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Sample records for semiinsulating gaas irradiated

  1. Native and irradiation-induced monovacancies in n -type and semi-insulating GaAs

    SciTech Connect

    Corbel, C.; Pierre, F. ); Hautojaervi, P.; Saarinen, K. ); Moser, P. )

    1990-05-15

    Defects induced by electron irradiation in semi-insulating and {ital n}-type GaAs crystals have been characterized by positron-lifetime measurements. We conclude that electron irradiation with energies of 1.5--3 MeV produces negative monovacancies and negative ions at low and room temperature. The results also show that the native monovacancy defects in lightly {ital n}-type GaAs change their properties under irradiation. We relate this change to the existence of an ionization level {minus}{r arrow}0 or 0{r arrow}+ of the native monovacancy defects in the upper half of the band gap. We propose that irradiation produces negative Ga{sub As} antisites and negative {ital V}{sub Ga} vacancies. In {ital n}-type GaAs the behavior of the native defects under irradiation is in agreement with their earlier assignment to {ital V}{sub As}.

  2. Photoquenching phenomenon enhanced by proton irradiation in semi-insulating GaAs

    SciTech Connect

    Kuriyama, K.; Takahashi, H.; Kawahara, H. ); Hayashi, N.; Watanabe, H.; Sakamoto, I. ); Kohno, I. )

    1990-12-15

    In undoped semi-insulating GaAs, we have found that the quenching phenomena of photoconductance and infrared absorption are enhanced by proton irradiation above 10{sup 13} /cm{sup 2}, accompanied by an increase in near-band-edge infrared absorption. These phenomena disappear with the annihilation of the proton-induced near-band absorption by annealing at 350 {degree}C. It is suggested that the enhanced photoquenching phenomena arise from the increase in the quenchable component due to the transition from the ionized midgap electron trap (EL2{sup +}) to the neutral EL2{sup 0}.

  3. Introduction of metastable vacancy defects in electron-irradiated semi-insulating GaAs

    SciTech Connect

    Saarinen, K.; Kuisma, S.; Maekinen, J.; Hautojaervi, P.; Toernqvist, M.; Corbel, C.

    1995-05-15

    Positron-lifetime experiments have been performed to investigate the metastability of the point defects produced in the electron irradiation of semi-insulating GaAs. The measurements in darkness indicate the presence of Ga vacancies and Ga antisite defects in a negative charge state. Illumination at 25 K reveals another type of a defect, which has a vacancy in its metastable state. The metastable vacancies can be observed most effectively after illumination with 1.1-eV photons and they are persistent up to the annealing temperature of 80--100 K. The introduction rate of the metastable defects is about 0.3 cm{sup {minus}1}, which is close to the values reported earlier for the As antisite. The metastable properties of the defects resemble those of the well-known {ital EL}2 center in as-grown GaAs. We associate these defects to As antisites, which exhibit the metastability predicted by the theory: in the metastable configuration the As antisite atom relaxes away from the lattice position, leaving a Ga site vacant.

  4. Continuous wave terahertz radiation from antennas fabricated on C¹²-irradiated semi-insulating GaAs.

    PubMed

    Deshmukh, Prathmesh; Mendez-Aller, M; Singh, Abhishek; Pal, Sanjoy; Prabhu, S S; Nanal, Vandana; Pillay, R G; Döhler, G H; Preu, S

    2015-10-01

    We demonstrate continuous wave (CW) terahertz generation from antennas fabricated on C12-irradiated semi-insulating (SI) GaAs substrates. The dark current drawn by the antennas fabricated on irradiated substrates is ∼3 to 4 orders of magnitude lower compared to antennas fabricated on un-irradiated substrates, while the photocurrents decrease by only ∼1.5 orders of magnitude. This can be attributed to the strong reduction of the carrier lifetime that is 2.5 orders of magnitude, with values around τ(rec)=0.2  ps. Reduced thermal heating allows for higher bias voltages to the irradiated antenna devices resulting in higher CW terahertz power, just slightly lower than that of low-temperature grown GaAs (LT GaAs)at similar excitation conditions.

  5. Gallium vacancies and gallium antisites as acceptors in electron-irradiated semi-insulating GaAs

    SciTech Connect

    Corbel, C.; Pierre, F. ); Saarinen, K.; Hautojaervi, P. ); Moser, P. )

    1992-02-15

    Positron-lifetime measurements show that acceptors are produced in semi-insulating GaAs by 1.5-MeV electron irradiation at 20 K. Two types of acceptors can be separated. The first ones are negative vacancy-type defects which anneal out over a very broad range of temperature between 77 and 500 K. The second ones are negative ion-type defects which are stable still at 450 K. The data show that these two types of defects are independent and do not form close pairs. We attribute both to gallium-related defects. We identify the ion-type acceptors as isolated gallium antisites. The vacancy-type acceptors are identified as gallium vacancies which are isolated or involved in negatively charged complexes. The introduction rate of the gallium antisite is estimated to be 1.8{plus minus}0.3 cm{sup {minus}1} in the fluence range 10{sup 17}--10{sup 18} cm{sup {minus}2} for 1.5-MeV electron irradiation at 20 K.

  6. Modifications of EL2 related stable and metastable defects in semi-insulating GaAs by high energy light ion irradiation

    NASA Astrophysics Data System (ADS)

    Kabiraj, D.; Ghosh, S.

    2005-10-01

    We report the effect of high energy light ion irradiation on the defect energy levels related to the stable and metastable states of EL2 in undoped semi-insulating GaAs. GaAs samples have been irradiated at different fluences with 50 MeV Li ions. The energy of the irradiated ions is chosen in such a way that the range of the ions is more than the sample thickness. So the implantation of the irradiated ions and the formation of the extended defects at the end of the range could be avoided. The modification of the existing native point defects and the formation of new point defects under irradiation have been studied by photocurrent and thermally stimulated current spectroscopic measurements under the photoexcitation of both sub-band gap and above band gap lights.

  7. Optical evaluation of the ionized EL2 fraction in proton (24 GeV) irradiated semi-insulating GaAs

    SciTech Connect

    Ferrini, R.; Galli, M.; Guizzetti, G.; Patrini, M.; Nava, F.

    1997-11-01

    Semi-insulating SI GaAs samples from a zone refined crystal were irradiated with high energy protons (24 GeV/c, fluences up to 1.64{times}10{sup 14}p/cm{sup 2}). Optical spectra in transmittance and reflectance were accurately measured in the energy range of 0.6{endash}1.4 eV to determine, through the absorption coefficient, the concentrations of both neutral and ionized EL2 defects as a function of the proton fluence. Both these concentrations have been shown to increase linearly with the proton fluence; this behavior well explains the remarkable decrease of the charge collection efficiency observed in proton irradiated GaAs detectors at doses associated with high luminosity beams at a new particle collider accelerator (e.g., the LHC at the CERN laboratory). {copyright} {ital 1997 American Institute of Physics.}

  8. Characterisation of semi-insulating GaAs

    NASA Technical Reports Server (NTRS)

    Walukiewicz, W.; Pawlowicz, L.; Lagowski, J.; Gatos, H. C.

    1982-01-01

    Hole and electron mobilities as functions of temperature and ionised impurity concentration are calculated for GaAs. It is shown that these calculations, when used to analyse electrical properties of semi-insulating GaAs, enable an assessment of the Fermi energy position and ionised impurity concentration to be made. In contrast to previous work, the analysis does not require any phenomenological assumptions.

  9. Highly efficient and electrically robust carbon irradiated semi-insulating GaAs based photoconductive terahertz emitters

    NASA Astrophysics Data System (ADS)

    Singh, Abhishek; Pal, Sanjoy; Surdi, Harshad; Prabhu, S. S.; Nanal, Vandana; Pillay, R. G.

    2014-02-01

    We demonstrate here an efficient photoconductive THz source with low electrical power consumption. We have increased the maximum THz radiation power emitted from SI-GaAs based photoconductive emitters (PCEs) by two orders of magnitude. By irradiating the SI-GaAs substrate with Carbon-ions up to 2 μm deep, we have created lot of defects and decreased the lifetime of photo-excited carriers inside the substrate. Depending on the irradiation dose, we find 1 to 2 orders of magnitude decrease in total current flowing in the substrate, resulting in subsequent decrease of heat dissipation in the device. This has resulted in increasing maximum cut-off of the applied voltage across PCE electrodes to operate the device without thermal breakdown from ˜35 V to >150 V for the 25 μm electrode gaps. At optimum operating conditions, carbon irradiated (1014 ions/cm2) PCEs give THz pulses with power about 100 times higher in comparison to the usual PCEs on SI-GaAs and electrical to THz power conversion efficiency has improved by a factor of ˜800.

  10. Slow domains in semi-insulating GaAs

    SciTech Connect

    Neumann, A.

    2001-07-01

    Semi-insulating GaAs shows current oscillations if a high dc voltage is applied to a sample. These oscillations are caused by traveling high-electric-field domains that are formed as a result of electric-field-enhanced electron trapping. This article describes the various types of experiments that have been carried out with this system, including recent ones that use the electro-optic Pockels effect in order to measure the local electric fields in the sample in a highly accurate manner. An historical overview of the theoretical developments is given and shows that no satisfying theory is currently available. A list of all the required ingredients for a successful theory is provided and the experimental data are explained in a qualitative manner. Furthermore, the main electron trap in semi-insulating GaAs is the native defect EL2, the main properties of which are described. {copyright} 2001 American Institute of Physics.

  11. Complete set of deep traps in semi-insulating GaAs

    NASA Astrophysics Data System (ADS)

    Pavlović, M.; Desnica, U. V.; Gladić, J.

    2000-10-01

    Reevaluation and recalculation of thermally stimulated current (TSC) data from semi-insulating (SI) GaAs, published by many different authors over a period of three decades were done by means of the new analytical method, simultaneous multiple peak analysis (SIMPA). The SIMPA procedure clearly resolved contributions from various overlapping TSC peaks and enabled the precise determination of signatures (activation energy, Ea and capture cross section, σ) of all observed deep traps. The analyzed TSC spectra refer to SI GaAs samples that have been grown/treated in quite different ways (various growth techniques, growth under As or Ga rich conditions, different annealing procedures, irradiation with neutrons, γ rays, etc.). Although the SIMPA procedure was applied to apparently quite different TSC spectra, in all cases excellent fits were achieved, with the unique set (or subset from it) of eleven different deep traps, the only difference being in relative and absolute concentrations of traps. Despite a broad variety of samples analyzed in this article, the set of deep traps obtained is the same as the one being previously seen in the narrow range of SI GaAs samples. This finding suggests that this set of traps is a finite and complete set of all defects with deep levels in SI GaAs. It was also concluded that these defects are primarily complexes containing simple native defects.

  12. Undoped semi-insulating LEC GaAs - A model and a mechanism. [Liquid Encapsulated Czochralski

    NASA Technical Reports Server (NTRS)

    Oliver, J. R.; Fairman, R. D.; Chen, R. T.; Yu, P. W.

    1981-01-01

    Undoped semi-insulating GaAs grown by the high-pressure liquid encapsulated Czochralski (LEC) method has been produced for use in direct ion implantation in several laboratories. A clear understanding of the factors controlling impurity transport and compensation in these materials has been lacking to date. In this work, detailed characterization has been performed on undoped semi-insulating crystals grown from both SiO2 and PBN crucibles followed by a proposed impurity model and compensation mechanism.

  13. Deep levels in semi-insulating LEC GaAs before and after silicon implantation

    SciTech Connect

    Dindo, S.; Abdel-Motaleb, I.; Lowe, K.; Tang, W.; Young, L.

    1985-11-01

    The deep trapping levels present before ion implantation of silicon into the semi-insulating LEC GaAs starting material were investigated using optical transient current spectroscopy (OTCS). MESFET channel current deep level transient spectroscopy (DLTS) was used for the implanted material. With a silicon nitride layer used t encapsulate the GaAs for postimplantation annealing and with implantation directly into the GaAs, it was found tha of seven or more deep levels seen in the semi-insulating substrate prior to silicon implantation only the level believed to be EL12 remained. On implanting through a thin Si/sub 3/N/sub 4/ encapsulating layer and annealing under Si/sub 3/N/sub 4/, only EL2 was found. With a silicon dioxide layer as an encapsulant, two traps remained and two apparently unreported levels appeared.

  14. Role of electrode metallization in performance of semi-insulating GaAs radiation detectors

    NASA Astrophysics Data System (ADS)

    Dubecký, František; Boháček, Pavol; Sekáčová, Mária; Zaťko, Bohumír; Lalinský, Tibor; Linhart, Vladimír; Šagátová-Perd'ochová, Andrea; Mudroň, Ján; Pospíšil, Stanislav

    2007-06-01

    In the present work, a comparative study of semi-insulating (SI) GaAs radiation detectors with different blocking (Schottky) and ohmic contact metallization is presented. The detectors fabricated from "detector-grade" bulk SI GaAs are characterized by current-voltage measurements and their detection performance is evaluated from pulse-height spectra of 241Am and 57Co γ-sources. Observed results are evaluated and discussed. Importance of the optimized electrodes technology of SI GaAs detector with good performance is demonstrated.

  15. Depth uniformity of electrical properties and doping limitation in neutron-transmutation-doped semi-insulating GaAs

    SciTech Connect

    Satoh, M.; Kuriyama, K. ); Kawakubo, T. )

    1990-04-01

    Depth uniformity of electrical properties has been evaluated for neutron-transmutation-doped (NTD), semi-insulating GaAs irradiated with thermal neutrons of 1.5{times}10{sup 18} cm{sup {minus}2} by the van der Pauw method combined with iterative etching of the surface. In NTD-GaAs wafers (thickness {similar to}410 {mu}m) annealed for 30 min at 700 {degree}C, the depth profiles of the resistivity, the carrier concentration, and the Hall mobility show constant values of 1{times}10{sup {minus}2} {Omega} cm, 2.0{times}10{sup 17} cm{sup {minus}3}, and 3100 cm{sup 2}/V s, respectively, within an experimental error of 5%. In an annealing process, the redistribution and/or the segregation of NTD impurities is not observed. We also discuss the limitations of low-level NTD in semi-insulating GaAs. It is suggested that the activation of the NTD-impurities below {similar to}1{times}10{sup 16} cm{sup {minus}3} is mainly restricted by the presence of the midgap electron trap (EL2).

  16. 20 THz broadband generation using semi-insulating GaAs interdigitated photoconductive antennas.

    PubMed

    Hale, P J; Madeo, J; Chin, C; Dhillon, S S; Mangeney, J; Tignon, J; Dani, K M

    2014-10-20

    We demonstrate broadband (20 THz), high electric field, terahertz generation using large area interdigitated antennas fabricated on semi-insulating GaAs. The bandwidth is characterized as a function of incident pulse duration (15-35 fs) and pump energy (2-30 nJ). Broadband spectroscopy of PTFE is shown. Numerical Drude-Lorentz simulations of the generated THz pulses are performed as a function of the excitation pulse duration, showing good agreement with the experimental data.

  17. ``EL2'' revisited: Observation of metastable and stable energy levels of EL2 in semi-insulating GaAs

    NASA Astrophysics Data System (ADS)

    Kabiraj, D.; Ghosh, Subhasis

    2005-12-01

    By using a combination of detailed experimental studies, we identify the metastable and stable energy levels of EL2 in semi-insulating GaAs. These results are discussed in light of the recently proposed models for EL2 in GaAs.

  18. Microscopic modelling of semi-insulating GaAs detectors

    NASA Astrophysics Data System (ADS)

    Cola, A.; Vasanelli, L.; Reggiani, L.; Cavallini, A.; Nava, F.

    1997-08-01

    We present a drift-diffusion model of semi-insulating n-GaAs detectors, taking into account the presence of hot-carrier dynamics, conduction band features and the kinetics of trapping and detrapping from deep and shallow centres. We provide unambiguous evidence of a field-enhanced capture cross section for EL2 and EL3 centres as conjectured by McGregor [1] for the case of EL2. This result is shown to be strictly correlated with the active thickness of the detector varying almost linearly with the applied voltage, in excellent agreement with recent experimental measurements performed with the Optical Beam-Induced Currents (OBIC) technique. Evidence of Poole-Frenkel effects at the highest applied voltages is provided by the current-voltage characteristics.

  19. Improved thermally stimulated current analysis in semi-insulating GaAs: New conclusions

    SciTech Connect

    Fang, Z.Q.; Look, D.C.

    1996-12-01

    Measurements of EL2{degrees} and EL2{sup +} concentrations by IR absorption and temperature-dependent photocurrent (1.13 eV) and dark current at 80K < T < 300K in semiinsulating GaAs, allow a more accurate analysis of the thermally stimulated current spectrum. We conclude that trap T{sub 2}, at 220K, is related to ASG. and controlled by both EL2{degrees} and EL2{sup +}, and T{sub 3}, at 200K is most likely a V{sub As}-related defect complex.

  20. Evidence for field enhanced electron capture by EL2 centers in semi-insulating GaAs and the effect on GaAs radiation detectors

    SciTech Connect

    McGregor, D.S.; Rojeski, R.A.; Knoll, G.F. ); Terry, F.L. Jr.; East, J. ); Eisen, Y. )

    1994-06-15

    The performance of Schottky contact semiconductor radiation detectors fabricated from semi-insulating GaAs is highly sensitive to charged impurities and defects in the material. The observed behavior of semi-insulating GaAs Schottky barrier alpha particle detectors does not match well with models that treat the semi-insulating material as either perfectly intrinsic or as material with deep donors (EL2) of constant capture cross section compensated with shallow acceptors. We propose an explanation for the discrepancy based on enhanced capture of electrons by EL2 centers at high electric fields and the resulting formation of a quasineutral region in the GaAs. Presented is a simple model including field enhanced electron capture which shows good agreement with experimental alpha particle pulse height measurements.

  1. Semi-insulating GaAs based detector of fast neutrons produced by D-T nuclear reaction

    NASA Astrophysics Data System (ADS)

    Šagátová, A.; Kubanda, D.; Zat'ko, B.; Sedlačková, K.; Nečas, V.; Solar, M.; Granja, C.

    2016-12-01

    We have examined semi-insulating (SI) GaAs detectors with high density polyethylene (HDPE) conversion layer by a mono-energetic neutrons with kinetic energy of 16.755 MeV generated by a deuterium—tritium nuclear reaction. First, the influence of HDPE layer thickness on the relative detection efficiency of fast neutrons was studied. The MCNPX (Monte Carlo N-particle eXtended) code has been used to support the analysis of the experiment. The theoretical optimum thickness of the conversion layer was determined to 1.9 mm using the MCNPX code. The HDPE conversion layers of various thicknesses, in the range from 50 μ m to 3200 μ m, were glued on the top Schottky contact of SI GaAs detector in the experiment. The neutron detection efficiency was evaluated from measured spectra and compared to results from simulations. The experimental data showed very good agreement with simulation results. Then the effect of active detector thickness modified by detector reverse bias on neutron detection efficiency was studied. Finally, the effect of the angle of irradiation on neutron detection efficiency was evaluated exhibiting decreasing tendency with increasing deviation from perpendicular direction of impinging neutrons.

  2. Gettering of donor impurities by V in GaAs and the growth of semi-insulating crystals

    NASA Technical Reports Server (NTRS)

    Ko, K. Y.; Lagowski, J.; Gatos, H. C.

    1989-01-01

    Vanadium added to the GaAs melt getters shallow donor impurities (Si and S) and decreases their concentration in the grown crystals. This gettering is driven by chemical reactions in the melt rather than in the solid. Employing V gettering, reproducibly semi-insulating GaAs were grown by horizontal Bridgman and liquid-encapsulated Czochralski techniques, although V did not introduce any midgap energy levels. The compensation mechanism in these crystals was controlled by the balance between the native midgap donor EL2 and residual shallow acceptors. Vanadium gettering contributed to the reduction of the concentration of shallow donors below the concentration of acceptors. The present findings clarify the long-standing controversy on the role of V in achieving semi-insulating GaAs.

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

    NASA Astrophysics Data System (ADS)

    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.

  4. Low frequency oscillations in semi-insulating GaAs: a nonlinear analysis.

    PubMed

    Rubinger, R M; da Silva, R L; de Oliveira, A G; Ribeiro, G M; Albuquerque, H A; Rodrigues, W N; Moreira, M V B

    2003-06-01

    We have observed low frequency current oscillations in a semi-insulating GaAs sample grown by low temperature molecular beam epitaxy. For this, an experimental setup proper to measure high impedance samples with small external noise was developed. Spontaneous oscillations in the current were observed for some bias conditions. Although measurements were carried out from room temperature down to liquid helium, the dynamical analysis was carried out around 200 K where the signal to noise ratio was fairly favorable. To increase the data quality we have also used a noise reduction algorithm suitably developed for nonlinear systems. We observed attractors having low embedding dimension, limit cycle bifurcations, and chaotic behavior characteristic of nonlinear dynamical processes in route to chaos. Attractor reconstruction, Poincare sections, Lyapunov exponents, and correlation dimension were also analyzed.

  5. Detection of fast neutrons using detectors based on semi-insulating GaAs

    NASA Astrophysics Data System (ADS)

    Zat'ko, B.; Sedlačková, K.; Dubecký, F.; Boháček, P.; Sekáčová, M.; Nečas, V.

    2011-12-01

    Detectors with AuZn square Schottky contact of the area of 2.5 × 2.5 mm2 were fabricated. On the back side, the whole area AuGeNi eutectic ohmic contact was evaporated. The thickness of the base material (semi-insulating GaAs) was 220 μm. The connection of 4 detectors in parallel was tested to get the detection area of 25 mm2. The 239Pu-Be fast neutron source with energies between 0.5 and 12 MeV was used in experimental measurements. We have investigated the optimal thickness of HDPE (high-density polyethylene) conversion layer for fast neutron detection. The spectra of the neutrons were measured by detectors covered by HDPE converter of different thicknesses. The fast neutron detection efficiency proved experimentally was compared with results from simulations performed by MCNPX (Monte Carlo N-Particle eXtended) code.

  6. Effects of macroscopic inhomogeneities on electron mobility in semi-insulating GaAs

    NASA Technical Reports Server (NTRS)

    Walukiewicz, W.; Wang, L.; Pawlowicz, L. M.; Lagowski, J.; Gatos, H. C.

    1986-01-01

    It is shown that defect inhomogeneities of sizes larger than the electron mean free path are responsible for the low values and anomalous temperature dependence of the electron mobility in semi-insulating (SI) GaAs. The room-temperature electron mobility values below about 6000 sq cm/V s cannot be uniquely used for the determination of the concentration of ionized defects, since the contribution from inhomogeneities usually exceeds that from scattering by ionized impurities. The effects of the macroscopically inhomogeneous distribution of residual acceptors and the major deep donor EL2 diminish at elevated temperatures between 600 and 900 K, which offers a means for identification of inhomogeneities, and furthermore explains recently reported steplike mobility versus temperature behavior in SI-GaAs.

  7. Effects of macroscopic inhomogeneities on electron mobility in semi-insulating GaAs

    SciTech Connect

    Walukiewicz, W.; Wang, L.; Pawlowicz, L.M.; Lagowski, J.; Gatos, H.C.

    1986-05-01

    We show that defect inhomogeneities of sizes larger than the electron mean free path are responsible for the low values and anomalous temperature dependence of the electron mobility in semi-insulating (SI) GaAs. The room-temperature electron mobility values below about 6000 cm/sup 2//V s cannot be uniquely used for the determination of the concentration of ionized defects, since the contribution from inhomogeneities usually exceeds that from scattering by ionized impurities. The effects of the macroscopically inhomogeneous distribution of residual acceptors and the major deep donor EL2 diminish at elevated temperatures between 600 and 900 K, which offers a means for identification of inhomogeneities, and furthermore explains recently reported steplike mobility versus temperature behavior in SI-GaAs.

  8. Characterization of semi-insulating GaAs by photoreflectance and photoluminescence

    SciTech Connect

    Durbin, C.M.

    1992-12-31

    Semi-insulating (SI) GaAs was characterized using photoreflectance, a modulation spectroscopy technique. Anomalous splitting was observed in the photoreflectance (PR) response of SI:GaAs in the vicinity of the exciton at 78 K. Recent photoluminescence (PL) measurements suggest the splitting is correlated with the EL2 content of the samples. Separation between the two peaks in PR measurements range from about 2 to 4 meV. A striking effect is that each peak is maximized by a different phase setting of the lock-in. The splitting is sample dependent and is also affected by several other factors including surface conditions, temperature, pump beam intensity and modulation frequency.

  9. Defects induced by protons and {gamma}-rays in semi-insulating GaAs detectors

    SciTech Connect

    Castaldini, A.; Cavallini, A.; Del Papa, C. |; Fuochi, G.; Alietti, M.; Canali, C.; Nava, F. |; Paccagnella, A.; Lanzieri, C.

    1995-09-01

    Semi-insulating gallium arsenide has been irradiated by protons and by gamma-rays with different doses. The irradiation-induced deep level defects have been investigated by current transient spectroscopy to find their energy, capture cross sections and generation rate. Two electron traps at E{sub c}{minus}0.14V(E13) and E{sub c}{minus}0.70eV(E4) and a hole trap at E{sub v}+0.41eV(H2) in addition to the levels existing before the irradiation have been detected in the irradiated samples. These findings have been related to the performance of gallium arsenide charge particle detectors.

  10. Infrared absorption related to the metastable state of arsenic antisite defects in electron-irradiated GaAs

    SciTech Connect

    Kuisma, S.; Saarinen, K.; Hautojaervi, P.; Corbel, C.

    1996-12-31

    A metastable irradiation-induced vacancy is detected by positrons in semi-insulating GaAs. The vacancy is associated with the metastable state of an irradition-induced As-antisite-related defect. This metastable state absorbs IR light in contrast to the metastable state of the As-antisite-related native EL2 defect. This property can be explained by the presence of other defects complexed with the As antisite in electron-irradiated GaAs.

  11. Controlling chaos with magnetic field in semi-insulating GaAs

    SciTech Connect

    Oliveira, A. G. de; Ribeiro, G. M.; Moreira, M. V. B.; Gonzalez, J. C.; Silva, R. L. da; Rubinger, R. M.

    2007-10-15

    Chaos control has stimulated a large amount of work. We have studied the effect of an external parallel magnetic field on the low-frequency current oscillations observed on a molecular beam epitaxy GaAs sample grown at 265 deg. C, and we have shown that it can be efficiently used for chaos control. The study of the magnetoresistance indicates that the effect of the magnetic field on the charges of the hopping conduction mechanism induces changes in the low-frequency oscillations. Due to this, we have used the magnetic field to control chaos assessed through direct observation low-frequency oscillations, their attractors, and bifurcation diagrams. We also found that the magnetic field interferes indirectly with the Coulombian interaction between the free charges in the conduction band and the hopping carriers, as well as with the recombination mechanism of field enhanced trapping. Controlling the low-frequency oscillations in semi-insulating GaAs by means of an external magnetic field permits probing the interaction of the slow hopping carriers and the fast free carriers in the electric-field domains.

  12. Investigation of the compensation mechanism in semi-insulating GaAs from alpha-spectra studies at low temperature

    SciTech Connect

    Chen, J.W.; Ebling, D.G.; Geppert, R.; Irsigler, R.; Schmid, T.; Rogalla, M.; Ludwig, J.; Runge, K.

    1997-05-01

    We present the results of charge collection measurements on liquid encapsulated Czochralski grown semi-insulating GaAs devices for alpha particles. Experimental evidence is given which demonstrates a drastic enhancement of charge collection efficiency after prolonged illumination with 1.086 {mu}m below-gap light. The recovery of EL2 from metastable state to normal state can also be achieved by electric field at high bias voltage. The experimental result shows that the EL2 defect is practically the dominant trap for free charge carriers and together with other shallow defects responsible for the electric compensation in semi-insulating GaAs. The metastable transition of the EL2 defect is always simultaneously accompanied by the neutralization of a shallow acceptor. No change in the type of conductivity was found. {copyright} {ital 1997 American Institute of Physics.}

  13. Photoinduced absorption of THz radiation in semi-insulating GaAs crystal

    NASA Astrophysics Data System (ADS)

    Kurdyubov, A. S.; Trifonov, A. V.; Gerlovin, I. Ya.; Ignatiev, I. V.; Kavokin, A. V.

    2017-07-01

    The influence of optical illumination on transmission of THz radiation through a bulk crystal of semi-insulating GaAs is experimentally studied. It is established that, without additional illumination, absorption of electromagnetic waves with a frequency of about 1 THz in the studied crystal is almost absent. Optical illumination in the spectral range of fundamental absorption of the crystal does not affect the transmission of THz waves. At the same time, if the illumination photon energy is a little below the edge of fundamental absorption, i.e., actually in the transparency region, the transmission of THz radiation drops sharply. At liquid helium temperature, the maximum effect is achieved for the energy of optical photons lower by approximately 30 meV than the crystal band gap. Further shift of the illumination toward lower photon energies is accompanied by almost complete recovery of the transmission. With increasing sample temperature, the spectral range of efficient action of the illumination shifts together with the edge of fundamental absorption toward lower photon energies.

  14. Role of deep level trapping on surface photovoltage of semi-insulating GaAs

    SciTech Connect

    Liu, Q.; Ruda, H.E.; Koutzarov, I.P.; Jedral, L.; Chen, G.; Prasad, M.

    1996-12-31

    Dual beam (bias and probe) transient Surface Photovoltage (SPV) measurements were made on undoped Semi-Insulating (SI) GaAs over an extended temperature range. Above 270 K, SPV recovery transients following a bias pulse were shown to reflect near surface conductivity changes; these are in turn controlled by surface/interface state thermal emission. Owing to the absence of a strong surface electric field in this material, the emitted carriers are not immediately removed from the near surface region. The recapturing of the emitted carriers is shown to be responsible for non-exponential conductivity and reciprocal-SPV transients. This behavior is considered to be characteristic of relaxation-type semiconductors with near-surface ungated structures. Below 150 K, the photoinduced transition of EL2 from its ground to metastable state El2* was shown to change the effective electron and hole mobilities and augment the SPV signals immediately following the bias pulse. Thermally induced EL2* recovery above 120 K decreases the SPV signal from its maximum. This decay transient was analyzed and the decay rate fitted to a single exponential. An activation energy of 0.32 eV and a pre-exponential constant of 1.9 {times} 10{sup 12} s{sup {minus}1} were obtained, and attributed to the thermal recovery rate for EL2*.

  15. EBIC spectroscopy - A new approach to microscale characterization of deep levels in semi-insulating GaAs

    NASA Technical Reports Server (NTRS)

    Li, C.-J.; Sun, Q.; Lagowski, J.; Gatos, H. C.

    1985-01-01

    The microscale characterization of electronic defects in (SI) GaAs has been a challenging issue in connection with materials problems encountered in GaAs IC technology. The main obstacle which limits the applicability of high resolution electron beam methods such as Electron Beam-Induced Current (EBIC) and cathodoluminescence (CL) is the low concentration of free carriers in semiinsulating (SI) GaAs. The present paper provides a new photo-EBIC characterization approach which combines the spectroscopic advantages of optical methods with the high spatial resolution and scanning capability of EBIC. A scanning electron microscope modified for electronic characterization studies is shown schematically. The instrument can operate in the standard SEM mode, in the EBIC modes (including photo-EBIC and thermally stimulated EBIC /TS-EBIC/), and in the cathodo-luminescence (CL) and scanning modes. Attention is given to the use of CL, Photo-EBIC, and TS-EBIC techniques.

  16. Formation of a semi-insulating layer in n-type 4H-SiC by electron irradiation

    SciTech Connect

    Kaneko, Hiromi; Kimoto, Tsunenobu

    2011-06-27

    Electron irradiation has been applied to the formation of a semi-insulating 4H-SiC(0001) layer. The resistivity of the semi-insulating layer, which was irradiated with a fluence of 1.9 x 10{sup 18} cm{sup -2} at 400 keV, exceeded 10{sup 10{Omega}} cm at room temperature. From capacitance-voltage characteristics of Schottky structure, the depth of the semi-insulating layer was estimated to be 10 {mu}m, indicating that the whole region of lightly-doped n-type epilayer was converted to the semi-insulating layer by electron irradiation. The semi-insulating property can be ascribed to electron trapping at the Z{sub 1/2} and EH{sub 6/7} centers generated by electron irradiation. The threshold energy for the generation of Z{sub 1/2} center was about 100 keV.

  17. Carbon irradiated semi insulating GaAs for photoconductive terahertz pulse detection

    NASA Astrophysics Data System (ADS)

    Singh, Abhishek; Pal, Sanjoy; Surdi, Harshad; Prabhu, S. S.; Mathimalar, S.; Nanal, Vandana; Pillay, R. G.; Döhler, G. H.

    2015-03-01

    We report here a photoconductive material for THz generation and detection with sub-picosecond carrier lifetime made by C12 (Carbon) irradiation on commercially available semi-insulating (SI) GaAs. We are able to reduce the carrier lifetime of SI-GaAs down to sub-picosecond by irradiating it with various irradiation dosages of Carbon (C12) ions. With an increase of the irradiation dose from ~1012 /cm2 to ~1015 /cm2 the carrier lifetime of SI-GaAs monotonously decreases to 0.55 picosecond, resulting in strongly improved THz pulse detection compared with normal SI-GaAs.

  18. On the optical evaluation of the EL2 deep level concentration in semi-insulating GaAs

    NASA Technical Reports Server (NTRS)

    Walukiewicz, W.; Lagowski, J.; Gatos, H. C.

    1983-01-01

    A practical procedure for the evaluation of the Fermi energy in semi-insulating (SI)GaAs from electrical measurements is presented. This procedure makes it possible to reliably extend the determination of the major deep level (EL2) concentration, by near-infrared absorption measurements, to SIGaAs. Employing this procedure, it is shown that the EL2 concentration in Czochralski-grown GaAs increases monotonically with increasing As/Ga ratio (throughout the conversion from SI n type to semiconducting p-type crystals) rather than abruptly as previously proposed.

  19. Emission characteristics of photoconductive antennas based on low-temperature-grown GaAs and semi-insulating GaAs.

    PubMed

    Tani, M; Matsuura, S; Sakai, K; Nakashima, S

    1997-10-20

    Terahertz radiation was generated with several designs of photoconductive antennas (three dipoles, a bow tie, and a coplanar strip line) fabricated on low-temperature-grown (LT) GaAs and semi-insulating (SI) GaAs, and the emission properties of the photoconductive antennas were compared with each other. The radiation spectrum of each antenna was characterized with the photoconductive sampling technique. The total radiation power was also measured by a bolometer for comparison of the relative radiation power. The radiation spectra of the LT-GaAs-based and SI-GaAs-based photoconductive antennas of the same design showed no significant difference. The pump-power dependencies of the radiation power showed saturation for higher pump intensities, which was more serious in SI-GaAs-based antennas than in LT-GaAs-based antennas. We attributed the origin of the saturation to the field screening of the photocarriers.

  20. Study on the high-power semi-insulating GaAs PCSS with quantum well structure

    SciTech Connect

    Luan, Chongbiao; Wang, Bo; Huang, Yupeng; Li, Xiqin; Li, Hongtao; Xiao, Jinshui

    2016-05-15

    A high-power semi-insulating GaAs photoconductive semiconductor switch (PCSS) with quantum well structure was fabricated. The AlGaAs layer was deposited on the surface of the GaAs material, and the reflecting film and the antireflection film have been made on the surface of the GaAs and AlGaAs, respectively. When the prepared PCSS worked at a bias voltage of 9.8 kV and triggered by a laser pulse with an incident optical energy of 5.4 mJ, a wavelength of 1064 nm and an optical pulse width of 25 ns, the on-state resistance of the AlGaAs/GaAs PCSS was only 0.45 Ω, and the longevity of the AlGaAs/GaAs PCSS was larger than 10{sup 6} shots. The results show that this structure reduces the on-state resistance and extends the longevity of the GaAs PCSS.

  1. Photoresistances of semi-insulating GaAs photoconductive switch illuminated by 1.064 μm laser pulse

    NASA Astrophysics Data System (ADS)

    Wu, Minghe; Zheng, Xiaoming; Ruan, Chengli; Yang, Hongchun; Sun, Yunqing; Wang, Shan; Zhang, Kedi; Liu, Hong

    2009-07-01

    The Shockley-Read-Hall model (SRHM) and its simplified model (SSRHM) were used to describe the characteristics of a photoconductive semiconductor switch (PCSS) made from a semi-insulating (SI) gallium arsenide (GaAs) chip, biased at low voltage, and illuminated by a 1.064 μm laser pulse. These characteristics include the free carrier densities, dynamic photoresistance, and time evolution of output pulses of the PCSS. The deep donor EL2 centers in SI GaAs play a dominant role in both the SRHM and SSRHM as electrons at EL2 unionized centers are strongly excited by the subband-gap photons at the wavelength of 1.064 μm. Theoretical modeling on the evolution of the experimental measured output pulses led to a two-step micromechanism of electron excitation process within the GaAs chip. The minimum photoresistances predicted by the SSRHM are in good agreement with experimental measurements, which confirms the dominant role of EL2 in the generation of electric pulses from a SI GaAs photoconductivity switch on which the 1064 nm laser pulse is illuminated.

  2. EL2 deep level defects and above-band gap two-photon absorption in high gain lateral semi-insulating GaAs photoconductive switch

    NASA Astrophysics Data System (ADS)

    Shi, Wei; Wang, Wei; Niu, Hongjian; Zhang, Xianbin; Ji, Weili

    2005-01-01

    Experiments of a lateral semi-insulating GaAs photoconductive switch, both linear and nonlinear mode of the switch were observed when the switch was triggered by 1064 nm laser pulses, with energy of 1.9 mJ and the pulse width of 60 ns, and operated at biased electric field of 4.37 kV/cm. It"s wavelength is longer than 876nm, but the experiments indicate that the semi-insulating GaAs photoconductive switches can absorb 1064 nm laser obviously, which is out of the absorption range of the GaAs material. It is not possible to explain this behavior by using intrinsic absorption mechanism. We think that there are two mostly kinds of absorption mechanisms play a key part in absorption process, they are the two-steps-single-photon absorption that based on the EL2 energy level and two-photon absorption.

  3. Precise determination of deep trap signatures and their relative and absolute concentrations in semi-insulating GaAs

    NASA Astrophysics Data System (ADS)

    Pavlović, M.; Desnica, U. V.

    1998-08-01

    The new analytical method, simultaneous multiple peak analysis (SIMPA) which comprises simultaneous fitting of whole measured thermally stimulated current (TSC) spectra is presented. The procedure clearly resolves contributions from various overlapping TSC peaks, which results in precise determination of trap parameters (signature) for each trap. In combination with photocurrent temperature dependent measurements, IPC(T), which reflects free carrier lifetime temperature dependence, the estimates of relative and absolute trap concentrations were made as well. The advantage of the SIMPA method in comparison with the single peak approach was demonstrated and analyzed. The SIMPA method was applied to different semi-insulating (SI) GaAs samples, particularly to samples having very high and others having very low deep trap concentrations; and for both extremes excellent fits were achieved. The method also seems very promising for characterization of deep levels and other similar SI materials, like SI InP or SI CdTe.

  4. Distributions of residual stress, dislocations, and EL2 in Czochralski-grown semi-insulating GaAs

    SciTech Connect

    Dobrilla, P.; Blakemore, J.S.

    1986-07-01

    Distributions of stress, dislocations, and the EL2 midgap defect have been optically mapped in semi-insulating GaAs wafers, from (100)-grown crystals created by the liquid-encapsulated Czochralski method. The evolution of EL2 along the growth axis indicates that assessment of this property through the majority of the crystal volume is often poorly represented by wafers from near the two end regions. A comparison of maps for stress, dislocation and EL2 patterns as all measured with a given wafer does not support hypotheses that EL2 is a direct consequence either of stress or of dislocations. Other mechanisms, such as segregation and melt dynamics, thus appear more likely to control the formation and distribution of EL2.

  5. Influence of EL2 deep level on photoconduction of semi-insulating GaAs under ultrashort pulse photoinjection

    NASA Astrophysics Data System (ADS)

    Shi, Wei; Xie, Guangyong

    2016-02-01

    To investigate the influence of EL2 deep level on photoconduction of in semi-insulating GaAs (SI-GaAs), a 3 mm-electrode-gap lateral SI-GaAs photoconductive chip was manufactured and tested by using ultrashort pulse laser with 1064 nm wavelength, 10 ns pulsewidth, 3.0 mm light spot diameter and single pulse energy mean of 3.0 mJ. Based on the experimental results and the theory of trapping effect, the photon absorption process of EL2 defects in SI-GaAs is analyzed. For the influence of EL2 deep level, the lifetime of the electron gets shorter and the persistent photoconductivity (PPC) is significant. With increasing of voltage, the decay time constant of photoconduction is reduced and the decay index gets bigger for the ultrashort pulse photoinjection.

  6. Current oscillations in semi-insulating GaAs associated with field-enhanced capture of electrons by the major deep donor EL2

    NASA Technical Reports Server (NTRS)

    Kaminska, M.; Parsey, J. M.; Lagowski, J.; Gatos, H. C.

    1982-01-01

    Current oscillations thermally activated by the release of electrons from deep levels in undoped semiinsulating GaAs were observed for the first time. They were attributed to electric field-enhanced capture of electrons by the dominant deep donor EL2 (antisite AsGa defect). This enhanced capture is due to the configurational energy barrier of EL2, which is readily penetrated by hot electrons.

  7. Simulating and modeling the breakdown voltage in a semi-insulating GaAs P+N junction diode

    NASA Astrophysics Data System (ADS)

    Resfa, A.; Menezla, Brahimi. R.; Benchhima, M.

    2014-08-01

    This work aims to determine the characteristic I (breakdown voltage) of the inverse current in a GaAs PN junction diode, subject to a reverse polarization, while specifying the parameters that influence the breakdown voltage of the diode. In this work, we simulated the behavior of the ionization phenomenon by impact breakdown by avalanche of the PN junctions, subject to an inverse polarization. We will take into account both the trapping model in a stationary regime in the P+N structure using like material of basis the III-V compounds and mainly the GaAs semi-insulating in which the deep centers have in important densities. We are talking about the model of trapping in the space charge region (SCR) and that is the trap density donor and acceptor states. The carrier crossing the space charge region (SCR) of W thickness creates N electron—hole pairs: for every created pair, the electron and the hole are swept quickly by the electric field, each in an opposite direction, which comes back, according to an already accepted reasoning, to the crossing of the space charge region (SCR) by an electron or a hole. So the even N pair created by the initial particle provoke N2 ionizations and so forth. The study of the physical and electrical behaviour of semiconductors is based on the influence of the presence of deep centers on the characteristic I(V) current-tension, which requires the calculation of the electrostatic potential, the electric field, the integral of ionization, the density of the states traps, the diffusion current of minority in the regions (1) and (3), the current thermal generation in the region (2), the leakage current in the surface, and the breakdown voltage.

