, Irene [Lund University; Wallenberg, L. Reine [Lund University; Deppert, Knut [Lund University; Samuelson, Lars [Lund University; Magnusson, Martin [Lund University

    2018-04-17

    Controlled doping in semiconductor nanowires modifies their electrical and optical properties, which are important for high efficiency optoelectronic devices. We have grown n-type (Sn) doped GaAs nanowires in Aerotaxy, a new continuous gas phase mass production technique. The morphology of Sn doped nanowires is found to be a strong function of dopant, tetraethyltin to trimethylgallium flow ratio, Au-Ga-Sn alloying, and nanowire growth temperatures. High temperature and high flow ratios result in low morphological quality nanowires and in parasitic growth on the wire base and surface. Alloying and growth temperatures of 400 and 530 degrees C, respectively, resulted in good morphological quality nanowires for a flow ratio of TESn to TMGa up to 2.25 x 10-3. The wires are pure Zinc-blende for all investigated growth conditions, whereas nanowires grown by MOVPE with the same growth conditions are usually mainly Wurtzite. The growth rate of the doped wires is found to be dependent more on the TESn flow fraction than on alloying and nanowire growth temperatures. Our photoluminescence measurements, supported by four-point probe resistivity measurements, reveal that the carrier concentration in the doped wires varies only slightly (1- 3) x 1019 cm-3 with TESn flow fraction and both alloying and growth temperatures, indicating that good morphological quality wires with high carrier density can be grown with low TESn flow. Carrier concentrations lower than 1019 cm-3 can be grown by further reducing the flow fraction of TESn, which may give better morphology wires.

  5. Atomistic spin dynamics simulations on Mn-doped GaAs and CuMn

    Energy Technology Data Exchange (ETDEWEB)

    Hellsvik, Johan, E-mail: johan.hellsvik@fysik.uu.s [Department of Physics and Materials Science, Uppsala University, Box 530, SE-751 21 Uppsala (Sweden)

    2010-01-01

    The magnetic dynamical behavior of two random alloys have been investigated in atomistic spin dynamics (ASD) simulations. For both materials, magnetic exchange parameters calculated with first principles electronic structure methods were used. From experiments it is well known that CuMn is a highly frustrated magnetic system and a good manifestation of a Heisenberg spin glass. In our ASD simulations the behavior of the autocorrelation function indicate spin glass behavior. The diluted magnetic semiconductor (DMS) Mn-doped GaAs is engineered with hopes of high enough Curie temperatures to operate in spintronic devices. Impurities such as As antisites and Mn interstitials change the exhange couplings from being mainly ferromagnetic to also have antiferromagnetic components. We explore how the resulting frustration affects the magnetization dynamics for a varying rate of As antisites.

  6. Reflectance-difference spectroscopy as an optical probe for in situ determination of doping levels in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Lastras-Martinez, A.; Lara-Velazquez, I.; Balderas-Navarro, R.E.; Ortega-Gallegos, J.; Guel-Sandoval, S.; Lastras-Martinez, L.F. [Instituto de Investigacion en Comunicacion Optica, Universidad Autonoma de San Luis Potosi, Alvaro Obregon 64, San Luis Potosi, SLP 78000 (Mexico)

    2008-07-01

    We report on in situ Reflectance Difference Spectroscopy measurements carried out on GaAs(001). Measurements were performed at temperatures of 580 C and 430 C, in both n and p-type doped films and for both (2 x 4) and c(4 x 4) reconstructions. Samples employed were grown by Molecular Beam Epitaxy with doping levels in the range from 10{sup 16}-10{sup 19} cm{sup -3}. We demonstrate the potential of Reflectance Difference Spectroscopy for impurity level determinations under growth conditions. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Specific features of the photoconductivity of semi-insulating cadmium telluride

    Energy Technology Data Exchange (ETDEWEB)

    Golubyatnikov, V. A.; Grigor’ev, F. I.; Lysenko, A. P., E-mail: aplysenko@hse.ru; Strogankova, N. I.; Shadov, M. B. [National Research University Higher School of Economics, Moscow Institute of Electronics and Mathematics (Russian Federation); Belov, A. G. [OAO GIREDMET State Research and Design Institute of the Rare-Metal Industry (Russian Federation)

    2014-12-15

    The effect of local illumination providing a high level of free-carrier injection on the conductivity of a sample of semi-insulating cadmium telluride and on the properties of ohmic contacts to the sample is studied. It is found that, irrespective of the illumination region, the contact resistance of ohmic contacts decreases and the concentration of majority carriers in the sample grows in proportion to the illumination intensity. It is shown that inherent heterogeneities in crystals of semi-insulating semiconductors can be studied by scanning with a light probe.

  8. Emission of circularly polarized recombination radiation from p-doped GaAs and GaAs0.62P0.38 under the impact of polarized electrons

    International Nuclear Information System (INIS)

    Fromme, B.; Baum, G.; Goeckel, D.; Raith, W.

    1989-01-01

    Circularly polarized light is emitted in radiative transitions of polarized electrons from the conduction to the valence band in GaAs or GaAs 1-x P x crystals. The degree of light polarization is directly related to the polarization of the conduction-band electrons at the instant of recombination and allows conclusions about the depolarization of electrons in the conduction band. The depolarization is caused by spin-relaxation processes. The efficiency of these processes depends on crystal type, crystal temperature, degree of doping, and kinetic energy of the electrons. Highly p-doped GaAs and GaAs 0.62 P 0.38 crystals (N A >1x10 19 atoms/cm 3 ) were bombarded with polarized electrons (initial polarization 38%), and the spectral distribution and the circular polarization of the emitted recombination radiation were measured. The initial kinetic energy of the electrons in the conduction band was varied between 5 and 1000 eV. The measurements of the spectral distribution show that the electrons are thermalized before recombination occurs, independent of their initial energy. An important thermalization process in this energy range is the excitation of crystal electrons by electron-hole pair creation. The circular polarization of the recombination radiation lies below 1% in the whole energy range. It decreases with increasing electron energy but is still of measurable magnitude at 100 eV in the case of GaAs 0.62 P 0.38 . The circular polarization is smaller for GaAs than for GaAs 0.62 P 0.38 , which we attribute to more efficient spin relaxation in GaAs

  9. Radial space-charge-limited electron flow in semi-insulating GaN:Fe

    Czech Academy of Sciences Publication Activity Database

    Mareš, Jiří J.; Hubík, Pavel; Krištofik, Jozef; Prušáková, Lucie; Uxa, Štěpán; Paskova, T.; Evans, K.

    2011-01-01

    Roč. 110, č. 1 (2011), 013723/1-013723/6 ISSN 0021-8979 R&D Projects: GA ČR GAP204/10/0212 Institutional research plan: CEZ:AV0Z10100521 Keywords : gallium nitride * semi-insulator * space-charge-limited current Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.168, year: 2011

  10. Low-energy particle treatment of GaAs surface

    International Nuclear Information System (INIS)

    Pincik, E.; Ivanco, J.; Brunner, R.; Jergel, M.; Falcony, C.; Ortega, L.; Kucera, J. M.

    2002-01-01

    The paper presents results of a complex study of surface properties of high-doped (2x10 18 cm -3 ) and semi-insulating GaAs after an interaction with the particles coming from low-energy ion sources such as RF plasma and ion beams. The virgin samples were mechano-chemically polished liquid-encapsulated Czochralski-grown GaAs (100) oriented wafers. The crystals were mounted on the grounded electrode (holder). The mixture Ar+H 2 as well as O 2 and CF 4 were used as working gases: In addition, a combination of two different in-situ exposures was applied, such as e.g. hydrogen and oxygen. Structural, electrical and optical properties of the exposed surfaces were investigated using X-ray diffraction at grazing incidence, quasi-static and high-frequency C-V curve measurements, deep-level transient spectroscopy, photo-reflectance, and photoluminescence. Plasma and ion beam exposures were performed in a commercial RF capacitively coupled plasma equipment SECON XPL-200P and a commercial LPAI device, respectively. The evolution of surface properties as a function of the pressure of working gas and the duration of exposure was observed. (Authors)

  11. Electron-spin dynamics in Mn-doped GaAs using time-resolved magneto-optical techniques

    Science.gov (United States)

    Akimov, I. A.; Dzhioev, R. I.; Korenev, V. L.; Kusrayev, Yu. G.; Zhukov, E. A.; Yakovlev, D. R.; Bayer, M.

    2009-08-01

    We study the electron-spin dynamics in p -type GaAs doped with magnetic Mn acceptors by means of time-resolved pump-probe and photoluminescence techniques. Measurements in transverse magnetic fields show a long spin-relaxation time of 20 ns that can be uniquely related to electrons. Application of weak longitudinal magnetic fields above 100 mT extends the spin-relaxation times up to microseconds which is explained by suppression of the Bir-Aronov-Pikus spin relaxation for the electron on the Mn acceptor.

  12. Optical and electrical properties of vanadium-doped GaAs

    International Nuclear Information System (INIS)

    Ulrici, W.; Friedland, K.

    1985-01-01

    The results of optical absorption, luminescence, and temperature-dependent Hall-effect measurements on GaAs:V, p-type GaAs:V:Zn, and n-type GaAs:V:Si grown by LEC-technique are reported. It is found that the V/sub Ga//sup 3+/ ground state is located very close to or within the valence band and that the V/sub Ga//sup 2+/ acceptor level is at E/sub c/ - 0.14 eV. The near mid-gap level in GaAs:V responsible for its semi-insulating behaviour is proposed to be due to the complex (V/sub Ga//sup 2+/-X), where the correlation between the photoionization absorption connected with this centre and the EL2 concentration suggests that X is an arsenic vacancy. From this level scheme conditions for growing GaAs:V which is semi-insulating at room temperature are derived. The optical experiments on GaAs:V with different Fermi-level positions confirm the assignment of the triple-peaked absorption band at 1.1 eV to the 3 A 2 → 3 T 1 (F) transition of V/sub Ga//sup 3+/. The weak absorption due to the 3 A 2 → 3 T 2 (F) transition is found at 0.79 eV. The analysis of the temperature dependence of the line shape of the → 3 T 1 (F) absorption band as due to strong dynamical Txtau 2 Jahn-Teller effect provides the JT-parameters E/sub JT/ = 780 cm -1 , h/2ω/sub tau/ = 75 cm -1 , and c = 4.7 eV/nm. The temperature dependent asymmetry of the line shape is explained on the basis of earlier theoretical predictions of the simultaneous action of strong linear and quadratic JT-coupling. (author)

  13. Magnetic properties of zigzag (0,9 GaAs nanotube doped with 3d transition metals

    Directory of Open Access Journals (Sweden)

    R Fathi

    2016-06-01

    Full Text Available of 3d transition metals (Sc, Ti, Cr, Mn , Fe, Co, Ni in both far and close situations were studied based on spin polarised density functional theory using the generalized gradient approximation (LDA with SIESTA code. The electronic structures show that zigzag (0,9 GaAs nanotubes are non-magnetic semiconductors with direct band gap. It was revealed that doping of 11.11 % Fe and Mn concentrations substituted in Ga sites in ferromagnetic phase in far situation and Cr sites in ferromagnetic phase in near situation introduces half metallic behavior with %100 spin polarization. The unique structure of spin polarised energy levels is primarily attributed to strong hybridization of 3d transition metal and its nearest-neighbor As-4p orbitals. The results of this study can be useful for empirical studies on diluted magnetic semiconductors (DMSs and systemic investigation in 3d transitional metals. We suggest that GaAs nanotubes doped by transition metals would have a potential application as a spin polarised electron source for spintronic devices in the future.

  14. Strong coupling between bi-dimensional electron gas and nitrogen localized states in heavily doped GaAs1-xN x structures

    International Nuclear Information System (INIS)

    Hamdouni, A.; Bousbih, F.; Ben Bouzid, S.; Oueslati, M.; Chtourou, R.; Harmand, J.C.

    2005-01-01

    We report a low-temperature photoluminescence spectra (LTPL) of GaAs 1-x N x layers and two-dimension electron gas (2DEG) GaAs 1-x N x /AlGaAs modulation doped heterostructure grown on GaAs substrates by molecular beam epitaxy (MBE) with low nitrogen content [N] = 2 x 10 18 cm -3 . At low temperature, PL spectra of GaAs 1-x N x layers are governed by several features associate to the excitons bound to nitrogen complexes, these features disappear in (2DEG) GaAs 1-x N x /AlGaAs modulation doped heterostructure and the PL peak energy decrease with the laser power excitation. This effect is explained by the strongly coupling of the (2DEG) fundamental state with the nitrogen localized states. An activated energy of about 55 meV is deduced by photoluminescence measurements in the 10-300 K range for a laser power excitation P = 6 W/cm 2

  15. First-principles electronic structure of Mn-doped GaAs, GaP, and GaN semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Schulthess, T C [Computer Science and Mathematics Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6164 (United States); Temmerman, W M [Daresbury Laboratory, Daresbury, Warrington WA4 4AD (United Kingdom); Szotek, Z [Daresbury Laboratory, Daresbury, Warrington WA4 4AD (United Kingdom); Svane, A [Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark); Petit, L [Computer Science and Mathematics Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6164 (United States)

    2007-04-23

    We present first-principles electronic structure calculations of Mn-doped III-V semiconductors based on the local spin-density approximation (LSDA) as well as the self-interaction corrected local spin-density method (SIC-LSD). We find that it is crucial to use a self-interaction free approach to properly describe the electronic ground state. The SIC-LSD calculations predict the proper electronic ground state configuration for Mn in GaAs, GaP, and GaN. Excellent quantitative agreement with experiment is found for the magnetic moment and p-d exchange in (GaMn)As. These results allow us to validate commonly used models for magnetic semiconductors. Furthermore, we discuss the delicate problem of extracting binding energies of localized levels from density functional theory calculations. We propose three approaches to take into account final state effects to estimate the binding energies of the Mn d levels in GaAs. We find good agreement between computed values and estimates from photoemission experiments.

  16. First-principles electronic structure of Mn-doped GaAs, GaP, and GaN semiconductors

    International Nuclear Information System (INIS)

    Schulthess, T C; Temmerman, W M; Szotek, Z; Svane, A; Petit, L

    2007-01-01

    We present first-principles electronic structure calculations of Mn-doped III-V semiconductors based on the local spin-density approximation (LSDA) as well as the self-interaction corrected local spin-density method (SIC-LSD). We find that it is crucial to use a self-interaction free approach to properly describe the electronic ground state. The SIC-LSD calculations predict the proper electronic ground state configuration for Mn in GaAs, GaP, and GaN. Excellent quantitative agreement with experiment is found for the magnetic moment and p-d exchange in (GaMn)As. These results allow us to validate commonly used models for magnetic semiconductors. Furthermore, we discuss the delicate problem of extracting binding energies of localized levels from density functional theory calculations. We propose three approaches to take into account final state effects to estimate the binding energies of the Mn d levels in GaAs. We find good agreement between computed values and estimates from photoemission experiments

  17. Current-induced spin polarization in InGaAs and GaAs epilayers with varying doping densities

    Science.gov (United States)

    Luengo-Kovac, M.; Huang, S.; Del Gaudio, D.; Occena, J.; Goldman, R. S.; Raimondi, R.; Sih, V.

    2017-11-01

    The current-induced spin polarization and momentum-dependent spin-orbit field were measured in InxGa1 -xAs epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the extrinsic contributions to the spin-polarization mechanism must be considered. Theoretical calculations based on a model that includes extrinsic contributions to the spin dephasing and the spin Hall effect, in addition to the intrinsic Rashba and Dresselhaus spin-orbit coupling, are found to reproduce the experimental finding that the crystal direction with the smaller net spin-orbit field has larger electrical spin generation efficiency and are used to predict how sample parameters affect the magnitude of the current-induced spin polarization.

  18. Field control of anisotropic spin transport and spin helix dynamics in a modulation-doped GaAs quantum well

    Science.gov (United States)

    Anghel, S.; Passmann, F.; Singh, A.; Ruppert, C.; Poshakinskiy, A. V.; Tarasenko, S. A.; Moore, J. N.; Yusa, G.; Mano, T.; Noda, T.; Li, X.; Bristow, A. D.; Betz, M.

    2018-03-01

    Electron spin transport and dynamics are investigated in a single, high-mobility, modulation-doped, GaAs quantum well using ultrafast two-color Kerr-rotation microspectroscopy, supported by qualitative kinetic theory simulations of spin diffusion and transport. Evolution of the spins is governed by the Dresselhaus bulk and Rashba structural inversion asymmetries, which manifest as an effective magnetic field that can be extracted directly from the experimental coherent spin precession. A spin-precession length λSOI is defined as one complete precession in the effective magnetic field. It is observed that application of (i) an out-of-plane electric field changes the spin decay time and λSOI through the Rashba component of the spin-orbit coupling, (ii) an in-plane magnetic field allows for extraction of the Dresselhaus and Rashba parameters, and (iii) an in-plane electric field markedly modifies both the λSOI and diffusion coefficient.

  19. Equivalent Method of Solving Quantum Efficiency of Reflection-Mode Exponential Doping GaAs Photocathode

    International Nuclear Information System (INIS)

    Jun, Niu; Zhi, Yang; Ben-Kang, Chang

    2009-01-01

    The mathematical expression of the electron diffusion and drift length L DE of exponential doping photocathode is deduced. In the quantum efficiency equation of the reffection-mode uniform doping cathode, substituting L DE for L D , the equivalent quantum efficiency equation of the reffection-mode exponential doping cathode is obtained. By using the equivalent equation, theoretical simulation and experimental analysis shows that the equivalent index formula and formula-doped cathode quantum efficiency results in line. The equivalent equation avoids complicated calculation, thereby simplifies the process of solving the quantum efficiency of exponential doping photocathode

  20. Determination of deep-level impurities and their effects on the small-single and LF noise properties of ion-implanted GaAs MESFETs

    International Nuclear Information System (INIS)

    Sriram, S.; Kim, B.; Ghosh, P.K.; Das, M.B.; Pennsylvania State Univ., University Park; Pennsylvania State Univ., University Park

    1982-01-01

    A large number of deep levels, with energies ranging from Esub(c)-0.19eV to Esub(c)-0.9eV, have been identified and characterized using ion-implanted MESFET's on undoped and Cr-doped LEC-grown semi-insulating GaAs substrates. Measurement techniques used include deep level transient (DLTS) and steady state spectroscopic (DLSS) methods. Large capture cross-section values are obtained for levels below Esub(c)-0.5eV, possibly due to high electric field. Spectral densities of LF noise with distinct bulges have been shown to be related to deep levels. In some samples, natural deep level related oscillations have been observed and their ionization energies have been determined. (author)

  1. Electrical characterisation of Sn doped InAs grown by MOVPE

    International Nuclear Information System (INIS)

    Shamba, P.; Botha, L.; Krug, T.; Venter, A.; Botha, J.R.

    2008-01-01

    The feasibility of tetraethyl tin (TESn) as an n-type dopant for InAs is investigated. The electrical properties of Sn doped InAs films grown on semi-insulating GaAs substrates by MOVPE are extensively studied as a function of substrate temperature, V/III ratio, substrate orientation and TESn flow rate. Results from this study show that Sn concentrations can be controlled over 2 orders of magnitude. The Sn doped InAs layers exhibit carrier concentrations between 2.7 x 10 17 and 4.7 x 10 19 cm -3 with 77 K mobilities ranging from 12 000 to 1300 cm 2 /Vs. Furthermore, the influence of the variation of these parameters on the structural properties of InAs are also reported. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  2. Variations in first principles calculated defect energies in GaAs and ...

    Indian Academy of Sciences (India)

    Keywords. Ab initio calculations; semi-insulating GaAs; point defects. ... We are focusing on gallium arsenide. .... gallium vacancy in S & L, P et al and N & Z will exist in triple ... gallium antisite defect that include relaxation, a negative. U-effect is ...

  3. The X-ray sensitivity of semi-insulating polycrystalline CdZnTe thick films

    International Nuclear Information System (INIS)

    Won, Jae Ho; Kim, Ki Hyun; Suh, Jong Hee; Cho, Shin Hang; Cho, Pyong Kon; Hong, Jin Ki; Kim, Sun Ung

    2008-01-01

    The X-ray sensitivity is one of the important parameters indicating the detector performance. The X-ray sensitivity of semi-insulating polycrystalline CdZnTe:Cl thick films was investigated as a function of electric field, mean photon energy, film thickness, and charge carrier transport parameters and, compared with another promising detector materials. The X-ray sensitivities of the polycrystalline CdZnTe films with 350 μm thickness were about 2.2 and 6.2 μC/cm 2 /R in the ohmic-type and Schottky-type detector at 0.83 V/μm, respectively

  4. Selfsimilar and fractal analysis of n-type delta-doped quasiregular GaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    García-Cervantes, H.; Rodríguez-Vargas, I. [Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad Esquina Con Paseo La Bufa S/N, 98060 Zacatecas, Zac. (Mexico)

    2014-05-15

    We study the electronic structure of n-type delta-doped quantum wells in GaAs in which the multiple well system is built according to the Fibonacci sequence. The building blocks A and B correspond to delta-doped wells with impurities densities n{sub 2DA} and n{sub 2DB}, and the same well width. The Thomas-Fermi approximation, the semi-empirical sp{sub 3}s* tight-binding model including spin, the Surface Green Function Matching method and the Transfer Matrix approach were implemented to obtain the confining potential, the electronic structure and the selfsimilarity of the spectrum. The fragmentation of the electronic spectra is observed whenever the building blocks A and B interact and it increases as the difference of impurities density between A and B increases as well. The wave function of the first sate of the fragmented bands presents critical characteristics, this is, it is not a localized state nor a extended one as well as it has selfsimilar features. So, the quasiregular characteristics are preserved irrespective of the complexity of the system and can affect the performance of devices based on these structures.

  5. Selfsimilar and fractal analysis of n-type delta-doped quasiregular GaAs quantum wells

    International Nuclear Information System (INIS)

    García-Cervantes, H.; Rodríguez-Vargas, I.

    2014-01-01

    We study the electronic structure of n-type delta-doped quantum wells in GaAs in which the multiple well system is built according to the Fibonacci sequence. The building blocks A and B correspond to delta-doped wells with impurities densities n 2DA and n 2DB , and the same well width. The Thomas-Fermi approximation, the semi-empirical sp 3 s* tight-binding model including spin, the Surface Green Function Matching method and the Transfer Matrix approach were implemented to obtain the confining potential, the electronic structure and the selfsimilarity of the spectrum. The fragmentation of the electronic spectra is observed whenever the building blocks A and B interact and it increases as the difference of impurities density between A and B increases as well. The wave function of the first sate of the fragmented bands presents critical characteristics, this is, it is not a localized state nor a extended one as well as it has selfsimilar features. So, the quasiregular characteristics are preserved irrespective of the complexity of the system and can affect the performance of devices based on these structures

  6. Low defect densities in molecular beam epitaxial GaAs achieved by isoelectronic In doping

    Science.gov (United States)

    Bhattacharya, P. K.; Dhar, S.; Berger, P.; Juang, F.-Y.

    1986-01-01

    A study has been made of the effects of adding small amounts of In (0.2-1.2 pct) to GaAs grown by molecular beam epitaxy. The density of four electron traps decreases in concentration by an order of magnitude, and the peak intensities of prominent emissions in the excitonic spectra are reduced with increase in In content. Based on the higher surface migration rate of In, compared to Ga, at the growth temperatures it is apparent that the traps and the excitonic transitions are related to point defects. This agrees with earlier observations by Briones and Collins (1982) and Skromme et al. (1985).

  7. Effect of post-growth annealing on secondary phase formation in low-temperature-grown Mn-doped GaAs

    DEFF Research Database (Denmark)

    Kovács, A.; Sadowski, J.; Kasama, Takeshi

    2013-01-01

    The microstructures of annealed GaAs layers containing 0.1%, 0.5% and 2% Mn are studied using aberration-corrected transmission electron microscopy (TEM). The layers were grown by molecular beam epitaxy at 270 °C. After heat treatment at 400, 560 and 630 °C, they are found to contain precipitate...... in annealed GaMnAs layers doped with low Mn concentrations is proposed....

  8. Identification of defects in undoped semi-insulating InP by positron lifetime

    International Nuclear Information System (INIS)

    Mao Weidong; Wang Shaojie; Wang Zhu

    2001-01-01

    Positron lifetime measurements, carried out over the temperature range of 10-300 K, have been used to investigate defects in two undoped semi-insulating InP samples. The positron lifetime spectra were analysed by both PATFIT and MELT techniques. The results at room temperature reveal a positron lifetime of around 273 ps, which is associated with indium vacancies V In or V In -hydrogen complexes. The positron average lifetime is temperature dependent and decreases with increasing temperature at the beginning (≤ 80 K and ≤ 120 K), and then remains unchanged, which is attributed to the influence of negative vacancies and detrapping of the positron from those negative ions of Mg, Zn, Ag and Ca with ionization level (1-)

  9. Analysis and comparison of the breakdown performance of semi- insulator and dielectric passivated Si strip detectors

    CERN Document Server

    Ranjan, Kirti; Chatterji, S; Srivastava-Ajay, K; Shivpuri, R K

    2002-01-01

    The harsh radiation environment in future high-energy physics (HEP) experiments like LHC provides a challenging task to the performance of Si microstrip detectors. Normal operating condition for silicon detectors in HEP experiments are in most cases not as favourable as for experiments in nuclear physics. In HEP experiments the detector may be exposed to moisture and other adverse atmospheric environment. It is therefore utmost important to protect the sensitive surfaces against such poisonous effects. These instabilities can be nearly eliminated and the performance of Si detectors can be improved by implementing suitably passivated metal-overhang structures. This paper presents the influence of the relative permittivity of the passivant on the breakdown performance of the Si detectors using computer simulations. The semi-insulator and the dielectric passivated metal-overhang structures are compared under optimal conditions. The influence of various parameters such as passivation layer thickness, junction dep...

  10. Two-photon spin-polarization spectroscopy in silicon-doped GaAs.

    Science.gov (United States)

    Miah, M Idrish

    2009-05-14

    We generate spin-polarized electrons in bulk GaAs using circularly polarized two-photon pumping with excess photon energy (DeltaE) and detect them by probing the spin-dependent transmission of the sample. The spin polarization of conduction band electrons is measured and is found to be strongly dependent on DeltaE. The initial polarization, pumped with DeltaE=100 meV, at liquid helium temperature is estimated to be approximately 49.5%, which is very close to the theoretical value (50%) permitted by the optical selection rules governing transitions from heavy-hole and light-hole states to conduction band states in a bulk sample. However, the polarization pumped with larger DeltaE decreases rapidly because of the exciting carriers from the split-off band.

  11. LEC- and VGF-growth of SI GaAs single crystals—recent developments and current issues

    Science.gov (United States)

    Jurisch, M.; Börner, F.; Bünger, Th.; Eichler, St.; Flade, T.; Kretzer, U.; Köhler, A.; Stenzenberger, J.; Weinert, B.

    2005-02-01

    The paper reviews the progress made in crystal growth of semi-insulating GaAs by liquid encapsulation Czochralski and vertical gradient freeze techniques during the last few years under the continuous need for cost reduction of the production process.

  12. Heat load of a P-doped GaAs photocathode in SRF electron gun

    International Nuclear Information System (INIS)

    Wang, E.; Ben-Zvi, I.; Kewisch, J.; Burrill, A.; Rao, T.; Wu, Q.; Jain, A.; Gupta, R.; Holmes, D.

    2010-01-01

    Many efforts were made over the last decades to develop a better polarized electron source for the high energy physics. Several laboratories operate DC guns with the Gallium-Arsenide photo-cathode, which yield a highly polarized electron beam. However, the beam's emittance might well be improved using a Superconducting RF electron gun, which delivers beams of higher brightness than DC guns does, because the field gradient at the cathode is higher. SRF guns with metal cathodes and CsTe cathodes have been tested successfully. To produce polarized electrons, a Gallium-Arsenide photo-cathode must be used: an experiment to do so in a superconducting RF gun is under way at BNL. Since the cathode will be normal conducting, the problem about the heat load stemming from the cathode arises. We present our measurements of the electrical resistance of GaAs at cryogenic temperatures, a prediction of the heat load and the verification by measuring the quality factor of the gun with and without cathode.

  13. Germanium diffusion with vapor-phase GeAs and oxygen co-incorporation in GaAs

    Science.gov (United States)

    Wang, Wei-Fu; Cheng, Kai-Yuan; Hsieh, Kuang-Chien

    2018-01-01

    Vapor-phase germanium diffusion has been demonstrated in Zn-doped and semi-insulating GaAs in sealed ampoules with GeAs powders and excess arsenic. Secondary-ion-mass spectroscopy (SIMS) profiles indicate the presence of unintentional co-incorporation of oxygen in high densities (>1017/cm3) along with diffused germanium donors whose concentration (>>1018/cm3) determined by electro-chemical capacitance-voltage (ECV) profiler shows significant compensation near the surface. The source of oxygen mainly originates from the GeAs powder which contains Ge-O surface oxides. Variable-temperature photoluminescence (PL) shows that in GeAs-diffused samples, a broad peak ranging from 0.86-1.38 eV with the peak position around 1.1 eV predominates at low temperatures while the near band-edge luminescence quenches. The broad band is attributed to the GeGa-VGa self-activated (SA) centers possibly associated with nearby oxygen-related defect complex, and its luminescence persists up to 400 K. The configurational-coordinate modeling finds that the SA defect complex has a thermal activation energy of 150-180 meV and a vibrational energy 26.8 meV. The presence of oxygen does not much affect the SA emission intensity but may have influenced the peak position, vibration frequency and activation energy as compared to other common donor-VGa defects in GaAs.

  14. Germanium diffusion with vapor-phase GeAs and oxygen co-incorporation in GaAs

    Directory of Open Access Journals (Sweden)

    Wei-Fu Wang

    2018-01-01

    Full Text Available Vapor-phase germanium diffusion has been demonstrated in Zn-doped and semi-insulating GaAs in sealed ampoules with GeAs powders and excess arsenic. Secondary-ion-mass spectroscopy (SIMS profiles indicate the presence of unintentional co-incorporation of oxygen in high densities (>1017/cm3 along with diffused germanium donors whose concentration (>>1018/cm3 determined by electro-chemical capacitance-voltage (ECV profiler shows significant compensation near the surface. The source of oxygen mainly originates from the GeAs powder which contains Ge-O surface oxides. Variable-temperature photoluminescence (PL shows that in GeAs-diffused samples, a broad peak ranging from 0.86-1.38 eV with the peak position around 1.1 eV predominates at low temperatures while the near band-edge luminescence quenches. The broad band is attributed to the GeGa-VGa self-activated (SA centers possibly associated with nearby oxygen-related defect complex, and its luminescence persists up to 400 K. The configurational-coordinate modeling finds that the SA defect complex has a thermal activation energy of 150-180 meV and a vibrational energy 26.8 meV. The presence of oxygen does not much affect the SA emission intensity but may have influenced the peak position, vibration frequency and activation energy as compared to other common donor-VGa defects in GaAs.

  15. The correlation of the results of capacitance mapping and of sheet resistance mapping in semi-insulating 6H-SiC

    International Nuclear Information System (INIS)

    Lin Shenghuang; Chen Zhiming; Liang Peng; Jiang Dong; Xie Huajie; Yang Ying

    2010-01-01

    A combination of complex surface capacitance mapping and sheet resistance mapping is applied to establish the origin of resistance variations on semi-insulating (SI) 6H-SiC substrates. The direct correlation between the capacitance quadrature and the sheet resistance is found in vanadium-doped SI samples. Regions with low capacitance quadrature show high sheet resistance. This indicates, associated with the nonhomogeneity of sheet resistance on the substrate, that the quality of crystallization is not good enough, which also leads to resistivity nonhomogeneity when comparing with different types of deep defects. According to the capacitance mapping, the region with bad crystallization quality has a high radio absorption coefficient. Another correlation is established between the capacitance in-phase and sheet resistance for the vanadium-doped sample. In this sample, the capacitance in-phase map shows not only the surface topography, but also the same distribution trend as the sheet resistance, namely, regions of high capacitance in-phase reveal high sheet resistance.

  16. Transparency of Semi-Insulating, n-Type, and p-Type Ammonothermal GaN Substrates in the Near-Infrared, Mid-Infrared, and THz Spectral Range

    Directory of Open Access Journals (Sweden)

    Robert Kucharski

    2017-06-01

    Full Text Available GaN substrates grown by the ammonothermal method are analyzed by Fast Fourier Transformation Spectroscopy in order to study the impact of doping (both n- and p-type on their transparency in the near-infrared, mid-infrared, and terahertz spectral range. It is shown that the introduction of dopants causes a decrease in transparency of GaN substrates in a broad spectral range which is attributed to absorption on free carriers (n-type samples or dopant ionization (p-type samples. In the mid-infrared the transparency cut-off, which for a semi-insulating GaN is at ~7 µm due to an absorption on a second harmonic of optical phonons, shifts towards shorter wavelengths due to an absorption on free carriers up to ~1 µm at n ~ 1020 cm−3 doping level. Moreover, a semi-insulating GaN crystal shows good transparency in the 1–10 THz range, while for n-and p-type crystal, the transparency in this spectral region is significantly quenched below 1%. In addition, it is shown that in the visible spectral region n-type GaN substrates with a carrier concentration below 1018 cm−3 are highly transparent with the absorption coefficient below 3 cm−1 at 450 nm, a satisfactory condition for light emitting diodes and laser diodes operating in this spectral range.

  17. Suppression of Electron Spin Relaxation in Mn-Doped GaAs

    Science.gov (United States)

    Astakhov, G. V.; Dzhioev, R. I.; Kavokin, K. V.; Korenev, V. L.; Lazarev, M. V.; Tkachuk, M. N.; Kusrayev, Yu. G.; Kiessling, T.; Ossau, W.; Molenkamp, L. W.

    2008-08-01

    We report a surprisingly long spin relaxation time of electrons in Mn-doped p-GaAs. The spin relaxation time scales with the optical pumping and increases from 12 ns in the dark to 160 ns upon saturation. This behavior is associated with the difference in spin relaxation rates of electrons precessing in the fluctuating fields of ionized or neutral Mn acceptors, respectively. For the latter, the antiferromagnetic exchange interaction between a Mn ion and a bound hole results in a partial compensation of these fluctuating fields, leading to the enhanced spin memory.

  18. Ion-beam doping of GaAs with low-energy (100 eV) C + using combined ion-beam and molecular-beam epitaxy

    Science.gov (United States)

    Iida, Tsutomu; Makita, Yunosuke; Kimura, Shinji; Winter, Stefan; Yamada, Akimasa; Fons, Paul; Uekusa, Shin-ichiro

    1995-01-01

    A combined ion-beam and molecular-beam-epitaxy (CIBMBE) system has been developed. This system consists of an ion implanter capable of producing ions in the energy range of 30 eV-30 keV and conventional solid-source MBE. As a successful application of CIBMBE, low-energy (100 eV) carbon ion (C+) irradiation during MBE growth of GaAs was carried out at substrate temperatures Tg between 500 and 590 °C. C+-doped layers were characterized by low-temperature (2 K) photoluminescence (PL), Raman scattering, and van der Pauw measurements. PL spectra of undoped GaAs grown by CIBMBE revealed that unintentional impurity incorporation into the epilayer is extremely small and precise doping effects are observable. CAs acceptor-related emissions such as ``g,'' [g-g], and [g-g]β are observed and their spectra are significantly changed with increasing C+ beam current density Ic. PL measurements showed that C atoms were efficiently incorporated during MBE growth by CIBMBE and were optically well activated as an acceptor in the as-grown condition even for Tg as low as 500 °C. Raman measurement showed negligible lattice damage of the epilayer bombarded with 100 eV C+ with no subsequent heat treatment. These results indicate that contamination- and damage-free impurity doping without postgrowth annealing can be achieved by the CIBMBE method.

  19. Ion-beam doping of GaAs with low-energy (100 eV) C(+) using combined ion-beam and molecular-beam epitaxy

    Science.gov (United States)

    Lida, Tsutomu; Makita, Yunosuke; Kimura, Shinji; Winter, Stefan; Yamada, Akimasa; Fons, Paul; Uekusa, Shin-Ichiro

    1995-01-01

    A combined ion-beam and molecular-beam-epitaxy (CIBMBE) system has been developed. This system consists of an ion implanter capable of producing ions in the energy range of 30 eV - 30 keV and conventional solid-source MBE. As a successful application of CIBMBE, low-energy (100 eV) carbon ion (C(+)) irradiation during MBE growth of GaAs was carried out at substrate temperatures T(sub g) between 500 and 590 C. C(+)-doped layers were characterized by low-temperature (2 K) photoluminescence (PL), Raman scattering, and van der Pauw measurements. PL spectra of undoped GaAs grown by CIBMBE revealed that unintentional impurity incorporation into the epilayer is extremely small and precise doping effects are observable. C(sub As) acceptor-related emissions such as 'g', (g-g), and (g-g)(sub beta) are observed and their spectra are significantly changed with increasing C(+) beam current density I(sub c). PL measurements showed that C atoms were efficiently incorporated during MBE growth by CIBMBE and were optically well activated as an acceptor in the as-grown condition even for T(sub g) as low as 500 C. Raman measurement showed negligible lattice damage of the epilayer bombarded with 100 eV C(+) with no subsequent heat treatment. These results indicate that contamination- and damage-free impurity doping without postgrowth annealing can be achieved by the CIBMBE method.

  20. Characterization of epitaxial GaAs MOS capacitors using atomic layer-deposited TiO2/Al2O3 gate stack: study of Ge auto-doping and p-type Zn doping.

    Science.gov (United States)

    Dalapati, Goutam Kumar; Shun Wong, Terence Kin; Li, Yang; Chia, Ching Kean; Das, Anindita; Mahata, Chandreswar; Gao, Han; Chattopadhyay, Sanatan; Kumar, Manippady Krishna; Seng, Hwee Leng; Maiti, Chinmay Kumar; Chi, Dong Zhi

    2012-02-02

    Electrical and physical properties of a metal-oxide-semiconductor [MOS] structure using atomic layer-deposited high-k dielectrics (TiO2/Al2O3) and epitaxial GaAs [epi-GaAs] grown on Ge(100) substrates have been investigated. The epi-GaAs, either undoped or Zn-doped, was grown using metal-organic chemical vapor deposition method at 620°C to 650°C. The diffusion of Ge atoms into epi-GaAs resulted in auto-doping, and therefore, an n-MOS behavior was observed for undoped and Zn-doped epi-GaAs with the doping concentration up to approximately 1017 cm-3. This is attributed to the diffusion of a significant amount of Ge atoms from the Ge substrate as confirmed by the simulation using SILVACO software and also from the secondary ion mass spectrometry analyses. The Zn-doped epi-GaAs with a doping concentration of approximately 1018 cm-3 converts the epi-GaAs layer into p-type since the Zn doping is relatively higher than the out-diffused Ge concentration. The capacitance-voltage characteristics show similar frequency dispersion and leakage current for n-type and p-type epi-GaAs layers with very low hysteresis voltage (approximately 10 mV).PACS: 81.15.Gh.

  1. Diodes based on semi-insulating CdTe crystals with Mo/MoO{sub x} contacts for X- and γ-ray detectors

    Energy Technology Data Exchange (ETDEWEB)

    Maslyanchuk, O.; Kulchynsky, V.; Solovan, M. [Chernivtsi National University, Chernivtsi (Ukraine); Gnatyuk, V. [Institute of Semiconductor Physics, NAS of Ukraine, Kyiv (Ukraine); Potiriadis, C. [Greek Atomic Energy Commission, Attiki (Greece); Kaissas, I. [Greek Atomic Energy Commission, Attiki (Greece); Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki (Greece); Brus, V. [Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Berlin (Germany)

    2017-03-15

    This paper reports on the possible applications of molybdenum oxide (Mo/MoO{sub x}) contacts in combination with semi-insulating CdTe crystals. The electrical contacts to p-type Cl-doped CdTe crystals were formed by the deposition of molybdenum oxide and pure molybdenum thin films by the DC reactive magnetron sputtering. Electrical properties of the prepared Mo-MoO{sub x}/p-CdTe/MoO{sub x}-Mo surface-barrier structures were investigated at different temperatures. It is shown that the rapid growth of the reverse current with increasing bias voltage higher than 10 V is caused by the space-charge limited currents. Spectrometric properties of the Mo-MoO{sub x}/p-CdTe/MoO{sub x}-Mo structures have been also analyzed. It is revealed that the developed heterojunction has shown promising characteristics for its practical application in X- and γ-ray radiation detector fabrication. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  2. Plasma Deposited SiO2 for Planar Self-Aligned Gate Metal-Insulator-Semiconductor Field Effect Transistors on Semi-Insulating InP

    Science.gov (United States)

    Tabory, Charles N.; Young, Paul G.; Smith, Edwyn D.; Alterovitz, Samuel A.

    1994-01-01

    Metal-insulator-semiconductor (MIS) field effect transistors were fabricated on InP substrates using a planar self-aligned gate process. A 700-1000 A gate insulator of Si02 doped with phosphorus was deposited by a direct plasma enhanced chemical vapor deposition at 400 mTorr, 275 C, 5 W, and power density of 8.5 MW/sq cm. High frequency capacitance-voltage measurements were taken on MIS capacitors which have been subjected to a 700 C anneal and an interface state density of lxl0(exp 11)/eV/cq cm was found. Current-voltage measurements of the capacitors show a breakdown voltage of 107 V/cm and a insulator resistivity of 10(exp 14) omega cm. Transistors were fabricated on semi-insulating InP using a standard planar self-aligned gate process in which the gate insulator was subjected to an ion implantation activation anneal of 700 C. MIS field effect transistors gave a maximum extrinsic transconductance of 23 mS/mm for a gate length of 3 microns. The drain current drift saturated at 87.5% of the initial current, while reaching to within 1% of the saturated value after only 1x10(exp 3). This is the first reported viable planar InP self-aligned gate transistor process reported to date.

  3. Nanostructure formation during relatively high temperature growth of Mn-doped GaAs by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Del Río-De Santiago, A.; Méndez-García, V.H. [CIACyT-UASLP, Sierra Leona Av. # 550, Lomas 2a Secc, San Luis Potosí, S.L.P. 78210, México (Mexico); Martínez-Velis, I.; Casallas-Moreno, Y.L. [Physics Department, CINVESTAV-IPN, Apdo. Postal 14470 D. F. México, México (Mexico); López-Luna, E. [CIACyT-UASLP, Sierra Leona Av. # 550, Lomas 2a Secc, San Luis Potosí, S.L.P. 78210, México (Mexico); Yu Gorbatchev, A. [IICO-UASLP, Av. Karakorum 1470, Lomas 4a. Sección, San Luis Potosí, S.L.P. 78210, México (Mexico); López-López, M. [Physics Department, CINVESTAV-IPN, Apdo. Postal 14470 D. F. México, México (Mexico); Cruz-Hernández, E., E-mail: esteban.cruz@uaslp.mx [CIACyT-UASLP, Sierra Leona Av. # 550, Lomas 2a Secc, San Luis Potosí, S.L.P. 78210, México (Mexico)

    2015-04-01

    Highlights: • The formation of different kind of nanostructures in GaMnAs layers depending on Mn concentration at relative HT-MBE is reported. In this Mn% range, it is found the formation of nanogrooves, nanoleaves, and nanowires. • It is shown the progressive photoluminescence transitions from purely GaAsMn zinc blende (for Mn% = 0.01) to a mixture of zinc blende and wurtzite GaAsMn (for Mn% = 0.2). • A critical thickness for the Mn catalyst effect was determined by RHEED. - Abstract: In the present work, we report on molecular beam epitaxy growth of Mn-doped GaAs films at the relatively high temperature (HT) of 530 °C. We found that by increasing the Mn atomic percent, Mn%, from 0.01 to 0.2, the surface morphology of the samples is strongly influenced and changes from planar to corrugated for Mn% values from 0.01 to 0.05, corresponding to nanostructures on the surface with dimensions of 200–300 nm and with the shape of leave, to nanowire-like structures for Mn% values above 0.05. From reflection high-energy electron diffraction patterns, we observed the growth mode transition from two- to three-dimensional occurring at a Mn% exceeding 0.05. The optical and electrical properties were obtained from photoluminescence (PL) and Hall effect measurements, respectively. For the higher Mn concentration, besides the Mn related transitions at approximately 1.41 eV, PL spectra sharp peaks are present between 1.43 and 1.49 eV, which we related to the coexistence of zinc blende and wurtzite phases in the nanowire-like structures of this sample. At Mn% of 0.04, an increase of the carrier mobility up to a value of 1.1 × 10{sup 3} cm{sup 2}/Vs at 77 K was found, then decreases as Mn% is further increased due to the strengthening of the ionized impurity scattering.

  4. Two-band analysis of hole mobility and Hall factor for heavily carbon-doped p-type GaAs

    Science.gov (United States)

    Kim, B. W.; Majerfeld, A.

    1996-02-01

    We solve a pair of Boltzmann transport equations based on an interacting two-isotropic-band model in a general way first to get transport parameters corresponding to the relaxation time. We present a simple method to calculate effective relaxation times, separately for each band, which compensate for the inherent deficiencies in using the relaxation time concept for polar optical-phonon scattering. Formulas for calculating momentum relaxation times in the two-band model are presented for all the major scattering mechanisms of p-type GaAs for simple, practical mobility calculations. In the newly proposed theoretical framework, first-principles calculations for the Hall mobility and Hall factor of p-type GaAs at room temperature are carried out with no adjustable parameters in order to obtain direct comparisons between the theory and recently available experimental results. In the calculations, the light-hole-band nonparabolicity is taken into account on the average by the use of energy-dependent effective mass obtained from the kṡp method and valence-band anisotropy is taken partly into account by the use the Wiley's overlap function.. The calculated Hall mobilities show a good agreement with our experimental data for carbon-doped p-GaAs samples in the range of degenerate hole densities. The calculated Hall factors show rH=1.25-1.75 over hole densities of 2×1017-1×1020 cm-3.

  5. Direct identification of interstitial Mn in heavily p-type doped GaAs and evidence of its high thermal stability

    CERN Document Server

    Pereira, LMC; Correia, JG; Decoster, S; da Silva, MR; Araújo, JP; Vantomme, A

    2011-01-01

    We report on the lattice location of Mn in heavily p-type doped GaAs by means of $\\beta^{-}$-emission channeling from the decay of $^{56}$Mn. The majority of the Mn atoms substitute for Ga and up to 31% occupy the tetrahedral interstitial site with As nearest neighbors. Contrary to the general belief, we find that interstitial Mn is immobile up to 400$^{\\circ}$C, with an activation energy for diffusion of 1.7–2.3 eV. Such high thermal stability of interstitial Mn has significant implications on the strategies and prospects for achieving room temperature ferromagnetism in Ga$_{1−x}$Mn$_{x}$As.

  6. Effect of dopant density on contact potential difference across n-type GaAs homojunctions using Kelvin Probe Force Microscopy

    Science.gov (United States)

    Boumenou, C. Kameni; Urgessa, Z. N.; Djiokap, S. R. Tankio; Botha, J. R.; Nel, J.

    2018-04-01

    In this study, cross-sectional surface potential imaging of n+/semi-insulating GaAs junctions is investigated by using amplitude mode kelvin probe force microscopy. The measurements have shown two different potential profiles, related to the difference in surface potential between the semi-insulating (SI) substrate and the epilayers. It is shown that the contact potential difference (CPD) between the tip and the sample is higher on the semi-insulating substrate side than on the n-type epilayer side. This change in CPD across the interface has been explained by means of energy band diagrams indicating the relative Fermi level positions. In addition, it has also been found that the CPD values across the interface are much smaller than the calculated values (on average about 25% of the theoretical values) and increase with the electron density. Therefore, the results presented in study are only in qualitative agreement with the theory.

  7. Effect of the magnetic field on the nonlinear optical rectification and second and third harmonic generation in double δ-doped GaAs quantum wells

    Science.gov (United States)

    Martínez-Orozco, J. C.; Rojas-Briseño, J. G.; Rodríguez-Magdaleno, K. A.; Rodríguez-Vargas, I.; Mora-Ramos, M. E.; Restrepo, R. L.; Ungan, F.; Kasapoglu, E.; Duque, C. A.

    2017-11-01

    In this paper we are reporting the computation for the Nonlinear Optical Rectification (NOR) and the Second and Third Harmonic Generation (SHG and THG) related with electronic states of asymmetric double Si-δ-doped quantum well in a GaAs matrix when this is subjected to an in-plane (x-oriented) constant magnetic field effect. The work is performed in the effective mass and parabolic band approximations in order to compute the electronic structure for the system by a diagonalization procedure. The expressions for the nonlinear optical susceptibilities, χ0(2), χ2ω(2), and χ3ω(3), are those arising from the compact matrix density formulation and stand for the NOR, SHG, and THG, respectively. This asymmetric double δ-doped quantum well potential profile actually exhibits nonzero NOR, SHG, and THG responses which can be easily controlled by the in-plane (x-direction) externally applied magnetic field. In particular we find that for the chosen configuration the harmonic generation is in the far-infrared/THz region, thus and becoming suitable building blocks for photodetectors in this range of the electromagnetic spectra.

  8. Doped Aluminum Gallium Arsenide (AlGaAs)/Gallium Arsenide (GaAs) Photoconductive Semiconductor Switch (PCSS) Fabrication

    Science.gov (United States)

    2016-09-27

    it as-grown and it densifies as the H leaves when annealed above approximately 500 °C. This densification causes the film to contract, becoming...tensile. The final deposition recipe shown in the Appendix, Section 2 was found after numerous trials and results in a minimum between compressive...marks b) ULVAC etch: 500 -W ICP, 50-W RIE, 4 mT, 16-sccm BCl3, 4-sccm Ar, 12 s (~50 nm)  GaAs etches at 7.54 nm/s after 6-s etch delay. PR etches at

  9. Subgap time of flight: A spectroscopic study of deep levels in semi-insulating CdTe:Cl

    Energy Technology Data Exchange (ETDEWEB)

    Pousset, J.; Farella, I.; Cola, A., E-mail: adriano.cola@le.imm.cnr.it [Institute for Microelectronics and Microsystems—Unit of Lecce, National Council of Research (IMM/CNR), Lecce I-73100 (Italy); Gambino, S. [Dipartimento di Matematica e Fisica “Ennio De Giorgi,” Università del Salento, Lecce I-73100 (Italy); CNR NANOTEC—Istituto di Nanotecnologia, Polo di Nanotecnologia c/o Campus Ecotekne, via Monteroni, 73100 Lecce (Italy)

    2016-03-14

    We report on a study of deep levels in semi-insulating CdTe:Cl by means of a time-of-flight spectral approach. By varying the wavelength of a pulsed optical source within the CdTe energy gap, transitions to/from localized levels generate free carriers which are analysed through the induced photocurrent transients. Both acceptor-like centers, related to the A-center, and a midgap level, 0.725 eV from the valence band, have been detected. The midgap level is close to the Fermi level and is possibly a recombination center responsible for the compensation mechanism. When the irradiance is varied, either linear or quadratic dependence of the electron and hole collected charge are observed, depending on the dominant optical transitions. The analysis discloses the potentiality of such a novel approach exploitable in the field of photorefractive materials as well as for deep levels spectroscopy.

  10. Photodetectors based on carbon nanotubes deposited by using a spray technique on semi-insulating gallium arsenide

    Directory of Open Access Journals (Sweden)

    Domenico Melisi

    2014-11-01

    Full Text Available In this paper, a spray technique is used to perform low temperature deposition of multi-wall carbon nanotubes on semi-insulating gallium arsenide in order to obtain photodectors. A dispersion of nanotube powder in non-polar 1,2-dichloroethane is used as starting material. The morphological properties of the deposited films has been analysed by means of electron microscopy, in scanning and transmission mode. Detectors with different layouts have been prepared and current–voltage characteristics have been recorded in the dark and under irradiation with light in the range from ultraviolet to near infrared. The device spectral efficiency obtained from the electrical characterization is finally reported and an improvement of the photodetector behavior due to the nanotubes is presented and discussed.

  11. Subgap time of flight: A spectroscopic study of deep levels in semi-insulating CdTe:Cl

    International Nuclear Information System (INIS)

    Pousset, J.; Farella, I.; Cola, A.; Gambino, S.

    2016-01-01

    We report on a study of deep levels in semi-insulating CdTe:Cl by means of a time-of-flight spectral approach. By varying the wavelength of a pulsed optical source within the CdTe energy gap, transitions to/from localized levels generate free carriers which are analysed through the induced photocurrent transients. Both acceptor-like centers, related to the A-center, and a midgap level, 0.725 eV from the valence band, have been detected. The midgap level is close to the Fermi level and is possibly a recombination center responsible for the compensation mechanism. When the irradiance is varied, either linear or quadratic dependence of the electron and hole collected charge are observed, depending on the dominant optical transitions. The analysis discloses the potentiality of such a novel approach exploitable in the field of photorefractive materials as well as for deep levels spectroscopy.

  12. Nuclear spin-lattice relaxation in n -type insulating and metallic GaAs single crystals

    Science.gov (United States)

    Lu, J.; Hoch, M. J. R.; Kuhns, P. L.; Moulton, W. G.; Gan, Z.; Reyes, A. P.

    2006-09-01

    The coupling of electron and nuclear spins in n-GaAs changes significantly as the donor concentration n increases through the insulator-metal critical concentration nC˜1.2×1016cm-3 . The present measurements of the Ga71 relaxation rates W made as a function of magnetic field (1-13T) and temperature (1.5-300K) for semi-insulating GaAs and for three doped n-GaAs samples with donor concentrations n=5.9×1015 , 7×1016 , and 2×1018cm-3 , show marked changes in the relaxation behavior with n . Korringa-like relaxation is found in both metallic samples for T30K phonon-induced nuclear quadrupolar relaxation is dominant. The relaxation rate measurements permit determination of the electron probability density at Ga71 sites. A small Knight shift of -3.3ppm was measured on the most metallic (2×1018cm-3) sample using magic-angle spinning at room temperature. For the n=5.9×1015cm-3 sample, a nuclear relaxation model involving the Fermi contact hyperfine interaction, rapid spin diffusion, and exchange coupled local moments is proposed. While the relaxation rate behavior with temperature for the weakly metallic sample, n=7×1016cm-3 , is similar to that found for the just-insulating sample, the magnetic field dependence is quite different. For the 5.9×1015cm-3 sample, increasing the magnetic field leads to a decrease in the relaxation rate, while for the 7×1016cm-3 sample this results in an increase in the relaxation rate ascribed to an increase in the density of states at the Fermi level as the Landau level degeneracy is increased.

  13. Optical and magnetic resonance signatures of deep levels in semi-insulating 4H SiC

    International Nuclear Information System (INIS)

    Carlos, W.E.; Glaser, E.R.; Shanabrook, B.V.

    2003-01-01

    We have studied semi-insulating (SI) 4H SiC grown by physical vapor transport (PVT) and by high-temperature chemical vapor deposition (HTCVD) using electron paramagnetic resonance (EPR) and infrared photoluminescence (IR-PL) to better understand the defect(s) responsible for the SI behavior. Although intrinsic defects such as the isolated carbon vacancy and in some cases the isolated Si vacancies have previously been observed by EPR in undoped SI SiC, their concentrations are an order of magnitude too low to be responsible for the SI behavior. We are able to observe the EPR signature of the carbon vacancy-carbon antisite pair (V C -C Si ) pair defect in an excited state of its 2+ charge state in all PVT samples and some HTCVD samples. We also establish the IR-PL signature of this EPR center as the UD2 spectrum - a set of four sharp lines between 1.1 and 1.15 eV previously observed by Magnusson et al. in neutron-irradiated 4H-SiC. We also observe the UD1 line, a pair of sharp IR-PL lines at ∼1.06 eV and UD3, a single sharp line at ∼1.36 eV. We propose a simple model for the SI behavior in material in which the (V C -C Si ) pair defect is the dominant deep defect

  14. Application of GaAs and CdTe photoconductor detectors to x-ray flash radiography

    International Nuclear Information System (INIS)

    Mathy, F.; Cuzin, M.; Gagelin, J.J.; Mermet, R.; Piaget, B.; Rustique, J.; Verger, L.

    1991-01-01

    Semi-insulating GaAs and CdTe:Cl photoconductor probes were qualified on high energy X ray single shot flash generators. The estimated minimum detected dose per flash corresponding to a 230 mrad direct beam attenuated by 200 mm lead was 20 μrad. The dynamic range was about 4 decades in amplitude or charges, with a good linearity. Such detectors, by locating the origin of the parasitic scattered beam, could be used to eliminate this parasitic beam in X ray flash radiography in detonics experiments. Imaging possibilities are mentioned, as well as X ray generator monitoring with such detectors or with neutron preirradiated photoconductors

  15. Application of GaAs and CdTe photoconductor detectors to x-ray flash radiography

    Energy Technology Data Exchange (ETDEWEB)

    Mathy, F.; Cuzin, M.; Gagelin, J.J.; Mermet, R.; Piaget, B.; Rustique, J.; Verger, L. [CEA Centre d`Etudes de Grenoble, 38 (FR). Direction des Technologies Avancees; Hauducoeur, A.; Nicolas, P.; Le Dain, L.; Hyvernage, M. [CEA Centre d`Etudes de Vaujours, 77 - Courtry (FR)

    1991-12-31

    Semi-insulating GaAs and CdTe:Cl photoconductor probes were qualified on high energy X ray single shot flash generators. The estimated minimum detected dose per flash corresponding to a 230 mrad direct beam attenuated by 200 mm lead was 20 {mu}rad. The dynamic range was about 4 decades in amplitude or charges, with a good linearity. Such detectors, by locating the origin of the parasitic scattered beam, could be used to eliminate this parasitic beam in X ray flash radiography in detonics experiments. Imaging possibilities are mentioned, as well as X ray generator monitoring with such detectors or with neutron preirradiated photoconductors.