  8. Interaction of deep levels and potential fluctuations in scattering and recombination phenomena in semi-insulating GaAs

    NASA Astrophysics Data System (ADS)

    Kažukauskas, V.; Storasta, J.; Vaitkus, J.-V.

    1996-08-01

    The complex influence of recombination centers and potential fluctuations of the band gap on the scattering and recombination phenomena in n-type semiinsulating liquid- encapsulated-Czochralski-grown GaAs were investigated by using the transient photoconductivity and photo-Hall effects. The inhomogeneities cause a hyperbolic decrease of nonequilibrium carrier concentration and the saturation of Hall mobility, while the exponential parts of the decay appear due to the recharge of deep levels. The mean recombination barrier heights of potential fluctuations were evaluated. We propose a complex ``island'' model of scattering and recombination centers, consisting of defect clusters and their associations around dislocations, surrounded by potential barriers. At low light intensities and at the temperatures below 330 K they are insulating for majority charge carriers, thus reducing an effective crystal volume and causing percolation transport effects. At the temperature higher than 330-360 K the main barrier of the island can be recharged or screened by nonequilibrium carriers and its fine barrier structure appears as an effective scatterer, causing a sharp decrease of the nonequilibrium Hall mobility. It was demonstrated that although doping with Sb reduce dislocation density, it can intensify the effect of smaller defects on transport phenomena.

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

    SciTech Connect

    Ma, Deming Qiao, Hongbo; Shi, Wei; Li, Enling

    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.

  10. Deep levels induced by high fluence proton irradiation in undoped GaAs diodes

    SciTech Connect

    Castaldini, A.; Cavallini, A.; Polenta, L.; Canali, C.; Nava, F.; Ferrini, R.; Galli, M.

    1998-12-31

    Semi-insulating liquid encapsulated Czochralski grown GaAs has been investigated after irradiation at high fluences of high-energy protons. Electron beam induced current observations of scanning electron microscopy evidenced a radiation stimulated ordering. An analysis has been carried out of the deep levels associated with defects as a function of the irradiation fluence, using complementary current transient spectroscopies. By increasing the irradiation fluence, the concentration of the native traps at 0.37 eV together with that of the EL2 defect significantly increases and, at the same time, two new electron traps at 0.15 eV and 0.18 eV arise and quickly increase in density.

  11. Photoluminescence of PbS Quantum Dots on Semi-Insulating GaAs (Postprint)

    DTIC Science & Technology

    2010-07-01

    ns ity (a rb .u ni ts ) Energy (eV) 5 K 100 K 200 K 300 K InGaAs...detector. 0 20 40 60 80 100 120 140 0.20 0.40 0.60 0.80 1.00 PL in te ns ity (a rb .u ni ts ) Energy (eV) 5 K 20 K 50 K 100 K 150 K 200 K 250 K 300 K InSb...3.0 0 10 20 30 40 50 0.2 0.4 0.6 0.8 1.0 PL in te ns ity (a rb .u ni ts ) Energy (eV) SI GaAs PbS/SI GaAs5 K FIG. 4. Color online Comparison of the

  12. Carbon irradiated semi insulating GaAs for photoconductive terahertz pulse detection.

    PubMed

    Singh, Abhishek; Pal, Sanjoy; Surdi, Harshad; Prabhu, S S; Mathimalar, S; Nanal, Vandana; Pillay, R G; Döhler, G H

    2015-03-09

    We report here a photoconductive material for THz detection with sub-picosecond carrier lifetime made by C(12) (Carbon) irradiation on commercially available semi-insulating (SI) GaAs. We are able to reduce the carrier lifetime of SI-GaAs down to sub-picosecond by irradiating it with various irradiation dosages of Carbon (C(12)) ions. With an increase of the irradiation dose from ~10(12) /cm(2) to ~10(15) /cm(2) the carrier lifetime of SI-GaAs monotonously decreases to 0.55 picosecond, whereas that of usual non-irradiated SI-GaAs is ~70 picosecond. This decreased carrier lifetime has resulted in a strong improvement in THz pulse detection compared with normal SI-GaAs. Improvement in signal to noise ratio as well as in detection bandwidth is observed. Carbon irradiated SI-GaAs appears to be an economical alternative to low temperature grown GaAs for fabrication of THz devices.

  13. Optical characterization of semi-insulating GaAs - Determination of the Fermi energy, the concentraion of the midgap EL2 level and its occupancy

    NASA Technical Reports Server (NTRS)

    Lagowski, J.; Bugajski, M.; Matsui, M.; Gatos, H. C.

    1987-01-01

    The key electronic characteristics of semiinsulating GaAs, i.e., the Fermi energy, concentration, and occupancy of the midgap donor EL2, and the net concentration of ionized acceptors can all be determined from high-resolution measurements of the EL2 intracenter absorption. The procedure is based on the measurement of zero-phonon line intensity before and after the complete transfer of EL2 to its metastable state followed by thermal recovery. The procedure is quantitative, involves no fitting parameters, and unlike existing methods, is applicable even when a significant part of the EL2 is ionized.

  14. Measured and computed performance of a microstrip filter composed of semi-insulating GaAs on a fused quartz substrate

    NASA Technical Reports Server (NTRS)

    Siegel, Peter H.; Dengler, Robert J.; Oswald, John E.; Sheen, David M.; Ali, Sami M.

    1991-01-01

    The performance of a microstrip hammerhead filter that has been fabricated on an electrically thin layer of semiinsulating GaAs backed by a fused quartz substrate was measured and compared to results of a three-dimensional finite-difference time-domain (FD-TD) program used to calculate the response of the filter both with and without the GaAs layer. The program, presented by Sheen et al. (1990), discretizes the entire structure and then simulates the propagation of a Gaussian pulse through the filter. The microstrip filter is intended for applications involving ultrathin lifted-off or etched-back GaAs containing both active devices and passive microstrip circuitry backed by a much thicker mechanically rigid low-loss, low-dielectric-constant substrate. The low-pass characteristics of the hammerhead filter with the intermediate GaAs layer are compared with those of the same filter on quartz alone. Both the measured and computed data show a significant shift in cutoff frequency (about 10 percent at the 3 dB points) for a GaAs layer that is 0.007 wavelengths thick at 4 GHz.

  15. Measured and computed performance of a microstrip filter composed of semi-insulating GaAs on a fused quartz substrate

    NASA Technical Reports Server (NTRS)

    Siegel, Peter H.; Dengler, Robert J.; Oswald, John E.; Sheen, David M.; Ali, Sami M.

    1991-01-01

    The performance of a microstrip hammerhead filter that has been fabricated on an electrically thin layer of semiinsulating GaAs backed by a fused quartz substrate was measured and compared to results of a three-dimensional finite-difference time-domain (FD-TD) program used to calculate the response of the filter both with and without the GaAs layer. The program, presented by Sheen et al. (1990), discretizes the entire structure and then simulates the propagation of a Gaussian pulse through the filter. The microstrip filter is intended for applications involving ultrathin lifted-off or etched-back GaAs containing both active devices and passive microstrip circuitry backed by a much thicker mechanically rigid low-loss, low-dielectric-constant substrate. The low-pass characteristics of the hammerhead filter with the intermediate GaAs layer are compared with those of the same filter on quartz alone. Both the measured and computed data show a significant shift in cutoff frequency (about 10 percent at the 3 dB points) for a GaAs layer that is 0.007 wavelengths thick at 4 GHz.

  16. Electron-paramagnetic-resonance study of the isolated arsenic antisite in electron irradiated GaAs and its relation to the EL2 center

    SciTech Connect

    Rong, F.C.; Buchwald, W.R.; Harmatz, M.; Poindexter, E.H. ); Warren, W.L. )

    1991-10-28

    Arsenic antisites produced in GaAs by room-temperature electron irradiation (RTEI) are examined by electron paramagnetic resonance (EPR). For the first time, this RTEI antisite, which has been believed to be the isolated antisite, is found to be metastable. The most efficient photon energy for photoquenching is found to be approximately 1.15 eV, which is very close to that observed for the well-known EL2 center in undoped semi-insulating GaAs. However, the thermal recovery temperature is about 200--250 K, much higher than that for the EL2 center.

  17. Semi-insulating GaAs detectors with HDPE layer for detection of fast neutrons from D-T nuclear reaction

    NASA Astrophysics Data System (ADS)

    Sagatova, Andrea; Zatko, Bohumir; Sedlackova, Katarina; Pavlovic, Marius; Necas, Vladimir; Fulop, Marko; Solar, Michael; Granja, Carlos

    2016-09-01

    Bulk semi-insulating (SI) GaAs detectors optimized for fast-neutron detection were examined using mono-energetic neutrons. The detectors have an active area of 7.36 mm2 defined by a multi-pixel structure of a AuZn Schottky contact allowing a relatively high breakdown voltage (300 V) sufficient for full depletion of the detector structure. The Schottky contact is covered by a HDPE (high density polyethylene) conversion layer, where neutrons transfer their kinetic energy to hydrogen atoms through elastic nuclear collisions. The detectors were exposed to mono-energetic neutrons generated by a deuterium (D)-tritium (T) nuclear reaction at a Van de Graaff accelerator. Neutrons reached a kinetic energy of 16.8 MeV when deuterons were accelerated by 1 MV potential. The influence of the HDPE layer thickness on the detection efficiency of the fast neutrons was studied. The thickness of the conversion layer varied from 50 μm to 1300 μm. The increase of the HDPE layer thickness led to a higher detection efficiency due to higher conversion efficiency of the HDPE layer. The effect of the active detector thickness modified by the detector reverse bias voltage on the detection efficiency was also evaluated. By increasing the detector reverse voltage, the detector active volume expands to the depth and also to the sides, slightly increasing the neutron detection efficiency.

  18. High Resolution Parameter-Space from a Two-Level Model on Semi-Insulating GaAs

    NASA Astrophysics Data System (ADS)

    da Silva, S. L.; Viana, E. R.; de Oliveira, A. G.; Ribeiro, G. M.; da Silva, R. L.

    Semi-insulating Gallium Arsenide (SI-GaAs) samples experimentally show, under high electric fields and even at room temperature, negative differential conductivity in N-shaped form (NNDC). Since the most consolidated model for n-GaAs, namely, "the model", proposed by E. Schöll was not capable to generate the NNDC curve for SI-GaAs, in this work we have proposed an alternative model. The model proposed, "the two-valley model" is based on the minimal set of generation-recombination equations for two valleys inside of the conduction band, and an equation for the drift velocity as a function of the applied electric field, that covers the physical properties of the nonlinear electrical conduction of the SI-GaAs system. The "two-valley model" was capable to generate theoretically the NNDC region for the first time, and with that, we were able to build a high resolution parameter-space of the periodicity (PSP) using a Periodicity-Detection (PD) routine. In the parameter-space were observed self-organized periodic structures immersed in chaotic regions. The complex regions are presented in a "shrimp" shape rotated around a focal point, which forms in large-scale a "snail shell" shape, with intricate connections between different "shrimps". The knowledge of detailed information on parameter spaces is crucial to localize wide regions of smooth and continuous chaos.

  19. High energy oxygen irradiation-induced defects in Fe-doped semi-insulating indium phosphide by positron annihilation technique

    NASA Astrophysics Data System (ADS)

    Pan, S.; Mandal, A.; Sohel, Md. A.; Saha, A. K.; Das, D.; Sen Gupta, A.

    2017-02-01

    Positron annihilation technique is applied to study the recovery of radiation-induced defects in 140 MeV oxygen (O6+) irradiated Fe-doped semi-insulating indium phosphide during annealing over a temperature region of 25∘C-650∘C. Lifetime spectra of the irradiated sample are fitted with three lifetime components. Trapping model analysis is used to characterize defect states corresponding to the de-convoluted lifetime values. After irradiation, the observed average lifetime of positron τavg = 263 ps at room temperature is higher than the bulk lifetime by 21 ps which reveals the presence of radiation-induced defects in the material. A decrease in τavg occurs during room temperature 25∘C to 200∘C indicating the dissociation of higher order defects, might be due to positron trapping in acceptor-type of defects (VIn). A reverse annealing stage is found at temperature range of 250∘C-425∘C for S-parameter probably due to the migration of vacancies and the formation of vacancy clusters. Increase in R-parameter from 325∘C to 425∘C indicates the change in the nature of predominant positron trapping sites. Beyond 425∘C, τavg, S-parameter and R-parameter starts decreasing and around 650∘C, τavg and S-parameter approached almost the bulk value showing the annealing out of radiation-induced defects.

  20. Neutron irradiation effects on the infrared absorption of the EL2 defect in GaAs: New interpretation for the intracenter transition

    SciTech Connect

    Manasreh, M.O.; Fischer, D.W.; Covington, B.C.

    1988-04-15

    The effect of neutron irradiation on the optical properties of the EL2 center in semi-insulating GaAs was studied using the infrared absorption technique. The results show that the absorption band known as the intracenter transition between 1.03 and 1.27 eV is decreased by neutron irradiation. This absorption band is interpreted as a charge-transfer transition between the As/sub Ga/ antisite and an X component(s) assuming that EL2equivalentAs/sub Ga/+X. The neutron irradiation increases the As/sub Ga/ antisite concentration and reduces the EL2 concentration. The reduction of the EL2 concentration is due to the decrease of the X-component concentration. The zero-phonon line observed at 1.039 eV may not be an internal optical excitation within the isolated As/sub Ga/ antisite.

  1. Formation and coarsening of Ga droplets on focused-ion-beam irradiated GaAs surfaces

    SciTech Connect

    Wu, J. H.; Ye, W.; Cardozo, B. L.; Saltzman, D.; Sun, K.; Sun, H.; Mansfield, J. F.; Goldman, R. S.

    2009-10-12

    We have investigated the formation and coarsening of Ga droplets on focused-ion-beam (FIB) irradiated GaAs surfaces. To separately examine formation and coarsening, Ga droplets were fabricated by Ga{sup +} FIB irradiation of GaAs substrates with and without pre-patterned holes. We determined the droplet growth rate and size distribution as a function of FIB energy following irradiation. The data suggest a droplet formation mechanism that involves Ga precipitation from a Ga-rich layer, followed by droplet coarsening via a combination of diffusion and Ostwald ripening or coalescence via droplet migration (dynamic coalescence)

  2. The influence of the scatter of heat flux at the m/c interface on the frequency of appearance of poly body and twin defects during 6″ semi-insulating GaAs crystal growth by the VGF method

    NASA Astrophysics Data System (ADS)

    Marchenko, Marina P.; Liu, Weiguo; Badawi, M. Hani; Yin, Phil

    2008-04-01

    The challenge of increasing and maintaining a high yield for 6″ GaAs crystal growth is of utmost importance for meeting the price requirements dictated by today's requirements for semi-insulating GaAs substrates. For maintaining a low dislocation density in the grown ingots, the growth process time is typically long and, sometimes, the final ingots may exhibit twins and poly-crystalline formation. These defects may occur at the beginning of the cylindrical part of the ingot, or even at the conical part of pBN crucible so the whole ingot is rejected. On the other hand, these defects may appear further away from the seed and the location of the onset of these defects will determine the extent of the useful (production worthy) crystal length, also known as "yield". The reasons for the onset of these defects are, however, not fully understood [M. Jurisch, F. Borner, Th. Bunger, St. Eichler, T. Flade, U. Kretser, A. Kohler, J. Stenzenberger, B. Weinert. J. Crystal Growth 275 (2005) 283]. In this study, we conducted numerical simulation using the transient two-dimensional mathematical model of the GaAs crystal growth by vertical gradient freeze method (VGF-method). We defined a new parameter " A" that is equal to the scatter of heat fluxes at m/c interface. Our study showed that some correlation exists between the defect appearance and A-value at m/c interface close to crucible wall. We have found that the frequency of a totally bad crystal length is higher if the A-value exceeds a certain value. Close to the crystal tail the scatter must be less than a defined A-value at the beginning of crystallization. Reduction in A-value was found to occur due to anomalies in the melt flow close to the m/c interface and crucible wall leading to the higher frequency of defects close to the crystal tail. Based on the correlation found, we developed a new technology regime that results in crystals grown with a lower frequency of defect occurrence at crucible wall.

  3. 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

    SciTech Connect

    Biswas, Pranab; Banerji, P.; Halder, Nripendra N.; Kundu, Souvik; Shripathi, T.; Gupta, M.

    2014-05-15

    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 × 10{sup 18} cm{sup −3} and 2.8 × 10{sup 19} cm{sup −3} respectively, whereas those annealed at 800 ºC showed n-type conductivity with a carrier concentration of 6.5 × 10{sup 16} cm{sup −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, (As{sub Zn}–2V{sub Zn}), by substituting Zn atoms (As{sub Zn}) and thereby creating two zinc vacancies (V{sub Zn}). 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, Ga{sub Zn}. 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.

  4. Detection of Ga vacancies in electron irradiated GaAs by positrons

    SciTech Connect

    Hautojaervi, P.; Moser, P.; Stucky, M.; Corbel, C.; Plazaola, F.

    1986-03-24

    Positron lifetime measurements have been used to study the recovery of electron irradiated GaAs between 77 and 800 K. Below room temperature positrons are trapped by vacancies in Ga sublattices. The Ga vacancies recover between 200 and 350 K.

  5. Study on Nonlinear Absorption Effect of Nanosecond Pulse Laser Irradiation for GaAs.

    PubMed

    Sun, Wenjun; Liu, Zhongyang; Zhou, Haijiao

    2016-04-01

    In order to research nonlinear absorption effect of pulse laser irradiation for GaAs, a physical model of Gaussian distribution pulse laser irradiation for semiconductor material was established by software COMSOL Multiphysics. The thermal effects of semiconductor material GaAs was analyzed under irradiation of nanosecond pulse laser with wavelength of 1064 nm. The radial and transverse temperature distribution of semiconductor material GaAs was calculated under irradiation of nanosecond pulse laser with different power density by solving the thermal conduction equations. The contribution of one-photon absorption, two-photon absorption and free carrier absorption to temperature of GaAs material were discussed. The results show that when the pulse laser power density rises to 10(10) W/cm2, free carrier absorption played a leading role and it was more than that of one-photon absorption of material. The temperature contribution of two-photon absorption and free carrier absorption could be ignored at laser power density lower than 10(8) W/cm2. The result is basically consistent with relevant experiments, which shows that physical model constructed is valid.

  6. Photo-recovery of electron-irradiated GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Meulenberg, Andrew

    1995-01-01

    The first long-term (3000 hours) UV testing of unirradiated and 1 MeV electron-irradiated GaAs solar cells, with multilayer-coated coverslides to reduce solar array operating temperature, has produced some unexpected and important results. Two results, independent of the coverslide coatings, are of particular importance in terms of the predictability of GaAs solar-array lifetime in space: ( 1) The GaAs/Ge solar cells used for this series of tests displayed a much higher radiation degradation than that predicted based on JPL Solar Cell Radiation Handbook data. Covered cells degraded more in Isc than did bare cells. Short-term illumination at 60 C did not produce significant recovery (-1%) of the radiation damage. (2) However, electron radiation damage to these GaAs solar celIs anneals at 40 C when exposed to approximately 1 sun AM0 UV light sources for extended periods. The effect appears to be roughly linear with time (-1% of lsc per 1000 UVSH), is large (greater than or equal to 3%), and has not yet saturated (at 3000 hours). This photo-recovery of radiation damage to GaAs solar cells is a new effect and potentially important to the spacecraft community. The figure compares the effects of extended UV on irradiated and unirradiated GaAs solar cells with INTELSAT-6 Si cells. The effect and its generality, the extent of and conditions for photo-recovery, and the implications of such recovery for missions in radiation environments have not yet been determined.

  7. Variation of deep electron traps created by. gamma. irradiation of GaAs

    SciTech Connect

    Hashizume, T. ); Hasegawa, H. )

    1990-11-01

    The effect of {gamma} irradiation on deep electron states in liquid encapsulated Czochralski (LEC) grown GaAs has been investigated by deep-level transient spectroscopy (DLTS) and photocapacitance measurements. With {gamma} rays of 2{times}10{sup 8} R, EL6 was reduced in concentration by a factor of 3--5, whereas EL3 was increased about one order of magnitude, as compared with those in as-grown material. In addition to {ital E} traps that were previously reported in electron-irradiated material, two new traps were observed near the surface region. From their concentration profiles and annealing behavior, the new traps were most likely created by the interaction of the primary irradiation-induced defects with the grown-in defects. In contrast to these results, neither the DLTS spectrum nor the metastable behavior of EL2 was affected by {gamma} irradiation.

  8. Effect of semiconductor GaAs laser irradiation on pain perception in mice

    SciTech Connect

    Zarkovic, N.; Manev, H.; Pericic, D.; Skala, K.; Jurin, M.; Persin, A.; Kubovic, M.

    1989-01-01

    The influence of subacute exposure (11 exposures within 16 days) of mice to the low power (GaAs) semiconductive laser-stimulated irradiation on pain perception was investigated. The pain perception was determined by the latency of foot-licking or jumping from the surface of a 53 degrees C hot plate. Repeated hot-plate testing resulted in shortening of latencies in both sham- and laser-irradiated mice. Laser treatment (wavelength, 905 nm; frequency, 256 Hz; irradiation time, 50 sec; pulse duration, 100 nsec; distance, 3 cm; peak irradiance, 50 W/cm2 in irradiated area; and total exposure, 0.41 mJ/cm2) induced further shortening of latencies, suggesting its stimulatory influence on pain perception. Administration of morphine (20 mg/kg) prolonged the latency of response to the hot plate in both sham- and laser-irradiated mice. This prolongation tended to be lesser in laser-irradiated animals. Further investigations are required to elucidate the mechanism of the observed effect of laser.

  9. Performance of Hughes GaAs concentrator cells under 1-MeV electron irradiation

    NASA Technical Reports Server (NTRS)

    Curtis, H. B.; Swartz, C. K.

    1985-01-01

    Several Hughes gallium arsenide (GaAs) concentrator cells were exposed to 1-MeV electrons at fluences up to 1x10 to the 15th power electrons/sq cm. Performance data were taken after several fluences, at two temperatures, and at concentration levels from 1 to approx. 150x AMO. Data at 1 sun and 25 deg C were taken with an X-25 xenon-lamp solar simulator. Data at concentration were taken using a pulsed solar simulator with the assumption of a linear relationship between short-circuit current and irradiance. The cells are 5 by 5 mm with a 4-mm diameter illuminated area.

  10. NIEL calculations for estimating the displacement damage introduced in GaAs irradiated with charged particles

    NASA Astrophysics Data System (ADS)

    El Allam, E.; Inguimbert, C.; Addarkaoui, S.; Meulenberg, A.; Jorio, A.; Zorkani, I.

    2017-03-01

    The application of Non-Ionizing Energy Loss (NIEL) in estimating the impact of electron, proton, and heavy ion irradiations on Gallium Arsenide is presented in this paper. The NIEL for deuteron, alpha particle, lithium ion and oxygen ion is computed using the SR-NIEL and NEMO codes. The NIEL calculations are compared with the introduction rate of displacement damage measured in n-type GaAs. Very good agreement is found between the NIEL and experimental results for protons (< 20 MeV), electrons, and a variety of ions. However, a discrepancy can be observed for high-energy protons.

  11. Radiation Resistance Study of Semi-Insulating GaAs-Based Radiation Detectors to Extremely High Gamma Doses

    NASA Astrophysics Data System (ADS)

    Ly Anh, T.; Perd'ochová, A.; Nečas, V.; Pavlicová, V.

    2006-01-01

    In our previous paper [V. Nečas et al.: Nucl. Inst. and Meth. A 458 (2001) 348-351] we reported on the study on radiation stability of semi-insulating (SI) LEG GaAs detectors to doses of photons from 60Co up to 19.2 kGy. Later we presented a study, which covered radiation hardness to the same doses on the base of detector material itself, where strong dependence has been proved [T. Ly Anh et al., Proceedings of the XII th International Conference on Semiconducting and Insulating Materials (SIMC-XII-2002). Smolenice Castle, Slovakia (2002) 292-295 (0-7803-7418-5)]. In this paper we present both the key electrical and detection characteristics of SI GaAs radiation detectors prepared using substrates from four various supplies and two different types of contacts, which were exposed to several gamma doses from 60Co up to the integral dose of about 1 MGy. The obtained results show that SI LEG GaAs detectors provide good spectroscopic performances and even their slight improvement after low to middle gamma irradiation doses (3 -10 kGy) was observed. Further dose exposure caused the degradation of detection properties with an extreme and following improvement depending on detector material properties. SI GaAs detector still retains its working capabilities even after very high doses applied, up to 1 MGy.

  12. Void evolution and porosity under arsenic ion irradiation in GaAs1‑x Sb x alloys

    NASA Astrophysics Data System (ADS)

    Alkhaldi, H. S.; Kluth, P.; Kremer, F.; Lysevych, M.; Li, L.; Ridgway, M. C.; Williams, J. S.

    2017-03-01

    We have studied the formation of porosity in crystalline GaAs0.25Sb0.75 and GaAs0.5Sb0.5 alloys under irradiation with 140 keV As‑ ions over a wide range of temperature (‑180 to 400 °C) and ion fluences ranging from 1× {{10}13} to 2× {{10}17} ions cm‑2. The GaAs0.25Sb0.75 alloy showed only little swelling (in comparison with GaSb), with void formation and sputtering both playing an important role in the materials modification. The initiation of voids and their evolution in the alloy strongly depends on the ion fluence and irradiation temperature, as well as the As content in the alloy. Porosity is largely suppressed in the GaAs0.25Sb0.75 alloy, with the major change being void formation. For the GaAs0.5Sb0.5 alloy, it was rendered amorphous with no apparent pores or void structures and only sputtering effects were observed at high ion fluence. In addition, the transformations from crystalline to amorphous and to a void or a porous structure occurred simultaneously in the GaAs0.25Sb0.75 alloy. The mechanisms responsible for such changes are consistent with point defect movement and segregation.

  13. Inverted thermal conversion - GaAs, a new alternative material for integrated circuits

    NASA Technical Reports Server (NTRS)

    Lagowski, J.; Gatos, H. C.; Kang, C. H.; Skowronski, M.; Ko, K. Y.

    1986-01-01

    A new type of GaAs is developed which exhibits inverted thermal conversion (ITC); i.e., it converts from conducting to semiinsulating upon annealing at about 850 C. In device fabrication, its low resistivity prior to high-temperature processing differentiates ITC GaAs from the standard semiinsulating GaAs. The ITC characteristics are obtained through control of the concentration of the midgap donor EL2 based on heat treatment and crystal-growth modification. Thus EL2 does not exist in the conducting state of ITC GaAs. Conversion to the semiinsulating state during 850 C annealing is caused by the formation of EL2.

  14. Defect production in electron-irradiated, n-type GaAs

    NASA Astrophysics Data System (ADS)

    Look, D. C.; Sizelove, J. R.

    1987-11-01

    Energies and production rates for a pure vapor-phase epitaxial GaAs layer irradiated by 1-MeV electrons were obtained from measurements of temperature-dependent Hall (TDH) effect and were compared with published data based on deep-level transient spectroscopy (DLTS). The TDH energy and production rates of two dominant defect centers, C2 and C3, were in good agreement with DLTS data. The most important result of this study is a very high production rate (4 + or - 1/cm) for 'shallow' acceptors C(AS) lying below C3-energy. C(AS) were found to be produced at a much higher rate than all of the DLTS traps observed in this energy range, indicating that close to half of the primary defects in electron-irradiated GaAs are not seen by DLTS. For microscopic models of the electron traps C1 and C2, the high C(AS) production rate renders unnecessary the assumption that one of these centers must be an acceptor in order to explain the Hall-effect results. It is shown that all available HDT and DLTS data are consistent with the C(AS) representing Ga-sublattice damage, a fact which has not been observed before.

  15. LEC GaAs for integrated circuit applications

    NASA Technical Reports Server (NTRS)

    Kirkpatrick, C. G.; Chen, R. T.; Homes, D. E.; Asbeck, P. M.; Elliott, K. R.; Fairman, R. D.; Oliver, J. D.

    1984-01-01

    Recent developments in liquid encapsulated Czochralski techniques for the growth of semiinsulating GaAs for integrated circuit applications have resulted in significant improvements in the quality and quantity of GaAs material suitable for device processing. The emergence of high performance GaAs integrated circuit technologies has accelerated the demand for high quality, large diameter semiinsulating GaAs substrates. The new device technologies, including digital integrated circuits, monolithic microwave integrated circuits and charge coupled devices have largely adopted direct ion implantation for the formation of doped layers. Ion implantation lends itself to good uniformity and reproducibility, high yield and low cost; however, this technique also places stringent demands on the quality of the semiinsulating GaAs substrates. Although significant progress was made in developing a viable planar ion implantation technology, the variability and poor quality of GaAs substrates have hindered progress in process development.

  16. Observing visible-range photoluminescence in GaAs nanowires modified by laser irradiation

    NASA Astrophysics Data System (ADS)

    Alekseev, P. A.; Dunaevskiy, M. S.; Kirilenko, D. A.; Smirnov, A. N.; Davydov, V. Yu.; Berkovits, V. L.

    2017-02-01

    We study the structural and chemical transformations induced by focused laser beam in GaAs nanowires with an axial zinc-blende/wurtzite (ZB/WZ) heterostructure. The experiments are performed using a combination of transmission electron microscopy, energy-dispersive X-ray spectroscopy, Raman scattering, and photoluminescence spectroscopy. For both the components of heterostructure, laser irradiation under atmospheric air is found to produce a double surface layer which is composed of crystalline arsenic and of amorphous GaOx. The latter compound is responsible for the appearance of a peak at 1.76 eV in photoluminescence spectra of GaAs nanowires. Under an increased laser power density, due to sample heating, evaporation of the surface crystalline arsenic and formation of β-Ga2O3 nanocrystals proceed on the surface of the zinc-blende part of nanowire. The formed nanocrystals reveal a photoluminescence band in a visible range of 1.7-2.4 eV. At the same power density for wurtzite part of the nanowire, total amorphization with the formation of β-Ga2O3 nanocrystals occurs. Observed transformation of WZ-GaAs to β-Ga2O3 nanocrystals presents an available way for the creation of axial and radial heterostructures ZB-GaAs/β-Ga2O3 for optoelectronic and photonic applications.

  17. Investigation of new semiinsulating behavior of III-V compounds

    NASA Technical Reports Server (NTRS)

    Lagowski, Jacek

    1990-01-01

    The investigation of defect interactions and properties related to semiinsulating behavior of III-V semiconductors resulted in about twenty original publications, six doctoral thesis, one masters thesis and numerous conference presentations. The studies of new compensation mechanisms involving transition metal impurities have defined direct effects associated with deep donor/acceptor levels acting as compensating centers. Electrical and optical properties of vanadium and titanium levels were determined in GaAs, InP and also in ternary compounds InGaAs. The experimental data provided basis for the verification of chemical trends and the VRBE method. They also defined compositional range for III-V mixed crystals whereby semiinsulating behavior can be achieved using transition elements deep levels and a suitable codoping with shallow donor/acceptor impurities.

  18. Comparison of neutron and electron irradiation on the EL2 defect in GaAs

    NASA Astrophysics Data System (ADS)

    Lai, S. T.; Nener, B. D.; Alexiev, D.; Faraone, L.; Ku, T. C.; Dytlewski, N.

    1995-04-01

    The deep level transient spectroscopy technique has been used to study the EL2 defect in n-type semiconducting GaAs subjected to 1 MeV fast neutrons at room temperature. After neutron irradiation, the EL3 defect which is usually detected between 180 and 210 K disapperared and the EL2 defect measured between 280 and 320 K was found to remain single exponential (Ec-0.820 eV) despite the creation of a broad U band measured between 100 and 270 K. From this result, together with our earlier reports on the double exponential capacitance transient of the EL2 defect after 1 MeV electron irradiation [Lai, Nener, Faraone, Nassibian, and Hotchkis, J. Appl. Phys. 73, 640 (1993)] and the behavior of the electron irradiated EL2 defect upon isochronal annealing [Lai and Nener, J. Appl. Phys. 75, 2354 (1994)], we observe a difference in the behavior of the EL2 defect after neutron and electron irradiation. The results of the present study indicate that the EL2-B level reported in an earlier work is not due to any interaction of the stable EL2 (or EL2-A) level with either the U-band or EL6 defect. The EL2 defect is likely to be a complex defect which can manifest itself as a number of different defect levels depending on the particular details of the irradiation used. The U band is likely to be a cluster defect caused by the large number of atoms displaced from lattice sites by the fast neutrons, and is not likely to be due to any interaction mechanism between the EL2 and EL6 defects.

  19. Pulsed laser irradiation of GaAs under oxygen and silane atmosphere: Incorporation, losses, influence of native oxide

    NASA Astrophysics Data System (ADS)

    Cohen, C.; Siejka, J.; Berti, M.; Drigo, A. V.; Bentini, G. G.; Pribat, D.; Jannitti, E.

    1984-06-01

    Gallium arsenide single crystals and thin GaAs amorphous deposits (in the 100-nm range) on Si have been irradiated by pulsed (15 ns) ruby laser under various pressures of 16O2. All the samples were anodically preoxidized in order to obtain a 10-nm-thick 18O enriched oxide, the aim being to study the influence of native oxide on oxygen incorporation during irradiation. Nuclear microanalysis and channeling experiments provide information on (i) 16O incorporation, (ii) 18O losses and concentration profile, (iii) Ga and As atoms out of crystallographic sites for single crystal irradiations, and (iv) Ga and As losses for thin films irradations. Our results demonstrate that a surface oxide is formed with a composition near the Ga2O3-As2O3 stoichiometry via oxygen penetration in the melted layer once the native oxide has been evaporated at irradiation energies above 1 J/cm2. Before complete evaporation,this latter oxide diffuses in GaAs and is responsible for defect creation at irradiation energies as low as 0.4 J/cm2. We also find that for irradiation in vacuum the surface composition varies continuously, from Ga to As rich, when the irradiation energy density goes from 0.4 to 1.5 J/cm2. Pulsed irradiations at 0.53 μm under silane atmosphere lead to strong Si doping. We show that the mechanism involved is pyrolisis of SiH4, surface deposition of the Si formed and finally diffusion of the deposited layer in GaAs during melting.

  20. Defect characterization of proton irradiated GaAs pn-junction diodes with layers of InAs quantum dots

    NASA Astrophysics Data System (ADS)

    Sato, Shin-ichiro; Schmieder, Kenneth J.; Hubbard, Seth M.; Forbes, David V.; Warner, Jeffrey H.; Ohshima, Takeshi; Walters, Robert J.

    2016-05-01

    In order to expand the technology of III-V semiconductor devices with quantum structures to both terrestrial and space use, radiation induced defects as well as native defects generated in the quantum structures should be clarified. Electrically active defects in GaAs p+n diodes with embedded ten layers of InAs quantum dots (QDs) are investigated using Deep Level Transient Fourier Spectroscopy. Both majority carrier (electron) and minority carrier (hole) traps are characterized. In the devices of this study, GaP layers are embedded in between the QD layers to offset the compressive stress introduced during growth of InAs QDs. Devices are irradiated with high energy protons for three different fluences at room temperature in order to characterize radiation induced defects. Seven majority electron traps and one minority hole trap are found after proton irradiation. It is shown that four electron traps induced by proton irradiation increase in proportion to the fluence, whereas the EL2 trap, which appears before irradiation, is not affected by irradiation. These defects correspond to electron traps previously identified in GaAs. In addition, a 0.53 eV electron trap and a 0.14 eV hole trap are found in the QD layers before proton irradiation. It is shown that these native traps are also unaffected by irradiation. The nature of the 0.14 eV hole trap is thought to be Ga-vacancies in the GaP strain balancing layers.

  1. Surface patterning of GaAs under irradiation with very heavy polyatomic Au ions

    NASA Astrophysics Data System (ADS)

    Bischoff, L.; Böttger, R.; Heinig, K.-H.; Facsko, S.; Pilz, W.

    2014-08-01

    Self-organization of surface patterns on GaAs under irradiation with heavy polyatomic Au ions has been observed. The patterns depend on the ion mass, and the substrate temperature as well as the incidence angle of the ions. At room temperature, under normal incidence the surface remains flat, whereas above 200 °C nanodroplets of Ga appear after irradiation with monatomic, biatomic as well as triatomic Au ions of kinetic energies in the range of 10-30 keV per atom. In the intermediate temperature range of 100-200 °C meander- and dot-like patterns form, which are not related to Ga excess. Under oblique ion incidence up to 45° from the surface normal, at room temperature the surface remains flat for mon- and polyatomic Au ions. For bi- and triatomic ions in the range of 60° ≤ α ≤ 70° ripple patterns have been found, which become shingle-like for α ≥ 80°, whereas the surface remains flat for monatomic ions.

  2. Investigation of New Semiinsulating Behavior of III-V Compounds.

    DTIC Science & Technology

    1990-02-23

    Publications SuDported by AFOSR Grant A.M. Hennel, C.D. Brandt, K.Y. Ko, J. Lagowski, and H.C. Gatos , "Optical and electronic properties of vanadium in...gallium arsenide", J. Appl. Phys. 62. 163 (1987) J. Lagowski, M. Bugajski, M. Matsui, and H.C. Gatos , "Optical characterization of semi-insulating GaAs...Lagowski, M. Milshtein, C.H. Kang, F.P. Dabkuwski, A. Hennel, and H.C. Gatos , "Effect of plastic deformation on electronic properties of GaAs". J. Appl

  3. Mixed conduction in semi-insulating gallium arsenide

    NASA Astrophysics Data System (ADS)

    Winter, J. J.; Leupold, H. A.; Ross, R. L.; Ballato, A.

    1982-12-01

    Hall effect and conductivity measurements made on semi-insulating bulk GaAs are examined by a new approach to mixed conduction analysis. Based on Fermi level and electron mobility analyses of conductivity and Hall coefficient, it uses revised values of effective densities of states at the band edges, and electron/hole mobility ratios recently adopted by other workers. The treatment provides a visual analysis of the system in terms of the electrical parameters and impurity densities, and establishes criteria for the onset of mixed conduction.

  4. Experimental verification of thermal damage mechanism in single junction GaAs solar cells irradiated by laser

    NASA Astrophysics Data System (ADS)

    Li, Yunpeng; Feng, Guobin; Zhang, Jianmin; Lin, Xinwei; Shi, Yubin; Dou, Pengcheng

    2017-05-01

    Three types of laser irradiating experiments on single junction GaAs solar cells with the same laser energy coupling intensity were carried out, which were irradiated by in-band (808 nm) and out-of-band (1.07 μm) continuous wave lasers respectively and simultaneously. On the basis of the changes of current-voltage characteristic curves of irradiated solar cells, the damage degrees could be divided into three stages which were gently, seriously and thoroughly damaged stages. The damage mechanism was studied from two aspects: output changes of solar cell equivalent circuit under different configuration settings, thermal analysis model. The results show that damage degrees of gently and thoroughly damaged stages is insensitive to irradiation intensity. However, the damage degree of seriously damaged stage is sensitive to irradiation intensity and this is regarded to be related to thermal decomposition of GaAs. Moreover, the increase of PN junction defects leads to performance degradation of irradiated solar cells. In conclusion, the thermal damage leads to the increase of PN junction defects, thus results in the performance degradation of cells.

  5. Defect characterization of proton irradiated GaAs pn-junction diodes with layers of InAs quantum dots

    SciTech Connect

    Sato, Shin-ichiro; Schmieder, Kenneth J.; Warner, Jeffrey H.; Walters, Robert J.; Hubbard, Seth M.; Forbes, David V.; Ohshima, Takeshi

    2016-05-14

    In order to expand the technology of III-V semiconductor devices with quantum structures to both terrestrial and space use, radiation induced defects as well as native defects generated in the quantum structures should be clarified. Electrically active defects in GaAs p{sup +}n diodes with embedded ten layers of InAs quantum dots (QDs) are investigated using Deep Level Transient Fourier Spectroscopy. Both majority carrier (electron) and minority carrier (hole) traps are characterized. In the devices of this study, GaP layers are embedded in between the QD layers to offset the compressive stress introduced during growth of InAs QDs. Devices are irradiated with high energy protons for three different fluences at room temperature in order to characterize radiation induced defects. Seven majority electron traps and one minority hole trap are found after proton irradiation. It is shown that four electron traps induced by proton irradiation increase in proportion to the fluence, whereas the EL2 trap, which appears before irradiation, is not affected by irradiation. These defects correspond to electron traps previously identified in GaAs. In addition, a 0.53 eV electron trap and a 0.14 eV hole trap are found in the QD layers before proton irradiation. It is shown that these native traps are also unaffected by irradiation. The nature of the 0.14 eV hole trap is thought to be Ga-vacancies in the GaP strain balancing layers.

  6. GaAs 904-nm laser irradiation improves myofiber mass recovery during regeneration of skeletal muscle previously damaged by crotoxin.

    PubMed

    Silva, Lucila H; Silva, Meiricris T; Gutierrez, Rita M; Conte, Talita C; Toledo, Cláudio A; Aoki, Marcelo S; Liebano, Richard E; Miyabara, Elen H

    2012-09-01

    This work investigated the effect of gallium arsenide (GaAs) irradiation (power: 5 mW; intensity: 77.14 mW/cm(2), spot: 0.07 cm(2)) on regenerating skeletal muscles damaged by crotoxin (CTX). Male C57Bl6 mice were divided into six groups (n = 5 each): control, treated only with laser at doses of 1.5 J or 3 J, CTX-injured and, CTX-injured and treated with laser at doses of 1.5 J or 3 J. The injured groups received a CTX injection into the tibialis anterior (TA) muscle. After 3 days, TA muscles were submitted to GaAs irradiation at doses of 1.5 or 3 J (once a day, during 5 days) and were killed on the eighth day. Muscle histological sections were stained with hematoxylin and eosin (H&E) in order to determine the myofiber cross-sectional area (CSA), the previously injured muscle area (PIMA) and the area density of connective tissue. The gene expression of MyoD and myogenin was detected by real-time PCR. GaAs laser at a dose of 3 J, but not 1.5 J, significantly increased the CSA of regenerating myofibers and reduced the PIMA and the area density of intramuscular connective tissue of CTX-injured muscles. MyoD gene expression increased in the injured group treated with GaAs laser at a dose of 1.5 J. The CTX-injured, 3-J GaAs laser-treated, and the CTX-injured and treated with 3-J laser groups showed an increase in myogenin gene expression when compared to the control group. Our results suggest that GaAs laser treatment at a dose of 3 J improves skeletal muscle regeneration by accelerating the recovery of myofiber mass.

  7. Effect of melting on the acoustic response of CdTe and GaAs subjected to the pulsed laser irradiation

    SciTech Connect

    Baidullaeva, A.; Veleshchuk, V. P. Vlasenko, A. I.; Dauletmuratov, B. K.; Lyashenko, O. V.; Mozol', P. E.

    2008-03-15

    The effect of a threshold process of surface melting on the acoustic response in CdTe and GaAs subjected to pulsed laser radiation is considered and the mechanisms of excitation of sonic signals are analyzed. Melting thresholds of the surface of binary compounds CdTe and GaAs are established under irradiation by pulses of nanosecond duration of ruby and neodymium lasers from measurements of the amplitude of the acoustic response.

  8. A model for proton-irradiated GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.; Walker, G. H.; Outlaw, R. A.; Stock, L. V.

    1982-01-01

    A simple model for proton radiation damage in GaAs heteroface solar cells is developed. The model includes the effects of spatial nonuniformity of low energy proton damage. Agreement between the model and experimental proton damage data for GaAs heteroface solar cells is satisfactory. An extension of the model to include angular isotropy, as is appropriate for protons in space, is shown to result in significantly less cell damage than for normal proton incidence.

  9. High acceptor production rate in electron-irradiated n-type GaAs: Impact on defect models

    NASA Astrophysics Data System (ADS)

    Look, D. C.

    1987-09-01

    Defect production rates have been studied in electron-irradiated GaAs by temperature-dependent Hall-effect (TDH) measurements. The TDH results agree well with deep level transient spectroscopy (DLTS) results for the well-known electron traps E1, E2, and E3, but conclusively demonstrate a much higher production rate (4±1 cm-1) of acceptors below E3 than the total of all other DLTS traps. These findings strongly affect current defect models, and, e.g., are consistent with the existence of Ga sublattice damage, not seen before.

  10. Effects of laser irradiation on the self-assembly of MnAs nanoparticles in a GaAs matrix

    SciTech Connect

    Hai, Pham Nam; Nomura, Wataru; Yatsui, Takashi; Ohtsu, Motoichi; Tanaka, Masaaki

    2012-11-05

    We investigate the effects of laser irradiation on the self-assembly of MnAs nanoparticles during solid-phase decomposition in a GaAs matrix. It is found that laser irradiation suppresses the growth of MnAs nanoparticles from small to large size, and that the median diameter D{sub 1} in the size distribution of small MnAs nanoparticles depends on the incident photon energy E following D{sub 1} {approx} E{sup -1/5}. We explain this behavior by the desorption of Mn atoms on the MnAs nanoparticle surface due to resonant optical absorption, in which incident photons excite intersubband electronic transitions between the quantized energy levels in the MnAs nanoparticles.

  11. Defect engineering in GaAs using high energy light ion irradiation: Role of electronic energy loss

    SciTech Connect

    Kabiraj, D.; Ghosh, Subhasis

    2011-02-01

    We report on the application of high energy light ions (Li and O) irradiation for modification of defects, in particular, for annihilation of point defects using electronic energy loss in GaAs to minimize the defects produced by nuclear collisions. The high resolution x-ray diffraction and micro-Raman spectroscopy have been used to monitor that no lattice damage or amorphization take place due to irradiating ions. The effects of irradiation on defects and their energy levels have been studied using thermally stimulated current spectroscopy. It has been observed that till an optimum irradiation fluence of 10{sup 13} ions/cm{sup 2} there is annihilation of native defects but further increase in irradiation fluence results in accumulation of defects, which scales with the nuclear energy loss process, indicating that the rate of defects produced by the binary collision process exceeds rate of defect annihilation. Defect annihilation due to electronic energy loss has been discussed on the basis of breaking of bonds and enhanced diffusivity of ionized native defects.

  12. Electrical performances of commercial GaN and GaAs based optoelectronics under neutron irradiation

    NASA Astrophysics Data System (ADS)

    Fauzi, D. Ahmad; Rashid, N. K. A. Md; Karim, J. Abdul; Zin, M. R. Mohamed; Hasbullah, N. F.; Sheik Fareed, O. A.

    2013-12-01

    This paper aims to demonstrate the effects of displacement damage caused by high energetic neutron particle towards the electrical performances of gallium arsenide (GaAs) and gallium nitride (GaN) p-n based diodes. The investigations are carried out through current-voltage (I-V) and capacitance-voltage (C-V) measurements using Keithley 4200 SCS. Two different commercial optoelectronics diodes; GaN on SiC light emitting diode (LED) and GaAs infrared emitting diode (IRED) were radiated with neutron using pneumatic transfer system (PTS) in the PUSPATI TRIGA Mark II research reactor under total neutron flux of 1×1012 neutron/cm2.s. Following the neutron exposure for 1, 3 and 5 minutes, the I-V forward bias and reverse bias leakage current increase for GaAs IREDs, but minimal changes were observed in the GaN LEDs. The C-V measurements revealed that the capacitance and carrier concentration of GaAs IREDs decrease with increasing radiation flux.

  13. Deep level transient spectroscopy study of electron traps in n-type GaAs after pulsed electron beam irradiation

    SciTech Connect

    Marrakchi, G.; Barbier, D.; Guillot, G.; Nouailhat, A.

    1987-10-01

    Electrical and deep level transient spectroscopy measurements on Schottky barriers were performed in order to characterize electrically active defects in n-type GaAs (Bridgman substrates or liquid-phase epitaxial layers) after pulsed electron beam annealing. Both surface damage and bulk defects were observed in the Bridgman substrates depending on the pulse energy density. No electron traps were detected in the liquid-phase epitaxial layers before and after annealing for an energy density of 0.4 J/cm/sup 2/. The existence of an interfacial insulating layer at the metal-semiconductor interface, associated with As out-diffusion during the pulsed electron irradiation, was revealed by the abnormally high values of the Schottky barrier diffusion potential. Moreover, two new electron traps with activation energy of 0.35 and 0.43 eV, called EP1 and EP2, were introduced in the Bridgman substrates after pulsed electron beam annealing. The presence of these traps, related to the As evaporation, was tentatively attributed to the decrease of the EL2 electron trap signal after 0.4-J/cm/sup 2/ annealing. It is proposed that these new defects states are due to the decomposition of the As/sub Ga/-As/sub i/ complex recently considered as the most probable defect configuration for the dominant EL2 electron trap usually detected in as-grown GaAs substrates.

  14. Image processing by four-wave mixing in photorefractive GaAs

    NASA Technical Reports Server (NTRS)

    Gheen, Gregory; Cheng, Li-Jen

    1987-01-01

    Three image processing experiments were performed by degenerate four-wave mixing in photorefractive GaAs. The experiments were imaging by phase conjugation, edge enhancement, and autocorrelation. The results show that undoped, semiinsulating, liquid-encapsulated Czochralski-grown GaAs crystals can be used as effective optical processing media despite their small electrooptic coefficient.

  15. Image processing by four-wave mixing in photorefractive GaAs

    NASA Technical Reports Server (NTRS)

    Gheen, Gregory; Cheng, Li-Jen

    1987-01-01

    Three image processing experiments were performed by degenerate four-wave mixing in photorefractive GaAs. The experiments were imaging by phase conjugation, edge enhancement, and autocorrelation. The results show that undoped, semiinsulating, liquid-encapsulated Czochralski-grown GaAs crystals can be used as effective optical processing media despite their small electrooptic coefficient.

  16. Preparation of Large-Diameter GaAs Crystals.

    DTIC Science & Technology

    1981-09-18

    implantation as a reliable, cost-effective fabrication technology for high-performance GaAs MESFET and integrated circuits . To address these problems, the...have been prepared by in-situ synthesis and pulled from pyrolytic boron nitride (PBN) crucibles, and improved FET channels by direct ion-implantation of...viii SUMMARY Significant progress has been made toward developing large- diai.3ter, semi-insulating GaAs crystals of improved quality by LEC growth for

  17. Epitaxial Growth of Semi-Insulating GaAs

    DTIC Science & Technology

    1980-01-01

    83 APPENDIX - Van der Pauw Measurements of High-Resistivity Materials .... 84 vi LIST OF ILLUSTRATIONS...79 A-I. Schematic of guarded high-impedance van der Pauw system ......... 84 .i xi hL LIST OF TABLES * Table Page 1. Van der Pauw Measurement...this method has been described previously in the literature [I], we have been able to grow thicker layers than that achieved previously. Van der Pauw measurements

  18. Epitaxial Growth of Semi-Insulating GaAs

    DTIC Science & Technology

    1978-03-01

    CA 95051 Mr. R . Bell, K 101 Varlan Associates 6ll Hansen Way Palo Äl^o, CA 9^301+ \\ Mr. R . Bierl Raytheon Compa 28 Seyon Street Walthon, MA...BASI Program Code No. 7D10 78 Monitored by Office of Naval Research Arlington, Virginia 22217 Under Contract No. N 00014077 C 0542 06 - • r ...Supervisor and S. T. Jolly is the Project Scientist. D. S. Yaney and D. R . Capewell also participated in the research project. £> iii/iv 1 r

  19. Optical and magnetic properties of Mn{sup +}-implanted GaAs

    SciTech Connect

    Shon, Yoon; Park, Y.S.; Chung, K.J.; Fu, D.J.; Kim, D.Y.; Kim, H.S.; Kim, H.J.; Kang, T.W.; Kim, Yongmin; Fan, X.J.; Park, Y.J.

    2004-12-15

    Neutron-transmutation-doped GaAs samples were prepared by irradiating the middle-level neutrons into the semi-insulating GaAs grown by a liquid encapsulated Czochralski method and subsequently implanted with Mn{sup +}. The characteristics of the Mn{sup +}-implanted neutron-transmutation-doped GaAs (namely, the implantation of Mn{sup +} subsequent to neutron-transmutation-doping) were investigated by various measurements. The result of the energy dispersive x-ray peak displayed an injected Mn concentration of 9.65%. The photoluminescence peaks related to carbon and germanium acceptors were resolved, and the peaks related to Mn due to a neutral Mn acceptor were evidently observed. It is found that the proper activation for the neutral Mn acceptor starts from a relatively low annealing temperature of 600 deg. C for 15 min. The atomic force microscopy and magnetic forcemicroscopy images showed that magnetic clusters were well formed. The ferromagnetic hysteresis loop measured at 10 K was observed, and the temperature-dependent magnetization revealed that the two different phases exist at 135 and 360 K. The Curie temperature (T{sub c}{approx}360 K) is caused by MnAs, which agrees with the clusters of the magnetic force microscopy image.

  20. Growth of silver nanowires on GaAs wafers.

    PubMed

    Sun, Yugang

    2011-05-01

    Silver (Ag) nanowires with chemically clean surfaces have been directly grown on semi-insulating gallium arsenide (GaAs) wafers through a simple solution/solid interfacial reaction (SSIR) between the GaAs wafers themselves and aqueous solutions of silver nitrate (AgNO(3)) at room temperature. The success in synthesis of Ag nanowires mainly benefits from the low concentration of surface electrons in the semi-insulating GaAs wafers that can lead to the formation of a low-density of nuclei that facilitate their anisotropic growth into nanowires. The resulting Ag nanowires exhibit rough surfaces and reasonably good electric conductivity. These characteristics are beneficial to sensing applications based on single-nanowire surface-enhanced Raman scattering (SERS) and possible surface-adsorption-induced conductivity variation.

  1. Wavelength shifting in GaAs quantum well lasers by proton irradiation

    SciTech Connect

    Tan, H.H.; Jagadish, C.

    1997-11-01

    Proton irradiation followed by rapid thermal annealing was used to selectively induce layer intermixing and thus shift the emission wavelengths of GaAs{endash}AlGaAs graded-index separate-confinement-heterostructure quantum well lasers. Up to 40 nm shifts were observed in 4 {mu}m ridge waveguide devices irradiated to a dose of 1.5{times}10{sup 16}cm{sup {minus}2}. Although the wavelength shifts were accompanied by some degradation in the lasing threshold current and differential quantum efficiency, they were still quite acceptable at moderate wavelength shifts. This technique provides a simple and promising postgrowth process of integrating lasers of different wavelengths for wavelength-division-multiplexing applications. {copyright} {ital 1997 American Institute of Physics.}

  2. Terahertz refractive anisotropy on femtosecond laser pulse ablated semi-insulating gallium arsenide surface

    NASA Astrophysics Data System (ADS)

    Zhao, Zhenyu; Song, Zhiqiang; Bai, Feng; Shi, Wangzhou; Zhao, Quan-Zhong

    2017-04-01

    We present an artificial variation of THz refractive index ellipse from isotropy to anisotropy at the surface of <100>-oriented semi-insulating gallium arsenide (SI-GaAs) via femtosecond pulse laser ablation. The refractive index ellipse is determined by the frequency and the polarization of incident THz radiation. The THz wave is localized in the gap of columns of micro-ripples when the polarization of THz is parallel to the micro-ripples, while no electric energy localization occurs when the polarization of THz is perpendicular to the micro-ripples. We found that the laser ablation process can induce a periodic distribution of n-type GaAs at the surface of SI-GaAs. These n-type GaAs micro-ripples work as plasmonic resonators, which are proposed to be the origin of the induced refractive index anisotropy.

  3. Studies of boron on the arsenic site in electron-irradiated GaAs

    SciTech Connect

    Moore, W.J.; Hawkins, R.L.

    1988-06-15

    The introduction of boron on the arsenic site in gallium arsenide, as monitored by the strength of its local vibrational modes (LVM) at 601.7 and 628.3 cm/sup -1/, has been observed as a function of 2 MeV electron fluence. Simultaneous monitoring of the strength of the 1S-2P electronic transitions of the neutral shallow acceptors and of the neutral 78 meV acceptor and its singly ionized 203 meV level provides an accurate knowledge of the position of the Fermi level throughout most of the irradiation sequence. The results are inconsistent with previous models for the formation of boron on the arsenic site. We propose a model based on enhanced boron diffusion when the Fermi level lies above 78 meV. A compensation rate for electron irradiation, an introduction rate for the B/sub As/ center, and an infrared cross section for the B/sub As/ LVM are determined

  4. Kinetics of formation of the midgap donor EL2 in neutron irradiated GaAs materials

    SciTech Connect

    Martin, G.M.; Esteve, E.; Langlade, P.; Makram-Ebeid, S.

    1984-11-15

    Fast neutron irradiation of n-GaAs mainly induces two deep electron traps in the band gap. The first of these is referred to as EL6 and has an energy level at E/sub c/ -0.35 eV, where E/sub c/ is the conduction band minimum; the second one has a wide energy distribution around E/sub c/ -0.5 V and is referred to as the U band. The annealing kinetics of these two levels is studied, and it is found that EL6 vanishes by a pair-defect (short-range) type recombination while the U band anneals by a long range migration process. Both annealing processes can be observed between 400 and 500 /sup 0/C. In this annealing temperature range, the concentration of deep donor level EL2 (E/sub c/ -0.75 eV) increases with temperature. It is suggested that the defect giving rise to the EL2 level is created during irradiation but that medium range (tens to hundreds of A) interactions with other neighboring defects strongly influence the electric properties of the overall defect, which is then detected as the U band. Due to long range migration, annealing reduces medium range interaction and the U band disappears in favor of the well-defined EL2 level (E/sub c/ -0.75 eV). This allows us to reconcile the apparent contradiction between DLTS (deep level transient spectroscopy) and EPR (electron paramagnetic resonance) and to identify the EL2 level with the EPR signal attributed to the As/sub Ga/ defect.

  5. A comparison of the amorphization induced in Al sub x Ga sub 1 minus x As and GaAs by heavy-ion irradiation

    SciTech Connect

    Jencic, I.; Bench, M.W.; Robertson, I.M. ); Kirk, M.A. )

    1991-02-01

    The response of Al{sub {ital x}}Ga{sub 1{minus}{ital x}}As/GaAs samples to bombardment with heavy ions (50 keV Kr{sup +}, 50 keV and 1.5 MeV Xe{sup +}) was studied as a function of ion dose at temperatures of 30 and 300 K using transmission electron microscopy. Samples with {ital x}=0.2 and 0.85 were used. Under all irradiation temperature and ion combinations, the AlGaAs was more resistant to amorphization than GaAs. The resistance increased with increasing Al content and decreased with decreasing irradiation temperature. This difference in the response may be attributed to differences either in the mechanisms by which a region is rendered amorphous (i.e., by direct impact amorphization or by the buildup of point defects) or to differences in the inherent stability (recrystallization temperature and rate) of individual amorphous zones in AlGaAs and GaAs.

  6. Improvement in GaAs Device Yield and Performance through Substrate Defect Gettering

    DTIC Science & Technology

    1980-06-01

    defects will be retained at tempera- tures aproaching those normally encountered in routine device fabrication or processing procedures. Therefore, we...insulating GaAs wafers or direct ion implantation and annealing of bulk insulating substrates. The latter method would appear to be straight forward process...capsulated Czochralski (LEC) growth methods to reduce the residual donor level and, thereby, produce semi-insulating GaAs without the intentional addition

  7. Numerical simulation of the effect of recombination centres and traps created by electron irradiation on the performance degradation of GaAs solar cells.

    PubMed

    Meftah, A F; Sengouga, N; Belghachi, A; Meftah, A M

    2009-05-27

    In this paper, we report a detailed numerical study of the electron irradiation effect on the photoelectrical parameters of a GaAs based p(+)-n-n(+) solar cell which operates under an AM0 solar spectrum. As a consequence of irradiation different types of defects are created in the semiconductor lattice. These defects introduce energy levels in the gap of the material. The majority of studies dealing with irradiation-induced degradation in solar cells relate it mainly to recombination centres, which are deep levels lying near the mid gap. In the present study, numerical simulation is used to demonstrate that the irradiation-induced degradation is not solely due to recombination centres. Other less deep levels, or traps, play a major role in this degradation. When only recombination centres are taken into account, the short circuit current density (J(sc)) is hardly affected while the other cell output parameters such as the open circuit voltage (V(oc)), the conversion efficiency (η) and the fill factor (FF) are strongly deteriorated. However, if less deep levels or traps are taken into account together with recombination centres, J(sc) becomes sensitive to electron irradiation and the other output parameter deteriorations become less sensitive.

  8. A simple and reliable method of thermoelectic effect spectroscopy for semi-insulating III-V semiconductors

    NASA Astrophysics Data System (ADS)

    Huang, Z. C.; Xie, K.; Wie, C. R.

    1991-08-01

    We have developed a simpler and more reliable method of thermoelectric effect spectroscopy (TEES), eliminating the second heater in the technique. We have applied this method to the deep level studies in the semi-insulating undoped or Cr-doped GaAs materials and in the GaAs epitaxial layers grown at a low temperature by molecular beam epitaxy. We have found that the electrical contacts made on front and back surfaces of the sample are more reliable for the TEES measurement than both contacts made on the same surface. In this contact arrangement, the temperature difference of about 1-2 K between the back and front surfaces is enough to produce a clear and reliable TEES data, without the need for a second heater. The results obtained by TEES are consistent with the results obtained by photoinduced transient spectroscopy (PITS) and by thermally stimulated current (TSC) measurements. The TEES results clearly distinguish between the electron traps and the hole traps. We discuss the results on the various semi-insulating GaAs samples and the advantages and limitations of the TEES technique.

  9. Performances of SI GaAs detectors fabricated with implanted ohmic contacts

    SciTech Connect

    Nava, F.; Alietti, M.; Canali, C.; Chiossi, C. |; Cavallini, A. |; Papa, C. del |; Re, V. |; Lanzieri, C.

    1996-06-01

    The slow component of the output pulse of Semi-Insulating (SI) Gallium Arsenide (GaAs) particle detectors, which affects charge collection efficiency (cce), has been generally attributed to trapping/detrapping effects. However, most of the detectors analyzed in the literature can only be operated below the voltage V{sub d} necessary to extend the electric field all the way to the ohmic contact, making difficult to distinguish between the effect of the non-active part of the detector and that of trapping/detrapping. To do that, the authors have carefully analyzed the output signals of SI GaAs detectors, operated below and above V{sub d} and irradiated with {sup 241}Am {alpha} particles. When the detector is biased below V{sub d} the output signals are affected also by the non-active part of the detector itself, while, when the detector is operated above V{sub d}, the output signals are only affected by trapping/detrapping of charge carriers. The authors found that trapping/detrapping is only relevant for the hole contribution to the signal. Trapping/detrapping effects are in agreement with the characteristics of deep levels present in the detectors as analyzed by means of PICTS (Photo Induced Current Transient Spectroscopy) and P-DLTS (Photo Deep Level Transient Spectroscopy).

  10. Development of bulk GaAs room temperature radiation detectors

    SciTech Connect

    McGregor, D.S.; Knoll, G.F. . Dept. of Nuclear Engineering); Eisen, Y. . Soreq Nuclear Research Center); Brake, R. )

    1992-10-01

    This paper reports on GaAs, a wide band gap semiconductor with potential use as a room temperature radiation detector. Various configurations of Schottky diode detectors were fabricated with bulk crystals of liquid encapsulated Czochralski (LEC) semi-insulating undoped GaAs material. Basic detector construction utilized one Ti/Au Schottky contact and one Au/Ge/Ni alloyed ohmic contact. Pulsed X-ray analysis indicated pulse decay times dependent on bias voltage. Pulse height analysis disclosed non-uniform electric field distributions across the detectors tentatively explained as a consequence of native deep level donors (EL2) in the crystal.

  11. Microscopic determination of stress distribution in GaAs grown at low temperature on GaAs (100)

    NASA Astrophysics Data System (ADS)

    Liliental-Weber, Z.; Tanaka, M.; Ishikawa, A.; Teriauchi, M.

    1991-01-01

    A microscopic strain distribution across commensurate interfaces between GaAs layers grown on semi-insulating GaAs substrates was observed by means of convergent beam electron diffraction (CBED) and large angle convergent beam methods (LACBED). Strain relaxation at a specific distance from the interface was observed in these layers without formation of misfit dislocations. It was proposed that specific point defects distributed close to the interface can explain the asymmetric broadening of high-order Laue zone (HOLZ) lines in the CBED patterns.

  12. Characteristics of GaAs with inverted thermal conversion

    NASA Technical Reports Server (NTRS)

    Kang, C. H.; Lagowski, J.; Gatos, H. C.

    1987-01-01

    GaAs crystals exhibiting inverted thermal conversion (ITC) of resistivity were investigated in conjunction with standard semiinsulating (SI) GaAs regarding characteristics important in device processing. It was established that dislocation density and Si implant activation are unaffected by transformation to the ITC state. However, in ITC GaAs the controlled increase of the EL2 (native midgap donor) concentration during annealing makes it possible to attain resistivities one order of magnitude greater (e.g., about 10 to the 9th ohm cm of 300 K) than those attained in standard SI GaAs (e.g., 10 to the 7th-10 to the 8th ohm cm).

  13. Implementation of Neural Network Method to Investigate Defect Centers in Semi-Insulating Materials

    NASA Astrophysics Data System (ADS)

    Jankowski, S.; Wierzbowski, M.; Kaminski, P.; Pawlowski, M.

    A neural network (NN) method has been proposed as a new algorithm for extraction of defect centers parameters in semi-insulating materials from experimental data obtained by photoinduced transient spectroscopy (PITS). The new algorithm is applied to investigate irradiation-induced defect centers in high resistive silicon. The folds on the PITS spectral surface formed due to the presence of defect levels are best fitted with a two-dimensional approximation function with implementation of the NN learning process. As a result, the Arrhenius plots for defect centers are obtained and the parameters of these centers are determined.

  14. Two-beam coupling gain in undoped GaAs with applied dc electric field and moving grating

    NASA Technical Reports Server (NTRS)

    Liu, Duncan T. H.; Cheng, Li-Jen; Chiou, Arthur E.; Yeh, Pochi

    1989-01-01

    Experimental results of two-beam coupling gain efficiency in an undoped, semiinsulating GaAs crystal are reported. The highest gain coefficient measured is about 4.5/cm under the condition of an applied electric field of 13 kV/cm and a grating periodicity of 20 microns. The experimental results and theoretical calculations are in reasonable agreement with each other.

  15. Laser Annealing of GaAs

    DTIC Science & Technology

    1978-12-01

    annealing implanted layers. Sheet resistance measurements made on the irradiated semi- insulating GaAs samples indicate no significant change in the... sheet resistance after laser irradiation (typical decrease in the sheet resistance after laser irradiation was found to be less than a factor of two...OF THE SHEET - RESISTANCE (P ) THE EFFECTIVE SHEET ELECTRON CONCENTRATION (N ), AND THE EFFECTIVE MOBILITY _u)FOR SEMIb- INSULATING GaAs IMPLANTED WITH

  16. Performance of AlGaAs, GaAs and InGaAs cells after 1 MeV electron irradiation

    NASA Technical Reports Server (NTRS)

    Curtis, Henry B.; Hart, Russell E., Jr.

    1987-01-01

    Electron irradiations were made on three different types of III-V cells. AlGaAs, GaAs, and InGaAs cells with bandgaps of approximately 1.72, 1.43, and 1.1 eV, respectively, were tested. All of the cells were concentrator cells and performance data from one sun to beyond 100x AMO were taken. The total 1 MeV electron fluence was 3 times 10 to the 15th power e/square cm with data taken at several intermediate fluences. Cell performance is presented as a function of electron fluence for various concentration ratios and two different temperatures (25 and 80 C). Since these three cell types are potential candidates for the individual cells in a cascade structure, it is possible to calculate the loss in performance of cascade cells under 1 MeV irradiation. Data are presented which show the calculated performance of both series-connected and separately connected cascade cells.

  17. Compensation mechanism in liquid encapsulated Czochralski GaAs Importance of melt stoichiometry

    NASA Technical Reports Server (NTRS)

    Holmes, D. E.; Chen, R. T.; Elliott, K. R.; Kirkpatrick, C. G.; Yu, P. W.

    1982-01-01

    It is shown that the key to reproducible growth of undoped semi-insulating GaAs by the liquid encapsulated Czochralski (LEC) technique is the control over the melt stoichiometry. Twelve crystals were grown from stoichiometric and nonstoichiometric melts. The material was characterized by secondary ion mass spectrometry, localized vibrational mode far infrared spectroscopy, Hall-effect measurements, optical absorption, and photoluminescence. A quantitative model for the compensation mechanism in the semi-insulating material was developed based on these measurements. The free carrier concentration is controlled by the balance between EL2 deep donors and carbon acceptors; furthermore, the incorporation of EL2 is controlled by the melt stoichiometry, increasing as the As atom fraction in the melt increases. As a result, semi-insulating material can be grown only from melts above a critical As composition. The practical significance of these results is discussed in terms of achieving high yield and reproducibility in the crystal growth process.

  18. Infrared absorption properties of the EL2 and the isolated As/sub Ga/ defects in neutron-transmutation-doped GaAs: Generation of an EL2-like defect

    SciTech Connect

    Manasreh, M.O.; Fischer, D.W.

    1989-02-15

    The EL2 and the isolated As/sub Ga/ antisite defects in neutron-transmutation-doped (NTD) GaAs were studied by using the infrared (ir) absorption technique concurrent with thermal annealing. The results show that irradiation with low thermal-neutron doses partially decomposes the EL2 complex in semi-insulating (si) GaAs grown by the liquid-encapsulated Czochralski (LEC) growth technique. On the other hand, a small amount of EL2 is generated in as-grown Ga-rich undoped p-type LEC GaAs. The EL2 defect in low-dose thermal-neutron-irradiated samples (both si and p-type) was found to be stable up to 850 /sup 0/C. High neutron-irradiation doses, however, completely annihilate EL2 but generate a different EL2-like defect (DL2). The DL2 defect is observed after annealing the high-dose NTD samples for 6 min at 600 /sup 0/C. The DL2 concentration is observed to be larger than that of EL2 in as-grown LEC si GaAs by a factor of 2.3 or higher. The photoquenching and thermal recovery properties of DL2 and EL2 defects are identical. However, the DL2 defect does not exhibit the same thermal stability or the zero-phonon line of the EL2 defect. Thermal annealing kinetics shows that DL2 is composed of three point defects. The residual absorption (unquenchable component) after photoquenching the EL2 (DL2) defect is interpreted as the photoionization of the isolated As/sub Ga/ antisite.

  19. Oxygen in GaAs - Direct and indirect effects

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Skowronski, M.; Pawlowicz, L.; Lagowski, J.

    1984-01-01

    Oxygen has profound effects on the key electronic properties and point defects of GaAs crystals. Thus, when added in the growth system, it decreases the free electron concentration and enhances the concentration of deep donors in the resulting crystals. Both of these effects are highly beneficial for achieving semi-insulating material and have been utilized for that purpose. They have been attributed to the tendency of oxygen to getter silicon impurities during crystal growth. Only recently, it has been found that oxygen in GaAs introduces also a midgap level, ELO, with essentially the same activation energy as EL2 but with four times greater electron capture cross section. The present report reassesses the electrical and optical properties of the midgap levels in GaAs crystals grown by the horizontal Bridgman (HB) and the Czochralski-LEC techniques. Emphasis is placed on the identification of the specific effects of ELO.

  20. Comparison of Intersubband GaAs/AlGaAs Multiple Quantum Well Infrared Photodetectors on GaAs and GaAs-on-Si Subtrates

    NASA Technical Reports Server (NTRS)

    Sengupta, D.; Gunapala, S.; George, T.; Bandara, S.; Chang-Chien, C. N.; Leon, R.; Kayali, S.; Kuo, H.; Fang, W.; Liu, H.; Stillman, G.

    1998-01-01

    We have successfully fabricated intersubband GaAs/AlGaAs quantum well infrared photodetectors grown on GaAs-on-Si substrate and evaluated their structural, electrical, and optical characteristics. We have found that the performance is comparable to a similar detector structure grown on a semi-insulating GaAs substrate.

  1. Studies of Nonradiative Recombination Centers in GaAs and InP*

    NASA Astrophysics Data System (ADS)

    Tuzemen, S.; Liang, Difei; Ucer, K. B.; Williams, R. T.

    2001-03-01

    The "reverse contrast" recombination center in semi-insulating GaAs, so named because of its anti-correlation with EL2 defects in spatial mapping, has been attributed to As-vacancy centers.^1 Several details of the nature of its optical transitions and of its spatial distribution are among questions open to experimental investigation. We report experiments on spectroscopy and spatial mapping of defects in semi-insulating GaAs and Fe-doped InP. *ST acknowledges the CIES for support as a Fulbright Scholar at WFU. The research at WFU is supported by NSF grant DMR-9732023. Confocal microscopy in cooperation with K. Grant and the MicroMed Facility of WFU. 1. C. Le Berre, C. Corbel, R. Mih, M. R. Brozel, S. Tüzemen, S. Kuisma, K. Saarinen, P. Hautojarvi, and R. Fornari, Appl. Phys. Lett. 66, 2354 (1995).

  2. Liquid encapsulated Czochralski growth of low dislocation GaAs

    NASA Technical Reports Server (NTRS)

    Kirkpatrick, C. G.; Chen, R. T.; Holmes, D. E.

    1982-01-01

    The availability of high-quality, large-diameter GaAs substrates is key to the successful development and production of high-speed GaAs devices and high-efficiency GaAs solar cells. The liquid encapsulated Czochralski (LEC) technique has provided a means for producing large-diameter GaAs. Progress in improving the LEC growth process which has resulted in 3-inch GaAs crystals with exceptionally low dislocation densities and reduced propensity for twinning is reported. Undoped, semi-insulating GaAs ingots were grown in a Melbourn high-pressure LEC system. The effects of seed perfection, seed necking, cone angle, melt stoichiometry, ambient pressure, thickness of the B2O3 encapsulating layer, and diameter control on the dislocation density were investigated. The material was characterized by preferential etching and X-ray topography. It is shown that 3-inch diameter substrates can be produced with dislocation densities as low as 6000 per sq cm through proper selection and control of growth parameters. Also, the incidence of twinning can be reduced significantly by growing from slightly As-rich melts.

  3. Inherent photoluminescence Stokes shift in GaAs.

    PubMed

    Ullrich, Bruno; Singh, Akhilesh K; Barik, Puspendu; Xi, Haowen; Bhowmick, Mithun

    2015-06-01

    The intrinsic photoluminescence Stokes shift, i.e., the energy difference between optical band gap and emission peak, of 350 μm thick semi-insulating GaAs wafers is found to be 4 meV at room temperature. The result is based on the determination of the optical bulk band gap from the transmission trend via modified Urbach rule whose result is confirmed with the transmission derivative method. The findings reveal the detailed balance of the optically evoked transitions and disclose the intrinsic link between Stokes shift and the Urbach tail slope parameter.

  4. Ohmic contacts to GaAs for high-temperature device applications

    NASA Technical Reports Server (NTRS)

    Anderson, W. T., Jr.; Christou, A.; Giuliani, J. F.; Dietrich, H. B.

    1981-01-01

    Ohmic contacts to n-type GaAs were developed for high temperature device applications up to 300 C. Refractory metallizations were used with epitaxial Ge layers to form the contacts: TiW/Ge/GaAs, Ta/Ge/GaAs, Mo/Ge/GaAs, and Ni/Ge/GaAs. Contacts with high dose Si or Se ion implantation of the Ge/GaAs interface were also investigated. The contacts were fabricated on epitaxial GaAs layer grown on N+ or semi-insulating GaAs substrates. Ohmic contact was formed by both thermal annealing (at temperatures up to 700 C) and laser annealing (pulsed Ruby). Examination of the Ge/GaAs interface revealed Ge migration into GaAs to form an N+ doping layer. The specific contact resistances of specimens annealed by both methods are given.

  5. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Anomalous behaviours of terahertz reflected waves transmitted from GaAs induced by optical pumping

    NASA Astrophysics Data System (ADS)

    Shi, Yu-Lei; Zhou, Qing-Li; Zhao, Dong-Mei; Zhang, Cun-Lin

    2009-12-01

    Femtosecond pump-terahertz probe studies of carrier dynamics in semi-insulating GaAs have been investigated in detail for various pump powers. It is observed that, at high pump powers, the reflection peaks flip to the opposite polarity and dramatically enhance as the pump arrival time approaches the reflected wave of the terahertz pulse. The abnormal polarity-flip and enhancement can be interpreted by the pump-induced enhancement in the photoconductivity of GaAs and half-wave loss. Moreover, the carrier relaxation processes and surface states filling in GaAs are also studied in these measurements.

  6. Electronic spin polarization and the spin-dependent bandstructure in GaAs probed by optically pumped NMR

    SciTech Connect

    Crooker, Scott A; Ramaswamy, Kannan; Mui, Stacy; Hayes, Sophia E; Pan, Xingyuan; Sanders, Gary D; Stanton, Christopher J

    2008-01-01

    High resolution optically pumped NMR (OPNMR) experiments are used to resolve fine features in the spin-dependent electronic structure of the valence bands in semi-insulating GaAs. By theoretically calculating oscillations in the OPNMR signal intensity with respect to the excitation energy, we have mapped out the conduction band electronic spin polarization under optical pumping. Comparison with a theoretical analysis of the oscillatory experimental features allows the extraction of semiconductor energy band parameters.

  7. A New Radiation Hard Semiconductor — Semi-Insulating GaN: Photoelectric Properties

    NASA Astrophysics Data System (ADS)

    Vaitkus, J.; Gaubas, E.; Kazukauskas, V.; Blue, A.; Cunningham, W.; Rahman, M.; Smith, K.; Sakai, S.

    2005-06-01

    The anticipated upgrade of the CERN Large Hadron Collider to ten times brighter luminosity poses a severe challenge to semiconductor detectors in the CERN experiments. The suitability of semi-insulating GaN (SI-GaN), proposed as an alternative to silicon for the fabrication of radiation hard detectors, is investigated here in MOCVD GaN layers grown on sapphire. The electrical properties of SI-GaN were studied by dc and microwave techniques, and defect parameters determined by the method of thermally stimulated currents. Variations of charge collection efficiency (CCE) in SI-GaN diodes induced by ionizing radiation of 5.48 MeV alpha particles were revealed. Samples were also irradiated by X-rays, reactor neutrons and high-energy proton fluences of up to 1016 cm-2. The high radiation hardness of SI-GaN was demonstrated by the modest reduction in CCE, from 92% to 77%, in the material irradiated by neutrons (up to a fluence of 1015 cm-2). The CCE was unaffected by an X-rays dose of 600 MRad), but decreased to a few % after proton and neutron fluences of 1016 cm-2. The electrical characteristics vary more significantly, depending on irradiation type and dose. Fast decay components and a significant role of percolation effects are observed in the photoconductivity transients.

  8. Nonlinear optical properties of GaAs at 1. 06 micron, picosecond pulse investigation and applications

    SciTech Connect

    Cui, A.G.

    1992-01-01

    The author explores absorptive and refractive optical nonlinearities at 1.06 [mu]m in bulk, semi-insulating, undoped GaAs with a particular emphasis on the influence of the native deep-level defect known as EL2. Picosecond pump-probe experimental technique is used to study the speed, magnitude, and origin of the absorptive and refractive optical nonlinearities and to characterize the dynamics of the optical excitation of EL2 in three distinctly different undoped, semi-insulating GaAs samples. Intense optical excitation of these materials leads to the redistribution of charge among the EL2 states resulting in an absorptive nonlinearity due to different cross sections for electron and hole generation through this level. This absorptive nonlinearity is used in conjunction with the linear optical properties of the material and independent information regarding the EL2 concentration to extract the cross section ratio [sigma][sub p]/[sigma][sub e] [approx equal]0.8, where [sigma][sub p](e) is the absorption cross section for hole (electron) generation from EL2[sup +] (EL2[sup 0]). The picosecond pump-probe technique can be used to determine that EL2/EL2[sup +]density ratio in an arbitrary undoped, semi-insulating GaAs sample. The author describes the use of complementary picosecond pump-probe techniques that are designed to isolate and quantify cumulative and instantaneous absorptive and refractive nonlinear processes. Numerical simulations of the measurements are achieved by solving Maxwell equations with the material equations in a self-consistent manner. The numerical analysis together with the experimental data allows extraction of a set of macroscopic nonlinear optical parameters in undoped GaAs. The nonlinearities in this material have been used to construct three proof-of-principle nonlinear optical devices for use at 1.06 [mu]m: (1) a weak beam amplifier, (2) a polarization rotation optical switch, and (3) optical limiters.

  9. Development and characterization of zone melt growth GaAs for gamma-ray detectors

    SciTech Connect

    King, S.E.; Dietrich, H.B.; Henry, R.L.; Katzer, D.S.; Moore, W.J.; Phillips, G.W.; Mania, R.C.

    1996-06-01

    GaAs is a potentially attractive material for room temperature x-ray and {gamma}-ray spectrometers. To date, the only high resolution GaAs devices were produced by epitaxial growth. The usefulness of detectors made from bulk grown semi-insulating (SI) GaAs has been limited by low charge collection efficiency caused, it is believed, by the high density of EL2 deep donor defects. Vertical zone melt (VZM) growth of GaAs has recently been developed at the Naval Research Laboratory. Zone refining and zone leveling techniques were used with VZM to reduce the level of impurities and the EL2 defects in bulk SI-GaAs. Schottky barrier and PIN diodes have been fabricated from the newly grown material. These devices were characterized using {alpha} particles and {gamma}-rays. In this paper, the measurements and analysis of the first VZM GaAs devices are presented and compared with commercially available GaAs. The intent is to test the hypothesis that high purity, low defect GaAs material growth could lead to improved radiation detectors.

  10. Optical absorption and photocurrent enhancement in semi-insulating gallium arsenide by femtosecond laser pulse surface microstructuring.

    PubMed

    Zhao, Zhen-Yu; Song, Zhi-Qiang; Shi, Wang-Zhou; Zhao, Quan-Zhong

    2014-05-19

    We observe an enhancement of optical absorption and photocurrent from semi-insulating gallium arsenide (SI-GaAs) irradiated by femtosecond laser pulses. The SI-GaAs wafer is treated by a regeneratively amplified Ti: Sapphire laser of 120 fs laser pulse at 800 nm wavelength. The laser ablation induced 0.74 μm periodic ripples, and its optical absorption-edge is shifted to a longer wavelength. Meanwhile, the steady photocurrent of irradiated SI-GaAs is found to enhance 50%. The electrical properties of samples are calibrated by van der Pauw method. It is found that femtosecond laser ablation causes a microscale anti-reflection coating surface which enhances the absorption and photoconductivity.

  11. Defect studies in one MeV electron irradiated GaAs and in Al/sub x Ga/sub l-x As P-N junction solar cells

    NASA Technical Reports Server (NTRS)

    Li, S. S.; Wang, W. L.; Loo, R. Y.; Rahilly, W. P.

    1984-01-01

    Deep level transient spectroscopy reveals that the main electron traps for one-MeV electron irradiated GaAs cells are E9c)-0.31, E(c)-0.90 eV, and the main hole trap is due to the level. Electron trap density was found to vary from 3/tens-trillion ccm for 2/one quadrillion cm 3/3.7 quadrillion cm for 21 sextillion cm electron fluence for electron fluence; a similar result was also obtained for the hole trap density. As for the grown-in defects in the Al(x)Ga(1-x)As p-n junciton cells, only two electron traps with energies of E(c)-0.20 and E(c)-0.34 eV were observed in samples with x = 0.17, and none was found for x 0.05. Auger analysis on the Al(x)Ga(1-x) As window layer of the GaAs solar cell showed a large amount of oxygen and carbon contaminants near the surface of the AlGaAs epilayer. Thermal annealing experiment performed at 250 C for up to 100 min. showed a reduction in the density of both electron traps.

  12. 30 MeV Electron Beam Irradiation Effects on GaAs(1-x)P(x) LEDs (Light Emitting Diodes).

    DTIC Science & Technology

    1985-06-01

    n . . .. , , - devices were inversely proportional to their purity and quality. Aukerman and Millesa (Refs. 3 thru 61 accomplished an...DEVICE SUMMARY group # area ToK (10-4) (10-14) (cm2 ) (cm2 /e) 9 4.95 2.9 3 8.44 1.4 A5 9.70 2.6 In comparison with other research, Millea and Aukerman ...x 10-14 cm2 /e), and group 3 (1.37 x 10-14 cm2 /e). Nillea and Aukerman [Ref. 43 report a damage constant of 2 x 10-15 cm2 /e for GaAs LEDs, which is

  13. The Study of Femtosecond Laser Irradiation on GaAs Solar Cells With TiO2/SiO2 Anti-Reflection Films

    NASA Astrophysics Data System (ADS)

    Hua, Yinqun; Shi, Zhiguo; Wu, Wenhui; Chen, Ruifang; Rong, Zhen; Ye, Yunxia; Liu, Haixia

    Femtosecond laser ablation on GaAs solar cells for space power has been investigated. In particular, we studied the effects of laser energy and laser number on the ablation of solar cells. Furthermore, the morphologies and microstructure of ablation were characterized by the non-contact optical profilometer and scanning electron microscope (SEM). The photovoltaic properties were tested by the volt ampere characteristic test system. The abaltion threshold of the TiO2/SiO2 anti-reflection film of GaAs solar cells was obtained from the linear fit of the dependence of the square diameter of the ablated area with the natural logarithm of the femtosecond laser pulse energy, the resulting threshold of the laser fluence is about 0.31J/cm2, and the corresponding energy is 5.4uJ. The ablation depth showed nonlinear dependence of energy. With the fixed energy 6uJ and the increasing laser number, the damage degree increases obviously. Furthermore, the electric properties also suffer a certain degradation. Among all the evaluated electric properties, the photoelectric conversion efficiency (η) degraded remarkably.