  16. Surface behavior based on ion-induced secondary electron emission from semi-insulating materials in breakdown evolution

    Energy Technology Data Exchange (ETDEWEB)

    Koc, Emrah; Karakoese, Sema [Department of Physics, Faculty of Sciences, Gazi University, 06500 Ankara (Turkey); Salamov, Bahtiyar G. [Department of Physics, Faculty of Sciences, Gazi University, 06500 Ankara (Turkey); Institute of Physics, National Academy of Science, 1143 Baku (Azerbaijan)

    2013-09-15

    This study focuses on analyses of secondary electron emission (SEE) at semiconductor surfaces when the sufficient conditions of space-time distribution occur. Experimental measurements and calculations with the approach of Townsend coefficients, which include the evaluations of ionization coefficient ({alpha}) and SEE coefficient ({gamma}) were performed in high-ohmic InP, GaAs, and Si semiconductor cathodes with argon and air environments in a wide range of E/N (300-10 000 Td). The direct calculations of {gamma} were carried out to determine the behavior of cold-semiconductor cathode current in a wide range of microgaps (45-525 {mu}m). Paschen curves are interpreted in the dependence of large pd range on breakdown voltage through {gamma} and {alpha}/N. Ion-induced secondary electrons exhibit the direct behaviors affecting the timescale of breakdown evolution in the vicinity of the Paschen minimum during the natural bombardment process with ions of semiconductor cathodes. Also, when {alpha}/N rapidly drops and the excitations of gas atoms densely occupy the gas volume, we determined that the photoelectric effect provides a growth for electron emission from semiconductor surfaces at the breakdown stage at the reduced values of E/N. At all pressures, the emission magnitudes of electrons liberated by semiconductor cathodes into vacuum are found as {gamma}{sub InP} > {gamma}{sub GaAs} > {gamma}{sub Si} in breakdown evolution. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  17. Growth and electrical characterization of Zn-doped InAs and InAs1-xSbx

    International Nuclear Information System (INIS)

    Venter, A.; Shamba, P.; Botha, L.; Botha, J.R.

    2009-01-01

    The electrical properties of Zn doped InAs and InAsSb layers grown on semi-insulating GaAs by metal organic vapour phase epitaxy, using dimethyl zinc as the p-type dopant source, have been studied. The influence of dopant flow rate, V/III ratio and substrate orientation on the electrical properties of these InAs and InAs 1-x Sb x layers have been studied at a few appropriate growth temperatures. A promising group V source, tertiary butyl arsenic was used as an alternative to arsenic hydride in the case of InAs growth. The electrical properties of the InAs and InAs 1-x Sb x epitaxial layers were mainly studied by the Hall effect. However, surface accumulation in these materials results in deceptive Hall results being extracted. A two layer model (assuming the layer to consist of two parallel conducting paths viz. surface and bulk) has therefore been used to extract sensible transport properties. In addition, conventional Hall measurements ignores the high electron to hole mobility ratio in InAs and InAsSb leading to erroneous transport properties.

  18. Analysis of high field effects on the steady-state current-voltage response of semi-insulating 4H-SiC for photoconductive switch applications

    Energy Technology Data Exchange (ETDEWEB)

    Tiskumara, R. [Department of Electrical and Computer Engineering, Old Dominion University, Norfolk, Virginia 23529 (United States); Joshi, R. P., E-mail: ravi.joshi@ttu.edu; Mauch, D.; Dickens, J. C.; Neuber, A. A. [Department of Electrical and Computer Engineering, Texas Tech University, Lubbock, Texas 79409 (United States)

    2015-09-07

    A model-based analysis of the steady-state, current-voltage response of semi-insulating 4H-SiC is carried out to probe the internal mechanisms, focusing on electric field driven effects. Relevant physical processes, such as multiple defects, repulsive potential barriers to electron trapping, band-to-trap impact ionization, and field-dependent detrapping, are comprehensively included. Results of our model match the available experimental data fairly well over orders of magnitude variation in the current density. A number of important parameters are also extracted in the process through comparisons with available data. Finally, based on our analysis, the possible presence of holes in the samples can be discounted up to applied fields as high as ∼275 kV/cm.

  19. Evaluation of 320x240 pixel LEC GaAs Schottky barrier X-ray imaging arrays, hybridized to CMOS readout circuit based on charge integration

    CERN Document Server

    Irsigler, R; Alverbro, J; Borglind, J; Froejdh, C; Helander, P; Manolopoulos, S; O'Shea, V; Smith, K

    1999-01-01

    320x240 pixels GaAs Schottky barrier detector arrays were fabricated, hybridized to silicon readout circuits, and subsequently evaluated. The detector chip was based on semi-insulating LEC GaAs material. The square shaped pixel detector elements were of the Schottky barrier type and had a pitch of 38 mu m. The GaAs wafers were thinned down prior to the fabrication of the ohmic back contact. After dicing, the chips were indium bump, flip-chip bonded to CMOS readout circuits based on charge integration, and finally evaluated. A bias voltage between 50 and 100 V was sufficient to operate the detector. Results on I-V characteristics, noise behaviour and response to X-ray radiation are presented. Images of various objects and slit patterns were acquired by using a standard dental imaging X-ray source. The work done was a part of the XIMAGE project financed by the European Community (Brite-Euram). (author)

  20. Design and characterisation of high electron mobility transistors for use in a monolithic GaAs X-ray imaging sensor

    International Nuclear Information System (INIS)

    Boardman, D.A.; Sellin, P.J.

    2001-01-01

    A new design of monolithic GaAs pixel detector is proposed for medical and synchrotron applications. In this device a semi-insulating GaAs wafer will be used as both the detector element and the substrate for the integrated charge readout matrix. The charge readout matrix consists of High Electron Mobility Transistors (HEMTs), which are grown epitaxially onto the GaAs substrate. Experimental characterisation of HEMTs has been carried out and their suitability for the proposed imaging device is assessed. Temperature measurements on initial devices showed the threshold voltage to be stable from room temperature down to -15 degree sign C. HEMT designs with lower leakage current that operate in enhancement mode have been fabricated and modelled using the Silvaco simulation package. These optimised devices have been fabricated using a gate recess, and exhibit enhancement mode operation and significantly reduced gate leakage currents

  1. High temperature annealing effects on deep-level defects in a high purity semi-insulating 4H-SiC substrate

    Energy Technology Data Exchange (ETDEWEB)

    Iwamoto, Naoya, E-mail: naoya.iwamoto@smn.uio.no; Azarov, Alexander; Svensson, Bengt G. [Department of Physics, Center for Materials Science and Nanotechnology, University of Oslo, P.O. Box 1048 Blindern, N-0316 Oslo (Norway); Ohshima, Takeshi [Japan Atomic Energy Agency, 1233 Watanuki, Takasaki, 370-1292 Gunma (Japan); Moe, Anne Marie M. [Washington Mills AS, N-7300 Orkanger (Norway)

    2015-07-28

    Effects of high-temperature annealing on deep-level defects in a high-purity semi-insulating 4H silicon carbide substrate have been studied by employing current-voltage, capacitance-voltage, junction spectroscopy, and chemical impurity analysis measurements. Secondary ion mass spectrometry data reveal that the substrate contains boron with concentration in the mid 10{sup 15 }cm{sup −3} range, while other impurities including nitrogen, aluminum, titanium, vanadium and chromium are below their detection limits (typically ∼10{sup 14 }cm{sup −3}). Schottky barrier diodes fabricated on substrates annealed at 1400–1700 °C exhibit metal/p-type semiconductor behavior with a current rectification of up to 8 orders of magnitude at bias voltages of ±3 V. With increasing annealing temperature, the series resistance of the Schottky barrier diodes decreases, and the net acceptor concentration in the substrates increases approaching the chemical boron content. Admittance spectroscopy results unveil the presence of shallow boron acceptors and deep-level defects with levels in lower half of the bandgap. After the 1400 °C annealing, the boron acceptor still remains strongly compensated at room temperature by deep donor-like levels located close to mid-gap. However, the latter decrease in concentration with increasing annealing temperature and after 1700 °C, the boron acceptor is essentially uncompensated. Hence, the deep donors are decisive for the semi-insulating properties of the substrates, and their thermal evolution limits the thermal budget for device processing. The origin of the deep donors is not well-established, but substantial evidence supporting an assignment to carbon vacancies is presented.

  2. Changes in the positron-electron momentum distribution in GaAs brought about by chopped light

    International Nuclear Information System (INIS)

    Li, S.; Fung, S.; Beling, C.D.; Ling, C.C.

    2001-01-01

    We report on an attempt to observe the EL2→ EL2 * transition in semi-insulating GaAs using Doppler broadening of annihilation radiation spectroscopy. Unlike the original observation of this transition using positron annihilation spectroscopy, the present method has sought to observe the production of EL2 * through a light chopping experiment, where on the half cycle of illumination the EL2 * state is formed and on the second half cycle the EL2 * thermally quenches back to EL2. While results are at a preliminary state we have obtained evidence for the production of EL2 * from the broad-band emission of a Xenon lamp. While calculations suggest that we should be able to see the EL2 * from the IR emission (1.3eV) of GaAs light emitting diodes we have not yet been able to achieve this. Reasons why are discussed. (orig.)

  3. Role of electrode metallization in the performance of bulk semi-insulating InP radiation detectors

    International Nuclear Information System (INIS)

    Zatko, B.; Dubecky, F.; Prochazkova, O.; Necas, V.

    2007-01-01

    This work deals with the study of three different electrode metallizations with the aim to form a Schottky barrier contact. Electrode geometry corresponds to the requirements of digital radiography systems. As substrates bulk Liquid Encapsulated Czochralski (LEC) SI InP wafers doped with Fe and Fe+Zn are used. Results of this study show that no one of the used metallization performs as a blocking contact. However, detectors with Ti/Pt/Au metallization attained a relatively good energy resolution of 7.0 keV in full-width at half-maximum (FWHM) and the charge collection efficiency (CCE) higher than 83% for 122 keV γ-photons at 255 K. The development of SI InP radiation detectors and in particular their electrode technology is discussed in the light of observed results

  4. Growth and electrical characterization of Zn-doped InAs and InAs{sub 1-x}Sb{sub x}

    Energy Technology Data Exchange (ETDEWEB)

    Venter, A., E-mail: andre.venter@nmmu.ac.z [Department of Physics, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth (South Africa); Shamba, P.; Botha, L.; Botha, J.R. [Department of Physics, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth (South Africa)

    2009-06-01

    The electrical properties of Zn doped InAs and InAsSb layers grown on semi-insulating GaAs by metal organic vapour phase epitaxy, using dimethyl zinc as the p-type dopant source, have been studied. The influence of dopant flow rate, V/III ratio and substrate orientation on the electrical properties of these InAs and InAs{sub 1-x}Sb{sub x} layers have been studied at a few appropriate growth temperatures. A promising group V source, tertiary butyl arsenic was used as an alternative to arsenic hydride in the case of InAs growth. The electrical properties of the InAs and InAs{sub 1-x}Sb{sub x} epitaxial layers were mainly studied by the Hall effect. However, surface accumulation in these materials results in deceptive Hall results being extracted. A two layer model (assuming the layer to consist of two parallel conducting paths viz. surface and bulk) has therefore been used to extract sensible transport properties. In addition, conventional Hall measurements ignores the high electron to hole mobility ratio in InAs and InAsSb leading to erroneous transport properties.

  5. Crystal structure of LT GaAs layers before and after annealing

    International Nuclear Information System (INIS)

    Litiental-Weber, Z.

    1992-01-01

    In this paper the structural quality of GaAs layers grown at low temperatures by solid-source and gas-source MBE at different growth conditions is described. Dependence on the growth temperature and concentration of As [expressed at As/Ga beam equivalent pressure (BEP)] used for the growth is discussed. A higher growth temperature is required top obtain the same monocrystalling layer thickness with increased BEP. The annealing of these layers is associated with the formation of As precipitates. Semicoherent precipitates with lowest formation energies are formed in the monocrystalline parts of the layers grown with the lowest BEP. Precipitates with higher formation energies are formed when higher BEP is applied; they are also formed in the vicinity of structural defects. Formation of As precipitates releases strain in the layers. Arsenic precipitates are not formed in annealed ternary (InAlAs) layers despite their semi-insulating properties. The role of As precipitates in semi-insulating properties and the short lifetime of minority carriers in these layers is discussed

  6. Nonlinear absorption coefficient and relative refraction index change for an asymmetrical double δ-doped quantum well in GaAs with a Schottky barrier potential

    International Nuclear Information System (INIS)

    Rojas-Briseño, J.G.; Martínez-Orozco, J.C.; Rodríguez-Vargas, I.; Mora-Ramos, M.E.; Duque, C.A.

    2013-01-01

    In this work we are reporting the energy level spectrum for a quantum system consisting of an n-type double δ-doped quantum well with a Schottky barrier potential in a Gallium Arsenide matrix. The calculated states are taken as the basis for the evaluation of the linear and third-order nonlinear contributions to the optical absorption coefficient and to the relative refractive index change, making particular use of the asymmetry of the potential profile. These optical properties are then reported as a function of the Schottky barrier height (SBH) and the separation distance between the δ-doped quantum wells. Also, the effects of the application of hydrostatic pressure are studied. The results show that the amplitudes of the resonant peaks are of the same order of magnitude of those obtained in the case of single δ-doped field effect transistors; but tailoring the asymmetry of the confining potential profile allows the control the resonant peak positions

  7. Nonlinear absorption coefficient and relative refraction index change for an asymmetrical double δ-doped quantum well in GaAs with a Schottky barrier potential

    Energy Technology Data Exchange (ETDEWEB)

    Rojas-Briseño, J.G.; Martínez-Orozco, J.C.; Rodríguez-Vargas, I. [Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad esquina con Paseo la Bufa S/N, C.P. 98060, Zacatecas, Zac. (Mexico); Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, CP 62209, Cuernavaca, Morelos (Mexico); Instituto de Física, Universidad de Antioquia, AA 1226, Medellín (Colombia); Duque, C.A., E-mail: cduque@fisica.udea.edu.co [Instituto de Física, Universidad de Antioquia, AA 1226, Medellín (Colombia)

    2013-09-01

    In this work we are reporting the energy level spectrum for a quantum system consisting of an n-type double δ-doped quantum well with a Schottky barrier potential in a Gallium Arsenide matrix. The calculated states are taken as the basis for the evaluation of the linear and third-order nonlinear contributions to the optical absorption coefficient and to the relative refractive index change, making particular use of the asymmetry of the potential profile. These optical properties are then reported as a function of the Schottky barrier height (SBH) and the separation distance between the δ-doped quantum wells. Also, the effects of the application of hydrostatic pressure are studied. The results show that the amplitudes of the resonant peaks are of the same order of magnitude of those obtained in the case of single δ-doped field effect transistors; but tailoring the asymmetry of the confining potential profile allows the control the resonant peak positions.

  8. Evaluation of the quality of semi-insulating CdTe for radiation detectors by measurement of lux-ampere characteristics

    International Nuclear Information System (INIS)

    Franc, J.; Kubat, J.; Grill, R.; Dedic, V.; Hlidek, P.; Moravec, P.; Belas, E.

    2011-01-01

    Accumulation of space charge on deep levels represents one of the major problems in fabrication of semi-insulating CdTe and CdZnTe X-ray and gamma-ray detectors, because it influences the applied electric field and can even result in a complete breakdown of the field in part of the sample (polarization and dead layer formation). The goal of the study was to evaluate possibilities of localization of areas of potential space charge accumulation in as grown crystals by steady state measurement of lux-ampere characteristics. All measurements were done at room temperature using He-Ne laser. Voltage was applied parallel to the direction of light propagation in the range 10-100 V. It was observed that all lux-ampere characteristics are sub-linear. Screening effects caused by space charge accumulated on deep levels explain these results. Crystals prepared by Vertical gradient freeze method in our laboratory are compared to a commercially available detector-grade sample prepared by Travelling heater method. Comparison of crystals grown from precursors of different starting purity shows an increase of the slope of lux-ampere characteristics with a decrease of impurity content. A correlation between the slope of lux-ampere characteristics and the mobility-lifetime product of electrons was observed, too.

  9. Evaluation of the quality of semi-insulating CdTe for radiation detectors by measurement of lux-ampere characteristics

    Science.gov (United States)

    Franc, J.; Kubát, J.; Grill, R.; Dědič, V.; Hlídek, P.; Moravec, P.; Belas, E.

    2011-05-01

    Accumulation of space charge on deep levels represents one of the major problems in fabrication of semi-insulating CdTe and CdZnTe X-ray and gamma-ray detectors, because it influences the applied electric field and can even result in a complete breakdown of the field in part of the sample (polarization and dead layer formation). The goal of the study was to evaluate possibilities of localization of areas of potential space charge accumulation in as grown crystals by steady state measurement of lux-ampere characteristics. All measurements were done at room temperature using He-Ne laser. Voltage was applied parallel to the direction of light propagation in the range 10-100 V. It was observed that all lux-ampere characteristics are sub-linear. Screening effects caused by space charge accumulated on deep levels explain these results. Crystals prepared by Vertical gradient freeze method in our laboratory are compared to a commercially available detector-grade sample prepared by Travelling heater method. Comparison of crystals grown from precursors of different starting purity shows an increase of the slope of lux-ampere characteristics with a decrease of impurity content. A correlation between the slope of lux-ampere characteristics and the mobility-lifetime product of electrons was observed, too.

  10. Room-temperature particle detectors with guard rings based on semi-insulating InP co-doped with Ti and Zn

    Czech Academy of Sciences Publication Activity Database

    Yatskiv, Roman; Žďánský, Karel; Pekárek, Ladislav

    2009-01-01

    Roč. 598, č. 3 (2009), s. 759-763 ISSN 0168-9002 R&D Projects: GA AV ČR KAN400670651 Institutional research plan: CEZ:AV0Z20670512 Keywords : radiation detector * InP * crystal growth Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering Impact factor: 1.317, year: 2009

  11. Evidence for plasma effect on charge collection efficiency in proton irradiated GaAs detectors

    CERN Document Server

    Nava, F; Canali, C; Vittone, E; Polesello, P; Biggeri, U; Leroy, C

    1999-01-01

    The radiation damage in 100 mu m thick Schottky diodes made on semi-insulating undoped GaAs materials, were studied using alpha-, beta-, proton- and gamma-spectroscopy as well as I-V measurements. The results have been analysed within the framework of the Hecht model to investigate the influence of the plasma produced by short-range strongly ionising particles on the detector performance after 24 GeV proton irradiation. It has been found that with the mean free drift lengths for electrons and holes determined from alpha-spectra in overdepleted detectors, the charge collection efficiency for beta-particles, cce subbeta, is well predicted in the unirradiated detectors, while in the most irradiated ones, the cce subbeta is underestimated by more than 40%. The observed disagreement can be explained by assuming that the charge carrier recombination in the plasma region of such detectors, becomes significant.

  12. Scanning microwave microscopy applied to semiconducting GaAs structures

    Science.gov (United States)

    Buchter, Arne; Hoffmann, Johannes; Delvallée, Alexandra; Brinciotti, Enrico; Hapiuk, Dimitri; Licitra, Christophe; Louarn, Kevin; Arnoult, Alexandre; Almuneau, Guilhem; Piquemal, François; Zeier, Markus; Kienberger, Ferry

    2018-02-01

    A calibration algorithm based on one-port vector network analyzer (VNA) calibration for scanning microwave microscopes (SMMs) is presented and used to extract quantitative carrier densities from a semiconducting n-doped GaAs multilayer sample. This robust and versatile algorithm is instrument and frequency independent, as we demonstrate by analyzing experimental data from two different, cantilever- and tuning fork-based, microscope setups operating in a wide frequency range up to 27.5 GHz. To benchmark the SMM results, comparison with secondary ion mass spectrometry is undertaken. Furthermore, we show SMM data on a GaAs p-n junction distinguishing p- and n-doped layers.

  13. Simulated and experimental spectroscopic performance of GaAs X-ray pixel detectors

    International Nuclear Information System (INIS)

    Bisogni, M.G.; Cola, A.; Fantacci, M.E.

    2001-01-01

    In pixel detectors, the electrode geometry affects the signal shape and therefore the spectroscopic performance of the device. This effect is enhanced in semiconductors where carrier trapping is relevant. In particular, semi insulating (SI) GaAs crystals present an incomplete charge collection due to a high concentration of deep traps in the bulk. In the last few years, SI GaAs pixel detectors have been developed as soft X-ray detectors for medical imaging applications. In this paper, we present a numerical method to evaluate the local charge collection properties of pixel detectors. A bi-dimensional description has been used to represent the detector geometry. According to recent models, the active region of a reverse biased SI GaAs detector is almost neutral. Therefore, the electrostatic potential inside a full active detector has been evaluated using the Laplace equation. A finite difference method with a fixed step orthogonal mesh has been adopted. The photon interaction point has been generated with a Monte Carlo method according to the attenuation length of a monochromatic X-ray beam in GaAs. The number of photogenerated carriers for each interaction has been extracted using a gaussian distribution. The induced signal on the collecting electrode has been calculated according to the Ramo's theorem and the trapping effect has been modeled introducing electron and hole lifetimes. The noise of the charge preamplifier have been also taken into account. A comparison between simulated and experimental X-ray spectra from a 241 Am source acquired with different GaAs pixel detectors has been carried out

  14. Electrodeposition of Metal on GaAs Nanowires

    Science.gov (United States)

    Liu, Chao; Einabad, Omid; Watkins, Simon; Kavanagh, Karen

    2010-10-01

    Copper (Cu) electrical contacts to freestanding gallium arsenide (GaAs) nanowires have been fabricated via electrodeposition. The nanowires are zincblende (111) oriented grown epitaxially on n-type Si-doped GaAs (111)B substrates by gold-catalyzed Vapor Liquid Solid (VLS) growth in a metal organic vapour phase epitaxy (MOVPE) reactor. The epitaxial electrodeposition process, based on previous work with bulk GaAs substrates, consists of a substrate oxide pre-etch in dilute ammonium-hydroxide carried out prior to galvanostatic electrodeposition in a pure Cu sulphate aqueous electrolyte at 20-60^oC. For GaAs nanowires, we find that Cu or Fe has a preference for growth on the gold catalyst avoiding the sidewalls. After removing gold, both metals still prefer to grow only on top of the nanowire, which has the largest potential field.

  15. a Positron 2D-ACAR Study of the Silicon-Dioxide Interface and the Point Defects in the Semi-Insulating Gallium Arsenide

    Science.gov (United States)

    Peng, Jianping

    The SiO_2-Si system has been the subject of extensive study for several decades. Particular interest has been paid to the interface between Si single crystal and the amorphous SiO_2 which determines the properties and performances of devices. This is significant because of the importance of Si technology in the semiconductor industry. The development of the high-intensity slow positron beam at Brookhaven National Laboratory make it possible to study this system for the first time using the positron two-dimensional angular correlation of annihilation radiation (2D-ACAR) technique. 2D-ACAR is a well established and is a non-destructive microscopic probe for studying the electronic structure of materials, and for doing the depth-resolved measurements. Some unique information was obtained from the measurements performed on the SiO_2-Si system: Positronium (Ps) atoms formation and trapping in microvoids in both oxide and interface regions; and positron annihilation at vacancy-like defects in the interface region which can be attributed to the famous Pb centers. The discovery of the microvoids in the interface region may have some impact on the fabrication of the next generation electronic devices. Using the conventional 2D-ACAR setup with a ^{22}Na as positron source, we also studied the native arsenic (As) vacancy in the semi -insulating gallium-arsenide (SI-GaAs), coupled with in situ infrared light illumination. The defect spectrum was obtained by comparing the spectrum taken without photo -illumination to the spectrum taken with photo-illumination. The photo-illumination excited electrons from valence band to the defect level so that positrons can become localized in the defects. The two experiments may represent a new direction of the application of positron 2D-ACAR technique on the solid state physics and materials sciences.

  16. Absorption coefficient and relative refractive index change for a double δ-doped GaAs MIGFET-like structure: Electric and magnetic field effects

    Science.gov (United States)

    Martínez-Orozco, J. C.; Rodríguez-Magdaleno, K. A.; Suárez-López, J. R.; Duque, C. A.; Restrepo, R. L.

    2016-04-01

    In this work we present theoretical results for the electronic structure as well as for the absorption coefficient and relative refractive index change for an asymmetric double δ-doped like confining potential in the active region of a Multiple Independent Gate Field Effect Transistor (MIGFET) system. We model the potential profile as a double δ-doped like potential profile between two Schottky (parabolic) potential barriers that are just the main characteristics of the MIGFET configuration. We investigate the effect of external electromagnetic fields in this kind of quantum structures, in particular we applied a homogeneous constant electric field in the growth direction z as well as a homogeneous constant magnetic field in the x-direction. In general we conclude that by applying electromagnetic fields we can modulate the resonant peaks of the absorption coefficient as well as their energy position. Also with such probes it is possible to control the nodes and amplitude of the relative refractive index changes related to resonant intersubband optical transitions.

  17. Modelling of OPNMR phenomena using photon energy-dependent 〈Sz〉 in GaAs and InP

    Science.gov (United States)

    Wheeler, Dustin D.; Willmering, Matthew M.; Sesti, Erika L.; Pan, Xingyuan; Saha, Dipta; Stanton, Christopher J.; Hayes, Sophia E.

    2016-12-01

    We have modified the model for optically-pumped NMR (OPNMR) to incorporate a revised expression for the expectation value of the z-projection of the electron spin, 〈Sz 〉 and apply this model to both bulk GaAs and a new material, InP. This expression includes the photon energy dependence of the electron polarization when optically pumping direct-gap semiconductors in excess of the bandgap energy, Eg . Rather than using a fixed value arising from coefficients (the matrix elements) for the optical transitions at the k = 0 bandedge, we define a new parameter, Sopt (Eph) . Incorporating this revised element into the expression for 〈Sz 〉 , we have simulated the photon energy dependence of the OPNMR signals from bulk semi-insulating GaAs and semi-insulating InP. In earlier work, we matched calculations of electron spin polarization (alone) to features in a plot of OPNMR signal intensity versus photon energy for optical pumping (Ramaswamy et al., 2010). By incorporating an electron spin polarization which varies with pump wavelength into the penetration depth model of OPNMR signal, we are able to model features in both III-V semiconductors. The agreement between the OPNMR data and the corresponding model demonstrates that fluctuations in the OPNMR intensity have particular sensitivity to light hole-to-conduction band transitions in bulk systems. We provide detailed plots of the theoretical predictions for optical pumping transition probabilities with circularly-polarized light for both helicities of light, broken down into illustrative plots of optical magnetoabsorption and spin polarization, shown separately for heavy-hole and light-hole transitions. These plots serve as an effective roadmap of transitions, which are helpful to other researchers investigating optical pumping effects.

  18. Modelling of OPNMR phenomena using photon energy-dependent 〈Sz〉 in GaAs and InP.

    Science.gov (United States)

    Wheeler, Dustin D; Willmering, Matthew M; Sesti, Erika L; Pan, Xingyuan; Saha, Dipta; Stanton, Christopher J; Hayes, Sophia E

    2016-12-01

    We have modified the model for optically-pumped NMR (OPNMR) to incorporate a revised expression for the expectation value of the z-projection of the electron spin, 〈S z 〉 and apply this model to both bulk GaAs and a new material, InP. This expression includes the photon energy dependence of the electron polarization when optically pumping direct-gap semiconductors in excess of the bandgap energy, E g . Rather than using a fixed value arising from coefficients (the matrix elements) for the optical transitions at the k=0 bandedge, we define a new parameter, S opt (E ph ). Incorporating this revised element into the expression for 〈S z 〉, we have simulated the photon energy dependence of the OPNMR signals from bulk semi-insulating GaAs and semi-insulating InP. In earlier work, we matched calculations of electron spin polarization (alone) to features in a plot of OPNMR signal intensity versus photon energy for optical pumping (Ramaswamy et al., 2010). By incorporating an electron spin polarization which varies with pump wavelength into the penetration depth model of OPNMR signal, we are able to model features in both III-V semiconductors. The agreement between the OPNMR data and the corresponding model demonstrates that fluctuations in the OPNMR intensity have particular sensitivity to light hole-to-conduction band transitions in bulk systems. We provide detailed plots of the theoretical predictions for optical pumping transition probabilities with circularly-polarized light for both helicities of light, broken down into illustrative plots of optical magnetoabsorption and spin polarization, shown separately for heavy-hole and light-hole transitions. These plots serve as an effective roadmap of transitions, which are helpful to other researchers investigating optical pumping effects. Copyright © 2016 Elsevier Inc. All rights reserved.

  19. X-ray Imaging Using a Hybrid Photon Counting GaAs Pixel Detector

    CERN Document Server

    Schwarz, C; Göppert, R; Heijne, Erik H M; Ludwig, J; Meddeler, G; Mikulec, B; Pernigotti, E; Rogalla, M; Runge, K; Smith, K M; Snoeys, W; Söldner-Rembold, S; Watt, J

    1999-01-01

    The performance of hybrid GaAs pixel detectors as X-ray imaging sensors were investigated at room temperature. These hybrids consist of 300 mu-m thick GaAs pixel detectors, flip-chip bonded to a CMOS Single Photon Counting Chip (PCC). This chip consists of a matrix of 64 x 64 identical square pixels (170 mu-m x 170 mu-m) and covers a total area of 1.2 cm**2. The electronics in each cell comprises a preamplifier, a discriminator with a 3-bit threshold adjust and a 15-bit counter. The detector is realized by an array of Schottky diodes processed on semi-insulating LEC-GaAs bulk material. An IV-charcteristic and a detector bias voltage scan showed that the detector can be operated with voltages around 200 V. Images of various objects were taken by using a standard X-ray tube for dental diagnostics. The signal to noise ratio (SNR) was also determined. The applications of these imaging systems range from medical applications like digital mammography or dental X-ray diagnostics to non destructive material testing (...

  20. Damage related deep electron levels in ion implanted GaAs

    International Nuclear Information System (INIS)

    Allsopp, D.W.E.; Peaker, A.R.

    1986-01-01

    A study has been made of the deep electron levels in semi-insulating GaAs implanted with either 78 Se + or 29 Si + ions and rendered n-type by subsequent annealing without encapsulation in partial pressures of arsenic or arsine. Three implantation related deep states were detected with concentration profiles approximating to the type of Gaussian distributions expected for point defects related to ion implantation damage. Further heat treatment of the samples at 500 0 C in a gas ambient of U 2 /H 2 substantially reduced concentration of these deep levels. Two of these states were thought to be related to displacements of the substrate atoms. The third, at Esubc -0.67 eV, was found in only 78 Se + ion implanted GaAs substrates and was thought to be a defect involving both Se and As atoms, rather than intrinsic lattice disorder. It is proposed that the annealing rate of these implantation related deep levels depends crucially on the in-diffusion of arsenic vacancies during heat treatments. (author)

  1. Spatial distribution of the X- and γ- rays induced energy deposition on semi-insulating GaAs:Cr based pixel radiation detector

    International Nuclear Information System (INIS)

    Meneses Gonzalez, Annie; Leyva Fabelo, Antonio; Pinnera Hernandez, Ibrahin; Cruz Inclan, Carlos M.; Abreu Alfonso, Yamiel; Chelkov, Georgy; Zhemchugov, Alexey

    2015-01-01

    Radiation detectors based on Cr compensated GaAs are characterized by high resistivity and good electron transport properties. These characteristics, its high atomic number and good radiation hardness, make GaAs:Cr a promising semiconductor detector within a wide photon energy range. The excellent imaging performance of these detectors for medical and other several applications are already reported in the literature. In this study, the spatial distributions of photon radiation energy deposition on a GaAs:Cr pixel detector with the real device dimensions (900 μm thick, pixels of 45x45 μm 2 and pitch of 55 μm) are presented. The charge carrier distribution profiles generated by the incident photons was additionally determined and discussed. Using the calculated weighting potential for the detector was possible to estimate the percent of charge carriers that shall contribute to the signal generated in the device electrodes. All the calculations were made for the typical photon energies of 241 Am and the energy corresponding to the K α1 characteristic lines of Mo. The MCNPX code system and ARCHIMEDES program were used for mathematical modeling of radiation transport in matter and for semiconductor device simulations respectively. (Author)

  2. The effects of illumination on deep levels observed in as-grown and low-energy electron irradiated high-purity semi-insulating 4H-SiC

    Science.gov (United States)

    Alfieri, G.; Knoll, L.; Kranz, L.; Sundaramoorthy, V.

    2018-05-01

    High-purity semi-insulating 4H-SiC can find a variety of applications, ranging from power electronics to quantum computing applications. However, data on the electronic properties of deep levels in this material are scarce. For this reason, we present a deep level transient spectroscopy study on HPSI 4H-SiC substrates, both as-grown and irradiated with low-energy electrons (to displace only C-atoms). Our investigation reveals the presence of four deep levels with activation energies in the 0.4-0.9 eV range. The concentrations of three of these levels increase by at least one order of magnitude after irradiation. Furthermore, we analyzed the behavior of these traps under sub- and above-band gap illumination. The nature of the traps is discussed in the light of the present data and results reported in the literature.

  3. Stable Amplification and High Current Drop Bistable Switching in Supercritical GaAs Tills

    DEFF Research Database (Denmark)

    Izadpanah, S.H; Jeppsson, B; Jeppesen, Palle

    1974-01-01

    Bistable switching with current drops of 40% and switching times of 100 ps are obtained in pulsed operation of 10¿m supercritically doped n+ nn+ GaAs Transferred Electron Devices (TEDs). When CW-operated the same devices exhibit a 5-17 GHz bandwidth for the stable negative resistance.......Bistable switching with current drops of 40% and switching times of 100 ps are obtained in pulsed operation of 10¿m supercritically doped n+ nn+ GaAs Transferred Electron Devices (TEDs). When CW-operated the same devices exhibit a 5-17 GHz bandwidth for the stable negative resistance....

  4. Design of a GaAs X-ray imaging sensor with integrated HEMT readout circuitry

    Energy Technology Data Exchange (ETDEWEB)

    Boardman, D

    2002-01-01

    A new monolithic semi-insulating (SI) GaAs sensor design for X-ray imaging applications between 10-100keV has been proposed. Monolithic pixel detectors offer a number of advantages over hybrid bump-bonded detectors, such as high device yield, low costs and are easier to produce large scale arrays. In this thesis, an investigation is made of the use of a SI GaAs wafer as both a detector element and substrate for the epitaxially grown High Electron Mobility Transistors (HEMTs). The design of the HEMT transistors, optimised for this application, were produced with the aid of the Silvaco 'Virtual Wafer Fab' simulation package. It was determined that the device characteristics would consist of a small positive threshold voltage, a low off-state drain current and high transconductance. The final HEMT transistor design, that would be integrated to a pixel detector, had a threshold voltage of 0.17V, an off-state leakage current of {approx}1nA and a transconductance of 7.4mS. A number of test detectors were characterised using an ion beam induced charge technique. Charge collection efficiency maps of the test detectors were produced to determine their quality as a X-ray detection material. From the results, the inhomogeneity of SI GaAs, homogeneity of epitaxial GaAs and granular nature of polycrystalline GaAs, were observed. The best of these detectors was used in conjunction with a commercial field effect transistor to produce a hybrid device. The charge switching nature of the hybrid device was shown and a sensitivity of 0.44pC/{mu}Gy mm{sup 2}, for a detector bias of 60V, was found. The functionality of the hybrid sensor was the same to that proposed for the monolithic sensor. The fabrication of the monolithic sensor, with an integrated HEMT transistor and external capacitor, was achieved. To reach the next stage of producing a monolithic sensor that integrates charge, requires further work in the design and the fabrication process. (author)

  5. Design of a GaAs X-ray imaging sensor with integrated HEMT readout circuitry

    International Nuclear Information System (INIS)

    Boardman, D.

    2002-01-01

    A new monolithic semi-insulating (SI) GaAs sensor design for X-ray imaging applications between 10-100keV has been proposed. Monolithic pixel detectors offer a number of advantages over hybrid bump-bonded detectors, such as high device yield, low costs and are easier to produce large scale arrays. In this thesis, an investigation is made of the use of a SI GaAs wafer as both a detector element and substrate for the epitaxially grown High Electron Mobility Transistors (HEMTs). The design of the HEMT transistors, optimised for this application, were produced with the aid of the Silvaco 'Virtual Wafer Fab' simulation package. It was determined that the device characteristics would consist of a small positive threshold voltage, a low off-state drain current and high transconductance. The final HEMT transistor design, that would be integrated to a pixel detector, had a threshold voltage of 0.17V, an off-state leakage current of ∼1nA and a transconductance of 7.4mS. A number of test detectors were characterised using an ion beam induced charge technique. Charge collection efficiency maps of the test detectors were produced to determine their quality as a X-ray detection material. From the results, the inhomogeneity of SI GaAs, homogeneity of epitaxial GaAs and granular nature of polycrystalline GaAs, were observed. The best of these detectors was used in conjunction with a commercial field effect transistor to produce a hybrid device. The charge switching nature of the hybrid device was shown and a sensitivity of 0.44pC/μGy mm 2 , for a detector bias of 60V, was found. The functionality of the hybrid sensor was the same to that proposed for the monolithic sensor. The fabrication of the monolithic sensor, with an integrated HEMT transistor and external capacitor, was achieved. To reach the next stage of producing a monolithic sensor that integrates charge, requires further work in the design and the fabrication process. (author)

  6. Influence of magnetic and ultrasonic fields on coefficient of reflectivity of GaAs, GaSb and InAs crystals

    International Nuclear Information System (INIS)

    Zaveryukhin, B.N.; Zaveryukhina, N.N.; Zaveryukhina, E.V.; Volodarskiy, V.V.

    2007-01-01

    Full text: Previously we demonstrated for the first time in the world that ultrasonic waves of the megahertz range can change the transport properties and a structure of semiconductors. In this work we have experimentally studied the influence of ultrasonic treatment on the spectral coefficients of reflection R in the magnetic fields of the samples of GaAs-, GaSb- and InAs-crystals. The reflectance spectra in the magnetic field of the samples before and after the ultrasonic treatment (UST) for a certain time were measured in a broad wavelength range including ultraviolet, visible, and infrared spectral regions. The semi-insulating GaAs-crystals had a thickness d=100 μm and a working area S of up to 3sm 2 . The p-GaSb- crystals had an area of S=0.25sm 2 and d =250 μm. The base p-GaSb-layers possessed the concentration N=2·10 17 sm 3 and n-GaSb-layers with a thickness of 0.5 m were created by diffusion doping with phosphorus. Besides, the experiments were performed also for of the n-InAs-crystals. The samples of the InAs-n crystals had a thickness of 100 μm an area S = 0.25 sm 2 . Some remains of sulfuric (S) were discovered in InAs-samples. As could was see from the experiments, all the initial IR spectra measured for the samples with various dopant concentrations NP exhibit maximums (peaks) for 0.2 μm and minimum (holes) for. The reflectance spectra measured after UST for time of t > l hour clearly reveal a shift of the R minima toward longer wavelengths and a general decrease in the reflectance of each sample. The shift of the R is unambiguous evidence of the acoustically stimulated diffusion of impurity (phosphorus) inward of the samples. Discovered peaks and holes slitted and changed their sizes in the magnetic fields. It should be emphasized that behavior of the R spectra of the GaAs-, In As- and GaSb- samples is determined by the same mechanisms. Changes of the R spectra after the UST are explained by acoustically stimulated diffusion of the dopant inward

  7. Sidewall GaAs tunnel junctions fabricated using molecular layer epitaxy

    Directory of Open Access Journals (Sweden)

    Takeo Ohno and Yutaka Oyama

    2012-01-01

    Full Text Available In this article we review the fundamental properties and applications of sidewall GaAs tunnel junctions. Heavily impurity-doped GaAs epitaxial layers were prepared using molecular layer epitaxy (MLE, in which intermittent injections of precursors in ultrahigh vacuum were applied, and sidewall tunnel junctions were fabricated using a combination of device mesa wet etching of the GaAs MLE layer and low-temperature area-selective regrowth. The fabricated tunnel junctions on the GaAs sidewall with normal mesa orientation showed a record peak current density of 35 000 A cm-2. They can potentially be used as terahertz devices such as a tunnel injection transit time effect diode or an ideal static induction transistor.

  8. Plasma treatment of porous GaAs surface formed by electrochemical etching method: Characterization and properties

    International Nuclear Information System (INIS)

    Naddaf, M.; Saloum, S.

    2008-12-01

    Porous GaAs samples were formed by electrochemical anodic etching of Zn doped p-type GaAs (100) wafers at different etching parameters (time, mode of applied voltage or current and electrolyte). The effect of etching parameters and plasma surface treatment on the optical properties of the prepared sample has been investigated by using room temperature photoluminescence (PL), Raman spectroscopy and reflectance spectroscopic measurements in the range (400-800 nm). The surface morphological changes were studied by using atomic force microscope. It has been found that etching parameters can be controlled to produce a considerably low optical reflectivity porous GaAs layer, attractive for use in solar cells. In addition, it has been observed that the deposition of plasma polymerized HMDSO thin film on porous GaAs surface can be utilized to produce a surface with novel optical properties interesting for solar cells and optoelectronic devices. (author)

  9. Photovoltaic X-ray detectors based on epitaxial GaAs structures

    Energy Technology Data Exchange (ETDEWEB)

    Achmadullin, R.A. [Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 1 Ac. Vvedenski square, Fryazino 141190, Moscow region (Russian Federation); Artemov, V.V. [Shubnikov Institute of Crystallography, Russian Academy of Sciences, 59 Leninski pr., Moscow B-333, 117333 (Russian Federation); Dvoryankin, V.F. [Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 1 Ac. Vvedenski square, Fryazino 141190, Moscow region (Russian Federation)]. E-mail: vfd217@ire216.msk.su; Dvoryankina, G.G. [Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 1 Ac. Vvedenski square, Fryazino 141190, Moscow region (Russian Federation); Dikaev, Yu.M. [Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 1 Ac. Vvedenski square, Fryazino 141190, Moscow region (Russian Federation); Ermakov, M.G. [Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 1 Ac. Vvedenski square, Fryazino 141190, Moscow region (Russian Federation); Ermakova, O.N. [Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 1 Ac. Vvedenski square, Fryazino 141190, Moscow region (Russian Federation); Chmil, V.B. [Scientific State Center, High Energy Physics Institute, Protvino, Moscow region (Russian Federation); Holodenko, A.G. [Scientific State Center, High Energy Physics Institute, Protvino, Moscow region (Russian Federation); Kudryashov, A.A.; Krikunov, A.I.; Petrov, A.G.; Telegin, A.A. [Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 1 Ac. Vvedenski square, Fryazino 141190, Moscow region (Russian Federation); Vorobiev, A.P. [Scientific State Center, High Energy Physics Institute, Protvino, Moscow region (Russian Federation)

    2005-12-01

    A new type of the photovoltaic X-ray detector based on epitaxial p{sup +}-n-n'-n{sup +} GaAs structures which provides a high efficiency of charge collection in the non-bias operation mode at room temperature is proposed. The GaAs epitaxial structures were grown by vapor-phase epitaxy on heavily doped n{sup +}-GaAs(1 0 0) substrates. The absorption efficiency of GaAs X-ray detector is discussed. I-V and C-V characteristics of the photovoltaic X-ray detectors are analyzed. The built-in electric field profiles in the depletion region of epitaxial structures are measured by the EBIC method. Charge collection efficiency to {alpha}-particles and {gamma}-radiation are measured. The application of X-ray detectors is discussed.

  10. ECV profiling of GaAs and GaN HEMT heterostructures

    Science.gov (United States)

    Yakovlev, G.; Zubkov, V.

    2018-03-01

    AlGaAs/InGaAs/GaAs and AlGaN/GaN HEMT heterostructures were investigated by means of electrochemical capacitance-voltage technique. A set of test structures were fabricated using various doping techniques: standard doping, δ-doping GaAs pHEMT and nondoping GaN HEMT. The concentration profiles of free charge carriers across the samples were experimentally obtained. The QW filling was analyzed and compared for different mechanisms of emitter doping and 2DEG origins.

  11. Breakover mechanism of GaAs photoconductive switch triggering spark gap for high power applications

    Science.gov (United States)

    Tian, Liqiang; Shi, Wei; Feng, Qingqing

    2011-11-01

    A spark gap (SG) triggered by a semi-insulating GaAs photoconductive semiconductor switch (PCSS) is presented. Currents as high as 5.6 kA have been generated using the combined switch, which is excited by a laser pulse with energy of 1.8 mJ and under a bias of 4 kV. Based on the transferred-electron effect and gas streamer theory, the breakover characteristics of the combined switch are analyzed. The photoexcited carrier density in the PCSS is calculated. The calculation and analysis indicate that the PCSS breakover is caused by nucleation of the photoactivated avalanching charge domain. It is shown that the high output current is generated by the discharge of a high-energy gas streamer induced by the strong local electric field distortion or by overvoltage of the SG resulting from quenching of the avalanching domain, and periodic oscillation of the current is caused by interaction between the gas streamer and the charge domain. The cycle of the current oscillation is determined by the rise time of the triggering electric pulse generated by the PCSS, the pulse transmission time between the PCSS and the SG, and the streamer transit time in the SG.

  12. Strain buildup in GaAs due to 100 MeV Ag ion irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Mishra, Shramana; Bhaumik, Sudipta; Panda, Jaya Kumar [Department of Physics and Meteorology, Indian Institute of Technology, Kharagpur 721 302 (India); Ojha, Sunil [Inter-University Accelerator Center, Aruna Asaf Ali Marg, New Delhi 110 067 (India); Dhar, Achintya [Department of Physics and Meteorology, Indian Institute of Technology, Kharagpur 721 302 (India); Kabiraj, D. [Inter-University Accelerator Center, Aruna Asaf Ali Marg, New Delhi 110 067 (India); Roy, Anushree, E-mail: anushree@phy.iitkgp.ernet.in [Department of Physics and Meteorology, Indian Institute of Technology, Kharagpur 721 302 (India)

    2013-12-01

    The formation of strained layers and a non-monotonic evolution of strain in high energy (100 MeV) silver ion (Ag{sup 7+}) irradiated undoped semi-insulating GaAs are observed and analyzed using Raman scattering and high resolution X-ray diffraction (HRXRD) measurements. At low fluence, compressively strained layers are formed, whereas, with increase in fluence both compressive and tensile strains appear as observed from HRXRD measurements. Further, at low fluence, the change in compressive strain with increase in fluence is found to be sharper than what is observed at higher fluence, thereby suggesting a critical fluence value, beyond which there is a simultaneous generation and annihilation of vacancy type defects. The initial blue shift and subsequent relative red shift beyond above critical fluence in the Raman peak also qualitatively reveal non-monotonic evolution of strain in this case. Finally, we demonstrate the sensitivity of Raman spectroscopy in detecting the decrease in lattice ordering in the crystal in the low fluence regime, below the detection limit of Rutherford back-scattering channeling (c-RBS) measurements.

  13. Experimental studies of the charge limit phenomenon in NEA GaAs photocathodes

    International Nuclear Information System (INIS)

    Tang, H.; Alley, R.K.; Aoyagi, H.; Clendenin, J.E.; Frisch, J.C.; Mulhollan, G.A.; Saez, P.J.; Schultz, D.C.; Turner, J.L.

    1994-06-01

    Negative electron affinity GaAs photocathodes have been in continuous use at SLAC for generating polarized electron beams since early 1992. If the quantum efficiency of a GaAs cathode is below a critical value, the maximum photoemitted charge with photons of energies close to the band gap in a 2-ns pulse is found to be limited by the intrinsic properties of the cathode instead of by the space charge limit. We have studied this novel charge limit phenomenon in a variety of GaAs photocathodes of different structures and doping densities. We find that the charge limit is strongly dependent on the cathode's quantum efficiency and the extraction electric field, and to a lesser degree on the excitation laser wavelength. In addition, we show that the temporal behavior of the charge limit depends critically on the doping density

  14. Schottky barrier measurements on individual GaAs nanowires by X-ray photoemission microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Di Mario, Lorenzo [IMM-CNR, via del Fosso del Cavaliere 100, 00133 Rome (Italy); Turchini, Stefano, E-mail: stefano.turchini@cnr.it [ISM-CNR, via del Fosso del Cavaliere 100, 00133 Rome (Italy); Zamborlini, Giovanni; Feyer, Vitaly [Peter Grünberg Institute (PGI-6) and JARA-FIT, Research Center Jülich, 52425 Jülich (Germany); Tian, Lin [IMM-CNR, via del Fosso del Cavaliere 100, 00133 Rome (Italy); Schneider, Claus M. [Peter Grünberg Institute (PGI-6) and JARA-FIT, Research Center Jülich, 52425 Jülich (Germany); Fakultät für Physik and Center for Nanointegration Duisburg-Essen (CENIDE), Universität Duisburg-Essen, D-47048 Duisburg (Germany); Rubini, Silvia [IOM-CNR, TASC Laboratory, Basovizza 34149, Trieste (Italy); Martelli, Faustino, E-mail: faustino.martelli@cnr.it [IMM-CNR, via del Fosso del Cavaliere 100, 00133 Rome (Italy)

    2016-11-15

    Highlights: • The Schottky barrier at the interface between Cu and GaAs nanowires was measured. • Individual nanowires were investigated by X-ray Photoemission Microscopy. • The Schottky barrier at different positions along the nanowire was evaluated. - Abstract: We present measurements of the Schottky barrier height on individual GaAs nanowires by means of x-ray photoelectron emission microscopy (XPEEM). Values of 0.73 and 0.51 eV, averaged over the entire wires, were measured on Cu-covered n-doped and p-doped GaAs nanowires, respectively, in agreement with results obtained on bulk material. Our measurements show that XPEEM can become a feasible and reliable investigation tool of interface formation at the nanoscale and pave the way towards the study of size-dependent effects on semiconductor-based structures.

  15. Radiation hardness of GaAs sensors against gamma-rays, neutrons and electrons

    Energy Technology Data Exchange (ETDEWEB)

    Šagátová, Andrea, E-mail: andrea.sagatova@stuba.sk [Institute of Nuclear and Physical Engineering, Faculty of Electrical Engineering and Information Technology, Slovak University of Technology, Ilkovičova 3, 812 19 Bratislava (Slovakia); University Centre of Electron Accelerators, Slovak Medical University, Ku kyselke 497, 911 06 Trenčín (Slovakia); Zaťko, Bohumír; Dubecký, František [Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava (Slovakia); Ly Anh, Tu [Faculty of Applied Science, University of Technology VNU HCM, 268 Ly Thuong Kiet Street, District 10, Ho Chi Minh City (Viet Nam); Nečas, Vladimír; Sedlačková, Katarína; Pavlovič, Márius [Institute of Nuclear and Physical Engineering, Faculty of Electrical Engineering and Information Technology, Slovak University of Technology, Ilkovičova 3, 812 19 Bratislava (Slovakia); Fülöp, Marko [University Centre of Electron Accelerators, Slovak Medical University, Ku kyselke 497, 911 06 Trenčín (Slovakia)

    2017-02-15

    Highlights: • Radiation hardness of SI GaAs detectors against gamma-rays, neutrons and electrons was compared. • Good agreement was achieved between the experimental results and displacement damage factor of different types of radiation. • CCE and FWHM first slightly improved (by 1–8%) and just then degraded with the cumulative dose. • An increase of detection efficiency with cumulative dose was observed. - Abstract: Radiation hardness of semi-insulating GaAs detectors against {sup 60}Co gamma-rays, fast neutrons and 5 MeV electrons was compared. Slight improvements in charge collection efficiency (CCE) and energy resolution in FWHM (Full Width at Half Maximum) were observed at low doses with all kinds of radiation followed by their degradation. The effect occurred at a dose of about 10 Gy of neutrons (CCE improved by 1%, FWHM by 5% on average), at 1 kGy of electrons (FWHM decreased by 3% on average) and at 10 kGy of gamma-rays (CCE raised by 5% and FWHM dropped by 8% on average), which is in agreement with the relative displacement damage of the used types of radiation. Gamma-rays of MeV energies are 1000-times less damaging than similar neutrons and electrons about 10-times more damaging than photons. On irradiating the detectors with neutrons and electrons, we observed a global increase in their detection efficiency, which was caused probably by enlargement of the active detector area as a consequence of created radiation defects in the base material. Detectors were still functional after a dose of 1140 kGy of ∼1 MeV photons, 104 kGy of 5 MeV electrons but only up to 0.576 kGy of fast (∼2 to 30 MeV) neutrons.

  16. Effect of thermal annealing on optical properties of implanted GaAs

    NARCIS (Netherlands)

    Kulik, M; Komarov, FF; Maczka, D

    GaAs samples doped with indium atoms by ion implantation and thermal annealed were studied using a channelling method, Rutherford backscattering, and an ellipsometry. From these measurements it was observed that the layer implanted with 3 x 10(16) cm(-2) indium dose was totally damaged and its

  17. Resistance Fluctuations in GaAs Nanowire Grids

    Directory of Open Access Journals (Sweden)

    Ivan Marasović

    2014-01-01

    Full Text Available We present a numerical study on resistance fluctuations in a series of nanowire-based grids. Each grid is made of GaAs nanowires arranged in parallel with metallic contacts crossing all nanowires perpendicularly. Electrical properties of GaAs nanowires known from previous experimental research are used as input parameters in the simulation procedure. Due to the nonhomogeneous doping, the resistivity changes along nanowire. Allowing two possible nanowire orientations (“upwards” or “downwards”, the resulting grid is partially disordered in vertical direction which causes resistance fluctuations. The system is modeled using a two-dimensional random resistor network. Transfer-matrix computation algorithm is used to calculate the total network resistance. It is found that probability density function (PDF of resistance fluctuations for a series of nanowire grids changes from Gaussian behavior towards the Bramwell-Holdsworth-Pinton distribution when both nanowire orientations are equally represented in the grid.

  18. Asymmetric GaAs n-type double δ-doped quantum wells as a source of intersubband-related nonlinear optical response: Effects of an applied electric field

    Energy Technology Data Exchange (ETDEWEB)

    Rodríguez-Magdaleno, K.A.; Martínez-Orozco, J.C.; Rodríguez-Vargas, I. [Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calz. Solidaridad Esq. Paseo a La Bufa S/N. C.P. 98060 Zacatecas (Mexico); Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, CP 62209 Cuernavaca, Morelos (Mexico); Física Teórica y Aplicada, Escuela de Ingeniería de Antioquia, AA 7516 Medellín (Colombia); Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia); Duque, C.A., E-mail: cduque@fisica.udea.edu.co [Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia)

    2014-03-15

    In this work, the conduction band electron states and the associated intersubband-related linear and nonlinear optical absorption coefficient and relative refractive index change are calculated for an asymmetric double n-type δ-doped quantum well in a GaAs-matrix. The effects of an external applied static electric field are included. Values of the two-dimensional impurities density (N{sub 2d}) of each single δ-doped quantum well are taken to vary within the range of 1.0×10{sup 12} to 7.0×10{sup 12} cm{sup −2}, consistent with the experimental data growth regime. The optical responses are reported as a function of the δ-doped impurities density and the applied electric field. It is shown that single electron states and the related optical quantities are significantly affected by the structural asymmetry of the double δ-doped quantum well system. In addition, a brief comparison with the free-carrier-related optical response is presented. -- Highlights: • Nonlinear optics in asymmetric double n-type δ-doped quantum well in a GaAs-matrix. • The system is considered under external applied electric field in growth direction. • The 2D impurity density is consistent with the experimental data growth regime. • The optical quantities are significantly affected by the structural asymmetry of the system.

  19. Asymmetric GaAs n-type double δ-doped quantum wells as a source of intersubband-related nonlinear optical response: Effects of an applied electric field

    International Nuclear Information System (INIS)

    Rodríguez-Magdaleno, K.A.; Martínez-Orozco, J.C.; Rodríguez-Vargas, I.; Mora-Ramos, M.E.; Duque, C.A.

    2014-01-01

    In this work, the conduction band electron states and the associated intersubband-related linear and nonlinear optical absorption coefficient and relative refractive index change are calculated for an asymmetric double n-type δ-doped quantum well in a GaAs-matrix. The effects of an external applied static electric field are included. Values of the two-dimensional impurities density (N 2d ) of each single δ-doped quantum well are taken to vary within the range of 1.0×10 12 to 7.0×10 12 cm −2 , consistent with the experimental data growth regime. The optical responses are reported as a function of the δ-doped impurities density and the applied electric field. It is shown that single electron states and the related optical quantities are significantly affected by the structural asymmetry of the double δ-doped quantum well system. In addition, a brief comparison with the free-carrier-related optical response is presented. -- Highlights: • Nonlinear optics in asymmetric double n-type δ-doped quantum well in a GaAs-matrix. • The system is considered under external applied electric field in growth direction. • The 2D impurity density is consistent with the experimental data growth regime. • The optical quantities are significantly affected by the structural asymmetry of the system

  20. Thermal conductivity of bulk GaN—Effects of oxygen, magnesium doping, and strain field compensation

    International Nuclear Information System (INIS)

    Simon, Roland B.; Anaya, Julian; Kuball, Martin

    2014-01-01

    The effect of oxygen doping (n-type) and oxygen (O)-magnesium (Mg) co-doping (semi-insulating) on the thermal conductivity of ammonothermal bulk GaN was studied via 3-omega measurements and a modified Callaway model. Oxygen doping was shown to significantly reduce thermal conductivity, whereas O-Mg co-doped GaN exhibited a thermal conductivity close to that of undoped GaN. The latter was attributed to a decreased phonon scattering rate due the compensation of impurity-generated strain fields as a result of dopant-complex formation. The results have great implications for GaN electronic and optoelectronic device applications on bulk GaN substrates

  1. Radiation effects in pigtailed GaAs and GaA1As LEDs

    International Nuclear Information System (INIS)

    Barnes, C.E.