  14. Temperature and intensity dependence of photorefractive effect in GaAs

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Partovi, Afshin

    1986-01-01

    The photorefractive effect in semi-insulating Cr-doped GaAs as measured by the beam coupling technique was investigated as functions of temperature (295-386 K) and intensity (0.15-98 mW/sq cm of 1.15-micron light beams from a He-Ne laser). Results show that the photorefractive effect deteriorates rapidly over a narrow range of temperature as temperature rises, and that this characteristic temperature increases with the logarithm of beam intensity. The observed phenomenon is attributed to the competing effects of the dark- and light-induced conductivities.

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

    SciTech Connect

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

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    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.

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

    PubMed

    Melisi, Domenico; Nitti, Maria Angela; Valentini, Marco; Valentini, Antonio; Ligonzo, Teresa; De Pascali, Giuseppe; Ambrico, Marianna

    2014-01-01

    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.

  18. Index grating lifetime in photorefractive GaAs

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Partovi, Afshin

    1988-01-01

    The index grating lifetime in liquid encapsulated Czochralski-grown undoped semi-insulating GaAs was measured using a beam coupling technique. The largest lifetime measure was about 8 s under a read beam intensity of 0.7 mW/sq cm with the grating periodicity being 0.63 microns. The measured value decreases to milliseconds as the read beam intensity and the grating periodicity increase to about 10 mW/sq cm and 4 microns, respectively. This range of grating lifetime in this material is adequate for its use in real-time spatial light modulators, reconfigurable beam steering devices, and dynamic memory elements, for optical computing. In addition, the results suggest that the lifetime is sensitive to residual imperfections in the crystal.

  19. Enhanced NMR with Optical Pumping Yields (75)As Signals Selectively from a Buried GaAs Interface.

    PubMed

    Willmering, Matthew M; Ma, Zayd L; Jenkins, Melanie A; Conley, John F; Hayes, Sophia E

    2017-03-22

    We have measured the (75)As signals arising from the interface region of single-crystal semi-insulating GaAs that has been coated and passivated with an aluminum oxide film deposited by atomic layer deposition (ALD) with optically pumped NMR (OPNMR). Using wavelength-selective optical pumping, the laser restricts the volume from which OPNMR signals are collected. Here, OPNMR signals were obtained from the interface region and distinguished from signals arising from the bulk. The interface region is highlighted by interactions that disrupt the cubic symmetry of the GaAs lattice, resulting in quadrupolar satellites for nuclear [Formula: see text] isotopes, whereas NMR of the "bulk" lattice is nominally unsplit. Quadrupolar splitting at the interface arises from strain based on lattice mismatch between the GaAs and ALD-deposited aluminum oxide due to their different coefficients of thermal expansion. Such spectroscopic evidence of strain can be useful for measuring lattice distortions at heterojunction boundaries and interfaces.

  20. GaAs Solar Cell Radiation Handbook

    NASA Technical Reports Server (NTRS)

    Anspaugh, B. E.

    1996-01-01

    The handbook discusses the history of GaAs solar cell development, presents equations useful for working with GaAs solar cells, describes commonly used instrumentation techniques for assessing radiation effects in solar cells and fundamental processes occurring in solar cells exposed to ionizing radiation, and explains why radiation decreases the electrical performance of solar cells. Three basic elements required to perform solar array degradation calculations: degradation data for GaAs solar cells after irradiation with 1 MeV electrons at normal incidence; relative damage coefficients for omnidirectional electron and proton exposure; and the definition of the space radiation environment for the orbit of interest, are developed and used to perform a solar array degradation calculation.

  1. Transient surface photoconductivity of GaAs emitter studied by terahertz pump-emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Shi, Yulei; Zhou, Qing-li; Zhang, Cunlin

    2010-11-01

    The ultrafast carrier dynamics and surface photoconductivity of unbiased semi-insulating GaAs have been investigated in detail by using terahertz pump-emission technique. Through theoretical modeling based on Hertz vector potential, it is found that transient photoconductivity plays a very important role in the temporal waveform of terahertz radiation pulse. Anomalous enhancement in both terahertz radiation and transient photoconductivity is observed subsequent to the excitation of pump pulse, and our modeling gives successful analyses for the dynamics of photogenerated carriers in the GaAs. We attribute these phenomena to carrier capture in the EL2 centers. Moreover, the pump power- and temperaturedependent measurements are also performed to verify this model.

  2. EL2 distributions in vertical gradient freeze GaAs crystals

    SciTech Connect

    Gray, M.L.; Sargent, L.; Blakemore, J.S.; Parsey J.M. Jr.; Clemans, J.E.

    1988-06-15

    Spatial distributions of EL2 in undoped, semi-insulating GaAs crystals grown by a novel vertical gradient freeze (VGF) method are reported. As a result of the low-temperature gradients present during growth and post-solidification cooling, these crystals exhibit lower EL2 concentrations and lower dislocation densities than liquid-encapsulated Czochralski crystals. Both the EL2 distribution and dislocation density over the area of a wafer do not display the fourfold symmetric pattern prevalent for LEC-grown GaAs. The radial distributions of EL2 in as-grown VGF crystals have been found to be independent of the dislocation density. Axial and radial Hall-effect measurements are included. Thermal activation energies are also presented and the compensation mechanism for this material is discussed.

  3. Stoichiometry-controlled compensation in liquid encapsulated Czochralski GaAs

    NASA Technical Reports Server (NTRS)

    Holmes, D. E.; Chen, R. T.; Elliott, K. R.; Kirkpatrick, C. G.

    1982-01-01

    It is shown that the electrical compensation of undoped GaAs grown by the liquid encapsulated Czochralski technique is controlled by the melt stoichiometry. The concentration of the deep donor EL2 in the crystal depends on the As concentration in the melt, increasing from about 5 x 10 to the 15th per cu cm to 1.7 x 10 to the 16th per cu cm as the As atom fraction increases from 0.48 to 0.51. Furthermore, it is shown that the free-carrier concentration of semi-insulating GaAs is determined by the relative concentrations of EL2 and carbon acceptors. As a result, semi-insulating material can be obtained only above a critical As concentration (0.475-atom fraction in the material here) where the concentration of EL2 is sufficient to compensate residual acceptors. Below the critical As concentration the material is p type due to excess acceptors.

  4. Synthesis solute diffusion growth of bulk GaAs: Effects of growth temperature and stoichiometry

    NASA Astrophysics Data System (ADS)

    Markov, A. V.; Biberin, V. I.; Polyakov, A. Y.; Smirnov, N. B.; Govorkov, A. V.; Gavrin, V. N.; Kalikhov, A. V.; Kozlova, J. P.; Veretenkin, E. P.; Bowles, T. J.

    2007-07-01

    Bulk GaAs crystals were grown by synthesis solute diffusion (SSD) technique in a wide range of growth temperatures between 990 and 1150 °C. Electrical properties of these crystals were studied by means of van der Pauw, admittance spectroscopy, deep levels transient spectroscopy and photoinduced current spectroscopy techniques. It was shown that the main defects determining the properties were the GaAs antisites acceptors and the A center acceptors with the levels, respectively, Ev +0.078 eV and Ev +0.43 eV. The conductivity of the grown crystals was p-type and showed a pronounced maximum at a level of 10 4-10 5 Ω cm for growth temperatures between 1020 and 1080 °C. If the crystals were additionally compensated either by unintentional Si donors contamination from quartz crucibles or by intentional light Te doping one could get semi-insulating material with the room temperature resistivity higher than 10 6 Ω cm. The Fermi level in such crystals was pinned near Ec -0.8 eV, i.e. close to the EL2 donors. Measurements by deep levels transient spectroscopy on n-type doped crystals or by low frequency capacitance-voltage on semi-insulating crystals showed that the density of EL2 in these samples was in the low 10 14 cm -3 and that thus the EL2 donors were not the main compensating agents.

  5. Investigation of GaAs photoconductive switches triggered by 900nm semiconductor lasers

    NASA Astrophysics Data System (ADS)

    Ma, Deming; Shi, Wei; Ma, Xiangrong; Wang, Xinmei; Pei, Tao

    2008-12-01

    Experiment of a lateral semi-insulating GaAs photoconductive semiconductor switch (SI-GaAs PCSS) with different electrode gaps triggered by 900nm semiconductor laser is reported. With the biased voltage of 0.2KV~3.0KV, the linear electrical pulse is outputted by SI-GaAs PCSS. When laser energy is very low, the semi-insulating GaAs PCSS with 1.5mm electrode gap is triggered by laser pulse, the output electrical pulse samples is instable. When the energy of the laser increases, the amplitude and the width of the electrical pulse also increase. It indicates that a stable electrical pulse is obtained while laser energy is high. With the biased voltage of 2.8kV, the SI-GaAs PCSS with 3mm electrode gap is triggered by laser pulse about 10nJ in 200ns at 900nm. The SI-GaAs PCSS switches a electrical pulse with a voltage up to 80V. The absorption mechanism by Franz-Keldysh effect under high-intensity electric field and EL2 deep level defects is discussed.

  6. Advanced BCD technology with vertical DMOS based on a semi-insulation structure

    NASA Astrophysics Data System (ADS)

    Kui, Ma; Xinghua, Fu; Jiexin, Lin; Fashun, Yang

    2016-07-01

    A new semi-insulation structure in which one isolated island is connected to the substrate was proposed. Based on this semi-insulation structure, an advanced BCD technology which can integrate a vertical device without extra internal interconnection structure was presented. The manufacturing of the new semi-insulation structure employed multi-epitaxy and selectively multi-doping. Isolated islands are insulated with the substrate by reverse-biased PN junctions. Adjacent isolated islands are insulated by isolation wall or deep dielectric trenches. The proposed semi-insulation structure and devices fixed in it were simulated through two-dimensional numerical computer simulators. Based on the new BCD technology, a smart power integrated circuit was designed and fabricated. The simulated and tested results of Vertical DMOS, MOSFETs, BJTs, resistors and diodes indicated that the proposed semi-insulation structure is reasonable and the advanced BCD technology is validated. Project supported by the National Natural Science Foundation of China (No. 61464002), the Science and Technology Fund of Guizhou Province (No. Qian Ke He J Zi [2014]2066), and the Dr. Fund of Guizhou University (No. Gui Da Ren Ji He Zi (2013)20Hao).

  7. Electrical properties of unintentionally doped semi-insulating and conducting 6H-SiC

    NASA Astrophysics Data System (ADS)

    Mitchel, W. C.; Mitchell, W. D.; Fang, Z. Q.; Look, D. C.; Smith, S. R.; Smith, H. E.; Khlebnikov, Igor; Khlebnikov, Y. I.; Basceri, C.; Balkas, C.

    2006-08-01

    Temperature dependent Hall effect (TDH), low temperature photoluminescence (LTPL), secondary ion mass spectrometry (SIMS), optical admittance spectroscopy (OAS), and thermally stimulated current (TSC) measurements have been made on 6H-SiC grown by the physical vapor transport technique without intentional doping. n- and p-type as well semi-insulating samples were studied to explore the compensation mechanism in semi-insulating high purity SiC. Nitrogen and boron were found from TDH and SIMS measurements to be the dominant impurities that must be compensated to produce semi-insulating properties. The electrical activation energy of the semi-insulating sample determined from the dependence of the resistivity was 1.0eV. LTPL lines near 1.00 and 1.34eV, identified with the defects designated as UD-1 and UD-3, were observed in all three samples but the intensity of the UD-1 line was almost a factor of 10 more in the n-type sample than in the the p-type sample with that in the semi-insulating sample being intermediate between those two. OAS and TSC experiments confirmed the high purity of this material. The results suggest that the relative concentrations of a dominant deep level and nitrogen and boron impurities can explain the electrical properties in this material.

  8. Study of electronic properties in proton- and electron-irradiated GaAlAs and GaAs solar cell materials

    NASA Technical Reports Server (NTRS)

    Li, S. S.

    1978-01-01

    Diagnostical measurement techniques such as dark I-V, C-V, the thermally insulated capacitance, and the deep level transient spectroscopy methods were employed to study defect properties in the proton-irradiated n-GaAs materials. Defect energy levels, thermal emission rates, and capture cross sections of electrons as well as trap densities were deduced from these measurements and the results are presented. Correlations between the measured defect parameters and the dark I-V characteristics of the n-GaAs Schottky barrier diodes are also discussed. Defect energy levels (i.e., electron traps) determined are also compared with published data in order to identify their physical origins.

  9. The Investigation of Ion Implantation as a Technique for Manufacturing GaAs Magneto-Sensitive Detectors

    NASA Astrophysics Data System (ADS)

    Karlova, G. F.; Avdochenko, B. I.

    2017-01-01

    This paper studies thin active layers of n-n i and n +-n-n i -types produced by means of silicon ion implantation into a semi-insulating GaAs substrate. The results of these structures’ physical parameters investigation are presented. Based on the structures the Hall-effect sensors are designed that have the linearity of Hall voltage dependency on magnetic density UH(B) of at least 1% in the range of up to B<1.2 T.

  10. Histometric evaluation of the healing of the dental alveolus in rats after irradiation with a low-powered GaA1As laser

    NASA Astrophysics Data System (ADS)

    Lizarelli, Rosane F. Z.; Lamano-Carvalho, Tereza L.; Brentegani, Luis G.

    1999-05-01

    The aim of the present work was to evaluate histometrically the effect of the irradiation with semiconductor diode GaAlAs 790 nm low-powered laser in the chronology of alveolar repair of rats. Lasers of low intensity possesses an eminently analgesic, anti-inflammatory and bioestimulant effect, producing an increase of the local micro-circulation and in the speed of healing. Groups of five animals had their upper right incisors extracted under anesthesia and the mucous sutured; three groups received 1.5 J/cm2 of irradiation immediately after the extraction with laser for sweeping on the operated area. After that, the animals were sacrificed in the periods of 7, 14 and 21 days after the dental extraction. The material was decalcified and processed for inclusion in paraffin. Longitudinal sections of 7 micrometers in the alveolus were made and stained with HE. The histometric analysis was performed with the Merz grid, and 2000 points were counted in each cervical, middle and apical thirds of the alveolus, assessing the percentage of the bone tissue. The result shows that low-powered intensity laser produced acceleration in osseous formation (10%) in some periods.

  11. Characterization of production GaAs solar cells for space

    NASA Technical Reports Server (NTRS)

    Anspaugh, B. E.

    1988-01-01

    The electrical performance of GaAs solar cells was characterized as a function of irradiation with protons and electrons with the underlying goal of producing solar cells suitable for use in space. Proton energies used varied between 50 keV and 10 MeV, and damage coefficients were derived for liquid phase epitaxy GaAs solar cells. Electron energies varied between 0.7 and 2.4 MeV. Cells from recent production runs were characterized as a function of electron and proton irradiation. These same cells were also characterized as a function of solar intensity and operating temperature, both before and after the electron irradiations. The long term stability of GaAs cells during photon exposure was examined. Some cells were found to degrade with photon exposure and some did not. Calibration standards were made for GaAs/Ge solar cells by flight on a high altitude balloon.

  12. Improvement of radiation stability of semi-insulating gallium arsenide crystals by deposition of diamond-like carbon films

    NASA Astrophysics Data System (ADS)

    Klyui, N. I.; Lozinskii, V. B.; Liptuga, A. I.; Izotov, V. Yu.; Han, Wei; Liu, Bingbing

    2016-12-01

    We studied the properties of optical elements for the IR spectral range based on semi-insulating gallium arsenide (SI-GaAs) and antireflecting diamond-like carbon films (DLCF). Particular attention has been paid to the effect of penetrating γ-radiation on transmission of the developed optical elements. A Co60 source and step-by-step gaining of γ-irradiation dose were used for treatment of both an initial SI-GaAs crystal and DLCF/SI-GaAs structures. It was shown that DLCF deposition essentially increases degradation resistance of the SI-GaAs-based optical elements to γ-radiation. Particularly, the transmittance of the DLCF/SI-GaAs structure after γ-irradiation with a dose 9ṡ104 Gy even exceeds that of initial structures. The possible mechanism that explains the effect of γ-radiation on the SI-GaAs crystals and the DLCF/SI-GaAs structures at different irradiation doses was proposed. The effect of small doses is responsible for non-monotonic transmission changes in both SI-GaAs crystals and DLCF/SI-GaAs structures. At further increasing the γ-irradiation dose, the variation of properties of both DLCF and SI-GaAs crystal influences on the transmission of DLCF/SI-GaAs system. At high γ-irradiation dose 1.4ṡ105 Gy, passivation of radiation defects in the SI-GaAs bulk by hydrogen diffused from DLCF leads to increasing the degradation resistance of the SI-GaAs crystals coated with DLCF as compared with the crystals without DLCF.

  13. Growth kinetics and electronic properties of unintentionally doped semi-insulating GaN on SiC and high-resistivity GaN on sapphire grown by ammonia molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Tang, H.; Fang, Z. Q.; Rolfe, S.; Bardwell, J. A.; Raymond, S.

    2010-05-01

    Growth of unintentionally doped (UID) semi-insulating GaN on SiC and highly resistive GaN on sapphire using the ammonia molecular-beam epitaxy technique is reported. The semi-insulating UID GaN on SiC shows room temperature (RT) resistivity of 1011 Ω cm and well defined activation energy of 1.0 eV. The balance of compensation of unintentional donors and acceptors is such that the Fermi level is lowered to midgap, and controlled by a 1.0 eV deep level defect, which is thought to be related to the nitrogen antisite NGa, similar to the "EL2" center (arsenic antisite) in unintentionally doped semi-insulating GaAs. The highly resistive GaN on sapphire shows RT resistivity in range of 106-109 Ω cm and activation energy varying from 0.25 to 0.9 eV. In this case, the compensation of shallow donors is incomplete, and the Fermi level is controlled by levels shallower than the 1.0 eV deep centers. The growth mechanisms for the resistive UID GaN materials were investigated by experimental studies of the surface kinetics during growth. The required growth regime involves a moderate growth temperature range of 740-780 °C, and a high ammonia flux (beam equivalent pressure of 1×10-4 Torr), which ensures supersaturated coverage of surface adsorption sites with NHx radicals. Such highly nitrogen rich growth conditions lead to two-dimensional layer by layer growth and reduced oxygen incorporation.

  14. Growth kinetics and electronic properties of unintentionally doped semi-insulating GaN on SiC and high-resistivity GaN on sapphire grown by ammonia molecular-beam epitaxy

    SciTech Connect

    Tang, H.; Rolfe, S.; Bardwell, J. A.; Raymond, S.; Fang, Z. Q.

    2010-05-15

    Growth of unintentionally doped (UID) semi-insulating GaN on SiC and highly resistive GaN on sapphire using the ammonia molecular-beam epitaxy technique is reported. The semi-insulating UID GaN on SiC shows room temperature (RT) resistivity of 10{sup 11} {Omega} cm and well defined activation energy of 1.0 eV. The balance of compensation of unintentional donors and acceptors is such that the Fermi level is lowered to midgap, and controlled by a 1.0 eV deep level defect, which is thought to be related to the nitrogen antisite N{sub Ga}, similar to the ''EL2'' center (arsenic antisite) in unintentionally doped semi-insulating GaAs. The highly resistive GaN on sapphire shows RT resistivity in range of 10{sup 6}-10{sup 9} {Omega} cm and activation energy varying from 0.25 to 0.9 eV. In this case, the compensation of shallow donors is incomplete, and the Fermi level is controlled by levels shallower than the 1.0 eV deep centers. The growth mechanisms for the resistive UID GaN materials were investigated by experimental studies of the surface kinetics during growth. The required growth regime involves a moderate growth temperature range of 740-780 deg. C, and a high ammonia flux (beam equivalent pressure of 1x10{sup -4} Torr), which ensures supersaturated coverage of surface adsorption sites with NH{sub x} radicals. Such highly nitrogen rich growth conditions lead to two-dimensional layer by layer growth and reduced oxygen incorporation.

  15. High-speed digital ICs - A comparison between silicon and GaAs

    NASA Astrophysics Data System (ADS)

    Ricco, Bruno

    1986-06-01

    High electron mobility and semi-insulating characteristics make GaAs a semiconductor material ideally suited for very fast logics. Nevertheless, for such purposes it must compete with the fully mature LSI and VLSI technologies of silicon. The choice depends on applications and technology options. If MESFETs are rated against Si MOSFETs and bipolar transistors, the scale of circuit integration plays a fundamental role. For fewer than a few hundred gates per chip, GaAs can provide circuits that are two to four times faster although the cost per bit is significantly higher; thus GaAs circuits seem attractive only for required performances above a few gigahertz (beyond the reach of silicon devices). The brighter perspectives for GaAs come from the potential of heterostructure devices which are under development and showing great promise. Sophisticated processing steps (such as molecular beam epitaxy) are still under development and still need to be assessed regarding their viability for circuit mass production. Various logics are compared.

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

    SciTech Connect

    Golubyatnikov, V. A.; Grigor’ev, F. I.; Lysenko, A. P. Strogankova, N. I.; Shadov, M. B.; Belov, A. G.

    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.

  17. EL2 and related defects in GaAs - Challenges and pitfalls. [microdefect introducing a deep donor level

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1985-01-01

    The incorporation process of nonequilibrium vacancies in melt-grown GaAs is strongly complicated by deviations from stoichiometry and the presence of two sublattices. Many of the microdefects originating in these vacancies and their interactions introduce energy levels (shallow and deep) within the energy gap. The direct identification of the chemical or structural signature of these defects and its direct correlation to their electronic behavior is not generally possible. It is necessary, therefore, to rely on indirect methods and phenomenological models and deal with the associated pitfalls. EL2, a microdefect introducing a deep donor level, has been in the limelight in recent years because it is believed to be responsible for the semi-insulating behavior of undoped GaAs. Although much progress has been made towards understanding its origin and nature, some relevant questions remain unanswered. An attempt is made to assess the present status of understanding of EL2 in the light of most recent results.

  18. Measuring Carrier Lifetime in GaAs by Luminescence

    NASA Technical Reports Server (NTRS)

    Von Roos, O.

    1986-01-01

    Luminescence proposed as nondestructive technique for measuring Shockley-Read-Hall (SRH) recombination lifetime GaAs. Sample irradiated, and luminescence escapes through surface. Measurement requires no mechanical or electrical contact with sample. No ohmic contacts or p/n junctions needed. Sample not scrapped after tested.

  19. Gallium arsenide (GaAs) power conversion concept

    NASA Technical Reports Server (NTRS)

    Nussberger, A. A.

    1980-01-01

    A summary design analysis of a GaAs power conversion system for the solar power satellite (SPS) is presented. Eight different satellite configuration options for the solar arrays are compared. Solar cell annealing effects after proton irradiation are considered. Mass estimates for the SPS and the effect of solar cell parameters on SPS array design are discussed.

  20. High-Resistivity Semi-insulating AlSb on GaAs Substrates Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Vaughan, E. I.; Addamane, S.; Shima, D. M.; Balakrishnan, G.; Hecht, A. A.

    2016-04-01

    Thin-film structures containing AlSb were grown using solid-source molecular beam epitaxy and characterized for material quality, carrier transport optimization, and room-temperature radiation detection response. Few surface defects were observed, including screw dislocations resulting from shear strain between lattice-mismatched layers. Strain was also indicated by broadening of the AlSb peak in x-ray diffraction measurements. Threading dislocations and interfacial misfit dislocations were seen with transmission electron microscopy imaging. Doping of the AlSb layer was introduced during growth using GaTe and Be to determine the effect on Hall transport properties. Hall mobility and resistivity were largest for undoped AlSb samples, at 3000 cm2/V s and 106 Ω cm, respectively, and increased doping levels progressively degraded these values. To test for radiation response, p-type/intrinsic/ n-type (PIN) diode structures were grown using undoped AlSb on n-GaAs substrates, with p-GaSb cap layers to protect the AlSb from oxidation. Alpha-particle radiation detection was achieved and spectra were produced for 241Am, 252Cf, and 239Pu sources. Reducing the detector surface area increased the pulse height observed, as expected based on voltage-capacitance relationships for diodes.

  1. Optical-Electrical Characteristics and Carrier Dynamics of Semi-Insulation GaAs by Terahertz Spectroscopic Technique

    NASA Astrophysics Data System (ADS)

    Han, Xiao-Wei; Hou, Lei; Yang, Lei; Wang, Zhi-Quan; Zhao, Meng-Meng; Shi, Wei

    2016-12-01

    Not Available Supported by the National Natural Science Foundation of China under Grant Nos 61575161 and 61427814, the National Basic Research Program of China under Grant No 2014CB339800, the Foundation of Shaanxi Key Science and Technology Innovation Team under Grant No 2014KTC-13, and the Special Financial Grant from the China Postdoctoral Science Foundation under Grant No 2013T60883.

  2. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Transient surface photoconductivity of GaAs emitter studied by terahertz pump-emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Shi, Yu-Lei; Zhou, Qing-Li; Zhang, Cun-Lin

    2009-10-01

    This paper investigates the ultrafast carrier dynamics and surface photoconductivity of unbiased semi-insulating GaAs in detail by using a terahertz pump-emission technique. Based on theoretical modelling, it finds that transient photoconductivity plays a very important role in the temporal waveform of terahertz radiation pulse. Anomalous enhancement in both terahertz radiation and transient photoconductivity is observed after the excitation of pump pulse and we attribute these phenomena to carrier capture in the EL2 centers. Moreover, the pump power- and temperature-dependent measurements are also performed to verify this trapping model.

  3. Origin and reduction of impurities at GaAs epitaxial layer-substrate interfaces

    NASA Astrophysics Data System (ADS)

    Kanber, H.; Yang, H. T.; Zielinski, T.; Whelan, J. M.

    1988-09-01

    Surface cleaning techniques used for semi-insulating GaAs substrates prior to epitaxial growth can have an important and sometimes detrimental effect on the quality and characteristics of epitaxial layers that are grown on them. We observe that a HF rinse followed by a 5:1:1 H 2SO 4:H 2O 2:H 2O etch and H 2O rinse drastically reduced the maximum concentrations and total amount of both SIMS detected S and Si for MOCVD grown GaAs undoped epitaxial layers. Subsequent final HCl and H 2O reduced the S interfacial residues to the SIMS detection limit. Total amounts of residual Si are estimated to be equivalent to 10 -2 to 10 -3 monolayers. Residual S is less. Alternately the S residue can be comparable reduced by a HF rinse followed by a NH 4OH:H 2O 2:H 2O etch and H 2O rinse. Hot aqueous HCl removes S but not Si residues. The Si residue is not electrically active and most likely exists as islands of SiO 2. The relative significance of the impurity residues is most pronounced for halide VPE, smaller for MBE and least for MOCVD grown GaAs epitaxial layers.

  4. X-ray imaging using a 320 x 240 hybrid GaAs pixel detector

    SciTech Connect

    Irsigler, R.; Andersson, J.; Alverbro, J.

    1999-06-01

    The authors present room temperature measurements on 200 {micro}m thick GaAs pixel detectors, which were hybridized to silicon readout circuits. The whole detector array contains 320 x 240 square shaped pixel with a pitch of 38 {micro}m and is based on semi-insulating liquid-encapsulated Czochralski (LEC) GaAs material. After fabricating and dicing, the detector chips were indium bump flip chip bonded to CMOS readout circuits based on charge integration and finally evaluated. This readout chip was originally designed for the readout of flip chip bonded infrared detectors, but appears to be suitable for X-ray applications as well. A bias voltage between 50 V and 100 V was sufficient to operate the detector at room temperature. The detector array did respond to x-ray radiation by an increase in current due to production of electron hole pairs by the ionization processes. Images of various objects and slit patterns were acquired by using a standard X-ray source for dental imaging. The new X-ray hybrid detector was analyzed with respect to its imaging properties. Due to the high absorption coefficient for X-rays in GaAs and the small pixel size, the sensor shows a high modulation transfer function up to the Nyquist frequency.

  5. Absorption edge determination of thick GaAs wafers using surface photovoltage spectroscopy

    NASA Astrophysics Data System (ADS)

    Sharma, T. K.; Porwal, S.; Kumar, R.; Kumar, Shailendra

    2002-04-01

    A procedure for choosing the appropriate chopping frequency (f) for the surface photovoltage spectroscopy (SPS) measurements in order to obtain the absorption related features is presented. We could obtain the absorption edge of thick n+ GaAs wafer (thickness ≈700 μm) by performing SPS measurements at f⩾1 kHz at room temperature (300 K). The similar information for semi-insulating (SI) GaAs could not be obtained due to the carrier trapping at deep levels or surface states at 300 K. However, we could obtain the absorption edge of SI-GaAs by performing SPS measurements at 395 K at f=3 kHz. Here, we demonstrate the capability of the SPS technique to measure large absorption coefficient (α) values for thick wafers by performing SPS measurements and normalizing this with the reported α value at one wavelength in the above band gap region. For comparison, we also perform quasisimultaneous SPS and transmission spectroscopy (TS) measurements. The SPS technique could provide α values up to 104cm-1 for 700-μm-thick GaAs wafers, whereas TS could only measure α values up to about 15 cm-1. An improved design of the sample holder for measuring the surface photovoltage in the chopped light geometry, which increases the signal strength by reducing the gap between the top electrode and the wafer in a controlled manner, is presented. This ensures that there is no sample damage or contamination.

  6. Low contrast imaging with a GaAs pixel digital detector

    NASA Astrophysics Data System (ADS)

    Amendolia, S. R.; Bisogni, M. G.; Bottigli, U.; Ciocci, M. A.; Delogu, P.; Dipasquale, G.; Fantacci, M. E.; Giannelli, M.; Maestro, P.; Marzulli, V. M.; Pernigotti, E.; Rosso, V.; Stefanini, A.; Stumbo, S.

    2000-08-01

    A digital mammography system based on a GaAs pixel detector has been developed by the INFN (Istituto Nazionale di Fisica Nucleare) collaboration MED46. The high atomic number makes the GaAs a very efficient material for low energy X-ray detection (10-30 keV is the typical energy range used in mammography). Low contrast details can be detected with a significant dose reduction to the patient. The system presented in this paper consists of a 4096 pixel matrix built on a 200 /spl mu/m thick semi-insulating GaAs substrate. The pixel size is 170/spl times/170 /spl mu/m/sup 2/ for a total active area of 1.18 cm/sup 2/. The detector is bump-bonded to a VLSI front-end chip which implements a single-photon counting architecture. This feature allows to enhance the radiographic contrast detection with respect to charge integrating devices. The system has been tested by using a standard mammographic tube. Images of mammographic phantoms will be presented and compared with radiographs obtained with traditional film/screen systems. Monte Carlo simulations have been also performed to evaluate the imaging capability of the system. Comparison with simulations and experimental results will be shown.

  7. Electron irradiation effects on photoconductive semiconductor switches (PCSSs) used in sub-nanosecond transient generators

    SciTech Connect

    Islam, N.E.; Schamiloglu, E.; Kirby, T.H.; Shipley, B.; Kemp, W.T.; Schoenberg, J.S.H.; Howard, J.W. Jr.

    1999-12-01

    Radiation-induced damage occurs in GaAs photoconductive semiconductor switches used in sub-nanosecond transient generators when subjected to 600 keV and 6 MeV electron irradiation. These switches are made from semi-insulating (SI) compensated material through a EL2/carbon compensation mechanism, and the liquid encapsulated Czochralski process. New defect levels are formed as a result of the non-ionizing energy loss (NIEL) process. The formation of new defect levels in the device alters the compensating balance between the existing deep level EL2 trap/donors and carbon acceptors, and changes the material properties. As a result, two important parameters of the device are adversely affected--the hold-off voltage of the switch at the pulse-charging (off) state, and the rise time during the conduction (on) state. The hold-off voltage shifts to a lower value since there are more trap-filled regions available that can fill up and alter the homogeneous nature of the device material. Unstable filamentary conduction then occurs at a lower voltage and leads to premature breakdown. As with EL2 trap levels, new defect states induced by electron irradiation will further contribute to the delay in the rise time of the switch. The rise time determines the maximum energy transferred to the load. The electron damage mechanism and its effects on the switch characteristics depend on the material properties. Intrinsic material, or material made through compensation other than through the deep donor and shallow acceptor balancing process are not expected to behave similarly. Simulation results at higher bias show a merged degradation of material properties. The switch current-voltage (I-V) characteristic when the bias increases to the kilovolt range is similar to trap-dominated semiconductors. An initial sublinear current regime at low bias is followed by a super-linear regime of current flow at higher bias, and is in agreement with earlier observations.

  8. Effect of the Photoquenching of EL2 in GaAs Substrate on the Piezoelectric Photothermal and Surface Photovoltage Spectra of a GaAs Single Quantum Well Confined by GaAs/AlAs Short-Period Superlattices

    NASA Astrophysics Data System (ADS)

    Wang, Ping; Fukuyama, Atsuhiko; Akashi, Yoshito; Ikari, Tetsuo

    2008-01-01

    Two nondestructive techniques, surface photovoltage (SPV) and piezoelectric photothermal (PPT) spectroscopies, were adopted to investigate a GaAs single quantum well (SQW) confined by GaAs/AlAs short-period superlattices (SPSs) fabricated on a semi-insulating (SI) GaAs substrate, whose absorption spectra cannot be obtained easily using conventional techniques. Excitonic absorptions associated with subband transitions in a GaAs SQW and SPSs were clearly observed. We also examined how a SI-GaAs substrate affects the PPT and SPV spectra, particularly the effect of the photoquenching of the deep donor level EL2. It was found that the photoquenching of EL2 causes a significant change in the total built-in potential at the interface between the epitaxial layers and the substrate, and affected the signal intensities observed in the PPT and SPV spectra. The present experimental results have shown that a large amount of carrier leakage occurs from a GaAs SQW and SPSs to the sample surface, even in the presence of Al0.3Ga0.7As buffer layers.

  9. EL2 distributions in doped and undoped liquid encapsulated Czochralski GaAs. [deep donor concentration

    NASA Technical Reports Server (NTRS)

    Holmes, D. E.; Chen, R. T.; Yang, J.

    1983-01-01

    The longitudinal and radial distributions of EL2 in undoped semi-insulating and intentionally doped n-type GaAs crystals grown by the liquid encapsulated Czochralski technique are compared. Longitudinal profiles in undoped crystals are controlled by changes in melt stoichiometry as the crystal is pulled from the melt. EL2 profiles along crystals doped above about 1 x 10 to the 17th/cu cm, on the other hand, are controlled primarily by the carrier concentration as a result of the suppression of EL2 by free electrons. Radial EL2 profiles are typically W shaped and M shaped in undoped and doped (above threshold) crystals, respectively. The origin of these radial profiles is discussed in terms of residual stress, melt stoichiometry, and the suppresion of EL2 by electrons. The results are also discussed in the light of the antisite model for EL2.

  10. EL2 distributions in doped and undoped liquid encapsulated Czochralski GaAs. [deep donor concentration

    NASA Technical Reports Server (NTRS)

    Holmes, D. E.; Chen, R. T.; Yang, J.

    1983-01-01

    The longitudinal and radial distributions of EL2 in undoped semi-insulating and intentionally doped n-type GaAs crystals grown by the liquid encapsulated Czochralski technique are compared. Longitudinal profiles in undoped crystals are controlled by changes in melt stoichiometry as the crystal is pulled from the melt. EL2 profiles along crystals doped above about 1 x 10 to the 17th/cu cm, on the other hand, are controlled primarily by the carrier concentration as a result of the suppression of EL2 by free electrons. Radial EL2 profiles are typically W shaped and M shaped in undoped and doped (above threshold) crystals, respectively. The origin of these radial profiles is discussed in terms of residual stress, melt stoichiometry, and the suppresion of EL2 by electrons. The results are also discussed in the light of the antisite model for EL2.

  11. Modification of GaAs surface by low-current Townsend discharge

    NASA Astrophysics Data System (ADS)

    Gurevich, E. L.; Kittel, S.; Hergenröder, R.; Astrov, Yu A.; Portsel, L. M.; Lodygin, A. N.; Tolmachev, V. A.; Ankudinov, A. V.

    2010-07-01

    The influence of stationary spatially homogeneous Townsend discharge on the (1 0 0) surface of semi-insulating GaAs samples is studied. Samples exposed to both electrons and ions in a nitrogen discharge at a current density j = 60 µA cm-2 are studied by means of x-ray photoelectron spectroscopy, ellipsometry and atomic force microscopy. It is shown that an exposure to low-energy ions (<1 eV) changes the crystal structure of the semiconductor for a depth of up to 10-20 nm, although the stoichiometric composition does not change. The exposure to low-energy electrons (<10 eV) forms an oxide layer, which is 5-10 nm thick. Atomic force microscopy demonstrates that the change in the surface potential of the samples may exceed 100 mV, for both discharge polarities, while the surface roughness does not increase.

  12. Deep levels in undoped horizontal Bridgman GaAs by Fourier transform photoconductivity and Hall effect

    NASA Astrophysics Data System (ADS)

    Mitchel, W. C.; Brown, Gail J.; Rea, Laura S.; Smith, S. R.

    1992-01-01

    Deep levels between 0.1 and 1.0 eV in semi-insulating and high resistivity undoped horizontal Bridgman GaAs have been studied by temperature-dependent Hall effect (TDH) and Fourier transform photoconductivity (FTPC). Activation energies at 0.77, 0.426, and 0.15 eV have been observed by TDH. Photoionization thresholds at 1.0, 0.8, 0.56, 0.44, and 0.25 are reported. The photoconductivity thresholds at 0.56 and 0.25 eV are reported for the first time. New features in the 0.44 eV threshold suggest that the defect responsible for this level has a small lattice relaxation and Frank-Condon shift. Possible associations of the FTPC and TDH energies with the deep-level transient spectroscopy levels EL2, EL3, and EL6 are presented.

  13. Ga nanoparticle-enhanced photoluminescence of GaAs

    SciTech Connect

    Kang, M.; Al-Heji, A. A.; Jeon, S.; Wu, J. H.; Lee, J.-E.; Saucer, T. W.; Zhao, L.; Sih, V.; Katzenstein, A. L.; Sofferman, D. L.; Goldman, R. S.

    2013-09-02

    We have examined the influence of surface Ga nanoparticles (NPs) on the enhancement of GaAs photoluminescence (PL) efficiency. We have utilized off-normal focused-ion-beam irradiation of GaAs surfaces to fabricate close-packed Ga NP arrays. The enhancement in PL efficiency is inversely proportional to the Ga NP diameter. The maximum PL enhancement occurs for the Ga NP diameter predicted to maximize the incident electromagnetic (EM) field enhancement. The PL enhancement is driven by the surface plasmon resonance (SPR)-induced enhancement of the incident EM field which overwhelms the SPR-induced suppression of the light emission.

  14. ZnSe Window Layers for GaAs and GaInP2 Solar Cells

    NASA Technical Reports Server (NTRS)

    Olsen, Larry C.

    1995-01-01

    This report concerns studies of the use of ZnSe as a window layer for GaAs solar cells. Well-oriented crystalline ZnSe films on (100) single crystal GaAs substrates were grown by MOCVD. In particular, ZnSe films were grown by reacting a zinc adduct with hydrogen selenide at temperatures in the range of 200 C to 400 C. X-ray diffraction studies and images obtained with an atomic force microscope determined that the films were highly oriented but were polycrystalline. Particular emphasis was placed on the use of a substrate temperature of 350 C. Using iodine as a dopant, n-type ZnSe films with resistivities in the range of .01 to .05 ohm-cm were grown on semi-insulating GaAs. Thus procedures have been developed for investigating the utility of n-type ZnSe window layers on n/p GaAs structures. Studies of recombination at n-ZnSe/n-GaAs interfaces in n-ZnSe/n-GaAs/p-GaAs cell structures are planned for future work.

  15. LSI/VLSI (Large Scale Integration/Very Large Scale Integration) ion implanted GaAs (Gallium Arsenide) IC processing

    NASA Astrophysics Data System (ADS)

    Zucca, R. R.; Kirkpatrick, C. G.; Asbeck, P. M.; Eisen, F. H.; Lee, C. P.

    1984-01-01

    This report covers a program designed to realize the full potential of GaAs integrated circuits by expanding and improving fabrication and material techniques. The main accomplishment of the program was the successful implementation of the fabrication of integrated circuits on 3-inch diameter GaAs wafers. In addition, this program covered many activities related to GaAs IC processing. These include: work on semi-insulating material growth and characterization, investigation of ion implantation techniques (work carried out at the California Institute of Technology); evaluation of device uniformity, and investigation of its controlling factors; investigation of metallization yield and reliability, and improvements of processing techniques resulting from this study; design and testing of a multiplier and programmable shift registers/pattern generators; evaluation of mask programmable logic arrays to meet ERADCOMs needs for high performance communication systems; investigation of the hardness of GaAs ICs to total dose and transient ionizing radiation, and modelling of MESFET devices (this work carried out at North Carolina State University).

  16. Photoluminescence of Undoped, Semi-Insulating, and Mg-Implanted Indium Phosphide.

    DTIC Science & Technology

    1979-12-01

    PH/79D-8 PHOTOLUMINESCENCE OF UNDOPED, SEMI-INSULATING, AND Mg- IMPLANTED INDIUM PHOSPHIDE THESIS Presented to the Faculty of the School of Engineering...Unannealed, Unimplanted and Mg- Implanted InP:Fe at 500 K ...... 132 Appendix H: Photoluminescence of Mg- Implanted , 750* C Annealed InP:Fe at 50 K...136 Appendix I: Photoluminescence of Mg- Implanted , 7000 C Annealed InP:Fe at 4.20 K ..................... 146 Appendix J

  17. Novel ways to grow thermally stable semi-insulating InP-based layers

    NASA Astrophysics Data System (ADS)

    Bimberg, D.; Dadgar, A.; Heitz, R.; Knecht, A.; Krost, A.; Kuttler, M.; Scheffler, H.; Näser, A.; Srocka, B.; Wolf, T.; Zinke, T.; Hyeon, J. Y.; Wernik, S.; Schumann, H.

    1994-12-01

    Semi-insulating InP is generally grown by Fe doping. In contact with p-type layers, however, semi-insulating characteristics turn out to be difficult to reproduce because of pronounced interdiffusion of Fe and p-type dopants. Co-doping of InP:Fe with Ti is shown to be a universal process for the preparation of thermally stable high-resistivity layers. Fe + Ti co-doping can compensate both excess shallow donors and excess shallow acceptors up to concentrations of 8 × 10 16 and 2 × 10 16 cm -3, respectively. In contrast to InP:Fe, resistivities in excess of 10 7 Ω cm are obtained in contact with both symmetric n- and p-type current injecting contacts. Moreover, co-doping of semi-insulating InP:Fe with Ti is found to suppress the interdiffusion of Fe and p-type dopants. Therefore, the out-diffusion and accumulation of Fe in other regions of complex device structures can be significantly reduced. A comprehensive model accounting for these phenomena is presented. A totally different way to produce thermally more stable semi-insulating InP layers is to replace Fe by a less diffusive deep acceptor. We propose the 4d transition metal Rh as a potential alternative. The diffusion of Rh is shown to be practically nonexistent and near-midgap Rh levels are found by means of DLTS in InP at Ev + 730 meV and in InGaAs at Ec - 380 meV below the conduction band. We conclude these levels to be the single acceptor states of Rh substitutionally incorporated on cation sites.

  18. Migration processes of the As interstitial in GaAs

    NASA Astrophysics Data System (ADS)

    Wright, A. F.; Modine, N. A.

    2016-12-01

    Thermal migration processes of the As interstitial in GaAs were investigated using density-functional theory and the local-density approximation for exchange and correlation. The lowest-energy processes were found to involve the -1, 0, and +1 charge states, and to produce migration along ⟨110⟩-type directions. In the -1 and 0 charge states, migration proceeds via hops between split-interstitial stable configurations at bulk As sites through bridging saddle-point configurations in which the interstitial atom is equidistant from two adjacent bulk As sites. In the +1 charge state, the roles of these two configurations are approximately reversed and migration proceeds via hops between bridging stable configurations through higher-energy split-interstitial stable configurations bounded by a pair of distorted split-interstitial saddle-point configurations. The predicted activation energies for migration in the 0 and +1 charge states agree well with measurements in semi-insulating and p-type material, respectively. Also consistent with experiments, the approximate reversal of the stable and saddle-point configurations between the 0 and +1 charge states is predicted to enable carrier-induced migration with a residual activation energy of 0.05 eV.

  19. Shallow-homojunction GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Fan, J. C. C.

    1979-01-01

    Single-crystal GaAs shallow-homojunction solar cells on GaAs or Ge substrates, without Ga sub 1-x Al sub x As window layers, that have conversion efficiencies exceeding 20% at AM1 (17% at AMO). Using a simple theoretical model, good fits were obtained between computer calculations and experimental data for external quantum efficiency and conversion efficiency of cells with different values of n+ layer thickness. The calculations not only yield values for material properties of the GaAs layers composing the cells but will also permit the optimization of cell designs for space and terrestrial applications. Preliminary measurements indicate that the shallow-homojunction cells are resistant to electron irradiation. In the best test so far, bombardment with 1 x 10 to the 16th power/sq cm fluence of 1 MeV electrons reduced the short-circuit current by only about 6%.

  20. Radiation damage in GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Conway, E. J.; Walker, G. H.

    1979-01-01

    Recent results of electron and proton irradiation and annealing of GaAs solar cells are presented along with some implications of these results. A comparison between the energy-levels produced by protons and by electrons which are not stopped in the material indicate that the damage produced by protons and electrons may be qualitatively different. Thus, annealing of proton damage may be very different from the annealing of electron damage.

  1. Carrier compensation in semi-insulating CdTe: First-principles calculations

    SciTech Connect

    Du, Mao-Hua; Singh, David J

    2008-01-01

    Carrier compensation in semi-insulating CdTe has been attributed to the compensation of surplus shallow acceptors by deep donors, usually assumed to be Te antisites. However, our first-principles calculations show that intrinsic defects should not have a significant effect on the carrier compensation due either to lack of deep levels near midgap or to low defect concentration. We demonstrate that an extrinsic defect, OTe-H complex, may play an important role in the carrier compensation in CdTe because of its amphoteric character and reasonably high concentration. Our findings have important consequences for improving device performance in CdTe-based radiation detectors and solar cells.

  2. Compensation Mechanism in High Purity Semi-Insulating 4H-SiC

    DTIC Science & Technology

    2007-01-01

    online 15 March 2007 A study of deep levels in high purity semi-insulating 4H-SiC has been made using temperature dependent Hall effect TDH , thermal and...optical admittance spectroscopies, and secondary ion mass spectrometry SIMS. Thermal activation energies from TDH varied from a low of 0.55 eV to a...high of 1.65 eV. All samples studied showed n-type conduction with the Fermi level in the upper half of the band gap. Fits of the TDH data to

  3. Fe-doping in hydride vapor-phase epitaxy for semi-insulating gallium nitride

    NASA Astrophysics Data System (ADS)

    Richter, E.; Gridneva, E.; Weyers, M.; Tränkle, G.

    2016-12-01

    Fe-doping of GaN layers of 3 in. in diameter and a thickness of 1 mm in a vertical AIX-HVPE reactor is studied. Ferrocen was used as Fe source. It is shown that a sufficient uniformity of growth conditions, a high purity of undoped GaN layers, and a moderate Fe incorporation of 2×1018 cm-3 allow for growth of semi-insulating GaN layers with a sufficiently high specific resistivity even at elevated temperature. This makes the material suitable as substrate for electronic power devices at high power or in harsh ambient.

  4. The Features of GaAs and GaP Semiconductor Cathodes in an Infrared Converter System

    NASA Astrophysics Data System (ADS)

    Kurt, H. Hilal; Tanrıverdi, Evrim

    2017-07-01

    The aim of this study is to examine the electrical and optical comparative analysis of semi-insulating GaAs and GaP photoconductive electrodes in an infrared converter system with a resistivity of >107 Ω cm for the same interelectrode distance d and gas pressure p experimentally and theoretically, when the discharge cell has been filled by argon. To provide the stability of the semiconductor electrode in Ar media, the experiments were carried out in Townsend and glow discharge regimes for various parameter sets of pressure, interelectrode gap and discharge voltage. When the discharge exceeds a critical voltage value, some N-shape CVC s, which stem from both semiconductors and Ar gas, have been observed. To compare the features of the GaAs and GaP cathodes, the COMSOL multiphysics programme is used under the Ar media. The mean electron energy, thermal velocity, surface charge density, space charge and initial electron densities, and electron mobilities have been calculated for both semiconductor materials. It has been found that the electron mobility μe, electron thermal velocity, surface charge density σ and mean electron energy of GaAs is higher than those of GaP; hence, GaAs has better opto-electronic features compared to GaP. In addition, the experiments on the optical explorations prove that GaAs exhibit better optical response in the infrared region. The explored transport characteristics of the semiconductor electrodes are of importance, and they have to be taken into account when studying plasma cells.

  5. Magnetic-field dependence of the optical Overhauser effect in GaAs

    SciTech Connect

    Kuhns, P.L.; Kleinhammes, A.; Schmiedel, T.; Moulton, W.G.; Chabrier, P.; Sloan, S.; Hughes, E.; Bowers, C.R.

    1997-03-01

    When nuclear spin order is induced by optical excitation near the band gap of a semiconductor such as GaAs, the effect is referred to as optical pumping. This paper presents measurements of the optical pumping rate in semi-insulating GaAs over the magnetic field range of 0{minus}24 T at temperatures of 1.5 K and 4.2 K. The enhanced nuclear polarization was sampled by radio wave detected NMR. The data were recorded using Bitter- type magnets which permitted rapid ramping between the pumping and sampling fields in a time short compared to the nuclear spin lattice relaxation time in the dark. The field dependence has been fitted to a relaxation model which includes spin diffusion and dark relaxation terms. Fits were obtained by fixing the g factor to its literature value. The fitted parameters include the correlation time for electron spin-density fluctuations, the average hyperfine field, and the nuclear spin diffusion coefficient. {copyright} {ital 1997} {ital The American Physical Society}

  6. Longevity improvement of optically activated, high gain GaAs photoconductive semiconductor switches

    SciTech Connect

    MAR,ALAN; LOUBRIEL,GUILLERMO M.; ZUTAVERN,FRED J.; O'MALLEY,MARTIN W.; HELGESON,WESLEY D.; BROWN,DARWIN JAMES; HJALMARSON,HAROLD P.; BACA,ALBERT G.

    2000-03-02

    The longevity of high gain GaAs photoconductive semiconductor switches (PCSS) has been extended to over 100 million pulses at 23A, and over 100 pulses at 1kA. This is achieved by improving the ohmic contacts by doping the semi-insulating GaAs underneath the metal, and by achieving a more uniform distribution of contact wear across the entire switch by distributing the trigger light to form multiple filaments. This paper will compare various approaches to doping the contacts, including ion implantation, thermal diffusion, and epitaxial growth. The device characterization also includes examination of the filament behavior using open-shutter, infra-red imaging during high gain switching. These techniques provide information on the filament carrier densities as well as the influence that the different contact structures and trigger light distributions have on the distribution of the current in the devices. This information is guiding the continuing refinement of contact structures and geometries for further improvements in switch longevity.

  7. EL2 and related defects in GaAs - Challenges and pitfalls

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1985-01-01

    The incorporation process of nonequilibrium vacancies in melt-grown GaAs is strongly complicated by deviations from stoichiometry, and the presence of two sublattices. Many of the microdefects originating in these vacancies and their interactions introduce energy levels (shallow and deep) within the energy gap. The direct identification of the chemical or structural signature of these defects and its direct correlation to their electronic behavior is not generally possible. It is therefore necessary to rely on indirect methods and phenomenological models and be confronted with the associated pitfalls. EL2, a microdefect introducing a deep donor level, has been in the limelight in recent years because it is believed to be responsible for the semi-insulating behavior of undoped GaAs. Although much progress has been made towards understanding its origin and nature, some relevant questions remain unanswered. An attempt is made to assess the present status of understanding of EL2 in the light of the most recent results.

  8. Effects of EL2 deep level in GaAs photoconductive switch

    NASA Astrophysics Data System (ADS)

    Shi, Wei; Liu, Rui; Wang, Jing-li

    2009-07-01

    The semi-insulating (SI) GaAs photoconductive switch is considered to be the higher efficient THz source recently. In order to make good use of the photoconductive switch to generate the more efficient THz wave, SI-GaAs photoconductive switch's working mechanism is discussed from the respect of EL2 deep level in this paper. It has three operation modes. The SI-GaAs material has many kinds of intrinsic-defects. One of the more notable defects is EL2 deep level. The EL2 level can become an impactful electron trap in the linear operation mode; The EL2 level is also the necessary condition of nonlinear (also known as Lock-on) operation mode emerging in III-V semiconductors such as GaAs and InP. At the same time, the compound operation mode is substantial related with the conversion from neutral energy level EL20 to metastable energy level EL2* and singly ionized energy level EL2+ in semiconductor under the light. So in this paper the effects of EL2 deep level are analyzed in photoconductive switch' there operation modes.

  9. Electrical properties of molecular beam epitaxial GaAs grown at 300-450{degrees}C

    SciTech Connect

    Look, D.C.; Robinson, G.D.; Sizelove, J.R.; Stutz, C.E.

    1993-12-01

    We use the Hall effect and a new charge-transfer technique to study molecular beam epitaxial GaAs grown at the low substrate temperatures of 300-450{degrees}C. Layers grown from 350-450{degrees}C are semi-insulating (resistivity greater than 10{sup 7}{Omega}-cm), as grown, because of an As{sub Ga}-related donor (not EL2) at E{sub c} - 0.65 eV. The donor concentrations are about 2 x 10{sup 18} cm{sup -3} and 2 x 10{sup 17} cm{sup -3} at growth temperatures of 300 and 400{degrees}C, respectively, and acceptor concentrations are about an order of magnitude lower. Relatively high mobilities ({approximately}5000 cm{sup 2}/V s) along with the high resistivities make this material potentially useful for certain device applications. 8 refs., 2 figs., 2 tabs.

  10. Evolution of ion-induced nanoparticle arrays on GaAs surfaces

    SciTech Connect

    Kang, M.; Al-Heji, A. A.; Shende, O.; Huang, S.; Jeon, S.; Goldman, R. S.; Beskin, I.

    2014-05-05

    We have examined the evolution of irradiation-induced Ga nanoparticle (NP) arrays on GaAs surfaces. Focused-ion-beam irradiation of pre-patterned GaAs surfaces induces monotonic increases in the NP volume and aspect ratio up to a saturation ion dose, independent of NP location within the array. Beyond the saturation ion dose, the NP volume continues to increase monotonically while the NP aspect ratio decreases monotonically. In addition, the NP volumes (aspect ratios) are highest (lowest) for the corner NPs. We discuss the relative influences of bulk and surface diffusion on the evolution of Ga NP arrays.

  11. Evolution of ion-induced nanoparticle arrays on GaAs surfaces

    NASA Astrophysics Data System (ADS)

    Kang, M.; Beskin, I.; Al-Heji, A. A.; Shende, O.; Huang, S.; Jeon, S.; Goldman, R. S.

    2014-05-01

    We have examined the evolution of irradiation-induced Ga nanoparticle (NP) arrays on GaAs surfaces. Focused-ion-beam irradiation of pre-patterned GaAs surfaces induces monotonic increases in the NP volume and aspect ratio up to a saturation ion dose, independent of NP location within the array. Beyond the saturation ion dose, the NP volume continues to increase monotonically while the NP aspect ratio decreases monotonically. In addition, the NP volumes (aspect ratios) are highest (lowest) for the corner NPs. We discuss the relative influences of bulk and surface diffusion on the evolution of Ga NP arrays.

  12. High-purity semi-insulating 4H-SiC for microwave device applications

    NASA Astrophysics Data System (ADS)

    Jenny, J. R.; Malta, D. P.; Müller, St G.; Powell, A. R.; Tsvetkov, V. F.; Hobgood, H. Mcd; Glass, R. C.; Carter, C. H., Jr.

    2003-05-01

    High-purity, semi-insulating (HPSI) 4H-SiC crystals with diameters up to 75 mm have been grown by the seeded sublimation technique without the intentional introduction of elemental deep-level dopants, such as vanadium. Wafers cut from these crystals exhibit homogeneous activation energies near mid gap and thermally stable semi-insulating (SI) behavior (>109 ohm-cm) throughout device processing. Secondary ion mass spectroscopy, deep-level transient spectroscopy, optical admittance spectroscopy, and electron paramagnetic resonance data suggest that the SI behavior originates from several deep levels associated with intrinsic point defects. Micropipe densities in HPSI substrates have been demonstrated to be as low as 10 cm-2 in 2-in. substrates, and the room-temperature thermal conductivity of this material is near the theoretical maximum of 5 W/cm·K for 4H-SiC. Devices fabricated on these HPSI wafers do not exhibit any substrate related back-gating effects and have power densities as high as 5.2 W/mm with 63% power added efficiency.

  13. Modelling of OPNMR phenomena using photon energy-dependent in GaAs and InP

    NASA Astrophysics Data System (ADS)

    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, 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 , 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.

  14. Investigation of New SemiInsulating Behavior of III-V Compounds

    DTIC Science & Technology

    1990-02-28

    encapsulated Czochralski and horizontal Bridgman techniques and in epitaxial crystals prepared by liquid-phase electroepitaxy. By employing deep-level...com- crystals by LEG9 ") and horizontal Bridgman (HB)-" tech- plexes could be responsible for deep levels in GaAs. 1 7 niques has also been reported...Fig. 7) became direct band-gap semiconductors (GaAs and CdSe ) and was clearly visible after quenching of the absorption. explained in terms of a

  15. Burst annealing of high temperature GaAs solar cells

    NASA Technical Reports Server (NTRS)

    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.

  16. Fracture mechanics evaluation of GaAs

    NASA Technical Reports Server (NTRS)

    Chen, C. P.

    1984-01-01

    A data base of mechanical and fracture properties for GaAs was generated. The data for single crystal GaAs will be used to design reusable GaAs solar modules. Database information includes; (1) physical property characterizations; (2) fracture behavior evaluations; and (3) strength of cells determined as a function of cell processing and material parameters.

  17. Mechanisms of the passage of dark currents through Cd(Zn)Te semi-insulating crystals

    NASA Astrophysics Data System (ADS)

    Sklyarchuk, V.; Fochuk, P.; Rarenko, I.; Zakharuk, Z.; Sklyarchuk, O.; Nykoniuk, Ye.; Rybka, A.; Kutny, V.; Bolotnikov, A. E.; James, R. B.

    2014-09-01

    We investigated the passage of dark currents through semi-insulating crystals of Cd(Zn)Te with weak n-type conductivity that are used widely as detectors of ionizing radiation. The crystals were grown from a tellurium solution melt at 800 оС by the zone-melting method, in which a polycrystalline rod in a quartz ampoule was moved through a zone heater at a rate of 2 mm per day. The synthesis of the rod was carried out at ~1150 оС. We determined the important electro-physical parameters of this semiconductor, using techniques based on a parallel study of the temperature dependence of current-voltage characteristics in both the ohmic and the space-charge-limited current regions. We established in these crystals the relationship between the energy levels and the concentrations of deep-level impurity states, responsible for dark conductivity and their usefulness as detectors.

  18. Growth of double doped semi-insulating indium phosphide single crystals

    NASA Astrophysics Data System (ADS)

    Toudic, Y.; Coquillé, R.; Gauneau, M.; Grandpierre, G.; Le Maréchal, L.; Lambert, B.

    1987-05-01

    Semi-insulating (SI) InP, co-doped with a shallow acceptor (Hg or Cd) and a deep donor (Ti or Cr) has been grown by the gradient freeze method or by the liquid encapsulated Czochralski (LEC) technique. Three dopant couples have been studied: Hg+Ti, Hg+Cr and Cd+Cr. The crystals have been characterized by spark source mass spectrometry (SSMS), secondary ion mass spectrometry (SIMS) and thermally dependent Hall (TDH) effect using the Van der Pauw technique. Deduced from the activation energy measurements, the donor deep levels of titanium and chromium have been found to be at Ec-0.53 eV and Ev+0.56 eV, respectively. SIMS profiles on SI substrates annealed at 975°C show that SI InP (Ti, Hg) is more thermally stable than SI InP(Fe) and SI InP(Cr, Hg or Cd).

  19. Semi-insulating behaviour of self-assembled tin(IV)corrole nanospheres.

    PubMed

    Sinha, Woormileela; Kumar, Mohit; Garai, Antara; Purohit, Chandra Shekhar; Som, Tapobrata; Kar, Sanjib

    2014-09-07

    Three novel tin(iv)corrole complexes have been prepared and characterized by various spectroscopic techniques including single crystal X-ray structural analysis. Packing diagrams of the tin(iv)corroles revealed that corrolato-tin(iv)-chloride molecules are interconnected by intermolecular C-HCl hydrogen bonding interactions. HCl distances are 2.848 Å, 3.051 Å, and 2.915 Å, respectively, for the complexes. In addition, the C-HCl angles are 119.72°, 144.70°, and 147.08°, respectively, for the complexes. It was also observed that in one of the three synthesized complexes dimers were formed, while in the other two cases 1D infinite polymer chains were formed. Well-defined and nicely organized three-dimensional hollow nanospheres (SEM images on silicon wafers) with diameters of ca. 676 nm and 661 nm are obtained in the complexes, forming 1D polymer chains. By applying a thin layer of tin(iv)corrole nanospheres to an ITO surface (AFM height images of ITO films; ∼200 nm in height), a device was fabricated with the following composition: Ag/ITO-coated glass/tin(iv)corrole nanospheres/ITO-coated glass/Ag. The resistivity (ρ) of the nanostructured film was calculated to be ∼2.4 × 10(8) Ω cm, which falls in the range of semi-insulating semiconductors. CAFM current maps at 10 V bias show bright spots with a 10-20 pA intensity and indicate that the nanospheres (∼250 nm in diameter) are the electron-conducting pathway in the device. The semi-insulating behavior arises from the non-facile electron transfer in the HOMOs of the tin(iv)corrole nanospheres.

  20. GaAs Computer Technology

    DTIC Science & Technology

    1992-01-07

    AD-A259 259 FASTC-ID FOREIGN AEROSPACE SCIENCE AND TECHNOLOGY CENTER GaAs COMPUTER TECHNOLOGY (1) by Wang Qiao-yu 93-00999 Distrir bution t,,,Nm ted...FASTC- ID(RS)T-0310-92 HUMAN TRANSLATION FASTC-ID(RS)T-0310-92 7 January 1993 GaAs COMPUTER TECHNOLOGY (1) By: Wang Qiao-yu English pages: 6 Source...SCIENCE AND DO NOT NECESSARILY REFLECT THE POSITION OR TECHNOLOGY CENiER OPINION OF THE FOREIGN AEROSPACE SCIENCE AND WPAFB, OHIO TECHNOLOGY CENTER

  1. Thermal annealing of GaAs concentrator solar cells

    NASA Technical Reports Server (NTRS)

    Curtis, H. B.; Brinker, David J.

    1991-01-01

    Isochronal and isothermal annealing tests were performed on GaAs concentrator cells which were irradiated with electrons of various energies to fluences up to 1 x 10(exp 16) e/sq cm. The results include: (1) For cells irradiated with electrons from 0.7 to 2.3 MeV, recovery decreases with increasing electron energy. (2) As determined by the un-annealed fractions, isothermal and isochronal annealing produce the same recovery. Also, cells irradiated to 3 x 10(exp 15) or 1 x 10(exp 16) e/sq cm recover to similar un-annealed fractions. (3) Some significant annealing is being seen at 150 C although very long times are required.

  2. Fabrication of Ohmic contact on semi-insulating 4H-SiC substrate by laser thermal annealing

    NASA Astrophysics Data System (ADS)

    Cheng, Yue; Lu, Wu-yue; Wang, Tao; Chen, Zhi-zhan

    2016-06-01

    The Ni contact layer was deposited on semi-insulating 4H-SiC substrate by magnetron sputtering. The as-deposited samples were treated by rapid thermal annealing (RTA) and KrF excimer laser thermal annealing (LTA), respectively. The RTA annealed sample is rectifying while the LTA sample is Ohmic. The specific contact resistance (ρc) is 1.97 × 10-3 Ω.cm2, which was determined by the circular transmission line model. High resolution transmission electron microscopy morphologies and selected area electron diffraction patterns demonstrate that the 3C-SiC transition zone is formed in the near-interface region of the SiC after the as-deposited sample is treated by LTA, which is responsible for the Ohmic contact formation in the semi-insulating 4H-SiC.

  3. An optimal annealing technique for ohmic contacts to ion-implanted n-layers in semi-insulating indium phosphide

    NASA Astrophysics Data System (ADS)

    Pande, K. P.; Martin, E.; Gutierrez, D.; Aina, O.

    1987-03-01

    An optimal annealing process was developed for sintering AuGe ohmic contacts to ion-implanted semi-insulating InP substrates. Contacts were annealed using a standard furnace, graphite strip heater and a lamp annealer. Alloying at 375°C for 3 min was found to be most suitable for achieving good contact morphology and lowest contact resistivity. Of the three techniques, the lamp annealing technique was found to give the best results when contacts were annealed under a SiO 2 cap. Contact resistivity as low as 8 × 10 -6 cm 2 was obtained for ion-implanted n+ layers in semi-insulating InP.

  4. Fabrication of Ohmic contact on semi-insulating 4H-SiC substrate by laser thermal annealing

    SciTech Connect

    Cheng, Yue; Lu, Wu-yue; Wang, Tao; Chen, Zhi-zhan

    2016-06-14

    The Ni contact layer was deposited on semi-insulating 4H-SiC substrate by magnetron sputtering. The as-deposited samples were treated by rapid thermal annealing (RTA) and KrF excimer laser thermal annealing (LTA), respectively. The RTA annealed sample is rectifying while the LTA sample is Ohmic. The specific contact resistance (ρ{sub c}) is 1.97 × 10{sup −3} Ω·cm{sup 2}, which was determined by the circular transmission line model. High resolution transmission electron microscopy morphologies and selected area electron diffraction patterns demonstrate that the 3C-SiC transition zone is formed in the near-interface region of the SiC after the as-deposited sample is treated by LTA, which is responsible for the Ohmic contact formation in the semi-insulating 4H-SiC.

  5. An Analytical Model for Silicon-on-Insulator Reduced Surface Field Devices with Semi-Insulating Polycrystalline Silicon Shielding Layer

    NASA Astrophysics Data System (ADS)

    Ho, Chi-Hon; Liao, Chien-Nan; Chien, Feng-Tso; Tsai, Yao-Tsung

    2008-07-01

    An analytical model is presented to determine the potential and electric field distribution along the semiconductor surface of new silicon-on-insulator (SOI) reduced surface field (RESURF) device. The SOI structure is characterized by a semi-insulating polycrystalline silicon (SIPOS) layer inserted between a silicon layer and a buried oxide. An improvement in the breakdown voltage due to the presence of the SIPOS shielding layer is demonstrated. Numerical simulations using medici are shown to support the analytical model.

  6. GaAs shallow-homojunction solar cells

    NASA Technical Reports Server (NTRS)

    Fan, J. C.

    1980-01-01

    With the objective of demonstrating the feasibility of fabricating 2 x 2 cm efficient, shallow homojunction GaAs solar cells for space applications, this program addresses the basic problems of material preparation and device fabrication. Significant progress was made and conversion efficiencies close to 16 percent at AM0 were obtained on 2 x 2 cm cells. Measurements and computer analyses on the n(+)/p/p(+) shallow homojunction cells indicate that such cell configuration should be very resistant to 1 MeV electron irradiation.

  7. Monolithic Series-Interconnected GaInAsSb/AlGaAsSb Thermophotovoltaic Devices Wafer Bonded to GaAs

    NASA Astrophysics Data System (ADS)

    Wang, C. A.; Huang, R. K.; Connors, M. K.; Shiau, D. A.; Murphy, P. G.; O'Brien, P. W.; Anderson, A. C.; Donetsky, D.; Anikeev, S.; Belenky, G.; Luryi, S.; Nichols, G.

    2004-11-01

    GaInAsSb/AlGaAsSb/GaSb epitaxial layers were wafer bonded to semi-insulating GaAs wafers for monolithic series interconnection of thermophotovoltaic (TPV) devices. SiOx/Ti/Au was used as a bonding layer to provide electrical isolation and to serve as an internal back-surface reflector (BSR). The minority-carrier lifetime in WB BSR structures is more than two times longer than that of control structures without a BSR. WB GaInAsSb/AlGaAsSb TPV cells were fabricated and monolithically interconnected in series. These cells exhibit nearly linear voltage building. At a short-circuit current density of 0.4 A/cm2, Voc of a single TPV cell is 0.2 V, compared to 0.37 and 1.8 V for 2- and 10-junction series-interconnected TPV cells, respectively.

  8. Two orders of magnitude reduction in the temperature dependent resistivity of Ga1-xMnxAs grown on (6 3 1) GaAs insulating substrates

    NASA Astrophysics Data System (ADS)

    Rangel-Kuopp, Victor-Tapio; Martinez-Velis, Isaac; Gallardo-Hernandez, Salvador; Lopez-Lopez, Maximo

    2013-12-01

    The temperature dependent van der Pauw (T-Pauw) technique was used to investigate the resistivity of three Ga1-xMnxAs layers grown on (6 3 1) GaAs semi-insulating substrates. The samples had Mn concentration of 3.52×l020 cm-3, 5.05×1020 cm-3 and 1.12×l021 cm-3, corresponding to Mn cell effusion temperature TMn of 700 °C, 715 °C and 745 °C, respectively. They were compared to samples grown under the same conditions but on (0 0 1) GaAs semi-insulating substrates. For the sample grown at TMn=700 °C on a (6 3 1) substrate, a two orders of magnitude decrease in the resistivity is observed, when compared with the sample grown on a (0 0 1) substrate. For the sample grown at TMn=715 °C the decrease is approximately four times, while for the sample grown at TMn=745 °C the decrease is approximately forty times. We plotted the resistivities as a function of temperature in Arrhenius plots, where we extracted two activation energies, the smallest one between 6 and 11 meV, and the largest one between 25 and 183 meV. Both activation energies increased as TMn increased. These results are in agreement with SIMS analysis where we observed that manganese concentration in the (6 3 1) orientation growth is around two order of magnitude larger than in the samples grown in the (0 0 1) orientation substrate.

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

    PubMed

    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.

  10. Spectroscopic constants and potential energy curves of GaAs, GaAs +, and GaAs -

    NASA Astrophysics Data System (ADS)

    Balasubramanian, K.

    1990-02-01

    Twenty electronic states of GaAs, 12 electronic states of GaAs +, and 13 electronic states of GaAs - are investigated using relativistic ab initio complete active space MCSCF (CASSCF) followed by large-scale configuration interaction calculations which included up to 700 000 configurations. Potential energy curves and spectroscopic constants of all these states of three radicals are obtained. Spectroscopic constants of low-lying states of GaAs are in very good agreement with both experiment and all-electron results. Two nearly-degenerate states of 2Σ +, 2Π ( 2Σ + lower) symmetries are found as candidates for the ground state of GaAs -. The GaAs - negative ion is found to be more stable compared to the neutral GaAs ( De(GaAs -) = 3 eV). The electron affinity of GaAs is computed as 0.89 and 1.3 eV at the FOCI and SOCI levels of theory, respectively. Calculated potential energy curves of GaAs are in accord with the experimentally observed predissociation in the 3Π( III) - X3Σ- system.

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

    NASA Astrophysics Data System (ADS)

    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. Gamma-Ray Response of Semi-Insulating CdMnTe Crystals

    SciTech Connect

    Kim, K.H.; Cho, S.H.; Suh, J.H.; Hong, J.; Kim, S.U.

    2009-06-10

    Semi-insulating Cd{sub 0.9}Mn{sub 0.1}Te:In crystals are grown by vertical Bridgman method. The segregation coefficient of Mn in CdTe is nearly 1 so that all the CdMnTe samples obtained from one ingot have nearly a same Mn composition. Also sulfur-based passivation effectively prevent the formation of Te-oxide but large amount of Mn exist as a MnO on the CdMnTe surface. The resistivity of CdMnTe samples are low 10{sup 10} Omegacm and well resolved {sup 241}Am gamma peaks are seen for all detectors. The difference in spectral response can be attributed to the effect of excess Te and conductivity change due to over-compensation induced by indium segregation in CdMnTe. The mobility-lifetime products evaluated from the dependence of peak location on the bias voltage are 1 times 10{sup -3} cm{sup 2}/V. The higher mobility-lifetime products in our CdMnTe crystals than other previous reports are assumed due to minimization of impurity contents in MnTe by several zone refining process.

  13. Compensation mechanism in high purity semi-insulating 4H-SiC

    NASA Astrophysics Data System (ADS)

    Mitchel, W. C.; Mitchell, William D.; Smith, H. E.; Landis, G.; Smith, S. R.; Glaser, E. R.

    2007-03-01

    A study of deep levels in high purity semi-insulating 4H-SiC has been made using temperature dependent Hall effect (TDH), thermal and optical admittance spectroscopies, and secondary ion mass spectrometry (SIMS). Thermal activation energies from TDH varied from a low of 0.55eV to a high of 1.65eV. All samples studied showed n-type conduction with the Fermi level in the upper half of the band gap. Fits of the TDH data to different charge balance equations and comparison of the fitting results with SIMS measurements indicated that the deep levels are acceptorlike even though they are in the upper half of the band gap. Carrier concentration measurements indicated that the deep levels are present in concentrations in the low 1015cm-3 range, while SIMS results demonstrate nitrogen and boron concentrations in the low to mid-1015-cm-3 range. The results suggest that compensation in this material is a complex process involving multiple deep levels.

  14. Final report on LDRD project 105967 : exploring the increase in GaAs photodiode responsivity with increased neutron fluence.

    SciTech Connect

    Blansett, Ethan L.; Geib, Kent Martin; Cich, Michael Joseph; Wrobel, Theodore Frank; Peake, Gregory Merwin; Fleming, Robert M.; Serkland, Darwin Keith; Wrobel, Diana L.

    2008-01-01

    A previous LDRD studying radiation hardened optoelectronic components for space-based applications led to the result that increased neutron irradiation from a fast-burst reactor caused increased responsivity in GaAs photodiodes up to a total fluence of 4.4 x 10{sup 13} neutrons/cm{sup 2} (1 MeV Eq., Si). The silicon photodiodes experienced significant degradation. Scientific literature shows that neutrons can both cause defects as well as potentially remove defects in an annealing-like process in GaAs. Though there has been some modeling that suggests how fabrication and radiation-induced defects can migrate to surfaces and interfaces in GaAs and lead to an ordering effect, it is important to consider how these processes affect the performance of devices, such as the basic GaAs p-i-n photodiode. In this LDRD, we manufactured GaAs photodiodes at the MESA facility, irradiated them with electrons and neutrons at the White Sands Missile Range Linac and Fast Burst Reactor, and performed measurements to show the effect of irradiation on dark current, responsivity and high-speed bandwidth.

  15. GaAs MMIC phase shifters

    NASA Astrophysics Data System (ADS)

    Lane, A. A.; Myers, F. A.

    This paper describes the design and performance of various GaAs MMIC phase shifters specifically designed for electronically scanned antennas. Phase shifting is achieved by using GaAs FETs to switch various circuits to realize the required functions. Some preliminary results on novel components and high packing density techniques leading to truly effective multifunction circuits are described.

  16. GaAs solar cell development

    NASA Technical Reports Server (NTRS)

    Knechtli, R. C.; Kamath, S.; Loo, R.

    1977-01-01

    The motivation for developing GaAs solar cells is based on their superior efficiency when compared to silicon cells, their lower degradation with increasing temperature, and the expectation for better resistance to space radiation damage. The AMO efficiency of GaAs solar cells was calculated. A key consideration in the HRL technology is the production of GaAs cells of large area (greater than 4 sg cm) at a reasonable cost without sacrificing efficiency. An essential requirement for the successful fabrication of such cells is the ability to grow epitaxially a uniform layer of high quality GaAs (buffer layer) on state-of-the-art GaAs substrates, and to grow on this buffer layer the required than layer of (AlGa)As. A modified infinite melt liquid phase epitaxy (LPE) growth technique is detailed.

  17. Carrier and defect dynamics in photoexcited semi-insulating epitaxial GaN layers

    NASA Astrophysics Data System (ADS)

    Gaubas, E.; Juršėnas, S.; Miasojedovas, S.; Vaitkus, J.; Žukauskas, A.

    2004-10-01

    Transients of fast free-carrier recombination and of multitrapping processes, determined by different types of defects, have been traced by photoluminescence (PL) and contact photoconductivity (CPC) in semi-insulating GaN epitaxial layers. To eliminate effects caused by the electrodes, the CPC decays were supplemented with noninvasive microwave absorption transients. The lifetimes of fast recombination and initial free-carrier capture processes were evaluated using ultraviolet (UV) time-resolved photoluminescence transients. The UV PL band peaked at 3.42 eV with contributions from both stimulated and spontaneous emission was attributed to band-to-band recombination. At the highest excitations, the initial PL decay time exhibited a value of 880 ps due to nonradiative free-carrier recombination. The radiative centers were revealed in continuous-wave PL spectra, where the UV band was accompanied with the bands of blue (B) PL, peaked in the range of 2.82-3.10 eV, and yellow (Y) PL, peaked at 2.19 eV, ascribed to dislocations and bulk donor-acceptor recombination, respectively. The time scale of the relaxation rate exhibited a crossover from picoseconds for stimulated emission to hundreds of nanoseconds for multitrapping. In the asymptotic part, a stretched-exponent decay on the millisecond scale was observed with the disorder factor of α =0.7. The asymptotic decay is explained by competition of centers of nonradiative recombination within bulk of the material and trapping attributed to the dislocations. Behavior of the dislocation-attributed capture centers was simulated using a model of capture cross section, which depends on the excess carrier concentration via screening.

  18. GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Conway, E. J.

    1982-01-01

    The major thrusts proposed for GaAs were increased efficiency and improved radiation damage data. Current laboratory production cells consistently achieve 16 percent AMO one-Sun efficiency. The user community wants 18-percent efficient cells as soon as possible, and such a goal is though to be achievable in 2 years with sufficient research funds. A 20-percent research cell is considered the efficiency limit with current technology, and such a cell seems realizable in approximately 4 years. Future efficiency improvements await improved substrates and materials. For still higher efficiencies, concentrator cells and multijunction cells are proposed as near-term directions.

  19. The investigation of custom grown vertical zone melt semi-insulating bulk gallium arsenide as a radiation spectrometer

    SciTech Connect

    McGregor, D.S.; Antolak, A.J.; Chui, H.C.

    1996-06-01

    Vertical zone melt (VZM) bulk GaAs boules have been zone refined (ZR) and zone leveled (ZL) to reduce EL2 deep donor levels and impurity concentrations with the intent of improving properties for gamma ray detectors. Zr and Zl GaAs boules had background impurity levels and deep donor EL2 concentrations near or below detectable limits. The crystal mosaic of the material at locations near the seed end was slightly superior to commercial liquid encapsulated Czochralski (LEC) material, and nearly equivalent to commercial vertical gradient freeze (VGF) material. The crystal mosaic in ZL material degraded towards the tail end. The homogeneity of the electrical properties for the ZL and ZR VZM material was inferior compared to commercially available bulk GaAs material. Post growth annealing may help to homogenize some electrical properties of the material. The charge collection efficiency of the ZR GaAs detectors was only 30% maximum, and only 25% maximum for the ZL GaAs detectors. Resulting gamma ray spectra was poor from detectors fabricated with the ZL or ZR VZM material. Detectors fabricated from material that was both ZR and ZL did not demonstrate gamma ray resolution, and operated mainly as counters. The poor spectroscopic performance is presently attributed to the inhomogeneity of the electrical properties of the ZR and ZL GaAs materials. Comparisons are made with detectors fabricated from VGF SI bulk GaAs.

  20. The remote electron beam-induced current analysis of grain boundaries in semiconducting and semi-insulating materials.

    PubMed

    Holt, D B

    2000-01-01

    When no charge collecting p-n junction or Schottky barrier is present in the specimen, but two contacts are applied, conductive mode scanning electron microscope (SEM) observations known as remote electron beam-induced current (REBIC) can be made. It was described as "remote" EBIC because the contacts to the specimen can lie at macroscopic distances from the beam impact point. In recent years, REBIC has been found to be useful not only for studies of grain boundaries in semiconducting silicon and germanium, but also in semi-insulating materials such as the wider bandgap II-VI compounds and electroceramic materials like varistor ZnO and positive temperature coefficient resistor (PTCR) BaTiO3. The principles of this method are outlined. Accounts are given of the five forms of charge collection and resistive contrast that appear at grain boundaries (GBs) in REBIC micrographs. These are (1) terraced contrast due to high resistivity boundary layers, (2) peak and trough (PAT) contrast due to charge on the boundary, (3) reversible contrast seen only under external voltage bias due to the beta-conductive effect in a low conductivity boundary layer, (4) dark contrast due to enhanced recombination, and (5) bright contrast apparently due to reduced recombination. For comparison, the results of the extensive EBIC studies of GBs in Si and Ge are first outlined and then the results of recent REBIC grain boundary studies in both semiconducting and semi-insulating materials are reviewed.

  1. Some optical and electron microscope comparative studies of excimer laser-assisted and nonassisted molecular-beam epitaxically grown thin GaAs films on Si

    NASA Technical Reports Server (NTRS)

    Lao, Pudong; Tang, Wade C.; Rajkumar, K. C.; Guha, S.; Madhukar, A.; Liu, J. K.; Grunthaner, F. J.

    1990-01-01

    The quality of GaAs thin films grown via MBE under pulsed excimer laser irradiation on Si substrates is examined in both laser-irradiated and nonirradiated areas using Raman scattering, Rayleigh scattering, and by photoluminescence (PL), as a function of temperature, and by TEM. The temperature dependence of the PL and Raman peak positions indicates the presence of compressive stress in the thin GaAs films in both laser-irradiated and nonirradiated areas. This indicates incomplete homogeneous strain relaxation by dislocations at the growth temperature. The residual compressive strain at the growth temperature is large enough such that even with the introduction of tensile strain arising from the difference in thermal expansion coefficients of GaAs and Si, a compressive strain is still present at room temperature for these thin GaAs/Si films.

  2. Multiple Applications of GaAs semiconductors

    NASA Astrophysics Data System (ADS)

    Martel, Jenrené; Wonka, Willy

    2003-03-01

    The object of this discussion will be to explore the many facets of Gallium Arsenide(GaAs) semiconductors. The session will begin with a brief overview of the basic properties of semiconductors in general(band gap, doping, charge mobility etc.). It will then follow with a closer look at the properties of GaAs and how these properties could potentially translate into some very exciting applications. Furthermore, current applications of GaAs semiconductors will be dicussed and analyzed. Finally, physical limits and advantages/disadvantages of GaAs will be considered.

  3. Cooperative transition of electronic states of antisite As defects in Be-doped low-temperature-grown GaAs layers

    NASA Astrophysics Data System (ADS)

    Ambri Mohamed, Mohd; Tien Lam, Pham; Bae, K. W.; Otsuka, N.

    2011-12-01

    Magnetic properties resulting from localized spins associated with antisite arsenic ions AsGa+ in Be-doped low-temperature-grown GaAs (LT-GaAs) layers were studied by measuring the magnetization of lift-off samples. With fast cooling, the magnetization of samples at 1.8 K becomes significantly lower than that expected from Curie-type paramagnetism in the range of the applied field to 7 T, and a transition from low magnetization to the magnetization of paramagnetism occurs upon the heating of samples to 4.5 K. With slow cooling, on the other hand, samples have a paramagnetic temperature dependence throughout the measurement-temperature range. The magnetization was found to decrease monotonically when a sample was kept at a fixed low temperature. These observations are explained by the cooperative transition of electron states of AsGa defects, which is closely related to the normal-metastable state transition of EL2 defects in semi-insulating GaAs. The results of the magnetization measurements in the present study suggest that AsGa+ ions are spontaneously displaced at low temperature without photoexcitation in Be-doped LT-GaAs. The similarity of the transition observed in this system to the normal-metastable state transition of the EL2 defect was also suggested by first-principle calculations of the electron state of an AsGa defect with a doped Be atom.