    1981-06-01

    Permanent and transient radiation effects have been studied in Plessey pigtailed, high radiance GaAs and GaAlAs LEDs using neutron, gamma ray and X-ray sources. The radiation-induced source of degradation in these devices was determined by also examining both bare, unpigtailed LEDs and separate samples of the Corning fibers used as pigtails. No transient effects were observed in the unpigtailed LEDs during either pulsed neutron or X-ray exposure. In contrast, the Corning doped silica fibers exhibited strong transient attenuation following pulsed X-ray bombardment. Permanent neutron damage in these pigtailed LEDs consisted essentially of light output degradation in the LED itself. Permanent gamma ray effects due to a Co-60 irradiation of 1 megarad were restricted to a small increase in attenuation in the fiber. The two primary radiation effects were then transient attenuation in the fiber pigtail and permanent neutron-induced degradation of the LED

  2. Effect of band gap narrowing on GaAs tunnel diode I-V characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Lebib, A.; Hannanchi, R. [Laboratoire d' énergie et de matériaux, LabEM-LR11ES34-Université de sousse (Tunisia); Beji, L., E-mail: lotbej_fr@yahoo.fr [Laboratoire d' énergie et de matériaux, LabEM-LR11ES34-Université de sousse (Tunisia); EL Jani, B. [Unité de Recherche sur les Hétéro-Epitaxies et Applications, Faculté des Sciences, Université de Monastir, 5019 Monastir (Tunisia)

    2016-12-01

    We report on experimental and theoretical study of current-voltage characteristics of C/Si-doped GaAs tunnel diode. For the investigation of the experimental data, we take into account the band-gap narrowing (BGN) effect due to heavily-doped sides of the tunnel diode. The BGN of the n- and p-sides of tunnel diode was measured by photoluminescence spectroscopy. The comparison between theoretical results and experimental data reveals that BGN effect enhances tunneling currents and hence should be considered to identify more accurately the different transport mechanisms in the junction. For C/Si-doped GaAs tunnel diode, we found that direct tunneling is the dominant transport mechanism at low voltages. At higher voltages, this mechanism is replaced by the rate-controlling tunneling via gap states in the forbidden gap.

  3. Effect of low and staggered gap quantum wells inserted in GaAs tunnel junctions

    Science.gov (United States)

    Louarn, K.; Claveau, Y.; Marigo-Lombart, L.; Fontaine, C.; Arnoult, A.; Piquemal, F.; Bounouh, A.; Cavassilas, N.; Almuneau, G.

    2018-04-01

    In this article, we investigate the impact of the insertion of either a type I InGaAs or a type II InGaAs/GaAsSb quantum well on the performances of MBE-grown GaAs tunnel junctions (TJs). The devices are designed and simulated using a quantum transport model based on the non-equilibrium Green’s function formalism and a 6-band k.p Hamiltonian. We experimentally observe significant improvements of the peak tunneling current density on both heterostructures with a 460-fold increase for a moderately doped GaAs TJ when the InGaAs QW is inserted at the junction interface, and a 3-fold improvement on a highly doped GaAs TJ integrating a type II InGaAs/GaAsSb QW. Thus, the simple insertion of staggered band lineup heterostructures enables us to reach a tunneling current well above the kA cm‑2 range, equivalent to the best achieved results for Si-doped GaAs TJs, implying very interesting potential for TJ-based components, such as multi-junction solar cells, vertical cavity surface emitting lasers and tunnel-field effect transistors.

  4. Biexciton emission from single isoelectronic traps formed by nitrogen-nitrogen pairs in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Takamiya, Kengo; Fukushima, Toshiyuki; Yagi, Shuhei; Hijikata, Yasuto; Yaguchi, Hiroyuki [Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku , Saitama 338-8570 (Japan); Mochizuki, Toshimitsu; Yoshita, Masahiro; Akiyama, Hidefumi [Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581 (Japan); Kuboya, Shigeyuki; Onabe, Kentaro [Department of Advanced Materials Science, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581 (Japan); Katayama, Ryuji [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan)

    2013-12-04

    We have studied photoluminescence (PL) from individual isoelectronic traps formed by nitrogen-nitrogen (NN) pairs in GaAs. Sharp emission lines due to exciton and biexciton were observed from individual isoelectronic traps in nitrogen atomic-layer doped (ALD) GaAs. The binding energy of biexciton bound to individual isoelectronic traps was approximately 8 meV. Both the exciton and biexciton luminescence lines show completely random polarization and no fine-structure splitting. These results are desirable to the application to the quantum cryptography used in the field of quantum information technology.

  5. Plasma treatment of porous GaAs surface formed by electrochemical etching method: Characterization and properties

    International Nuclear Information System (INIS)

    Saloum, S.; Naddaf, M.

    2010-01-01

    Porous GaAs samples were formed by electrochemical anodic etching of Zn doped p-type GaAs (100) wafers at different etching parameters (time, mode of applied voltage or current and electrolyte). The effect of etching parameters and plasma surface treatment on the optical properties of the prepared sample has been investigated by using room temperature photoluminescence (PL), Raman spectroscopy and reflectance spectroscopic measurements in the range (400-800 nm). The surface morphological changes were studied by using atomic force microscope. (author)

  6. Lifetime measurements by open circuit voltage decay in GaAs and InP diodes

    International Nuclear Information System (INIS)

    Bhimnathwala, H.G.; Tyagi, S.D.; Bothra, S.; Ghandhi, S.K.; Borrego, J.M.

    1990-01-01

    Minority carrier lifetimes in the base of solar cells made in GaAs and InP are measured by open circuit voltage decay method. This paper describes the measurement technique and the conditions under which the minority carrier lifetimes can be measured. Minority carrier lifetimes ranging from 1.6 to 34 ns in InP of different doping concentrations are measured. A minority carrier lifetime of 6 ns was measured in n-type GaAs which agrees well with the lifetime of 5.7 ns measured by transient microwave reflection

  7. Modeling and Design of Graphene GaAs Junction Solar Cell

    Directory of Open Access Journals (Sweden)

    Yawei Kuang

    2015-01-01

    Full Text Available Graphene based GaAs junction solar cell is modeled and investigated by Silvaco TCAD tools. The photovoltaic behaviors have been investigated considering structure and process parameters such as substrate thickness, dependence between graphene work function and transmittance, and n-type doping concentration in GaAs. The results show that the most effective region for photo photogenerated carriers locates very close to the interface under light illumination. Comprehensive technological design for junction yields a significant improvement of power conversion efficiency from 0.772% to 2.218%. These results are in good agreement with the reported experimental work.

  8. Influence of arsenic flow on the crystal structure of epitaxial GaAs grown at low temperatures on GaAs (100) and (111)A substrates

    Energy Technology Data Exchange (ETDEWEB)

    Galiev, G. B.; Klimov, E. A. [Russian Academy of Sciences, Institute of Ultra High Frequency Semiconductor Electronics (Russian Federation); Vasiliev, A. L.; Imamov, R. M. [Russian Academy of Sciences, Shubnikov Institute of Crystallography, Federal Scientific Research Centre “Crystallography and Photonics,” (Russian Federation); Pushkarev, S. S., E-mail: s-s-e-r-p@mail.ru [Russian Academy of Sciences, Institute of Ultra High Frequency Semiconductor Electronics (Russian Federation); Trunkin, I. N. [National Research Centre “Kurchatov Institute” (Russian Federation); Maltsev, P. P. [Russian Academy of Sciences, Institute of Ultra High Frequency Semiconductor Electronics (Russian Federation)

    2017-01-15

    The influence of arsenic flow in a growth chamber on the crystal structure of GaAs grown by molecular-beam epitaxy at a temperature of 240°C on GaAs (100) and (111)A substrates has been investigated. The flow ratio γ of arsenic As4 and gallium was varied in the range from 16 to 50. GaAs films were either undoped, or homogeneously doped with silicon, or contained three equidistantly spaced silicon δ-layers. The structural quality of the annealed samples has been investigated by transmission electron microscopy. It is established for the first time that silicon δ-layers in “low-temperature” GaAs serve as formation centers of arsenic precipitates. Their average size, concentration, and spatial distribution are estimated. The dependence of the film structural quality on γ is analyzed. Regions 100–150 nm in size have been revealed in some samples and identified (by X-ray microanalysis) as pores. It is found that, in the entire range of γ under consideration, GaAs films on (111)A substrates have a poorer structural quality and become polycrystalline beginning with a thickness of 150–200 nm.

  9. Photoelectrochemical Water Oxidation by GaAs Nanowire Arrays Protected with Atomic Layer Deposited NiO x Electrocatalysts

    Science.gov (United States)

    Zeng, Joy; Xu, Xiaoqing; Parameshwaran, Vijay; Baker, Jon; Bent, Stacey; Wong, H.-S. Philip; Clemens, Bruce

    2018-02-01

    Photoelectrochemical (PEC) hydrogen production makes possible the direct conversion of solar energy into chemical fuel. In this work, PEC photoanodes consisting of GaAs nanowire (NW) arrays were fabricated, characterized, and then demonstrated for the oxygen evolution reaction (OER). Uniform and periodic GaAs nanowire arrays were grown on a heavily n-doped GaAs substrates by metal-organic chemical vapor deposition selective area growth. The nanowire arrays were characterized using cyclic voltammetry and impedance spectroscopy in a non-aqueous electrochemical system using ferrocene/ferrocenium (Fc/Fc+) as a redox couple, and a maximum oxidation photocurrent of 11.1 mA/cm2 was measured. GaAs NW arrays with a 36 nm layer of nickel oxide (NiO x ) synthesized by atomic layer deposition were then used as photoanodes to drive the OER. In addition to acting as an electrocatalyst, the NiO x layer served to protect the GaAs NWs from oxidative corrosion. Using this strategy, GaAs NW photoanodes were successfully used for the oxygen evolution reaction. This is the first demonstration of GaAs NW arrays for effective OER, and the fabrication and protection strategy developed in this work can be extended to study any other nanostructured semiconductor materials systems for electrochemical solar energy conversion.

  10. Towards quantum dots on GaAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Moesl, Johannes; Ludwig, Stefan [Fakultaet fuer Physik, Center for NanoScience, LMU Munich, Geschwister-Scholl- Platz 1, D-80539 Muenchen (Germany); Fontcuberta i Morral, Anna [TU Munich, Walter Schottky Institut, Am Coulombwall 3, 85748 Garching (Germany); EPF, Lausanne (Switzerland)

    2009-07-01

    Semiconductor nanowires is an emergent research topic in the field of nanoelectronics, as they form an excellent building block for 0D and 1D applications and allow novel architectures and material combinations. We study electronic transport properties of catalyst-free MBE grown GaAs nanowires, p-doped at a number of different doping levels. Detailed characterization of the wires including electronic contacts fabricated by e-beam lithography and based on palladium or annealed zinc-silver alloys are discussed. Contact properties and a pronounced hysteresis of the current through the nanowires, as a backgate-voltage is swept, are explained within tentative models. In addition we present first transport measurements on quantum dots, which are defined electrostatically as well as by etched constrictions.

  11. High mobility single-crystalline-like GaAs thin films on inexpensive flexible metal substrates by metal-organic chemical vapor deposition

    International Nuclear Information System (INIS)

    Dutta, P.; Rathi, M.; Gao, Y.; Yao, Y.; Selvamanickam, V.; Zheng, N.; Ahrenkiel, P.; Martinez, J.

    2014-01-01

    We demonstrate heteroepitaxial growth of single-crystalline-like n and p-type doped GaAs thin films on inexpensive, flexible, and light-weight metal foils by metal-organic chemical vapor deposition. Single-crystalline-like Ge thin film on biaxially textured templates made by ion beam assisted deposition on metal foil served as the epitaxy enabling substrate for GaAs growth. The GaAs films exhibited strong (004) preferred orientation, sharp in-plane texture, low grain misorientation, strong photoluminescence, and a defect density of ∼10 7  cm −2 . Furthermore, the GaAs films exhibited hole and electron mobilities as high as 66 and 300 cm 2 /V-s, respectively. High mobility single-crystalline-like GaAs thin films on inexpensive metal substrates can pave the path for roll-to-roll manufacturing of flexible III-V solar cells for the mainstream photovoltaics market.

  12. Lithium compensation of GaAs

    International Nuclear Information System (INIS)

    Alexiev, D.; Tavendale, A.J.

    1988-08-01

    Defects generated following Li diffusion into GaAs were studied by optical deep level transient spectroscopy (ODLTS) and deep level transient spectroscopy (DLTS). In an exploratory series of experiments, the effect of Li diffusion on existing trap spectra, defect generation and as a means for the compensation of GaAs was studied. The variables included diffusion temperature, initial trap spectra of GaAs and annealing periods. Detailed measurements of trap energies were made

  13. Neutron transmutation doping of gallium arsenide

    International Nuclear Information System (INIS)

    Alexiev, D.

    1987-12-01

    Neutron transmutation doping (NTD) was studied as a means of compensating p-type Cd-doped GaAs. By introducing specific donor concentrations, the net acceptor level was measured and showed a progressive reduction. The NTD constant K = 0.32 donor atoms.cm 3 per cm 2 was also measured. Radiation damage caused by neutron bombardment was annealed and no additional traps were generated

  14. Sn nanothreads in GaAs: experiment and simulation

    Science.gov (United States)

    Semenikhin, I.; Vyurkov, V.; Bugaev, A.; Khabibullin, R.; Ponomarev, D.; Yachmenev, A.; Maltsev, P.; Ryzhii, M.; Otsuji, T.; Ryzhii, V.

    2016-12-01

    The gated GaAs structures like the field-effect transistor with the array of the Sn nanothreads was fabricated via delta-doping of vicinal GaAs surface by Sn atoms with a subsequent regrowth. That results in the formation of the chains of Sn atoms at the terrace edges. Two device models were developed. The quantum model accounts for the quantization of the electron energy spectrum in the self-consistent two-dimensional electric potential, herewith the electron density distribution in nanothread arrays for different gate voltages is calculated. The classical model ignores the quantization and electrons are distributed in space according to 3D density of states and Fermi-Dirac statistics. It turned out that qualitatively both models demonstrate similar behavior, nevertheless, the classical one is in better quantitative agreement with experimental data. Plausibly, the quantization could be ignored because Sn atoms are randomly placed along the thread axis. The terahertz hot-electron bolometers (HEBs) could be based on the structure under consideration.

  15. Bismuth alloying properties in GaAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Lu [State Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, PO Box 72, Beijing 100876 (China); Lu, Pengfei, E-mail: photon.bupt@gmail.com [State Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, PO Box 72, Beijing 100876 (China); Cao, Huawei; Cai, Ningning; Yu, Zhongyuan [State Key Laboratory of Information Photonics and Optical Communications, Ministry of Education, Beijing University of Posts and Telecommunications, PO Box 72, Beijing 100876 (China); Gao, Tao [Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065 (China); Wang, Shumin [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050 (China); Photonics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, 41296 Gothenburg (Sweden)

    2013-09-15

    First-principles calculations have been performed to investigate the structural, electronic and optical properties of bismuth alloying in GaAs nanowires. A typical model of Ga{sub 31}As{sub 31} nanowires is introduced for its reasonable band gap. The band gap of GaAs{sub 1−x}Bi{sub x} shrinks clearly with the increasing Bi concentration and the band edge shifts when spin–orbit coupling (SOC) is considered. The insertion of Bi atom leads to hybridization of Ga/As/Bi p states which contributes a lot around Fermi level. Scissor effect is involved. The optical properties are presented, including dielectric function, optical absorption spectra and reflectivity, which are also varied with the increasing of Bi concentrations. - Graphical abstract: Top view of Bi-doped GaAs nanowires. Ga, As, and Bi atoms are denoted with grey, purple and red balls, respectively. Display Omitted - Highlights: • A typical model of Ga{sub 31}As{sub 31} nanowires is introduced for its reasonable band gap. • The band gap of GaAs{sub 1−x}Bi{sub x} shrinks clearly with the increasing Bi concentration. • The band edge shifts when spin–orbit coupling (SOC) is considered. • The insertion of Bi atom leads to hybridization of Ga/As/Bi p states.

  16. Spin Hall Effect in Doped Semiconductor Structures

    Science.gov (United States)

    Tse, Wang-Kong; Das Sarma, Sankar

    2006-03-01

    We present a microscopic theory of the extrinsic spin Hall effect based on the diagrammatic perturbation theory. Side-jump (SJ) and skew-scattering (SS) contributions are explicitly taken into account to calculate the spin Hall conductivity, and we show their effects scale as σxy^SJ/σxy^SS ˜(/τ)/ɛF, where τ being the transport relaxation time. Motivated by recent experimental work we apply our theory to n-doped and p-doped 3D and 2D GaAs structures, obtaining analytical formulas for the SJ and SS contributions. Moreover, the ratio of the spin Hall conductivity to longitudinal conductivity is found as σs/σc˜10-3-10-4, in reasonable agreement with the recent experimental results of Kato et al. [Science 306, 1910 (2004)] in n-doped 3D GaAs system.

  17. Observation of the anomalous Hall effect in GaAs

    International Nuclear Information System (INIS)

    Miah, M Idrish

    2007-01-01

    Devices for the direct detection of the spin current, based on the anomalous Hall effect (AHE), are fabricated on n-type GaAs bulk semiconductor materials. The AHE is observed in the device when the photoinduced spin-polarized electrons are injected into it, and it is found that the effect depends on the applied electric field. The origin of the field-dependent observed Hall effect is discussed based on the D'yakonov-Perel' (DP) spin relaxation mechanism. The spin-dependent Hall effect is also found to be enhanced with increasing doping concentration. The present experimental results might have potential applications in semiconductor spintronic devices since the effect is closely related to the spin Hall effect

  18. Observation of the anomalous Hall effect in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Miah, M Idrish [Nanoscale Science and Technology Centre, School of Science, Griffith University, Nathan, Brisbane, QLD 4111 (Australia); Department of Physics, University of Chittagong, Chittagong, Chittagong - 4331 (Bangladesh)

    2007-03-21

    Devices for the direct detection of the spin current, based on the anomalous Hall effect (AHE), are fabricated on n-type GaAs bulk semiconductor materials. The AHE is observed in the device when the photoinduced spin-polarized electrons are injected into it, and it is found that the effect depends on the applied electric field. The origin of the field-dependent observed Hall effect is discussed based on the D'yakonov-Perel' (DP) spin relaxation mechanism. The spin-dependent Hall effect is also found to be enhanced with increasing doping concentration. The present experimental results might have potential applications in semiconductor spintronic devices since the effect is closely related to the spin Hall effect.

  19. Simulation of quantum dots size and spacing effect for intermediate band solar cell application based on InAs quantum dots arrangement in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Hendra, P. I. B., E-mail: ib.hendra@gmail.com; Rahayu, F., E-mail: ib.hendra@gmail.com; Darma, Y., E-mail: ib.hendra@gmail.com [Physical Vapor Deposition Laboratory, Physics of Material Electronics Research, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jl. Ganesha 10, Bandung 40132 (Indonesia)

    2014-03-24

    Intermediate band solar cell (IBSC) has become a promising technology in increasing solar cell efficiency. In this work we compare absorption coefficient profile between InAs quantum dots with GaAs bulk. We calculate the efficiency of GaAs bulk and GaAs doped with 2, 5, and 10 nm InAs quantum dot. Effective distances in quantum dot arrangement based on electron tunneling consideration were also calculated. We presented a simple calculation method with low computing power demand. Results showed that arrangement of quantum dot InAs in GaAs can increase solar cell efficiency from 23.9 % initially up to 60.4%. The effective distance between two quantum dots was found 2 nm in order to give adequate distance to prevent electron tunneling and wave functions overlap.

  20. Surface segregation and the Al problem in GaAs quantum wells

    Science.gov (United States)

    Chung, Yoon Jang; Baldwin, K. W.; West, K. W.; Shayegan, M.; Pfeiffer, L. N.

    2018-03-01

    Low-defect two-dimensional electron systems (2DESs) are essential for studies of fragile many-body interactions that only emerge in nearly-ideal systems. As a result, numerous efforts have been made to improve the quality of modulation-doped AlxGa1 -xAs /GaAs quantum wells (QWs), with an emphasis on purifying the source material of the QW itself or achieving better vacuum in the deposition chamber. However, this approach overlooks another crucial component that comprises such QWs, the AlxGa1 -xAs barrier. Here we show that having a clean Al source and hence a clean barrier is instrumental to obtain a high-quality GaAs 2DES in a QW. We observe that the mobility of the 2DES in GaAs QWs declines as the thickness or Al content of the AlxGa1 -xAs barrier beneath the QW is increased, which we attribute to the surface segregation of oxygen atoms that originate from the Al source. This conjecture is supported by the improved mobility in the GaAs QWs as the Al cell is cleaned out by baking.

  1. High-Performance GaAs Nanowire Solar Cells for Flexible and Transparent Photovoltaics.

    Science.gov (United States)

    Han, Ning; Yang, Zai-xing; Wang, Fengyun; Dong, Guofa; Yip, SenPo; Liang, Xiaoguang; Hung, Tak Fu; Chen, Yunfa; Ho, Johnny C

    2015-09-16

    Among many available photovoltaic technologies at present, gallium arsenide (GaAs) is one of the recognized leaders for performance and reliability; however, it is still a great challenge to achieve cost-effective GaAs solar cells for smart systems such as transparent and flexible photovoltaics. In this study, highly crystalline long GaAs nanowires (NWs) with minimal crystal defects are synthesized economically by chemical vapor deposition and configured into novel Schottky photovoltaic structures by simply using asymmetric Au-Al contacts. Without any doping profiles such as p-n junction and complicated coaxial junction structures, the single NW Schottky device shows a record high apparent energy conversion efficiency of 16% under air mass 1.5 global illumination by normalizing to the projection area of the NW. The corresponding photovoltaic output can be further enhanced by connecting individual cells in series and in parallel as well as by fabricating NW array solar cells via contact printing showing an overall efficiency of 1.6%. Importantly, these Schottky cells can be easily integrated on the glass and plastic substrates for transparent and flexible photovoltaics, which explicitly demonstrate the outstanding versatility and promising perspective of these GaAs NW Schottky photovoltaics for next-generation smart solar energy harvesting devices.

  2. Investigations of p-type signal for ZnO thin films grown on (100)GaAs substrates by pulsed laser deposition

    Energy Technology Data Exchange (ETDEWEB)

    Rogers, D.J. [Nanovation SARL, Orsay (France); Univ. de Technologie de Troyes, Troyes (France); Hosseini Teherani, F. [Nanovation SARL, Orsay (France); Monteiro, T.; Soares, M.; Neves, A.; Carmo, M.; Correia, M.R. [Physics Dept., Univ. of Aveiro (Portugal); Pereira, S. [Physics Dept., Univ. of Aveiro (Portugal); Inst. Tecnologico e Nuclear, Sacavem (Portugal); Lusson, A. [Inst. d' Electronique Fondamentale, Orsay Univ. (France); LPSC - CNRS, Meudon (France); Alves, E.; Barradas, N.P. [Inst. Tecnologico e Nuclear, Sacavem (Portugal); Morrod, J.K.; Prior, K.A. [Physics Dept., Heriot Watt Univ., Edinburgh Scotland (United Kingdom); Kung, P.; Yasan, A.; Razeghi, M. [Center for Quantum Devices, Dept. of Electrical and Computer Engineering, Northwestern Univ., Evanston, IL (United States)

    2006-03-15

    In this work we investigated ZnO films grown on semi-insulating (100)GaAs substrates by pulsed laser deposition. Samples were studied using techniques including X-ray diffraction (XRD), scanning electron microscopy, atomic force microscopy, Raman spectroscopy, temperature dependent photoluminescence, C-V profiling and temperature dependent Hall measurements. The Hall measurements showed a clear p-type response with a relatively high mobility ({proportional_to}260 cm{sup 2}/Vs) and a carrier concentration of {proportional_to}1.8 x 10{sup 19} cm{sup -3}. C-V profiling confirmed a p-type response. XRD and Raman spectroscopy indicated the presence of (0002) oriented wurtzite ZnO plus secondary phase(s) including (101) oriented Zn{sub 2}As{sub 2}O{sub 7}. The results suggest that significant atomic mixing was occurring at the film/substrate interface for films grown at substrate temperatures of 450 C (without post-annealing). (orig.)

  3. Terahertz radiation on the base of accelerated charge carriers in GaAs; Terahertz-Strahlung auf der Basis beschleunigter Ladungstraeger in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Dreyhaupt, Andre

    2008-07-01

    Electromagnetic radiation in the frequency range between about 100 GHz and 5 THz can be used for spectroscopy and microscopy, but it is also promising for security screening and even wireless communication. In the present thesis a planar photoconducting large-area THz radiation source is presented. The device exhibits outstanding properties, in particular high THz field strength and generation efficiency and large spectral bandwidth with short THz pulse length. The THz emission is based on acceleration and deceleration of photoexcited carriers in semiconductor substrates. A metallic interdigitated structure at the surface of semi-insulating GaAs provides the electrodes of an Auston switch. In a biased structure photoexcited charge carriers are accelerated. Hence electromagnetic waves are emitted. An appropriately structured second metallization, electrically isolated from the electrodes, prevents destructive interference of the emitted waves. The structure investigated here combines several advantages of different conventional photoconducting THz sources. First, it provides high electric acceleration fields at moderate voltages owing to the small electrode separation. Second, the large active area in the mm2 range allows excitation by large optical powers of some mW. Optical excitation with near-infrared femtosecond lasers is possible with repetition rates in the GHz range. The presented results point out the excellent characteristics regarding the emitted THz field strength, average power, spectral properties, and easy handling of the interdigitated structure in comparison to various conventional emitter structures. Various modifications of the semiconductor substrate and the optimum excitation conditions were investigated. In the second part of this thesis the dynamic conductivity of GaAs/Al{sub x}Ga{sub 1-x}As superlattices in an applied static electric field was investigated with time-resolved THz spectroscopy. The original goal was to explore whether the

  4. Electrical and optical deep level spectroscopy on Os doped p-InP

    International Nuclear Information System (INIS)

    Parveen, S.; Zafar, N.; Khan, A.; Qureshi, U.S.; Iqbal, M.Z.

    1997-01-01

    Transition metal (TM) impurities are introduced for obtaining semi insulating (III-V) compound semiconductors used as base material for electronic and optoelectronic devices. TM doping introduces near mid gap levels which are used to compensate shallow level donors and acceptors in (III-V) compound semiconductors. The study of electrical properties of heavier transition metals in InP has been turned to an active field of research owing to their potential to produce thermally stable semi insulating substrate materials. Osmium has been tried for this purpose in our work. InP: Os samples have been grown by low pressure metalorganic chemical vapour deposition (LP-MOCVD). Optical and electrical Deep Level Transient Spectroscopy Techniques have been used to characterise osmium related deep level defects in the p-type samples. Three majority carrier (Hole) emitting levels OsA, OsB, OsC and one minority carrier (electron) emitting level Osl are observed in the DLTS and ODLTS measurements on p-type InP:Os. ON optical injection, only Osl appears and all other majority carrier emitting levels disappear dramatically. Special emphasis is given to the detailed comparison by ODLTS and EDLTS, which yields important information on the relative capture cross-sections of Osmium induced levels in p-InP. (author)

  5. Molecular beam epitaxial growth and characterization of GaSb layers on GaAs (0 0 1) substrates

    International Nuclear Information System (INIS)

    Li Yanbo; Zhang Yang; Zhang Yuwei; Wang Baoqiang; Zhu Zhanping; Zeng Yiping

    2012-01-01

    We report on the growth of GaSb layers on GaAs (0 0 1) substrates by molecular beam epitaxy (MBE). We investigate the influence of the GaAs substrate surface treatment, growth temperature, and V/III flux ratios on the crystal quality and the surface morphology of GaSb epilayers. Comparing to Ga-rich GaAs surface preparation, the Sb-rich GaAs surface preparation can promote the growth of higher-quality GaSb material. It is found that the crystal quality, electrical properties, and surface morphology of the GaSb epilayers are highly dependent on the growth temperature, and Sb/Ga flux ratios. Under the optimized growth conditions, we demonstrate the epitaxial growth of high quality GaSb layers on GaAs substrates. The p-type nature of the unintentionally doped GaSb is studied and from the growth conditions dependence of the hole concentrations of the GaSb, we deduce that the main native acceptor in the GaSb is the Ga antisite (Ga Sb ) defect.

  6. The lower yield point of InP and GaAs

    International Nuclear Information System (INIS)

    Siethoff, H.

    1987-01-01

    A study of the strain-rate and temperature dependence of the lower yield stress (τ ly ) in undoped InP and of the strain-rate dependence of τ ly in undoped and Zn-doped GaAs is reported. The deformation along (123) orientation was carried out in compression at constant strain rates ranging from 10 -5 to 10 -2 s -1 . The temperature range extended from 540 to 780 0 C. The activation energy and stress exponent of the dislocation velocity were calculated. Experiments have shown that τ ly of InP depends on temperature and strain rate in a manner similar to other semiconductors like Si and InSb, whereas τ ly of GaAs shows an unusual strain-rate dependence

  7. Sulfur passivation and contact methods for GaAs nanowire solar cells

    International Nuclear Information System (INIS)

    Tajik, N; Peng, Z; Kuyanov, P; LaPierre, R R

    2011-01-01

    The effect of sulfur passivation on core-shell p-n junction GaAs nanowire (NW) solar cells has been investigated. Devices of two types were investigated, consisting of indium tin oxide contact dots or opaque Au finger electrodes. Lateral carrier transport from the NWs to the contact fingers was achieved via a p-doped GaAs surface conduction layer. NWs between the opaque contact fingers had sidewall surfaces exposed for passivation by sulfur. The relative cell efficiency increased by 19% upon passivation. The contribution of the thin film grown between the NWs to the total cell efficiency was estimated by removing the NWs using a sonication procedure. Mechanisms of carrier transport and photovoltaic effects are discussed on the basis of spatially resolved laser scanning measurements.

  8. Nondestructive evaluation of differently doped InP wafers by time-resolved four-wave mixing technique

    International Nuclear Information System (INIS)

    Kadys, A.; Sudzius, M.; Jarasiunas, K.; Mao Luhong; Sun Niefeng

    2006-01-01

    Photoelectric properties of semi-insulating, differently doped, and undoped indium phosphide wafers, grown by the liquid encapsulation Czochralski method, have been investigated by time-resolved picosecond four-wave mixing technique. Deep defect related carrier generation, recombination, and transport properties were investigated experimentally by measuring four-wave mixing kinetics and exposure characteristics. The presence of deep donor states in undoped InP was confirmed by a pronounced effect of a space charge electric field to carrier transport. On the other hand, the recharging dynamics of electrically active residual impurities was observed in undoped and Fe-doped InP through the process of efficient trapping of excess carriers. The bipolar diffusion coefficients and mobilities were determined for the all wafers

  9. Shallow doping of gallium arsenide by recoil implantation

    International Nuclear Information System (INIS)

    Sadana, D.K.; Souza, J.P. de; Rutz, R.F.; Cardone, F.; Norcott, M.H.

    1989-01-01

    Si atoms were recoil-implanted into GaAs by bombarding neutral (As + ) or dopant (Si + ) ions through a thin Si cap. The bombarded samples were subsequently rapid thermally or furnace annealed at 815-1000 degree C in Ar or arsine ambient. The presence of the recoiled Si in GaAs and resulting n + -doping was confirmed by secondary ion mass spectrometry and Hall measurements. It was found that sheet resistance of 19 cm 3 and the annealing temperature was > 850 degree C. The present electrical data show that the recoil implant method is a viable alternative to direct shallow implant for n + doping of GaAs. 7 refs., 3 figs., 1 tab

  10. Transparency of Semi-Insulating, n-Type, and p-Type Ammonothermal GaN Substrates in the Near-Infrared, Mid-Infrared, and THz Spectral Range

    OpenAIRE

    Robert Kucharski; Łukasz Janicki; Marcin Zajac; Monika Welna; Marcin Motyka; Czesław Skierbiszewski; Robert Kudrawiec

    2017-01-01

    GaN substrates grown by the ammonothermal method are analyzed by Fast Fourier Transformation Spectroscopy in order to study the impact of doping (both n- and p-type) on their transparency in the near-infrared, mid-infrared, and terahertz spectral range. It is shown that the introduction of dopants causes a decrease in transparency of GaN substrates in a broad spectral range which is attributed to absorption on free carriers (n-type samples) or dopant ionization (p-type samples). In the mid-in...

  11. Scanning tunneling spectroscopy of CdSe nanocrystals covalently bound to GaAs

    DEFF Research Database (Denmark)

    Walzer, K.; Marx, E.; Greenham, N.C.

    2003-01-01

    We present scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) measurements of CdSe nanocrystals covalently attached to doped GaAs substrates using monolayers of 1,6-hexanedithiol. STM measurements showed the formation of stable, densely packed, homogeneous monolayers...... of nanocrystals. STS measurements showed rectifying behaviour, with high currents at the opposite sample bias to that previously observed for CdSe nanocrystals adsorbed on Si substrates. We explain the rectifying behaviour by considering the interaction between the electronic states of the nanocrystals...

  12. Scanning tunnelling microscope imaging of nanoscale electron density gradients on the surface of GaAs

    International Nuclear Information System (INIS)

    Hamilton, B; Jacobs, J; Missous, M

    2003-01-01

    This paper is concerned with the scanning tunnelling microscope tunnelling conditions needed to produce constant current images dominated either by surface topology or by electronic effects. A model experimental structure was produced by cleaving a GaAs multiδ-doped layer in UHV and so projecting a spatially varying electron gas density onto the (110) surface. This cross sectional electron density varies on a nanometre scale in the [100] growth direction. The electronic structure and tunnelling properties of this system were modelled, and the tunnelling conditions favouring sensitivity to the surface electron gas density determined

  13. Spatial modulation of the Fermi level by coherent illumination of undoped GaAs

    Science.gov (United States)

    Nolte, D. D.; Olson, D. H.; Glass, A. M.

    1989-11-01

    The Fermi level in undoped GaAs has been modulated spatially by optically quenching EL2 defects. The spatial gradient of the Fermi level produces internal electric fields that are much larger than fields generated by thermal diffusion alone. The resulting band structure is equivalent to a periodic modulation-doped p-i-p structure of alternating insulating and p-type layers. The internal fields are detected via the electro-optic effect by the diffraction of a probe laser in a four-wave mixing geometry. The direct control of the Fermi level distinguishes this phenomenon from normal photorefractive behavior and introduces a novel nonlinear optical process.

  14. Mobility-lifetime product in epitaxial GaAs X-ray detectors

    Energy Technology Data Exchange (ETDEWEB)

    Sun, G.C. [GESEC R and D, Universite Pierre et Marie Curie, Bat.11, 140 rue de Lourmel, 75015 Paris (France)]. E-mail: guocsun@ccr.jussieu.fr; Zazoui, M. [LPMC, Faculte des Sciences et Techniques-Mohammedia, B.P. 146 Bd Hassan II, Mohammedia, Maroc (Morocco); Talbi, N. [Faculte des Sciences, Universite de Gabes, Route de Medenine, 6029 Gabes (Tunisia); Khirouni, K. [Faculte des Sciences, Universite de Gabes, Route de Medenine, 6029 Gabes (Tunisia); Bourgoin, J.C. [GESEC R and D, Universite Pierre et Marie Curie, Bat.11, 140 rue de Lourmel, 75015 Paris (France)

    2007-04-01

    Self-supported thick (200-500 {mu}m), non-intentionally doped, epitaxial GaAs layers are good candidates for X-ray imaging for the following reasons. Their electronic properties are homogeneous over large areas, they can be grown at low cost, the technology to realize pixel detectors of various size is standard, the defect concentration is low and the fluorescence yield is small. Here, we characterize the defects present in the material and evaluate the mobility-lifetime product, using Deep Level Transient Spectroscopy combined with current-voltage and charge collection measurements.

  15. Effect of the ion bombardment on the apparent barrier height in GaAs Schottky junctions

    International Nuclear Information System (INIS)

    Horvath, Zs. J.

    1994-01-01

    The bombardment of the semiconductor with different particles often results in the change of the doping concentration at the semiconductor surface. In this paper the effects of this near-interface concentration change on the apparent and real Schottky barrier heights are discussed. Experimental results obtained in GaAs Schottky junctions prepared on ion-bombarded semiconductor surfaces are analysed, and it is shown that their electrical characteristics are strongly influenced by the near-interface concentration change due to the ion bombardment. (author). 36 refs., 2 figs

  16. Heterojunction Diodes and Solar Cells Fabricated by Sputtering of GaAs on Single Crystalline Si

    Directory of Open Access Journals (Sweden)

    Santiago Silvestre

    2015-04-01

    Full Text Available This work reports fabrication details of heterojunction diodes and solar cells obtained by sputter deposition of amorphous GaAs on p-doped single crystalline Si. The effects of two additional process steps were investigated: A hydrofluoric acid (HF etching treatment of the Si substrate prior to the GaAs sputter deposition and a subsequent annealing treatment of the complete layered system. A transmission electron microscopy (TEM exploration of the interface reveals the formation of a few nanometer thick SiO2 interface layer and some crystallinity degree of the GaAs layer close to the interface. It was shown that an additional HF etching treatment of the Si substrate improves the short circuit current and degrades the open circuit voltage of the solar cells. Furthermore, an additional thermal annealing step was performed on some selected samples before and after the deposition of an indium tin oxide (ITO film on top of the a-GaAs layer. It was found that the occurrence of surface related defects is reduced in case of a heat treatment performed after the deposition of the ITO layer, which also results in a reduction of the dark saturation current density and resistive losses.

  17. Detecting Fermi-level shifts by Auger electron spectroscopy in Si and GaAs

    Science.gov (United States)

    Debehets, J.; Homm, P.; Menghini, M.; Chambers, S. A.; Marchiori, C.; Heyns, M.; Locquet, J. P.; Seo, J. W.

    2018-05-01

    In this paper, changes in surface Fermi-level of Si and GaAs, caused by doping and cleaning, are investigated by Auger electron spectroscopy. Based on the Auger voltage contrast, we compared the Auger transition peak energy but with higher accuracy by using a more accurate analyzer and an improved peak position determination method. For silicon, a peak shift as large as 0.46 eV was detected when comparing a cleaned p-type and n-type wafer, which corresponds rather well with the theoretical difference in Fermi-levels. If no cleaning was applied, the peak position did not differ significantly for both wafer types, indicating Fermi-level pinning in the band gap. For GaAs, peak shifts were detected after cleaning with HF and (NH4)2S-solutions in an inert atmosphere (N2-gas). Although the (NH4)2S-cleaning in N2 is very efficient in removing the oxygen from the surface, the observed Ga- and As-peak shifts are smaller than those obtained after the HF-cleaning. It is shown that the magnitude of the shift is related to the surface composition. After Si-deposition on the (NH4)2S-cleaned surface, the Fermi-level shifts back to a similar position as observed for an as-received wafer, indicating that this combination is not successful in unpinning the Fermi-level of GaAs.

  18. GaAs nanowire array solar cells with axial p-i-n junctions.

    Science.gov (United States)

    Yao, Maoqing; Huang, Ningfeng; Cong, Sen; Chi, Chun-Yung; Seyedi, M Ashkan; Lin, Yen-Ting; Cao, Yu; Povinelli, Michelle L; Dapkus, P Daniel; Zhou, Chongwu

    2014-06-11

    Because of unique structural, optical, and electrical properties, solar cells based on semiconductor nanowires are a rapidly evolving scientific enterprise. Various approaches employing III-V nanowires have emerged, among which GaAs, especially, is under intense research and development. Most reported GaAs nanowire solar cells form p-n junctions in the radial direction; however, nanowires using axial junction may enable the attainment of high open circuit voltage (Voc) and integration into multijunction solar cells. Here, we report GaAs nanowire solar cells with axial p-i-n junctions that achieve 7.58% efficiency. Simulations show that axial junctions are more tolerant to doping variation than radial junctions and lead to higher Voc under certain conditions. We further study the effect of wire diameter and junction depth using electrical characterization and cathodoluminescence. The results show that large diameter and shallow junctions are essential for a high extraction efficiency. Our approach opens up great opportunity for future low-cost, high-efficiency photovoltaics.

  19. Interface analysis of Ge ultra thin layers intercalated between GaAs substrates and oxide stacks

    Energy Technology Data Exchange (ETDEWEB)

    Molle, Alessandro, E-mail: alessandro.molle@mdm.infm.i [Laboratorio Nazionale MDM, CNR-INFM, Via C. Olivetti 2, 20041 Agrate Brianza (Italy); Lamagna, Luca; Spiga, Sabina [Laboratorio Nazionale MDM, CNR-INFM, Via C. Olivetti 2, 20041 Agrate Brianza (Italy); Fanciulli, Marco [Laboratorio Nazionale MDM, CNR-INFM, Via C. Olivetti 2, 20041 Agrate Brianza (MI) (Italy); Dipartimento di Scienza dei Materiali, Universita di Milano Bicocca, Milano (Italy); Brammertz, Guy; Meuris, Marc [IMEC, 75 Kapeldreef, B-3001 Leuven (Belgium)

    2010-01-01

    Capping III-V compound surfaces with Ge ultra-thin layer might be a viable pathway to passivate the electrically active interface traps which usually jeopardize the integration of III-V materials in metal-oxide-semiconductor devices. As the physical nature of such traps is intrinsically related to the chemical details of the interface composition, the structural and compositional features of the Ge/GaAs interface were thoroughly investigated in two different configurations, the atomic layer deposition of La-doped ZrO{sub 2} films on Ge-capped GaAs and the ultra-high vacuum based molecular beam deposition of GeO{sub 2}/Ge double stack on in situ prepared GaAs. In the former case, the intercalation of a Ge interface layer is shown to suppress the concentration of interface Ga-O, As-O and elemental As bonding which were significantly detected in case of the direct oxide deposition on GaAs. In the latter case, the incidence of two different in situ surface preparations, the Ar sputtering and the atomic H cleaning, on the interface composition is elucidated and the beneficial role played by the atomic H exposure in reducing the semiconductor-oxygen bonds at the interface level is demonstrated.

  20. Optimization of the doping profile of a MESFET, realized by ion implantation

    International Nuclear Information System (INIS)

    Cazaux, J.L.; Graffeuil, J.; Pavlidis, D.

    1986-01-01

    A method is proposed to investigate the influence of doping profiles on the performance of GaAs Field Effect Transistors. We consider in particular the effect of different ion implantation energies and doses, as well as, the influence of gate recess. The static and dynamic small signal characteristics of GaAs MESFETs with non-uniform doping profiles are studied by combining analytical and numerical techniques to reduce calculation time. Details of the FET analysis and computer simulation are presented. Results are compared with experimental data obtained from FETs with different implantation conditions and gate recess depths. The influence of the doping profile on the equivalent circuit elements of GaAs MESFETs is finally investigated in view of an optimization of their microwave properties [fr

  1. GaAs optoelectronic neuron arrays

    Science.gov (United States)

    Lin, Steven; Grot, Annette; Luo, Jiafu; Psaltis, Demetri

    1993-01-01

    A simple optoelectronic circuit integrated monolithically in GaAs to implement sigmoidal neuron responses is presented. The circuit integrates a light-emitting diode with one or two transistors and one or two photodetectors. The design considerations for building arrays with densities of up to 10,000/sq cm are discussed.

  2. Dephasing of LO-phonon-plasmon hybrid modes in n-type GaAs

    Science.gov (United States)

    Vallée, F.; Ganikhanov, F.; Bogani, F.

    1997-11-01

    The relaxation dynamics of coherent phononlike LO-phonon-plasmon hybrid modes is investigated in n-doped GaAs using an infrared time-resolved coherent anti-Stokes Raman scattering technique. Measurements performed for different crystal temperatures in the range 10-300 K as a function of the electron density injected by doping show a large reduction of the hybrid mode dephasing time compared to the bare LO-phonon one for densities larger than 1016 cm-3. The results are interpreted in terms of coherent decay of the LO-phonon-plasmon mixed mode in the weak-coupling regime and yield information on the plasmon and electron relaxation. The estimated average electron momentum relaxation times are smaller than those deduced from Hall mobility measurements, as expected from our theoretical model.

  3. Photoelectric properties of GaAs materials studied by pulsed laser techniques

    International Nuclear Information System (INIS)

    Aguir, Khalifa

    1981-01-01

    This research thesis addressed the photoelectric properties of single-crystal or epitaxial GaAs (N doped or P doped) materials. The objective is to characterize and to improve the electric quality of these materials and associated components, notably for the production of high performance solar cells for ground-based or space-based applications. More particularly, this research aimed at using an excitation by a pulsed laser to analyse recombination and trapping properties of carriers created by photo-excitation, and also at studying the effect of low doses of particle irradiation on the carrier properties. Thus, the author describes conduction characteristics of two different N-type epitaxial layers, discusses carrier excitation and recombination processes which may occur in semiconductors, and proposes an overview of trapping phenomena. Photoelectric properties of the considered epitaxial layers are then studied and discussed

  4. Subnanosecond photoconductive switching in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Druce, R.L.; Pocha, M.D.; Griffin, K.L.

    1991-04-01

    We are conducting research in photoconductive switching for the purpose of generating microwave pulses with amplitudes up to 50 kV. This technology has direct application to impulse radar and HPM sources. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as an on-off switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). In addition, we are exploring the potential GaAs to act as a closing switch in ``avalanche`` mode at high fields. We have observed switch closing times of less than 200 psec with a 100 psec duration laser pulse and opening times of less than 400 psec with neutron irradiated GaAs at fields of tens of kV/cm. If the field is increased and the laser energy decreased, the laser can be used to trigger photoconductive switches into ``avalanche`` mode of operation in which carrier multiplication occurs. This mode of operation is quite promising since the switches close in less than 1 nsec while realizing significant energy gain (ratio of electrical energy in the pulse to optical trigger energy). We are currently investigating both large area (1 sq cm) and small area (< 1 sq mm) switches illuminated by GaAlAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 micrometers. Preliminary results indicate that the closing time of the avalanche switches depends primarily on the material properties of the devices with closing times of 300--1300 psec at voltages of 6--35 kV. We will present experimental results for linear, lock on and avalanche mode operation of GaAs photoconductive switches and how these pulses may be applied to microwave generation. 3 refs.

  5. Subnanosecond photoconductive switching in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Druce, R.L.; Pocha, M.D.; Griffin, K.L.

    1991-04-01

    We are conducting research in photoconductive switching for the purpose of generating microwave pulses with amplitudes up to 50 kV. This technology has direct application to impulse radar and HPM sources. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as an on-off switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). In addition, we are exploring the potential GaAs to act as a closing switch in avalanche'' mode at high fields. We have observed switch closing times of less than 200 psec with a 100 psec duration laser pulse and opening times of less than 400 psec with neutron irradiated GaAs at fields of tens of kV/cm. If the field is increased and the laser energy decreased, the laser can be used to trigger photoconductive switches into avalanche'' mode of operation in which carrier multiplication occurs. This mode of operation is quite promising since the switches close in less than 1 nsec while realizing significant energy gain (ratio of electrical energy in the pulse to optical trigger energy). We are currently investigating both large area (1 sq cm) and small area (< 1 sq mm) switches illuminated by GaAlAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 micrometers. Preliminary results indicate that the closing time of the avalanche switches depends primarily on the material properties of the devices with closing times of 300--1300 psec at voltages of 6--35 kV. We will present experimental results for linear, lock on and avalanche mode operation of GaAs photoconductive switches and how these pulses may be applied to microwave generation. 3 refs.

  6. Subnanosecond photoconductive switching in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Druce, R.L.; Pocha, M.D.; Griffin, K.L.

    1990-01-01

    We are conducting research in photoconductive switching for the purpose of generating microwave pulses with amplitudes up to 50 kV. This technology has direct application to impulse radar and HPM sources. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as an on-off switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). In addition, we are exploring the potential of GaAs to act as a closing switch in avalanche'' mode at high fields. We have observed switch closing times of less than 200 psec with 100 psec duration laser pulse and opening times of less than 400 psec with neutron irradiated GaAs at fields of tens of kV/cm. If the field is increased and the laser energy decreased, the laser can be used to trigger photoconductive switches into an avalanche'' mode of operation in which carrier multiplication occurs. This mode of operation is quite promising since the switches close in less than 1 nsec while realizing significant energy gain (ratio of electrical energy in the pulse to optical trigger energy). We are currently investigating both large are (1 sq cm) and small area (<1 sq mm) switches illuminated by GaAlAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 micrometers. Preliminary results indicate that the closing time of the avalanche switches depends primarily on the material properties of the devices with closing times of 300--1300 psec at voltages of 6-35 kV. We will present experimental results for linear, lock on and avalanche mode operation of GaAs photoconductive switches and how these pulses may be applied to microwave generation. 3 refs., 11 figs.

  7. Subnanosecond photoconductive switching in GaAs

    Science.gov (United States)

    Druce, R. L.; Pocha, M. D.; Griffin, K. L.

    1991-04-01

    We are conducting research in photoconductive switching for the purpose of generating microwave pulses with amplitudes up to 50 kV. This technology has direct application to impulse radar and HPM sources. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as an on-off switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). In addition, we are exploring the potential GaAs to act as a closing switch in 'avalanche' mode at high fields. We have observed switch closing times of less than 200 psec with a 100 psec duration laser pulse and opening times of less than 400 psec with neutron irradiated GaAs at fields of tens of kV/cm. If the field is increased and the laser energy decreased, the laser can be used to trigger photoconductive switches into 'avalanche' mode of operation in which carrier multiplication occurs. This mode of operation is quite promising since the switches close in less than 1 nsec while realizing significant energy gain (ratio of electrical energy in the pulse to optical trigger energy). We are currently investigating both large area (1 sq cm) and small area (less than 1 sq mm) switches illuminated by GaAlAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 micrometers. Preliminary results indicate that the closing time of the avalanche switches depends primarily on the material properties of the devices with closing times of 300-1300 psec at voltages of 6-35 kV. We will present experimental results for linear, lock on, and avalanche mode operation of GaAs photoconductive switches and how these pulses may be applied to microwave generation.

  8. Lattice location of diffused Zn atoms in GaAs and InP single crystals

    International Nuclear Information System (INIS)

    Chan, L.Y.; Yu, K.M.; Ben-Tzur, M.; Haller, E.E.; Jaklevic, J.M.; Walukiewicz, W.; Hanson, C.M.

    1991-01-01

    We have investigated the saturation phenomenon of the free carrier concentration in p-type GaAs and InP single crystals doped by zinc diffusion. The free hole saturation occurs at 10 20 cm -3 for GaAs, but the maximum concentration for InP appears at mid 10 18 cm -3 . The difference in the saturation hole concentrations for these materials is investigated by studying the incorporation and the lattice location of the impurity zinc, an acceptor when located on a group III atom site. Zinc is diffused into the III-V wafers in a sealed quartz ampoule. Particle-induced x-ray emission with ion-channeling techniques are employed to determine the exact lattice location of the zinc atoms. We have found that over 90% of all zinc atoms occupy Ga sites in the diffused GaAs samples, while for the InP case, the zinc substitutionality is dependent on the cooling rate of the sample after high-temperature diffusion. For the slowly cooled sample, a large fraction (∼90%) of the zinc atoms form random precipitates of Zn 3 P 2 and elemental Zn. However, when rapidly cooled only 60% of the zinc forms such precipitates while the rest occupies specific sites in the InP. We analyze our results in terms of the amphoteric native defect model. We show that the difference in the electrical activity of the Zn atoms in GaAs and InP is a consequence of the different location of the Fermi level stabilization energy in these two materials

  9. P-type Ge epitaxy on GaAs (100) substrate grown by MOCVD

    Energy Technology Data Exchange (ETDEWEB)

    Jin, Y.J.; Chia, C.K.; Liu, H.F.; Wong, L.M.; Chai, J.W.; Chi, D.Z.; Wang, S.J., E-mail: sj-wang@imre.a-star.edu.sg

    2016-07-15

    Highlights: • The heterogeneous integration of p-Ge/GaAs by MOCVD indicates significance for the application in optoelectronic devices such as p-MOSFET, dual band photodetector, etc. • Many undesired pillar-structures were observed on the p-Ge epilayers and we found that the cause of the pillar-like structures was related to the Ge-Ga dimers formed during the growth. • We found that a GaAs substrate with fewer Ga or Ge danglings was helpful in suppressing the formation of the unwanted pillar-like structures and thus obtaining high quality p-Ge epilayers. - Abstract: In this work, Ga-doped Geranium (Ge) films have been grown on GaAs (100) substrates by metal-organic chemical vapor deposition (MOCVD). Undesired pillar structures have been observed on the epilayers prepared at relatively lower temperatures. Energy dispersive X-ray spectroscopy (EDX) indicated that the pillars are mainly consisted of Ga atoms, which is totally different from that of the Ge film. It was demonstrated that the pillar structures could be reduced by simply raising the growth temperature while keeping the other growth conditions unchanged. In this regard, the growth mechanism of the pillars was related to the Ge-Ga dimers formed during the growth of p-Ge films. By further studying the influence of a GaAs or Ge buffer layer on the growth of p-Ge layers, we found that the GaAs substrate with lower density of Ga or Ge dangling bonds was helpful in suppressing the formation of the undesired pillar structures.

  10. Optical orientation of Mn{sup 2+} ions in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Langer, Lukas; Bayer, Manfred [Experimentelle Physik 2, Technische Universitaet Dortmund, 44221 Dortmund (Germany); Akimov, Ilya A.; Yakovlev, Dmitri R. [Experimentelle Physik 2, Technische Universitaet Dortmund, 44221 Dortmund (Germany); A.F. Ioffe Physical-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation); Dzhioev, Roslan I.; Korenev, Vladimir L.; Kusrayev, Yuri G.; Sapega, Victor F. [A.F. Ioffe Physical-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation)

    2011-07-01

    We report on optical orientation of Mn{sup 2+} ions in bulk GaAs under application of weak longitudinal magnetic fields (B {<=}150 mT). The studied samples were grown by liquid phase epitaxy and Czochralski method and were doped with a low Mn acceptor concentration of 8 x 10{sup 18} cm{sup -3}. Time resolved measurements of circular polarization for donor-acceptor photoluminescence in Faraday geometry reveal nontrivial spin dynamics of donor localized electrons. Initially the degree of polarization of the electron spins is 40%. It then decays within some tens of ns to reach a plateau. The plateau is absent at B=0 T and saturates at B=150 mT reaching the value of 35%. It's sign changes with the helicity of incident light. It follows that the s-d exchange interaction with optically oriented electrons induces a steady state non-equilibrium polarization of the Mn{sup 2+} ions. The latter maintain their spin and return part of the polarization back to the electron spin system, resulting in the plateau. This provides a long-lived electron spin memory in GaAs doped with Mn. The dynamical polarization of ionized Mn acceptors was also directly monitored using spin flip Raman scattering spectroscopy, in agreement with time-resolved data.

  11. Semiconductor GaAs: electronic paramagnetic resonance new data

    International Nuclear Information System (INIS)

    Benchiguer, T.

    1994-04-01

    The topic of this study was to put to the fore, thanks to our electron spin resonance experiments, one charge transfer process, which was optically induced between the deep donor As + G a and the different acceptors, which were present in the material. We described these processes through a theoretical model, which we named charge transfer model. With this latter, we were able to trace a graph network, representing the As + G a concentration kinetics. Then we verified the compatibility of our model with one transport experiment. One experimental verification of our model were delivered, thanks to neutronic transmutation doping. The following stage was the study of defects, induced by thermal strains, to which the crystal was submitted during the cooling phase. At last we wanted to get round the non solved super hyperfine structure problem for GaAs by studying another III-V material for which she was resolved, namely gallium phosphide. (MML). 150 refs., 72 figs., 16 tabs., 3 annexes

  12. High mobility single-crystalline-like GaAs thin films on inexpensive flexible metal substrates by metal-organic chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Dutta, P., E-mail: pdutta2@central.uh.edu; Rathi, M.; Gao, Y.; Yao, Y.; Selvamanickam, V. [Department of Mechanical Engineering, University of Houston, Houston, Texas 77204 (United States); Zheng, N.; Ahrenkiel, P. [Department of Nanoscience and Nanoengineering, South Dakota School of Mines and Technology, Rapid City, South Dakota 57701 (United States); Martinez, J. [Materials Evaluation Laboratory, NASA Johnson Space Center, Houston, Texas 77085 (United States)

    2014-09-01

    We demonstrate heteroepitaxial growth of single-crystalline-like n and p-type doped GaAs thin films on inexpensive, flexible, and light-weight metal foils by metal-organic chemical vapor deposition. Single-crystalline-like Ge thin film on biaxially textured templates made by ion beam assisted deposition on metal foil served as the epitaxy enabling substrate for GaAs growth. The GaAs films exhibited strong (004) preferred orientation, sharp in-plane texture, low grain misorientation, strong photoluminescence, and a defect density of ∼10{sup 7 }cm{sup −2}. Furthermore, the GaAs films exhibited hole and electron mobilities as high as 66 and 300 cm{sup 2}/V-s, respectively. High mobility single-crystalline-like GaAs thin films on inexpensive metal substrates can pave the path for roll-to-roll manufacturing of flexible III-V solar cells for the mainstream photovoltaics market.

  13. Observation of linear I-V curves on vertical GaAs nanowires with atomic force microscope

    Science.gov (United States)

    Geydt, P.; Alekseev, P. A.; Dunaevskiy, M.; Lähderanta, E.; Haggrén, T.; Kakko, J.-P.; Lipsanen, H.

    2015-12-01

    In this work we demonstrate the possibility of studying the current-voltage characteristics for single vertically standing semiconductor nanowires on standard AFM equipped by current measuring module in PeakForce Tapping mode. On the basis of research of eight different samples of p-doped GaAs nanowires grown on different GaAs substrates, peculiar electrical effects were revealed. It was found how covering of substrate surface by SiOx layer increases the current, as well as phosphorous passivation of the grown nanowires. Elimination of the Schottky barrier between golden cap and the top parts of nanowires was observed. It was additionally studied that charge accumulation on the shell of single nanowires affects its resistivity and causes the hysteresis loops on I-V curves.

  14. Determination of the nitrogen concentration in epitaxial layers of GaAs /SUB 1-x/ p /SUB x/ by the optical method

    International Nuclear Information System (INIS)

    Lupal, M.V.; Klot, B; Nikhter, K.; Pikhtin, A.N.; Trapp, M.

    1986-01-01

    This paper determines the dependence of the cross section for absorption in the A /SUB N/ line of a bound exciton on the nitrogen content in the solid solution GaAs /SUB 1-x/ P /SUB x/ by comparing the results of optical measurements with the data from secondary ionic mass spectrometry, and these results are used to study the effect of technological factors on the nitrogen concentration epitaxial layers obtained by the gas-transport method. Doping was carried out with nitrogen by injecting ammonia into the reactor zone; the partial pressure of the ammonia was varied from 1 to 25 kPa. Aside from nitrogen, the authors doped the layers with shallow donor Te. It is established that the solubility of nitrogen in the solid solution decreases as the arsenic content increases when the convenient optical method for determining the nitrogen concentration in epitaxial GaAs /SUB 1-x/ P /SUB x/ layers is used

  15. Terahertz-radiation generation and detection in low-temperature-grown GaAs epitaxial films on GaAs (100) and (111)A substrates

    Energy Technology Data Exchange (ETDEWEB)

    Galiev, G. B.; Pushkarev, S. S., E-mail: s-s-e-r-p@mail.ru [Russian Academy of Sciences, Institute of Ultrahigh-Frequency Semiconductor Electronics (Russian Federation); Buriakov, A. M.; Bilyk, V. R.; Mishina, E. D. [Moscow Technological University “MIREA” (Russian Federation); Klimov, E. A. [Russian Academy of Sciences, Institute of Ultrahigh-Frequency Semiconductor Electronics (Russian Federation); Vasil’evskii, I. S. [National Research Nuclear University “MEPhI” (Russian Federation); Maltsev, P. P. [Russian Academy of Sciences, Institute of Ultrahigh-Frequency Semiconductor Electronics (Russian Federation)

    2017-04-15

    The efficiency of the generation and detection of terahertz radiation in the range up to 3 THz by LT-GaAs films containing equidistant Si doping δ layers and grown by molecular beam epitaxy on GaAs (100) and (111)Ga substrates is studied by terahertz spectroscopy. Microstrip photoconductive antennas are fabricated on the film surface. Terahertz radiation is generated by exposure of the antenna gap to femtosecond optical laser pulses. It is shown that the intensity of terahertz radiation from the photoconductive antenna on LT-GaAs/GaAs (111)Ga is twice as large as the intensity of a similar antenna on LT-GaAs/GaAs(100) and the sensitivity of the antenna on LT-GaAs/GaAs (111)Ga as a terahertz-radiation detector exceeds that of the antenna on LT-GaAs/GaAs(100) by a factor of 1.4.

  16. Structural and morphological TEM characterization of GaAs based nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Soda, Marcello

    2012-02-03

    The question of a structural and morphological characterization of GaAs based nanowires is the research interest of this thesis. For this purpose standard and analytical transmission electron microscopy techniques were employed. New investigation methodologies are introduced in order to obtain a reliable interpretation of the results. The principal motivation on developing a new investigation method is the necessity to relate the results of crystal structure and morphology characterizations to microscopic and NW-specific parameters and not to macroscopic and general growth parameters. This allows a reliable comparison of NW characteristics and enhances the comprehension of their growth mechanism.The analysis of the results on crystal structure investigations, assuming this new perspective, delivers the fundamental finding that the axial growth of Au-assisted GaAs NWs can change in a pseudo Ga-assisted growth due to a non steady-state regime of the Ga accumulation process in the liquid droplet. The attempt to associate the observed crystal structures to one of these two growth modes reveals that zinc blende segments are most probably generated when a pseudo Ga-assisted growth occurs. This experimental evidence is in accordance with investigations developed by Glas et al. and Spirkoska et al. and with the current understanding of the NW growth mechanism and unifies the interpretation of catalytic growth of GaAs NWs. A Mn doped GaAs shell deposited at low temperature on core GaAs NWs is characterized for the first time. The growth is found to be epitaxial and to confer the quality of the core crystal to the shell crystal. As a consequence a high stacking fault density of the core NW limits the temperature of the shell growth due to the formation of clusters. Cross sections of (Ga,Mn)As shells are investigated. Simple kinetic and thermodynamical considerations lead to the conclusion of morphological instability of the low temperature radial growth. Analytical

  17. Shallow Levels Characterization in Epitaxial GaAs by Acousto-Optic Reflectance Shallow Levels Characterization in Epitaxial GaAs by Acousto-Optic Reflectance

    Directory of Open Access Journals (Sweden)

    O. G. Ibarra-Manzano

    2012-02-01

    Full Text Available Optical spectra of light reflection are detected under an influence of ultrasonic wave (UWon a GaAs wafer. The differential spectrum is calculated as a difference between those taken under UW and without that influence on a sample. This acousto-optic differential reflectance(AODR spectrum contains some bands that represent the energetic levels of the shallow centers in a sample. A physical basis of this technique is related to a perturbation of local states by UW. Here, a method is developed for characterization of local states at the surfaces and interfaces in crystals and low-dimensional epitaxial structures based on microelectronics materials. A theoretical model is presented to explain AODR spectra. Also, experiments using epitaxial GaAs structures doped by Te were made. Finally, theoretical and experimental results show that acousto-optic reflectance is an effective tool for characterization of shallow trapping centers in epitaxial semiconductor structures.En este trabajo, utilizamos el espectro de la luz reflejada en una muestra de Arsenuro de Galio (GaAs bajo la influencia de una onda ultrasónica. El diferencial espectral es calculado como una diferencia entre el espectro del material obtenido bajo la influencia del ultrasonido y aquél obtenido sin dicha influencia. Este diferencial de reflectancia espectral acusto-óptico (AODR contiene algunas bandas que representan los niveles energéticos de los centros en la superficie de la muestra. Esta técnica está basada en la perturbación de los estados locales generada por el ultrasonido. Particularmente, este trabajo presenta un método para caracterizar los estados locales en la superficie y las interfaces en los cristales, así como estructuras epiteliales de baja dimensión basadas en materiales semiconductores. Para ello, se presenta un modelo teórico para explicar dicho espectro de reflectancia diferencial (AODR. También se realizaron experimentos con estructuras de GaAs epitelial

  18. Panel fabrication utilizing GaAs solar cells

    Science.gov (United States)

    Mardesich, N.

    1984-01-01

    The development of the GaAs solar cells for space applications is described. The activities in the fabrication of GaAs solar panels are outlined. Panels were fabricated while introducing improved quality control, soldering laydown and testing procedures. These panels include LIPS II, San Marco Satellite, and a low concentration panel for Rockwells' evaluation. The panels and their present status are discussed.

  19. Optical pumping of hot phonons in GaAs

    International Nuclear Information System (INIS)

    Collins, C.L.; Yu, P.Y.

    1982-01-01

    Optical pumping of hot LO phonons in GaAs has been studied as a function of the excitation photon frequency. The experimental results are in good agreement with a model calculation which includes both inter- and intra-valley electron-phonon scatterings. The GAMMA-L and GAMMA-X intervalley electron-phonon interactions in GaAs have been estimated

  20. Linearity of photoconductive GaAs detectors to pulsed electrons

    International Nuclear Information System (INIS)

    Ziegler, L.H.

    1995-01-01

    The response of neutron damaged GaAs photoconductor detectors to intense, fast (50 psec fwhm) pulses of 16 MeV electrons has been measured. Detectors made from neutron damaged GaAs are known to have reduced gain, but significantly improved bandwidth. An empirical relationship between the observed signal and the incident electron fluence has been determined

  1. Thermal process induced change of conductivity in As-doped ZnO

    Science.gov (United States)

    Su, S. C.; Fan, J. C.; Ling, C. C.

    2012-02-01

    Arsenic-doped ZnO films were fabricated by radio frequency magnetron sputtering method with different substrate temperature TS. Growing with the low substrate temperature of TS=200°C yielded n-type semi-insulating sample. Increasing the substrate temperature would yield p-type ZnO film and reproducible p-type film could be produced at TS~450°C. Post-growth annealing of the n-type As-doped ZnO sample grown at the low substrate temperature (TS=200°C) in air at 500°C also converted the film to p-type conductivity. Further increasing the post-growth annealing temperature would convert the p-type sample back to n-type. With the results obtained from the studies of positron annihilation spectroscopy (PAS), photoluminescence (PL), cathodoluminescence (CL), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and nuclear reaction analysis (NRA), we have proposed mechanisms to explain for the thermal process induced conduction type conversion as observed in the As-doped ZnO films.

  2. Peeled film GaAs solar cell development

    International Nuclear Information System (INIS)

    Wilt, D.M.; Thomas, R.D.; Bailey, S.G.; Brinker, D.J.; DeAngelo, F.L.

    1990-01-01

    Thin film, single crystal gallium arsenide (GaAs) solar cells could exhibit a specific power approaching 700 W/Kg including coverglass. A simple process has been described whereby epitaxial GaAs layers are peeled from a reusable substrate. This process takes advantage of the extreme selectivity (>10 6 ) of the etching rate of aluminum arsenide (AlAs) over GaAs in dilute hydrofloric acid (HF). The intent of this work is to demonstrate the feasibility of using the peeled film technique to fabricate high efficiency, low mass GaAs solar cells. We have successfully produced a peeled film GaAs solar cell. The device, although fractured and missing the aluminum gallium arsenide (Al x Ga 1 - x As) window and antireflective (AR) coating, had a Voc of 874 mV and a fill factor of 68% under AMO illumination

  3. Superconductor-semiconductor-superconductor planar junctions of aluminium on DELTA-doped gallium arsenide

    DEFF Research Database (Denmark)

    Taboryski, Rafael Jozef; Clausen, Thomas; Kutchinsky, jonatan

    1997-01-01

    We have fabricated and characterized planar superconductor-semiconductor-superconductor (S-Sm-S) junctions with a high quality (i.e. low barrier) interface between an n++ modulation doped conduction layer in MBE grown GaAs and in situ deposited Al electrodes. The Schottky barrier at the S...

  4. Rapid capless annealing of28Si,64Zn, and9Be implants in GaAs

    Science.gov (United States)

    Liu, S. G.; Narayan, S. Y.

    1984-11-01

    We report the use of tungsten-halogen lamps for rapid (-10 s) thermal annealing of ion-implanted (100) GaAs under AsH3/Ar and N2 atmospheres. Annealing under flowing AsH3/Ar was carried out without wafer encapsulation. Rapid capless annealing activated implants in GaAs with good mobility and surface morphology. Typical mobilities were 3700 4500 cm2/V-s for n-layers with about 2×1017cm-3 carrier concentration and 50 150 cm2/v-s for 0.1 5xl019 cm-3 doped p-layers. Rapid thermal annealing was performed in a vertical quartz tube where different gases (N2, AsH3/H2, AsH3/Ar) can be introduced. Samples were encapsulated with SiO when N2 was used. Tungsten-halogen lamps of 600 or 1000 W were utilized for annealing GaAs wafers ranging from 1 to 10 cm2 in area and 0.025 to 0.040 cm in thickness. The transient temperature at the wafer position was monitored using a fine thermocouple. We carried out experiments for energies of 30 to 200 keV, doses of 2×1012 to 1×1015 cm-2, and peak temperatures ranging from 600 to 1000‡C. Most results quoted are in the 700 to 870‡C temperature range. Data on implant conditions, optimum anneal conditions, electrical characteristics, carrier concentration profiles, and atomic profiles of the implanted layers are described.

  5. Polarization and charge limit studies of strained GaAs photocathodes

    International Nuclear Information System (INIS)

    Saez, P.J.

    1997-03-01

    This thesis presents studies on the polarization and charge limit behavior of electron beams produced by strained GaAs photocathodes. These photocathodes are the source of high-intensity, high-polarization electron beams used for a variety of high-energy physics experiments at the Stanford Linear Accelerator Center. Recent developments on P-type, biaxially-strained GaAs photocathodes have produced longitudinal polarization in excess of 80% while yielding beam intensities of ∼ 2.5 A/cm 2 at an operating voltage of 120 kV. The SLAC Gun Test Laboratory, which has a replica of the SLAC injector, was upgraded with a Mott polarimeter to study the polarization properties of photocathodes operating in a high-voltage DC gun. Both the maximum beam polarization and the maximum charge obtainable from these photocathodes have shown a strong dependence on the wavelength of illumination, on the doping concentration, and on the negative electron affinity levels. The experiments performed for this thesis included studying the effects of temperature, cesiation, quantum efficiency, and laser intensity on the polarization of high-intensity beams. It was found that, although low temperatures have been shown to reduce the spin relaxation rate in bulk semiconductors, they don't have a large impact on the polarization of thin photocathodes. It seems that the short active region in thin photocathodes does not allow spin relaxation mechanisms enough time to cause depolarization. Previous observations that lower QE areas on the photocathode yield higher polarization beams were confirmed. In addition, high-intensity, small-area laser pulses were shown to produce lower polarization beams. Based on these results, together with some findings in the existing literature, a new proposal for a high-intensity, high-polarization photocathode is given. It is hoped that the results of this thesis will promote further investigation on the properties of GaAs photocathodes

  6. A graphene/single GaAs nanowire Schottky junction photovoltaic device.

    Science.gov (United States)

    Luo, Yanbin; Yan, Xin; Zhang, Jinnan; Li, Bang; Wu, Yao; Lu, Qichao; Jin, Chenxiaoshuai; Zhang, Xia; Ren, Xiaomin

    2018-05-04

    A graphene/nanowire Schottky junction is a promising structure for low-cost high-performance optoelectronic devices. Here we demonstrate a graphene/single GaAs nanowire Schottky junction photovoltaic device. The Schottky junction is fabricated by covering a single layer graphene onto an n-doped GaAs nanowire. Under 532 nm laser excitation, the device exhibits a high responsivity of 231 mA W-1 and a short response/recover time of 85/118 μs at zero bias. Under AM 1.5 G solar illumination, the device has an open-circuit voltage of 75.0 mV and a short-circuit current density of 425 mA cm-2, yielding a remarkable conversion efficiency of 8.8%. The excellent photovoltaic performance of the device is attributed to the strong built-in electric field in the Schottky junction as well as the transparent property of graphene. The device is promising for self-powered high-speed photodetectors and low-cost high-efficiency solar cells.

  7. Surface photovoltage spectroscopy of real n-type GaAs(110) surfaces

    International Nuclear Information System (INIS)

    El-Dessouki, M.S.; El-Guiziri, S.B.; Gobrial, F.Z.

    1989-10-01

    N-type GaAs single crystals cut parallel to the (110) plane and doped with phosphorus by ion beam implantation were used in the present study. Temperature dependence of the bulk electrical conductivity showed two distinct activated regions with activation energies Et 1 =0.75±0.04eV, and Et 2 =0.12±0.04eV. The first activation energy is probably that of deep phosphorous impurities, while the second was related to long range disorder in the sample near room temperature. Surface photovoltage studies at room temperature were carried out at atmospheric pressure and in vacuum for etched and unetched samples. For n-type GaAs etched surface, the experimentally observed surface states were not found to change their positions by changing the pressure. But in the case of etched samples the surface states showed some redistribution under vacuum. The time constants for the initial rise and fall of CPD by illumination and after switching it off, τ 1 and τ 2 , respectively, were found to depend on the illumination intensity and photon energy. Their values range between 4 and 15 s. (author). 31 refs, 6 figs, 1 tab

  8. Electron spin dynamics and optical orientation of Mn2+ ions in GaAs

    Science.gov (United States)

    Akimov, I. A.; Dzhioev, R. I.; Korenev, V. L.; Kusrayev, Yu. G.; Sapega, V. F.; Yakovlev, D. R.; Bayer, M.

    2013-04-01

    We present an overview of spin-related phenomena in GaAs doped with low concentration of Mn-acceptors (below 1018 cm-3). We use the combination of different experimental techniques such as spin-flip Raman scattering and time-resolved photoluminescence. This allows to evaluate the time evolution of both electron and Mn spins. We show that optical orientation of Mn ions is possible under application of weak magnetic field, which is required to suppress the manganese spin relaxation. The optically oriented Mn2+ ions maintain the spin and return part of the polarization back to the electron spin system providing a long-lived electron spin memory. This leads to a bunch of spectacular effects such as non-exponential electron spin decay and spin precession in the effective exchange fields.

  9. Annealing-induced Fe oxide nanostructures on GaAs

    OpenAIRE

    Lu, Y X; Ahmad, E; Xu, Y B; Thompson, S M

    2005-01-01

    We report the evolution of Fe oxide nanostructures on GaAs(100) upon pre- and post-growth annealing conditions. GaAs nanoscale pyramids were formed on the GaAs surface due to wet etching and thermal annealing. An 8.0-nm epitaxial Fe film was grown, oxidized, and annealed using a gradient temperature method. During the process the nanostripes were formed, and the evolution has been demonstrated using transmission and reflection high energy electron diffraction, and scanning electron microscopy...

  10. Electrode pattern design for GaAs betavoltaic batteries

    International Nuclear Information System (INIS)

    Chen Haiyang; Yin Jianhua; Li Darang

    2011-01-01

    The sensitivities of betavoltaic batteries and photovoltaic batteries to series and parallel resistance are studied. Based on the study, an electrode pattern design principle of GaAs betavoltaic batteries is proposed. GaAs PIN junctions with and without the proposed electrode pattern are fabricated and measured under the illumination of 63 Ni. Results show that the proposed electrode can reduce the backscattering and shadowing for the beta particles from 63 Ni to increase the GaAs betavoltaic battery short circuit currents effectively but has little impact on the fill factors and ideal factors.

  11. Characterization of GaAs and hetero-structures of GaAs-(AlGa)As films, by Hall effect

    International Nuclear Information System (INIS)

    Diniz, R.P.

    1989-08-01

    Hall effect measurements were performed on a series of semiconductor gallium arsenide (GaAs) films, intentionally or unitentionally doped, grown by molecular beam epitaxy (MBE). These measurements made possible both the evaluation of the films quality and the calibration of the dopants (Si and Be) effusion cells on the growing machine. Measurements on modulation doped single interface heterostructures also grown by MBE followed. The two dimensional electron gas in the heterostructures shows low temperature high mobility. The application of a strong magnetic field perpendicular to the plane of the gas eliminated its degrees of freedom completely and permitted the observation of Schubnikov-deHaas oscillations and integer quantum Hall effect. During the work we have deviced and developed apparatus in order to make ohmic contacts and perform litography to semiconductors. (author) [pt

  12. Multiband corrections for the semi-classical simulation of interband tunneling in GaAs tunnel junctions

    Science.gov (United States)

    Louarn, K.; Claveau, Y.; Hapiuk, D.; Fontaine, C.; Arnoult, A.; Taliercio, T.; Licitra, C.; Piquemal, F.; Bounouh, A.; Cavassilas, N.; Almuneau, G.

    2017-09-01

    The aim of this study is to investigate the impact of multiband corrections on the current density in GaAs tunnel junctions (TJs) calculated with a refined yet simple semi-classical interband tunneling model (SCITM). The non-parabolicity of the considered bands and the spin-orbit effects are considered by using a recently revisited SCITM available in the literature. The model is confronted to experimental results from a series of molecular beam epitaxy grown GaAs TJs and to numerical results obtained with a full quantum model based on the non-equilibrium Green’s function formalism and a 6-band k.p Hamiltonian. We emphasize the importance of considering the non-parabolicity of the conduction band by two different measurements of the energy-dependent electron effective mass in N-doped GaAs. We also propose an innovative method to compute the non-uniform electric field in the TJ for the SCITM simulations, which is of prime importance for a successful operation of the model. We demonstrate that, when considering the multiband corrections and this new computation of the non-uniform electric field, the SCITM succeeds in predicting the electrical characteristics of GaAs TJs, and are also in agreement with the quantum model. Besides the fundamental study of the tunneling phenomenon in TJs, the main benefit of this SCITM is that it can be easily embedded into drift-diffusion software, which are the most widely-used simulation tools for electronic and opto-electronic devices such as multi-junction solar cells, tunnel field-effect transistors, or vertical-cavity surface-emitting lasers.

  13. Adding GaAs Monolayers to InAs Quantum-Dot Lasers on (001) InP

    Science.gov (United States)

    Qiu, Yueming; Chacon, Rebecca; Uhl, David; Yang, Rui

    2005-01-01

    In a modification of the basic configuration of InAs quantum-dot semiconductor lasers on (001)lnP substrate, a thin layer (typically 1 to 2 monolayer thick) of GaAs is incorporated into the active region. This modification enhances laser performance: In particular, whereas it has been necessary to cool the unmodified devices to temperatures of about 80 K in order to obtain lasing at long wavelengths, the modified devices can lase at wavelengths of about 1.7 microns or more near room temperature. InAs quantum dots self-assemble, as a consequence of the lattice mismatch, during epitaxial deposition of InAs on ln0.53Ga0.47As/lnP. In the unmodified devices, the quantum dots as thus formed are typically nonuniform in size. Strainenergy relaxation in very large quantum dots can lead to poor laser performance, especially at wavelengths near 2 microns, for which large quantum dots are needed. In the modified devices, the thin layers of GaAs added to the active regions constitute potential-energy barriers that electrons can only penetrate by quantum tunneling and thus reduce the hot carrier effects. Also, the insertion of thin GaAs layer is shown to reduce the degree of nonuniformity of sizes of the quantum dots. In the fabrication of a batch of modified InAs quantum-dot lasers, the thin additional layer of GaAs is deposited as an interfacial layer in an InGaAs quantum well on (001) InP substrate. The device as described thus far is sandwiched between InGaAsPy waveguide layers, then further sandwiched between InP cladding layers, then further sandwiched between heavily Zn-doped (p-type) InGaAs contact layer.

  14. Airplane dopes and doping

    Science.gov (United States)

    Smith, W H

    1919-01-01

    Cellulose acetate and cellulose nitrate are the important constituents of airplane dopes in use at the present time, but planes were treated with other materials in the experimental stages of flying. The above compounds belong to the class of colloids and are of value because they produce a shrinking action on the fabric when drying out of solution, rendering it drum tight. Other colloids possessing the same property have been proposed and tried. In the first stages of the development of dope, however, shrinkage was not considered. The fabric was treated merely to render it waterproof. The first airplanes constructed were covered with cotton fabric stretched as tightly as possible over the winds, fuselage, etc., and flying was possible only in fine weather. The necessity of an airplane which would fly under all weather conditions at once became apparent. Then followed experiments with rubberized fabrics, fabrics treated with glue rendered insoluble by formaldehyde or bichromate, fabrics treated with drying and nondrying oils, shellac, casein, etc. It was found that fabrics treated as above lost their tension in damp weather, and the oil from the motor penetrated the proofing material and weakened the fabric. For the most part the film of material lacked durability. Cellulose nitrate lacquers, however were found to be more satisfactory under varying weather conditions, added less weight to the planes, and were easily applied. On the other hand, they were highly inflammable, and oil from the motor penetrated the film of cellulose nitrate, causing the tension of the fabric to be relaxed.

  15. Carbon doped GaN buffer layer using propane for high electron mobility transistor applications: Growth and device results

    Energy Technology Data Exchange (ETDEWEB)

    Li, X.; Nilsson, D.; Danielsson, Ö.; Pedersen, H.; Janzén, E.; Forsberg, U. [Department of Physics, Chemistry, and Biology (IFM), Linköping University, Linköping 58183 (Sweden); Bergsten, J.; Rorsman, N. [Microwave Electronics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, Göteborg 41296 (Sweden)

    2015-12-28

    The creation of a semi insulating (SI) buffer layer in AlGaN/GaN High Electron Mobility Transistor (HEMT) devices is crucial for preventing a current path beneath the two-dimensional electron gas (2DEG). In this investigation, we evaluate the use of a gaseous carbon gas precursor, propane, for creating a SI GaN buffer layer in a HEMT structure. The carbon doped profile, using propane gas, is a two stepped profile with a high carbon doping (1.5 × 10{sup 18 }cm{sup −3}) epitaxial layer closest to the substrate and a lower doped layer (3 × 10{sup 16 }cm{sup −3}) closest to the 2DEG channel. Secondary Ion Mass Spectrometry measurement shows a uniform incorporation versus depth, and no memory effect from carbon doping can be seen. The high carbon doping (1.5 × 10{sup 18 }cm{sup −3}) does not influence the surface morphology, and a roughness root-mean-square value of 0.43 nm is obtained from Atomic Force Microscopy. High resolution X-ray diffraction measurements show very sharp peaks and no structural degradation can be seen related to the heavy carbon doped layer. HEMTs are fabricated and show an extremely low drain induced barrier lowering value of 0.1 mV/V, demonstrating an excellent buffer isolation. The carbon doped GaN buffer layer using propane gas is compared to samples using carbon from the trimethylgallium molecule, showing equally low leakage currents, demonstrating the capability of growing highly resistive buffer layers using a gaseous carbon source.

  16. Compensation and persistent photocapacitance in homoepitaxial Sn-doped β-Ga2O3

    Science.gov (United States)

    Polyakov, A. Y.; Smirnov, N. B.; Shchemerov, I. V.; Gogova, D.; Tarelkin, S. A.; Pearton, S. J.

    2018-03-01

    The electrical properties of epitaxial β-Ga2O3 doped with Sn (1016-9 × 1018 cm-3) and grown by metalorganic chemical vapor deposition on semi-insulating β-Ga2O3 substrates are reported. Shallow donors attributable to Sn were observed only in a narrow region near the film/substrate interface and with a much lower concentration than the total Sn density. For heavily Sn doped films (Sn concentration, 9 × 1018 cm-3), the electrical properties in the top portion of the layer were determined by deep centers with a level at Ec-0.21 eV not described previously. In more lightly doped layers, the Ec-0.21 eV centers and deeper traps at Ec-0.8 eV were present, with the latter pinning the Fermi level. Low temperature photocapacitance and capacitance voltage measurements of illuminated samples indicated the presence of high densities (1017-1018 cm-3) of deep acceptors with an optical ionization threshold of 2.3 eV. Optical deep level transient spectroscopy (ODLTS) and photoinduced current transient spectroscopy (PICTS) detected electron traps at Ec-0.8 eV and Ec-1.1 eV. For lightly doped layers, the compensation of film conductivity was mostly provided by the Ec-2.3 eV acceptors. For heavily Sn doped films, deep acceptor centers possibly related to Ga vacancies were significant. The photocapacitance and the photocurrent caused by illumination at low temperatures were persistent, with an optical threshold of 1.9 eV and vanished only at temperatures of ˜400 K. The capture barrier for electrons causing the persistent photocapacitance effect was estimated from ODLTS and PICTS to be 0.25-0.35 eV.

  17. Photoconductivity properties of {delta}-Si doped InGaAs quantum well

    Energy Technology Data Exchange (ETDEWEB)

    Campo, Junior, V Leira; Marega, Junior, E; Rossi, J C; Lubyshev, D I; Gonzalez Borrero, P P; Basmaji, P [Sao Paulo Univ., Sao Carlos, SP (Brazil). Inst. de Fisica

    1996-12-31

    Full text. The semiconductors thin films with doping level near Anderson transition have high photo sensitivity in the photo conductivity regime. The maximum sensitivity of these photodetectors occurs under illumination when the system transform from semi-insulating to semi-metal. The ratio between deep and shallow levels concentration in this case should be near the unity with a total impurity concentration near 10{sup 15} cm{sup -3}, that difficult to control at the bulk doping. The frequency response in these devices are limited by absorption thickness ({approx}500-300 nm). In present work we report the results of visible-infrared photo detector (PD) preparation by using molecular beam epitaxy. For development of frequency response and wavelength range increase to infrared area we use {delta}-doped In{sub 0.2} Ga{sub 0.8} As quantum well. The doping level in {delta}-Si layer on the middle of QW was 2 x 10{sup 12} cm{sup -3}, that was enough for shift of deep levels-shallow levels concentration ratio to anderson transition in the area near QW. At the illumination all photoexcited carriers was collected by QW. The deepness of photo sensitivity space area is limiters by few nanometers near the QW, that increase the frequency properties of PD. Photo current spectra show high sensibility ({Delta}) (R/R=15%) at cut-off frequency up 1.25 eV. This explain strong optical absorption by QW in the infrared area. The future work will focalized on introducing {delta}-doped In Ga As superlattice for linearization of PD spectrum characteristics. (author)

  18. Nonlinear optical rectification and second and third harmonic generation in GaAs δ-FET systems under hydrostatic pressure

    International Nuclear Information System (INIS)

    Martínez-Orozco, J.C.; Mora-Ramos, M.E.; Duque, C.A.

    2012-01-01

    The GaAs n-type delta-doped field effect transistor is proposed as a source for nonlinear optical responses such as second order rectification and second and third harmonic generation. Particular attention is paid to the effect of hydrostatic pressure on these properties, related with the pressure-induced modifications of the energy level spectrum. The description of the one-dimensional potential profile is made including Hartree and exchange and correlation effects via a Thomas–Fermi-based local density approximation. The allowed energy levels are calculated within the effective mass and envelope function approximations by means of an expansion over an orthogonal set of infinite well eigenfunctions. The results for the coefficients of nonlinear optical rectification and second and third harmonic generation are reported for several values of the hydrostatic pressure. - Highlights: ► GaAs n-type delta-doped field effect transistor. ► NOR and SHG are enhanced as a result of the pressure. ► THG is quenched as a result of the pressure. ► The zero pressure situation is the best scenario for the THG.

  19. Electrical transport in n-type ZnMgSSe grown by molecular beam epitaxy on GaAs

    International Nuclear Information System (INIS)

    Marshall, T.; Petruzzello, J.A.; Herko, S.P.

    1994-01-01

    Significant progress in improving the Performance of blue-green II-VI semiconductor injection lasers has come about from advances in the epitaxial growth and doping of ZnMgSSe on GaAs substrates. This paper investigates electrical transport and its relation to structural quality in n-type Zn 1-y Mg y S x Se 1-x epilayers doped with Cl, grown by molecular beam epitaxy. The composition parameters x and y vary from about 0.12-0.18 and 0.08-0.15, respectively. The quaternary epilayers studied are lattice-matched (or nearly so) to the GaAs substrate. Temperature-dependent Hall-effect measurements are performed on seven n-type ZnMgSSe:Cl epilayers, and a technique is presented whereby the resulting mobility-vs-temperature data is compared with data for ZnSe to obtain a structural figure of merit that is useful in characterizing the quaternary epilayer. 29 refs., 4 figs

  20. Spin injection into GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Endres, Bernhard

    2013-11-01

    In this work spin injection into GaAs from Fe and (Ga,Mn)As was investigated. For the realization of any spintronic device the detailed knowledge about the spin lifetime, the spatial distribution of spin-polarized carriers and the influence of electric fields is essential. In the present work all these aspects have been analyzed by optical measurements of the polar magneto-optic Kerr effect (pMOKE) at the cleaved edge of the samples. Besides the attempt to observe spin pumping and thermal spin injection into n-GaAs the spin solar cell effect is demonstrated, a novel mechanism for the optical generation of spins in semiconductors with potential for future spintronic applications. Also important for spin-based devices as transistors is the presented realization of electrical spin injection into a two-dimensional electron gas.

  1. Optical properties of GaAs

    International Nuclear Information System (INIS)

    Akinlami, J. O.; Ashamu, A. O.

    2013-01-01

    We have investigated the optical properties of gallium arsenide (GaAs) in the photon energy range 0.6–6.0 eV. We obtained a refractive index which has a maximum value of 5.0 at a photon energy of 3.1 eV; an extinction coefficient which has a maximum value of 4.2 at a photon energy of 5.0 eV; the dielectric constant, the real part of the complex dielectric constant has a maximum value of 24 at a photon energy of 2.8 eV and the imaginary part of the complex dielectric constant has a maximum value of 26.0 at a photon energy of 4.8 eV; the transmittance which has a maximum value of 0.22 at a photon energy of 4.0 eV; the absorption coefficient which has a maximum value of 0.22 × 10 8 m −1 at a photon energy of 4.8 eV, the reflectance which has a maximum value of 0.68 at 5.2eV; the reflection coefficient which has a maximum value of 0.82 at a photon energy of 5.2 eV; the real part of optical conductivity has a maximum value of 14.2 × 10 15 at 4.8 eV and the imaginary part of the optical conductivity has a maximum value of 6.8 × 10 15 at 5.0 eV. The values obtained for the optical properties of GaAs are in good agreement with other results. (semiconductor physics)

  2. Near-thermal limit gating in heavily doped III-V semiconductor nanowires using polymer electrolytes

    Science.gov (United States)

    Ullah, A. R.; Carrad, D. J.; Krogstrup, P.; Nygârd, J.; Micolich, A. P.

    2018-02-01

    Doping is a common route to reducing nanowire transistor on-resistance but it has limits. A high doping level gives significant loss in gate performance and ultimately complete gate failure. We show that electrolyte gating remains effective even when the Be doping in our GaAs nanowires is so high that traditional metal-oxide gates fail. In this regime we obtain a combination of subthreshold swing and contact resistance that surpasses the best existing p -type nanowire metal-oxide semiconductor field-effect transistors (MOSFETs). Our subthreshold swing of 75 mV/dec is within 25 % of the room-temperature thermal limit and comparable with n -InP and n -GaAs nanowire MOSFETs. Our results open a new path to extending the performance and application of nanowire transistors, and motivate further work on improved solid electrolytes for nanoscale device applications.

  3. Preparation of GaAs photocathodes at low temperature

    International Nuclear Information System (INIS)

    Mulhollan, G.; Clendenin, J.; Tang, H.

    1996-10-01

    The preparation of an atomically clean surface is a necessary step in the formation of negative electron affinity (NEA) GaAs. Traditional methods to this end include cleaving, heat cleaning and epitaxial growth. Cleaving has the advantage of yielding a fresh surface after each cleave, but is limited to small areas and is not suitable for specialized structures. Heat cleaning is both simple and highly successful, so it is used as a preparation method in virtually all laboratories employing a NEA source on a regular basis. Due to its high cost and complexity, epitaxial growth of GaAs with subsequent in vacuo transfer is not a practical solution for most end users of GaAs as a NEA electron source. While simple, the heating cleaning process has a number of disadvantages. Here, a variety of cleaning techniques related to preparation of an atomically clean GaAs surface without heating to 600 C are discussed and evaluated

  4. Comparisons of single event vulnerability of GaAs SRAMS

    Science.gov (United States)

    Weatherford, T. R.; Hauser, J. R.; Diehl, S. E.

    1986-12-01

    A GaAs MESFET/JFET model incorporated into SPICE has been used to accurately describe C-EJFET, E/D MESFET and D MESFET/resistor GaAs memory technologies. These cells have been evaluated for critical charges due to gate-to-drain and drain-to-source charge collection. Low gate-to-drain critical charges limit conventional GaAs SRAM soft error rates to approximately 1E-6 errors/bit-day. SEU hardening approaches including decoupling resistors, diodes, and FETs have been investigated. Results predict GaAs RAM cell critical charges can be increased to over 0.1 pC. Soft error rates in such hardened memories may approach 1E-7 errors/bit-day without significantly reducing memory speed. Tradeoffs between hardening level, performance and fabrication complexity are discussed.

  5. Diffusion of $^{52}$Mn in GaAs

    CERN Multimedia

    2002-01-01

    Following our previous diffusion studies performed with the modified radiotracer technique, we propose to determine the diffusion of Mn in GaAs under intrinsic conditions in a previously un-investigated temperature region. The aim of the presently proposed experiments is twofold. \\begin{itemize} \\item A quantitative study of Mn diffusion in GaAs at low Mn concentrations would be decisive in providing new information on the diffusion mechanism involved. \\item As Ga vacancies are expected to be involved in the Mn diffusion process it can be predicted that also the GaAs material growth technique most likely plays a role. To clarify this assumption diffusion experiments will be conducted for GaAs material grown by two different techniques. \\end{itemize} For such experiments we ask for two runs of 3 shifts (total of 6 shifts) with $^{52}$Mn$^{+}$ ion beam.

  6. Magnetic and electrical transport properties of delta-doped amorphous Ge:Mn magnetic semiconductors

    International Nuclear Information System (INIS)

    Li, H.L.; Lin, H.T.; Wu, Y.H.; Liu, T.; Zhao, Z.L.; Han, G.C.; Chong, T.C.

    2006-01-01

    We report on the growth and characterization of delta-doped amorphous Ge:Mn diluted magnetic semiconductor thin films on GaAs (0 0 1) substrates. The fabricated samples exhibit different magnetic behaviors, depending on the Mn doping concentration. The Curie temperature was found to be dependent on both the Mn doping concentration and spacing between the doping layers. A sharp drop in magnetization and rise in resistivity are observed at low temperature in samples with high Mn doping concentrations, which is also accompanied by a negative thermal remanent magnetization (TRM) in the higher temperature range. The temperature at which the magnetization starts to drop and the negative TRM appears show a correlation with the Mn doping concentration. The experimental results are discussed based on the formation of ferromagnetic regions at high temperature and antiferromagnetic coupling between these regions at low temperature

  7. Implantation annealing in GaAs by incoherent light

    International Nuclear Information System (INIS)

    Davies, D.E.; Ryan, T.G.; Soda, K.J.; Comer, J.J.

    1983-01-01

    Implanted GaAs has been successfully activated through concentrating the output of quartz halogen lamps to anneal in times of the order of 1 sec. The resulting layers are not restricted by the reduced mobilities and thermal instabilities of laser annealed GaAs. Better activation can be obtained than with furnace annealing but this generally requires maximum temperatures >= 1050degC. (author)

  8. Design optimization of GaAs betavoltaic batteries

    International Nuclear Information System (INIS)

    Chen Haiyanag; Jiang Lan; Chen Xuyuan

    2011-01-01

    GaAs junctions are designed and fabricated for betavoltaic batteries. The design is optimized according to the characteristics of GaAs interface states and the diffusion length in the depletion region of GaAs carriers. Under an illumination of 10 mCi cm -2 63 Ni, the open circuit voltage of the optimized batteries is about ∼0.3 V. It is found that the GaAs interface states induce depletion layers on P-type GaAs surfaces. The depletion layer along the P + PN + junction edge isolates the perimeter surface from the bulk junction, which tends to significantly reduce the battery dark current and leads to a high open circuit voltage. The short circuit current density of the optimized junction is about 28 nA cm -2 , which indicates a carrier diffusion length of less than 1 μm. The overall results show that multi-layer P + PN + junctions are the preferred structures for GaAs betavoltaic battery design.

  9. Characterization and technology of AlGaAs/GaAs phototransistor with double delta-doped base

    International Nuclear Information System (INIS)

    Radziewicz, D.; Sciana, B.; Pucicki, D.; Zborowska-Lindert, I.; Kovac, J.; Skriniarova, J.; Vincze, A.

    2011-01-01

    This work describes the fabrication and measurements of n-p-n AlGaAs/GaAs heterojunction phototransistor with double Zn-delta-doped 50 nm - thick GaAs base region. Parameters of the particular transistor epilayers were optimized by computer simulations using Silvaco Atlas program. (authors)

  10. Annealing effects on electrical and optical properties of ZnO thin-film samples deposited by radio frequency-magnetron sputtering on GaAs (001) substrates

    International Nuclear Information System (INIS)

    Liu, H. F.; Chua, S. J.; Hu, G. X.; Gong, H.; Xiang, N.

    2007-01-01

    The effects of thermal annealing on Hall-effect measurement and photoluminescence (PL) from undoped n-type ZnO/GaAs thin-film samples have been studied. The evolutions of carrier concentration, electrical resistivity, and PL spectrum at various annealing conditions reveal that the dominant mechanism that affects the electrical and PL properties is dependent on the amount of thermal energy and the ambient pressure applied during the annealing process. At low annealing temperatures, annihilation of native defects is dominant in reducing the carrier concentration and weakening the low-energy tail of the main PL peak, while the GaAs substrate plays only a minor role in carrier compensations. For the higher temperatures, diffusion of Ga atoms from the GaAs substrate into ZnO film leads to a more n-type conduction of the sample. As a result, the PL exhibits a high-energy tail due to the high-level doping

  11. Selenium passivation of GaAs(001): a combined experimental and theoretical study

    International Nuclear Information System (INIS)

    Gonzalez, C; Benito, I; Ortega, J; Jurczyszyn, L; Blanco, J M; Perez, R; Flores, F; Kampen, T U; Zahn, D R T; Braun, W

    2004-01-01

    The chemical and electronic properties of selenium passivated GaAs(001)-2 x 1 surfaces were investigated by a combination of theoretical calculations and core level photoemission experiments. An anion exchange results in gallium-selenide like layers showing a 2 x 1 reconstruction in low energy electron diffraction (LEED). The analysis of the different components in the core level spectra of As 3d, Ga 3d and Se 3d limits the number of possible structural models. The Se/GaAs(001)-2 x 1 reconstruction has been also analysed by means of DFT-LDA calculations and theoretical STM currents. In a first step, different geometries are considered and the most stable one, from the point of view of the thermodynamic potential, is determined. Then, STM currents and the corresponding surface corrugation are calculated and compared with the experimental evidence. We conclude that the Se/GaAs(001)-2 x 1 reconstruction has a single Se atom in the last crystal layer, bonded to two Ga atoms of the second layer, and another Se layer replacing the third As layer of the crystal. These surfaces may be considered as chemically stable because they withstand considerable exposure to air. In terms of electronic passivation, i.e. the removal of any surface band bending, the selenium modification is not successful. Band bending on n-type doped samples is reduced while band bending on the p-type doped samples is further increased

  12. 3-D GaAs radiation detectors

    International Nuclear Information System (INIS)

    Meikle, A.R.; Bates, R.L.; Ledingham, K.; Marsh, J.H.; Mathieson, K.; O'Shea, V.; Smith, K.M.

    2002-01-01

    A novel type of GaAs radiation detector featuring a 3-D array of electrodes that penetrate through the detector bulk is described. The development of the technology to fabricate such a detector is presented along with electrical and radiation source tests. Simulations of the electrical characteristics are given for detectors of various dimensions. Laser drilling, wet chemical etching and metal evaporation were used to create a cell array of nine electrodes, each with a diameter of 60 μm and a pitch of 210 μm. Electrical measurements showed I-V characteristics with low leakage currents and high breakdown voltages. The forward and reverse I-V measurements showed asymmetrical characteristics, which are not seen in planar diodes. Spectra were obtained using alpha particle illumination. A charge collection efficiency of 50% and a S/N ratio of 3 : 1 were obtained. Simulations using the MEDICI software package were performed on cells with various dimensions and were comparable with experimental results. Simulations of a nine-electrode cell with 10 μm electrodes with a 25 μm pitch were also performed. The I-V characteristics again showed a high breakdown voltage with a low leakage current but also showed a full depletion voltage of just 8 V

  13. Spectroscopy of GaAs quantum wells

    International Nuclear Information System (INIS)

    West, L.C.

    1985-07-01

    A new type of optical dipole transition in GaAs quantum wells has been observed. The dipole occurs between two envelope states of the conduction band electron wavefunction, and is called a quantum well envelope state transition (QWEST). The QWEST is observed by infrared absorption in three different samples with quantum well thicknesses 65, 82, and 92 A and resonant energies of 152, 121, and 108 MeV, respectively. The oscillator strength is found to have values of over 12, in good agreement with prediction. The linewidths are seen as narrow as 10 MeV at room temperature and 7 MeV at low temperature, thus proving a narrow line resonance can indeed occur between transitions of free electrons. Techniques for the proper growth of these quantum well samples to enable observation of the QWEST have also been found using (AlGa)As compounds. This QWEST is considered to be an ideal material for an all optical digital computer. The QWEST can be made frequency matched to the inexpensive Carbon Dioxide laser with an infrared wavelength of 10 microns. The nonlinearity and fast relaxation time of the QWEST indicate a logic element with a subpicosecond switch time can be built in the near future, with a power level which will eventually be limited only by the noise from a lack of quanta to above approximately 10 microwatts. 64 refs., 35 figs., 6 tabs

  14. Spectroscopy of GaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    West, L.C.

    1985-07-01

    A new type of optical dipole transition in GaAs quantum wells has been observed. The dipole occurs between two envelope states of the conduction band electron wavefunction, and is called a quantum well envelope state transition (QWEST). The QWEST is observed by infrared absorption in three different samples with quantum well thicknesses 65, 82, and 92 A and resonant energies of 152, 121, and 108 MeV, respectively. The oscillator strength is found to have values of over 12, in good agreement with prediction. The linewidths are seen as narrow as 10 MeV at room temperature and 7 MeV at low temperature, thus proving a narrow line resonance can indeed occur between transitions of free electrons. Techniques for the proper growth of these quantum well samples to enable observation of the QWEST have also been found using (AlGa)As compounds. This QWEST is considered to be an ideal material for an all optical digital computer. The QWEST can be made frequency matched to the inexpensive Carbon Dioxide laser with an infrared wavelength of 10 microns. The nonlinearity and fast relaxation time of the QWEST indicate a logic element with a subpicosecond switch time can be built in the near future, with a power level which will eventually be limited only by the noise from a lack of quanta to above approximately 10 microwatts. 64 refs., 35 figs., 6 tabs.

  15. Doping droops.

    Science.gov (United States)

    Chaturvedi, Aditi; Chaturvedi, Harish; Kalra, Juhi; Kalra, Sudhanshu

    2007-01-01

    Drug abuse is a major concern in the athletic world. The misconception among athletes and their coaches is that when an athlete breaks a record it is due to some "magic ingredient" and not because of training, hard work, mental attitude and championship performance. The personal motivation to win in competitive sports has been intensified by national, political, professional and economic incentives. Under this increased pressure athletes have turned to finding this "magic ingredient". Athlete turns to mechanical (exercise, massage), nutritional (vitamins, minerals), pharmacological (medicines) or gene therapies to have an edge over other players. The World Anti-Doping Agency (WADA) has already asked scientists to help find ways to prevent gene therapy from becoming the newest form of doping. The safety of the life of athletes is compromised with all forms of doping techniques, be it a side effect of a drug or a new technique of gene doping.

  16. Effect of doping on room temperature carrier escape mechanisms in InAs/GaAs quantum dot p-i-n junction photovoltaic cells

    Energy Technology Data Exchange (ETDEWEB)

    Sellers, D. G.; Chen, E. Y.; Doty, M. F. [Department of Materials Science and Engineering, University of Delaware, Newark, Delaware 19716 (United States); Polly, S. J.; Hubbard, S. M. [NanoPower Research Laboratory, Rochester Institute of Technology, Rochester, New York 14623 (United States)

    2016-05-21

    We investigate the effect of doping on the mechanisms of carrier escape from intermediate states in delta-doped InAs/GaAs intermediate band solar cells. The intermediate states arise from InAs quantum dots embedded in a GaAs p-i-n junction cell. We find that doping the sample increases the number of excited-state carriers participating in a cycle of trapping and carrier escape via thermal, optical, and tunneling mechanisms. However, we find that the efficiency of the optically-driven carrier escape mechanism is independent of doping and remains small.

  17. Spatial structure of single and interacting Mn acceptors in GaAs

    Science.gov (United States)

    Koenraad, Paul

    2005-03-01

    Ferromagnetic semiconductors such as Ga1-xMnxAs are receiving a lot of attention at the moment because of their application in spintronic devices. However, despite intense study of deep acceptors in III-V semiconductors such as MnGa, little information has been obtained on their electronic properties at the atomic scale. Yet the spatial shape of the Mn acceptor state will influence the hole-mediated Mn-Mn coupling and thus all of the magnetic properties of ferromagnetic semiconductors such as Ga1-xMnxAs. This study presents an experimental and theoretical description of the spatial symmetry of the Mn acceptor wave-function in GaAs. We present measurements of the spatial mapping of the anisotropic wavefunction of a hole localized at a Mn acceptor. To achieve this, we have used the STM tip not only to image the Mn acceptor but also to manipulate its charge state A^0/A^- at room temperature. Within an envelope function effective mass model (EFM) the anisotropy in the acceptor wave-function can be traced to the influence of the cubic symmetry of the GaAs crystal which selects specific d-states that mix into the ground state due to the spin-orbit interaction in the valence band. Comparison with calculations based on a tight-binding model (TBM) for the Mn acceptor structure supports this conclusion. Using the same experimental and theoretical approach we furthermore explored the interaction between Mn acceptors directly by analyzing close Mn-Mn pairs, which were separated by less than 2 nm. We will discuss some implications of these results for Mn delta-doped layers grown on differently oriented growth surfaces.

  18. Semiconductor GaAs: electronic paramagnetic resonance new data; GaAs semi-isolant: nouvelles donnees de resonance paramagnetique electronique

    Energy Technology Data Exchange (ETDEWEB)

    Benchiguer, T.

    1994-04-01

    The topic of this study was to put to the fore, thanks to our electron spin resonance experiments, one charge transfer process, which was optically induced between the deep donor As{sup +}{sub G}a and the different acceptors, which were present in the material. We described these processes through a theoretical model, which we named charge transfer model. With this latter, we were able to trace a graph network, representing the As{sup +}{sub G}a concentration kinetics. Then we verified the compatibility of our model with one transport experiment. One experimental verification of our model were delivered, thanks to neutronic transmutation doping. The following stage was the study of defects, induced by thermal strains, to which the crystal was submitted during the cooling phase. At last we wanted to get round the non solved super hyperfine structure problem for GaAs by studying another III-V material for which she was resolved, namely gallium phosphide. (MML). 150 refs., 72 figs., 16 tabs., 3 annexes.

  19. Atomic hydrogen cleaning of GaAs photocathodes

    International Nuclear Information System (INIS)

    Poelker, M.; Price, J.; Sinclair, C.

    1997-01-01

    It is well known that surface contaminants on semiconductors can be removed when samples are exposed to atomic hydrogen. Atomic H reacts with oxides and carbides on the surface, forming compounds that are liberated and subsequently pumped away. Experiments at Jefferson lab with bulk GaAs in a low-voltage ultra-high vacuum H cleaning chamber have resulted in the production of photocathodes with high photoelectron yield (i.e., quantum efficiency) and long lifetime. A small, portable H cleaning apparatus also has been constructed to successfully clean GaAs samples that are later removed from the vacuum apparatus, transported through air and installed in a high-voltage laser-driven spin-polarized electron source. These results indicate that this method is a versatile and robust alternative to conventional wet chemical etching procedures usually employed to clean bulk GaAs

  20. 35-kV GaAs subnanosecond photoconductive switches

    Energy Technology Data Exchange (ETDEWEB)

    Pocha, M.D.; Druce, R.L. (Lawrence Livermore National Lab., CA (United States))

    1990-12-01

    Photoconductive switches are one of the few devices that allow the generation of high-voltage electrical pulses with subnanosecond rise time. The authors are exploring high-voltage, fast-pulse generation using GaAs photoconductive switches. They have been able to generate 35-kV pulses with rise times as short as 135 ps using 5-mm gap switches and have achieved electric field hold-off of greater than 100 kV/cm. They have also been able to generate an approximately 500-ps FWHM on/off electrical pulse with an amplitude of approximately 3 kV using neutron-irradiated GaAs having short carrier life times. This paper describes the experimental results and discusses fabrication of switches and the diagnostics used to measure these fast signals. They also describe the experience with the nonlinear lock-on and avalanche modes of operation observed in GaAs.

  1. 35-kV GaAs subnanosecond photoconductive switches

    Science.gov (United States)

    Pocha, Michael D.; Druce, Robert L.

    1990-12-01

    High-voltage, fast-pulse generation using GaAs photoconductive switches is investigated. It is possible to to generate 35-kV pulses with risetimes as short as 135 ps using 5-mm gap switches, and electric field hold-off of greater than 100 kV/cm is achieved. An approximately 500-ps FWHM on/off electrical pulse is generated with an amplitude of approximately 3 kV using neutron-irradiated GaAs having short carrier lifetimes. Experimental results are described, and fabrication of switches and the diagnostics used to measure these fast signals are discussed. Experience with the nonlinear lock-on and avalanche modes of operation observed in GaAs is also described.

  2. GaAs strip detectors: the Australian production program

    International Nuclear Information System (INIS)

    Butcher, K.S.A.; Alexiev, D.

    1995-01-01

    The Australian High Energy Physics consortium (composed of the University of Melbourne, the University of Sydney and ANSTO) has been investigating the possibility of producing a large area wheel of SI GaAs detectors for the ATLAS detector array. To help assess the extent of Australia's role in this venture a few SI GaAs microstrip detectors are to be manufactured under contract by the CSIRO division of Radiophysics GaAs IC Prototyping Facility. The planned production of the devices is discussed. First, the reasons for producing the detectors here in Australia are examined, then some basic characteristics of the material are considered, and finally details are provided of the design used for the manufacture of the devices. Two sets of detectors will be produced using the standard Glasgow production recipe; SIGaAs and GaN. The Glasgow mask set is being used as a benchmark against which to compare the Australian devices

  3. Donor level of interstitial hydrogen in GaAs

    International Nuclear Information System (INIS)

    Dobaczewski, L.; Bonde Nielsen, K.; Nylandsted Larsen, A.; Peaker, A.R.

    2006-01-01

    The first data evidencing the existence of the donor level of the interstitial hydrogen in GaAs are presented. The abundant formation of the (0/+) donor level after in situ low-temperature implantation of hydrogen into the depletion layer of GaAs Schottky diodes has been observed and the activation energy and annealing properties have been determined by Laplace DLTS. The activation energy for electron emission of this donor state is 0.14eV. Above 100K the hydrogen deep donor state is unstable, converting to a more stable form when there are electrons available for the capture process. A slightly perturbed form of the hydrogen donor in its neutral charge state can be recovered by illuminating the sample. This process releases twice as many electrons as the ionisation process of the hydrogen donor state itself. This fact, by analogy with the silicon case, evidences the negative-U behaviour of hydrogen in GaAs

  4. Microwave GaAs Integrated Circuits On Quartz Substrates

    Science.gov (United States)

    Siegel, Peter H.; Mehdi, Imran; Wilson, Barbara

    1994-01-01

    Integrated circuits for use in detecting electromagnetic radiation at millimeter and submillimeter wavelengths constructed by bonding GaAs-based integrated circuits onto quartz-substrate-based stripline circuits. Approach offers combined advantages of high-speed semiconductor active devices made only on epitaxially deposited GaAs substrates with low-dielectric-loss, mechanically rugged quartz substrates. Other potential applications include integration of antenna elements with active devices, using carrier substrates other than quartz to meet particular requirements using lifted-off GaAs layer in membrane configuration with quartz substrate supporting edges only, and using lift-off technique to fabricate ultrathin discrete devices diced separately and inserted into predefined larger circuits. In different device concept, quartz substrate utilized as transparent support for GaAs devices excited from back side by optical radiation.

  5. Status of fully integrated GaAs particle detectors

    International Nuclear Information System (INIS)

    Braunschweig, W.; Breibach, J.; Kubicki, Th.; Luebelsmeyer, K.; Maesing, Th.; Rente, C.; Roeper, Ch.; Siemes, A.

    1999-01-01

    GaAs strip detectors are of interest because of their radiation hardness at room temperature and the high absorption coefficient of GaAs for x-rays. The detectors currently under development will be used in the VLQ-experiment at the H1 experiment at the HERA collider. This will be the first high energy physics experiment where GaAs detectors will be used. The detectors have a sensitive area of 5 x 4 cm with a pitch of 62 μ m. Due to the high density of channels the biasing resistors and coupling capacitors are integrated. For the resistors a resistive layer made of Cermet is used. The properties of the first fully integrated strip detector are presented

  6. Comment on ''Reassessment of space-change and central-cell scattering contributions to GaAs electron mobility''

    Science.gov (United States)

    Stringfellow, G. B.