  4. Subnanosecond, high voltage photoconductive switching in GaAs

    SciTech Connect

    Druce, R.L.; Pocha, M.D.; Griffin, K.L. ); O'Bannon, B.J. )

    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.

  5. Pulse transformer for GaAs laser

    NASA Technical Reports Server (NTRS)

    Rutz, E. M.

    1976-01-01

    High-radiance gallium arsenide (GaAs) laser operating at room temperature is utilized in optical navigation system. For efficient transformer-to-laser impedance match, laser should be connected directly to pulse transformer secondary winding.

  6. Ohmic contact to GaAs semiconductor

    NASA Technical Reports Server (NTRS)

    Hovel, H. J.; Woodall, J. M.

    1980-01-01

    Multimetallic layers produce stable, low-resistance contacts for p-type GaAs and p-type GaAlAs devices. Contacts present no leakage problems, and their series resistance is too small to measure at 1 Sun intensity. Ohmic contacts are stable and should meet 20-year-life requirement at 150 C for GaAs combined photothermal/photovoltaic concentrators.

  7. GaAs homojunction solar cell development

    NASA Technical Reports Server (NTRS)

    Flood, D. J.; Swartz, C. K.; Hart, R. E., Jr.

    1980-01-01

    The Lincoln Laboratory n(+)/p/p(+) GaAs shallow homojunction cell structure was successfully demonstrated on 2 by 2 cm GaAs substrates. Air mass zero efficiencies of the seven cells produced to date range from 13.6 to 15.6 percent. Current voltage (I-V) characteristics, spectral response, and measurements were made on all seven cells. Preliminary analysis of 1 MeV electron radiation damage data indicate excellent radiation resistance for these cells.

  8. Insight into the epitaxial growth of high optical quality GaAs1-xBix

    NASA Astrophysics Data System (ADS)

    Beaton, D. A.; Mascarenhas, A.; Alberi, K.

    2015-12-01

    The ternary alloy GaAs1-xBix is a potentially important material for infrared light emitting devices, but its use has been limited by poor optical quality. We report on the synthesis of GaAs1-xBix epi-layers that exhibit narrow, band edge photoluminescence similar to other ternary GaAs based alloys, e.g., InyGa1-yAs. The measured spectral linewidths are as low as 14 meV and 37 meV at low temperature (6 K) and room temperature, respectively, and are less than half of previously reported values. The improved optical quality is attributed to the use of incident UV irradiation of the epitaxial surface and the presence of a partial surface coverage of bismuth in a surfactant layer during epitaxy. Comparisons of samples grown under illuminated and dark conditions provide insight into possible surface processes that may be altered by the incident UV light. The improved optical quality now opens up possibilities for the practical use of GaAs1-xBix in optoelectronic devices.

  9. Decomposition Mechanism of Triethyl-Arsenic on a GaAs Surface for Metalorganic Molecular-Beam Epitaxy: Role of Hydrogen Radicals

    NASA Astrophysics Data System (ADS)

    Suemune, Ikuo; Hamaoka, Kazuhiko; Koui, Tomoaki; Kishimoto, Akihiro; Yamanishi, Masamichi

    1991-09-01

    Growth of GaAs in metalorganic molecular-beam epitaxy using triethyl-arsenic (TEAs) becomes possible only when TEAs is thermally precracked or when hydrogen (H) plasma is irradiated simultaneously. In this paper, it will be shown that the bottleneck in the growth of GaAs with TEAs is the quick desorption of the As-intermediate species before its decomposition to supply As to a GaAs surface. The Ga-stabilized GaAs surface after the TEAs supply is proposed to be covered with stable C2H4 species based on reflection high-energy electron diffraction and quadrupole mass spectrometric measurements. H radicals are shown to be effective in the initial stages of the decomposition process of TEAs, but once the surface is covered stably with C2H4, even the H radicals cannot enhance their desorption.

  10. A I-V analysis of irradiated Gallium Arsenide solar cells

    NASA Technical Reports Server (NTRS)

    Heulenberg, A.; Maurer, R. H.; Kinnison, J. D.

    1991-01-01

    A computer program was used to analyze the illuminated I-V characteristics of four sets of gallium arsenide (GaAs) solar cells irradiated with 1-MeV electrons and 10-MeV protons. It was concluded that junction regions (J sub r) dominate nearly all GaAs cells tested, except for irradiated Mitsubishi cells, which appear to have a different doping profile. Irradiation maintains or increases the dominance by J sub r. Proton irradiation increases J sub r more than does electron irradiation. The U.S. cells were optimized for beginning of life (BOL) and the Japanese for end of life (EOL). I-V analysis indicates ways of improving both the BOL and EOL performance of GaAs solar cells.

  11. A I-V analysis of irradiated Gallium Arsenide solar cells

    NASA Astrophysics Data System (ADS)

    Heulenberg, A.; Maurer, R. H.; Kinnison, J. D.

    1991-08-01

    A computer program was used to analyze the illuminated I-V characteristics of four sets of gallium arsenide (GaAs) solar cells irradiated with 1-MeV electrons and 10-MeV protons. It was concluded that junction regions (J sub r) dominate nearly all GaAs cells tested, except for irradiated Mitsubishi cells, which appear to have a different doping profile. Irradiation maintains or increases the dominance by J sub r. Proton irradiation increases J sub r more than does electron irradiation. The U.S. cells were optimized for beginning of life (BOL) and the Japanese for end of life (EOL). I-V analysis indicates ways of improving both the BOL and EOL performance of GaAs solar cells.

  12. Deep-defect-induced quenching effects in semi-insulating GaN layers detected by photoelectrical spectroscopic techniques

    NASA Astrophysics Data System (ADS)

    Witte, H.; Krtschil, A.; Lisker, M.; Schrenk, E.; Christen, J.; Krost, A.; Kuhn, B.; Scholz, F.

    2003-06-01

    Quenching effects induced by additional below-bandgap illumination in undoped semi-insulating GaN were investigated using optical admittance spectroscopy (OAS) and photocurrent (PC) spectroscopy as well as optically excited, thermally stimulated currents (TSC). In OAS and PC, a decrease of defect-related signals due to the quenching light was observed. The thermal quenching of the defect band between 2.7 and 3.3 eV shows a good agreement with thermal emissions as measured by TSC, indicating the same defects cause the optical transitions in OAS/PC and the thermal transitions in TSC. The thermal emission in the temperature region between 250 and 300 K, which is responsible for the thermal quenching of the blue band (BB) in OAS, also shows an optical quenching under below-bandgap excitation.

  13. Terahertz emission enhancement in semi-insulating gallium arsenide integrated with subwavelength one-dimensional metal line array.

    PubMed

    Faustino, Maria Angela B; Lopez, Lorenzo P; Pauline Afalla, Jessica; Muldera, Joselito; Hermosa, Nathaniel; Salvador, Arnel A; Somintac, Armando S; Estacio, Elmer S

    2016-10-01

    A one-order-of-magnitude terahertz (THz) emission enhancement in the transmission geometry, over a 0.7-THz broadband range, was observed in semi-insulating gallium arsenide (SI-GaAs) integrated with a subwavelength one-dimensional metal line array (1DMLA). THz emission of the 1DMLA samples showed an intensity increase and exhibited a full-width-at-half-maximum broadening relative to the emission of the bare substrate. Improved index matching could not account for the observed phenomenon. A nonlinear dependence of the integrated THz emission intensity on the number of illuminated lines and on the pump power was observed. The actual origin of the increased THz emission is still under investigation. At present, it is attributed to extraordinary optical transmission.

  14. Growth of Ru doped semi-insulating InP by low pressure metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Dadgar, A.; Stenzel, O.; Köhne, L.; Näser, A.; Straßburg, M.; Stolz, W.; Bimberg, D.; Schumann, H.

    1998-12-01

    Ruthenium doping has been successfully applied for the growth of semi-insulating (s.i.) InP. In contrast to the 3d-transition metal (TM) Fe, the isovalent 4d-TM Ru exhibits a four orders of magnitude lower diffusion coefficient and shows no interdiffusion with p-type dopants. Most important, Ru compensates electrons as well as holes, a prerequisite for complete compensation under double injection conditions. The growth of Ru doped InP layers has been investigated using bis( η5-2,4-dimethylpentadienyl)ruthenium(II) for Ru doping, different P-precursors (PH 3, TBP, DTBP) and H 2 or N 2 carrier gas.

  15. 4H-SiC Schottky barrier diodes with semi-insulating polycrystalline silicon field plate termination

    NASA Astrophysics Data System (ADS)

    Yuan, Hao; Tang, Xiao-Yan; Zhang, Yi-Men; Zhang, Yu-Ming; Song, Qing-Wen; Yang, Fei; Wu, Hao

    2014-05-01

    Based on the theoretical analysis of the 4H-SiC Schottky-barrier diodes (SBDs) with field plate termination, 4H-SiC SBD with semi-insulating polycrystalline silicon (SIPOS) FP termination has been fabricated. The relative dielectric constant of the SIPOS dielectric first used in 4H-SiC devices is 10.4, which is much higher than that of the SiO2 dielectric, leading to benefitting the performance of devices. The breakdown voltage of the fabricated SBD could reach 1200 V at leakage current 20 μA, about 70% of the theoretical breakdown voltage. Meanwhile, both of the simulation and experimental results show that the length of the SIPOS FP termination is an important factor for structure design.

  16. The electrical properties of 60 keV zinc ions implanted into semi-insulating gallium arsenide

    NASA Technical Reports Server (NTRS)

    Littlejohn, M. A.; Anikara, R.

    1972-01-01

    The electrical behavior of zinc ions implanted into chromium-doped semiinsulating gallium arsenide was investigated by measurements of the sheet resistivity and Hall effect. Room temperature implantations were performed using fluence values from 10 to the 12th to 10 to the 15th power/sq cm at 60 keV. The samples were annealed for 30 minutes in a nitrogen atmosphere up to 800 C in steps of 200 C and the effect of this annealing on the Hall effect and sheet resistivity was studied at room temperature using the Van der Pauw technique. The temperature dependence of sheet resistivity and mobility was measured from liquid nitrogen temperature to room temperature. Finally, a measurement of the implanted profile was obtained using a layer removal technique combined with the Hall effect and sheet resistivity measurements.

  17. Characterization Of Thermal Annealing Of Implanted GaAs Using Raman Scattering

    NASA Astrophysics Data System (ADS)

    Yaney, Perry P.; Baird, William E., Jr.; Park, Y. S.

    1981-04-01

    Raman spectra were recorded in backscattering from (100) oriented, Cr-doped, semi-insulating crystalline wafers of GaAs to characterize the changes introduced by implan-tation and by encapsulation and thermal anneal15ing. The studies were carried out at 300 and 100K. Implant fluences of lx1012 to 1x1015 S-ions/cm2 at 120 keV were used. Annealing temperatures ranged from 750 to 950°C for 15 minutes. The encapsulation was by means of rf-plasma-deposited Si3N4 films. The characteristics of a fixed annealing pro-cedure as a function of fluence and a fixed fluence at different annealing temperatures were determined. Unprocessed samples and a laser-annealed sample were studied. A pulsed, doubled YAG laser at 532 nm was used with about 16 mW of incident power in a 0.12-mm-diameter spot. A "triple" spectrometer, gated photon counting and computer pro-cessing of data were used. Following are the results: (1) the intensity of the LO pho-non line strongly varied with both implant dosage and annealing including a five-fold enhancement at 1012 S-ions/cm2 fluence, (2) the LO mode "softened" apparently due to implant-induced bond weakening, (3) polycrystalline and amorphous conditions of the implanted layer were identified, (4) thermal annealing itself was found to introduce disorder in the surface, at least for temperatures above 850°C, and (5) removal of amor-phous regions by laser annealing was observed.

  18. GaAs thin film epitaxy and x-ray detector development

    NASA Astrophysics Data System (ADS)

    Wynne, Dawnelle I.; Cardozo, B.; Haller, Eugene E.

    1999-10-01

    We report on the growth of high purity n-GaAs using Liquid Phase Epitaxy and on the fabrication of Schottky barrier diodes for use as x-ray detectors using these layers. Our epilayers are grown form an ultra-pure Ga solvent in a graphite boat in a hydrogen atmosphere. Growth is started at a temperature of approximately 800 degrees C; the temperature is ramped down at 2 degrees C/min. to room temperature. Our best epilayers show a net-residual-donor concentration of approximately 2 X 1012 cm-3, measured by Hall effect. Electron mobilities as high as 150,000 cm2 V-1 s-1 at 77K have been obtained. The residual donors have been analyzed by far IR photothermal ionization spectroscopy and found to be sulfur and silicon. Up to approximately 200 micrometers of epitaxial GaAs have been deposited using several sequential growth runs on semi-insulating and n+-doped substrates. Schottky barrier diodes have been fabricated using this epitaxial material and have been electrically characterized by current-voltage and capacitance-voltage measurements. The Schottky barriers are formed by electron beam evaporation of Pt films. The ohmic contacts are made by electron beam evaporated and alloyed Ni-Ge-Au films on the backside of the substrate. Several of our diodes exhibit dark currents of the order of 0.3-3.3 nA/mm2 at reverse biases depleting approximately 50 micrometers of the epilayer. Electrical characteristics and preliminary performance results of our Schottky diodes using 109Cd and 241Am gamma and x- ray radiation will be discussed.

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

    NASA Astrophysics Data System (ADS)

    Ranjan, Kirti; Bhardwaj, Ashutosh; Namrata; Chatterji, Sudeep; Srivastava, Ajay K.; Shivpuri, R. K.

    2002-12-01

    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 depth, metal-overhang width, device depth, substrate resistivity and fixed oxide charge on the junction breakdown voltage of these structures is extensively studied. The results presented in this work clearly demonstrate the superiority of the metal-overhang structure design employing semi-insulator passivated structures over dielectric passivated ones in realising a given breakdown voltage. The effect of bulk damage caused by hadron environment in the passivated Si detectors is simulated, to a first order approximation, by varying effective carrier concentration (calculated using Hamburg Model) and minority carrier lifetime. This approach allows getting an insight of the device behaviour after radiation damage by evaluating the electric field distribution, and thus proves helpful in predicting some interesting results.

  20. Surface characterization of excimer laser induced deposition of W on GaAs from WF 6 and H 2

    NASA Astrophysics Data System (ADS)

    Tabbal, Malek; Izquierdo, Ricardo; Meunier, Michel; Pépin, Corinne; Yelon, Arthur

    1997-04-01

    Deposition of W thin films has been induced by a KrF excimer laser incident perpendicularly on a GaAs substrate placed in an ambient containing WF 6, H 2 and Ar. In-situ X-Ray Photoelectron Spectroscopy (XPS) shows evidence of a surface interaction between WF 6 and GaAs under laser irradiation. At 50 mJ/cm 2, fluorinated W species adsorbed on the GaAs substrate are partially dissociated by the laser beam, leading to a loss in stoichiometry and the formation of GaF 3 on the surface. The generation of stable, non-volatile, GaF 3 has been identified as a possible obstacle to the nucleation of metallic tungsten films on GaAs in CVD processes using WF 6. At 67 mJ/cm 2, the gas-substrate interaction is further enhanced, but the dissociation of WF 6 into metallic W is achieved. However, at such laser energy densities, the substrate appears to be damaged. By using H 2 as a reducing gas for WF 6, 0.2 μm thick W deposits were obtained but the process was difficult to reproduce. Two competing phenomena, the fluorination of the GaAs surface and the nucleation of the metallic W films taking place simultaneously explain the difficulty in controlling the process. The Auger profiles show limited, but noticeable, As incorporation in the films resulting from the interaction between WF 6 and GaAs under laser irradiation.

  1. Radiation resistance of Ge, Ge0.93Si0.07, GaAs and Al0.08Ga0.92 as solar cells

    NASA Technical Reports Server (NTRS)

    Timmons, M. L.; Venkatasubramanian, R.; Iles, P. A.; Chu, C. L.

    1991-01-01

    Solar cells made of Ge, Ge(0.93)Si(0.07) alloys, GaAs and Al(0.08)Ga(0.92)As were irradiated in two experiments with 1-meV electrons at fluences as great as 1 x 10(exp 16) cm(exp-2). Several general trends have emerged. Low-band-gap Ge and Ge(0.93)Si(0.07) cells show substantial resistance to radiation-induced damage. The two experiments showed that degradation is less for Al(0.08)Ga(0.92)As cells than for similarly irradiated GaAs cells. Compared to homojunctions, cells with graded-band-gap emitters did not show the additional resistance to damage in the second experiment that had been seen in the first. The thickness of the emitter is a key parameter to limit the degradation in GaAs devices.

  2. Periodic surface structure bifurcation induced by ultrafast laser generated point defect diffusion in GaAs

    SciTech Connect

    Abere, Michael J.; Yalisove, Steven M.; Torralva, Ben

    2016-04-11

    The formation of high spatial frequency laser induced periodic surface structures (HSFL) with period <0.3 λ in GaAs after irradiation with femtosecond laser pulses in air is studied. We have identified a point defect generation mechanism that operates in a specific range of fluences in semiconductors between the band-gap closure and ultrafast-melt thresholds that produces vacancy/interstitial pairs. Stress relaxation, via diffusing defects, forms the 350–400 nm tall and ∼90 nm wide structures through a bifurcation process of lower spatial frequency surface structures. The resulting HSFL are predominately epitaxial single crystals and retain the original GaAs stoichiometry.

  3. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1979-01-01

    The optimization of space processing of GaAs is described. The detailed compositional, structural, and electronic characterization of GaAs on a macro- and microscale and the relationships between growth parameters and the properties of GaAs are among the factors discussed. The key parameters limiting device performance are assessed.

  4. Electron and proton radiation effects on GaAs and CuInSe2 thin film solar cells

    NASA Astrophysics Data System (ADS)

    Burgess, R. M.; Chen, W. S.; Devaney, W. E.; Doyle, D. H.; Kim, N. P.

    The effects of proton and electron radiation on the performances of GaAs and CuInSe2/CdZnS (CIS) thin-film solar cells are evaluated. Bare cells (i.e., with no coverglass) were exposed to several energies of electron and proton radiation, and their performances were monitored by illuminated I-V curves, dark I-V curves, and spectral response measurements at different fluence levels. These experiments reconfirm that no measurable damage occurs to CIS solar cells when exposed to 1 and 2 MeV electrons to a total fluence of 5.0 x 10 to the 15th/sq cm. For proton irradiations, the results indicate that CIS cells are more radiation resistant than GaAs cells, by a factor of ten, when compared at the same energy levels. Comparison of the electron and proton irradiation results to those reported in the literature shows that the thin-film GaAs solar cells are as radiation resistant as other GaAs bulk cells at 1.0 MeV protons and are more radiation resistant at both the 1.0-MeV electron and 200-keV proton energies.

  5. GaAs solar cell test facility

    NASA Astrophysics Data System (ADS)

    Kawashima, M.; Hosoda, Y.; Suzawa, C.; Shimada, T.; Motoyoshi, K.; Sasatani, Y.

    1982-01-01

    A hybrid type (electricity and heat) GaAs solar cell test facility has been made to evaluate total characteristics of GaAs cell and to study the energy conversion system. The size of a solar collector is 3.4 m x 2.1 m and 60 GaAs cells with Fresnel lenses are attached on it. The solar collector is controlled by a microcomputer to track the sun. Electric energy produced by the cells is stored in a lead-acid battery and then supplied to the load through a DC-AC inverter. The microcomputer also controls the data acquisition in parallel with tracking. This paper presents an overview of the facility and the experimental results of power generation obtained to date.

  6. Photoluminescence of Mn+ doped GaAs

    NASA Astrophysics Data System (ADS)

    Zhou, Huiying; Qu, Shengchun; Liao, Shuzhi; Zhang, Fasheng; Liu, Junpeng; Wang, Zhanguo

    2010-10-01

    Photoluminescence is one of the most useful techniques to obtain information about optoelectronic properties and defect structures of materials. In this work, the room-temperature and low temperature photoluminescence of Mn-doped GaAs were investigated, respectively. Mn-doped GaAs structure materials were prepared by Mn+ ion implantation at room temperature into GaAs. The implanted samples were subsequently annealed at various temperatures under N2 atmosphere to recrystallize the samples and remove implant damage. A strong peak was found for the sample annealed at 950 °C for 5 s. Transitions near 0.989 eV (1254 nm), 1.155 eV (1074 nm) and 1.329 eV (933 nm) were identified and formation of these emissions was analyzed for all prepared samples. This structure material could have myriad applications, including information storage, magnet-optical properties and energy level engineering.

  7. Carbon doping of GaAs NWs

    NASA Astrophysics Data System (ADS)

    Salehzadeh Einabad, Omid

    Nanowires (NWs) have been proposed and demonstrated as the building blocks for nanoscale electronic and photonic devices such as NW field effect transistors and NW solar cells which rely on doping and trap-free carrier transport. Controlled doping of NWs and a high degree of structure and morphology control are required for device applications. However, doping of III-V nanowires such as GaAs nanowires has not been reported extensively in the literature. Carbon is a well known p-type dopant in planar GaAs due to its low diffusivity and high solubility in bulk GaAs; however its use as an intentional dopant in NW growth has not yet been investigated. In this work we studied the carbon doping of GaAs nanowires using CBr4 as the dopant source. Gold nanoparticles (NP) at the tip ofthe NWs have been used to drive the NW growth. We show that carbon doping suppresses the migration ofthe gold NPs from the tip of the NWs. In addition, we show that the carbon doping of GaAs NWs is accompanied by an increase of the axial growth rate and decrease of the lateral growth rate ofthe NWs. Carbon-doped GaAs NWs, unlike the undoped ones which are highly tapered, are rod-like. The origin of the observed morphological changes is attributed to the carbon adsorbates on the sidewalls ofthe nanowires which suppress the lateral growth of the nanowires and increase the diffusion length of the gallium adatoms on the sidewalls. Stacking fault formation consisting of alternating regIOns of zincblende and wurtzite structures has been commonly observed in NWs grown along the (111) direction. In this work, based on transmission electron microscopy (TEM) analysis, we show that carbon doping ofGaAs NWs eliminates the stacking fault formation. Raman spectroscopy was used to investigate the effects of carbon doping on the vibrational properties of the carbon-doped GaAs nanowires. Carbon doping shows a strong impact on the intrinsic longitudinal and transverse optical (La and TO) modes of the GaAs

  8. GaAs photoconductive semiconductor switch

    DOEpatents

    Loubriel, G.M.; Baca, A.G.; Zutavern, F.J.

    1998-09-08

    A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device is disclosed. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices. 5 figs.

  9. GaAs photoconductive semiconductor switch

    DOEpatents

    Loubriel, Guillermo M.; Baca, Albert G.; Zutavern, Fred J.

    1998-01-01

    A high gain, optically triggered, photoconductive semiconductor switch (PCSS) implemented in GaAs as a reverse-biased pin structure with a passivation layer above the intrinsic GaAs substrate in the gap between the two electrodes of the device. The reverse-biased configuration in combination with the addition of the passivation layer greatly reduces surface current leakage that has been a problem for prior PCSS devices and enables employment of the much less expensive and more reliable DC charging systems instead of the pulsed charging systems that needed to be used with prior PCSS devices.

  10. Fe-doped semi-insulating GaN with solid Fe source grown on (110) Si substrates by NH3 molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Noh, Young Kyun; Lee, Sang Tae; Kim, Moon Deock; Oh, Jae Eung

    2017-02-01

    Iron doped GaN layers were grown on (110) Si substrates by ammonia molecular beam epitaxy (MBE) using solid elemental iron as a source. Specular films with concentrations up to 1×1020 cm-3, as determined by secondary ion mass spectroscopy, were grown, unlike a limited incorporation of Fe into GaN by metal-rich rf plasma MBE. The Fe concentration in the film showed an exponential dependence on the inverse of source temperature with an activation energy of 3.4 eV, which agrees well to the reported value for the sublimation of Fe. A 1.5 μm thick GaN film with a sheet resistance of 1 GΩ/sq. was obtained by compensating unintentional residual donors with a small Fe concentration of 1×1017 cm-3. X-ray diffraction rocking curves indicated high crystalline quality, very similar to an undoped film, showing that the Fe incorporation required to obtain the semi-insulating film properties did not affect the structural properties of the film. The low-temperature PL spectra of highly resistive and semi-insulating Fe:GaN in the range of 1017 1018 cm-3 show dominant exciton emissions and enhanced donor-acceptor-pair (DAP) emissions, implying that Fe ions contribute to the DAP transition between donor levels and Fe-related acceptor levels, possibly compensating the residual donors to achieve the semi-insulating electrical properties.

  11. Ion Implanted GaAs I.C. Process Technology

    DTIC Science & Technology

    1981-07-01

    in ion implantation in GaAs, coupled with better control of the substrate material. 1 Once ion implantation became a reliable processing technology it... Processing Technology for Planar GaAs Integrated Circuits," GaAs IC Symposium, Lake Tahoe, CA., Sept. 1979. 20. R.C. Eden, "GaAs Integrated Circuit Device...1980. 25. B.M. Welch, "Advances in GaAs LSI!VLSI Processing Technology ," Sol. St. Tech., Feb. 1980, pp. 95-101. 27. R. Zucca, B.M. Welch, P.M

  12. Surface and coordination chemistry related to GaAs

    NASA Astrophysics Data System (ADS)

    Keys, Andrea

    The vapor phase structures of Al(tBU)3 and Ga(tBU)3 have been investigated by gas phase electron diffraction and consist of planar three-coordinate monomers. Salient structural parameters (ra) include: Al-C = 2.005(3) A, Ga-C = 2.034(2) A. The geometries are controlled by inter-ligand interactions. The electron diffraction structures are compared to those determined by ab initio calculations for M(tBU)3 (M = Al, Ga, In). To understand the most suitable linkages for the surface of GaAs, model compounds were synthesized by reacting Ga(tBU)3 and [tBu2Ga(mu-Cl]2 with one molar equivalent of varying ligands. The synthesized compounds include chlorides, benzenethiolate, dithiocarbamates, carboxylates, amides, benzohydroxamate, and phenylphosphonate. The Ga ⋯ Ga and Ga-ligand interatomic distances for these compounds, as well as Group 15 and 16 donor bridging ligands, are compared to the values for the surface of GaAs and cubic-GaS in order to determine their suitability as linkage groups for self-assembled monolayers. The most suitable linkages were determined to be benzenethiol and phenylphophonic acid, and these were used to grow self-assembled monolayers on {100} GaAs. Carboxylic acid was also used, to determine the success of the organometallic model compounds in predicting the suitability of ligands for surface reaction. Self-assembled monolayers were also grown on Al2O3, using carboxylic acids and phenylphosphonic acids as the surface linkages. Metallo-organic chemical vapor deposition was performed using single-source precursors ( tBU)2Ga(S2CNR2). The tert -butyl gallium bis-dialkyl-dithiocarbamate compounds, (tBu)Ga(S2CNR2)2, are formed as minor products via ligand disproportionation reactions. Gallium sulfide (GaS) thin films have been grown at 375-425°C by atmospheric pressure metal-organic chemical vapor deposition using compounds (tBu) 2Ga(S2CNMe2) and (tBu)2Ga(S 2CNEt2) as single source precursors. Polycrystalline samples of the chalcogenides InSe, In2Se3

  13. Characterization of LT GaAs carrier lifetime in multilayer GaAs epitaxial wafers by the transient reflectivity technique

    SciTech Connect

    McMorrow, D.; Melinger, J.S.; Campbell, A.B.; Knudson, A.R.; Buchner, S.; Ikossi-Anastasiou, K.; Moss, S.C.; Engelhardt, D.; Childs, T.

    1997-12-01

    A methodology for determining the carrier lifetime of LT GaAs buffer layers in GaAs multilayer wafers utilizing the femtosecond transient reflectivity technique is introduced. Experimental results and computer simulations performed as a function of the LT GaAs growth temperature are presented for the multilayer GaAs structures that are used for device fabrication. The markedly non-exponential nature of the measured transients is a consequence of the multilayer structure of the wafers. The carrier lifetime measurements are correlated with available SEU data measured for structures fabricated with LT GaAs buffers with different growth temperatures.

  14. Au impact on GaAs epitaxial growth on GaAs (111)B substrates in molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Liao, Zhi-Ming; Chen, Zhi-Gang; Lu, Zhen-Yu; Xu, Hong-Yi; Guo, Ya-Nan; Sun, Wen; Zhang, Zhi; Yang, Lei; Chen, Ping-Ping; Lu, Wei; Zou, Jin

    2013-02-01

    GaAs growth behaviour under the presence of Au nanoparticles on GaAs {111}B substrate is investigated using electron microscopy. It has been found that, during annealing, enhanced Ga surface diffusion towards Au nanoparticles leads to the GaAs epitaxial growth into {113}B faceted triangular pyramids under Au nanoparticles, governed by the thermodynamic growth, while during conventional GaAs growth, growth kinetics dominates, resulting in the flatted triangular pyramids at high temperature and the epitaxial nanowires growth at relatively low temperature. This study provides an insight of Au nanoparticle impact on GaAs growth, which is critical for understanding the formation mechanisms of semiconductor nanowires.

  15. GaAs Solar Cell Radiation Handbook

    NASA Technical Reports Server (NTRS)

    Anspaugh, B. E.

    1996-01-01

    History of GaAs solar cell development is provided. Photovoltaic equations are described along with instrumentation techniques for measuring solar cells. Radiation effects in solar cells, electrical performance, and spacecraft flight data for solar cells are discussed. The space radiation environment and solar array degradation calculations are addressed.

  16. Image transfer in photorefractive GaAs

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Gheen, Gregory; Rau, Mann-Fu; Wang, Faa-Ching

    1987-01-01

    Image transfer from one beam to the other using counterpropagation beam coupling in GaAs was demonstrated. Good image quality was achieved. The results also reveal that local birefringence due to the residual stress/strain field in the crystal can degrade the image quality.

  17. GaAs optoelectronic neuron arrays

    NASA Technical Reports Server (NTRS)

    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.

  18. Image transfer in photorefractive GaAs

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Gheen, Gregory; Rau, Mann-Fu; Wang, Faa-Ching

    1987-01-01

    Image transfer from one beam to the other using counterpropagation beam coupling in GaAs was demonstrated. Good image quality was achieved. The results also reveal that local birefringence due to the residual stress/strain field in the crystal can degrade the image quality.

  19. Ion Implanted Gaas Integrated Optics Fabrication Technology

    NASA Astrophysics Data System (ADS)

    Mentzer, M. A.; Hunsperger, R. G.; Bartko, J.; Zavada, J. M.; Jenkinson, H. A.

    1985-01-01

    Ion implantation of semiconductor materials is a fabrication technique that offers a number of distinct advantages for the formation of guided-wave components and microelectronic devices. Implanted damage and dopants produce optical and electronic changes that can be utilized for sensing and signal processing applications. GaAs is a very attractive material for optical fabrication since it is transparent out to the far infrared. It can be used to fabricate optical waveguides, directional couplers, EO modulators, and detectors, as well as other guided wave structures. The presence of free carriers in GaAs lowers the refractive index from that of the pure semiconductor material. This depression of the refractive index is primarily due to the negative contribution of the free carrier plasma to the dielectric constant of the semiconductor. Bombardment of n-type GaAs by protons creates damage sites near the surface of the crystal structure where free carriers are trapped. This "free carrier compensated" region in the GaAs has a higher refractive index than the bulk region. If the compensated region is sufficiently thick and has a refractive index which is sufficiently larger than that of the bulk n-type region, an optical waveguide is formed. In this paper, a description of ion implantation techniques for the fabrication of both planar and channel integrated optical structures in GaAs is presented, and is related to the selection of ion species, implant energy and fluence, and to the physical processes involved. Lithographic technology and masking techniques are discussed for achieving a particular desired implant profile. Finally, the results of a set of ion implantation experiments are presented.

  20. Intrinsic radiation tolerance of ultra-thin GaAs solar cells

    NASA Astrophysics Data System (ADS)

    Hirst, L. C.; Yakes, M. K.; Warner, J. H.; Bennett, M. F.; Schmieder, K. J.; Walters, R. J.; Jenkins, P. P.

    2016-07-01

    Radiation tolerance is a critical performance criterion of photovoltaic devices for space power applications. In this paper we demonstrate the intrinsic radiation tolerance of an ultra-thin solar cell geometry. Device characteristics of GaAs solar cells with absorber layer thicknesses 80 nm and 800 nm were compared before and after 3 MeV proton irradiation. Both cells showed a similar degradation in Voc with increasing fluence; however, the 80 nm cell showed no degradation in Isc for fluences up to 1014 p+ cm-2. For the same exposure, the Isc of the 800 nm cell had severely degraded leaving a remaining factor of 0.26.

  1. Multiple-Scale Analysis of Charge Transport in Semiconductor Radiation Detectors: Application to Semi-Insulating CdZnTe

    NASA Astrophysics Data System (ADS)

    Bale, Derek S.; Szeles, Csaba

    2009-01-01

    The transport, trapping, and subsequent detrapping of charge in single crystals of semi-insulating cadmium zinc telluride (CdZnTe) has been analyzed using multiple-scale perturbation techniques. This method has the advantage of not only treating impulse charge generation typical in spectroscopic analysis, but also a large class of continuous generation sources more relevant to high-flux x-ray imaging applications. We first demonstrate that the multiple-scale solutions obtained for small-current transients induced by an impulse generation of charge are consistent with well-known exact solutions. Further, we use the multiple-scale solutions to derive an analytic generalization of the Hecht equation that incorporates detrapping over times much longer than the carrier transit time (i.e., delayed signal components). The method is then applied to a continuous charge generation source that approximates that of an x-ray source. The space-time solutions obtained are relevant to detector design in high-flux x-ray imaging applications. Throughout this work the multiple-scale solutions are compared with exact solutions as well as full numerical solutions of the fundamental charge conservation equations.

  2. Acoustic Wave Chemical Microsensors in GaAs

    SciTech Connect

    Albert G. Baca; Edwin J. Heller; Gregory C. Frye-Mason; John L. Reno; Richard Kottenstette; Stephen A. Casalnuovo; Susan L. Hietala; Vincent M. Hietala

    1998-09-20

    High sensitivity acoustic wave chemical microsensors are being developed on GaAs substrates. These devices take advantage of the piezoelectric properties of GaAs as well as its mature microelectronics fabrication technology and nascent micromachining technology. The design, fabrication, and response of GaAs SAW chemical microsensors are reported. Functional integrated GaAs SAW oscillators, suitable for chemical sensing, have been produced. The integrated oscillator requires 20 mA at 3 VK, operates at frequencies up to 500 MHz, and occupies approximately 2 mmz. Discrete GaAs sensor components, including IC amplifiers, SAW delay lines, and IC phase comparators have been fabricated and tested. A temperature compensation scheme has been developed that overcomes the large temperature dependence of GaAs acoustic wave devices. Packaging issues related to bonding miniature flow channels directly to the GaAs substrates have been resolved. Micromachining techniques for fabricating FPW and TSM microsensors on thin GaAs membranes are presented and GaAs FPW delay line performance is described. These devices have potentially higher sensitivity than existing GaAs and quartz SAW sensors.

  3. High-efficiency, radiation-resistant GaAs space cells

    NASA Technical Reports Server (NTRS)

    Bertness, K. A.; Ristow, M. Ladle; Grounner, M.; Kuryla, M. S.; Werthen, J. G.

    1991-01-01

    Although many GaAs solar cells are intended for space applicatons, few measurements of cell degradation after radiation are available, particularly for cells with efficiencies exceeding 20 percent (one-sun, AMO). Often the cell performance is optimized for the highest beginning-of-life (BOL) efficiency, despite the unknown effect of such design on end-of-life (EOL) efficiencies. The results of a study of the radiation effects on p-n GaAs cells are presented. The EOL efficiency of GaAs space cell can be increased by adjusting materials growth parameters, resulting in a demonstration of 16 percent EOL efficiency at one-sun, AMO. Reducing base doping levels to below 3 x 10(exp 17)/cu m and decreasing emitter thickness to 0.3 to 0.5 micron for p-n cells led to significant improvements in radiation hardness as measured by EOL/BOL efficiency ratios for irradiation of 10(exp -15)/sq cm electrons at 1 MeV. BOL efficiency was not affected by changes in emitter thickness but did improve with lower base doping.

  4. Space qualification of UV and IR reflecting coverslides for GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Meulenberg, Andrew

    1996-01-01

    As part of the space qualification effort for blue-red reflecting coverslides designed for use with GaAs solar cells, the first long-term (3000 hours) UV testing of unirradiated and 1 MeV electron-irradiated GaAs solar cells, with 4 types of multilayer-coated coverslides to reduce operating temperature, has produced some unexpected results. Important conclusions from this study, which includes two parallel tests, are as follows: (1) All of the GaAs solar cells with multilayer-coated coverslides display UV degradation. The laboratory data, extrapolated to 10 years in orbit, point to a significant loss mechanism from a combination of absorption and a reduction in optical match in such coatings from this portion of the space environment; (2) The effects of contamination in a vacuum system, on the measured degradation in solar-cell short-circuit current during a UV test, depend upon the type of coverslide coatings present on the coverslide surfaces. This has implications for both coated coverslides and optical solar reflectors (OSR's) in space; and (3) Because of the observed trends in this test and uncertainties in the extrapolation of data for multilayer coated coverslides, the use of any multilayer-coated coverslides for extended missions (greater than 1 year) cannot be recommended without prior flight testing.

  5. Space qualification of UV and IR reflecting coverslides for GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Meulenberg, Andrew

    1996-01-01

    As part of the space qualification effort for blue-red reflecting coverslides designed for use with GaAs solar cells, the first long-term (3000 hours) UV testing of unirradiated and 1 MeV electron-irradiated GaAs solar cells, with 4 types of multilayer-coated coverslides to reduce operating temperature, has produced some unexpected results. Important conclusions from this study, which includes two parallel tests, are as follows: (1) All of the GaAs solar cells with multilayer-coated coverslides display UV degradation. The laboratory data, extrapolated to 10 years in orbit, point to a significant loss mechanism from a combination of absorption and a reduction in optical match in such coatings from this portion of the space environment; (2) The effects of contamination in a vacuum system, on the measured degradation in solar-cell short-circuit current during a UV test, depend upon the type of coverslide coatings present on the coverslide surfaces. This has implications for both coated coverslides and optical solar reflectors (OSR's) in space; and (3) Because of the observed trends in this test and uncertainties in the extrapolation of data for multilayer coated coverslides, the use of any multilayer-coated coverslides for extended missions (greater than 1 year) cannot be recommended without prior flight testing.

  6. Ion beam mixing of GaAs with films of Al, Si, and their nitrides

    SciTech Connect

    Fastow, R.; Brener, R.; Kalish, R.; Eizenberg, M.

    1988-04-15

    Thin films of Al, AlN, Si, and Si/sub 3/N/sub 4/ deposited on GaAs substrates were irradiated with silicon ions. The amount of interfacial mixing was found to depend both on the composition of the thin film and on the ion dose. The greatest amount of mixing, as measured by Rutherford backscattering spectrometry and Auger depth profiling, occurred in the Al/GaAs system. Mixing in the Si/GaAs system showed a sublinear dose dependence as well as a deep diffusion of silicon into the substrate. Interfacial phase formation between the aluminum and silicon layers and the GaAs substrate was observed using Auger line shape analysis and low-energy electron loss spectroscopy. Small or negligible mixing was found in the AlN/GaAs and the Si/sub 3/N/sub 4//GaAs systems, presumably due to strong nitrogen bonding in these layers. The data suggest that an optimal cap for through-cap implantation and annealing is a two-layer structure consisting of a thin Si/sub 3/N/sub 4/ layer below a thick AlN layer.

  7. Comparison of nonlinear absorption and carrier recombination times in GaAs grown by hydride vapor phase epitaxy and Bridgman processes

    NASA Astrophysics Data System (ADS)

    Gonzalez, Leonel P.; Murray, Joel; Carpenter, Amelia; Upchurch, Derek; Barnes, Jacob O.; Schunemann, Peter G.; Zawilski, Kevin; Guha, Shekhar

    2010-02-01

    μA 760 μm thick GaAs crystal was grown using HVPE. Transmission spectrum of this sample showed minimal absorption for light having photon energy below the bandgap energy, indicating the absence of the EL2 defects commonly found in Bridgman grown samples. Irradiance dependent absorption measured at 1.535 μm using 100 ns duration laser pulses showed increased nonlinear absorption in the HVPE grown GaAs compared to Bridgman grown samples. The dominant nonlinear absorption process in both samples was absorption due to free carriers generated by two-photon absorption. The HVPE grown sample showed higher nonlinear absorption due to longer carrier lifetimes.

  8. Conference on Semi-Insulating III-V Materials (2nd), held 19-21 Apr 82, Evian (France),

    DTIC Science & Technology

    1983-02-28

    Dist Special 19. KEY WORDS (Continue on reverse side If neceary mud Identity by block numb ) Semiconductor devices Field effect transitors Integrated...Sun Tongnien (Hebei Semiconductor pit density. The W Research Institute, People’swith the etch ites of w Republic of China), and a compre-was...of impurities in touched on the topic of residual III-V semiconductors . The boron impurities in undoped GaAs, techniques discussed included a topic

  9. Radiation damage in proton irradiated indium phosphide solar cells

    NASA Technical Reports Server (NTRS)

    Weinberg, I.; Swartz, C. K.; Hart, R. E., Jr.; Yamaguchi, Masafumi

    1986-01-01

    Indium phosphide solar cells exposed to 10 MeV proton irradiations were found to have significantly greater radiation resistance than either GaAs or Si. Performance predictions were obtained for two proton dominated orbits and one in which both protons and electrons were significant cell degradation factors. Array specific power was calculated using lightweight blanket technology, a SEP array structure, and projected cell efficiencies. Results indicate that arrays using fully developed InP cells should out-perform those using GaAs or Si in orbits where radiation is a significant cell degradation factor.

  10. Radiation damage in proton irradiated indium phosphide solar cells

    NASA Technical Reports Server (NTRS)

    Weinberg, I.; Swartz, C. K.; Hart, R. E., Jr.; Yamaguchi, Masafumi

    1986-01-01

    Indium phosphide solar cells exposed to 10 MeV proton irradiations were found to have significantly greater radiation resistance than either GaAs or Si. Performance predictions were obtained for two proton dominated orbits and one in which both protons and electrons were significant cell degradation factors. Array specific power was calculated using lightweight blanket technology, a SEP array structure, and projected cell efficiencies. Results indicate that arrays using fully developed InP cells should out-perform those using GaAs or Si in orbits where radiation is a significant cell degradation factor.

  11. GaAs shallow-homojunction solar cells

    NASA Technical Reports Server (NTRS)

    Fan, J. C. C.