    1982-07-01

    Walukiewicz et al.1 have recently stated that previously reported contributions to the electron mobility of GaAs from space-charge and/or central-cell scattering are in fact insignificant, and that reports of a T-1/2 term in the mobility2,3 are artifacts due to the assumption of Mathiessen's rule. This conclusion is an overstatement of their results and in fact demonstrably incorrect. First, an analysis of the data reported by Stringfellow2 and Stringfellow and Kuenzel3 as well as others has already been performed by Chattopadhyay et al.4 without assuming Mathiessen's rule. Their conclusion is that central-cell scattering is indeed significant. Second, the particular data analyzed by Walukiewicz et al. are in fact acknowledged in Ref. 2 to have very little T-1/2 scattering. The magnitude of the scattering cross section for T-1/2 scattering, SCA, for other samples is more than an order of magnitude larger, too large to be ascribed to errors inherent in using Mathiessen's rule. Experimental data convincingly demonstrate this. The mobility versus temperature curves are lower, especially at higher temperatures, for C as opposed to Zn- or Ge-doped samples where all have the same values of ND+NA (see Fig. 2 of Ref. 3). In addition, recently published data5 for MBE GaAs grown with different C doping levels show that for constant ND+NA, SCA is three times larger for the more highly C doped samples. This could not be due to errors inherent in the use of Mathiessen's rule. For these samples C clearly introduces an increase in the T-1/2 scattering which is not observed for other acceptors. ufc15xr 1W. Walukiewicz, J. Lagowski, and H. C. Gatos, J. Appl. Phys. 52, 5853 (1981). 2G. B. Stringfellow, J. Appl. Phys. 50, 4178 (1979). 3G. B. Stringfellow and H. Kuenzel, J. Appl. Phys. 51, 3254 (1980). 4D. Chattopadhyay, H. J. Queisser, and G. B. Stringfellow, J. Phys. Soc. Jpn. 49, Suppl. A, 293 (1980). 5G. B. Stringfellow, R. Stall, and W. Koschel, Appl. Phys. Lett. 38, 156 (1981

  7. Nuclear spin warm up in bulk n -GaAs

    Science.gov (United States)

    Kotur, M.; Dzhioev, R. I.; Vladimirova, M.; Jouault, B.; Korenev, V. L.; Kavokin, K. V.

    2016-08-01

    We show that the spin-lattice relaxation in n -type insulating GaAs is dramatically accelerated at low magnetic fields. The origin of this effect, which cannot be explained in terms of well-known diffusion-limited hyperfine relaxation, is found in the quadrupole relaxation, induced by fluctuating donor charges. Therefore, quadrupole relaxation, which governs low field nuclear spin relaxation in semiconductor quantum dots, but was so far supposed to be harmless to bulk nuclei spins in the absence of optical pumping, can be studied and harnessed in the much simpler model environment of n -GaAs bulk crystal.

  8. The GaAs electron source: simulations and experiments

    International Nuclear Information System (INIS)

    Aleksandrov, A.V.; Ciullo, G.; Guidi, V.; Kudelainen, V.I.; Lamanna, G.; Lenisa, P.; Logachov, P.V.; Maciga, B.; Novokhatsky, A.; Tecchio, L.; Yang, B.

    1994-01-01

    In this paper we calculate electron emission from GaAs photocathodes using the Monte Carlo technique. Typical data of energy spread of the electron beam are presented. For photoenergy ranging from 1.6 to 2.1 eV, the calculated longitudinal and transverse energy spreads are 14.4-78 and 4-14.7 meV respectively. Temporal measurement of GaAs photocathodes has been performed. The preliminary results show that the temporal response is faster than 200 ps. (orig.)

  9. Performance of a GaAs electron source

    International Nuclear Information System (INIS)

    Calabrese, R.; Ciullo, G.; Della Mea, G.; Egeni, G.P.; Guidi, V.; Lamanna, G.; Lenisa, P.; Maciga, B.; Rigato, V.; Rudello, V.; Tecchio, L.; Yang, B.; Zandolin, S.

    1994-01-01

    We discuss the performance improvement of a GaAs electron source. High quantum yield (14%) and constant current extraction (1 mA for more than four weeks) are achieved after a little initial decay. These parameters meet the requirements for application of the GaAs photocathode as a source for electron cooling devices. We also present the preliminary results of a surface analysis experiment, carried out by means of the RBS technique to check the hypothesis of cesium evaporation from the surface when the photocathode is in operation. (orig.)

  10. Transient radiation effects in GaAs semiconductor devices

    International Nuclear Information System (INIS)

    Chang, J.Y.; Stauber, M.; Ezzeddine, A.; Howard, J.W.; Constantine, A.G.; Becker, M.; Block, R.C.

    1988-01-01

    This paper describes an ongoing program to identify the response of GaAs devices to intense pulses of ionizing radiation. The program consists of experimental measurements at the Rensselaer Polytechnic Institute's RPI electron linear accelerator (Linac) on generic GaAs devices built by Grumman Tachonics Corporation and the analysis of these results through computer simulation with the circuit model code SPICE (including radiation effects incorporated in the variations TRISPICE and TRIGSPICE and the device model code PISCES IIB). The objective of this program is the observation of the basic response phenomena and the development of accurate simulation tools so that results of Linac irradiations tests can be understood and predicted

  11. Molecular-beam epitaxy on shallow mesa gratings patterned on GaAs(311)A and (100) substrates

    NARCIS (Netherlands)

    Gong, Q.; Nötzel, R.; Schönherr, H.-P.; Ploog, K.H.

    2002-01-01

    We report on the morphology and properties of the surface formed by molecular-beam epitaxy on shallow mesa gratings on patterned GaAs(311)A and GaAs(100). On GaAs(311)A substrates, the corrugated surface formed after GaAs growth on shallow mesa gratings along [011] is composed of monolayer high

  12. LPCVD homoepitaxy of Si doped β-Ga2O3 thin films on (010) and (001) substrates

    Science.gov (United States)

    Rafique, Subrina; Karim, Md Rezaul; Johnson, Jared M.; Hwang, Jinwoo; Zhao, Hongping

    2018-01-01

    This paper presents the homoepitaxy of Si-doped β-Ga2O3 thin films on semi-insulating (010) and (001) Ga2O3 substrates via low pressure chemical vapor deposition with a growth rate of ≥1 μm/h. Both high resolution scanning transmission electron microscopy and X-ray diffraction measurements demonstrated high crystalline quality homoepitaxial growth of these thin films. Atomic resolution STEM images of the as-grown β-Ga2O3 thin films on (010) and (001) substrates show high quality material without extended defects or dislocations. The charge carrier transport properties of the as-grown Si-doped β-Ga2O3 thin films were characterized by the temperature dependent Hall measurement using van der Pauw patterns. The room temperature carrier concentrations achieved for the (010) and (001) homoepitaxial thin films were ˜1.2 × 1018 cm-3 and ˜9.5 × 1017 cm-3 with mobilities of ˜72 cm2/V s and ˜42 cm2/V s, respectively.

  13. Precision calibration of the silicon doping level in gallium arsenide epitaxial layers

    Science.gov (United States)

    Mokhov, D. V.; Berezovskaya, T. N.; Kuzmenkov, A. G.; Maleev, N. A.; Timoshnev, S. N.; Ustinov, V. M.

    2017-10-01

    An approach to precision calibration of the silicon doping level in gallium arsenide epitaxial layers is discussed that is based on studying the dependence of the carrier density in the test GaAs layer on the silicon- source temperature using the Hall-effect and CV profiling techniques. The parameters are measured by standard or certified measuring techniques and approved measuring instruments. It is demonstrated that the use of CV profiling for controlling the carrier density in the test GaAs layer at the thorough optimization of the measuring procedure ensures the highest accuracy and reliability of doping level calibration in the epitaxial layers with a relative error of no larger than 2.5%.

  14. Electronic properties of GaAs, InAs and InP nanowires studied by terahertz spectroscopy

    International Nuclear Information System (INIS)

    Joyce, Hannah J; Docherty, Callum J; Lloyd-Hughes, James; Herz, Laura M; Johnston, Michael B; Gao Qiang; Tan, H Hoe; Jagadish, Chennupati

    2013-01-01

    We have performed a comparative study of ultrafast charge carrier dynamics in a range of III–V nanowires using optical pump–terahertz probe spectroscopy. This versatile technique allows measurement of important parameters for device applications, including carrier lifetimes, surface recombination velocities, carrier mobilities and donor doping levels. GaAs, InAs and InP nanowires of varying diameters were measured. For all samples, the electronic response was dominated by a pronounced surface plasmon mode. Of the three nanowire materials, InAs nanowires exhibited the highest electron mobilities of 6000 cm 2 V −1 s −1 , which highlights their potential for high mobility applications, such as field effect transistors. InP nanowires exhibited the longest carrier lifetimes and the lowest surface recombination velocity of 170 cm s −1 . This very low surface recombination velocity makes InP nanowires suitable for applications where carrier lifetime is crucial, such as in photovoltaics. In contrast, the carrier lifetimes in GaAs nanowires were extremely short, of the order of picoseconds, due to the high surface recombination velocity, which was measured as 5.4 × 10 5   cm s −1 . These findings will assist in the choice of nanowires for different applications, and identify the challenges in producing nanowires suitable for future electronic and optoelectronic devices. (paper)

  15. Diffusion in Intrinsic and Highly Doped III-V Semiconductors

    CERN Multimedia

    Stolwijk, N

    2002-01-01

    %title\\\\ \\\\Diffusion plays a key role in the fabrication of semiconductor devices. The diffusion of atoms in crystals is mediated by intrinsic point defects. Investigations of the diffusion behaviour of self- and solute atoms on the Ga sublattice of gallium arsenide led to the conclusion that in intrinsic and n-type material charged Ga vacancies are involved in diffusion processes whereas in p-type material diffusion if governed by charged Ga self-interstitials. Concerning the As sublattice of gallium arsenide there is a severe lack of reliable diffusion data. The few available literature data on intrinsic GaAs are not mutually consistent. A systematic study of the doping dependence of diffusion is completely missing. The most basic diffusion process - self-diffusion of As and its temperature and doping dependence - is practically not known. For GaP a similar statement holds.\\\\ \\\\The aim of the present project is to perform a systematic diffusion study of As diffusion in intrinsic and doped GaAs and in GaP. P...

  16. Radiation annealing of gallium arsenide implanted with sulphur

    CERN Document Server

    Ardyshev, V M

    2002-01-01

    Sulfur ions were implanted in a semi-insulating GaAs. Photon annealing (805 deg C/(10-12) s) and the thermal one (800 deg C/30 min) were conducted under SiO sub 2 -films coating obtained by different ways. Contents of GaAs components in films were determined from Rutherford backscattering spectra; concentration profiles of electrons were measured by the voltage-capacitance method. Diffusion of sulfur was shown to go in two directions - to the surface and into bulk of GaAs. The first process was induced by vacancies that had been formed near the surface of semiconductors during the dielectric coating. The coefficient of the bulk-diffusion and diffusion-to-surface of sulfur ions under photon annealing was twice as much as that under thermal one. The doping efficiency was also larger

  17. A high resolution EELS study of free-carrier variations in H2+/H+ bombarded (100)GaAs

    International Nuclear Information System (INIS)

    Dubois, L.H.; Schwartz, G.P.

    1984-01-01

    High resolution electron energy loss spectroscopy (EELS) has been used to examine whether thermal recovery of the near-surface free-carrier concentration in Te-doped (100) GaAs is accomplished following low energy (250--1500 eV) hydrogen ion bombardment. For hydrogen ion impact energies below 500 eV, the nominal bulk free-carrier density is recovered by annealing at 725 K for 2 h. For comparable ion doses, the net free-carrier concentration decreases monotonically at higher impact energies under similar annealing conditions. The threshold for damage retention occurs close to the value of transmitted energy which is necessary to create either a Ga or an As interstitial point defect

  18. Preparation and properties of thick not intentionally doped GaInP(As)/GaAs layers

    CERN Document Server

    Nohavica, D; Zdansky, K

    1999-01-01

    We report on liquid-phase epitaxial growth of thick layers of GaInP(As), lattice matched to GaAs. Layers with thicknesses up to 10 mu m were prepared in a multi-melt bin, step-cooling, one-phase configuration. Unintentionally doped layers, grown from moderate purity starting materials, show a significant decrease in the residual impurity level when erbium is added to the melt. Fundamental electrical and optical properties of the layers were investigated. (author)

  19. Femtosecond coherent emission from GaAs bulk microcavities

    Science.gov (United States)

    Gurioli, Massimo; Bogani, Franco; Ceccherini, Simone; Colocci, Marcello; Beltram, Fabio; Sorba, Lucia

    1999-02-01

    The emission from a λ/2 GaAs bulk microcavity resonantly excited by femtosecond pulses has been characterized by using an interferometric correlation technique. It is found that the emission is dominated by the coherent signal due to light elastically scattered by disorder, and that scattering is predominantly originated from the lower polariton branch.

  20. Superconductivity and its pressure variation in GaAs

    International Nuclear Information System (INIS)

    Nirmala Louis, C.; Jayam, Sr. Gerardin; Amalraj, A.

    2005-01-01

    The electronic band structure, metallization, phase transition and superconducting transition of gallium arsenide under pressure are studied using TB-LMTO method. Metallization occurs via indirect closing of band gap between Γ and X points. GaAs becomes superconductor under high pressure but before that it undergoes structural phase transition from ZnS phase to NaCl phase. The ground state properties are analyzed by fitting the calculated total energies to the Birch-Murnaghan's equation of state. The superconducting transition temperatures (T c ) obtained as a function of pressure for both the ZnS and NaCl structures and GaAs comes under the class of pressure induced superconductor. When pressure is increased T c increases in both the normal and high pressure structures. The dependence of T c on electron-phonon mass enhancement factor λ shows that GaAs is an electron-phonon-mediated superconductor. Also it is found that GaAs retained in their normal structure under high pressure give appreciably high T c . (author)

  1. Density-dependent electron scattering in photoexcited GaAs

    DEFF Research Database (Denmark)

    Mics, Zoltán; D'’Angio, Andrea; Jensen, Søren A.

    2013-01-01

    —In a series of systematic optical pump - terahertz probe experiments we study the density-dependent electron scattering rate in photoexcited GaAs in a large range of carrier densities. The electron scattering time decreases by as much as a factor of 4, from 320 to 60 fs, as the electron density...

  2. Picosecond relaxation of X-ray excited GaAs

    Czech Academy of Sciences Publication Activity Database

    Tkachenko, V.; Medvedev, Nikita; Lipp, V.; Ziaja, B.

    2017-01-01

    Roč. 24, Sep (2017), s. 15-21 ISSN 1574-1818 Institutional support: RVO:68378271 Keywords : GaAS * X-ray excitation * picosecond relaxation Subject RIV: BL - Plasma and Gas Discharge Physics OBOR OECD: Fluids and plasma physics (including surface physics) Impact factor: 0.908, year: 2016

  3. Gene doping.

    Science.gov (United States)

    Haisma, H J; de Hon, O

    2006-04-01

    Together with the rapidly increasing knowledge on genetic therapies as a promising new branch of regular medicine, the issue has arisen whether these techniques might be abused in the field of sports. Previous experiences have shown that drugs that are still in the experimental phases of research may find their way into the athletic world. Both the World Anti-Doping Agency (WADA) and the International Olympic Committee (IOC) have expressed concerns about this possibility. As a result, the method of gene doping has been included in the list of prohibited classes of substances and prohibited methods. This review addresses the possible ways in which knowledge gained in the field of genetic therapies may be misused in elite sports. Many genes are readily available which may potentially have an effect on athletic performance. The sporting world will eventually be faced with the phenomena of gene doping to improve athletic performance. A combination of developing detection methods based on gene arrays or proteomics and a clear education program on the associated risks seems to be the most promising preventive method to counteract the possible application of gene doping.

  4. Implantation doping of GaN

    International Nuclear Information System (INIS)

    Zolper, J.C.

    1996-01-01

    Ion implantation has played an enabling role in the realization of many high performance photonic and electronic devices in mature semiconductor materials systems such as Si and GaAs. This can also be expected to be the case in III-Nitride based devices as the material quality continues to improve. This paper reviews the progress in ion implantation processing of the III-Nitride materials, namely, GaN, AlN, InN and their alloys. Details are presented of the successful demonstrations of implant isolation as well as n- and p-type implantation doping of GaN. Implant doping has required activation annealing at temperatures in excess of 1,000 C. The nature of the implantation induced damage and its response to annealing is addressed using Rutherford Backscattering. Finally, results are given for the first demonstration of a GaN device fabricated using ion implantation doping, a GaN junction field effect transistor (JFET)

  5. Spin dynamics in GaAs and (110)-GaAs heterostructures; Spindynamik in GaAs und (110)-GaAs-Heterostrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Oertel, Stefan

    2012-07-01

    This thesis investigates the spin dynamics in both bulk GaAs and (llO)GaAs heterostructures using time- and polarization-resolved photoluminescence spectroscopy. In bulk GaAs the spin relaxation t ime is measured for the first time in the high temperature regime from 280 K to 400 K and is compared to numerical calculations. The numerical calculations are based on the spin relaxation theory of the Dyakonov-Perel mechanism effected by momentum scattering with polar optical phonons and electron-electron scattering and are in good agreement with the experimental results. Measurements of the dependence on the electron density serve to determine the energy dependent proportional factor between the electron density and the effective electron-electron scattering time. Also in bulk GaAs the interaction between the electron spin system and the nuclear spin system is investigated. The measured electron Lande g-factor under the influence of the nuclear magnetic field is used as an indicator to monitor the temporal evolution of the nuclear magnetic field under sustained dynamic nuclear polarization. Measurements with polarization modulated excitation enable the determination of the relevant time scale at which dynamic nuclear polarization takes place. Furthermore, the temporal evolution of the measured electron Lande g-factor shows the complex interplay of the dynamic nuclear polarization, the nuclear spin diffusion and the nuclear spin relaxation. In symmetric (110)-GaAs quantum wells the dependence of the inplane anisotropy of the electron Lande g-factor on the quantum well thickness is determined experimentally. The measurements are in very good agreement with calculations based upon k . p-theory and reveal a maximum of the anisotropy at maximum carrier localization in the quantum well. The origin of the anisotropy that is not present in symmetric (001) quantum wells is qualitatively described by means of a simplified model based on fourth-order perturbation theory. A

  6. Preferential adsorption of gallium on GaAs(111)B surfaces during the initial growth of Au-assisted GaAs nanowires

    International Nuclear Information System (INIS)

    Shu Haibo; Chen Xiaoshuang; Ding Zongling; Dong Ruibin; Lu Wei

    2010-01-01

    The mechanism of the preferential adsorption of Ga on GaAs(111)B surfaces during the initial growth of Au-assisted GaAs nanowires is studied by using first-principles calculations within density functional theory. The calculated results show that Au preadsorption on GaAs(111)B surface significantly enhances the stability of the Ga adatom in comparison with the adsorption of Ga on clean GaAs(111)B surface. The stabilization of the Ga adatom is due to charge transfers from the Ga 4p and 4s states to the Au 6s and As 4p states. The number of Ga adatoms stabilized on GaAs(111)B surfaces depends on the size of surface Au cluster. The reason is that Au acted as an electron acceptor on GaAs(111)B surface assists the charge transfer of Ga adatoms for filling the partial unoccupied bands of GaAs(111)B surface. Our results are helpful to understand the growth of Au-assisted GaAs nanowires.

  7. Femtosecond pulsed laser ablation of GaAs

    International Nuclear Information System (INIS)

    Trelenberg, T.W.; Dinh, L.N.; Saw, C.K.; Stuart, B.C.; Balooch, M.

    2004-01-01

    The properties of femtosecond-pulsed laser deposited GaAs nanoclusters were investigated. Nanoclusters of GaAs were produced by laser ablating a single crystal GaAs target in vacuum or in a buffer gas using a Ti-sapphire laser with a 150 fs minimum pulse length. For in-vacuum deposition, X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) revealed that the average cluster size was approximately 7 nm for laser pulse lengths between 150 fs and 25 ps. The average cluster size dropped to approximately 1.5 nm at a pulse length of 500 ps. It was also observed that film thickness decreased with increasing laser pulse length. A reflective coating, which accumulated on the laser admission window during ablation, reduced the amount of laser energy reaching the target for subsequent laser shots and developed more rapidly at longer pulse lengths. This observation indicates that non-stoichiometric (metallic) ablatants were produced more readily at longer pulse lengths. The angular distribution of ejected material about the target normal was well fitted to a bi-cosine distribution of cos 47 θ+ cos 4 θ for ablation in vacuum using 150 fs pulses. XPS and AES revealed that the vacuum-deposited films contained excess amorphous Ga or As in addition to the stoichiometric GaAs nanocrystals seen with XRD. However, films containing only the GaAs nanocrystals were produced when ablation was carried out in the presence of a buffer gas with a pressure in excess of 6.67 Pa. At buffer gas pressure on the order of 1 Torr, it was found that the stoichiometry of the ablated target was also preserved. These experiments indicate that both laser pulse length and buffer gas pressure play important roles in the formation of multi-element nanocrystals by laser ablation. The effects of gas pressure on the target's morphology and the size of the GaAs nanocrystals formed will also be discussed

  8. GaAs nanocrystals: Structure and vibrational properties

    International Nuclear Information System (INIS)

    Nayak, J.; Sahu, S.N.; Nozaki, S.

    2006-01-01

    GaAs nanocrystals were grown on indium tin oxide substrate by an electrodeposition technique. Atomic force microscopic measurement indicates an increase in the size of the nanocrystal with decrease in the electrolysis current density accompanied by the change in the shape of the crystallite. Transmission electron microscopic measurements identify the crystallite sizes to be in the range of 10-15 nm and the crystal structure to be orthorhombic. On account of the quantum size effect, the first optical transition was blue shifted with respect to the band gap of the bulk GaAs and the excitonic peak appeared prominent. A localized phonon mode ascribed to certain point defect occurred in the room temperature micro-Raman spectrum

  9. Testing a GaAs cathode in SRF gun

    International Nuclear Information System (INIS)

    Wang, E.; Kewisch, J.; Ben-Zvi, I.; Burrill, A.; Rao, T.; Wu, Q.; Holmes, D.

    2011-01-01

    RF electron guns with a strained superlattice GaAs cathode are expected to generate polarized electron beams of higher brightness and lower emittance than do DC guns, due to their higher field gradient at the cathode's surface and lower cathode temperature. We plan to install a bulk GaAs:Cs in a SRF gun to evaluate the performance of both the gun and the cathode in this environment. The status of this project is: In our 1.3 GHz 1/2 cell SRF gun, the vacuum can be maintained at nearly 10 -12 Torr because of cryo-pumping at 2K. With conventional activation of bulk GaAs, we obtained a QE of 10% at 532 nm, with lifetime of more than 3 days in the preparation chamber and have shown that it can survive in transport from the preparation chamber to the gun. The beam line has been assembled and we are exploring the best conditions for baking the cathode under vacuum. We report here the progress of our test of the GaAs cathode in the SRF gun. Future particle accelerators, such as eRHIC and the ILC require high-brightness, high-current polarized electrons. Strained superlattice GaAs:Cs has been shown to be an efficient cathode for producing polarized electrons. Activation of GaAs with Cs,O(F) lowers the electron affinity and makes it energetically possible for all the electrons, excited into the conduction band that drift or diffuse to the emission surface, to escape into the vacuum. Presently, all operating polarized electron sources, such as the CEBAF, are DC guns. In these devices, the excellent ultra-high vacuum extends the lifetime of the cathode. However, the low field gradient on the photocathode's emission surface of the DC guns limits the beam quality. The higher accelerating gradients, possible in the RF guns, generate a far better beam. Until recently, most RF guns operated at room temperature, limiting the vacuum to ∼10 -9 Torr. This destroys the GaAs's NEA surface. The SRF guns combine the excellent vacuum conditions of DC guns and the high accelerating

  10. X-ray electron density distribution of GaAs

    International Nuclear Information System (INIS)

    Pietsch, U.

    1986-01-01

    Using ten X-ray structure amplitudes of strong reflections and nine weak reflections both, the valence electron and the difference electron density distribution of GaAs, are calculated. The experimental data are corrected for anomalous dispersion using a bond charge model. The calculated plots are compared with up to now published band structure-based and semiempirically calculated density plots. Taking into account the experimental data of germanium, measured on the same absolute scale, the difference density between GaAs and Ge is calculated. This exhibits the charge transfer between both the f.c.c.-sublattices as well as both, the shift and the decrease of the bond charge, quite closely connected to the theoretical results published by Baur et al. (author)

  11. Spin transport anisotropy in (110)GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Odilon, D.D.C. Jr.; Rudolph, Joerg; Hey, Rudolf; Santos, Paulo V. [Paul-Drude-Institut fuer Festkoerperelektronik, Berlin (Germany); Iikawa, Fernando [Universidade Estadual de Campinas, IFGW, Campinas SP (Brazil)

    2007-07-01

    Mobile piezoelectric potentials are used to coherently transport electron spins in GaAs(110) quantum wells (QW) over distances exceeding 60{mu}m. We demonstrate that the dynamics of mobile spins under external magnetic fields depends on the direction of motion in the QW plane. The weak piezoelectric fields impart a non-vanishing average velocity to the carriers, allowing for the direct observation of the carrier momentum dependence of the spin polarization dynamics. While transport along [001] direction presents high in-plane spin relaxation rates, transport along [ anti 110] shows a much weaker external field dependence due to the non-vanishing internal magnetic field. We show that the anisotropy is an intrinsic property of the underling GaAs matrix, associated with the bulk inversion asymmetry contribution to the LS-coupling.

  12. Vacancies and negative ions in GaAs

    International Nuclear Information System (INIS)

    Corbel, C.

    1991-01-01

    We use positron lifetime studies performed in GaAs materials to show the defect properties which can be investigated by implanting positive positrons in semiconductors. The studies concern native and electron irradiation induced defects. These studies show that vacancy charge state and vacancy ionization levels can be determined from positron annihilation. They show also that positrons are trapped by negative ions and give information on their concentration

  13. Ion induced charge collection in GaAs MESFETs

    International Nuclear Information System (INIS)

    Campbell, A.; Knudson, A.; McMorrow, D.; Anderson, W.; Roussos, J.; Espy, S.; Buchner, S.; Kang, K.; Kerns, D.; Kerns, S.

    1989-01-01

    Charge collection measurements on GaAs MESFET test structures demonstrate that more charge can be collected at the gate than is deposited in the active layer and more charge can be collected at the drain than the total amount of charge produced by the ion. Enhanced charge collection at the gate edge is also observed. The current transients produced by the energetic ions have been measured directly with about 20 picosecond resolution

  14. Epitaxial growth on porous GaAs substrates

    Czech Academy of Sciences Publication Activity Database

    Grym, Jan; Nohavica, Dušan; Gladkov, Petar; Hulicius, Eduard; Pangrác, Jiří; Piksová, K.

    2013-01-01

    Roč. 16, č. 1 (2013), s. 59-64 ISSN 1631-0748 R&D Projects: GA ČR GAP102/10/1201; GA ČR GAP108/10/0253 Institutional support: RVO:67985882 ; RVO:68378271 Keywords : Electrochemical etching * Porous semiconductors * Epitaxial growth * GaAs Subject RIV: BH - Optics, Masers, Lasers; JA - Electronics ; Optoelectronics, Electrical Engineering (FZU-D) Impact factor: 1.483, year: 2013

  15. Fast GaAs photoconductor responses to subnanosecond proton pulses

    International Nuclear Information System (INIS)

    Pochet, T.

    1993-01-01

    GaAs photoconductors have been tailored to detect ultrafast proton pulses having energies ranging between 4 and 9 MeV. The sensitivity, the linearity and the speed of response of the devices are analyzed as a function of their neutron pre-irradiation treatment. The dependence of the sensitivity on the proton energy and the applied polarization is also studied. Finally, the experimental results are compared with a simple theoretical model

  16. Solar heating of GaAs nanowire solar cells.

    Science.gov (United States)

    Wu, Shao-Hua; Povinelli, Michelle L

    2015-11-30

    We use a coupled thermal-optical approach to model the operating temperature rise in GaAs nanowire solar cells. We find that despite more highly concentrated light absorption and lower thermal conductivity, the overall temperature rise in a nanowire structure is no higher than in a planar structure. Moreover, coating the nanowires with a transparent polymer can increase the radiative cooling power by 2.2 times, lowering the operating temperature by nearly 7 K.

  17. Gaas Displacement Damage Dosimeter Based on Diode Dark Currents

    Directory of Open Access Journals (Sweden)

    Warner Jeffrey H.

    2017-01-01

    Full Text Available GaAs diode dark currents are correlated over a very large proton energy range as a function of displacement damage dose (DDD. The linearity of the dark current increase with DDD over a wide range of applied voltage bias deems this device an excellent candidate for a displacement damage dosimeter. Additional proton testing performed in situ enabled error estimate determination to within 10% for simulated space use.

  18. Ab initio study of hot electrons in GaAs

    OpenAIRE

    Bernardi, Marco; Vigil-Fowler, Derek; Ong, Chin Shen; Neaton, Jeffrey B.; Louie, Steven G.

    2015-01-01

    Hot carrier dynamics critically impacts the performance of electronic, optoelectronic, photovoltaic, and plasmonic devices. Hot carriers lose energy over nanometer lengths and picosecond timescales and thus are challenging to study experimentally, whereas calculations of hot carrier dynamics are cumbersome and dominated by empirical approaches. In this work, we present ab initio calculations of hot electrons in gallium arsenide (GaAs) using density functional theory and many-body perturbation...

  19. Stark shift of impurity doped quantum dots: Role of noise

    Science.gov (United States)

    Arif, Sk. Md.; Bera, Aindrila; Ghosh, Anuja; Ghosh, Manas

    2018-02-01

    Present study makes a punctilious investigation of the profiles of Stark shift (SS) of doped GaAs quantum dot (QD) under the supervision of Gaussian white noise. A few physical parameters have been varied and the consequent variations in the SS profiles have been monitored. The said physical parameters comprise of magnetic field, confinement potential, dopant location, dopant potential, noise strength, aluminium concentration (only for AlxGa1-x As alloy QD), position-dependent effective mass (PDEM), position-dependent dielectric screening function (PDDSF), anisotropy, hydrostatic pressure (HP) and temperature. The SS profiles unfurl interesting features that heavily depend upon the particular physical quantity concerned, presence/absence of noise and the manner (additive/multiplicative) noise enters the system. The study highlights feasible means of maximizing SS of doped QD in presence of noise by suitable adjustment of several control parameters. The study deems importance in view of technological applications of QD devices where noise plays some prominent role.

  20. Burst annealing of high temperature GaAs solar cells

    Science.gov (United States)

    Brothers, P. R.; Horne, W. E.

    1991-01-01

    One of the major limitations of solar cells in space power systems is their vulnerability to radiation damage. One solution to this problem is to periodically heat the cells to anneal the radiation damage. Annealing was demonstrated with silicon cells. The obstacle to annealing of GaAs cells was their susceptibility to thermal damage at the temperatures required to completely anneal the radiation damage. GaAs cells with high temperature contacts and encapsulation were developed. The cells tested are designed for concentrator use at 30 suns AMO. The circular active area is 2.5 mm in diameter for an area of 0.05 sq cm. Typical one sun AMO efficiency of these cells is over 18 percent. The cells were demonstrated to be resistant to damage after thermal excursions in excess of 600 C. This high temperature tolerance should allow these cells to survive the annealing of radiation damage. A limited set of experiments were devised to investigate the feasibility of annealing these high temperature cells. The effect of repeated cycles of electron and proton irradiation was tested. The damage mechanisms were analyzed. Limitations in annealing recovery suggested improvements in cell design for more complete recovery. These preliminary experiments also indicate the need for further study to isolate damage mechanisms. The primary objective of the experiments was to demonstrate and quantify the annealing behavior of high temperature GaAs cells. Secondary objectives were to measure the radiation degradation and to determine the effect of repeated irradiation and anneal cycles.

  1. Burst annealing of high temperature GaAs solar cells

    International Nuclear Information System (INIS)

    Brothers, P.R.; Horne, W.E.

    1991-01-01

    One of the major limitations of solar cells in space power systems is their vulnerability to radiation damage. One solution to this problem is to periodically heat the cells to anneal the radiation damage. Annealing was demonstrated with silicon cells. The obstacle to annealing of GaAs cells was their susceptibility to thermal damage at the temperatures required to completely anneal the radiation damage. GaAs cells with high temperature contacts and encapsulation were developed. The cells tested are designed for concentrator use at 30 suns AMO. The circular active area is 2.5 mm in diameter for an area of 0.05 sq cm. Typical one sun AMO efficiency of these cells is over 18 percent. The cells were demonstrated to be resistant to damage after thermal excursions in excess of 600 degree C. This high temperature tolerance should allow these cells to survive the annealing of radiation damage. A limited set of experiments were devised to investigate the feasibility of annealing these high temperature cells. The effect of repeated cycles of electron and proton irradiation was tested. The damage mechanisms were analyzed. Limitations in annealing recovery suggested improvements in cell design for more complete recovery. These preliminary experiments also indicate the need for further study to isolate damage mechanisms. The primary objective of the experiments was to demonstrate and quantify the annealing behavior of high temperature GaAs cells. Secondary objectives were to measure the radiation degradation and to determine the effect of repeated irradiation and anneal cycles

  2. Metallization systems for stable ohmic contacts to GaAs

    International Nuclear Information System (INIS)

    Tandon, J.L.; Douglas, K.D.; Vendura, G.; Kolawa, E.; So, F.C.T.; Nicolet, M.A.

    1986-01-01

    A metallization scheme to form reproducible and stable ohmic contacts to GaAs is described. The approach is based on the configuration: GaAs/X/Y/Z; where X is a thin metal film (e.g. Pt, Ti, Pd, Ru), Y is an electrically conducting diffusion barrier layer (TiN, W or W/sub 0.7/N/sub 0.3/), and Z is a thick metal layer (e.g. Ag) typically required for bonding or soldering purposes. The value and reproducibility of the contact resistance in these metallization systems results from the uniform steady-state solid-phase reaction of the metal X with GaAs. The stability of the contacts is achieved by the diffusion barrier layer Y, which not only confines the reaction of X with GaAs, but also prevents the top metal layer Z from interfering with this reaction. Applications of such contacts in fabricating stable solar cells are also discussed

  3. Nitridation of porous GaAs by an ECR ammonia plasma

    International Nuclear Information System (INIS)

    Naddaf, M; Hullavarad, S S; Ganesan, V; Bhoraskar, S V

    2006-01-01

    The effect of surface porosity of GaAs on the nature of growth of GaN, by use of plasma nitridation of GaAs, has been investigated. Porous GaAs samples were prepared by anodic etching of n-type (110) GaAs wafers in HCl solution. Nitridation of porous GaAs samples were carried out by using an electron-cyclotron resonance-induced ammonia plasma. The formation of mixed phases of GaN was investigated using the grazing angle x-ray diffraction method. A remarkable improvement in the intensity of photoluminescence (PL) compared with that of GaN synthesized by direct nitriding of GaAs surface has been observed. The PL intensity of nitrided porous GaAs at the temperature of 380 deg. C was found to be about two orders of magnitude higher as compared with the directly nitrided GaAs at the temperature of 500 deg. C. The changes in the morphology of nitrided porous GaAs have been investigated using both scanning electron microscopy and atomic force microscopy

  4. Nitridation of porous GaAs by an ECR ammonia plasma

    Energy Technology Data Exchange (ETDEWEB)

    Naddaf, M [Center for Advanced Studies in Material Science and Solid State Physics, University of Pune, Pune 411 007 (India); Department of Physics, Atomic Energy Commission of Syria, PO Box 6091, Damascus (Syrian Arab Republic); Hullavarad, S S [Center for Superconductivity Research, Department of Physics, University of Maryland, College Park, MD 20742 (United States); Ganesan, V [Inter University Consortium, Indore (India); Bhoraskar, S V [Center for Advanced Studies in Material Science and Solid State Physics, University of Pune, Pune 411 007 (India)

    2006-02-15

    The effect of surface porosity of GaAs on the nature of growth of GaN, by use of plasma nitridation of GaAs, has been investigated. Porous GaAs samples were prepared by anodic etching of n-type (110) GaAs wafers in HCl solution. Nitridation of porous GaAs samples were carried out by using an electron-cyclotron resonance-induced ammonia plasma. The formation of mixed phases of GaN was investigated using the grazing angle x-ray diffraction method. A remarkable improvement in the intensity of photoluminescence (PL) compared with that of GaN synthesized by direct nitriding of GaAs surface has been observed. The PL intensity of nitrided porous GaAs at the temperature of 380 deg. C was found to be about two orders of magnitude higher as compared with the directly nitrided GaAs at the temperature of 500 deg. C. The changes in the morphology of nitrided porous GaAs have been investigated using both scanning electron microscopy and atomic force microscopy.

  5. Nitridation of porous GaAs by an ECR ammonia plasma

    Science.gov (United States)

    Naddaf, M.; Hullavarad, S. S.; Ganesan, V.; Bhoraskar, S. V.

    2006-02-01

    The effect of surface porosity of GaAs on the nature of growth of GaN, by use of plasma nitridation of GaAs, has been investigated. Porous GaAs samples were prepared by anodic etching of n-type (110) GaAs wafers in HCl solution. Nitridation of porous GaAs samples were carried out by using an electron-cyclotron resonance-induced ammonia plasma. The formation of mixed phases of GaN was investigated using the grazing angle x-ray diffraction method. A remarkable improvement in the intensity of photoluminescence (PL) compared with that of GaN synthesized by direct nitriding of GaAs surface has been observed. The PL intensity of nitrided porous GaAs at the temperature of 380 °C was found to be about two orders of magnitude higher as compared with the directly nitrided GaAs at the temperature of 500 °C. The changes in the morphology of nitrided porous GaAs have been investigated using both scanning electron microscopy and atomic force microscopy.

  6. Temperature dependent magnetic properties of the GaAs substrate of spin-LEDs

    International Nuclear Information System (INIS)

    Ney, A; Harris, J S Jr; Parkin, S S P

    2006-01-01

    The temperature dependence of the magnetization of a light emitting diode having a ferromagnetic contact (spin-LED) is measured from 2 to 300 K in magnetic fields from 30 to 70 kOe and it is found that it originates from the GaAs substrate. The magnetization of GaAs comprises a van Vleck-type paramagnetic contribution to the susceptibility which scales inversely with the band gap of the semiconductor. Thus, the temperature dependence of the band gap of GaAs accounts for the non-linear temperature dependent magnetic susceptibility of GaAs and thus, at large magnetic fields, for the spin-LED

  7. X-ray diffraction from single GaAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Biermanns, Andreas

    2012-11-12

    In recent years, developments in X-ray focussing optics have allowed to produce highly intense, coherent X-ray beams with spot sizes in the range of 100 nm and below. Together with the development of new experimental stations, X-ray diffraction techniques can now be applied to study single nanometer-sized objects. In the present work, X-ray diffraction is applied to study different aspects of the epitaxial growth of GaAs nanowires. Besides conventional diffraction methods, which employ X-ray beams with dimensions of several tens of {mu}m, special emphasis lies on the use of nanodiffraction methods which allow to study single nanowires in their as-grown state without further preparation. In particular, coherent X-ray diffraction is applied to measure simultaneously the 3-dimensional shape and lattice parameters of GaAs nanowires grown by metal-organic vapor phase epitaxy. It is observed that due to a high density of zinc-blende rotational twins within the nanowires, their lattice parameter deviates systematically from the bulk zinc-blende phase. In a second step, the initial stage in the growth of GaAs nanowires on Si (1 1 1) surfaces is studied. This nanowires, obtained by Ga-assisted growth in molecular beam epitaxy, grow predominantly in the cubic zinc-blende structure, but contain inclusions of the hexagonal wurtzite phase close to their bottom interface. Using nanodiffraction methods, the position of the different structural units along the growth axis is determined. Because the GaAs lattice is 4% larger than silicon, these nanowires release their lattice mismatch by the inclusion of dislocations at the interface. Whereas NWs with diameters below 50 nm are free of strain, a rough interface structure in nanowires with diameters above 100 nm prevents a complete plastic relaxation, leading to a residual strain at the interface that decays elastically along the growth direction. Finally, measurements on GaAs-core/InAs-shell nanowire heterostructures are presented

  8. Photoreflectance study of InAs ultrathin layer embedded in Si-delta-doped GaAs/AlGaAs quantum wells

    International Nuclear Information System (INIS)

    Dhifallah, I.; Daoudi, M.; Bardaoui, A.; Eljani, B.; Ouerghi, A.; Chtourou, R.

    2011-01-01

    Photoreflectance and photoluminescence studies were performed to characterize InAs ultrathin layer embedded in Si-delta-doped GaAs/AlGaAs high electron mobility transistors. These structures were grown by Molecular Beam Epitaxy on (1 0 0) oriented GaAs substrates with different silicon-delta-doped layer densities. Interband energy transitions in the InAs ultrathin layer quantum well were observed below the GaAs band gap in the photoreflectance spectra, and assigned to electron-heavy-hole (E e-hh ) and electron-light-hole (E e-lh ) fundamental transitions. These transitions were shifted to lower energy with increasing silicon-δ-doping density. This effect is in good agreement with our theoretical results based on a self-consistent solution of the coupled Schroedinger and Poisson equations and was explained by increased escape of photogenerated carriers and enhanced Quantum Confined Stark Effect in the Si-delta-doped InAs/GaAs QW. In the photoreflectance spectra, not only the channel well interband energy transitions were observed, but also features associated with the GaAs and AlGaAs bulk layers located at about 1.427 and 1.8 eV, respectively. By analyzing the Franz-Keldysh Oscillations observed in the spectral characteristics of Si-δ-doped samples, we have determined the internal electric field introduced by ionized Si-δ-doped centers. We have observed an increase in the electric field in the InAs ultrathin layer with increasing silicon content. The results are explained in terms of doping dependent ionized impurities densities and surface charges. - Research highlights: → Studying HEMTs structures with different silicon doping content. → An increase of the electric field in the InAs layer with increasing Si content. → The interband energy transitions in the HEMTs structures have been obtained from PR. → Experimental and theoretical values of transitions energies were in good agreement.

  9. Tolerance of GaAs as an original substrate for HVPE growth of free standing GaN

    Science.gov (United States)

    Suzuki, Mio; Sato, T.; Suemasu, T.; Hasegawa, F.

    2004-09-01

    In order to investigate possibility of thick GaN growth on a GaAs substrate by halide vapar phase epitaxy (HVPE), GaN was grown on GaAs(111)/Ti wafer with Ti deposited by E-gun. It was found that surface treatment of the GaAs substrate by HF solution deteriorated greatly the tolerence of GaAs and that Ti can protected GaAs from erosion by NH3. By depositing Ti on GaAs(111)A surface, a millor-like GaN layer could be grown at 1000 °C for 1 hour without serious deterioration of the original GaAs substrate. By increasing the growth rate, a thick free standing GaN will be obtained with GaAs as an original substrate in near future.

  10. Tolerance of GaAs as an original substrate for HVPE growth of free standing GaN

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, Mio; Sato, T.; Suemasu, T.; Hasegawa, F. [University of Tsukuba, Institute of Applied Physics, Tsukuba, Ibaraki 305-8573 (Japan)

    2004-09-01

    In order to investigate possibility of thick GaN growth on a GaAs substrate by halide vapar phase epitaxy (HVPE), GaN was grown on GaAs(111)/Ti wafer with Ti deposited by E-gun. It was found that surface treatment of the GaAs substrate by HF solution deteriorated greatly the tolerance of GaAs and that Ti can protected GaAs from erosion by NH{sub 3}. By depositing Ti on GaAs(111)A surface, a mirror-like GaN layer could be grown at 1000 C for 1 hour without serious deterioration of the original GaAs substrate. By increasing the growth rate, a thick free standing GaN will be obtained with GaAs as an original substrate in near future. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  11. Photo-Induced conductivity of heterojunction GaAs/Rare-Earth doped SnO2

    Directory of Open Access Journals (Sweden)

    Cristina de Freitas Bueno

    2013-01-01

    Full Text Available Rare-earth doped (Eu3+ or Ce3+ thin layers of tin dioxide (SnO2 are deposited by the sol-gel-dip-coating technique, along with gallium arsenide (GaAs films, deposited by the resistive evaporation technique. The as-built heterojunction has potential application in optoelectronic devices, because it may combine the emission from the rare-earth-doped transparent oxide, with a high mobility semiconductor. Trivalent rare-earth-doped SnO2 presents very efficient emission in a wide wavelength range, including red (in the case of Eu3+ or blue (Ce3+. The advantage of this structure is the possibility of separation of the rare-earth emission centers, from the electron scattering, leading to an indicated combination for electroluminescence. Electrical characterization of the heterojunction SnO2:Eu/GaAs shows a significant conductivity increase when compared to the conductivity of the individual films. Monochromatic light excitation shows up the role of the most external layer, which may act as a shield (top GaAs, or an ultraviolet light absorber sink (top RE-doped SnO2. The observed improvement on the electrical transport properties is probably related to the formation of short conduction channels in the semiconductors junction with two-dimensional electron gas (2DEG behavior, which are evaluated by excitation with distinct monochromatic light sources, where the samples are deposited by varying the order of layer deposition.

  12. Wavelength dependent laser-induced etching of Cr–O doped GaAs ...

    Indian Academy of Sciences (India)

    Administrator

    sub-bandgap photon illumination the etching process starts vigorously through the mediation of intermediate defect states. ... shows creation of shallow optical depth as visible from .... tron is lifted from valence band to deep inside the con-.

  13. Wavelength dependent laser-induced etching of Cr–O doped GaAs ...

    Indian Academy of Sciences (India)

    2016-08-26

    Aug 26, 2016 ... It is observed that under sub-bandgap photon illumination the etching process starts vigorously through the mediation of intermediate defect states. The defect states initiate the pits formation and subsequently pore propagation occurs due to asymmetric electric field in the pore. Formation of GaAs ...

  14. Electrical performance of conducting polymer (SPAN) grown on GaAs with different substrate orientations

    Science.gov (United States)

    Jameel, D. A.; Aziz, M.; Felix, J. F.; Al Saqri, N.; Taylor, D.; Albalawi, H.; Alghamdi, H.; Al Mashary, F.; Henini, M.

    2016-11-01

    This article reports the effect of n-type GaAs substrate orientation, namely (100), (311)A and (311)B, on the electrical properties of sulfonated polyaniline (SPAN)/GaAs heterojunction devices. In addition, the inhomogeneity of the interface between various GaAs substrates and SPAN is investigated in terms of barrier height and ideality factor by performing I-V measurements at different temperatures (20-420 K). The I-V results indicate that the value of the rectification ratio (IF/IR) at 0.5 V is higher for SPAN/(311)B GaAs samples than for SPAN/(100) GaAs and SPAN/(311)A GaAs samples. Moreover, the barrier height decreases and the ideality factor increases with decreasing temperature for all three heterostructure devices. The high value of mean barrier Φbarb of SPAN/(311)B (calculated from the plots of Φb 0 as a function of 1/2kT) confirms that the GaAs substrate orientation results in an increase of barrier homogeneities. Furthermore, the C-V characteristics were obtained at room temperature. The C-V measurements showed that the carrier distributions at the interface and away from the interface in high index (311) GaAs orientations are more uniform and have better barrier homogeneity than those grown on the conventional (100) GaAs substrates.

  15. Characterization of a Ga-assisted GaAs nanowire array solar cell on si substrate

    DEFF Research Database (Denmark)

    Boulanger, J. P.; Chia, A. C. E.; Wood, B.

    2016-01-01

    A single-junction core-shell GaAs nanowire (NW) solar cell on Si (1 1 1) substrates is presented. A Ga-assisted vapor–liquid–solid growth mechanism was used for the formation of a patterned array of radial p-i-n GaAs NWs encapsulated in AlInP passivation. Novel device fabrication utilizing facet-...

  16. Structure and homoepitaxial growth of GaAs(6 3 1)

    International Nuclear Information System (INIS)

    Mendez-Garcia, V.H.; Ramirez-Arenas, F.J.; Lastras-Martinez, A.; Cruz-Hernandez, E.; Pulzara-Mora, A.; Rojas-Ramirez, J.S.; Lopez-Lopez, M.

    2006-01-01

    We have studied the surface atomic structure of GaAs(6 3 1), and the GaAs growth by molecular beam epitaxy (MBE) on this plane. After the oxide desorption process at 585 deg. Creflection high-energy electron diffraction (RHEED) showed along the [-1 2 0] direction a 2x surface reconstruction for GaAs(6 3 1)A, and a 1x pattern was observed for GaAs(6 3 1)B. By annealing the substrates for 60 min, we observed that on the A surface appeared small hilly-like features, while on GaAs(6 3 1)B surface pits were formed. For GaAs(6 3 1)A, 500 nm-thick GaAs layers were grown at 585 deg. C. The atomic force microscopy (AFM) images at the end of growth showed the self-formation of nanoscale structures with a pyramidal shape enlarged along the [5-9-3] direction. Transversal views of the bulk-truncated GaAs(6 3 1) surface model showed arrays of atomic grooves along this direction, which could influence the formation of the pyramidal structures

  17. Amateurism in an Age of Professionalism: An Empirical Examination of an Irish Sporting Culture: The GAA

    Directory of Open Access Journals (Sweden)

    Ian Keeler

    2013-07-01

    This research study recommends that the GAA adopt an innovative approach, through strategic decision-making, to allow the GAA to maintain its amateur ethos, and, yet, successfully compete in the professional sporting market. The strong links with the community must be both nurtured and enhanced. The GAA and Gaelic games must embrace the challenges that the branding success of foreign sports has brought. Player welfare issues for the elite players must be addressed while continuing to protect the club and its amateur structures. The study looks at the key metrics that are required to evolve the GAA. This entails not only focusing on the perceived importance of the amateur ethos to the GAA, but also developing the marketing, branding and profiling of Gaelic games to enhance the performance of an amateur sporting organization in an era of increased professionalism in sport.

  18. Laser-induced bandgap collapse in GaAs

    Science.gov (United States)

    Siegal, Y.; Glezer, Eli N.; Huang, Li; Mazur, Eric

    1994-05-01

    We present recent time-resolved measurements of the linear dielectric constant of GaAs at 2.2 eV and 4.4 eV following femtosecond laser pulse excitation. In sharp contrast to predictions based on the widely used Drude model, the data show an interband absorption peak coming into resonance first with the 4.4 eV probe photon energy and then with the 2.2 eV probe photon energy, indicating major changes in the band structure. The time scale for these changes ranges from within 100 fs to a few picoseconds, depending on the incident pump pulse fluence.

  19. Investigation of Optically Induced Avalanching in GaAs

    Science.gov (United States)

    1989-06-01

    by Bovino , et al 4 to increase the hold off voltage. The button switch design of Fig. 4c has been used by several researchers5 ’ 7 to obtain the...ul Long flashover palh Figure 3b. 434 Optical Jlatlern a. Mourou Switch b. Bovino Switch c. Button Switch Figure 4. Photoconductive Switches...Technology and Devices Laboratory, ERADCOM (by L. Bovino , et. all) 4 • The deposition recipe for the contacts is 1) 50 ANi (provides contact to GaAs

  20. Study of irradiation defects in GaAs

    International Nuclear Information System (INIS)

    Loualiche, S.

    1982-11-01

    Characterization techniques: C(V) differential capacity, DLTS deep level transient spectroscopy, DDLTS double deep level transient spectroscopy and DLOS deep level optical spectroscopy are studied and theoretical and experimental fundamentals are re-examined. In particular the centres created by ionic or electronic bombardment of p-type GaAs. New quantitative theoretical bases for the C(V) method are obtained. Study of the optical properties of traps due to irradiation using DLOS. The nature of irradiation defects are discussed [fr

  1. Surface passivation of liquid phase epitaxial GaAs

    International Nuclear Information System (INIS)

    Alexiev, D.; Butcher, K.S.A.; Mo, L.; Edmondson, M.

    1995-10-01

    Passivation of the liquid phase epitaxial GaAs surface was attempted using aqueous P 2 S 5 -NH 4 OH, (NH 4 ) 2 S x and plasma nitrogenation and hydrogenation. Results indicate that plasma nitrogenation with pretreatment of plasma hydrogenation produced consistent reduction in reverse leakage current at room temperature for all p and n type Schottky diodes. Some diodes showed an order of magnitude improvement in current density. (NH 4 ) 2 S x passivation also results in improved I-V characteristics, though the long term stability of this passivation is questionable. 26 refs., 6 figs

  2. Impact of GaAs buffer thickness on electronic quality of GaAs grown on graded Ge/GeSi/Si substrates

    International Nuclear Information System (INIS)

    Carlin, J. A.; Ringel, S. A.; Fitzgerald, E. A.; Bulsara, M.; Keyes, B. M.

    2000-01-01

    Minority carrier lifetimes and interface recombination velocities for GaAs grown on a Si wafer using compositionally graded GeSi buffers have been investigated as a function of GaAs buffer thickness using monolayer-scale control of the GaAs/Ge interface nucleation during molecular beam epitaxy. The GaAs layers are free of antiphase domain disorder, with threading dislocation densities measured by etch pit density of 5x10 5 -2x10 6 cm -2 . Analysis indicates no degradation in either minority carrier lifetime or interface recombination velocity down to a GaAs buffer thickness of 0.1 μm. In fact, record high minority carrier lifetimes exceeding 10 ns have been obtained for GaAs on Si with a 0.1 μm GaAs buffer. Secondary ion mass spectroscopy reveals that cross diffusion of Ga, As, and Ge at the GaAs/Ge interface formed on the graded GeSi buffers are below detection limits in the interface region, indicating that polarity control of the GaAs/Ge interface formed on GeSi/Si substrates can be achieved. (c) 2000 American Institute of Physics

  3. Three-dimensional lattice rotation in GaAs nanowire growth on hydrogen-silsesquioxane covered GaAs (001) using molecular beam epitaxy

    Science.gov (United States)

    Tran, Dat Q.; Pham, Huyen T.; Higashimine, Koichi; Oshima, Yoshifumi; Akabori, Masashi

    2018-05-01

    We report on crystallographic behaviors of inclined GaAs nanowires (NWs) self-crystallized on GaAs (001) substrate. The NWs were grown on hydrogen-silsesquioxane (HSQ) covered substrates using molecular beam epitaxy (MBE). Commonly, the epitaxial growth of GaAs B (B-polar) NWs is prominently observed on GaAs (001); however, we yielded a remarkable number of epitaxially grown GaAs A (A-polar) NWs in addition to the majorly obtained B-polar NWs. Such NW orientations are always accompanied by a typical inclined angle of 35° from (001) plane. NWs with another inclined angle of 74° were additionally observed and attributed to be -oriented, not in direct epitaxial relation with the substrate. Such 74° NWs' existence is related to first-order three-dimensional (3D) lattice rotation taking place at the very beginning of the growth. It turns out that spatially 60° lattice rotation around directions at GaAs seeds is essentially in charge of A- and B-polar 74° NWs. Transmission electron microscope observations reveal a high density of twinning in the B-polar NWs and twin-free characteristic in the A-polar NWs.

  4. Heavily doped GaAs:Te layers grown by MOVPE using diisopropyl telluride as a source

    Energy Technology Data Exchange (ETDEWEB)

    Daniltsev, V. M.; Demidov, E. V.; Drozdov, M. N.; Drozdov, Yu. N., E-mail: drozdyu@ipmras.ru; Kraev, S. A.; Surovegina, E. A.; Shashkin, V. I.; Yunin, P. A. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

    2016-11-15

    The capabilities of GaAs epitaxial layers extremely heavily doped with tellurium by metal-organic vapor-phase epitaxy using diisopropyl telluride as a source are studied. It is shown that tellurium incorporation into GaAs occurs to an atomic concentration of 10{sup 21} cm{sup –3} without appreciable diffusion and segregation effects. Good carrier concentrations (2 × 10{sup 19} cm{sup –3}) and specific contact resistances of non-alloyed ohmic contacts (1.7 × 10{sup –6} Ω cm{sup 2}) give grounds to use such layers to create non-alloyed ohmic contacts in electronic devices. A sharp decrease in the electrical activity of Te atoms, a decrease in the electron mobility, and an increase in the contact resistance at atomic concentrations above 2 × 10{sup 20} cm{sup –3} are detected.

  5. Fast X-ray detection systems based on GaAs diodes grown by LPE

    International Nuclear Information System (INIS)

    Rente, C.; Lauter, J.; Apetz, R.; Lueth, H.

    1996-01-01

    We report on the fabrication and characterization of GaAs based X-ray detectors. The detector structures are grown by liquid phase epitaxy (LPE) and show typical background doping in the order of 10 14 cm -3 (n-type) so that active regions up to 43 μm could be realized. Schottky diodes were processed with active areas up to 1mm 2 . Typical dark current densities are as low as 360pA/mm 2 at 100V. The energy resolution of the detector in combination with a charge sensitive preamplifier was determined to be 1.6keV (FWHM) for x-rays with an energy between 6 and 60keV. The time response of the devices coupled to a fast transimpedance amplifier with a bandwidth of 100MHz was investigated. Single photon detection at room temperature was achieved for X-rays having energies of 14 keV and higher. The measured time resolutions were 600ps (FWHM=1.4ns) and 430ps (FWHM=1.0ns) for X-ray photons of 14.4keV and 21.5keV, respectively. The efficiency of the detector having a 43μm thick depleted layer was determined to be 70% at 14.4 keV and 40% at 21.5keV. These detectors open a new field of X-ray spectroscopy especially for high rate applications and timing measurements at synchrotron radiation facilities

  6. Effects of Y incorporation in TaON gate dielectric on electrical performance of GaAs metal-oxide-semiconductor capacitor

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Li Ning; Choi, Hoi Wai; Lai, Pui To [Department of Electrical and Electronic Engineering, The University of Hong Kong (China); Xu, Jing Ping [School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan (China)

    2016-09-15

    In this study, GaAs metal-oxide-semiconductor (MOS) capacitors using Y-incorporated TaON as gate dielectric have been investigated. Experimental results show that the sample with a Y/(Y + Ta) atomic ratio of 27.6% exhibits the best device characteristics: high k value (22.9), low interfacestate density (9.0 x 10{sup 11} cm{sup -2} eV{sup -1}), small flatband voltage (1.05 V), small frequency dispersion and low gate leakage current (1.3 x 10{sup -5}A/cm{sup 2} at V{sub fb} + 1 V). These merits should be attributed to the complementary properties of Y{sub 2}O{sub 3} and Ta{sub 2}O{sub 5}:Y can effectively passivate the large amount of oxygen vacancies in Ta{sub 2}O{sub 5}, while the positively-charged oxygen vacancies in Ta{sub 2}O{sub 5} are capable of neutralizing the effects of the negative oxide charges in Y{sub 2}O{sub 3}. This work demonstrates that an appropriate doping of Y content in TaON gate dielectric can effectively improve the electrical performance for GaAs MOS devices. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  7. Subnanosecond, high voltage photoconductive switching in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Druce, R.L.; Pocha, M.D.; Griffin, K.L. (Lawrence Livermore National Lab., CA (USA)); O' Bannon, B.J. (Rockwell International Corp., Anaheim, CA (USA))

    1990-01-01

    We are conducting research on the switching properties of photoconductive materials to explore their potential for generating high-power microwaves (HPM) and for high rep-rate switching. We have investigated the performance of Gallium Arsenide (GaAs) in linear mode (the conductivity of the device follows the optical pulse) as well as an avalanche-like mode (the optical pulse only controls switch closing). Operating in the linear mode, we have observed switch closing times of less than 200 ps with a 100 ps duration laser pulse and opening times of less than 400 ps at several kV/cm fields using neutron irradiated GaAs. In avalanche and lock-on modes, high fields are switched with lower laser pulse energies, resulting in higher efficiencies; but with measurable switching delay and jitter. We are currently investigating both large area (1 cm{sup 2}) and small area (<1 mm{sup 2}) switches illuminated by AlGaAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 {mu}m.

  8. Subnanosecond, high-voltage photoconductive switching in GaAs

    Science.gov (United States)

    Druce, Robert L.; Pocha, Michael D.; Griffin, Kenneth L.; O'Bannon, Jim

    1991-03-01

    We are conducting research on the switching properties of photoconductive materials to explore their potential for generating highpower microwaves (HPM) and for high reprate switching. We have investigated the performance of Gallium Arsenide (GaAs) in linear mode (the conductivity of the device follows the optical pulse) as well as an avalanchelike mode (the optical pulse only controls switch closing) . Operating in the unear mode we have observed switch closing times of less than 200 Ps with a 100 ps duration laser pulse and opening times of less than 400 ps at several kV/cm fields using neutron irradiated GaAs. In avalanche and lockon modes high fields are switched with lower laser pulse energies resulting in higher efficiencies but with measurable switching delay and jitter. We are currently investigating both large area (1 cm2) and small area 1 mm2) switches illuminated by AlGaAs laser diodes at 900 nm and Nd:YAG lasers at 1. 06 tim.

  9. X-ray imaging bilinear staggered GaAs detectors

    Energy Technology Data Exchange (ETDEWEB)

    Achmadullin, R.A.; Dvoryankin, V.F. E-mail: vfd217@ire216.msk.su; Dvoryankina, G.G.; Dikaev, Y.M.Yu.M.; Krikunov, A.I.; Kudryashov, A.A.; Panova, T.M.; Petrov, A.G.; Telegin, A.A

    2004-09-21

    The multichannel bilinear X-ray detector based on epitaxial GaAs structures is developed to obtain a digital X-ray image. Each detector operates in photovoltaic mode without reverse bias that enables almost complete elimination of detector noise arising due to leakage currents. The sensitivity range of the epitaxial GaAs photovoltaic X-ray detector covers the effective energies from 8 to 120 keV. A maximum response of the detector operating in the short-circuit mode was observed at an energy of 35 keV and amounted to 30 {mu}A min/(Gy cm{sup 2}). The multichannel detector was made of 1024 pixels with pitch of 0.8 mm. The spatial resolution of double staggered sensor row is twice as high as the resolution of that of single sensor row with the same pitch. Measured spatial resolution is 1.2 line-pairs/mm, contrast sensitivity not worse 1% and dynamic range defined as the ratio of maximum detectable X-ray signal to electronic noise level more than 2000 are received.

  10. X-ray imaging bilinear staggered GaAs detectors

    International Nuclear Information System (INIS)

    Achmadullin, R.A.; Dvoryankin, V.F.; Dvoryankina, G.G.; Dikaev, Y.M.Yu.M.; Krikunov, A.I.; Kudryashov, A.A.; Panova, T.M.; Petrov, A.G.; Telegin, A.A.

    2004-01-01

    The multichannel bilinear X-ray detector based on epitaxial GaAs structures is developed to obtain a digital X-ray image. Each detector operates in photovoltaic mode without reverse bias that enables almost complete elimination of detector noise arising due to leakage currents. The sensitivity range of the epitaxial GaAs photovoltaic X-ray detector covers the effective energies from 8 to 120 keV. A maximum response of the detector operating in the short-circuit mode was observed at an energy of 35 keV and amounted to 30 μA min/(Gy cm 2 ). The multichannel detector was made of 1024 pixels with pitch of 0.8 mm. The spatial resolution of double staggered sensor row is twice as high as the resolution of that of single sensor row with the same pitch. Measured spatial resolution is 1.2 line-pairs/mm, contrast sensitivity not worse 1% and dynamic range defined as the ratio of maximum detectable X-ray signal to electronic noise level more than 2000 are received

  11. SXPS study of model GaAs(100)/electrolyte interface

    Energy Technology Data Exchange (ETDEWEB)

    Lebedev, Mikhail V. [A.F. Ioffe Physico-Technical Institute, Russian Academy of Sciences, St. Petersburg (Russian Federation); Mankel, Eric; Mayer, Thomas; Jaegermann, Wolfram [Institute of Material Sciences, Darmstadt University of Technology, Darmstadt (Germany)

    2010-02-15

    Model GaAs(100)/electrolyte interfaces are prepared in vacuum by co-adsorption of Cl{sub 2} and 2-propanol molecules at LN{sub 2} temperature. On adsorption of Cl{sub 2} molecules gallium chlorides, elemental arsenic and arsenic chlorides are formed. Co-adsorption of 2-propanol causes formation of additional GaCl{sub 3} and AsCl, as well as soluble/volatile As-based complexes, which are released from the surface depleting the sur- face by arsenic. Comparison of the As 3d and Ga 3d spectra obtained after heating the model interface to room temperature with the corresponding spectra obtained after emersion of the GaAs(100) surface from HCl/2-propanol solution allows to conclude that in HCl solution Cl{sup -} ions attack gallium sites and H{sup +} ions mostly attack arsenic sites. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Capless Annealing of Ion Implanted GaA.

    Science.gov (United States)

    1980-12-01

    powder is used in PAT.processes. The purity of the graphite powder is thus a critical factor in PAT annealing. Comparison of doping profiles in Se and S...9... . D Rockwell Interntonal ERC41013.3FR SCO0.10178 SEMICONDUCTOR DOPING PROFILE 375 KeV So 3.5 x 101 2/cm 2 1017 \\850C 30 main! A120 3 BACK CAPm

  13. Doped Organic Transistors.

    Science.gov (United States)

    Lüssem, Björn; Keum, Chang-Min; Kasemann, Daniel; Naab, Ben; Bao, Zhenan; Leo, Karl

    2016-11-23

    Organic field-effect transistors hold the promise of enabling low-cost and flexible electronics. Following its success in organic optoelectronics, the organic doping technology is also used increasingly in organic field-effect transistors. Doping not only increases device performance, but it also provides a way to fine-control the transistor behavior, to develop new transistor concepts, and even improve the stability of organic transistors. This Review summarizes the latest progress made in the understanding of the doping technology and its application to organic transistors. It presents the most successful doping models and an overview of the wide variety of materials used as dopants. Further, the influence of doping on charge transport in the most relevant polycrystalline organic semiconductors is reviewed, and a concise overview on the influence of doping on transistor behavior and performance is given. In particular, recent progress in the understanding of contact doping and channel doping is summarized.

  14. Periodic nanostructures fabricated on GaAs surface by UV pulsed laser interference

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Wei; Huo, Dayun; Guo, Xiaoxiang; Rong, Chen; Shi, Zhenwu, E-mail: zwshi@suda.edu.cn; Peng, Changsi, E-mail: changsipeng@suda.edu.cn

    2016-01-01

    Graphical abstract: - Highlights: • Periodic nanostructures were fabricated on GaAs wafers by four-beam laser interference patterning which have potential applications in many fields. • Significant different results were obtained on epi-ready and homo-epitaxial GaAs substrate surfaces. • Two-pulse patterning was carried out on homo-epitaxial GaAs substrate, a noticeable morphology transformation induced by the second pulse was observed. • Temperature distribution on sample surface as a function of time and position was calculated by solving the heat diffusion equations. The calculation agrees well with the experiment results. - Abstract: In this paper, periodic nanostructures were fabricated on GaAs wafers by four-beam UV pulsed laser interference patterning. Significant different results were observed on epi-ready and homo-epitaxial GaAs substrate surfaces, which suggests GaAs oxide layer has an important effect on pulsed laser irradiation process. In the case of two-pulse patterning, a noticeable morphology transformation induced by the second pulse was observed on homo-epitaxial GaAs substrate. Based on photo-thermal mode, temperature distribution on sample surface as a function of time and position was calculated by solving the heat diffusion equations.

  15. Synthesis of GaAs quantum dots on Si-layers on AlGaAs films grown on GaAs(100) substrates

    International Nuclear Information System (INIS)

    Mendez-Garcia, V. H.; Zamora-Peredo, L.; Saucedo-Zeni, N.

    2002-01-01

    In this work we report a novel method for obtaining GaAs quantum dots by molecular beam epitaxy (MBE) on an AlGaAs underlying film. We propose to use a Si monolayer (ML) grown on AlGaAs, in order to induce a 3D nucleation during the GaAs overgrowth. The samples were prepared in a Riber 32P MBE system employing undoped Si-GaAs(100) substrates. First, a 500 nm thick layer of Al x Ga 1-x As was grown with a nominal concentration x=0.35. Several samples were grown in order to analyze the effects of changing the Si interlayer thickness, and the amount of GaAs overgrowth, on the final structures. Previous to the Si-exposure, the AlGaAs presented a (1x3) surface reconstruction which gradually turned to a (3x1) structure when the Si-thickness was 1 ML, as observed in the reflection high-energy electron diffraction (RHEED) patterns. When the GaAs overgrowth started on this surface, transmission RHEED spots appeared and showed a considerable increase in intensity until reaching a maximum. This behavior is typical from a 3D island growth. If the GaAs overgrowth continues, the initial streaky RHEED patterns recovered indicating a 2D-growth. Thus, we prepared a sample stopping the GaAs overgrowth at the time when the diffraction 3D spot reached the maximum intensity, equivalent to 2ML of GaAs. The sample surface was analyzed in air by atomic force microscopy (AFM). Islands of 1.5 nm-height and 20x20 nm of base were clearly observed, these dimensions are suitable for applications in quantum dots. (Authors)

  16. Strain in GaAs / InAs core-shell nanowire heterostructures grown on GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Biermanns, Andreas; Davydok, Anton; Pietsch, Ullrich [Universitaet Siegen, Festkoerperphysik (Germany); Rieger, Torsten; Lepsa, Mihail Ion [Peter Gruenberg Institut 9, Forschungszentrum Juelich (Germany); JARA - Fundamentals of Future Information Technology (Germany)

    2012-07-01

    The growth of semiconductor nanowires (NWs) has attracted significant interest in recent years due to the possible fabrication of novel semiconductor devices for future electronic and opto-electronic applications. Compared to planar heterostructures, the nanowire approach offers an advantage regarding the possibility to form heterostructures between highly lattice mismatched systems, because the free surface of the nanowires allows to relieve the strain more efficiently. One particular way to form heterostructures in the NW geometry, is the fabrication of core-shell devices, in which a NW core is surrounded by a shell of different material. The understanding of the mutual strain between core and shell, as well as the relaxation behavior of the system are crucial for the fabrication of functional devices. In this contribution we report on first X-ray diffraction measurements of GaAs-core/InAs-shell nanowires grown on GaAs(111) by molecular beam epitaxy. Using symmetric- and grazing-incidence X-ray diffraction, the relaxation state of the InAs shell as well as the strain in the GaAs core are measured as function of the InAs shell thickness, showing a gradual relaxation behavior of the shell.

  17. Electric field and space-charge distribution in SI GaAs: effect of high-energy proton irradiation

    CERN Document Server

    Castaldini, A; Polenta, L; Canali, C; Nava, F

    1999-01-01

    The effect of irradiation on semi-insulating gallium arsenide Schottky diodes has been investigated by means of surface potential measurements and spectroscopic techniques. Before and after irradiation the electric field exhibits a Mott barrier-like distribution, and the box-shaped space charge modifies its distribution with irradiation. The increase in density or the generation of some traps changes the compensation ratio producing a deeper active region and a more homogeneous distribution of the electric field. The latter phenomenon is also observed by EBIC images of edge-mounted diodes.

  18. Nonlinear dynamics of non-equilibrium holes in p-type modulation-doped GaInNAs/GaAs quantum wells

    Directory of Open Access Journals (Sweden)

    Amann Andreas

    2011-01-01

    Full Text Available Abstract Nonlinear charge transport parallel to the layers of p-modulation-doped GaInNAs/GaAs quantum wells (QWs is studied both theoretically and experimentally. Experimental results show that at low temperature, T = 13 K, the presence of an applied electric field of about 6 kV/cm leads to the heating of the high mobility holes in the GaInNAs QWs, and their real-space transfer (RST into the low-mobility GaAs barriers. This results in a negative differential mobility and self-generated oscillatory instabilities in the RST regime. We developed an analytical model based upon the coupled nonlinear dynamics of the real-space hole transfer and of the interface potential barrier controlled by space-charge in the doped GaAs layer. Our simulation results predict dc bias-dependent self-generated current oscillations with frequencies in the high microwave range.

  19. Arsenic ambient conditions preventing surface degradation of GaAs during capless annealing at high temperatures

    Science.gov (United States)

    Kang, C. H.; Kondo, K.; Lagowski, J.; Gatos, H. C.

    1987-01-01

    Changes in surface morphology and composition caused by capless annealing of GaAs were studied as a function of annealing temperature, T(GaAs), and the ambient arsenic pressure controlled by the temperature, T(As), of an arsenic source in the annealing ampul. It was established that any degradation of the GaAs surface morphology could be completely prevented, providing that T(As) was more than about 0.315T(GaAs) + 227 C. This empirical relationship is valid up to the melting point temperature of GaAs (1238 C), and it may be useful in some device-processing steps.

  20. Growth Interruption Effect on the Fabrication of GaAs Concentric Multiple Rings by Droplet Epitaxy

    Directory of Open Access Journals (Sweden)

    Fedorov A

    2010-01-01

    Full Text Available Abstract We present the molecular beam epitaxy fabrication and optical properties of complex GaAs nanostructures by droplet epitaxy: concentric triple quantum rings. A significant difference was found between the volumes of the original droplets and the final GaAs structures. By means of atomic force microscopy and photoluminescence spectroscopy, we found that a thin GaAs quantum well-like layer is developed all over the substrate during the growth interruption times, caused by the migration of Ga in a low As background.

  1. Lightweight, Light-Trapped, Thin GaAs Solar Cells for Spacecraft Applications.

    Science.gov (United States)

    1995-10-05

    improve the efficiency of this type of cell. 2 The high efficiency and light weight of the cover glass supported GaAs solar cell can have a significant...is a 3-mil cover glass and 1-mil silicone adhesive on the front surface of the GaAs solar cell. Power Output 3000 400 -{ 2400 { N 300 S18200 W/m2...the ultra-thin, light-trapped GaAs solar ceill 3. Incorporate light trapping. 0 external quantum efficiency at 850 nm increased by 5.2% 4. Develop

  2. Photo-Hall-effect study of excitation and recombination in Fe-doped GaN

    Science.gov (United States)

    Look, David C.; Leach, Jacob H.; Metzger, Robert

    2017-02-01

    The photo-Hall-effect was applied to the study of electron dynamics in semi-insulating Fe-doped GaN. High-powered light-emitting diodes of wavelengths λ = 940, 536, 449, 402, and 365 nm were used to excite steady-state free-electron volume concentrations Δn = 105-108 cm-3, depending on λ and intensity I0. Electron lifetime τ was determined from the energy E dependence of the excited sheet electron concentration Δns through the relationship Δns = I0τA(E), where the absorbance A(E) is a known function of sample thickness d and absorption coefficient α, and the energy dependence of α is taken from a theory of deep-center photoionization. The major sample impurities were Fe, Si, and C, with [Fe] ≫ [Si] and [C]. Fitted lifetimes τ ranged from 15 to 170 ps, depending on [Fe]. It was found that Δns ∝ I0 for [Si] > [C] and ∝ I01/2 for [Si] [C], some of the neutral Fe3+ is converted to Fe2+ with ground state Fe2+(5E) and excited state Fe2+(5T2); a fit of n vs. temperature T over the range of 290-325 K in the dark establishes E5E with respect to the conduction band: ECB - E5E = 0.564 eV - β5ET, where β5E = 3.6 × 10-4 eV/K. At room temperature, 294 K, ECB - E5E = 0.46 eV and ECB - E5T2 = 0.07 eV.

  3. The electronic and optical properties of quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs: a first-principles study.

    Science.gov (United States)

    Ma, Xiaoyang; Li, Dechun; Zhao, Shengzhi; Li, Guiqiu; Yang, Kejian

    2014-01-01

    First-principles calculations based on density functional theory have been performed for the quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs. Using the state-of-the-art computational method with the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, electronic, and optical properties were obtained, including band structures, density of states (DOSs), dielectric function, absorption coefficient, refractive index, energy loss function, and reflectivity. It is found that the lattice constant of GaAs1-x-y N x Bi y alloy with y/x =1.718 can match to GaAs. With the incorporation of N and Bi into GaAs, the band gap of GaAs1-x-y N x Bi y becomes small and remains direct. The calculated optical properties indicate that GaAs1-x-y N x Bi y has higher optical efficiency as it has less energy loss than GaAs. In addition, it is also found that the electronic and optical properties of GaAs1-x-y N x Bi y alloy can be further controlled by tuning the N and Bi compositions in this alloy. These results suggest promising applications of GaAs1-x-y N x Bi y quaternary alloys in optoelectronic devices.

  4. Highly conductive homoepitaxial Si-doped Ga2O3 films on (010) β-Ga2O3 by pulsed laser deposition

    Science.gov (United States)

    Leedy, Kevin D.; Chabak, Kelson D.; Vasilyev, Vladimir; Look, David C.; Boeckl, John J.; Brown, Jeff L.; Tetlak, Stephen E.; Green, Andrew J.; Moser, Neil A.; Crespo, Antonio; Thomson, Darren B.; Fitch, Robert C.; McCandless, Jonathan P.; Jessen, Gregg H.

    2017-07-01

    Si-doped Ga2O3 thin films were fabricated by pulsed laser deposition on semi-insulating (010) β-Ga2O3 and (0001) Al2O3 substrates. Films deposited on β-Ga2O3 showed single crystal, homoepitaxial growth as determined by high resolution transmission electron microscopy and x-ray diffraction. Corresponding films deposited on Al2O3 were mostly single phase, polycrystalline β-Ga2O3 with a preferred (20 1 ¯ ) orientation. An average conductivity of 732 S cm-1 with a mobility of 26.5 cm2 V-1 s-1 and a carrier concentration of 1.74 × 1020 cm-3 was achieved for films deposited at 550 °C on β-Ga2O3 substrates as determined by Hall-Effect measurements. Two orders of magnitude improvement in conductivity were measured using native substrates versus Al2O3. A high activation efficiency was obtained in the as-deposited condition. The high carrier concentration Ga2O3 thin films achieved by pulsed laser deposition enable application as a low resistance ohmic contact layer in β-Ga2O3 devices.

  5. Surface plasmon enhanced SWIR absorption at the ultra n-doped substrate/PbSe nanostructure layer interface

    Science.gov (United States)

    Wittenberg, Vladimir; Rosenblit, Michael; Sarusi, Gabby

    2017-08-01

    This work presents simulation results of the plasmon enhanced absorption that can be achieved in the short wavelength infrared (SWIR - 1200 nm to 1800 nm) spectral range at the interface between ultra-heavily doped substrates and a PbSe nanostructure non-epitaxial growth absorbing layer. The absorption enhancement simulated in this study is due to surface plasmon polariton (SPP) excitation at the interface between these ultra-heavily n-doped GaAs or GaN substrates, which are nearly semimetals to SWIR light, and an absorption layer made of PbSe nano-spheres or nano-columns. The ultra-heavily doped GaAs or GaN substrates are simulated as examples, based on the Drude-Lorentz permittivity model. In the simulation, the substrates and the absorption layer were patterned jointly to forma blazed lattice, and then were back-illuminated using SWIR with a central wavelength of 1500 nm. The maximal field enhancement achieved was 17.4 with a penetration depth of 40 nm. Thus, such architecture of an ultra-heavily doped semiconductor and infrared absorbing layer can further increase the absorption due to the plasmonic enhanced absorption effect in the SWIR spectral band without the need to use a metallic layer as in the case of visible light.

  6. Improvements of MCT MBE Growth on GaAs

    Science.gov (United States)

    Ziegler, J.; Wenisch, J.; Breiter, R.; Eich, D.; Figgemeier, H.; Fries, P.; Lutz, H.; Wollrab, R.

    2014-08-01

    In recent years, continuous progress has been published in the development of HgCdTe (MCT) infrared (IR) focal plane arrays (FPAs) fabricated by molecular beam epitaxy on GaAs substrates. In this publication, further characterization of the state-of-the art 1280 × 1024 pixel, 15- μm pitch detector fabricated from this material in both the mid-wavelength (MWIR) and long-wavelength (LWIR) IR region will be presented. For MWIR FPAs, the percentage of defective pixel remains below 0.5% up to an operating temperature ( T OP) of around 100 K. For the LWIR FPA, an operability of 99.25% was achieved for a T OP of 76 K. Additionally, the beneficial effect of the inclusion of MCT layers with a graded composition region was investigated and demonstrated on current-voltage ( IV) characteristics on test diodes in a MWIR FPA.

  7. Self-healing in fractured GaAs nanowires

    International Nuclear Information System (INIS)

    Wang Jun; Lu Chunsheng; Wang Qi; Xiao Pan; Ke Fujiu; Bai Yilong; Shen Yaogen; Wang Yanbo; Chen Bin; Liao Xiaozhou; Gao Huajian

    2012-01-01

    Molecular dynamics simulations are performed to investigate a spontaneous self-healing process in fractured GaAs nanowires with a zinc blende structure. The results show that such self-healing can indeed occur via rebonding of Ga and As atoms across the fracture surfaces, but it can be strongly influenced by several factors, including wire size, number of healing cycles, temperature, fracture morphology, oriented attachment and atomic diffusion. For example, it is found that the self-healing capacity is reduced by 46% as the lateral dimension of the wire increases from 2.3 to 9.2 nm, and by 64% after 24 repeated cycles of fracture and healing. Other factors influencing the self-healing behavior are also discussed.

  8. The apparent effect of sample surface damage on the dielectric parameters of GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Engelbrecht, J.A.A. [Physics Department, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031 (South Africa)], E-mail: Japie.Engelbrecht@nmmu.ac.za; Hashe, N.G. [Physics Department, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031 (South Africa); Hillie, K.T. [CSIR-NML Laboratory, P.O. Box 395, Pretoria 0001 (South Africa); Claassens, C.H. [Physics Department, University of the Free State, Bloemfontein 9300 (South Africa)

    2007-12-15

    The dielectric and optical parameters determined by infrared reflectance spectroscopy and computer simulation of a set of GaAs substrates of various surface topologies are reported. The influence of surface damage on the parameters is noted.

  9. Development of GaAs Detectors for Physics at the LHC

    CERN Multimedia

    Chu, Zhonghua; Krais, R; Rente, C; Syben, O; Tenbusch, F; Toporowsky, M; Xiao, Wenjiang; Cavallini, A; Fiori, F; Edwards, M; Geppert, R; Goppert, R; Haberla, C; Hornung, M F; Irsigler, R; Rogalla, M; Beaumont, S; Raine, C; Skillicorn, I; Margelevicius, J; Meshkinis, S; Smetana, S; Jones, B; Santana, J; Sloan, T; Zdansky, K; Alexiev, D; Donnelly, I J; Canali, C; Chiossi, C; Nava, F; Pavan, P; Kubasta, J; Tomiak, Z; Tchmil, V; Tchountonov, A; Tsioupa, I; Dogru, M; Gray, R; Hou, Yuqian; Manolopoulos, S; Walsh, S; Aizenshtadt, G; Budnitsky, D L; Gossen, A; Khludkov, S; Koretskaya, O B; Okaevitch, L; Potapov, A; Stepanov, V E; Tolbanov, O; Tyagev, A; Matulionis, A; Pozela, J; Kavaliauskiene, G; Kazukauskas, V; Kiliulis, R; Rinkevicius, V; Slenys, S; Storasta, J V

    2002-01-01

    % RD-8 Development of GaAs Detectors for Physics at the LHC \\\\ \\\\The aims of the collaboration are to investigate the available material options, performance and limitations of simple pad, pixel and microstrip GaAs detectors for minimum ionising particles with radiation hardness and speed which are competitive with silicon detectors. This new technology was originally developed within our university laboratories but now benefits from increasing industrial interest and collaboration in detector fabrication. Initial steps have also been taken towards the fabrication of GaAs preamplifiers to match the detectors in radiation hardness. The programme of work aims to construct a demonstration detector module for an LHC forward tracker based on GaAs.

  10. The apparent effect of sample surface damage on the dielectric parameters of GaAs

    International Nuclear Information System (INIS)

    Engelbrecht, J.A.A.; Hashe, N.G.; Hillie, K.T.; Claassens, C.H.

    2007-01-01

    The dielectric and optical parameters determined by infrared reflectance spectroscopy and computer simulation of a set of GaAs substrates of various surface topologies are reported. The influence of surface damage on the parameters is noted

  11. Two-Photon Pumped Synchronously Mode-Locked Bulk GaAs Laser

    Science.gov (United States)

    Cao, W. L.; Vaucher, A. M.; Ling, J. D.; Lee, C. H.

    1982-04-01

    Pulses 7 picoseconds or less in duration have been generated from a bulk GaAs crystal by a synchronous mode-locking technique. The GaAs crystal was optically pumped by two-photon absorption of the emission from a mode-locked Nd:glass laser. Two-photon absorption as the means of excitation increases the volume of the gain medium by increasing the pene-tration depth of the pump intensity, enabling generation of intra-cavity pulses with peak power in the megawatt range. Tuning of the wavelength of the GaAs emission is achieved by varying the temperature. A tuning range covering 840 nm to 885 nm has been observed over a temperature range from 97°K to 260°K. The intensity of the GaAs emission has also been observed to decrease as the temperature of the crystal is increased.

  12. CMOS compatible route for GaAs based large scale flexible and transparent electronics

    KAUST Repository

    Nour, Maha A.; Ghoneim, Mohamed T.; Droopad, Ravi; Hussain, Muhammad Mustafa

    2014-01-01

    Flexible electronics using gallium arsenide (GaAs) for nano-electronics with high electron mobility and optoelectronics with direct band gap are attractive for many applications. Here we describe a state-of-the-art CMOS compatible batch fabrication process of transforming traditional electronic circuitry into large-area flexible, semitransparent platform. We show a simple release process for peeling off 200 nm of GaAs from 200 nm GaAs/300 nm AlAs stack on GaAs substrate using diluted hydrofluoric acid (HF). This process enables releasing a single top layer compared to peeling off all layers with small sizes at the same time. This is done utilizing a network of release holes which contributes to the better transparency (45 % at 724 nm wavelength) observed.

  13. Initial test of an rf gun with a GaAs cathode installed

    International Nuclear Information System (INIS)

    Aulenbacher, K.; Bossart, R.; Braun, H.

    1996-09-01

    The operation of an rf gun with a GaAs crystal installed as the cathode has been tested in anticipation of eventually producing a polarized electron beam for a future e + /e - collider using an rf photoinjector

  14. High microwave performance ion-implanted GaAs MESFETs on InP substrates

    International Nuclear Information System (INIS)

    Wada, M.; Kato, K.

    1990-01-01

    Ion implantation was employed, for the first time, in fabricating GaAs MESFETs in undoped 2 μm thick GaAs epitaxial layers directly grown on InP substrates by low-pressure MOVPE. The Si-ion-implanted GaAs layer on InP substrates showed excellent electrical characteristics: a mobility of 4300 cm 2 /Vs with a carrier density of 2 x 10 17 cm -3 at room temperature. The MESFET (0.8 μm gate length) exhibited a current-gain cutoff frequency of 25 GHz and a maximum frequency of oscillation of 53 GHz, the highest values yet reported to GaAs MESFETs on InP substrates. These results demonstrate the high potential of ion-implanted MESFETs as electronic devices for high-speed InP-based OEICs. (author)

  15. Accelerated life testing and temperature dependence of device characteristics in GaAs CHFET devices

    Science.gov (United States)

    Gallegos, M.; Leon, R.; Vu, D. T.; Okuno, J.; Johnson, A. S.

    2002-01-01

    Accelerated life testing of GaAs complementary heterojunction field effect transistors (CHFET) was carried out. Temperature dependence of single and synchronous rectifier CHFET device characteristics were also obtained.

  16. CMOS compatible route for GaAs based large scale flexible and transparent electronics

    KAUST Repository

    Nour, Maha A.

    2014-08-01

    Flexible electronics using gallium arsenide (GaAs) for nano-electronics with high electron mobility and optoelectronics with direct band gap are attractive for many applications. Here we describe a state-of-the-art CMOS compatible batch fabrication process of transforming traditional electronic circuitry into large-area flexible, semitransparent platform. We show a simple release process for peeling off 200 nm of GaAs from 200 nm GaAs/300 nm AlAs stack on GaAs substrate using diluted hydrofluoric acid (HF). This process enables releasing a single top layer compared to peeling off all layers with small sizes at the same time. This is done utilizing a network of release holes which contributes to the better transparency (45 % at 724 nm wavelength) observed.

  17. High Purity GaAs Far IR Photoconductor With Enhanced Quantum Efficieny, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — This proposal introduces an innovative concept aimed to significantly enhance the quantum efficiency of a far-infrared GaAs photoconductor and achieve sensitivity...

  18. RF-MMW Dipole Antenna Arrays From Laser Illuminated GaAs

    National Research Council Canada - National Science Library

    Umphenour, D

    1998-01-01

    High resistivity photoconductive Gallium Arsenide (GaAs) can be used as elemental Hertzian dipole antenna arrays in which the time varying dipole current is produced by temporally modulating a laser (0.63um...

  19. Growth and characterization of molecular beam epitaxial GaAs layers on porous silicon

    Science.gov (United States)

    Lin, T. L.; Liu, J. K.; Sadwick, L.; Wang, K. L.; Kao, Y. C.

    1987-01-01

    GaAs layers have been grown on porous silicon (PS) substrates with good crystallinity by molecular beam epitaxy. In spite of the surface irregularity of PS substrates, no surface morphology deterioration was observed on epitaxial GaAs overlayers. A 10-percent Rutherford backscattering spectroscopy minimum channeling yield for GaAs-on-PS layers as compared to 16 percent for GaAs-on-Si layers grown under the same condition indicates a possible improvement of crystallinity when GaAs is grown on PS. Transmission electron microscopy reveals that the dominant defects in the GaAs-on-PS layers are microtwins and stacking faults, which originate from the GaAs/PS interface. GaAs is found to penetrate into the PS layers. n-type GaAs/p-type PS heterojunction diodes were fabricated with good rectifying characteristics.

  20. Deep levels in p-type InGaAsN lattice matched to GaAs

    International Nuclear Information System (INIS)

    Kwon, D.; Kaplar, R.J.; Ringel, S.A.; Allerman, A.A.; Kurtz, S.R.; Jones, E.D.

    1999-01-01

    Deep-level transient spectroscopy measurements were utilized to investigate deep-level defects in metal - organic chemical vapor deposition-grown, unintentionally doped p-type InGaAsN films lattice matched to GaAs. The as-grown material displayed a high concentration of deep levels distributed within the band gap, with a dominant hole trap at E v +0.10eV. Postgrowth annealing simplified the deep-level spectra, enabling the identification of three distinct hole traps at 0.10, 0.23, and 0.48 eV above the valence-band edge, with concentrations of 3.5x10 14 , 3.8x10 14 , and 8.2x10 14 cm -3 , respectively. A direct comparison between the as-grown and annealed spectra revealed the presence of an additional midgap hole trap, with a concentration of 4x10 14 cm -3 in the as-grown material. The concentration of this trap is sharply reduced by annealing, which correlates with improved material quality and minority-carrier properties after annealing. Of the four hole traps detected, only the 0.48 eV level is not influenced by annealing, suggesting this level may be important for processed InGaAsN devices in the future. copyright 1999 American Institute of Physics

  1. The Design and Optimization of GaAs Single Solar Cells Using the Genetic Algorithm and Silvaco ATLAS

    Directory of Open Access Journals (Sweden)

    Kamal Attari

    2017-01-01

    Full Text Available Single-junction solar cells are the most available in the market and the most simple in terms of the realization and fabrication comparing to the other solar devices. However, these single-junction solar cells need more development and optimization for higher conversion efficiency. In addition to the doping densities and compromises between different layers and their best thickness value, the choice of the materials is also an important factor on improving the efficiency. In this paper, an efficient single-junction solar cell model of GaAs is presented and optimized. In the first step, an initial model was simulated and then the results were processed by an algorithm code. In this work, the proposed optimization method is a genetic search algorithm implemented in Matlab receiving ATLAS data to generate an optimum output power solar cell. Other performance parameters such as photogeneration rates, external quantum efficiency (EQE, and internal quantum efficiency (EQI are also obtained. The simulation shows that the proposed method provides significant conversion efficiency improvement of 29.7% under AM1.5G illumination. The other results were Jsc = 34.79 mA/cm2, Voc = 1 V, and fill factor (FF = 85%.

  2. The investigation of alloy formation during InAs nanowires growth on GaAs (111)B substrate

    Energy Technology Data Exchange (ETDEWEB)

    Saqib, Muhammad; Biermanns, Andreas; Davydok, Anton; Pietsch, Ullrich [Festkoerperphysik, Universitaet Siegen, Walter-Flex-Str. 3, Siegen 57072 (Germany); Rieger, Torsten; Grap, Thomas; Lepsa, Mihail [Peter Gruenberg Institute (PGI-9), Forschungzentrum Juelich, Juelich 52425 (Germany)

    2013-07-01

    A possible way to obtain nanowires is the growth in molecular beam epitaxy (MBE) on the (111) oriented surface of the desired substrate, covered by a thin oxide layer. A crucial parameter in this method is the initial thickness of the oxide layer, often determined by an etching procedure. In this contribution, we report on the structural investigation of two different series (etched and unetched) of NWs samples. Vertically aligned InAs nanowires (NWs) doped with Si were self-assisted grown by molecular beam epitaxy on GaAs [111]B substrates covered with a thin SiO{sub x} layer. Using a combination of symmetric and asymmetric X-ray diffraction we study the influence of Si supply on the growth process and nanostructure formation. We find that the number of parasitic crystallites grown between the NWs increases with increasing Si flux. In addition, we observe the formation of a Ga{sub 0.2}In{sub 0.8}As alloy if the growth is performed on samples covered by a defective (etched) oxide layer. This alloy formation is observed within the crystallites and not within the nanowires. The Gallium concentration is determined from the lattice mismatch of the crystallites relative to the InAs nanowires. No alloy formation is found for samples with faultless oxide layers.

  3. Subband structure comparison between n- and p- type double delta-doped Ga As quantum wells

    International Nuclear Information System (INIS)

    Rodriguez V, I.; Gaggero S, L.M.

    2004-01-01

    We compute the electron level structure (n-type) and the hole subband structure (p-type) of double -doped GaAs (DDD) quantum wells, considering exchange effects. The Thomas-Fermi (TF), and Thomas-Fermi-Dirac (TFD) approximations have been applied in order to describe the bending of the conduction and valence band, respectively. The electron and the hole subband structure study indicates that exchange effects are more important in p-type DDD quantum wells than in n-type DDD Also our results agree with the experimental data available. (Author) 33 refs., 2 tabs., 5 figs

  4. Dynamical properties of tertiarybutylarsine on GaAs(0 0 1) surface

    CERN Document Server

    Ozeki, M; Tanaka, Y

    2002-01-01

    The dynamical properties of tertiarybutylarsine (TBA) was studied on GaAs(0 0 1) surface using a supersonic molecular beam. The temperature and incident energy dependence of the reflected beam revealed a reaction channel of TBA on GaAs surface with a large decrease in the activation energy from 2.7 to 1.8 eV as the incident energy increases from 0.04 to 2.5 eV.

  5. Basic mechanisms study for MIS solar cell structures on GaAs

    Science.gov (United States)

    Fonash, S. J.

    1978-01-01

    The solar cell structure examined is the MIS configuration on (n) GaAs. The metal room temperature oxide/(n) GaAs materials system was studied. Metals with electronegativities varying from 2.4 (Au) to 1.5 (Al) were used as the upper electrode. The thinnest metallization that did not interfere with the measurement techniques (by introducing essentially transmission line series resistance problems across a device) was used. Photovoltaic response was not optimized.

  6. GaAs thin film solar cells. Final report; Duennschicht-Solarzellen aus Galliumarsenid; Abschlussbericht

    Energy Technology Data Exchange (ETDEWEB)

    Bett, A.; Bronner, W.; Cardona, S.; Ehrhardt, A.; Habermann, G.; Habich, A.; Lanyi, P.; Lutz, F.; Nguyen, T.; Schetter, C.; Sulima, O.; Welter, H.; Yavas, O.

    1992-11-01

    This R and D project focused on the development of materials and technologies for the production of GaAs solar cells on GaAs and other substrates. Three subjects were gone into on particular: Material preparation (epitaxy), solar cell technology, characterisation of materials and processes. (orig.) [Deutsch] Das vorliegende Forschungsvorhaben hatte die Material- und Technologieentwickung fuer die Herstellung von GaAs-Solarzellen auf Eigen- und Fremdsubstrat zum Gegenstand. Drei Hauptaufgabenbereiche waren: Materialpraeparation (Epitaxie), Solarzellentechnologie, sowie Material- und Prozesscharakterisierung. (orig.)

  7. Structural and optical properties of vapor-etched porous GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Smida, A.; Laatar, F. [Photovoltaic Laboratory, Centre for Research and Technology Energy, Tourist Route Soliman, BP 95, 2050 Hammam-Lif (Tunisia); Hassen, M., E-mail: mhdhassen@yahoo.fr [Photovoltaic Laboratory, Centre for Research and Technology Energy, Tourist Route Soliman, BP 95, 2050 Hammam-Lif (Tunisia); Higher Institute of Applied Science and Technology of Sousse, City Taffala (Ibn Khaldun), 4003 Sousse (Tunisia); Ezzaouia, H. [Photovoltaic Laboratory, Centre for Research and Technology Energy, Tourist Route Soliman, BP 95, 2050 Hammam-Lif (Tunisia)

    2016-08-15

    This paper consists to present first results concerning the structure of porous GaAs layer (por-GaAs-L) prepared by using HF/HNO{sub 3} as acidic solution in vapor etching (VE) method. In order to clarify this method, we detail here its principle and explain how por-GaAs-Ls are formed, taking into account the influencing of the exposure time of the GaAs substrate to the acid vapor. The etched GaAs layers have been investigated by UV–visible and PL analysis. One porous layer was performed to be characterised by Atomic Force Microscopy (AFM), FTIR spectroscopy, and X-Ray Diffraction (XRD). The porous structure was constituted by a nanocrystals with an average size about 6 nm. These nanocrystals were calculated from XRD peak using Scherrer's formula, AFM imaging, and also by using effective mass approximation model from effective band gap. - Highlights: • Porous GaAs layer was prepared by using Vapor etching (VE) method. • Effect of VE duration on the microstructural optical properties of the GaAs substrate • Porous structure of GaAs layer was demonstrated by using SEM and AFM microscopy.

  8. Structural and optical properties of vapor-etched porous GaAs

    International Nuclear Information System (INIS)

    Smida, A.; Laatar, F.; Hassen, M.; Ezzaouia, H.

    2016-01-01

    This paper consists to present first results concerning the structure of porous GaAs layer (por-GaAs-L) prepared by using HF/HNO 3 as acidic solution in vapor etching (VE) method. In order to clarify this method, we detail here its principle and explain how por-GaAs-Ls are formed, taking into account the influencing of the exposure time of the GaAs substrate to the acid vapor. The etched GaAs layers have been investigated by UV–visible and PL analysis. One porous layer was performed to be characterised by Atomic Force Microscopy (AFM), FTIR spectroscopy, and X-Ray Diffraction (XRD). The porous structure was constituted by a nanocrystals with an average size about 6 nm. These nanocrystals were calculated from XRD peak using Scherrer's formula, AFM imaging, and also by using effective mass approximation model from effective band gap. - Highlights: • Porous GaAs layer was prepared by using Vapor etching (VE) method. • Effect of VE duration on the microstructural optical properties of the GaAs substrate • Porous structure of GaAs layer was demonstrated by using SEM and AFM microscopy.

  9. Singularities of current-voltage characteristics of GaAs films fabricated by pulsed ions ablation

    International Nuclear Information System (INIS)

    Kabyshev, A.V.; Konusov, F.V.; Lozhnikov, S.N.; Remnev, G.E.; Saltymakov, M.S.

    2009-01-01

    A singularities and advantages of the optical, photoelectric and electrical properties of GaAs in comparison with other available materials for electronics, for example, silicon allow to manufacture on it base the devices having an advanced characteristics. The GaAs for electronics, obtained from the dense ablation plasma, possess some preferences as compared to material manufactured by traditional methods of vacuum deposition. The electrical characteristics of GaAs produced by chemical deposition were extensively studied. Purpose of this work is investigation the current-voltage characteristics of thin films of GaAs, deposited on polycrystalline corundum (polycor) from plasma forming the power ions bunch and determination of the thermal vacuum annealing effect on photoelectric and electrical properties of films. Peculiarities of optical, photoelectric and current-voltage characteristics of films obtained by ions ablation are determined by deposition conditions and resistance of initial target GaAs. The transitions between the states with low- and high conduction were revealed directly after deposition in films having the optical properties similar to amorphous materials and/or after annealing in films with properties similar to initial target GaAs. Behavior of current-voltage characteristics at vacuum annealing correlates with Schottky barrier height and photosensitivity and is accompanies of the transport mechanism change. The stable properties of films are formed at its dark conduction 10 -10 -10 -8 s and after annealing at T an =600-700 K. (authors)

  10. Structural Evolution During Formation and Filling of Self-patterned Nanoholes on GaAs (100 Surfaces

    Directory of Open Access Journals (Sweden)

    Zhou Lin

    2008-01-01

    Full Text Available Abstract Nanohole formation on an AlAs/GaAs superlattice gives insight to both the “drilling” effect of Ga droplets on AlAs as compared to GaAs and the hole-filling process. The shape and depth of the nanoholes formed on GaAs (100 substrates has been studied by the cross-section transmission electron microscopy. The Ga droplets “drill” through the AlAs layer at a much slower rate than through GaAs due to differences in activation energy. Refill of the nanohole results in elongated GaAs mounds along the [01−1] direction. As a result of capillarity-induced diffusion, GaAs favors growth inside the nanoholes, which provides the possibility to fabricate GaAs and AlAs nanostructures.

  11. Electronic structure of p type Delta doped systems

    International Nuclear Information System (INIS)

    Gaggero S, L.M.; Perez A, R.

    1998-01-01

    We summarize of the results obtained for the electronic structure of quantum wells that consist in an atomic layer doped with impurities of p type. The calculations are made within the frame worth of the wrapper function approach to independent bands and with potentials of Hartree. We study the cases reported experimentally (Be in GaAs and B in Si). We present the levels of energy, the wave functions and the rate of the electronic population between the different subbands, as well as the dependence of these magnitudes with the density of impurities in the layer. The participation of the bans of heavy holes is analysed, light and split-off band in the total electronic population. The effect of the temperature is discussed and we give a possible qualitative explanation of the experimental optical properties. (Author)

  12. Doping control in sport

    DEFF Research Database (Denmark)

    Overbye, Marie Birch

    2016-01-01

    Doping testing is a key component enforced by anti-doping authorities to detect and deter doping in sport. Policy is developed to protect athletes' right to participate in doping-free sport; and testing is a key tool to secure this right. Accordingly, athletes' responses to anti-doping efforts...... are important. This article explores how the International Standards for Testing, which face different interpretations and challenges when policy is implemented, are perceived by elite athletes. Particularly, this article aims to investigate how elite athletes perceive the functioning of the testing system (i.......e., the efforts of stakeholders involved in testing) in their own sport both nationally and worldwide. Moreover, it seeks to identify whether specific factors such as previous experience of testing and perceived proximity of doping have an impact on athletes' perceptions of the testing system. The study comprises...

  13. The Anti-Doping Movement.

    Science.gov (United States)

    Willick, Stuart E; Miller, Geoffrey D; Eichner, Daniel

    2016-03-01

    Historical reports of doping in sports date as far back as the ancient Greek Olympic Games. The anti-doping community considers doping in sports to be cheating and a violation of the spirit of sport. During the past century, there has been an increasing awareness of the extent of doping in sports and the health risks of doping. In response, the anti-doping movement has endeavored to educate athletes and others about the health risks of doping and promote a level playing field. Doping control is now undertaken in most countries around the world and at most elite sports competitions. As athletes have found new ways to dope, however, the anti-doping community has endeavored to strengthen its educational and deterrence efforts. It is incumbent upon sports medicine professionals to understand the health risks of doping and all doping control processes. Copyright © 2016 American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved.

  14. ITER TASK T252 (1995):Gamma radiation testing of a GaAs operational amplifier for instrument applications

    International Nuclear Information System (INIS)

    Hiemstra, D.

    1996-03-01

    The purpose of this 1995 ITER task was : to build an improved operational amplifier using GaAs MESFET technology, to build a reference voltage subcircuit using GaAs MESFET technology and to investigate the potential of GaAs HBT's to improve the noise performance of the GaAs MESFET operational amplifier. This work addresses the need for instrumentation-grade components to read sensors in an experimental fusion reactor, where the anticipated total dose for a useful service life is 3Grad(GaAs). It is an extension of our 1994 work. 3 tabs., 6 figs

  15. Temperature effects in contacts between a metal and a semiconductor nanowire near the degenerate doping

    Science.gov (United States)

    Sun, Zhuting; Burgess, Tim; Tan, H. H.; Jagadish, Chennupati; Kogan, Andrei

    2018-04-01

    We have investigated the nonlinear conductance in diffusion-doped Si:GaAs nanowires contacted by patterned metal films in a wide range of temperatures T. The wire resistance R W and the zero bias resistance R C, dominated by the contacts, exhibit very different responses to temperature changes. While R W shows almost no dependence on T, R C varies by several orders of magnitude as the devices are cooled from room temperature to T = 5 K. We develop a model that employs a sharp donor level very low in the GaAs conduction band and show that our observations are consistent with the model predictions. We then demonstrate that such measurements can be used to estimate carrier properties in nanostructured semiconductors and obtain an estimate for N D, the doping density in our samples. We also discuss the effects of surface states and dielectric confinement on carrier density in semiconductor nanowires.

  16. Impurity-related nonlinear optical properties in delta-doped quantum rings: Electric field effects

    Energy Technology Data Exchange (ETDEWEB)

    Restrepo, R.L., E-mail: rrestre@gmail.com [Escuela de Ingeniería de Antioquia-EIA, Medellín (Colombia); Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia); Morales, A.L. [Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia); Martínez-Orozco, J.C. [Unidad Académica de Física, Universidad Autónoma de Zacatecas, CP 98060, Zacatecas (Mexico); Baghramyan, H.M.; Barseghyan, M.G. [Department of Solid State Physics, Yerevan State University, Al. Manookian 1, 0025 Yerevan (Armenia); Mora-Ramos, M.E. [Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia); Facultad de Ciencias, Universidad Autónoma del Estado de Morelos, Ave. Universidad 1001, CP 62209, Cuernavaca, Morelos (Mexico); Duque, C.A. [Grupo de Materia Condensada-UdeA, Instituto de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín (Colombia)

    2014-11-15

    Using a variational procedure within the effective mass approximation, we have calculated the donor impurity binding energy for the ground (1s-like) and the excited (2p{sub z}-like) states as well as the impurity-related nonlinear optical absorption and relative changes in the refraction index in a GaAs single quantum ring with axial n-type delta-doping. The delta-like potential along the z-direction is an approximate model analytically described using a Lorentzian function with two parameters. Additionally we consider the application of an electric field along the z-direction. It is found that the changes in the geometry of the quantum ring, the change in the 2D impurity density of the delta-like doping, and different values of the electric field lead to a shifting of the resonant peaks of the optical responses spectrum.

  17. Effect of impurity correlation on the density of states in slightly compensated heavily doped semiconductors

    International Nuclear Information System (INIS)

    Doan Nhat Quang; Nguyen Nhu Dat; Dinh Van An

    1993-07-01

    A theory is developed of the electron density of states (DOS) in slightly compensated heavily doped semiconductors which undergo a thermal treatment. The calculation is carried out within the semiclassical approach to the random impurity field, taking adequately into account high-temperature correlation among the impurities and low temperature screening due to the free carriers as well. Then, a simple analytic expression for the DOS is obtained which exhibits the same energy dependence as in the case of a random impurity distribution, but now with some correlation-induced changes in the coefficients. A numerical estimation on non-compensated n-type sample of GaAs at a doping level of 5 x 10 18 cm -3 shows that in the tail region the correlated DOS turns out to be somewhat larger and cut less sharply than the random one. (author). 45 refs, 2 figs, 1 tab

  18. Impurity-related nonlinear optical properties in delta-doped quantum rings: Electric field effects

    International Nuclear Information System (INIS)

    Restrepo, R.L.; Morales, A.L.; Martínez-Orozco, J.C.; Baghramyan, H.M.; Barseghyan, M.G.; Mora-Ramos, M.E.; Duque, C.A.

    2014-01-01

    Using a variational procedure within the effective mass approximation, we have calculated the donor impurity binding energy for the ground (1s-like) and the excited (2p z -like) states as well as the impurity-related nonlinear optical absorption and relative changes in the refraction index in a GaAs single quantum ring with axial n-type delta-doping. The delta-like potential along the z-direction is an approximate model analytically described using a Lorentzian function with two parameters. Additionally we consider the application of an electric field along the z-direction. It is found that the changes in the geometry of the quantum ring, the change in the 2D impurity density of the delta-like doping, and different values of the electric field lead to a shifting of the resonant peaks of the optical responses spectrum

  19. To dope or not to dope

    DEFF Research Database (Denmark)

    Overbye, Marie Birch; Knudsen, Mette Lykke; Pfister, Gertrud Ursula

    2013-01-01

    tAim: This study aims to examine the circumstances which athletes say affect their (hypothetical) consid-erations of whether to dope or not and explore the differences between athletes of different gender, ageand sport type.Methods: 645 elite athletes (mean age: 22.12; response rate: 43%) represe......tAim: This study aims to examine the circumstances which athletes say affect their (hypothetical) consid-erations of whether to dope or not and explore the differences between athletes of different gender, ageand sport type.Methods: 645 elite athletes (mean age: 22.12; response rate: 43......%) representing 40 sports completed aweb-based questionnaire. Participants were asked to imagine themselves in a situation in which theyhad to decide whether to dope or not to dope and then evaluate how different circumstances would affecttheir decisions.Results: Multiple circumstances had an effect on athletes......’ hypothetical decisions. The most effective deter-rents were related to legal and social sanctions, side-effects and moral considerations. Female athletesand younger athletes evaluated more reasons as deterrents than older, male athletes. When confrontedwith incentives to dope, the type of sport was often...

  20. High temperature GaAs X-ray detectors

    Science.gov (United States)

    Lioliou, G.; Whitaker, M. D. C.; Barnett, A. M.

    2017-12-01

    Two GaAs p+-i-n+ mesa X-ray photodiodes were characterized for their electrical and photon counting X-ray spectroscopic performance over the temperature range of 100 °C to -20 °C. The devices had 10 μm thick i layers with different diameters: 200 μm (D1) and 400 μm (D2). The electrical characterization included dark current and capacitance measurements at internal electric field strengths of up to 50 kV/cm. The determined properties of the two devices were compared with previously reported results that were made with a view to informing the future development of photon counting X-ray spectrometers for harsh environments, e.g., X-ray fluorescence spectroscopy of planetary surfaces in high temperature environments. The best energy resolution obtained (Full Width at Half Maximum at 5.9 keV) decreased from 2.00 keV at 100 °C to 0.66 keV at -20 °C for the spectrometer with D1, and from 2.71 keV at 100 °C to 0.71 keV at -20 °C for the spectrometer with D2. Dielectric noise was found to be the dominant source of noise in the spectra, apart from at high temperatures and long shaping times, where the main source of photopeak broadening was found to be the white parallel noise.

  1. GaAs integrated circuits and heterojunction devices

    Science.gov (United States)

    Fowlis, Colin

    1986-06-01

    The state of the art of GaAs technology in the U.S. as it applies to digital and analog integrated circuits is examined. In a market projection, it is noted that whereas analog ICs now largely dominate the market, in 1994 they will amount to only 39 percent vs. 57 percent for digital ICs. The military segment of the market will remain the largest (42 percent in 1994 vs. 70 percent today). ICs using depletion-mode-only FETs can be constructed in various forms, the closest to production being BFL or buffered FET logic. Schottky diode FET logic - a lower power approach - can reach higher complexities and strong efforts are being made in this direction. Enhancement type devices appear essential to reach LSI and VLSI complexity, but process control is still very difficult; strong efforts are under way, both in the U.S. and in Japan. Heterojunction devices appear very promising, although structures are fairly complex, and special fabrication techniques, such as molecular beam epitaxy and MOCVD, are necessary. High-electron-mobility-transistor (HEMT) devices show significant performance advantages over MESFETs at low temperatures. Initial results of heterojunction bipolar transistor devices show promise for high speed A/D converter applications.

  2. Mechanical response of wall-patterned GaAs surface

    International Nuclear Information System (INIS)

    Le Bourhis, E.; Patriarche, G.

    2005-01-01

    Wall-patterned GaAs surfaces have been elaborated by photolithography and dry etching. Different surfaces were produced in order to change the aspect ratio of the walls formed at the substrate surface. The mechanical behaviour of individual walls was investigated by nanoindentation and the responses were compared to that of a standard bulk reference (flat surface). Deviation from the bulk response is detected in a load range of 1-25 mN depending on the aspect ratio of the walls. A central plastic zone criterion is proposed in view of transmission electron microscopy images of indented walls and allows the prediction of the response deviation of a given wall if its width is known. The mechanical response of the different types of walls is further investigated in terms of stiffness, total penetration of indenter and apparent hardness, and is scanned in relation to the proximity of a wall side. Overall results show that contact stiffness remains almost unaffected by aspect ratio, while penetration drastically increases because of the free sides of the wall as compared to a flat surface (bulk substrate). The application of substrate patterning for optoelectronic devices is discussed in the perspective of eliminating residual dislocations appearing in mismatched structures

  3. Point defects in GaAs and other semiconductors

    International Nuclear Information System (INIS)

    Ehrhart, P.; Karsten, K.; Pillukat, A.

    1993-01-01

    In order to understand the properties of intrinsic point defects and their interactions at high defect concentrations GaAs wafers were irradiated at 4.5 K with 3 MeV electrons up to a dose of 4 · 10 19 e - /cm 2 . The irradiated samples were investigated by X-ray Diffraction and optical absorption spectroscopy. The defect production increases linearly with irradiation dose and characteristic differences are observed for the two sublattices. The Ga-Frenkel pairs are strongly correlated and are characterized by much larger lattice relaxations (V rel = 2--3 atomic volumes) as compared to the As-Frenkel pairs (V rel ∼1 at. vol.). The dominating annealing stage around 300 K is attributed to the mobility of the Ga interstitial atoms whereas the As-interstitial atoms can recombine with their vacancies only around 500 K. These results are compared to those for InP, ZnSe and Ge. Implications for the understanding of the damage after ion irradiation and implantation are discussed

  4. Doped graphene supercapacitors

    Science.gov (United States)

    Ashok Kumar, Nanjundan; Baek, Jong-Beom

    2015-12-01

    Heteroatom-doped graphitic frameworks have received great attention in energy research, since doping endows graphitic structures with a wide spectrum of properties, especially critical for electrochemical supercapacitors, which tend to complement or compete with the current lithium-ion battery technology/devices. This article reviews the latest developments in the chemical modification/doping strategies of graphene and highlights the versatility of such heteroatom-doped graphitic structures. Their role as supercapacitor electrodes is discussed in detail. This review is specifically focused on the concept of material synthesis, techniques for electrode fabrication and metrics of performance, predominantly covering the last four years. Challenges and insights into the future research and perspectives on the development of novel electrode architectures for electrochemical supercapacitors based on doped graphene are also discussed.