    1981-01-01

    The feasibility of fabricating space resistant, high efficiency, light weight, low cost GaAs shallow homojunction solar cells for space application is investigated. The material preparation of ultrathin GaAs single crystal layers, and the fabrication of efficient GaAs solar cells on bulk GaAs substrates are discussed. Considerable progress was made in both areas, and conversion efficiency about 16% AMO was obtained using anodic oxide as a single layer antireflection coating. A computer design shows that even better cells can be obtained with double layer antireflection coating. Ultrathin, high efficiency solar cells were obtained from GaAs films prepared by the CLEFT process, with conversion efficiency as high as 17% at AMI from a 10 micrometers thick GaAs film. A organometallic CVD was designed and constructed.

  12. Modeling charge collection efficiency degradation in partially depleted GaAs photodiodes using the 1- and 2-carrier Hecht equations

    NASA Astrophysics Data System (ADS)

    Auden, E. C.; Vizkelethy, G.; Serkland, D. K.; Bossert, D. J.; Doyle, B. L.

    2017-05-01

    The Hecht equation can be used to model the nonlinear degradation of charge collection efficiency (CCE) in response to radiation-induced displacement damage in both fully and partially depleted GaAs photodiodes. CCE degradation is measured for laser-generated photocurrent as a function of fluence and bias in Al0.3Ga0.7As/GaAs/Al0.25Ga0.75As p-i-n photodiodes which have been irradiated with 12 MeV C and 7.5 MeV Si ions. CCE is observed to degrade more rapidly with fluence in partially depleted photodiodes than in fully depleted photodiodes. When the intrinsic GaAs layer is fully depleted, the 2-carrier Hecht equation describes CCE degradation as photogenerated electrons and holes recombine at defect sites created by radiation damage in the depletion region. If the GaAs layer is partially depleted, CCE degradation is more appropriately modeled as the sum of the 2-carrier Hecht equation applied to electrons and holes generated within the depletion region and the 1-carrier Hecht equation applied to minority carriers that diffuse from the field-free (non-depleted) region into the depletion region. Enhanced CCE degradation is attributed to holes that recombine within the field-free region of the partially depleted intrinsic GaAs layer before they can diffuse into the depletion region.

  13. Modeling charge collection efficiency degradation in partially depleted GaAs photodiodes using the 1- and 2-carrier Hecht equations

    DOE PAGES

    Auden, E. C.; Vizkelethy, G.; Serkland, D. K.; ...

    2017-03-24

    Here, the Hecht equation can be used to model the nonlinear degradation of charge collection efficiency (CCE) in response to radiation-induced displacement damage in both fully and partially depleted GaAs photodiodes. CCE degradation is measured for laser-generated photocurrent as a function of fluence and bias in Al0.3Ga0.7As/GaAs/Al0.25Ga0.75As p-i-n photodiodes which have been irradiated with 12 MeV C and 7.5 MeV Si ions. CCE is observed to degrade more rapidly with fluence in partially depleted photodiodes than in fully depleted photodiodes. When the intrinsic GaAs layer is fully depleted, the 2-carrier Hecht equation describes CCE degradation as photogenerated electrons and holesmore » recombine at defect sites created by radiation damage in the depletion region. If the GaAs layer is partially depleted, CCE degradation is more appropriately modeled as the sum of the 2-carrier Hecht equation applied to electrons and holes generated within the depletion region and the 1-carrier Hecht equation applied to minority carriers that diffuse from the field-free (non-depleted) region into the depletion region. Enhanced CCE degradation is attributed to holes that recombine within the field-free region of the partially depleted intrinsic GaAs layer before they can diffuse into the depletion region.« less

  14. GaAs FET microwave oscillators

    NASA Astrophysics Data System (ADS)

    Sautereau, J.-F.

    Techniques for establishing the temporal stability of functioning of GaAs FETs are presented, along with a theory of negative resistance oscillators and an analysis of noise in GaAs FETs. Conditions of stable oscillation are discussed, as are techniques for designing solid state devices. An analog microwave circuit is described and is characterized in terms of inherent nonlinearities, which allows precise determination of the period, power, and harmonic distortion for the output signal. A coefficient is defined for expressing low frequency noise in microwave terms and methods for minimizing oscillator noise are presented, based on results from experimentation in X-band and low frequency devices. A computer model is developed which includes allowances for constantly repartitioned circuitry looping impedances. The model is concluded to be useful for the design of integrated monolithic microwave circuits.

  15. Wafer Bonding and Epitaxial Transfer of GaSb-based Epitaxy to GaAs for Monolithic Interconnection of Thermophotovoltaic Devices

    SciTech Connect

    C.A. Wang; D.A. Shiau; P.G. Murphy; P.W. O'brien; R.K. Huang; M.K. Connors; A.C. Anderson; D. Donetsky; S. Anikeev; G. Belenky; D.M. Depoy; G. Nichols

    2003-06-16

    GaInAsSb/AlGaAsSb/InAsSb/GaSb epitaxial layers were bonded to semi-insulating GaAs handle wafers with SiO{sub x}/Ti/Au as the adhesion layer for monolithic interconnection of thermophotovoltaic (TPV) devices. Epitaxial transfer was completed by removal of the GaSb substrate, GaSb buffer, and InAsSb etch-stop layer by selective chemical etching. The SiO{sub x}/TiAu provides not only electrical isolation, but also high reflectivity and is used as an internal back-surface reflector. Characterization of wafer-bonded epitaxy by high-resolution x-ray diffraction and time-decay photoluminescence indicates minimal residual stress and enhancement in optical quality. 0.54-eV GaInAsSb cells were fabricated and monolithically interconnected in series. A 10-junction device exhibited linear voltage building with an open-circuit voltage of 1.8 V.

  16. LSI/VLSI Ion Implanted GaAs IC Processing

    DTIC Science & Technology

    1982-02-10

    insulating High Speed Logic Ion Implantation GaAs IC FET Integrated Circuits MESFET 20. ABSTRACT (Coalki. on.. roersie if oookay and IdoeI by WOOe tw**, This...The goal of this program is to realize the full potential of GaAs digital integrated circuits employing depletion mode MESFETs by developing the...Processing. The main objective of this program is to realize the full potential of GaAs digital integrated circuits by expanding and improving

  17. Eight-Bit-Slice GaAs General Processor Circuit

    NASA Technical Reports Server (NTRS)

    Weissman, John; Gauthier, Robert V.

    1989-01-01

    Novel GaAs 8-bit slice enables quick and efficient implementation of variety of fast GaAs digital systems ranging from central processing units of computers to special-purpose processors for communications and signal-processing applications. With GaAs 8-bit slice, designers quickly configure and test hearts of many digital systems that demand fast complex arithmetic, fast and sufficient register storage, efficient multiplexing and routing of data words, and ease of control.

  18. New Passivation Methods for GaAs

    DTIC Science & Technology

    1975-01-01

    a shutter for a short ........ t .. Tl() to cover all freely exposed elements present in the chamber with an Aluminium film which will avoid oxidation...formation of an insulating layer by suitable means on the free surface to prevent carrier injection from outside and to improve the overall dielectric...conducting layers in the coses of both GaAs and GaAQ2,s. In order to prevent mixingj up cf 5lifferent dopants, a thorough cleaning procedure was appliecd

  19. Passivation of GaAs Surfaces.

    DTIC Science & Technology

    1980-08-15

    hour at indicated temperatures. Each symbol indicates one of four pieces of the same starting crystal . Three of the pieces were treated four times. The...Each symbol indicates one of four pieces of the same starting crystal . Three of the pieces were treated three times ................................ 9... crystal 11 11. Luminescence intensity of GaAs treated in ammonia plasma at 575*C as a function of treatment time. Each symbol represents one of five

  20. Piezoelectric field in strained GaAs.

    SciTech Connect

    Chow, Weng Wah; Wieczorek, Sebastian Maciej

    2005-11-01

    This report describes an investigation of the piezoelectric field in strained bulk GaAs. The bound charge distribution is calculated and suitable electrode configurations are proposed for (1) uniaxial and (2) biaxial strain. The screening of the piezoelectric field is studied for different impurity concentrations and sample lengths. Electric current due to the piezoelectric field is calculated for the cases of (1) fixed strain and (2) strain varying in time at a constant rate.

  1. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1984-01-01

    The crystal growth, device processing and device related properties and phenomena of GaAs are investigated. Our GaAs research evolves about these key thrust areas. The overall program combines: (1) studies of crystal growth on novel approaches to engineering of semiconductor materials (i.e., GaAs and related compounds); (2) investigation and correlation of materials properties and electronic characteristics on a macro- and microscale; (3) investigation of electronic properties and phenomena controlling device applications and device performance. The ground based program is developed which would insure successful experimentation with and eventually processing of GaAs in a near zero gravity environment.

  2. High efficiency, low cost thin GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Fan, J. C. C.

    1982-01-01

    The feasibility of fabricating space-resistant, high efficiency, light-weight, low-cost GaAs shallow-homojunction solar cells for space application is demonstrated. This program addressed the optimal preparation of ultrathin GaAs single-crystal layers by AsCl3-GaAs-H2 and OMCVD process. Considerable progress has been made in both areas. Detailed studies on the AsCl3 process showed high-quality GaAs thin layers can be routinely grown. Later overgrowth of GaAs by OMCVD has been also observed and thin FaAs films were obtained from this process.

  3. Radiation effects in GaAs AMOS solar cells

    NASA Technical Reports Server (NTRS)

    Shin, B. K.; Stirn, R. J.

    1979-01-01

    The results of radiation damage produced in AMOS (Antireflecting-Metal-Oxide-Semiconductor) cells with Sb2O3 interfacial oxide layers by 1-MeV electrons are presented. The degradation properties of the cells as a function of irradiation fluences were correlated with the changes in their spectral response, C-V, dark forward, and light I-V characteristics. The active n-type GaAs layers were grown by the OM-CVD technique, using sulfur doping in the range between 3 x 10 to the 15th power and 7 x 10 to the 16th power/cu cm. At a fluence of 10 to the 16th power e/sq cm, the low-doped samples showed I sub sc degradation of 8% and V sub oc degradation of 8%. The high-doped samples showed I sub sc and V sub oc degradation of 32% and 1%, respectively, while the fill factor remained relatively unchanged for both. AMOS cells with water vapor-grown interfacial layers showed no significant change in V sub oc.

  4. Damage production in GaAs and GaAsN induced by light and heavy ions

    SciTech Connect

    Bjoerkas, C.; Nordlund, K.; Arstila, K.; Keinonen, J.; Dhaka, V. D. S.; Pessa, M.

    2006-09-01

    Ion irradiation causes damage in semiconductor crystal structures and affects charge carrier dynamics. We have studied the damage production by high-energy (100 keV-10 MeV) H, He, Ne, and Ni ions in GaAs and GaAs{sub 90}N{sub 10} using molecular dynamics computer simulations. We find that the heavier Ne and Ni ions produce a larger fraction of damage in large clusters than H and He. These large clusters are either in the form of amorphous zones or (after room-temperature aging or high-temperature annealing) in the form of vacancy and antisite clusters. The total damage production in GaAs and GaAs{sub 90}N{sub 10} is found to be practically the same for all the ions. A clearly smaller fraction of the damage in GaAs{sub 90}N{sub 10} compared to GaAs is in large clusters, however. Our results indicate that experimentally observed differences in charge carrier lifetimes between light and heavy ion irradiations, and before and after annealing, can be understood in terms of the large defect clusters. An increasing amount of damage in large clusters decreases the carrier decay time.

  5. Defect studies in low-temperature-grown GaAs

    SciTech Connect

    Bliss, D.E.

    1992-11-01

    High content of excess As is incorporated in GaAs grown by low-temperature molecular-beam-epitaxy (LTMBE). The excess As exists primarily as As antisite defects AsGa and a lesser extent of gallium vacancies V[sub Ga]. The neutral AsGa-related defects were measured by infrared absorption at 1[mu]m. Gallium vacancies, V[sub Ga], was investigated by slow positron annihilation. Dependence of defect contents on doping was studied by Si and Be dopants. No free carriers are generated by n-type or p-type doping up to 10[sup 19] cm[sup [minus]3] Si or Be. Raman data indicate Be occupies Ga substitutional sites but Si atom is not substitutional. Si induces more As[sub Ga] in the layer. As As[sub Ga] increases, photoquenchable As[sub Ga] decreases. Fraction of photoquenchable defects correlates to defects within 3 nearest neighbor separations disrupting the metastability. Annealing reduces neutral As[sub Ga] content around 500C, similar to irradiation damaged and plastically deformed Ga[sub As], as opposed to bulk grown GaAs in which As[sub Ga]-related defects are stable up to 1100C. The lower temperature defect removal is due to V[sub Ga] enhanced diffusion of As[sub Ga] to As precipitates. The supersaturated V[sub GA] and also decreases during annealing. Annealing kinetics for As[sub Ga]-related defects gives 2.0 [plus minus] 0.3 eV and 1.5 [plus minus] 0.3 eV migration enthalpies for the As[sub Ga] and V[sub Ga]. This represents the difference between Ga and As atoms hopping into the vacancy. The non-photoquenchable As[sub Ga]-related defects anneal with an activation energy of 1.1 [plus minus] 0.3eV. Be acceptors can be activated by 800C annealing. Temperature difference between defect annealing and Be activation formation of As[sub Ga]-Be[sub Ga] pairs. Si donors can only be partially activated.

  6. Defect studies in low-temperature-grown GaAs

    SciTech Connect

    Bliss, David Emory

    1992-11-01

    High content of excess As is incorporated in GaAs grown by low-temperature molecular-beam-epitaxy (LTMBE). The excess As exists primarily as As antisite defects AsGa and a lesser extent of gallium vacancies VGa. The neutral AsGa-related defects were measured by infrared absorption at 1μm. Gallium vacancies, VGa, was investigated by slow positron annihilation. Dependence of defect contents on doping was studied by Si and Be dopants. No free carriers are generated by n-type or p-type doping up to 1019 cm-3 Si or Be. Raman data indicate Be occupies Ga substitutional sites but Si atom is not substitutional. Si induces more AsGa in the layer. As AsGa increases, photoquenchable AsGa decreases. Fraction of photoquenchable defects correlates to defects within 3 nearest neighbor separations disrupting the metastability. Annealing reduces neutral AsGa content around 500C, similar to irradiation damaged and plastically deformed GaAs, as opposed to bulk grown GaAs in which AsGa-related defects are stable up to 1100C. The lower temperature defect removal is due to VGa enhanced diffusion of AsGa to As precipitates. The supersaturated VGa and also decreases during annealing. Annealing kinetics for AsGa-related defects gives 2.0 ± 0.3 eV and 1.5 ± 0.3 eV migration enthalpies for the AsGa and VGa. This represents the difference between Ga and As atoms hopping into the vacancy. The non-photoquenchable AsGa-related defects anneal with an activation energy of 1.1 ± 0.3eV. Be acceptors can be activated by 800C annealing. Temperature difference between defect annealing and Be activation formation of AsGa-BeGa pairs. Si donors can only be partially activated.

  7. Panel fabrication utilizing GaAs solar cells

    NASA Technical Reports Server (NTRS)

    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.

  8. GaAs IMPATT diodes for microstrip circuit applications.

    NASA Technical Reports Server (NTRS)

    Wisseman, W. R.; Tserng, H. Q.; Shaw, D. W.; Mcquiddy, D. N.

    1972-01-01

    GaAs IMPATT diodes with plated heat sinks are shown to be particularly well suited for microstrip circuit applications. Details of materials growth and device fabrication procedures are given, and experimental results are presented for a GaAs IMPATT microstrip oscillator operating at X band.

  9. GaAs IMPATT diodes for microstrip circuit applications.

    NASA Technical Reports Server (NTRS)

    Wisseman, W. R.; Tserng, H. Q.; Shaw, D. W.; Mcquiddy, D. N.

    1972-01-01

    GaAs IMPATT diodes with plated heat sinks are shown to be particularly well suited for microstrip circuit applications. Details of materials growth and device fabrication procedures are given, and experimental results are presented for a GaAs IMPATT microstrip oscillator operating at X band.

  10. Panel fabrication utilizing GaAs solar cells

    NASA Technical Reports Server (NTRS)

    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.

  11. Computational analysis of the maximum power point for GaAs sub-cells in InGaP/GaAs/Ge triple-junction space solar cells

    NASA Astrophysics Data System (ADS)

    Cappelletti, M. A.; Cédola, A. P.; Blancá, E. L. Peltzer y.

    2014-11-01

    The radiation resistance in InGaP/GaAs/Ge triple-junction solar cells is limited by that of the middle GaAs sub-cell. In this work, the electrical performance degradation of different GaAs sub-cells under 1 MeV electron irradiation at fluences below 4 × 1015 cm-2 has been analyzed by means of a computer simulation. The numerical simulations have been carried out using the one-dimensional device modeling program PC1D. The effects of the base and emitter carrier concentrations of the p- and n-type GaAs structures on the maximum power point have been researched using a radiative recombination lifetime, a damage constant for the minority carrier lifetime and carrier removal rate models. An analytical model has been proposed, which is useful to either determine the maximum exposure time or select the appropriate device in order to ensure that the electrical parameters of different GaAs sub-cells will have a satisfactory response to radiation since they will be kept above 80% with respect to the non-irradiated values.

  12. Peeled film GaAs solar cell development

    NASA Astrophysics Data System (ADS)

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

    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 of the etching rate of aluminum arsenide (AlAs) over GaAs in dilute hydrofluoric acid. The feasibility of using the peeled film technique to fabricate high-efficiency, low-mass GaAs solar cells is presently demonstrated. A peeled film GaAs solar cell was successfully produced. The device, although fractured and missing the aluminum gallium arsenide window and antireflective coating, had a Voc of 874 mV and a fill factor of 68 percent under AM0 illumination.

  13. Peeled film GaAs solar cell development

    NASA Technical Reports Server (NTRS)

    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 of the etching rate of aluminum arsenide (AlAs) over GaAs in dilute hydrofluoric acid. The feasibility of using the peeled film technique to fabricate high-efficiency, low-mass GaAs solar cells is presently demonstrated. A peeled film GaAs solar cell was successfully produced. The device, although fractured and missing the aluminum gallium arsenide window and antireflective coating, had a Voc of 874 mV and a fill factor of 68 percent under AM0 illumination.

  14. Peeled film GaAs solar cell development

    NASA Technical Reports Server (NTRS)

    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 of the etching rate of aluminum arsenide (AlAs) over GaAs in dilute hydrofluoric acid. The feasibility of using the peeled film technique to fabricate high-efficiency, low-mass GaAs solar cells is presently demonstrated. A peeled film GaAs solar cell was successfully produced. The device, although fractured and missing the aluminum gallium arsenide window and antireflective coating, had a Voc of 874 mV and a fill factor of 68 percent under AM0 illumination.

  15. N/P GaAs concentrator solar cells with an improved grid and bushbar contact design

    NASA Technical Reports Server (NTRS)

    Desalvo, G. C.; Mueller, E. H.; Barnett, A. M.

    1985-01-01

    The major requirements for a solar cell used in space applications are high efficiency at AMO irradiance and resistance to high energy radiation. Gallium arsenide, with a band gap of 1.43 eV, is one of the most efficient sunlight to electricity converters (25%) when the the simple diode model is used to calculate efficiencies at AMO irradiance, GaAs solar cells are more radiation resistant than silicon solar cells and the N/P GaAs device has been reported to be more radiation resistant than similar P/N solar cells. This higher resistance is probably due to the fact that only 37% of the current is generated in the top N layer of the N/P cell compared to 69% in the top layer of a P/N solar cell. This top layer of the cell is most affected by radiation. It has also been theoretically calculated that the optimized N/P device will prove to have a higher efficiency than a similar P/N device. The use of a GaP window layer on a GaAs solar cell will avoid many of the inherent problems normally associated with a GaAlAs window while still proving good passivation of the GaAs surface. An optimized circular grid design for solar cell concentrators has been shown which incorporates a multi-layer metallization scheme. This multi-layer design allows for a greater current carrying capacity for a unit area of shading, which results in a better output efficiency.

  16. Au impact on GaAs epitaxial growth on GaAs (111){sub B} substrates in molecular beam epitaxy

    SciTech Connect

    Liao, Zhi-Ming; Chen, Zhi-Gang; Xu, Hong-Yi; Guo, Ya-Nan; Sun, Wen; Zhang, Zhi; Yang, Lei; Lu, Zhen-Yu; Chen, Ping-Ping; Lu, Wei; Zou, Jin

    2013-02-11

    GaAs growth behaviour under the presence of Au nanoparticles on GaAs {l_brace}111{r_brace}{sub B} substrate is investigated using electron microscopy. It has been found that, during annealing, enhanced Ga surface diffusion towards Au nanoparticles leads to the GaAs epitaxial growth into {l_brace}113{r_brace}{sub B} faceted triangular pyramids under Au nanoparticles, governed by the thermodynamic growth, while during conventional GaAs growth, growth kinetics dominates, resulting in the flatted triangular pyramids at high temperature and the epitaxial nanowires growth at relatively low temperature. This study provides an insight of Au nanoparticle impact on GaAs growth, which is critical for understanding the formation mechanisms of semiconductor nanowires.

  17. Deep level defect studies in semi-insulating 4H- and 6H-silicon carbide using optical admittance spectroscopy

    NASA Astrophysics Data System (ADS)

    Lee, Wonwoo

    The objective of this study is to determine the deep vanadium defect levels in semi-insulating 4H- and 6H- silicon carbide using optical admittance spectroscopy. Also infrared spectroscopy and electron paramagnetic resonance spectroscopy are conducted to support the evidence of vanadium donor and acceptor levels obtained from OAS measurements. Vanadium acts as an amphoteric impurity in silicon carbide with a V3+/4+ acceptor level and V4+/5+ donor level. Although the value for the donor level is well established, the V3+/4+ defect level remains controversial. OAS shows that the vanadium donor level is isolated near Ec-1.7 eV, and the vanadium acceptor level is located at Ec-0.75 eV at a cubic site and Ec-0.94 eV at a hexagonal site in 4H-SiC, while the vanadium donor level of 6H-SiC samples is about Ec-1.5 eV. The acceptor levels of 6H-SiC were assigned to Ec-0.67 eV, E c -0.70 eV at two cubic sites, and Ec-0.87 eV at a hexagonal site. IR spectra demonstrated that the signatures of the vanadium V 3+ and V4+ charge states are present in the samples. EPR and photo-induced EPR are used to identify the V3+/4+ and V4+/5+ levels as well as the V3+ and V 4+ charge states. EPR spectra represent both V3+ and V4+ in 4H- and 6H samples consistent with FTIR data. EPR and photo-induced EPR suggest that the va nadium acceptor level is between 0.7 eV and 0.86 eV, while the donor level is near Ec-1.5 eV in 6H-SiC. The donor level of 4H-SiC is located at Ec-1.6 eV. Thus, the data obtained from EPR and FTIR support the assignment of the vanadium defect levels determined by OAS. Vanadium complexes induced by other elements such as titanium, hydrogen, and nitrogen atoms are also observed in OAS spectra and will be discussed in the text.

  18. GaAs VLSI for aerospace electronics

    NASA Technical Reports Server (NTRS)

    Larue, G.; Chan, P.

    1990-01-01

    Advanced aerospace electronics systems require high-speed, low-power, radiation-hard, digital components for signal processing, control, and communication applications. GaAs VLSI devices provide a number of advantages over silicon devices including higher carrier velocities, ability to integrate with high performance optical devices, and high-resistivity substrates that provide very short gate delays, good isolation, and tolerance to many forms of radiation. However, III-V technologies also have disadvantages, such as lower yield compared to silicon MOS technology. Achieving very large scale integration (VLSI) is particularly important for fast complex systems. At very short gate delays (less than 100 ps), chip-to-chip interconnects severely degrade circuit clock rates. Complex systems, therefore, benefit greatly when as many gates as possible are placed on a single chip. To fully exploit the advantages of GaAs circuits, attention must be focused on achieving high integration levels by reducing power dissipation, reducing the number of devices per logic function, and providing circuit designs that are more tolerant to process and environmental variations. In addition, adequate noise margin must be maintained to ensure a practical yield.

  19. Implantation of carbon in GaAs

    SciTech Connect

    Moll, Amy Jo

    1992-03-01

    Carbon implanted into GaAs and thermally annealed typically exhibits very low (<3%) electrical activity. It has been demonstrated that the electrical activity of C can be significantly enhanced by co-implantation with Ga. Improved activation may result from either additional damage of the crystal lattice or from stoichiometric changes, forcing the C atoms onto As sites. To determine the relative importance of each of these effects, I have undertaken a systematic study of carbon activation in GaAs. A range of co-implants have been used: group III (B, Ga), group V (N, P, As) and noble gases (Ar, Kr). The damage introduced to the substrate will depend on the mass of the ion implanted. The group III and group V co-implants will affect the crystal stoichiometry. The results indicate that both lattice damage and crystal stoichiometry are important for high electrical activity of C. Increasing the damage will increase the activation due to the increased number of As vacancies but maximum activation can be obtained only by a co-implant which not only damages the lattice but also forces the C to occupy an As site.

  20. Pulsed-laser therapy (GA-As) in combined treatment of post-traumatic swellings and some dermatological disorders

    NASA Astrophysics Data System (ADS)

    Antipa, Ciprian; Dona, Dumitru; Podoleanu, Adrian Gh.

    1994-02-01

    The effect of a pulsed gallium arsenide infrared laser radiation was studied on 64 patients with post traumatic swellings, allergic vasculitis and varicose crural ulcers, therapy resistant. The soft laser therapy was conducted in combination with classical therapy and was compared with a non irradiated control group of 52 patients treated only by classical therapy. Laser irradiation was directed to the skin damage by laser scanning. Segmental and dermatomic areas of the skin lesions were irradiated by laserpuncture. Therapeutic protocol included an average of nine sessions. The statistical analysis shows a significant difference of the efficiency between Ga-As pulsed laser treated group and the control group, especially in the case of post-traumatic swellings and less in the case of allergic vasculitis. The effects reported by this study are relevant for clinical application of infrared pulsed low lasers in dermatology.

  1. Study of neutron irradiated structures of ammonothermal GaN

    NASA Astrophysics Data System (ADS)

    Gaubas, E.; Ceponis, T.; Deveikis, L.; Meskauskaite, D.; Miasojedovas, S.; Mickevicius, J.; Pavlov, J.; Pukas, K.; Vaitkus, J.; Velicka, M.; Zajac, M.; Kucharski, R.

    2017-04-01

    Study of the radiation damage in GaN-based materials becomes an important aspect for possible application of the GaN detectors in the harsh radiation environment at the Large Hadron Collider and at other particle acceleration facilities. Intentionally doped and semi-insulating bulk ammonothermal GaN materials were studied to reveal the dominant defects introduced by reactor neutron irradiations. These radiation defects have been identified by combining electron spin resonance and transmission spectroscopy techniques. Characteristics of carrier lifetime dependence on neutron irradiation fluence were examined. Variations of the response of the capacitor-type sensors with neutron irradiation fluence have been correlated with the carrier lifetime changes. The measurements of the photoconductivity and photoluminescence transients have been used to study the variation of the parameters of radiative and non-radiative recombination. The examined characteristics indicate that AT GaN as a particle sensing material is radiation hard up to high hadron fluences  ⩾1016 cm‑2.

  2. Space qualification of IR-reflecting coverslides for GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Meulenberg, Andrew

    1995-01-01

    Improvements to GaAs solar array performance, from the use on solar cell coverslides of several reflecting coatings that reject unusable portions of the solar spectrum, are quantified. Blue-red-rejection (BRR) coverslides provide both infrared reflection (IRR) and ultraviolet rejection (UVR). BRR coverslides were compared to conventional antireflection (AR) and ultraviolet (UV) coated coverslides. A 2% improvement in peak-power output, relative to that from Ar-coated coverslides, is seen for cells utilizing BRR coverslides with the widest bandpass. Coverslide BRR-filter bandpass width and covered-solar-cell short-circuit current is a function of incident light angle and the observed narrower-bandpass filters are more sensitive to change in angle from the normal than are wide-bandpass filters. The first long-term (3000 hours) UV testing of unirradiated and 1 MeV electron-irradiated GaAs solar cells, with multilayer-coated coverslides to reduce solar array operating temperature, has indicated that all multilayer coatings on coverslides and solar cells will experience degradation from the space environment (UV and/or electrons). Five types of coverslide coatings, designed for GaAs solar cells, were tested as part of a NASA-sponsored space-flight qualification for BRR, multi-layer-coated, coverslides. The reponse to the different radiations varied with the coatings. The extent of degradation and its consequences on the solar cell electrical characteristics depend upon the coatings and the radiation. In some cases, an improved optical coupling was observed during long-term UV exposure to the optical stack. The benefits of multi-layered solar cell optics may depend upon both the duration and the radiation environment of a mission.

  3. Metalorganic molecular beam epitaxy growth of GaAs on patterned GaAs substrates

    NASA Astrophysics Data System (ADS)

    Marx, D.; Asahi, H.; Liu, X. F.; Okuno, Y.; Inoue, K.; Gonda, S.; Shimomura, S.; Hiyamizu, S.

    1994-03-01

    GaAs layers were grown on etch-patterned (100) GaAs substrates by MOMBE (metalorganic molecular beam epitaxy) using TEGa (triethylgallium) and thermally cracked TEAs (triethylarsine). Morphology and orientation dependencies of the grown facets on the growth temperature (400-630°C) and V/III ratio (2-4) are investigated. Good morphology of grown layers was obtained on (111)A side facets at a low V/III ratio of 3 and low growth temperatures of 450-500°C. We also found strong evidence that the formation of facets is not only governed by the migration of Ga precursors and/or Ga atoms, but also by a preferential catalytic decomposition of Ga precursors on the facet edges.

  4. GaAs core--shell nanowires for photovoltaic applications.

    PubMed

    Czaban, Josef A; Thompson, David A; LaPierre, Ray R

    2009-01-01

    We report the use of Te as an n-type dopant in GaAs core-shell p-n junction nanowires for use in photovoltaic devices. Te produced significant change in the morphology of GaAs nanowires grown by the vapor-liquid-solid process in a molecular beam epitaxy system. The increase in radial growth of nanowires due to the surfactant effect of Te had a significant impact on the operating characteristics of photovoltaic devices. A decrease in solar cell efficiency occurred when the Te-doped GaAs growth duration was increased.

  5. GaAs VLSI technology and circuit elements for DSP

    NASA Astrophysics Data System (ADS)

    Mikkelson, James M.

    1990-10-01

    Recent progress in digital GaAs circuit performance and complexity is presented to demonstrate the current capabilities of GaAs components. High density GaAs process technology and circuit design techniques are described and critical issues for achieving favorable complexity speed power and cost tradeoffs are reviewed. Some DSP building blocks are described to provide examples of what types of DSP systems could be implemented with present GaAs technology. DIGITAL GaAs CIRCUIT CAPABILITIES In the past few years the capabilities of digital GaAs circuits have dramatically increased to the VLSI level. Major gains in circuit complexity and power-delay products have been achieved by the use of silicon-like process technologies and simple circuit topologies. The very high speed and low power consumption of digital GaAs VLSI circuits have made GaAs a desirable alternative to high performance silicon in hardware intensive high speed system applications. An example of the performance and integration complexity available with GaAs VLSI circuits is the 64x64 crosspoint switch shown in figure 1. This switch which is the most complex GaAs circuit currently available is designed on a 30 gate GaAs gate array. It operates at 200 MHz and dissipates only 8 watts of power. The reasons for increasing the level of integration of GaAs circuits are similar to the reasons for the continued increase of silicon circuit complexity. The market factors driving GaAs VLSI are system design methodology system cost power and reliability. System designers are hesitant or unwilling to go backwards to previous design techniques and lower levels of integration. A more highly integrated system in a lower performance technology can often approach the performance of a system in a higher performance technology at a lower level of integration. Higher levels of integration also lower the system component count which reduces the system cost size and power consumption while improving the system reliability

  6. Localized corrosion of GaAs surfaces and formation of porous GaAs

    SciTech Connect

    Schmuki, P.; Vitus, C.M.; Isaacs, H.S.; Fraser, J.; Graham, M.J.

    1995-12-01

    The present work deals with pitting corrosion of p- and n-type GaAs (100). Pit growth can be electrochemically initiated on both conduction types in chloride-containing solutions and leads after extended periods of time to the formation of a porous GaAs structure. In the case of p-type material, localized corrosion is only observed if a passivating film is present on the surface, otherwise -- e.g. in acidic solutions -- the material suffers from a uniform attack (electropolishing) which is independent of the anion present. In contrast, pitting corrosion of n-type material can be triggered independent of the presence of an oxide film. This is explained in terms of the different current limiting factor for the differently doped materials (oxide film in the case of the p- and a space charge layer in the case of the n-GaAs). The porous structure was characterized by SEM, EDX and AES, and consists mainly of GaAs. From scratch experiments it is clear that the pit initiation process is strongly influenced by surface defects. For n-type material, AFM investigations show that light induced roughening of the order of several hundred nm occurs under non-passivating conditions. This nm- scale roughening however does not affect the pitting process.

  7. A GaAs pixel detectors-based digital mammographic system: Performances and imaging tests results

    NASA Astrophysics Data System (ADS)

    Annovazzi, A.; Amendolia, S. R.; Bigongiari, A.; Bisogni, M. G.; Catarsi, F.; Cesqui, F.; Cetronio, A.; Colombo, F.; Delogu, P.; Fantacci, M. E.; Gilberti, A.; Lanzieri, C.; Lavagna, S.; Novelli, M.; Passuello, G.; Paternoster, G.; Pieracci, M.; Poletti, M.; Quattrocchi, M.; Rosso, V.; Stefanini, A.; Testa, A.; Venturelli, L.

    2007-06-01

    The prototype presented in this paper is based on GaAs pixel detectors read-out by the PCC/MEDIPIX I circuit. The active area of a sensor is about 1 cm 2 therefore to cover the typical irradiation field used in mammography (18×24 cm 2), 18 GaAs detection units have been organized in two staggered rows of nine chips each and moved by a stepper motor in the orthogonal direction. The system is integrated in a mammographic equipment which comprehends the X-ray tube, the bias and data acquisition systems and the PC-based control system. The prototype has been developed in the framework of the Integrated Mammographic Imaging (IMI) project, an industrial research activity aiming to develop innovative instrumentation for morphologic and functional imaging. The project has been supported by the Italian Ministry of Education, University and Research (MIUR) and by five Italian High Tech companies, Alenia Marconi Systems (AMS), CAEN, Gilardoni, LABEN and Poli.Hi.Tech., in collaboration with the universities of Ferrara, Roma "La Sapienza", Pisa and the Istituto Nazionale di Fisica Nucleare (INFN). In this paper, we report on the electrical characterization and the first imaging test results of the digital mammographic system. To assess the imaging capability of such a detector we have built a phantom, which simulates the breast tissue with malignancies. The radiographs of the phantom, obtained by delivering an entrance dose of 4.8 mGy, have shown particulars with a measured contrast below 1%.

  8. Development of GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Mcnally, P. J.

    1972-01-01

    Calculations of GaAs solar cell output parameters were refined and a computer model was developed for parameter optimization. The results were analyzed to determine the material characteristics required for a high efficiency solar cell. Calculated efficiencies for a P/N cell polarity are higher than an N/P cell. Both cell polarities show efficiency to have a larger dependence on short circuit current than an open circuit voltage under nearly all conditions considered. The tolerances and requirements of a cell fabrication process are more critical for an N/P type than for a P/N type cell. Several solar cell fabrication considerations relative to junction formation using ion implantation are also discussed.

  9. Low power laser irradiation does not affect the generation of signals in a sensory receptor

    SciTech Connect

    Lundeberg, T.; Zhou, J.

    1989-01-01

    The effect of low power Helium-Neon (He-Ne) and Gallium-Arsenide (Ga-As) laser on the slowly adapting crustacean stretch receptor was studied. The results showed that low power laser irradiation did not affect the membrane potential of the stretch receptor. These results are discussed in relation to the use of low power laser irradiation on the skin overlaying acupuncture points in treatment of pain syndrome.

  10. Transient space charge limited current spectroscopy method of measuring the position and concentration of trap levels in semi-insulating materials

    NASA Astrophysics Data System (ADS)

    Yuan, S. H.; Pardavi-Horvath, M.; Wigen, P. E.

    1988-11-01

    A new method is reported to measure the position and concentration of trap levels in semi-insulating materials where the regular deep level transient spectroscopy method is not applicable. In the proposed method, a transient space charge limited current (TSCLC) associated with the trap levels is measured using a capacitance balanced square wave voltage source, a voltage limiter-amplifier and a double box car averager. The TSCLC method is demonstrated on a p-type Y2.01Ca0.99Ge0.91Fe4.09O12 magnetic garnet sample ρ300=107 Ω cm. The trap level is located at 0.36 eV above the valence band edge and the concentration of the trapped holes is found to be 1013-1015 cm-3.

  11. Low temperature planar regrowth of semi-insulating InP by low pressure hydride vapour phase epitaxy for device application

    NASA Astrophysics Data System (ADS)

    Alexandre, F.; Parillaud, O.; Nguyen, D. C.; Azoulay, R.; Quillec, M.; Bouchoule, S.; Le Mestreallan, G.; Juhel, M.; Le Roux, G.; Rao, E. V. K.

    1998-05-01

    The growth of both undoped and iron doped InP on planar as well as non-planar (0 0 1)InP substrates has been explored using low pressure hydride vapour phase epitaxy (LP-HVPE) in the temperature range of 500-620°C. Secondary ion mass spectroscopy (SIMS), X-ray diffraction and photoluminescence measurements have shown no drastic degradation in the crystal quality with decreasing growth temperature. The Fe incorporation in the layers is found to be independent of the substrate temperature ( Ts) and in all experiments semi-insulating InP : Fe layers with resistivities close to 10 9 Ω cm have been obtained. A perfect growth selectivity with no deposition on masked areas and a good planarized regrowth on mesas has been demonstrated even at low Ts.

  12. Influence of low-temperature annealing on Schottky barrier height and surface electrical properties of semi-insulating CdTe

    NASA Astrophysics Data System (ADS)

    Rejhon, M.; Franc, J.; Zázvorka, J.; Dědič, V.; Kunc, J.

    2017-08-01

    We investigated the influence of low-temperature annealing in ambient air on the fundamental properties of semi-insulating CdTe doped with In and Cl in planar configuration, with gold and indium contacts prepared by evaporation at temperatures up to 373 K. The Au contact was formed by a central electrode and a guard ring, which allows us to separate bulk and surface leakage currents. We measured I-V characteristics and ellipsometry after each annealing step at room temperature. We determined that the change of the Schottky barrier height is responsible for the change of the bulk current, while the surface leakage current is affected by TeO2 layer thickness.

  13. On the relation between deep level compensation, resistivity and electric field in semi-insulating CdTe:Cl radiation detectors

    NASA Astrophysics Data System (ADS)

    Cola, Adriano; Farella, Isabella; Pousset, Jeremy; Valletta, Antonio

    2016-12-01

    A compensation model for semi-insulating CdTe:Cl based on a single dominant deep level 0.725 eV above the valence band is proposed. The model is corroborated by experimental evidence: resistivity measurements as a function of temperature on bulk crystals and stationary electric field distributions in Ohmic/Schottky radiation detectors, obtained by the Pockels effect. The latter are in close agreement with the numerical solutions of transport equations when considering the deep centre concentration in the range 2 - 4 × 1012 cm-3, and a compensation ratio R = 2.1, this one being consistent with an original ambipolar analysis of resistivity. More generally, the approach elucidates the role of electrical contacts and deep levels in controlling the electric fields in devices based on compensated materials.

  14. Thermally stimulated current spectroscopy applied on defect characterization in semi-insulating Cd0.9Zn0.1Te

    NASA Astrophysics Data System (ADS)

    Nan, Ruihua; Jie, Wanqi; Zha, Gangqiang; Wang, Bei; Yu, Hui

    2012-12-01

    Defects exhibiting trapping behaviors in semi-insulating (SI) materials were investigated by thermally stimulated current (TSC) spectroscopy. The variation of measurement conditions during the initial photoexcitation and thermal emission, such as the heating rate, bias voltage, illumination time and delay time, may bring some significant effects on TSC spectra, leading to incomplete characterization of trap levels. In this work, defects with deep levels in the band gap of SI-Cd0.9Zn0.1Te crystal, grown by the modified vertical Bridgman (MVB) method, were studied via TSC measurements. TSC measurement of the SI-CZT sample was performed with the optimized measurement conditions. Ten different traps and a deep donor (EDD) level were characterized from the as-obtained spectrum in the temperature range from 25 to 310 K with the aid of simultaneous multiple peak analysis (SIMPA). The origins of these traps were identified in detail as well.

  15. Analysis of intensity dependent near-bandedge absorption in semi-insulating 4H–SiC for photoconductive switch applications

    NASA Astrophysics Data System (ADS)

    Meyers, V.; Chowdhury, A. R.; Mauch, D.; Dickens, J. C.; Neuber, A. A.; Joshi, R. P.

    2017-04-01

    We report on the intensity-dependent behavior of the absorption coefficient (α) in semi-insulating 4H–SiC material. Data from as-received samples show a monotonic decrease in α with incident energy density, with a pronounced change in slope at around 10 mJ cm‑2. Annealed samples, on the other hand, exhibit an experimental trend of increasing α with intensity. Qualitative explanation of the observed behavior is presented that probes the possible role of spontaneous and stimulated emission for as-received samples. With annealing, trap related recombination is strongly reduced leading to higher carrier densities and increased free-carrier absorption with incident intensity. The role of band-filling and permittivity changes are shown to be inconsequential, while changes in internal fields could contribute to decreases in absorption.

  16. Crystal Growth of Device Quality Gaas in Space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.

    1985-01-01

    The GaAs research evolves about these key thrust areas. The overall program combines: (1) studies of crystal growth on novel approaches to engineering of semiconductor material (i.e., GaAs and related compounds); (2) investigation and correlation of materials properties and electronic characteristics on a macro- and microscale; and (3) investigation of electronic properties and phenomena controlling device applications and device performance. This effort is aimed at the essential ground-based program which would insure successful experimentation with and eventually processing of GaAs in near zero gravity environment. It is believed that this program addresses in a unique way materials engineering aspects which bear directly on the future exploitation of the potential of GaAs and related materials in device and systems applications.

  17. Preparation of GaAs photocathodes at low temperature

    SciTech Connect

    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.

  18. Ultrafast spectroscopy of GaAs under magnetic field

    SciTech Connect

    Mycek, M.A.; Siegner, U.; Glutsch, S.

    1995-03-01

    Surprising and novel results are obtained for both the linear and the nonlinear optical response of GaAs under magnetic field. Using a variety of spectroscopic techniques, we measure field dependent effects due to Coulomb correlation.