  5. Doped graphene supercapacitors

    International Nuclear Information System (INIS)

    Kumar, Nanjundan Ashok; Baek, Jong-Beom

    2015-01-01

    Heteroatom-doped graphitic frameworks have received great attention in energy research, since doping endows graphitic structures with a wide spectrum of properties, especially critical for electrochemical supercapacitors, which tend to complement or compete with the current lithium-ion battery technology/devices. This article reviews the latest developments in the chemical modification/doping strategies of graphene and highlights the versatility of such heteroatom-doped graphitic structures. Their role as supercapacitor electrodes is discussed in detail. This review is specifically focused on the concept of material synthesis, techniques for electrode fabrication and metrics of performance, predominantly covering the last four years. Challenges and insights into the future research and perspectives on the development of novel electrode architectures for electrochemical supercapacitors based on doped graphene are also discussed. (topical review)

  6. Ab initio structural and vibrational properties of GaAs diamondoids and nanocrystals

    Directory of Open Access Journals (Sweden)

    Mudar Ahmed Abdulsattar

    2014-12-01

    Full Text Available Gallium arsenide diamondoids structural and vibrational properties are investigated using density functional theory at the PBE/6-31(d level and basis including polarization functions. Variation of energy gap as these diamondoids increase in size is seen to follow confinement theory for diamondoids having nearly equiaxed dimensions. Density of energy states transforms from nearly single levels to band structure as we reach larger diamondoids. Bonds of surface hydrogen with As atoms are relatively localized and shorter than that bonded to Ga atoms. Ga-As bonds have a distribution range of values due to surface reconstruction and effect of bonding to hydrogen atoms. Experimental bulk Ga-As bond length (2.45 Å is within this distribution range. Tetrahedral and dihedral angles approach values of bulk as we go to higher diamondoids. Optical-phonon energy of larger diamondoids stabilizes at 0.037 eV (297 cm-1 compared to experimental 0.035 eV (285.2 cm-1. Ga-As force constant reaches 1.7 mDyne/Å which is comparable to Ga-Ge force constant (1.74 mDyne/Å. Hydrogen related vibrations are nearly constant and serve as a fingerprint of GaAs diamondoids while Ga-As vibrations vary with size of diamondoids.

  7. Modeling of altered layer formation during reactive ion etching of GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Mutzke, A. [Max-Planck-Institute of Plasmaphysics, EURATOM Association, D-17491 Greifswald (Germany); Rai, A., E-mail: Abha.Rai@ipp.mpg.de [Max-Planck-Institute of Plasmaphysics, EURATOM Association, D-17491 Greifswald (Germany); Schneider, R.; Angelin, E.J.; Hippler, R. [Institute of Physics, Ernst-Moritz-Arndt-University Greifswald, Felix-Hausdorff-Str.6, D-17489 Greifswald (Germany)

    2012-12-15

    Highlights: Black-Right-Pointing-Pointer Experimental result showing the preferential sputtering of GaAs (150 keV Ar{sup +} and thermal O on GaAs) during reactive ion beam etching (RIBE) has been reported. Black-Right-Pointing-Pointer A model based on binary collisions (SDTrimSP) is presented to simulate RIBE. Black-Right-Pointing-Pointer The model is used to explain the reported experimental data and also the results by Grigonis and co-workers [1]. - Abstract: The binary collision based SDTrimSP model has been used to simulate the reactive ion beam etching (RIBE) of GaAs in the presence of energetic Ar ions and thermal O atoms. It includes the collisional effects, diffusive processes and chemical reactions taking place in the system. The model parameters are fitted using the experimental observations of Grigonis and co-workers [1] and validated with the experimental results obtained during the GaAs ion etching presented in this paper. A detailed analysis is presented to understand the effect of the diffusive processes and the role of O during RIBE of GaAs. It is shown how the presence of damage caused by the energetic Ar coupled with the presence of thermal O opens up chemical reaction channels which eventually leads to the preferential sputtering of Ga observed at the ion etching facility at University of Greifswald.

  8. Multilayer self-organization of InGaAs quantum wires on GaAs surfaces

    International Nuclear Information System (INIS)

    Wang, Zhiming M.; Kunets, Vasyl P.; Xie, Yanze Z.; Schmidbauer, Martin; Dorogan, Vitaliy G.; Mazur, Yuriy I.; Salamo, Gregory J.

    2010-01-01

    Molecular-Beam Epitaxy growth of multiple In 0.4 Ga 0.6 As layers on GaAs (311)A and GaAs (331)A has been investigated by Atomic Force Microscopy and Photoluminescence. On GaAs (311)A, uniformly distributed In 0.4 Ga 0.6 As quantum wires (QWRs) with wider lateral separation were achieved, presenting a significant improvement in comparison with the result on single layer [H. Wen, Z.M. Wang, G.J. Salamo, Appl. Phys. Lett. 84 (2004) 1756]. On GaAs (331)A, In 0.4 Ga 0.6 As QWRs were revealed to be much straighter than in the previous report on multilayer growth [Z. Gong, Z. Niu, Z. Fang, Nanotechnology 17 (2006) 1140]. These observations are discussed in terms of the strain-field interaction among multilayers, enhancement of surface mobility at high temperature, and surface stability of GaAs (311)A and (331)A surfaces.

  9. Measurement of electron beam polarization produced by photoemission from bulk GaAs using twisted light

    Science.gov (United States)

    Clayburn, Nathan; Dreiling, Joan; McCarter, James; Ryan, Dominic; Poelker, Matt; Gay, Timothy

    2012-06-01

    GaAs photocathodes produce spin polarized electron beams when illuminated with circularly polarized light with photon energy approximately equal to the bandgap energy [1, 2]. A typical polarization value obtained with bulk GaAs and conventional circularly polarized light is 35%. This study investigated the spin polarization of electron beams emitted from GaAs illuminated with ``twisted light,'' an expression that describes a beam of light having orbital angular momentum (OAM). In the experiment, 790nm laser light was focused to a near diffraction-limited spot size on the surface of the GaAs photocathode to determine if OAM might couple to valence band electron spin mediated by the GaAs lattice. Our polarization measurements using a compact retarding-field micro-Mott polarimeter [3] have established an upper bound on the polarization of the emitted electron beam of 2.5%. [4pt] [1] D.T. Pierce, F. Meier, P. Zurcher, Appl. Phys. Lett. 26 670 (1975).[0pt] [2] C.K. Sinclair, et al., PRSTAB 10 023501 (2007).[0pt] [3] J.L. McCarter, M.L. Stutzman, K.W. Trantham, T.G. Anderson, A.M. Cook, and T.J. Gay Nucl. Instrum. and Meth. A (2010).

  10. Paths to light trapping in thin film GaAs solar cells.

    Science.gov (United States)

    Xiao, Jianling; Fang, Hanlin; Su, Rongbin; Li, Kezheng; Song, Jindong; Krauss, Thomas F; Li, Juntao; Martins, Emiliano R

    2018-03-19

    It is now well established that light trapping is an essential element of thin film solar cell design. Numerous light trapping geometries have already been applied to thin film cells, especially to silicon-based devices. Less attention has been paid to light trapping in GaAs thin film cells, mainly because light trapping is considered less attractive due to the material's direct bandgap and the fact that GaAs suffers from strong surface recombination, which particularly affects etched nanostructures. Here, we study light trapping structures that are implemented in a high-bandgap material on the back of the GaAs active layer, thereby not perturbing the integrity of the GaAs active layer. We study photonic crystal and quasi-random nanostructures both by simulation and by experiment and find that the photonic crystal structures are superior because they exhibit fewer but stronger resonances that are better matched to the narrow wavelength range where GaAs benefits from light trapping. In fact, we show that a 1500 nm thick cell with photonic crystals achieves the same short circuit current as an unpatterned 4000 nm thick cell. These findings are significant because they afford a sizeable reduction in active layer thickness, and therefore a reduction in expensive epitaxial growth time and cost, yet without compromising performance.

  11. Pump-probe studies of travelling coherent longitudinal acoustic phonon oscillations in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Y.; Qi, J.; Tolk, Norman [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, 37235 (United States); Miller, J. [Naval air Warfare Center Weapons Division, China Lake, CA 93555 (United States); Cho, Y.J.; Liu, X.; Furdyna, J.K. [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Shahbazyan, T.V. [Department of Physics, Jackson State University, MS 39217 (United States)

    2008-07-01

    We report comprehensive studies of long-lived oscillations in femtosecond optical pump-probe measurements on GaAs based systems. The oscillations arise from a photo-generated coherent longitudinal acoustic phonon wave at the sample surface, which subsequently travels from the surface into the GaAs substrate, thus providing information on the optical properties of the material as a function of time/depth. Wavelength-dependent studies of the oscillations near the bandgap of GaAs indicate strong correlations to the optical properties of GaAs. We also use the coherent longitudinal acoustic phonon waves to probe a thin buried Ga{sub 0.1}In{sub 0.9}As layers non-invasively. The observed phonon oscillations experience a reduction in amplitude and a phase change at wavelengths near the bandgap of the GaAs, when it passes through the thin Ga{sub x}In{sub 1-x}As layer. The layer depth and thicknesses can be extracted from the oscillation responses. A model has been developed that satisfactorily characterizes the experimental results. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  12. Temperature conditions for GaAs nanowire formation by Au-assisted molecular beam epitaxy

    International Nuclear Information System (INIS)

    Tchernycheva, M; Harmand, J C; Patriarche, G; Travers, L; Cirlin, G E

    2006-01-01

    Molecular beam epitaxial growth of GaAs nanowires using Au particles as a catalyst was investigated. Prior to the growth during annealing, Au alloyed with Ga coming from the GaAs substrate, and melted. Phase transitions of the resulting particles were observed in situ by reflection high-energy electron diffraction (RHEED). The temperature domain in which GaAs nanowire growth is possible was determined. The lower limit of this domain (320 deg. C) is close to the observed catalyst solidification temperature. Below this temperature, the catalyst is buried by GaAs growth. Above the higher limit (620 deg. C), the catalyst segregates on the surface with no significant nanowire formation. Inside this domain, the influence of growth temperature on the nanowire morphology and crystalline structure was investigated in detail by scanning electron microscopy and transmission electron microscopy. The correlation of the nanowire morphology with the RHEED patterns observed during the growth was established. Wurtzite GaAs was found to be the dominant crystal structure of the wires

  13. Health-enhancing doping controls

    DEFF Research Database (Denmark)

    Christiansen, Ask Vest

    2010-01-01

    Editorial published at International Network of Humanistic Doping Research (INHDR) website: http://www.doping.au.dk/en/online-resources/editorials/......Editorial published at International Network of Humanistic Doping Research (INHDR) website: http://www.doping.au.dk/en/online-resources/editorials/...

  14. Origin of the suppression in low frequency terahertz conductivity in dilute GaAs nitride and bismide alloys

    DEFF Research Database (Denmark)

    Cocker, Tylor; Lu, Xianfeng; Cooke, David

    We have performed time-resolved terahertz spectroscopy on GaAs1-xBix (x=7%) and observed a low-frequency suppression of the real conductivity previously seen only in dilute GaAs nitrides. We have developed a modified Drude model with a frequency-dependent scattering time that provides excellent...

  15. Disruption of Higher Order DNA Structures in Friedreich's Ataxia (GAA)(n) Repeats by PNA or LNA Targeting

    DEFF Research Database (Denmark)

    Bergquist, Helen; Rocha, Cristina S. J.; Alvarez-Asencio, Ruben

    2016-01-01

    Expansion of (GAA)n repeats in the first intron of the Frataxin gene is associated with reduced mRNA and protein levels and the development of Friedreich’s ataxia. (GAA)n expansions form non-canonical structures, including intramolecular triplex (H-DNA), and R-loops and are associated with epigen...

  16. Gene doping in sports.

    Science.gov (United States)

    Unal, Mehmet; Ozer Unal, Durisehvar

    2004-01-01

    Gene or cell doping is defined by the World Anti-Doping Agency (WADA) as "the non-therapeutic use of genes, genetic elements and/or cells that have the capacity to enhance athletic performance". New research in genetics and genomics will be used not only to diagnose and treat disease, but also to attempt to enhance human performance. In recent years, gene therapy has shown progress and positive results that have highlighted the potential misuse of this technology and the debate of 'gene doping'. Gene therapies developed for the treatment of diseases such as anaemia (the gene for erythropoietin), muscular dystrophy (the gene for insulin-like growth factor-1) and peripheral vascular diseases (the gene for vascular endothelial growth factor) are potential doping methods. With progress in gene technology, many other genes with this potential will be discovered. For this reason, it is important to develop timely legal regulations and to research the field of gene doping in order to develop methods of detection. To protect the health of athletes and to ensure equal competitive conditions, the International Olympic Committee, WADA and International Sports Federations have accepted performance-enhancing substances and methods as being doping, and have forbidden them. Nevertheless, the desire to win causes athletes to misuse these drugs and methods. This paper reviews the current status of gene doping and candidate performance enhancement genes, and also the use of gene therapy in sports medicine and ethics of genetic enhancement. Copyright 2004 Adis Data Information BV

  17. Nanoscale footprints of self-running gallium droplets on GaAs surface.

    Directory of Open Access Journals (Sweden)

    Jiang Wu

    Full Text Available In this work, the nanoscale footprints of self-driven liquid gallium droplet movement on a GaAs (001 surface will be presented and analyzed. The nanoscale footprints of a primary droplet trail and ordered secondary droplets along primary droplet trails are observed on the GaAs surface. A well ordered nanoterrace from the trail is left behind by a running droplet. In addition, collision events between two running droplets are investigated. The exposed fresh surface after a collision demonstrates a superior evaporation property. Based on the observation of droplet evolution at different stages as well as nanoscale footprints, a schematic diagram of droplet evolution is outlined in an attempt to understand the phenomenon of stick-slip droplet motion on the GaAs surface. The present study adds another piece of work to obtain the physical picture of a stick-slip self-driven mechanism in nanoscale, bridging nano and micro systems.

  18. Nitride surface passivation of GaAs nanowires: impact on surface state density.

    Science.gov (United States)

    Alekseev, Prokhor A; Dunaevskiy, Mikhail S; Ulin, Vladimir P; Lvova, Tatiana V; Filatov, Dmitriy O; Nezhdanov, Alexey V; Mashin, Aleksander I; Berkovits, Vladimir L

    2015-01-14

    Surface nitridation by hydrazine-sulfide solution, which is known to produce surface passivation of GaAs crystals, was applied to GaAs nanowires (NWs). We studied the effect of nitridation on conductivity and microphotoluminescence (μ-PL) of individual GaAs NWs using conductive atomic force microscopy (CAFM) and confocal luminescent microscopy (CLM), respectively. Nitridation is found to produce an essential increase in the NW conductivity and the μ-PL intensity as well evidence of surface passivation. Estimations show that the nitride passivation reduces the surface state density by a factor of 6, which is of the same order as that found for GaAs/AlGaAs nanowires. The effects of the nitride passivation are also stable under atmospheric ambient conditions for six months.

  19. Electric characterization of GaAs deposited on porous silicon by electrodeposition technique

    International Nuclear Information System (INIS)

    Lajnef, M.; Chtourou, R.; Ezzaouia, H.

    2010-01-01

    GaAs thin films were synthesized on porous Si substrate by the electrodeposition technique. The X-ray diffraction studies showed that the as-grown films were crystallised in mixed phase nature orthorhombic and cubic of GaAs. The GaAs film was then electrically characterized using current-voltage (I-V) and capacitance-voltage (C-V) techniques by the way of Al/GaAs Schottky junctions. The electric analysis allowed us to determine the n factor and the barrier height φ b0 parameters of Al/GaAs Schottky junctions. The (C-V) characteristics were recorded at frequency signal 1 MHz in order to identify the effect of the surface states on the behaviour of the capacitance of the device.

  20. Electric characterization of GaAs deposited on porous silicon by electrodeposition technique

    Energy Technology Data Exchange (ETDEWEB)

    Lajnef, M., E-mail: Mohamed.lajnef@yahoo.fr [Laboratoire de Photovoltaique et de Semi-conducteurs, Centre de Recherche et des Technologies de l' Energie, BP. 95, Hammam-Lif 2050 (Tunisia); Chtourou, R.; Ezzaouia, H. [Laboratoire de Photovoltaique et de Semi-conducteurs, Centre de Recherche et des Technologies de l' Energie, BP. 95, Hammam-Lif 2050 (Tunisia)

    2010-03-01

    GaAs thin films were synthesized on porous Si substrate by the electrodeposition technique. The X-ray diffraction studies showed that the as-grown films were crystallised in mixed phase nature orthorhombic and cubic of GaAs. The GaAs film was then electrically characterized using current-voltage (I-V) and capacitance-voltage (C-V) techniques by the way of Al/GaAs Schottky junctions. The electric analysis allowed us to determine the n factor and the barrier height {phi}{sub b0} parameters of Al/GaAs Schottky junctions. The (C-V) characteristics were recorded at frequency signal 1 MHz in order to identify the effect of the surface states on the behaviour of the capacitance of the device.

  1. Self-assisted GaAs nanowires with selectable number density on Silicon without oxide layer

    International Nuclear Information System (INIS)

    Bietti, S; Somaschini, C; Esposito, L; Sanguinetti, S; Frigeri, C; Fedorov, A; Geelhaar, L

    2014-01-01

    We present the growth of self-assisted GaAs nanowires (NWs) with selectable number density on bare Si(1 1 1), not covered by the silicon oxide. We determine the number density of the NWs by initially self-assembling GaAs islands on whose top a single NW is nucleated. The number density of the initial GaAs base islands can be tuned by droplet epitaxy and the same degree of control is then transferred to the NWs. This procedure is completely performed during a single growth in an ultra-high vacuum environment and requires neither an oxide layer covering the substrate, nor any pre-patterning technique. (paper)

  2. Electronic structure of GaAs with InAs (001) monolayer

    International Nuclear Information System (INIS)

    Tit, N.; Peressi, M.

    1995-04-01

    The effect on the electronic structure of an InAs monomolecular plane inserted in bulk GaAs is investigated theoretically. The (InAs) 1 (GaAs) n (001) strained superlattice is studied via ab-initio self-consistent pseudopotential calculations. Both electrons and holes are localized nearby the inserted InAs monolayer, which therefore acts as a quantum well for all the charge carriers. The small thickness of the inserted InAs slab is responsible of high confinement energies for the charge carriers, and therefore the interband electron-heavy-hole transition energy is close to the energy gap of the bulk GaAs, in agreement with recent experimental data. (author). 18 refs, 4 figs

  3. Low energy Ar ion bombardment damage of Si, GaAs, and InP surfaces

    International Nuclear Information System (INIS)

    Williams, R.S.

    1982-01-01

    Argon bombardment damage to (100) surfaces of Si, GaAs, and InP for sputter ion-gun potentials of 1, 2, and 3 kilovolts was studied using Rutherford backscattering. Initial damage rates and saturation damage levels were determined. Bombardment damage sensitivity increased for the sequence Si, GaAs, and InP. Saturation damage levels for Si and GaAs correspond reasonably to LSS projected range plus standard deviation estimates; damage to InP exceeded this level significantly. For an ion-gun potential of 3 keV, the initial sputter yield of P from an InP surface exceeded the sputter yield of In by four atoms per incident Ar projectile. (author)

  4. Self-assembled colloidal PbS quantum dots on GaAs substrates

    International Nuclear Information System (INIS)

    Lue, Wei; Yamada, Fumihiko; Kamiya, Itaru

    2010-01-01

    We report the fabrication and analysis of self-assembled monolayer and bilayer films of colloidal PbS quantum dots (QDs) on GaAs (001) substrates. 1,6-hexanedithiol is used as link molecule between QDs and GaAs substrates. Atomic force microscopy (AFM) and photoluminescence (PL) measurements confirm the formation of PbS QD film on GaAs. For the monolayer PbS QD film, the temperature-dependent PL shows a feature typical of close-packed film. For the bilayer PbS QD film fabricated from two different mean-sized PbS QDs, we find that the stacking sequence of QDs with different size affects the quantum yield and emission wavelength of the film.

  5. Optimization of the GaAs et GaAs/Si annealing using halogen lamp flashes

    International Nuclear Information System (INIS)

    Blanck, H.

    1989-01-01

    The aim of the work is to check whether the flash annealing of GaAs and GaAs/Si, using halogen lamps, allows an improvement in the results obtained by usual methods. The electrical activation, defects behavior and results uniformity are studied. The results on the activation and diffusion of implanted impurities are shown to be equivalent to those obtained with classical annealing methods. However, residual impurities (or defects) diffusion phenomena are restrained by the flash annealing technique. The Hall effect cartographic measurements showed an improvement of the uniformity of the implanted coating surface resistance. Flash annealing is a suitable method for the Si activation in GaAs. It allows an improvement of the GaAs results obtained with standard techniques, as well as the formation, by means of ion implantation, of active zones in the GaAs/Si layers [fr

  6. An ultra-high-speed direct digital frequency synthesizer implemented in GaAs HBT technology

    International Nuclear Information System (INIS)

    Chen Gaopeng; Wu Danyu; Jin Zhi; Liu Xinyu

    2010-01-01

    This paper presents a 10-GHz 8-bit direct digital synthesizer (DDS) microwave monolithic integrated circuit implemented in 1 μm GaAs HBT technology. The DDS takes a double-edge-trigger (DET) 8-stage pipeline accumulator with sine-weighted DAC-based ROM-less architecture, which can maximize the utilization ratio of the GaAs HBT's high-speed potential. With an output frequency up to 5 GHz, the DDS gives an average spurious free dynamic range of 23.24 dBc through the first Nyquist band, and consumes 2.4 W of DC power from a single -4.6 V DC supply. Using 1651 GaAs HBT transistors, the total area of the DDS chip is 2.4 x 2.0 mm 2 . (semiconductor integrated circuits)

  7. Performance of Series Connected GaAs Photovoltaic Converters under Multimode Optical Fiber Illumination

    Directory of Open Access Journals (Sweden)

    Tiqiang Shan

    2014-01-01

    Full Text Available In many military and industrial applications, GaAs photovoltaic (PV converters are connected in series in order to generate the required voltage compatible with most common electronics. Multimode optical fibers are usually used to carry high-intensity laser and illuminate the series connected GaAs PV converters in real time. However, multimode optical fiber illumination has a speckled intensity pattern. The series connected PV array is extremely sensitive to nonuniform illumination; its performance is limited severely by the converter that is illuminated the least. This paper quantifies the effects of multimode optical fiber illumination on the performance of series connected GaAs PV converters, analyzes the loss mechanisms due to speckles, and discusses the maximum illumination efficiency. In order to describe the illumination dependent behavior detailedly, modeling of the series connected PV array is accomplished based on the equivalent circuit for PV cells. Finally, a series of experiments are carried out to demonstrate the theory analysis.

  8. Influence of substrate orientation on the structural properties of GaAs nanowires in MOCVD

    Energy Technology Data Exchange (ETDEWEB)

    Muhammad, R., E-mail: rosnita@utm.my; Othaman, Z., E-mail: zulothaman@gmail.com; Ibrahim, Z., E-mail: zuhairi@utm.my; Sakrani, S., E-mail: samsudi3@yahoo.com [Faculty of Science, UniversitiTeknologi Malaysia, 81310 UTM, Johor (Malaysia); Wahab, Y., E-mail: wyussof@gmail.com [Razak School, UniversitiTeknologi Malaysia, 54100 Kuala Lumpur (Malaysia)

    2016-04-19

    In this study, the effect of substrate orientation on the structural properties of GaAs nanowires grown by a metal organic chemical vapor deposition has been investigated. Gold colloids were used as catalyst to initiate the growth of nanowiresby the vapour-liquid-solid (VLS) mechanism. From the field-emission scanning electron microscopy (FE-SEM), the growth of the nanowires were at an elevation angle of 90°, 60°, 65° and 35° with respect to the GaAs substrate for (111)B, (311)B, (110) and (100) orientations respectively. The preferential NW growth direction is always <111>B. High-resolution transmission electron microscope (HRTEM) micrograph showed the NWs that grew on the GaAs(111)B has more structural defects when compared to others. Energy dispersive X-ray analysis (EDX) indicated the presence of Au, Ga and As. The bigger diameter NWs dominates the (111)B substrate surface.

  9. Optical techniques to feed and control GaAs MMIC modules for phased array antenna applications

    Science.gov (United States)

    Bhasin, K. B.; Anzic, G.; Kunath, R. R.; Connolly, D. J.

    1986-01-01

    A complex signal distribution system is required to feed and control GaAs monolithic microwave integrated circuits (MMICs) for phased array antenna applications above 20 GHz. Each MMIC module will require one or more RF lines, one or more bias voltage lines, and digital lines to provide a minimum of 10 bits of combined phase and gain control information. In a closely spaced array, the routing of these multiple lines presents difficult topology problems as well as a high probability of signal interference. To overcome GaAs MMIC phased array signal distribution problems optical fibers interconnected to monolithically integrated optical components with GaAs MMIC array elements are proposed as a solution. System architecture considerations using optical fibers are described. The analog and digital optical links to respectively feed and control MMIC elements are analyzed. It is concluded that a fiber optic network will reduce weight and complexity, and increase reliability and performance, but higher power will be required.

  10. Neutron-damaged GaAs detectors for use in a Compton spectrometer

    International Nuclear Information System (INIS)

    Kammeraad, J.E.; Sale, K.E.; Wang, C.L.; Baltrusaitis, R.M.

    1992-01-01

    Detectors made of GaAs are being studies for use on the focal plane of a Compton spectrometer which measures 1-MeV to 25-MeV gamma rays with high energy resolution (1% or 100 keV, whichever is greater) and 200-ps time resolution. The detectors are GaAs chips that have been neutron-damaged to improve the time response. The detectors will be used to measure fast transient signals in the current mode. The properties of various GaAs detector configurations are being studied by bombarding sample detectors with short pulses of 4-MeV to 16-MeV electrons at the Linac Facility at EG ampersand G Energy Measurements, Inc., Santa Barbara Operations. Measurements of detector sensitivity and impulse response versus detector bias, thickness, and electron beam energy and intensity have been performed and are presented. 5 refs

  11. Investigations on liquid phase electroepitaxial growth kinetics of GaAs

    International Nuclear Information System (INIS)

    Mouleeswaran, D.; Dhanasekaran, R.

    2004-01-01

    This paper presents a model based on solving a two-dimensional diffusion equation incorporating the electromigration effect by numerical simulation method corresponding to liquid phase electroepitaxial (LPEE) growth of GaAs, whose growth is limited by diffusion and electro migration of solute species. Using the numerical simulation method, the concentration profiles of As in Ga rich solution during the electroepitaxial growth of GaAs have been constructed in front of the growing crystal interface. Using the concentration gradient at the interface, the growth rate and thickness of the epitaxial layer of GaAs have been determined for different experimental growth conditions. The proposed model is based on the assumption that there is no convection in the solution. The results are discussed in detail

  12. Determination of deep levels in semi-insulating cadmium telluride by thermally stimulated current measurements

    International Nuclear Information System (INIS)

    Scharager, C.; Muller, J.C.; Stuck, R.; Siffert, P.

    1975-01-01

    Thermally stimulated current (TSC) measurements have been performed in high resistivity (rho approximately 10 7 ohms.cm) CdTe γ-ray detectors between 35 and 300K. The TSC curves have been analyzed by different methods, including those taking into account the retrapping of the carriers. The trap characteristics have been determined; especially three levels located at E(v)+0.13eV, E(v)+0.30eV and E(c)-0.55eV have been investigated [fr

  13. Semi-insulating Sn-Zr-O: Tunable resistance buffer layers

    Energy Technology Data Exchange (ETDEWEB)

    Barnes, Teresa M.; Burst, James M.; Reese, Matthew O.; Perkins, Craig L. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)

    2015-03-02

    Highly resistive and transparent (HRT) buffer layers are critical components of solar cells and other opto-electronic devices. HRT layers are often undoped transparent conducting oxides. However, these oxides can be too conductive to form an optimal HRT. Here, we present a method to produce HRT layers with tunable electrical resistivity, despite the presence of high concentrations of unintentionally or intentionally added dopants in the film. This method relies on alloying wide-bandgap, high-k dielectric materials (e.g., ZrO{sub 2}) into the host oxide to tune the resistivity. We demonstrate Sn{sub x}Zr{sub 1−x}O{sub 2}:F films with tunable resistivities varying from 0.001 to 10 Ω cm, which are controlled by the Zr mole fraction in the films. Increasing Zr suppresses carriers by expanding the bandgap almost entirely by shifting the valence-band position, which allows the HRT layers to maintain good conduction-band alignment for a low-resistance front contact.

  14. Secondary electron emission and self-consistent charge transport in semi-insulating samples

    Energy Technology Data Exchange (ETDEWEB)

    Fitting, H.-J. [Institute of Physics, University of Rostock, Universitaetsplatz 3, D-18051 Rostock (Germany); Touzin, M. [Unite Materiaux et Transformations, UMR CNRS 8207, Universite de Lille 1, F-59655 Villeneuve d' Ascq (France)

    2011-08-15

    Electron beam induced self-consistent charge transport and secondary electron emission (SEE) in insulators are described by means of an electron-hole flight-drift model (FDM) now extended by a certain intrinsic conductivity (c) and are implemented by an iterative computer simulation. Ballistic secondary electrons (SE) and holes, their attenuation to drifting charge carriers, and their recombination, trapping, and field- and temperature-dependent detrapping are included. As a main result the time dependent ''true'' secondary electron emission rate {delta}(t) released from the target material and based on ballistic electrons and the spatial distributions of currents j(x,t), charges {rho}(x,t), field F(x,t), and potential V(x,t) are obtained where V{sub 0} = V(0,t) presents the surface potential. The intrinsic electronic conductivity limits the charging process and leads to a conduction sample current to the support. In that case the steady-state total SE yield will be fixed below the unit: i.e., {sigma} {eta} + {delta} < 1.

  15. Surface chemistry and growth mechanisms studies of homo epitaxial (1 0 0) GaAs by laser molecular beam epitaxy

    International Nuclear Information System (INIS)

    Yan Dawei; Wu Weidong; Zhang Hong; Wang Xuemin; Zhang Hongliang; Zhang Weibin; Xiong Zhengwei; Wang Yuying; Shen Changle; Peng Liping; Han Shangjun; Zhou Minjie

    2011-01-01

    In this paper, GaAs thin film has been deposited on thermally desorbed (1 0 0) GaAs substrate using laser molecular beam epitaxy. Scanning electron microscopy, in situ reflection high energy electron diffraction and in situ X-ray photoelectron spectroscopy are applied for evaluation of the surface morphology and chemistry during growth process. The results show that a high density of pits is formed on the surface of GaAs substrate after thermal treatment and the epitaxial thin film heals itself by a step flow growth, resulting in a smoother surface morphology. Moreover, it is found that the incorporation of As species into GaAs epilayer is more efficient in laser molecular beam epitaxy than conventional molecular beam epitaxy. We suggest the growth process is impacted by surface chemistry and morphology of GaAs substrate after thermal treatment and the growth mechanisms are discussed in details.

  16. Doping of organic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Luessem, B.; Riede, M.; Leo, K. [Institut fuer Angewandte Photophysik, TU Dresden (Germany)

    2013-01-15

    The understanding and applications of organic semiconductors have shown remarkable progress in recent years. This material class has been developed from being a lab curiosity to the basis of first successful products as small organic LED (OLED) displays; other areas of application such as OLED lighting and organic photovoltaics are on the verge of broad commercialization. Organic semiconductors are superior to inorganic ones for low-cost and large-area optoelectronics due to their flexibility, easy deposition, and broad variety, making tailor-made materials possible. However, electrical doping of organic semiconductors, i.e. the controlled adjustment of Fermi level that has been extremely important to the success of inorganic semiconductors, is still in its infancy. This review will discuss recent work on both fundamental principles and applications of doping, focused primarily to doping of evaporated organic layers with molecular dopants. Recently, both p- and n-type molecular dopants have been developed that lead to efficient and stable doping of organic thin films. Due to doping, the conductivity of the doped layers increases several orders of magnitude and allows for quasi-Ohmic contacts between organic layers and metal electrodes. Besides reducing voltage losses, doping thus also gives design freedom in terms of transport layer thickness and electrode choice. The use of doping in applications like OLEDs and organic solar cells is highlighted in this review. Overall, controlled molecular doping can be considered as key enabling technology for many different organic device types that can lead to significant improvements in efficiencies and lifetimes. (Copyright copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  17. Doping of organic semiconductors

    International Nuclear Information System (INIS)

    Luessem, B.; Riede, M.; Leo, K.

    2013-01-01

    The understanding and applications of organic semiconductors have shown remarkable progress in recent years. This material class has been developed from being a lab curiosity to the basis of first successful products as small organic LED (OLED) displays; other areas of application such as OLED lighting and organic photovoltaics are on the verge of broad commercialization. Organic semiconductors are superior to inorganic ones for low-cost and large-area optoelectronics due to their flexibility, easy deposition, and broad variety, making tailor-made materials possible. However, electrical doping of organic semiconductors, i.e. the controlled adjustment of Fermi level that has been extremely important to the success of inorganic semiconductors, is still in its infancy. This review will discuss recent work on both fundamental principles and applications of doping, focused primarily to doping of evaporated organic layers with molecular dopants. Recently, both p- and n-type molecular dopants have been developed that lead to efficient and stable doping of organic thin films. Due to doping, the conductivity of the doped layers increases several orders of magnitude and allows for quasi-Ohmic contacts between organic layers and metal electrodes. Besides reducing voltage losses, doping thus also gives design freedom in terms of transport layer thickness and electrode choice. The use of doping in applications like OLEDs and organic solar cells is highlighted in this review. Overall, controlled molecular doping can be considered as key enabling technology for many different organic device types that can lead to significant improvements in efficiencies and lifetimes. (Copyright copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  18. Si and gaas pixel detectors for medical imaging applications

    International Nuclear Information System (INIS)

    Bisogni, M. G.

    2001-01-01

    As the use of digital radiographic equipment in the morphological imaging field is becoming the more and more diffuse, the research of new and more performing devices from public institutions and industrial companies is in constant progress. Most of these devices are based on solid-state detectors as X-ray sensors. Semiconductor pixel detectors, originally developed in the high energy physics environment, have been then proposed as digital detector for medical imaging applications. In this paper a digital single photon counting device, based on silicon and GaAs pixel detector, is presented. The detector is a thin slab of semiconductor crystal where an array of 64 by 64 square pixels, 170- m side, has been built on one side. The data read-out is performed by a VLSI integrated circuit named Photon Counting Chip (PCC), developed within the MEDIPIX collaboration. Each chip cell geometrically matches the sensor pixel. It contains a charge preamplifier, a threshold comparator and a 15 bits pseudo-random counter and it is coupled to the detector by means of bump bonding. Most important advantages of such system, with respect to a traditional X-rays film/screen device, are the wider linear dynamic range (3x104) and the higher performance in terms of MTF and DQE. Besides the single photon counting architecture allows to detect image contrasts lower than 3%. Electronics read-out performance as well as imaging capabilities of the digital device will be presented. Images of mammographic phantoms acquired with a standard Mammographic tube will be compared with radiographs obtained with traditional film/screen systems

  19. Analysis of GAA/TTC DNA triplexes using nuclear magnetic resonance and electrospray ionization mass spectrometry.

    Science.gov (United States)

    Mariappan, S V Santhana; Cheng, Xun; van Breemen, Richard B; Silks, Louis A; Gupta, Goutam

    2004-11-15

    The formation of a GAA/TTC DNA triplex has been implicated in Friedreich's ataxia. The destabilization of GAA/TTC DNA triplexes either by pH or by binding to appropriate ligands was analyzed by nuclear magnetic resonance (NMR) and positive-ion electrospray mass spectrometry. The triplexes and duplexes were identified by changes in the NMR chemical shifts of H8, H1, H4, 15N7, and 15N4. The lowest pH at which the duplex is detectable depends upon the overall stability and the relative number of Hoogsteen C composite function G to T composite function A basepairs. A melting pH (pHm) of 7.6 was observed for the destabilization of the (GAA)2T4(TTC)2T4(CTT)2 triplex to the corresponding Watson-Crick duplex and the T4(CTT)2 overhang. The mass spectrometric analyses of (TTC)6.(GAA)6 composite function(TTC)6 triplex detected ions due to both triplex and single-stranded oligonucleotides under acidic conditions. The triplex ions disappeared completely at alkaline pH. Duplex and single strands were detectable only at neutral and alkaline pH values. Mass spectrometric analyses also showed that minor groove-binding ligands berenil, netropsin, and distamycin and the intercalating ligand acridine orange destabilize the (TTC)6.(GAA)6 composite function (TTC)6 triplex. These NMR and mass spectrometric methods may function as screening assays for the discovery of agents that destabilize GAA/TTC triplexes and as general methods for the characterization of structure, dynamics, and stability of DNA and DNA-ligand complexes.

  20. Modeling the effect of deep impurity ionization on GaAs photoconductive switches

    Energy Technology Data Exchange (ETDEWEB)

    Yee, J.H.; Khanaka, G.H.; Druce, R.L.; Pocha, M.D.

    1992-01-01

    The ionization coefficient of deep traps in GaAs is determined from a gas breakdown model together with the recent experimental data obtained at LLNL (Lawrence Livermore National Laboratory) and Boeing. Using this coefficient in our nonlinear device transport code, we have investigated theoretically the nonlinear switching phenomena in GaAs devices. The results obtained from our investigations show that if we take into consideration the effect of the field ionization of the deep traps, we can show how the Lock-On'' phenomena could occur in the device.

  1. Modeling the effect of deep impurity ionization on GaAs photoconductive switches

    Energy Technology Data Exchange (ETDEWEB)

    Yee, J.H.; Khanaka, G.H.; Druce, R.L.; Pocha, M.D.

    1992-01-01

    The ionization coefficient of deep traps in GaAs is determined from a gas breakdown model together with the recent experimental data obtained at LLNL (Lawrence Livermore National Laboratory) and Boeing. Using this coefficient in our nonlinear device transport code, we have investigated theoretically the nonlinear switching phenomena in GaAs devices. The results obtained from our investigations show that if we take into consideration the effect of the field ionization of the deep traps, we can show how the ``Lock-On`` phenomena could occur in the device.

  2. Pseudo-Rhombus-Shaped Subwavelength Crossed Gratings of GaAs for Broadband Antireflection

    International Nuclear Information System (INIS)

    Chen Xi; Zhang Jing; Song Guo-Feng; Chen Liang-Hui; Fan Zhong-Chao

    2010-01-01

    Holographic lithography coupled with the nonlinear response of photoresist to the exposure is adopted to fabricate porous photoresist (PR) mask. Conventional dot PR mask is also generated, and both patterns are transferred into a underlying GaAs substrate by the optimal dry etching process to obtain tapered subwavelength crossed gratings (SWCGs) to mimic the moth-eye structure. In comparison of the experiment and simulation, the closely-packed pseudo-rhombus-shaped GaAs SWCGs resulting from the porous mask outperforms the conical counterpart which comes from the dot mask, and achieves a reported lowest mean spectral reflectance of 1.1%. (fundamental areas of phenomenology(including applications))

  3. Electrical properties of Ga ion beam implanted GaAs epilayer

    International Nuclear Information System (INIS)

    Hirayama, Yoshiro; Okamoto, Hiroshi

    1985-01-01

    Resistivity enhancement by 5 orders or more was realized by Ga focused ion beam implantation into n + and p + GaAs epilayers. For originally n + epilayers, this resistivity enhancement is maintained after annealing as high as 800 deg C. However this enhancement disappears after annealing at above 650 deg C for p + epilayer. This property makes GaAs high resistive only in a limited area whose minimum dimension is 0.1 μm or less, and is attractive for a device fabrication process to electrically isolate integrated elements. (author)

  4. Sulfidic photochemical passivation of GaAs surfaces in alcoholic solutions

    International Nuclear Information System (INIS)

    Simonsmeier, T.; Ivankov, A.; Bauhofer, W.

    2005-01-01

    We report on a remarkable enhancement of the passivation effect of sulfidic solutions through illumination with above band gap light. Luminescence measurements on GaAs surfaces which have been illuminated during chemical passivation reveal in comparison to nonilluminated samples a further reduction of their surface density of states as well as a significantly increased stability of the passivation. Investigations with photoelectron spectroscopy show that illumination leads to a nearly complete removal of oxides on the surface. Measurements on Schottky diodes which have been manufactured with photochemically passivated GaAs indicate a noticeable decrease in band bending and a depinning of the Fermi level

  5. X-ray diffraction study on pressure-induced phase transformation in nanocrystalline GaAs

    DEFF Research Database (Denmark)

    Jiang, Jianzhong; Olsen, J. S.; Gerward, Leif

    2002-01-01

    We have shown that the onset and transition pressures of the GaAs I --> II transition are 17 GPa and 20 GPa, respectively, for both bulk and nanophase material. The observed gradual change in resistivity of nanophase GaAs,at the semiconductor-to-metal transition is explained by the two-component ......We have shown that the onset and transition pressures of the GaAs I --> II transition are 17 GPa and 20 GPa, respectively, for both bulk and nanophase material. The observed gradual change in resistivity of nanophase GaAs,at the semiconductor-to-metal transition is explained by the two...

  6. Pulse GaAs field transistor amplifier with subnanosecond time transient

    International Nuclear Information System (INIS)

    Sidnev, A.N.

    1987-01-01

    Pulse amplifier on fast field effect GaAs transistors with Schottky barrier is described. The amplifier contains four cascades, the first three of which are made on combined transistors on the common-drain circuit. The last cascade is made on high-power field effect GaAs transistor for coordination with 50 ohm load. The amplifier operates within the range of input signals from 0.5 up to 100 mV with repetition frequency up to 16 Hz, The gain of the amplifier is ≅ 20 dB. The setting time at output pulses amplitude up to 1 V constitutes ∼ 0.2 ns

  7. Polarity influence on the indentation punching of thin {111} GaAs foils at elevated temperatures

    International Nuclear Information System (INIS)

    Patriarche, G; Largeau, L; Riviere, J P; Bourhis, E Le

    2005-01-01

    Thin {111} GaAs substrates were deformed by a Vickers indenter at 350 deg. C-370 deg. C under loads ranging between 0.4 and 1.9 N. Optical microscopy and interferometry were used to observe the indented and opposite faces of the thin foils and hence to investigate the plastic flow through the samples. Attention was paid to the polarity (A or B) of the specimen surface, as GaAs is known to show a large difference between α and β dislocations mobilities. A model considering the influence of polarity is proposed to describe the material flow throughout thin samples

  8. Some Aspects of the RHEED Behavior of Low-Temperature GaAs Growth

    International Nuclear Information System (INIS)

    Nemcsics, A.

    2005-01-01

    The reflection high-energy electron diffraction (RHEED) behavior manifested during MBE growth on a GaAs(001) surface under low-temperature (LT) growth conditions is examined in this study. RHEED and its intensity oscillations during LT GaAs growth exhibit some particular behavior. The intensity, phase, and decay of the oscillations depend on the beam equivalent pressure (BEP) ratio and substrate temperature, etc. Here, the intensity dependence of RHEED behavior on the BEP ratio, substrate temperature, and excess of As content in the layer are examined. The change in the decay constant of the RHEED oscillations is also discussed

  9. Temperature-Driven Change in the Unstable Growth Mode on Patterned GaAs(001)

    International Nuclear Information System (INIS)

    Tadayyon-Eslami, T.; Phaneuf, R. J.; Kan, H.-C.; Calhoun, L. C.

    2006-01-01

    We observe a dramatic change in the unstable growth mode during GaAs molecular beam epitaxy on patterned GaAs(001) as the temperature is lowered through approximately 540 deg. C, roughly coincident with the preroughening temperature. Observations of the As 2 flux dependence, however, rule out thermodynamic preroughening as driving the growth mode change. Similar observations rule out the change in surface reconstruction as the cause. Instead, we find evidence that the change in the unstable growth mode can be explained by a competition between the decreased adatom collection rate on small terraces and a small anisotropic barrier to adatom diffusion downward across step bunches

  10. Photoreflectance study of InAs ultrathin layer embedded in Si-delta-doped GaAs/AlGaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Dhifallah, I., E-mail: ines.dhifallah@gmail.co [Laboratoire de Photovoltaique, des Semiconducteurs et des Nanostructures, Centre de Recherche et des Technologies de l' energie, BP 95 Hammam-Lif 2050 (Tunisia); Daoudi, M.; Bardaoui, A. [Laboratoire de Photovoltaique, des Semiconducteurs et des Nanostructures, Centre de Recherche et des Technologies de l' energie, BP 95 Hammam-Lif 2050 (Tunisia); Eljani, B. [Unite de recherche sur les Hetero-Epitaxie et Applications, Faculte des Sciences de Monastir (Tunisia); Ouerghi, A. [Laboratoire de Photonique et de Nanostructures, CNRS Route de Nozay 91 46a0, Marcoussis (France); Chtourou, R. [Laboratoire de Photovoltaique, des Semiconducteurs et des Nanostructures, Centre de Recherche et des Technologies de l' energie, BP 95 Hammam-Lif 2050 (Tunisia)

    2011-05-15

    Photoreflectance and photoluminescence studies were performed to characterize InAs ultrathin layer embedded in Si-delta-doped GaAs/AlGaAs high electron mobility transistors. These structures were grown by Molecular Beam Epitaxy on (1 0 0) oriented GaAs substrates with different silicon-delta-doped layer densities. Interband energy transitions in the InAs ultrathin layer quantum well were observed below the GaAs band gap in the photoreflectance spectra, and assigned to electron-heavy-hole (E{sub e-hh}) and electron-light-hole (E{sub e-lh}) fundamental transitions. These transitions were shifted to lower energy with increasing silicon-{delta}-doping density. This effect is in good agreement with our theoretical results based on a self-consistent solution of the coupled Schroedinger and Poisson equations and was explained by increased escape of photogenerated carriers and enhanced Quantum Confined Stark Effect in the Si-delta-doped InAs/GaAs QW. In the photoreflectance spectra, not only the channel well interband energy transitions were observed, but also features associated with the GaAs and AlGaAs bulk layers located at about 1.427 and 1.8 eV, respectively. By analyzing the Franz-Keldysh Oscillations observed in the spectral characteristics of Si-{delta}-doped samples, we have determined the internal electric field introduced by ionized Si-{delta}-doped centers. We have observed an increase in the electric field in the InAs ultrathin layer with increasing silicon content. The results are explained in terms of doping dependent ionized impurities densities and surface charges. - Research highlights: {yields} Studying HEMTs structures with different silicon doping content. {yields} An increase of the electric field in the InAs layer with increasing Si content. {yields} The interband energy transitions in the HEMTs structures have been obtained from PR. {yields} Experimental and theoretical values of transitions energies were in good agreement.

  11. Borazino-Doped Polyphenylenes.

    Science.gov (United States)

    Marinelli, Davide; Fasano, Francesco; Najjari, Btissam; Demitri, Nicola; Bonifazi, Davide

    2017-04-19

    The divergent synthesis of two series of borazino-doped polyphenylenes, in which one or more aryl units are replaced by borazine rings, is reported for the first time, taking advantage of the decarbonylative [4 + 2] Diels-Alder cycloaddition reaction between ethynyl and tetraphenylcyclopentadienone derivatives. Because of the possibility of functionalizing the borazine core with different groups on the aryl substituents at the N and B atoms of the borazino core, we have prepared borazino-doped polyphenylenes featuring different doping dosages and orientations. To achieve this, two molecular modules were prepared: a core and a branching unit. Depending on the chemical natures of the central aromatic module and the reactive group, each covalent combination of the modules yields one exclusive doping pattern. By means of this approach, three- and hexa-branched hybrid polyphenylenes featuring controlled orientations and dosages of the doping B 3 N 3 rings have been prepared. Detailed photophysical investigations showed that as the doping dosage is increased, the strong luminescent signal is progressively reduced. This suggests that the presence of the B 3 N 3 rings engages additional deactivation pathways, possibly involving excited states with an increasing charge-separated character that are restricted in the full-carbon analogues. Notably, a strong effect of the orientational doping on the fluorescence quantum yield was observed for those hybrid polyphenylene structures featuring low doping dosages. Finally, we showed that Cu-catalyzed 1,3-dipolar cycloaddition is also chemically compatible with the BN core, further endorsing the inorganic benzene as a versatile aromatic scaffold for engineering of molecular materials with tailored and exploitable optoelectronic properties.

  12. Carbon doped GaAs/AlGaAs heterostructures with high mobility two dimensional hole gas

    Energy Technology Data Exchange (ETDEWEB)

    Hirmer, Marika; Bougeard, Dominique; Schuh, Dieter [Institut fuer Experimentelle und Angewandte Physik, Universitaet Regensburg, D 93040 Regensburg (Germany); Wegscheider, Werner [Laboratorium fuer Festkoerperphysik, ETH Zuerich, 8093 Zuerich (Switzerland)

    2011-07-01

    Two dimensional hole gases (2DHG) with high carrier mobilities are required for both fundamental research and possible future ultrafast spintronic devices. Here, two different types of GaAs/AlGaAs heterostructures hosting a 2DHG were investigated. The first structure is a GaAs QW embedded in AlGaAs barrier grown by molecular beam epitaxy with carbon-doping only at one side of the quantum well (QW) (single side doped, ssd), while the second structure is similar but with symmetrically arranged doping layers on both sides of the QW (double side doped, dsd). The ssd-structure shows hole mobilities up to 1.2*10{sup 6} cm{sup 2}/Vs which are achieved after illumination. In contrast, the dsd-structure hosts a 2DHG with mobility up to 2.05*10{sup 6} cm{sup 2}/Vs. Here, carrier mobility and carrier density is not affected by illuminating the sample. Both samples showed distinct Shubnikov-de-Haas oscillations and fractional quantum-Hall-plateaus in magnetotransport experiments done at 20mK, indicating the high quality of the material. In addition, the influence of different temperature profiles during growth and the influence of the Al content of the barrier Al{sub x}Ga{sub 1-x}As on carrier concentration and mobility were investigated and are presented here.

  13. Reflectance-anisotropy study of the dynamics of molecular beam epitaxy growth of GaAs and InGaAs on GaAs(001)

    Energy Technology Data Exchange (ETDEWEB)

    Ortega-Gallegos, J.; Lastras-Martinez, A.; Lastras-Martinez, L.F. [Instituto de Investigacion en Comunicacion Optica, Universidad Autonoma de San Luis Potosi. Alvaro Obregon 64, San Luis Potosi (Mexico); Balderas-Navarro, R.E. [Instituto de Investigacion en Comunicacion Optica, Universidad Autonoma de San Luis Potosi. Alvaro Obregon 64, San Luis Potosi (Mexico); Facultad de Ciencias, Universidad Autonoma de San Luis Potosi. Alvaro Obregon 64, San Luis Potosi (Mexico)

    2008-07-01

    Reflectance-Anisotropy (RA) observations during the Molecular Beam Epitaxy (MBE) growth of zincblende semiconductors films were carried out using the E{sub 1} optical transition as a probe. We follow the kinetics of the deposition of GaAs and In{sub 0.3}Ga{sub 0.7}As on GaAs(001) at growth rates of 0.2 and 0.25 ML/s, respectively. During growth we used a constant As{sub 4} or As{sub 2} flux pressure of 5 x 10{sup -6} Torr. Clear RA-oscillations were observed during growth with a period that nearly coincides with the growth period for a Ga-As bilayer. RHEED was used as an auxiliary technique in order to obtain a correlation between RHEED and RA oscillations. On the basis of our results, we argue that RAS oscillations are mainly associated to periodic changes in surface atomic structure. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. Reflectance-anisotropy study of the dynamics of molecular beam epitaxy growth of GaAs and InGaAs on GaAs(001)

    International Nuclear Information System (INIS)

    Ortega-Gallegos, J.; Lastras-Martinez, A.; Lastras-Martinez, L.F.; Balderas-Navarro, R.E.

    2008-01-01

    Reflectance-Anisotropy (RA) observations during the Molecular Beam Epitaxy (MBE) growth of zincblende semiconductors films were carried out using the E 1 optical transition as a probe. We follow the kinetics of the deposition of GaAs and In 0.3 Ga 0.7 As on GaAs(001) at growth rates of 0.2 and 0.25 ML/s, respectively. During growth we used a constant As 4 or As 2 flux pressure of 5 x 10 -6 Torr. Clear RA-oscillations were observed during growth with a period that nearly coincides with the growth period for a Ga-As bilayer. RHEED was used as an auxiliary technique in order to obtain a correlation between RHEED and RA oscillations. On the basis of our results, we argue that RAS oscillations are mainly associated to periodic changes in surface atomic structure. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  15. Electronic and optical properties of HEMT heterostructures with δ-Si doped GaAs/AlGaAs quantum rings — quantum well system

    Science.gov (United States)

    Sibirmovsky, Y. D.; Vasil'evskii, I. S.; Vinichenko, A. N.; Zhigunov, D. M.; Eremin, I. S.; Kolentsova, O. S.; Safonov, D. A.; Kargin, N. I.

    2017-11-01

    Samples of δ-Si doped AlGaAs/GaAs/AlGaAs HEMT heterostructures with GaAs quantum rings (QRs) on top of the quantum well (QW) were grown by molecular beam epitaxy and their properties were compared to the reference samples without QRs. The thickness of the QW was 6 - 10 nm for the samples with QRs and 20 nm for the reference samples. Photoluminescence measurements at low temperatures for all samples show at least two distinct lines in addition to the bulk GaAs line. The Hall effect and low temperature magnetotransport measurements at 4 - 320 K show that conductivity with and without illumination decreases significantly with QRs introduction, however the relative photoconductivity increases. Samples with 6 nm QW are insulating, which could be caused by the strong localization of the charge carriers in the QRs.

  16. GaAs detectors with an ultra-thin Schottky contact for spectrometry of charged particles

    Energy Technology Data Exchange (ETDEWEB)

    Chernykh, S.V., E-mail: chsv_84@mail.ru [National University of Science and Technology “MISIS”, Moscow (Russian Federation); Research Institute of Experimental and Theoretical Physics, Almaty (Kazakhstan); Chernykh, A.V. [National University of Science and Technology “MISIS”, Moscow (Russian Federation); Didenko, S.I.; Baryshnikov, F.M. [National University of Science and Technology “MISIS”, Moscow (Russian Federation); Research Institute of Experimental and Theoretical Physics, Almaty (Kazakhstan); Burtebayev, N. [Research Institute of Experimental and Theoretical Physics, Almaty (Kazakhstan); Institute of Nuclear Physics, Almaty (Kazakhstan); Britvich, G.I. [Institute of High Energy Physics, Protvino, Moscow region (Russian Federation); Chubenko, A.P. [Research Institute of Experimental and Theoretical Physics, Almaty (Kazakhstan); P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow (Russian Federation); Guly, V.G.; Glybin, Yu.N. [LLC “SNIIP Plus”, Moscow (Russian Federation); Zholdybayev, T.K.; Burtebayeva, J.T.; Nassurlla, M. [Research Institute of Experimental and Theoretical Physics, Almaty (Kazakhstan); Institute of Nuclear Physics, Almaty (Kazakhstan)

    2017-02-11

    For the first time, samples of particle detectors based on high-purity GaAs epilayers with an active area of 25 and 80 mm{sup 2} and an ultra-thin Pt Schottky barrier were fabricated for use in the spectrometry of charged particles and their operating characteristics were studied. The obtained FWHM of 14.2 (for 25 mm{sup 2} detector) and 15.5 keV (for 80 mm{sup 2} detector) on the 5.499 MeV line of {sup 238}Pu is at the level of silicon spectrometric detectors. It was found that the main component that determines the energy resolution of the detector is a fluctuation in the number of collected electron–hole pairs. This allows us to state that the obtained energy resolution is close to the limit for VPE GaAs. - Highlights: • VPE GaAs particle detectors with an active area of 25 and 80 mm{sup 2} were fabricated. • 120 Å ultra-thin Pt Schottky barrier was used as a rectifying contact. • The obtained FWHM of 14.2 keV ({sup 238}Pu) is at the level of Si spectrometric detectors. • Various components of the total energy resolution were analyzed. • It was shown that obtained energy resolution is close to its limit for VPE GaAs.

  17. Annealing of proton-damaged GaAs and 1/f noise

    NARCIS (Netherlands)

    Chen, X.Y.; Folter, de L.C.

    1997-01-01

    GaAs layers were grown by MBE. The layers were then damaged by 3 MeV proton irradiation and later annealed. We performed Hall effect and low-frequency noise measurements at temperatures between 77 K and 300 K after each step. Several generation - recombination noise components created by proton

  18. Modified energetics and growth kinetics on H-terminated GaAs (110)

    International Nuclear Information System (INIS)

    Galiana, B.; Benedicto, M.; Díez-Merino, L.; Tejedor, P.; Lorbek, S.; Hlawacek, G.; Teichert, C.

    2013-01-01

    Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As 4 , has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å 2 measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As 4 molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed

  19. Enhancement of conductance of GaAs sub-microwires under external stimuli

    Science.gov (United States)

    Qu, Xianlin; Deng, Qingsong; Zheng, Kun

    2018-03-01

    Semiconductors with one dimension on the micro-nanometer scale have many unique physical properties that are remarkably different from those of their bulk counterparts. Moreover, changes in the external field will further modulate the properties of the semiconductor micro-nanomaterials. In this study, we used focused ion beam technology to prepare freestanding ⟨111⟩-oriented GaAs sub-microwires from a GaAs substrate. The effects of laser irradiation and bending or buckling deformation induced by compression on the electrical transport properties of an individual GaAs sub-microwire were studied. The experimental results indicate that both laser irradiation and bending deformation can enhance their electrical transport properties, the laser irradiation resulted in a conductance enhancement of ˜30% compared to the result with no irradiation, and in addition, bending deformation changed the conductance by as much as ˜180% when the average strain was approximately 1%. The corresponding mechanisms are also discussed. This study provides beneficial insight into the fabrication of electronic and optoelectronic devices based on GaAs micro/nano-wires.

  20. Etching of GaAs substrates to create As-rich surface

    Indian Academy of Sciences (India)

    WINTEC

    during the manipulations of the substrate after the chemi- cal etching process. ... using the four techniques described in table 1 and for an. *Author for ... Etching of GaAs substrates to create As-rich surface. 563. Table 1. Treatment procedures used. Treatment. Techniques. 1st stage. 2nd stage. 3rd stage. 4th stage. 1. Treated ...

  1. 1 GHz GaAs Buck Converter for High Power Amplifier Modulation Applications

    NARCIS (Netherlands)

    Busking, E.B.; Hek, A.P. de; Vliet, F.E. van

    2012-01-01

    A fully integrated 1 GHz buck converter output stage, including on-chip inductor and DC output filtering has been realized, in a standard high-voltage breakdown GaAs MMIC technology. This is a significant step forward in designing highspeed power control of supply-modulated HPAs (high power

  2. Effects of surface passivation on twin-free GaAs nanosheets.

    Science.gov (United States)

    Arab, Shermin; Chi, Chun-Yung; Shi, Teng; Wang, Yuda; Dapkus, Daniel P; Jackson, Howard E; Smith, Leigh M; Cronin, Stephen B

    2015-02-24

    Unlike nanowires, GaAs nanosheets exhibit no twin defects, stacking faults, or dislocations even when grown on lattice mismatched substrates. As such, they are excellent candidates for optoelectronic applications, including LEDs and solar cells. We report substantial enhancements in the photoluminescence efficiency and the lifetime of passivated GaAs nanosheets produced using the selected area growth (SAG) method with metal organic chemical vapor deposition (MOCVD). Measurements are performed on individual GaAs nanosheets with and without an AlGaAs passivation layer. Both steady-state photoluminescence and time-resolved photoluminescence spectroscopy are performed to study the optoelectronic performance of these nanostructures. Our results show that AlGaAs passivation of GaAs nanosheets leads to a 30- to 40-fold enhancement in the photoluminescence intensity. The photoluminescence lifetime increases from less than 30 to 300 ps with passivation, indicating an order of magnitude improvement in the minority carrier lifetime. We attribute these enhancements to the reduction of nonradiative recombination due to the compensation of surface states after passivation. The surface recombination velocity decreases from an initial value of 2.5 × 10(5) to 2.7 × 10(4) cm/s with passivation.

  3. Spin-Relaxation Anisotropy in a GaAs Quantum Dot

    NARCIS (Netherlands)

    Scarlino, P.; Kawakami, E.; Stano, P.; Shafiei, M.; Reichl, C.; Wegscheider, W.; Vandersypen, L.M.K.

    2014-01-01

    We report that the electron spin-relaxation time T1 in a GaAs quantum dot with a spin-1/2 ground state has a 180° periodicity in the orientation of the in-plane magnetic field. This periodicity has been predicted for circular dots as being due to the interplay of Rashba and Dresselhaus spin orbit

  4. Spin-Dephasing Anisotropy for Electrons in a Diffusive Quasi-1D GaAs Wire

    NARCIS (Netherlands)

    Liu, J.; Last, T.; Koop, E. J.; Denega, S.; van Wees, B. J.; van der Wal, C. H.

    We present a numerical study of dephasing of electron spin ensembles in a diffusive quasi-one-dimensional GaAs wire due to the D'yakonov-Perel' spin-dephasing mechanism. For widths of the wire below the spin precession length and for equal strength of Rashba and linear Dresselhaus spin-orbit fields

  5. Accelerated GaAs growth through MOVPE for low-cost PV applications

    Science.gov (United States)

    Ubukata, Akinori; Sodabanlu, Hassanet; Watanabe, Kentaroh; Koseki, Shuichi; Yano, Yoshiki; Tabuchi, Toshiya; Sugaya, Takeyoshi; Matsumoto, Koh; Nakano, Yoshiaki; Sugiyama, Masakazu

    2018-05-01

    The high growth rate of epitaxial GaAs was investigated using a novel horizontal metalorganic vapor phase epitaxy (MOVPE) reactor, from the point of view of realizing low-cost photovoltaic (PV) solar cells. The GaAs growth rate exhibited an approximately linear relationship with the amount of trimethylgalium (TMGa) supplied, up to a rate of 90 μm/h. The distribution of growth rate was observed for a two-inch wafer, along the flow direction, and the normalized profile of the distribution was found to be independent of the precursor input, from 20 to 70 μm/h. These tendencies indicated that significant parasitic prereaction did not occur in the gaseous phase, for this range of growth rate. GaAs p-n single-junction solar cells were successfully fabricated at growth rates of 20, 60, and 80 μm/h. The conversion efficiency of the cell grown at 80 μm/h was comparable to that of the 20 μm/h cell, indicating the good quality and properties of GaAs. The epitaxial growth exhibited good uniformity, as evidenced by the uniformity of the cell performance across the wafer, from the center to the edge. The result indicated the potential of high-throughput MOVPE for low-cost production, not only for PV devices but also for other semiconductor applications.

  6. Electric field effect of GaAs monolayer from first principles

    Directory of Open Access Journals (Sweden)

    Jiongyao Wu

    2017-03-01

    Full Text Available Using first-principle calculations, we investigate two-dimensional (2D honeycomb monolayer structures composed of group III-V binary elements. It is found that such compound like GaAs should have a buckled structure which is more stable than graphene-like flat structure. This results a polar system with out-of-plane dipoles arising from the non-planar structure. Here, we optimized GaAs monolayer structure, then calculated the electronic band structure and the change of buckling height under external electric field within density functional theory using generalized gradient approximation method. We found that the band gap would change proportionally with the electric field magnitude. When the spin-orbit coupling (SOC is considered, we revealed fine spin-splitting at different points in the reciprocal space. Furthermore, the valence and conduction bands spin-splitting energies due to SOC at the K point of buckled GaAs monolayers are found to be weakly dependent on the electric field strength. Finally electric field effects on the spin texture and second harmonic generation are discussed. The present work sheds light on the control of physical properties of GaAs monolayer by the applied electric field.

  7. Measurement and model of the infrared two-photon emission spectrum of GaAs.

    Science.gov (United States)

    Hayat, Alex; Ginzburg, Pavel; Orenstein, Meir

    2009-07-10

    Two-photon emission from semiconductors was recently observed, but not fully interpreted. We develop a dressed-state model incorporating intraband scattering-related level broadening, yielding nondivergent emission rates. The spectrum calculations for high carrier concentrations including the time dependence of the screening buildup correspond well to our measured two-photon emission spectrum from GaAs.

  8. Modified energetics and growth kinetics on H-terminated GaAs (110)

    Energy Technology Data Exchange (ETDEWEB)

    Galiana, B. [Instituto de Ciencia de Materiales de Madrid, CSIC, Sor Juana Inés de la Cruz 3, 28049 Madrid (Spain); Departamento de Física, Universidad Carlos III de Madrid, Avenida de la Universidad 30, 28911 Madrid (Spain); Benedicto, M.; Díez-Merino, L.; Tejedor, P. [Instituto de Ciencia de Materiales de Madrid, CSIC, Sor Juana Inés de la Cruz 3, 28049 Madrid (Spain); Lorbek, S.; Hlawacek, G.; Teichert, C. [Institut für Physik, Montanuniversität Leoben, Franz Josef St., 18A-8700 Leoben (Austria)

    2013-10-28

    Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As{sub 4}, has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å{sup 2} measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As{sub 4} molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed.

  9. Promotion effect of monovalent metals (K and Cs) on the GaAs (110) surface oxidation

    International Nuclear Information System (INIS)

    Valeri, S.; Sberveglieri, P.; Angeli, E.

    1987-01-01

    The effect of thin (∼ 1 monolayer) overlayers of low electronegativity metals (Cs and K) on the RT oxidation behaviour of GaAs(110) cleavage surface is studied. This study was with Auger and Photoemission spectroscopies. Attention has been focused on the core-valence-valence and Auger lineshapes on the Ga and As 3d peaks. Presence of the alkali metal enhances the GaAs (110) oxidation rate several orders of magnitude above the clean surface value has been found. The range 0-100 Langmuir is investigated in detail. The oxidation process of the GaAs(110) surface in the presence of both K and Cs overlayer follows a multi-step kinetic and reaches a saturation at exposure lower than 100 Langmuir. Both Ga and As atoms are involved in the oxygen bonding. The metal enhanced semiconductor oxidation is generally reported to be a process involving predominantly the semiconductor surface atoms. However in the Cs - and K - GaAs case, an involvement of the alkali metal atoms too, reflected in the shape modification of their Auger line has been found. The promotion effect of K and Cs is discussed in terms of their low electronegativity and in comparison with the results recently reported in the literature for the other low electronegativity metals

  10. Integration of single-photon sources and detectors on GaAs

    NARCIS (Netherlands)

    Digeronimo, G.E.; Petruzzella, Maurangelo; Birindelli, Simone; Gaudio, Rosalinda; Poor, Sartoon Fattah; van Otten, Frank W.M.; Fiore, Andrea

    2016-01-01

    Quantum photonic integrated circuits (QPICs) on a GaAs platform allow the generation, manipulation, routing, and detection of non-classical states of light, which could pave the way for quantum information processing based on photons. In this article, the prototype of a multi-functional QPIC is

  11. Passively model-locked Nd: YAG laser with a component GaAs

    International Nuclear Information System (INIS)

    Zhang Zhuhong; Qian Liejia; Chen Shaohe; Fan Dianyuan; Mao Hongwei

    1992-01-01

    An all solid-state passively mode-locked Nd: YAG laser with a 400 μm, (100) oriented GaAs component is reported for the first time and model locked pulses with a duration of 16 ps, average energy of 10 μJ were obtained with a probability of 90%

  12. Merging Standard CVD Techniques for GaAs and Si Epitaxial Growth

    NARCIS (Netherlands)

    Sammak, A.; De Boer, W.; Van den Bogaard, A.; Nanver, L.K.

    2010-01-01

    A commercial Chemical Vapor Deposition (CVD) system, the ASMI Epsilon 2000 designed for Si and SiGe epitaxy, has, for the first time, been equipped for the growth of GaAs compounds in a manner that does not exclude the use of the system also for Si-based depositions. With the new system, intrinsic,

  13. Manipulation and analysis of a single dopant atom in GaAs

    NARCIS (Netherlands)

    Wijnheijmer, A.P.

    2011-01-01

    This thesis focuses on the manipulation and analysis of single dopant atoms in GaAs by scanning tunneling microscopy (STM) and spectroscopy (STS) at low temperatures. The observation of ionization rings is one of the key results, showing that we can control the charge state of a single dopant atom

  14. Effects produced in GaAs by MeV ion bombardment

    International Nuclear Information System (INIS)

    Wie, C.R.

    1985-01-01

    The first part of this thesis presents work performed on the ionizing energy beam induced adhesion enhancement of thin (approx.500 A) Au films on GaAs substrates. The ionizing beam, employed in the present thesis, is the MeV ions (i.e., 16 O, 19 F, and 35 Cl), with energies between 1 and 20 MeV. Using the Scratch test for adhesion measurement, and ESCA for chemical analysis of the film substrate interface, the native oxide layer at the interface is shown to play an important role in the adhesion enhancement by the ionizing radiation. A model is discussed that explains the experimental data on the dependence of adhesion enhancement on the energy which was deposited into electronic processes at the interface. The second part of the thesis presents research results on the radiation damage in GaAs crystals produced by MeV ions. Lattice parameter dilatation in the surface layers of the GaAs crystals becomes saturated after a high dose bombardment at room temperature. The strain produced by nuclear collisions is shown to relax partially due to electronic excitation (with a functional dependence on the nuclear and electronic stopping power of bombarding ions. Data on the GaAs and GaP crystals suggest that low temperature recovery stage defects produce major crystal distortion

  15. Role of wave functions in electromagnetism : RAS from GaAs (110)

    NARCIS (Netherlands)

    Wijers, C.M.J.; de Boeij, P.L.

    2001-01-01

    We have calculated the reflectance anisotropy for the GaAs (110) surface using the discrete cellular method. This method extends the range of application of standard discrete dipole calculations by incorporating nonlocal polarizabilitites. The method adds a second quantum mechanical channel of

  16. A new structure for comparing surface passivation materials of GaAs solar cells

    Science.gov (United States)

    Desalvo, Gregory C.; Barnett, Allen M.

    1989-01-01

    The surface recombination velocity (S sub rec) for bare GaAs is typically as high as 10 to the 6th power to 10 to the 7th power cm/sec, which dramatically lowers the efficiency of GaAs solar cells. Early attempts to circumvent this problem by making an ultra thin junction (xj less than .1 micron) proved unsuccessful when compared to lowering S sub rec by surface passivation. Present day GaAs solar cells use an GaAlAs window layer to passivate the top surface. The advantages of GaAlAs in surface passivation are its high bandgap energy and lattice matching to GaAs. Although GaAlAs is successful in reducing the surface recombination velocity, it has other inherent problems of chemical instability (Al readily oxidizes) and ohmic contact formation. The search for new, more stable window layer materials requires a means to compare their surface passivation ability. Therefore, a device structure is needed to easily test the performance of different passivating candidates. Such a test device is described.

  17. Capacitance-voltage characteristics of GaAs ion-implanted structures

    Directory of Open Access Journals (Sweden)

    Privalov E. N.

    2008-08-01

    Full Text Available A noniterative numerical method is proposed to calculate the barrier capacitance of GaAs ion-implanted structures as a function of the Schottky barrier bias. The features of the low- and high-frequency capacitance-voltage characteristics of these structures which are due to the presence of deep traps are elucidated.

  18. A 2.5 gb/s GaAs ATM Mux Demux ASIC

    DEFF Research Database (Denmark)

    Madsen, Jens Kargaard; Lassen, Peter Stuhr

    1995-01-01

    This paper describes the design and implementation of a high speed GaAs ATM Mux Demur ASIC (AMDA) which is the key element in a high speed ATM Add-Drop unit. This unit is used in a new distributed ATM multiplexing-demultiplexing architecture for broadband switching systems. The Add-Drop unit...

  19. The role of proximity caps during the annealing of UV-ozone oxidized GaAs

    International Nuclear Information System (INIS)

    Ghosh, S. C.; Biesinger, M. C.; LaPierre, R. R.; Kruse, P.

    2007-01-01

    This study provides a deeper insight into the chemistry and physics of the common engineering practice of using a proximity cap, while annealing compound semiconductors such as GaAs. We have studied the cases of a GaAs proximity cap, a Si proximity cap, and no proximity cap. Using x-ray photoelectron spectroscopy, it has been found that annealing increases the gallium to arsenic ratio in the oxide layer in all cases. During the annealing of UV-ozone oxidized GaAs, it has been observed that GaAs proximity caps also serve as a sacrificial layer to accelerate the desorption of oxide species. In all cases surface deterioration due to pit formation has been observed, and the depth of pits is found to depend on the effective role played by the capping material. Energy dispersive x-ray analysis provides additional evidence that pits mainly consist of elemental As and gallium oxide, with most of the elemental As situated at the pit-substrate interface. Deposition of a thin layer of gold and subsequent annealing to 500 deg. C for 300 s under different capping conditions shows the use of a proximate cap to be practically insignificant in annealing Au deposited films

  20. Heat load of a GaAs photocathode in an SRF electron gun

    International Nuclear Information System (INIS)

    Wang Erdong; Zhao Kui; Jorg Kewisch; Ilan Ben-Zvi; Andrew Burrill; Trivini Rao; Wu Qiong; Animesh Jain; Ramesh Gupta; Doug Holmes

    2011-01-01

    A great deal of effort has been made over the last decades to develop a better polarized electron source for high energy physics. Several laboratories operate DC guns with a gallium arsenide photocathode, which yield a highly polarized electron beam. However, the beam's emittance might well be improved by using a superconducting radio frequency (SRF) electron gun, which delivers beams of a higher brightness than that from DC guns because the field gradient at the cathode is higher. SRF guns with metal and CsTe cathodes have been tested successfully. To produce polarized electrons, a Gallium-Arsenide photo-cathode must be used: an experiment to do so in a superconducting RF gun is under way at BNL. Since a bulk gallium arsenide (GaAs) photocathode is normal conducting, a problem arises from the heat load stemming from the cathode. We present our measurements of the electrical resistance of GaAs at cryogenic temperatures, a prediction of the heat load and verification by measuring the quality factor of the gun with and without the cathode at 2 K. We simulate heat generation and flow from the GaAs cathode using the ANSYS program. By following the findings with the heat load model, we designed and fabricated a new cathode holder (plug) to decrease the heat load from GaAs. (authors)

  1. GaAs Wideband Low Noise Amplifier Design for Breast Cancer Detection System

    DEFF Research Database (Denmark)

    Yan, Lei; Krozer, Viktor; Delcourt, Sebastien

    2009-01-01

    Modern wideband systems require low-noise receivers with bandwidth approaching 10 GHz. This paper presents ultra-wideband stable low-noise amplifier MMIC with cascode and source follower buffer configuration using GaAs technology. Source degeneration, gate and shunt peaking inductors are used...

  2. Energy Band Structure Studies Of Zinc-Blende GaAs and InAs ...

    African Journals Online (AJOL)

    A self-consistent calculation of the structural and electronic properties of zinc blende GaAs and InAs has been carried out. The calculations were done using the full potential-linearized augmented plane wave (FPLAPW) method within the density functional theory (DFT). The exchange-correlation energy used is the ...

  3. Optical characterization of MOVPE grown δ-InAs layers in GaAs

    Czech Academy of Sciences Publication Activity Database

    Hazdra, P.; Voves, J.; Hulicius, Eduard; Pangrác, Jiří

    2005-01-01

    Roč. 2, č. 4 (2005), s. 1319-1324 ISSN 1610-1634 R&D Projects: GA AV ČR(CZ) IAA1010318; GA MŠk(CZ) LC510 Institutional research plan: CEZ:AV0Z10100521 Keywords : δ-layer * MOVPE * GaAs * photoluminescence * photocurrent * photoreflectance Subject RIV: BM - Solid Matter Physics ; Magnetism

  4. X-ray structure amplitudes for GaAs and InP

    International Nuclear Information System (INIS)

    Pietsch, U.

    1985-01-01

    The structure amplitudes of GaAs and InP are calculated taking into account the nonspherical parts of the valence electron density by means of a static bond charge model. The best known temperature factors and dispersion coefficients are employed. The calculated structure amplitudes should help determining exactly the shape of X-ray diffraction patterns. (author)

  5. Wideband Monolithic Microwave Integrated Circuit Frequency Converters with GaAs mHEMT Technology

    DEFF Research Database (Denmark)

    Krozer, Viktor; Johansen, Tom Keinicke; Djurhuus, Torsten

    2005-01-01

    We present monolithic microwave integrated circuit (MMIC) frequency converter, which can be used for up and down conversion, due to the large RF and IF port bandwidth. The MMIC converters are based on commercially available GaAs mHEMT technology and are comprised of a Gilbert mixer cell core...

  6. Conversion Matrix Analysis of GaAs HEMT Active Gilbert Cell Mixers

    DEFF Research Database (Denmark)

    Jiang, Chenhui; Johansen, Tom Keinicke; Krozer, Viktor

    2006-01-01

    In this paper, the nonlinear model of the GaAs HEMT active Gilbert cell mixer is investigated. Based on the model, the conversion gain expression of active Gilbert cell mixers is derived theoretically by using conversion matrix analysis method. The expression is verified by harmonic balance simul...

  7. Antisites and anisotropic diffusion in GaAs and GaSb

    KAUST Repository

    Tahini, H. A.; Bracht, H.; Chroneos, Alexander; Grimes, R. W.; Murphy, S. T.; Schwingenschlö gl, Udo

    2013-01-01

    The significant diffusion of Ga under Ga-rich conditions in GaAs and GaSb is counter intuitive as the concentration of Ga vacancies should be depressed although Ga vacancies are necessary to interpret the experimental evidence for Ga transport

  8. Photon counting microstrip X-ray detectors with GaAs sensors

    Science.gov (United States)

    Ruat, M.; Andrä, M.; Bergamaschi, A.; Barten, R.; Brückner, M.; Dinapoli, R.; Fröjdh, E.; Greiffenberg, D.; Lopez-Cuenca, C.; Lozinskaya, A. D.; Mezza, D.; Mozzanica, A.; Novikov, V. A.; Ramilli, M.; Redford, S.; Ruder, C.; Schmitt, B.; Shi, X.; Thattil, D.; Tinti, G.; Tolbanov, O. P.; Tyazhev, A.; Vetter, S.; Zarubin, A. N.; Zhang, J.

    2018-01-01

    High-Z sensors are increasingly used to overcome the poor efficiency of Si sensors above 15 keV, and further extend the energy range of synchrotron and FEL experiments. Detector-grade GaAs sensors of 500 μm thickness offer 98% absorption efficiency at 30 keV and 50% at 50 keV . In this work we assess the usability of GaAs sensors in combination with the MYTHEN photon-counting microstrip readout chip developed at PSI. Different strip length and pitch are compared, and the detector performance is evaluated in regard of the sensor material properties. Despite increased leakage current and noise, photon-counting strips mounted with GaAs sensors can be used with photons of energy as low as 5 keV, and exhibit excellent linearity with energy. The charge sharing is doubled as compared to silicon strips, due to the high diffusion coefficient of electrons in GaAs.

  9. Transient four-wave mixing in T-shaped GaAs quantum wires

    DEFF Research Database (Denmark)

    Langbein, Wolfgang Werner; Gislason, Hannes; Hvam, Jørn Märcher

    1999-01-01

    The binding energy of excitons and biexcitons and the exciton dephasing in T-shaped GaAs quantum wires is investigated by transient four-wave mixing. The T-shaped structure is fabricated by cleaved-edge overgrowth, and its geometry is engineered to optimize the one-dimensional confinement. In thi...

  10. Spin-polarized tunneling with GaAs tips in scanning tunneling microscopy

    NARCIS (Netherlands)

    Prins, M.W.J.; Jansen, R.; Kempen, van H.

    1996-01-01

    We describe a model as well as experiments on spin-polarized tunneling with the aid of optical spin orientation. This involves tunnel junctions between a magnetic material and gallium arsenide (GaAs), where the latter is optically excited with circularly polarized light in order to generate

  11. Response of GaAs charge storage devices to transient ionizing radiation

    Science.gov (United States)

    Hetherington, D. L.; Klem, J. F.; Hughes, R. C.; Weaver, H. T.

    Charge storage devices in which non-equilibrium depletion regions represent stored charge are sensitive to ionizing radiation. This results since the radiation generates electron-hole pairs that neutralize excess ionized dopant charge. Silicon structures, such as dynamic RAM or CCD cells are particularly sensitive to radiation since carrier diffusion lengths in this material are often much longer than the depletion width, allowing collection of significant quantities of charge from quasi-neutral sections of the device. For GaAs the situation is somewhat different in that minority carrier diffusion lengths are shorter than in silicon, and although mobilities are higher, we expect a reduction of radiation sensitivity as suggested by observations of reduced quantum efficiency in GaAs solar cells. Dynamic memory cells in GaAs have potential increased retention times. In this paper, we report the response of a novel GaAs dynamic memory element to transient ionizing radiation. The charge readout technique is nondestructive over a reasonable applied voltage range and is more sensitive to stored charge than a simple capacitor.

  12. Temperature and 8 MeV electron irradiation effects on GaAs solar cells

    Indian Academy of Sciences (India)

    GaAs solar cells hold the record for the highest single band-gap cell efficiency. Successful application of these cells in advanced space-borne systems demand characterization of cell properties like dark current under different ambient conditions and the stability of the cells against particle irradiation in space. In this paper ...

  13. Twins and strain relaxation in zinc-blende GaAs nanowires grown on silicon

    Energy Technology Data Exchange (ETDEWEB)

    Piñero, J.C., E-mail: josecarlos.pinero@uca.es [Dpto. Ciencias de los Materiales, Universidad de Cádiz, 11510, Puerto Real, Cádiz (Spain); Araújo, D.; Pastore, C.E.; Gutierrez, M. [Dpto. Ciencias de los Materiales, Universidad de Cádiz, 11510, Puerto Real, Cádiz (Spain); Frigeri, C. [Istituto CNR-IMEM Parco Area delle Scienze 37/A, Fontanini, 43010, Parma (Italy); Benali, A.; Lelièvre, J.F.; Gendry, M. [INL-Institut des Nanotechnologies de Lyon, UMR 5270 Ecole Centrale de Lyon 36, Avenue Guy de Collongue, 69134, Ecully Cedex (France)

    2017-02-15

    Highlights: • A TEM-HREM study of GaAs nanowires, growth over Si, is presented. • Misfit dislocations are detected in the Si/GaAs magma interface. • The study demonstrates strain relaxation through twin formation in some nanowires. - Abstract: To integrate materials with large lattice mismatch as GaAs on silicon (Si) substrate, one possible approach, to improve the GaAs crystalline quality, is to use nanowires (NWs) technology. In the present contribution, NWs are grown on <111> oriented Si substrates by molecular beam epitaxy (MBE) using vapor-liquid-solid (VLS) method. Transmission electron microscopy (TEM) analyses show that NWs are mainly grown alternating wurtzite and zinc blend (ZB) phases, and only few are purely ZB. On the latter, High Resolution Electron Microscopy (HREM) evidences the presence of twins near the surface of the NW showing limited concordance with the calculations of Yuan (2013) [1], where {111} twin planes in a <111>-oriented GaAs NW attain attractive interactions mediated by surface strain. In addition, such twins allow slight strain relaxation and are probably induced by the local huge elastic strain observed by HREM in the lattice between the twin and the surface. The latter is attributed to some slight bending of the NW as shown by the inversion of the strain from one side to the other side of the NW.

  14. The Development of a GaAs MMIC Reliability and Space Qualification Guide

    Science.gov (United States)

    Ponchak, G.; Kayali, S.; Huang, H-C.

    1994-01-01

    This paper discusses the need for a space qualification guide, provides a brief description of some common GaAs failure mechanisms, the approach that the NASA MMIC Reliability Assurance Program is following to develop the guide, and the status of the program.

  15. GaAs circuit restructuring by multi-level laser-direct-written tungsten process

    International Nuclear Information System (INIS)

    Black, J.G.; Doran, S.P.; Rothschild, M.; Sedlacek, J.H.C.; Ehrlich, D.J.

    1987-01-01

    Laser-direct-writing processes are employed to fabricate a GaAs digital integrated circuit. The lithography-free techniques deposit and etch conductors and resistors, and remove insulating layers, thus enabling multilevel interconnections. These combined direct-write processes provide the flexibility of clip-lead prototyping on a micrometer scale

  16. Sanctions for doping in sport

    Directory of Open Access Journals (Sweden)

    Mandarić Sanja

    2014-01-01

    Full Text Available Top-level sport imposes new and more demanding physical and psychological pressures, and the desire for competing, winning and selfassertion leads athletes into temptation to use prohibited substances in order to achieve the best possible results. Regardless of the fact that the adverse consequences of prohibited substances are well-known, prestige and the need to dominate sports arenas have led to their use in sports. Doping is one of the biggest issues in sport today, and the fight against it is a strategic objective on both global and national levels. World Anti-Doping Agency, the International Olympic Committee, international sports federations, national anti-doping agencies, national sports federations, as well as governments and their repressive apparatuses are all involved in the fight against doping in sport. This paper points to a different etymology and phenomenology of doping, the beginnings of doping in sport, sports doping scandals as well as the most important international instruments regulating this issue. Also, there is a special reference in this paper to the criminal and misdemeanor sanctions for doping in sport. In Serbia doping in sport is prohibited by the Law on Prevention of Doping in Sports which came into force in 2005 and which prescribes the measures and activities aimed at prevention of doping in sport. In this context, the law provides for the following three criminal offenses: use of doping substances, facilitating the use of doping substances, and unauthorized production and putting on traffic of doping substances. In addition, aiming at curbing the abuse of doping this law also provides for two violations. More frequent and repetitive doping scandals indicate that doping despite long-standing sanctions is still present in sports, which suggests that sanctions alone have not given satisfactory results so far.

  17. Nonlinear THz spectroscopy on n-type GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Gaal, Peter

    2008-06-23

    In this thesis, the ultrafast dynamics of conduction band electrons in semiconductors are investigated by nonlinear terahertz (THz) spectroscopy. In particular, n-doped gallium arsenide samples with doping concentrations in the range of 10{sup 16} cm{sup -3} to 10{sup 17} cm{sup -3} are studied. A novel source for the generation of intense THz radiation is developed which yields single-cycle THz transients with field amplitudes of more then 400 kV/cm. The THz source uses ultrashort optical laser pulses provided by a Ti:sapphire oscillator. In addition, a two-color THz-pump mid-infrared-probe setup is implemented, which allows for two-dimensional time-resolved experiments in the far-infrared wavelength range. Field ionization of neutral shallow donors in gallium arsenide with intense, ultrashort THz pulses and subsequent coherent radiative recombination of electrons to impurity ground states is observed at room temperature. The superradiant decay of the nonlinear polarization results in the emission of a coherent signal with picosecond lifetimes. Such nonlinear signals, which exhibit a lifetime ten times longer than in the linear regime are observed for the first time. At low temperatures and THz field strengths below 5 kV/cm, Rabi flopping on shallow donor transitions is demonstrated. For the first time, the polar electron-LO phonon interaction is directly measured in the quantum kinetic transport regime. Quasi-instantaneous acceleration of conduction band electrons in the polar gallium arsenide lattice by the electric field of intense THz pulses and subsequent probing of the mid-infrared transmission reveals a modulation of the transmission along the THz-mid-infrared delay coordinate with the frequency of the LO phonon. These modulations directly display the relative phase between the electron motion and its surrounding virtual phonon cloud. Quantum kinetic model calculations fully account for the observed phenomena. (orig.)

  18. The influence of γ-irradiation cobalt 60 on electrical properties of undoped GaAs treated with hydrogen plasma

    International Nuclear Information System (INIS)

    Korshunov, F.P.; Kurilovich, N.F.; Prokhorenko, T.A.; Bumaj, Yu.A.; Ul'yashin, A.G.

    1999-01-01

    The influence of exposition to a hydrogen plasma (hydrogenation) on the electrical properties alteration under gamma-irradiation in bulk GaAs have been investigated. It is shown that crystals hydrogenation before irradiation leads to particularly passivation of electrically active defects that are responsible for carriers scattering and removing processes in irradiated crystals. Radiation defects thermostability in hydrogenated GaAs crystals is lower than that in non hydrogenated ones. The energetic levels position of main defect that effects on electrical properties alteration after irradiation in GaAs crystals was detected. It is equal to E D =E C -0,125±0,0005 eV

  19. Solvent-mediated self-assembly of hexadecanethiol on GaAs (0 0 1)

    International Nuclear Information System (INIS)

    Huang, Xiaohuan; Dubowski, Jan J.

    2014-01-01

    Graphical abstract: - Highlights: • Outstanding quality hexadecanethiol self-assembled monolayers (HDT SAM) produced on GaAs (0 0 1) due to the mediated role of water in an alcoholic environment. • HDT SAM formed in chloroform exhibit excellent electronic passivation properties in contrast to their structural characteristics. • Low dielectric constant solvents do not necessary provide conditions advantageous for the formation of high quality alkanethiol SAM. • Photoluminescence emitting materials allow to investigate the mechanisms of both electronic and chemical passivation and, thus, they are an excellent platform for studying the mechanisms of SAM formation on solid substrates. - Abstract: We have investigated the influence of solvents on the quality of hexadecanethiol (HDT) self-assembled monolayers (SAM) formed on GaAs (0 0 1) in chloroform, ethanol and ethanol/water 1:1 characterized by their increasing dielectric constants from 4.8 (chloroform) to 24.5 (ethanol) and water (80.1). Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) data show that the incubation in ethanol/water 1:1 solution creates conditions favouring inter-molecular interaction leading to the formation of an outstanding quality HDT SAM on GaAs (0 0 1). Incubation in low-dielectric constant solvents is not offering advantageous conditions for growing HDT SAM on GaAs. The chloroform environment, while weakening the thiol–thiol interaction, induces the oxidation of the GaAs surface and, in particular, formation of Ga 2 O 3 . This reduces the concentration of surface defects responsible for non-radiative recombination and leads to an enhanced photoluminescence emission, despite the fact that HDT SAM formed in chloroform are highly disordered, exhibiting the worst chemical passivation among the investigated samples

  20. Surface science analysis of GaAs photocathodes following sustained electron beam delivery

    Directory of Open Access Journals (Sweden)

    V. Shutthanandan

    2012-06-01

    Full Text Available Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power free electron lasers (FEL. Photocathode quantum efficiency degradation is due to residual gases in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes, which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include helium ion microscopy, Rutherford backscattering spectrometry (RBS, atomic force microscopy, and secondary ion mass spectrometry (SIMS. In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the continuous electron beam accelerator facility (CEBAF photoinjector and one unused, were also analyzed using transmission electron microscopy (TEM and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but show evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements, the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.

  1. Structural and electronic properties of isovalent boron atoms in GaAs

    Science.gov (United States)

    Krammel, C. M.; Nattermann, L.; Sterzer, E.; Volz, K.; Koenraad, P. M.

    2018-04-01

    Boron containing GaAs, which is grown by metal organic vapour phase epitaxy, is studied at the atomic level by cross-sectional scanning tunneling microscopy (X-STM) and spectroscopy (STS). In topographic X-STM images, three classes of B related features are identified, which are attributed to individual B atoms on substitutional Ga sites down to the second layer below the natural {110} cleavage planes. The X-STM contrast of B atoms below the surface reflects primarily the structural modification of the GaAs matrix by the small B atoms. However, B atoms in the cleavage plane have in contrast to conventional isovalent impurities, such as Al and In, a strong influence on the local electronic structure similar to donors or acceptors. STS measurements show that B in the GaAs {110} surfaces gives rise to a localized state short below the conduction band (CB) edge while in bulk GaAs, the B impurity state is resonant with the CB. The analysis of BxGa1-xAs/GaAs quantum wells reveals a good crystal quality and shows that the incorporation of B atoms in GaAs can be controlled along the [001] growth direction at the atomic level. Surprisingly, the formation of the first and fourth nearest neighbor B pairs, which are oriented along the directions, is strongly suppressed at a B concentration of 1% while the third nearest neighbor B pairs are found more than twice as often than expected for a completely spatially random pattern.

  2. Theoretical investigation of the heavily-doped semiconductor aspect of ultra-dilute GaAsN

    Science.gov (United States)

    Sukpitak, Jessada; Sa-yakanit, Virulh

    2015-12-01

    The model of GaAs1- y N y ( y = 0.001) as a heavily-doped semiconductor in the ultra-dilute region is attentively examined. The model enables GaAsN to be viewed as a disordered assembly of three-dimensional quantum dots (potential wells) caused by random potential fluctuations from nitrogen pairs in the system. Consequently, Feynman's path-integration technique is applied in order to quantify the density of states (DOS) in the vicinity of the conduction band edge. The obtained DOS tail, even though overestimated, still clearly shows a much shorter tail than that the experimental result does. This shows that the heavily-doped semiconductor viewpoint is not proper for GaAsN, not even in the ultra-dilute region. Furthermore, this also suggests that the impurity wave function overlap is not a basic mechanism of band gap reduction.

  3. Trap suppression by isoelectronic In or Sb doping in Si-doped n-GaAs grown by molecular-beam epitaxy

    International Nuclear Information System (INIS)

    Li, A.Z.; Kim, H.K.; Jeong, J.C.; Wong, D.; Schlesinger, T.E.; Milnes, A.G.

    1988-01-01

    The effects of isoelectronic doping of GaAs by In or Sb on the electron deep levels in n-GaAs grown by molecular-beam epitaxy have been investigated in the growth temperature range 500--600 0 C for Si doping levels of 4--7 x 10 16 cm -3 and As-stabilized conditions. The two dominant traps M3 and M6 are drastically reduced in concentration by up to three orders of magnitude for M3 (from 10 15 cm -3 down to 12 cm -3 ) and two and a half orders of magnitude for M6 by introducing 0.2--1 at.% In or Sb and increasing growth temperatures from 500 to 550 0 C. The trap concentrations of M3 and M6 were also significantly reduced by increasing the growth temperature to 600 0 C without In or Sb doping and by decreasing the growth rate from 1.0 to 0.3 μm/h. The incorporation coefficients of In and Sb have been measured and are found to decrease with increasing growth temperature. The growths with high M3 and M6 trap densities are shown to have short minority-carrier diffusion lengths. Indium isoelectronic doping, which is presumed to take place on a gallium sublattice site, and Sb doping, which is expected to take place on an arsenic sublattice site, appear to have rather similar effects in suppressing the concentration of the M3 and M6 electron traps. This suggest that both of these traps are in some way related to (V/sub As/V/sub Ga/) complexes or (V/sub As/XV/sub Ga/) complexes where X is different for M3 and M6 and might be interstitial or impurity related

  4. Structural and morphological characterizations of ZnO films grown on GaAs substrates by MOCVD

    Energy Technology Data Exchange (ETDEWEB)

    Agouram, S.; Zuniga Perez, J.; Munoz-Sanjose, V. [Universitat de Valencia, Departamento de Fisica Aplicada y Electromagnetismo, Burjassot (Spain)

    2007-07-15

    ZnO films were grown on GaAs(100), GaAs(111)A and GaAs(111)B substrates by metal organic chemical vapour deposition (MOCVD). Diethylzinc (DEZn) and tertiarybutanol (t-butanol) were used as Zn and O precursors, respectively. The influence of the growth temperature and GaAs substrate orientation on the crystalline orientation and morphology of the ZnO grown films has been analysed. Crystallinity of grown films was studied by X-ray diffraction (XRD); thickness and morphology of ZnO films were investigated by scanning electron microscopy (SEM). SEM results reveal significant differences between morphologies depending on growth temperature but not significant differences were detected on the texture of grown films. (orig.)

  5. High Pressure Spectroscopic Studies of AlGaAs, GaAs, and II-VI Semiconductors and Heterostructures

    National Research Council Canada - National Science Library

    Chandrasekhar, Meera

    1997-01-01

    We have conducted four studies on three different but related materials. The first is a temperature study of a pseudomorphic epilayer of ZnSe on GaAs, where we measured the temperature dependence of the interlayer biaxial strain...

  6. GaAs monolayer: Excellent SHG responses and semi metallic to metallic transition modulated by vacancy effect

    Science.gov (United States)

    Rozahun, Ilmira; Bahti, Tohtiaji; He, Guijie; Ghupur, Yasenjan; Ablat, Abduleziz; Mamat, Mamatrishat

    2018-05-01

    Monolayer materials are considered as a promising candidate for novel applications due to their attractive magnetic, electronic and optical properties. Investigation on nonlinear optical (NLO) properties and effect of vacancy on monolayer materials are vital to property modulations of monolayers and extending their applications. In this work, with the aid of first-principles calculations, the crystal structure, electronic, magnetic, and optical properties of GaAs monolayers with the vacancy were investigated. The result shows gallium arsenic (GaAs) monolayer produces a strong second harmonic generation (SHG) response. Meanwhile, the vacancy strongly affects structural, electronic, magnetic and optical properties of GaAs monolayers. Furthermore, arsenic vacancy (VAs) brings semi metallic to metallic transition, while gallium vacancy (VGa) causes nonmagnetic to magnetic conversion. Our result reveals that GaAs monolayer possesses application potentials in Nano-amplifying modulator and Nano-optoelectronic devices, and may provide useful guidance in designing new generation of Nano-electronic devices.

  7. Influence of implantation conditions of He+ ions on the structure of a damaged layer in GaAs(001)

    International Nuclear Information System (INIS)

    Shcherbachev, Kirill; Bailey, Melanie J.

    2011-01-01

    An investigation into the influence of implantation conditions (dose, energy, and target temperature) of He + ions on the damage structure of GaAs (100) substrates was performed by HRXRD, scanning electron microscopy, and Nomarski microscopy. Blistering is shown to become apparent as characteristic features of isolines in RSMs. We propose that the formation of the defects yielding a characteristic XRDS is defined by the behavior of implanted atoms in the GaAs matrix, depending on two competing processes: (1) formation of the gas-filled bubbles; (2) diffusion of the He atoms from the bubbles toward the surface and deep into the GaAs substrate. We conclude that the gas-filled bubbles change the structure of the irradiated layer, resulting in the formation of strained crystalline areas of the GaAs matrix. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  8. Cathodoluminescence studies of anomalous ion implantation defect introduction in lightly and heavily doped liquid phase epitaxial GaAs:Sn

    International Nuclear Information System (INIS)

    Norris, C.B.; Barnes, C.E.

    1980-01-01

    The anomalous postrange defect introduction produced by shallow ion implantation in GaAs has been investigated in Sn-doped liquid phase epitaxial (LPE) material using depth-resolved cathodoluminescence in conjunction with layer removal by chemical etching. 100-keV Ne + or 200-keV Zn + ions were implanted into lightly or heavily Sn-doped LPE layers at temperatures between 80 and 300 K. All implantations were subsequently annealed at 300 K. Although the projected ion ranges for the implants were on the order of 1000 A, significant postrange damage was observed at far greater depths. At depths up to several microns, the damage introduction produced severe nonradiative recombination but simultaneously caused an apparent increase in the concentration of incumbent luminescence centers responsible for an extrinsic band near 1.39 eV. A weak damage-related band near 1.2 eV could also be seen in one instance. At depths of 5--30 μm, the postrange damage had the opposite effect of annihilating incumbent 1.39-eV luminescence centers. The efficiency of the damage introduction has a complicated temperature dependence which is significantly different for the ion/substrate combinations investigated. However, no conditions were found for which the damage introduction could be inhibited. While our measurements are the most extensive to date concerning the anomalous ion implant damage introduction in GaAs, the detailed mechanisms responsible for this effect still remain obscure owing in part to the limited understanding of defects in GaAs

  9. Kramers-Kronig Relations in Representation of Modulation Polarimetry by an Example of the Transmission Spectra of GaAs Crystal

    Science.gov (United States)

    Matyash, I. E.; Minailova, I. A.; Mishchuk, O. N.; Serdega, B. K.

    2017-12-01

    The increments of the real and imaginary components of the complex refractive index Δ N = Δ n- iΔ k of a lightly doped GaAs crystal with a donor concentration of 1016 cm-3 have been measured using modulation polarimetry. It is shown that, within this representation, the birefringence and dichroism spectra (Δ n(ω) and Δ k(ω), respectively) obtained in the transparency window of a sample subjected to probe strain are derivatives of the corresponding functions: Δ n(ω) ≈ dn/ dω and Δ k(ω) ≈ dk/ dω. The experimental characteristics and primary dependences n(ω) and k(ω) derived from them by graphical integration are in agreement with the results of other researchers and measurements carried out by independent methods. The results obtained are compared (taking into account the integral (Kramers-Kronig) relations) with the resonance parameters: amplitude and phase in the Drude-Lorenz model. Agreement between the experimental characteristics and theoretical model predictions can be obtained by choosing an appropriate value of resonance damping parameter.

  10. Direct Growth of High-Quality InP Layers on GaAs Substrates by MOCVD

    Directory of Open Access Journals (Sweden)

    K. F. Yarn

    2003-01-01

    group V partial pressure, growth rate and V/III ratios. A mirror-like, uniform surface and high crystal quality of the metamorphic buffer layer directly grown on a GaAs substrate can be achieved. Finally, to investigate the performance of the metamorphic microwave devices, we also fabricate the InAlAs/InGaAs metamorphic HEMT on GaAs substrates.

  11. Mass and energy dispersive recoil spectrometry of GaAs structures

    International Nuclear Information System (INIS)

    Hult, M.

    1994-01-01

    Mass and energy dispersive Recoil Spectrometry (RS) using heavy ions at energies of about 0.2Α-0.8Α MeV has attracted much interest recently due to its potential for separately and unambiguously generating information on isotopic depth distributions. The principal advantages of mass and energy dispersive RS are that both light and heavy elements can be separately studied simultaneously and problems caused by chemical matrix effects are avoided since the technique is based on high energy nucleus-nucleus scattering. In order to elucidate reactions taking place in various GaAs structures, Time of flight-Energy (ToF-E) RS was developed to allow Ga and As to be studied separately down to depths of about 500-800 nm with a depth resolution of about 16 nm at the surface. This was shown in a study of an Al x Ga 1-x As quantum-well structure. The benefits of using ToF-E RS on GaAs structures were further demonstrated in studies of Co/GaAs and CoSi 2 /GaAs reactions, as well as in a study of the composition of MOCVD grown Al x Ga 1-x As. Most recoil measurements employed 127 I at energies of about 50-90 MeV as projectiles. The recoil detector telescope consisted of a silicon energy detector and two carbon foil time pick-off detectors separated by a variable flight length of 213.5-961 mm. The reactions taking place between various thin films and GaAs were also studied using complementary techniques such as XRD, XPS and SEM. Co was found to react extensively with GaAs, already at about 300 degrees C, making it unsuitable as a contact material. Thin films of Co and Si were found to react extensively with each other and to form CoSi 2 at 500 degrees C and above. CoSi 2 , a low resistivity silicide, turned out to be stable on GaAs, at least up to 700 degrees C. Considerable grain growth could cause problems, however, in the use of CoSi 2 -contacts. 112 refs, figs, tabs

  12. Electrical characterisation of p-doped distributed Bragg reflectors in electrically pumped GaInNAs VCSOAs for 1.3 {mu}m operation

    Energy Technology Data Exchange (ETDEWEB)

    Chaqmaqchee, F.A.I. [University of Essex, School of Computer Science and Electronic Engineering Colchester, CO43SQ (United Kingdom); Mazzucato, S., E-mail: smazzu@essex.ac.uk [University of Essex, School of Computer Science and Electronic Engineering Colchester, CO43SQ (United Kingdom); Sun, Y.; Balkan, N. [University of Essex, School of Computer Science and Electronic Engineering Colchester, CO43SQ (United Kingdom); Tiras, E. [Anadolu University, Faculty of Science, Physics Department, Yunus Emre Campus 26470, Eskisehir (Turkey); Hugues, M.; Hopkinson, M. [University of Sheffield, Electronic and Electrical Engineering Department, S1 3JD (United Kingdom)

    2012-06-05

    Highlights: Black-Right-Pointing-Pointer We electrically characterised two p-type doped DBRs for 1.3 {mu}m VCSOA applications. Black-Right-Pointing-Pointer Abrupt and graded structures were designed and investigated. Black-Right-Pointing-Pointer Longitudinal and vertical transports were measured as function of temperature. Black-Right-Pointing-Pointer Low series resistivity achieved using the interface composition grading technique. Black-Right-Pointing-Pointer Theoretical model confirmed the obtained results. - Abstract: The high resistivity that is encountered in p-type DBRs is an important problem in vertical cavity surface emitting lasers and optical amplifiers (VCSELs and VCSOAs). This is because the formation of potential barriers at the interfaces between layers of high and low refractive index inhibits the carrier flow, thus increasing the DBR series resistance. In this work, the electrical characteristics of two p-type doped DBR structures grown on undoped and p-type doped GaAs substrates have been investigated. The DBRs are designed for VCSOAs operating at 1.3 {mu}m and consist of 14-periods of alternating GaAs and Al{sub 0.9}Ga{sub 0.1}As in the first sample and 14-periods of GaAs and Al{sub 0.3}Ga{sub 0.7}As/Al{sub 0.9}Ga{sub 0.1}As in the second one. For the longitudinal transport sample, Hall mobility and sheet carrier density were measured in the temperature range from 77 to 300 K. In the vertical transport sample, current-voltage (I-V) measurements across the DBR layers were carried out at different temperatures in the range between 15 and 300 K. We achieved resistivity reduction in our samples by using an interface composition grading technique aimed at improving the VCSOA characteristics.

  13. Novel anti-reflection technology for GaAs single-junction solar cells using surface patterning and Au nanoparticles.

    Science.gov (United States)

    Kim, Youngjo; Lam, Nguyen Dinh; Kim, Kangho; Kim, Sangin; Rotermund, Fabian; Lim, Hanjo; Lee, Jaejin

    2012-07-01

    Single-junction GaAs solar cell structures were grown by low-pressure MOCVD on GaAs (100) substrates. Micro-rod arrays with diameters of 2 microm, 5 microm, and 10 microm were fabricated on the surfaces of the GaAs solar cells via photolithography and wet chemical etching. The patterned surfaces were coated with Au nanoparticles using an Au colloidal solution. Characteristics of the GaAs solar cells with and without the micro-rod arrays and Au nanoparticles were investigated. The short-circuit current density of the GaAs solar cell with 2 microm rod arrays and Au nanoparticles increased up to 34.9% compared to that of the reference cell without micro-rod arrays and Au nanoparticles. The conversion efficiency of the GaAs solar cell that was coated with Au nanoparticles on the patterned surface with micro-rod arrays can be improved from 14.1% to 19.9% under 1 sun AM 1.5G illumination. These results show that micro-rod arrays and Au nanoparticle coating can be applied together in surface patterning to achieve a novel cost-effective anti-reflection technology.

  14. Superconducting NbN single-photon detectors on GaAs with an AlN buffer layer

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, Ekkehart; Merker, Michael; Ilin, Konstantin; Siegel, Michael [Institut fuer Mikro- und Nanoelektronische Systeme (IMS), Karlsruher Institut fuer Technologie, Hertzstrasse 16, 76187 Karlsruhe (Germany)

    2015-07-01

    GaAs is the material of choice for photonic integrated circuits. It allows the monolithic integration of single-photon sources like quantum dots, waveguide based optical circuits and detectors like superconducting nanowire single-photon detectors (SNSPDs) onto one chip. The growth of high quality NbN films on GaAs is challenging, due to natural occurring surface oxides and the large lattice mismatch of about 27%. In this work, we try to overcome these problems by the introduction of a 10 nm AlN buffer layer. Due to the buffer layer, the critical temperature of 6 nm thick NbN films was increased by about 1.5 K. Furthermore, the critical current density at 4.2 K of NbN flim deposited onto GaAs with AlN buffer is 50% higher than of NbN film deposited directly onto GaAs substrate. We successfully fabricated NbN SNSPDs on GaAs with a AlN buffer layer. SNSPDs were patterned using electron-beam lithography and reactive-ion etching techniques. Results on the study of detection efficiency and jitter of a NbN SNSPD on GaAs, with and without AlN buffer layer will be presented and discussed.

  15. Growth of High-Quality GaAs on Ge by Controlling the Thickness and Growth Temperature of Buffer Layer

    Science.gov (United States)

    Zhou, Xu-Liang; Pan, Jiao-Qing; Yu, Hong-Yan; Li, Shi-Yan; Wang, Bao-Jun; Bian, Jing; Wang, Wei

    2014-12-01

    High-quality GaAs thin films grown on miscut Ge substrates are crucial for GaAs-based devices on silicon. We investigate the effect of different thicknesses and temperatures of GaAs buffer layers on the crystal quality and surface morphology of GaAs on Ge by metal-organic chemical vapor deposition. Through high resolution x-ray diffraction measurements, it is demonstrated that the full width at half maximum for the GaAs epilayer (Ge substrate) peak could achieve 19.3 (11.0) arcsec. The value of etch pit density could be 4×104 cm-2. At the same time, GaAs surfaces with no pyramid-shaped pits are obtained when the buffer layer growth temperature is lower than 360°C, due to effective inhibition of initial nucleation at terraces of the Ge surface. In addition, it is shown that large island formation at the initial stage of epitaxial growth is a significant factor for the final rough surface and that this initial stage should be carefully controlled when a device quality GaAs surface is desired.

  16. BLOOD DOPING AND RISKS

    Directory of Open Access Journals (Sweden)

    Goran Vasić

    2015-05-01

    Full Text Available Doping is the way in which athletes misuse of chemicals and other types of medical interventions (eg, blood replacement, try to get ahead in the results of other athletes or their performance at the expense of their own health. The aim of this work is the analysis of blood doping and the display of negative consequences that this way of increasing capabilities brings. Method: The methodological work is done descriptively. Results: Even in 1972 at the Stockholm Institute for gymnastics and sport, first Dr. Bjorn Ekblom started having blood doping. Taken from the blood, athletes through centifuge separating red blood cells from blood plasma, which is after a month of storage in the fridge, every athlete back into the bloodstream. Tests aerobic capacity thereafter showed that the concerned athletes can run longer on average for 25% of the treadmill than before. Discussion: Blood doping carries with it serious risks, excessive amount of red cells “thickens the blood,” increased hematocrit, which reduces the heart’s ability to pump blood to the periphery. All this makes it difficult for blood to flow through blood vessels, and there is a great danger that comes to a halt in the circulation, which can cause cardiac arrest, stroke, pulmonary edema, and other complications that can be fatal.

  17. Doped barium titanate nanoparticles

    Indian Academy of Sciences (India)

    Wintec

    nese doped BaTiO3 ceramics, sintered at 1400°C in air, changes from tetragonal to hexagonal between 0⋅5 and. 1⋅7 mole% of manganese (Langhammer et al 2000). As a driving force of the transformation from the cubic to the hexagonal crystal structure, the influence of the Jahn–. Teller distortion is proposed. The grain ...

  18. GaAs Solar Cells on V-Grooved Silicon via Selective Area Growth: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Warren, Emily L [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Jain, Nikhil [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Tamboli, Adele C [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Vaisman, Michelle [Yale University; Li, Qiang [Hong Kong University of Science and Technology; Lau, Kei May [Hong Kong University of Science and Technology

    2017-08-31

    Interest in integrating III-Vs onto Si has recently resurged as a promising pathway towards high-efficiency, low-cost tandem photovoltaics. Here, we present a single junction GaAs solar cell grown monolithically on polished Si (001) substrates using V-grooves, selective area growth, and aspect ratio trapping to mitigate defect formation without the use of expensive, thick graded buffers. The GaAs is free of antiphase domains and maintains a relatively low TDD of 4x107 cm-2, despite the lack of a graded buffer. This 6.25 percent-efficient demonstration solar cell shows promise for further improvements to III-V/Si tandems to enable cost-competitive photovoltaics.

  19. The miniband spectrum in (AlAs) sub M (GaAs) sub N (111)

    CERN Document Server

    Karavaev, G F; Egunov, R M

    2002-01-01

    The electron states for energies in the conduction band of (AlAs) sub M (GaAs) sub N (111) superlattices with M >= N (N < 10) are considered. The properties of such superlattices are mainly determined by electrons of X-valley in AlAs and L-valley in GaAs. The calculations are carried out on the basis of the envelope-function model of interface band mixing. Miniband spectra, symmetry and localization of wave functions, and also probabilities of the interminiband infrared absorption are defined and analyzed. It is shown that the latter have a significant magnitude not only at light polarization along the superlattice growth axis, but also at normal incidence of a light wave to the surface. The analysis has been normal incidence of a light wave to the surface. The analysis has shown the importance of consideration of X sub 5 -states belonging to the valence band for infrared absorption

  20. Optical anisotropy induced by mechanical strain around the fundamental gap of GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Ortega-Gallegos, J.; Lastras-Martinez, A.; Lastras-Martinez, L.F. [Instituto de Investigacion en Comunicacion Optica, Universidad Autonoma de San Luis Potosi, Alvaro Obregon 64, San Luis Potosi (Mexico); Balderas-Navarro, R.E. [Instituto de Investigacion en Comunicacion Optica, Universidad Autonoma de San Luis Potosi, Alvaro Obregon 64, San Luis Potosi (Mexico); Facultad de Ciencias, Universidad Autonoma de San Luis Potosi, Alvaro Obregon 64, San Luis Potosi (Mexico)

    2008-07-01

    We report on a theoretical-experimental study of reflectance anisotropy spectroscopy (RAS) of GaAs (001) crystals under uniaxial stress. The study was carried out in the energy region around the fundamental transition. RAS spectra in the energy range from 1.2-1.7 eV were measured with a photoelastic-modulator-based spectrometer. To induce an optical anisotropy, the GaAs crystals were thinned down to 400 {mu}m and an calibrated uniaxial stress was applied by deflection. RAS showed a line shape consisting of an oscillation at around E{sub 0}. On the basis of a perturbative approach employing the Pikus-Bir Hamiltonian, we calculated the RAS line shape and found a close agreement with the experimental spectra. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)