  19. Electrodeposition of Metal on GaAs Nanowires

    NASA Astrophysics Data System (ADS)

    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.

  20. More About V-Grooved GaAs Solar Cells

    NASA Technical Reports Server (NTRS)

    Bailey, S. G.; Wilt, D. M.; Landis, G. A.; Thomas, R. D.; Fatemi, N.

    1993-01-01

    NASA technical memorandum presents additional information about experimental devices described in "V-Grooved GaAs Solar Cell" (LEW-14954). Experimental V-groove cells exhibited improved optical coupling and greater short-circuit current.

  1. Interfacial Ga-As suboxide: Structural and electronic properties

    SciTech Connect

    Colleoni, Davide Pasquarello, Alfredo

    2015-07-20

    The structural and electronic properties of Ga-As suboxide representative of the transition region at the GaAs/oxide interface are studied through density functional calculations. Two amorphous models generated by quenches from the melt are taken under consideration. The absence of As–O bonds indicates that the structure is a mixture of GaAs and Ga-oxide, in accordance with photoemission experiments. The band edges of the models are found to be closely aligned to those of GaAs. The simulation of charging and discharging processes leads to the identification of an As-related defect with an energy level at ∼0.7 eV above the GaAs valence band maximum, in good agreement with the experimental density of interface states.

  2. Enhanced annealing of GaAs solar cell radiation damage

    NASA Technical Reports Server (NTRS)

    Loo, R.; Knechtli, R. C.; Kamath, G. S.

    1981-01-01

    Solar cells are degraded by radiation damage in space. Investigations have been conducted concerning possibilities for annealing this radiation damage in GaAs solar cells, taking into account the conditions favoring such annealing. It has been found that continuous annealing as well as the combination of injection annealing with thermal annealing can lead to recovery from radiation damage under particularly favorable conditions in GaAs solar cells. The damage caused by both electrons and protons in GaAs solar cells can be substantially reduced by annealing at temperatures as low as 150 C, under appropriate conditions. This possibility makes the GaAs solar cells especially attractive for long space missions, or for missions in severe radiation environments. Attention is given to results concerning periodic thermal annealing, continuous annealing, and injection annealing combined with thermal annealing.

  3. GaAs Films Prepared by RF-Magnetron Sputtering

    SciTech Connect

    L.H. Ouyang; D.L. Rode; T. Zulkifli; B. Abraham-Shrauner; N. Lewis; M.R. Freeman

    2001-08-01

    The authors reported on the optical absorption, adhesion, and microstructure of RF-magnetron sputtered films of hydrogenated amorphous and microcrystalline GaAs films for the 1 to 25 {micro}m infrared wavelength rate. Sputtering parameters which were varied include sputtering power, temperature and pressure, and hydrogen sputtering-gas concentration. TEM results show a sharp transition from purely amorphous GaAs to a mixture of microcrystalline GaAs in an amorphous matrix at 34 {+-} 2 C. By optimizing the sputtering parameters, the optical absorption coefficient can be decreased below 100 cm{sup -1} for wavelengths greater than about 1.25 {micro}m. These results represent the lowest reported values of optical absorption for sputtered films of GaAs directly measured by spectrophotometry for the near-infrared wavelength region.

  4. GaAs monolithic RF modules for SARSAT distress beacons

    NASA Technical Reports Server (NTRS)

    Cauley, Michael A.

    1991-01-01

    Monolithic GaAs UHF components for use in SARSAT Emergency Distress beacons are under development by Microwave Monolithics, Inc., Simi Valley, CA. The components include a bi-phase modulator, driver amplifier, and a 5 watt power amplifier.

  5. Possibilities for Superconductivity in 2-D GaAs Bilayers

    NASA Astrophysics Data System (ADS)

    Platzman, P. M.; Lenosky, T.

    1996-03-01

    We show that Coloumb coupled bilayers of the type which can be fabricated in GaAs systems can have a "conventional" BCS superconducting instability at reasonable temperatures, i.e., .1^circ K < Tc < 1^circ K

  6. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1983-01-01

    GaAs device technology has recently reached a new phase of rapid advancement, made possible by the improvement of the quality of GaAs bulk crystals. At the same time, the transition to the next generation of GaAs integrated circuits and optoelectronic systems for commercial and government applications hinges on new quantum steps in three interrelated areas: crystal growth, device processing and device-related properties and phenomena. Special emphasis is placed on the establishment of quantitative relationships among crystal growth parameters-material properties-electronic properties and device applications. The overall program combines studies of crystal growth on novel approaches to engineering of semiconductor material (i.e., GaAs and related compounds); investigation and correlation of materials properties and electronic characteristics on a macro- and microscale; and investigation of electronic properties and phenomena controlling device applications and device performance.

  7. Spatial Modulation Of Light In GaAs

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Gheen, Gregory; Partovi, Afshin

    1989-01-01

    Spatial modulation of light in gallium arsenide demonstrated by transferring image from one of two coherent, crossing beams of light to other one. Technique relies on cross-polarization beam coupling, product of photorefractive effect in GaAs crystal.

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

    SciTech Connect

    Iwamoto, Naoya Azarov, Alexander; Svensson, Bengt G.; Ohshima, Takeshi; Moe, Anne Marie M.

    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.

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

    NASA Astrophysics Data System (ADS)

    Iwamoto, Naoya; Azarov, Alexander; Ohshima, Takeshi; Moe, Anne Marie M.; Svensson, Bengt G.

    2015-07-01

    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 1015 cm-3 range, while other impurities including nitrogen, aluminum, titanium, vanadium and chromium are below their detection limits (typically ˜1014 cm-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.

  10. Air Force development of thin GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Masloski, K.

    1982-01-01

    The advantages of gallium arsenide (GaAs) over silicon (Si) type solar cells are well documented. However, two major disadvantages are weight and cost. Several ideas have recently surfaced that, if successful, will diminish these disadvantages. The CLEFT peeled film technique and the galicon cell are two of the more promising approaches. Low weight, low cost, high efficiency GaAs solar cell research is summarized.

  11. GaAs monolithic Lange and Wilkinson couplers

    NASA Astrophysics Data System (ADS)

    Waterman, R. C., Jr.; Fabian, W.; Pucel, R. A.; Tajima, Y.; Vorhaus, J. L.

    1981-02-01

    A monolithic GaAs X-band three-port Wilkinson coupler and a monolithic GaAs X-band four-port interdigitated Lange coupler are examined with reference to their design, fabrication technology, and experimental performance data. It is shown that fabrication of these couplers is compatible with present MMIC technologies. Measured loss minus fixture contributions is 0.25 dB and 0.75 dB for the Wilkinson and the Lange couplers, respectively.

  12. GaAs quantum well structures investigation by local cathodoluminescence

    NASA Astrophysics Data System (ADS)

    Shakhmin, A. A.; Zamoryanskaya, M. V.; Arsentyev, I. N.; Konnikov, S. G.; Vinokurov, D. A.; Stankevich, A. L.; Tarasov, I. S.

    2009-04-01

    The article shows the cathodoluminescence technique application to a quality analysis of a semiconductor multilayer heterostructures. Two structures with a GaAs quantum well embedded between the AlGaAs and GaInP barriers were investigated. The AlGaAs/GaAs/GaInP and GaInP/GaAs/AlGaAs structures were grown by MOCVD on a GaAs substrate. In this work we study the interface quality of quantum-dimensional GaAs layer by means of the local cathodoluminescence. Degradation and broadening of GaAs/GaInP interface occurring during the growth process of GaAs on GaInP layer was assumed to result in the formation of a layer with mixed composition at the interface. In addition, the presence of the layer prevented the formation of a quantum well in the GaAs layer. The transition layer was clearly observed by the cathodoluminescence. In the other case it was found that the growth of a structure with GaAs layer on top of AlGaAs produced a quantum well with a 10 nm thickness. The interface quality and layer thicknesses were also confirmed by the X-ray diffraction investigation of these structures.

  13. Intrinsic radiation tolerance of ultra-thin GaAs solar cells

    SciTech Connect

    Hirst, L. C.; Yakes, M. K.; Warner, J. H.; Schmieder, K. J.; Walters, R. J.; Jenkins, P. P.; Bennett, M. F.

    2016-07-18

    Radiation tolerance is a critical performance criterion of photovoltaic devices for space power applications. In this paper we demonstrate the intrinsic radiation tolerance of an ultra-thin solar cell geometry. Device characteristics of GaAs solar cells with absorber layer thicknesses 80 nm and 800 nm were compared before and after 3 MeV proton irradiation. Both cells showed a similar degradation in V{sub oc} with increasing fluence; however, the 80 nm cell showed no degradation in I{sub sc} for fluences up to 10{sup 14 }p{sup +} cm{sup −2}. For the same exposure, the I{sub sc} of the 800 nm cell had severely degraded leaving a remaining factor of 0.26.

  14. Enhanced sputtering and incorporation of Mn in implanted GaAs and ZnO nanowires

    NASA Astrophysics Data System (ADS)

    Johannes, A.; Noack, S.; Paschoal, W., Jr.; Kumar, S.; Jacobsson, D.; Pettersson, H.; Samuelson, L.; Dick, K. A.; Martinez-Criado, G.; Burghammer, M.; Ronning, C.

    2014-10-01

    We simulated and experimentally investigated the sputter yield of ZnO and GaAs nanowires, which were implanted with energetic Mn ions at room temperature. The resulting thinning of the nanowires and the dopant concentration with increasing Mn ion fluency were measured by accurate scanning electron microscopy (SEM) and nano-x-Ray Fluorescence (nanoXRF) quantification, respectively. We observed a clearly enhanced sputter yield for the irradiated nanowires compared to bulk, which is also corroborated by iradina simulations. These show a maximum if the ion range matches the nanowire diameter. As a consequence of the erosion thinning of the nanowire, the incorporation of the Mn dopants is also enhanced and increases non-linearly with increasing ion fluency.

  15. Influence of photoexcitation on hopping conduction in neutron-transmutation-doped GaAs

    SciTech Connect

    Satoh, M.; Kawahara, H.; Kuriyama, K.; Kawakubo, T.; Yoneda, K.; Kimura, I.

    1988-02-15

    The nature of the tunneling-assisted hopping conduction in neutron-transmutation-doped GaAs has been studied under photoexcitation with a photon energy of 1.32 eV. It is found that the dopants activated by annealing around 400 /sup 0/C provide the electrons to the defect levels originating the hopping conduction even when under photoexcitation. The hopping conduction under photoexcitation is affected by quenching in photoconductance below 120 K concerned with the main electron trap (EL2) and/or the As antisite defect (As/sub Ga/) induced by the neutron irradiation. The photoconductance of the samples with a lower radiation damage, As/sub Ga/less than or equal to1 x 10/sup 18/ cm/sup -3/, consists of the coexistence of the hopping and band conductions.

  16. Real-time observation of FIB-created dots and ripples on GaAs.

    PubMed

    Rose, F; Fujita, H; Kawakatsu, H

    2008-01-23

    We report a phenomenological study of Ga dots and ripples created by a focused ion beam (FIB) on the GaAs(001) surface. Real-time observation of dot diffusion and ripple formation was made possible by recording FIB movies. In the case of FIB irradiation with a 40 nA current of Ga(+) ions accelerated under 40 kV with an incidence angle of θ = 30°, increasing ion dose gives rise to three different regimes. In Regime 1, dots with lateral sizes in the range 50-460 nm are formed. Dots diffuse under continuous sputtering. In Regime 2, dots self-assemble into Bradley and Harper (BH) type ripples with a pseudo-period of λ = 1150 ± 25 nm. In Regime 3, ripples are eroded and the surface topology evolves into microplanes. In the case of normal incidence, FIB sputtering leads only to the formation of dots, without surface rippling.

  17. Nondestructive three-dimensional observation of defects in semi-insulating 6H-SiC single-crystal wafers using a scanning laser microscope (SLM) and infrared light-scattering tomography (IR-LST)

    NASA Astrophysics Data System (ADS)

    Wutimakun, Passapong; Buteprongjit, Chumpol; Morimoto, Jun

    2009-07-01

    Peripheral and central areas of a semi-insulating 6H-SiC single-crystal wafer were examined using a scanning laser microscope (SLM) and infrared light-scattering tomography (IR-LST). The form and density of the defects in each area were observed by SLM. We reconstructed three-dimensional (3D) IR-LST images of scatterers by stacking 2D layer-by-layer IR-LST images on different planes. Using these 3D IR-LST images, variations in the defect distribution with depth were observed for the first time. To study the defect distribution and defect form in detail, we observed the defect configuration in the same volume as for 3D IR-LST images by magnified SLM and merged the images from the two techniques. Information on defects obtained using this approach will be very important in the development of high-quality semi-insulating silicon carbide (SiC) substrates.

  18. Tissue irradiator

    DOEpatents

    Hungate, F.P.; Riemath, W.F.; Bunnell, L.R.

    1975-12-16

    A tissue irradiator is provided for the in-vivo irradiation of body tissue. The irradiator comprises a radiation source material contained and completely encapsulated within vitreous carbon. An embodiment for use as an in- vivo blood irradiator comprises a cylindrical body having an axial bore therethrough. A radioisotope is contained within a first portion of vitreous carbon cylindrically surrounding the axial bore, and a containment portion of vitreous carbon surrounds the radioisotope containing portion, the two portions of vitreous carbon being integrally formed as a single unit. Connecting means are provided at each end of the cylindrical body to permit connections to blood- carrying vessels and to provide for passage of blood through the bore. In a preferred embodiment, the radioisotope is thulium-170 which is present in the irradiator in the form of thulium oxide. A method of producing the preferred blood irradiator is also provided, whereby nonradioactive thulium-169 is dispersed within a polyfurfuryl alcohol resin which is carbonized and fired to form the integral vitreous carbon body and the device is activated by neutron bombardment of the thulium-169 to produce the beta-emitting thulium-170.

  19. [Food irradiation].

    PubMed

    Migdał, W

    1995-01-01

    A worldwide standard on food irradiation was adopted in 1983 by Codex Alimentarius Commission of the Joint Food Standard Programme of the Food and Agriculture Organization (FAO) of the United Nations and the World Health Organization (WHO). As a result, 41 countries have approved the use of irradiation for treating one or more food items and the number is increasing. Generally, irradiation is used to: food loses, food spoilage, disinfestation, safety and hygiene. The number of countries which use irradiation for processing food for commercial purposes has been increasing steadily from 19 in 1987 to 33 today. In the frames of the national programme on the application of irradiation for food preservation and hygienization an experimental plant for electron beam processing has been established in Institute of Nuclear Chemistry and Technology. The plant is equipped with a small research accelerator Pilot (19MeV, 1 kW) and an industrial unit Elektronika (10MeV, 10 kW). On the basis of the research there were performed at different scientific institutions in Poland, health authorities have issued permission for irradiation for: spices, garlic, onions, mushrooms, potatoes, dry mushrooms and vegetables.

  20. Evaluation of GaAs low noise and power MMIC technologies to neutron, ionizing dose and dose rate effects

    SciTech Connect

    Derewonko, H.; Bosella, A.; Pataut, G.; Perie, D.; Pinsard, J.L.; Sentubery, C.; Verbeck, C.; Bressy, P.; Augier, P.

    1996-06-01

    An evaluation program of Thomson CSF-TCS GaAs low noise and power MMIC technologies to 1 MeV equivalent neutron fluence levels, up to 1 {times} 10{sup 15} n/cm{sup 2}, ionizing 1.17--1.33 MeV CO{sup 60} dose levels in excess of 200 Mrad(GaAs) and dose rate levels reaching 1.89 {times} 10{sup 11} rad(GaAs)/s is presented in terms of proper components and parameter choices, DC/RF electrical measurements and test methods under irradiation. Experimental results are explained together with drift analyses of electrical parameters that have determined threshold limits of component degradations. Modelling the effects of radiation on GaAs components relies on degradation analysis of active layer which appears to be the most sensitive factor. MMICs degradation under neutron fluence was simulated from irradiated FET data. Finally, based on sensitivity of technological parameters, rad-hard design including material, technology and MMIC design enhancement is discussed.

  1. Spectroscopy of GaAs quantum wells

    SciTech Connect

    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.

  2. Vertical zone melt growth of GaAs

    SciTech Connect

    Henry, R.L.; Nordquist, P.E.R.; Gorman, R.J.

    1993-12-31

    A Vertical Zone Melt (VZM) technique has been applied to the single crystal growth of GaAs. A pyrolytic boron nitride crucible and a (100) oriented seed were used along with liquid encapsulation by boric oxide. In the case of GaAs, the ampoule was pressurized with either argon or argensic vapor from elemental arsenic at pressures ranging from 1 to 2 atmospheres. A molten zone length of 22 mm gave a growth interface which is nearly flat and resulted in routine single crystal growth. Temperature gradients of 4{degrees}C/cm. and 9{degrees}C/cm. have produced dislocation densities of <1000/cm{sup 2} and 2000-5000/cm{sup 2} respectively for 34 mm diameter crystals of GaAs. Post growth cooling rates for GaAs have been 35, 160 and 500{degrees}C/hr. The cooling rate has been found to affect the number and size of arsenic precipitates and the EL2 concentration in the GaAs crystal. The effects of these and other growth parameters on the crystalline perfection and electrical properties of the crystals will be discussed.

  3. Surface structure of GaAs(2 5 11)

    NASA Astrophysics Data System (ADS)

    Geelhaar, L.; Temko, Y.; Márquez, J.; Kratzer, P.; Jacobi, K.

    2002-04-01

    GaAs samples with orientations vicinal to (2 5 11) within 1° were prepared by molecular beam epitaxy and analyzed in situ by scanning tunneling microscopy, low-energy electron diffraction, and reflection high-energy electron diffraction. In addition, first-principles electronic structure calculations were carried out. GaAs(2 5 11) is a stable surface whose orientation is located within the stereographic triangle. For a wide range of As-rich conditions a (1×1) reconstruction forms that is characterized by an inclined series of three As dimers and that fulfills the electron counting rule. The terrace size is limited only by the macroscopic off-orientation of the samples. The surface is perturbed by thin stripes of the nearby orientation (3 7 15). While the dangling bond densities of GaAs(2 5 11) and GaAs(3 7 15) are almost equal, GaAs(3 7 15) violates the electron counting rule. The analysis of this perturbation suggests that, in general, on semiconductor surfaces the gain in stability arising from the minimization of the number of dangling bonds is significantly greater than the gain arising from reaching a semiconducting ground state. Upon annealing of the samples in ultrahigh vacuum, a fairly rough surface structure develops whose mean orientation is different from (2 5 11).

  4. 46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 8 2010-10-01 2010-10-01 false Operation under current GAA/MSTS Southeast Asia Program... AUTHORITY VOYAGE DATA Sec. 7 Operation under current GAA/MSTS Southeast Asia Program. In order to adapt the provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast...

  5. 46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 8 2011-10-01 2011-10-01 false Operation under current GAA/MSTS Southeast Asia Program... AUTHORITY VOYAGE DATA Sec. 7 Operation under current GAA/MSTS Southeast Asia Program. In order to adapt the provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast...

  6. Characterization of Heavily Doped ALUMINUM(X)GALLIUM(1 -X)ARSENIDE:TELLURIUM Grown on Semi-Insulating Gallium-Arsenide

    NASA Astrophysics Data System (ADS)

    Malloy, Kevin John

    The ability to dope a semiconductor into near metallic conduction widens its usefulness as a material and thereby permits the construction of new devices. Aluminum Gallium Arsenide is no exception. Heavily doped n-type Aluminum Gallium Arsenide has important device applications in tandem junction solar cells and in high electron mobility transistors. Aluminum Gallium Arsenide heavily doped with Tellurium was grown on semi-insulating Gallium Arsenide using liquid phase epitaxy. It was found that the addition of 0.4 atomic percent Tellurium to the melt reduced the Aluminum content of solid Aluminum Gallium Arsenide by up to 20 percent. A model was offered for this behavior involving a differential in the degree of association between Aluminum-Tellurium and Gallium-Tellurium in the liquid phase epitaxial melt. The electrical properties of n-type Aluminum Gallium Arsenide grown on semi-insulating Gallium Arsenide were modeled as a two sheet conductor. The two conductors consisted of the epitaxial n-type Aluminum Gallium Arsenide layer and the induced two dimensional electron gas present at the n-type Aluminum Gallium Arsenide-Gallium Arsenide heterojunction. This model showed the two dimensional electron gas as responsible for the constant low temperature carrier concentration observed experimentally. It also successfully explained the observation of a slope equal to the donor ionization potential instead of the donor ionization potential divided by two in the plot of the log of the carrier concentration versus reciprocal temperature. Because of the chemically independent nature of the deep donor ionization potential in Aluminum Gallium Arsenide, a minima interaction model was introduced to describe the donor level. The major matrix elements were determined to be V(,LX) = 4mV (+OR-) 1mV and V(,LL) = 40mV (+OR-) 10mV. These minima interaction matrix elements were an order of magnitude larger than suggested by theory, thus indicating the possible non-coulombic nature of

  7. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1985-01-01

    The present program has been aimed at solving the fundamental and technological problems associated with Crystal Growth of Device Quality in Space. The initial stage of the program was devoted strictly to ground-based research. The unsolved problems associated with the growth of bulk GaAs in the presence of gravitational forces were explored. Reliable chemical, structural and electronic characterization methods were developed which would permit the direct relation of the salient materials parameters (particularly those affected by zero gravity conditions) to the electronic characteristics of single crystal GaAs, in turn to device performance. These relationships are essential for the development of optimum approaches and techniques. It was concluded that the findings on elemental semiconductors Ge and Si regarding crystal growth, segregation, chemical composition, defect interactions, and materials properties-electronic properties relationships are not necessarily applicable to GaAs (and to other semiconductor compounds). In many instances totally unexpected relationships were found to prevail.

  8. Transient GaAs plasmonic metasurfaces at terahertz frequencies

    SciTech Connect

    Yang, Yuanmu; Kamaraju, N.; Campione, Salvatore; Liu, Sheng; Reno, John L.; Sinclair, Michael B.; Prasankumar, Rohit P.; Brener, Igal

    2016-12-09

    Here we demonstrate the ultrafast formation of terahertz (THz) metasurfaces through all-optical creation of spatially modulated carrier density profiles in a deep-subwavelength GaAs film. The switch-on of the transient plasmon mode, governed by the GaAs effective electron mass and electron–phonon interactions, is revealed by structured-optical pump THz probe spectroscopy, on a time scale of 500 fs. By modulating the carrier density using different pump fluences, we observe a wide tuning of the electric dipole resonance of the transient GaAs metasurface from 0.5 THz to 1.7 THz. Furthermore, we numerically demonstrate that the metasurface presented here can be generalized to more complex architectures for realizing functionalities such as perfect absorption, leading to a 30 dB modulation depth. In conclusion, the platform also provides a pathway to achieve ultrafast manipulation of infrared beams in the linear and, potentially, nonlinear regime.

  9. Studies of electron spin in GaAs quantum dots

    NASA Astrophysics Data System (ADS)

    Craft, Daniel; Colton, John; Park, Tyler; White, Phil

    2013-03-01

    We have studied electron spins in GaAs quantum dots with a pump-probe technique that normally yields the T1 spin lifetime, the time required for initially polarized electrons to relax and randomize. Using a circularly polarized laser tuned to the wavelength response of the quantum dot we can ``pump'' the spins into alignment. After aligning the spins we can detect them using a second, linearly polarized ``probe'' laser. By changing the delay between the two lasers we can trace out the spin response over time. In contrast with other samples (bulk GaAs and a GaAs quantum well), where the spin response decayed exponentially with time, initial data on the quantum dots has shown an unexpected, oscillating behavior which dies out on the order of 700 ns, independent of both temperature and magnetic field.

  10. Nonstoichiometric Low-Temperature Grown GaAs Nanowires.

    PubMed

    Díaz Álvarez, Adrian; Xu, Tao; Tütüncüoglu, Gözde; Demonchaux, Thomas; Nys, Jean-Philippe; Berthe, Maxime; Matteini, Federico; Potts, Heidi A; Troadec, David; Patriarche, Gilles; Lampin, Jean-François; Coinon, Christophe; Fontcuberta i Morral, Anna; Dunin-Borkowski, Rafal E; Ebert, Philipp; Grandidier, Bruno

    2015-10-14

    The structural and electronic properties of nonstoichiometric low-temperature grown GaAs nanowire shells have been investigated with scanning tunneling microscopy and spectroscopy, pump-probe reflectivity, and cathodoluminescence measurements. The growth of nonstoichiometric GaAs shells is achieved through the formation of As antisite defects, and to a lower extent, after annealing, As precipitates. Because of the high density of atomic steps on the nanowire sidewalls, the Fermi level is pinned midgap, causing the ionization of the subsurface antisites and the formation of depleted regions around the As precipitates. Controlling their incorporation offers a way to obtain unique electronic and optical properties that depart from the ones found in conventional GaAs nanowires.

  11. Microwave GaAs Integrated Circuits On Quartz Substrates

    NASA Technical Reports Server (NTRS)

    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.

  12. Heterojunction photovoltaics using GaAs nanowires and conjugated polymers.

    PubMed

    Ren, Shenqiang; Zhao, Ni; Crawford, Samuel C; Tambe, Michael; Bulović, Vladimir; Gradecak, Silvija

    2011-02-09

    We demonstrate an organic/inorganic solar cell architecture based on a blend of poly(3-hexylthiophene) (P3HT) and narrow bandgap GaAs nanowires. The measured increase of device photocurrent with increased nanowire loading is correlated with structural ordering within the active layer that enhances charge transport. Coating the GaAs nanowires with TiO(x) shells passivates nanowire surface states and further improves the photovoltaic performance. We find that the P3HT/nanowire cells yield power conversion efficiencies of 2.36% under white LED illumination for devices containing 50 wt % of TiO(x)-coated GaAs nanowires. Our results constitute important progress for the use of nanowires in large area solution processed hybrid photovoltaic cells and provide insight into the role of structural ordering in the device performance.

  13. Biomimetic subwavelength antireflective gratings on GaAs.

    PubMed

    Sun, Chih-Hung; Ho, Brian J; Jiang, Bin; Jiang, Peng

    2008-10-01

    We have developed a simple and scalable bottom-up approach for fabricating moth-eye antireflective coatings on GaAs substrates. Monolayer, non-close-packed silica colloidal crystals are created on crystalline GaAs wafers by a spin-coating-based single-layer reduction technique. These colloidal monolayers can be used as etching masks during a BCl(3) dry-etch process to generate subwavelength-structured antireflective gratings directly on GaAs substrates. The gratings exhibit excellent broadband antireflective properties, and the specular reflection matches with the theoretical prediction using a rigorous coupled-wave analysis model. These bioinspired antireflection coatings have important technological applications ranging from efficient solar cells to IR detectors.

  14. A GaAs phononic crystal with shallow noncylindrical holes.

    PubMed

    Petrus, Joseph A; Mathew, Reuble; Stotz, James A H

    2014-02-01

    A square lattice of shallow, noncylindrical holes in GaAs is shown to act as a phononic crystal (PnC) reflector. The holes are produced by wet-etching a GaAs substrate using a citric acid:H2O2 etching procedure and a photolithographed array pattern. Although nonuniform and asymmetric etch rates limit the depth and shape of the phononic crystal holes, the matrix acts as a PnC, as demonstrated by insertion loss measurements together with interferometric imaging of surface acoustic waves propagating on the GaAs surface. The measured vertical displacement induced by surface phonons compares favorably with finite-difference time-domain simulations of a PnC with rounded-square holes.

  15. Interface demarcation in GaAs by current pulsing

    NASA Technical Reports Server (NTRS)

    Matthiesen, D. H.; Kafalas, J. A.; Duchene, G. A.; Bellows, A. H.

    1990-01-01

    GTE Laboratories is currently conducting a program to investigate the effect of convection in the melt on the properties of bulk grown gallium arsenide (GaAs). In addition to extensive ground based experimentation, a Get Away Special growth system has been developed to grow two GaAs crystals aboard the Space Shuttle, each with a one inch diameter. In order to perform a complete segregation analysis of the crystals grown in space, it is necessary to measure the interface shape and growth rate as well as the spatial distribution of the selenium dopant. The techniques for interface demarcation in selenium doped GaAs by current pulsing have been developed at GTE Laboratories and successful interface demarcation has been achieved for current pulses ranging from 20 to 90 amps, in both single crystal and polycrystalline regions.

  16. High efficiency thin-film GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Zwerdling, S.; Wang, K. L.; Yeh, Y. C. M.

    1981-01-01

    The paper demonstrates the feasibility of producing high-efficiency GaAs solar cells with high power-to-weight ratios by organic metallic chemical vapor deposition (OM-CVD) growth of thin epi-layers on suitable substrates. An AM1 conversion efficiency of 18% (14% AM0), or 17% (13% AM0) with a 5% grid coverage is achieved for a single-crystal GaAs n(+)/p cell grown by OM-CVD on a Ge wafer. Thin GaAs epi-layers OM-CVD grown can be fabricated with good crystallographic quality using a Si-substrate on which a thin Ge epi-interlayer is first deposited by CVD from GeH4 and processed for improved surface morphology

  17. GaAs laser beacon for satellite communications

    NASA Technical Reports Server (NTRS)

    Richard, H. L.

    1981-01-01

    A low-power GaAs laser has been proposed as the beacon source for creating a high-data-rate laser communication link. GaAs sources have the necessary power output, stability and lifetime to provide relatively broad beamwidth beacon signals. Their signal strength permits adequate discrimination from background signals for beacon acquisition and lock-on during high-data-rate signal transmission. Link analysis is discussed in terms of a range equation identifying the power received on a low-earth-orbit satellite and indicating acceptable levels for the acquisition and tracking of the GaAs beacon source. Noise interference is discussed with reference to such sources as the galactic background, bright stars, and detector tube noise. Attention is likewise given to the signal source and the optical design of the beacon transmitter and beacon receiver.

  18. Interface demarcation in GaAs by current pulsing

    NASA Technical Reports Server (NTRS)

    Matthiesen, D. H.; Kafalas, J. A.; Duchene, G. A.; Bellows, A. H.

    1990-01-01

    GTE Laboratories is currently conducting a program to investigate the effect of convection in the melt on the properties of bulk grown gallium arsenide (GaAs). In addition to extensive ground based experimentation, a Get Away Special growth system has been developed to grow two GaAs crystals aboard the Space Shuttle, each with a one inch diameter. In order to perform a complete segregation analysis of the crystals grown in space, it is necessary to measure the interface shape and growth rate as well as the spatial distribution of the selenium dopant. The techniques for interface demarcation in selenium doped GaAs by current pulsing have been developed at GTE Laboratories and successful interface demarcation has been achieved for current pulses ranging from 20 to 90 amps, in both single crystal and polycrystalline regions.

  19. Irradiation subassembly

    DOEpatents

    Seim, O.S.; Filewicz, E.C.; Hutter, E.

    1973-10-23

    An irradiation subassembly for use in a nuclear reactor is described which includes a bundle of slender elongated irradiation -capsules or fuel elements enclosed by a coolant tube and having yieldable retaining liner between the irradiation capsules and the coolant tube. For a hexagonal bundle surrounded by a hexagonal tube the yieldable retaining liner may consist either of six segments corresponding to the six sides of the tube or three angular segments each corresponding in two adjacent sides of the tube. The sides of adjacent segments abut and are so cut that metal-tometal contact is retained when the volume enclosed by the retaining liner is varied and Springs are provided for urging the segments toward the center of the tube to hold the capsules in a closely packed configuration. (Official Gazette)

  20. Effects of 915 nm GaAs diode laser on mitochondria of human dermal fibroblasts: analysis with confocal microscopy.

    PubMed

    Belletti, Silvana; Uggeri, Jacopo; Mergoni, Giovanni; Vescovi, Paolo; Merigo, Elisabetta; Fornaini, Carlo; Nammour, Samir; Manfredi, Maddalena; Gatti, Rita

    2015-01-01

    Low-level laser therapy (LLLT) is widely used in tissue regeneration and pain therapy. Mitochondria are supposed to be one of the main cellular targets, due to the presence of cytochrome C oxidase as photo-acceptor. Laser stimulation could influence mitochondria metabolism affecting mainly transmembrane mitochondrial potential (Δψm). The aim of our study is to evaluate "in vitro" the early mitochondrial response after irradiation with a 915 GaAs laser. Since some evidences suggest that cellular response to LLLT can be differently modulated by the mode of irradiation, we would like to evaluate whether there are changes in the mitochondrial potential linked to the use of the laser treatments applied with continuous wave (CW) in respect to those applied with pulsed wave (PW). In this study, we analyzed effects of irradiation with a 915-nm GaAs diode laser on human dermal fibroblast. We compared effects of irradiation applied with either CW or PW at different fluences 45-15-5 J/cm(2) on Δψm. Laser scanning microscopy (LSM) was used in living cells to detect ROS (reactive oxygen species) using calcein AM and real-time changes of and Δψm following distribution of the potentiometric probe tetramethylrhodamine methyl ester (TMRM). At higher doses (45-15 J/cm(2)), fibroblasts showed a dose-dependent decrement of Δψm in either the modalities employed, with higher amplitudes in CW-treated cells. This behavior is transient and not followed by any sign of toxicity, even if reactive oxygen species generation was observed. At 5 J/cm(2), CW irradiation determined a little decrease (5%) of the baseline level of Δψm, while opposite behavior was shown when cells were irradiated with PW, with a 10% increment. Our results suggest that different responses observed at cellular level with low doses of irradiation, could be at the basis of efficacy of LLLT in clinical application, performed with PW rather than CW modalities.

  1. Crystal growth of GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.; Pawlowicz, L. M.; Dabkowski, F.; Li, C. J.

    1984-01-01

    It is shown that stoichiometry variations in the GaAs melt during growth constitute the most critical parameter regarding defect formations and their interactions; this defect structure determines all relevant characteristics of GaAs. Convection in the melt leads to stoichiometric variations. Growth in axial magnetic fields reduces convection and permits the study of defect structure. In order to control stoichiometry in space and to accommodate expansion during solidification, a partially confined configuration was developed. A triangular prism is employed to contain the growth melt. This configuration permits the presence of the desired vapor phase in contact with the melt for controlling the melt stoichiometry.

  2. MBE Growth of GaAs Whiskers on Si Nanowires

    NASA Astrophysics Data System (ADS)

    Maxwell Andrews, Aaron; Klang, Pavel; Detz, Hermann; Lugstein, Alois; Schramböck, Matthias; Steinmair, Mathias; Hyun, Youn-Joo; Bertagnolli, Emmerich; Müller, Thomas; Unterrainer, Karl; Schrenk, Werner; Strasser, Gottfried

    2010-01-01

    We present the growth of GaAs nanowhiskers by molecular beam epitaxy on Si (111) nanowires grown by low-pressure chemical vapor deposition. The whiskers grow in the wurtzite phase, along the [0001] direction, on the {112} facets of the Si nanowire, forming a star-like six-fold radial symmetry. The photoluminescence shows a 30 meV blue shift with respect to bulk GaAs, additionally a GaAs/AlAs core-shell heterostructure shows increased luminescence.

  3. Peeled film GaAs solar cells for space power

    NASA Technical Reports Server (NTRS)

    Wilt, D. M.; Deangelo, F. L.; Thomas, R. D.; Bailey, S. G.; Landis, G. A.; Brinker, D. J.; Fatemi, N. S.

    1990-01-01

    Gallium arsenide (GaAs) peeled film solar cells were fabricated, by Organo-Metallic Vapor Phase Epitaxy (OMVPE), incorporating an aluminum arsenide (AlAs) parting layer between the device structure and the GaAs substrate. This layer was selectively removed by etching in dilute hydrofloric (HF) acid to release the epitaxial film. Test devices exhibit high series resistance due to insufficient back contact area. A new design is presented which uses a coverglass superstrate for structural support and incorporates a coplanar back contact design. Devices based on this design should have a specific power approaching 700 W/Kg.

  4. Defect interactions in GaAs single crystals

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1984-01-01

    The two-sublattice structural configuration of GaAs and deviations from stoichiometry render the generation and interaction of electrically active point defects (and point defect complexes) critically important for device applications and very complex. Of the defect-induced energy levels, those lying deep into the energy band are very effective lifetime ""killers". The level 0.82 eV below the condition band, commonly referred to as EL2, is a major deep level, particularly in melt-grown GaAs. This level is associated with an antisite defect complex (AsGa - VAS). Possible mechanisms of its formation and its annihilation were further developed.

  5. Modelling of interband transitions in GaAs tunnel diode

    NASA Astrophysics Data System (ADS)

    Louarn, K.; Fontaine, C.; Arnoult, A.; Olivié, F.; Lacoste, G.; Piquemal, F.; Bounouh, A.; Almuneau, G.

    2016-06-01

    In this paper, an improved model for non-local band-to-band tunneling carrier transport is presented and compared to experimental measurement from GaAs tunnel junctions devices. By carefully taking into account the coupling between the conduction band and the light holes valence band, the model is able to predict, with realistic material parameters, the amplitude of the current density throughout the whole tunneling regime. The model suggests that elastic band-to-band tunneling instead of trap-assisted-tunneling is the predominant mechanism in GaAs tunnel junctions, which is of great interest for better understanding and improving III-V multi-junction solar cells.

  6. GaAs solar cells with V-grooved emitters

    NASA Technical Reports Server (NTRS)

    Bailey, S. G.; Fatemi, N.; Wilt, D. M.; Landis, G. A.; Thomas, R. D.

    1989-01-01

    A GaAs solar cell with a V-grooved front surface is described. It shows improved optical coupling and higher short-circuit current compared to planar cells. The GaAs homojunction cells, manufactured by OrganoMetallic Chemical Vapor Deposition (OMCVD), are described. The V-grooves were formed by anisotropic etching. Reflectivity measurements show significantly lower reflectance for the microgrooved cell compared to the planar structure. The short circuit current of the V-grooved solar cell is consistently higher than that of the planar controls.

  7. Experience with OMCVD production of GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Yeh, Y. C. M.; Iles, P. A.; Ho, P.; Ling, K. S.

    1985-01-01

    The projected promise of the OMCVD approach, i.e., to make high efficiency GaAs space cells, has been demonstrated. The properties and control of the deposited GaAs and AlGaAs layers and the uniformity of the post layer processing have been most satisfactory. In particular the control of the critical thin layers (p-GaAs, p-AlGaAs) has been impressive. Experience has also been gained in routine areas, connected with continuous operation at high capacity. There are still a few areas for improvement, to further increase capacity, and to anticipate and prevent mechanical equipment problems.

  8. Defect interactions in GaAs single crystals

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1984-01-01

    The two-sublattice structural configuration of GaAs and deviations from stoichiometry render the generation and interaction of electrically active point defects (and point defect complexes) critically important for device applications and very complex. Of the defect-induced energy levels, those lying deep into the energy band are very effective lifetime ""killers". The level 0.82 eV below the condition band, commonly referred to as EL2, is a major deep level, particularly in melt-grown GaAs. This level is associated with an antisite defect complex (AsGa - VAS). Possible mechanisms of its formation and its annihilation were further developed.

  9. MBE Growth of GaAs Whiskers on Si Nanowires

    SciTech Connect

    Maxwell Andrews, Aaron

    2010-01-04

    We present the growth of GaAs nanowhiskers by molecular beam epitaxy on Si (111) nanowires grown by low-pressure chemical vapor deposition. The whiskers grow in the wurtzite phase, along the [0001] direction, on the {l_brace}112{r_brace} facets of the Si nanowire, forming a star-like six-fold radial symmetry. The photoluminescence shows a 30 meV blue shift with respect to bulk GaAs, additionally a GaAs/AlAs core-shell heterostructure shows increased luminescence.

  10. Phosphine Functionalization GaAs(111)A Surfaces

    SciTech Connect

    Traub, M.; Biteen, J; Michalak, D; Webb, L; Brunschwig, B; Lewis, N

    2008-01-01

    Phosphorus-functionalized GaAs surfaces have been prepared by exposure of Cl-terminated GaAs(111)A surfaces to triethylphosphine (PEt3) or trichlorophosphine (PCl3), or by the direct functionalization of the native-oxide terminated GaAs(111)A surface with PCl3. The presence of phosphorus on each functionalized surface was confirmed by X-ray photoelectron spectroscopy. High-resolution, soft X-ray photoelectron spectroscopy was used to evaluate the As and Ga 3d regions of such surfaces. On PEt3 treated surfaces, the Ga 3d spectra exhibited a bulk Ga peak as well as peaks that were shifted to 0.35, 0.92 and 1.86 eV higher binding energy. These peaks were assigned to residual Cl-terminated Ga surface sites, surficial Ga2O and surficial Ga2O3, respectively. For PCl3-treated surfaces, the Ga 3d spectra displayed peaks ascribable to bulk Ga(As), Ga2O, and Ga2O3, as well as a peak shifted 0.30 eV to higher binding energy relative to the bulk signal. A peak corresponding to Ga(OH)3, observed on the Cl-terminated surface, was absent from all of the phosphine-functionalized surfaces. After reaction of the Cl-terminated GaAs(111)A surface with PCl3 or PEt3, the As 3d spectral region was free of As oxides and As0. Although native oxide-terminated GaAs surfaces were free of As oxides after reaction with PCl3, such surfaces contained detectable amounts of As0. Photoluminescence measurements indicted that phosphine-functionalized surfaces prepared from Cl-terminated GaAs(111)A surfaces had better electrical properties than the native-oxide capped GaAs(111)A surface, while the native-oxide covered surface treated with PCl3 showed no enhancement in PL intensity.

  11. Graphitized carbon on GaAs(100) substrates

    SciTech Connect

    Simon, J.; Simmonds, P. J.; Lee, M. L.; Woodall, J. M.

    2011-02-14

    We report on the formation of graphitized carbon on GaAs(100) surfaces by molecular beam epitaxy. We grew highly carbon-doped GaAs on AlAs, which was then thermally etched in situ leaving behind carbon atoms on the surface. After thermal etching, Raman spectra revealed characteristic phonon modes for sp{sup 2}-bonded carbon, consistent with the formation of graphitic crystallites. We estimate that the graphitic crystallites are 1.5-3 nm in size and demonstrate that crystallite domain size can be increased through the use of higher etch temperatures.

  12. Atomic Structure of the Stoichiometric GaAs(114) Surface.

    PubMed

    Márquez; Kratzer; Geelhaar; Jacobi; Scheffler

    2001-01-01

    The stoichiometric GaAs(114) surface has been prepared using molecular beam epitaxy followed by annealing in ultrahigh vacuum. Based on in situ scanning tunneling microscopy measurements and first-principles electronic-structure calculations, we determine the surface reconstruction which we call alpha2(2x1). Contrary to what is expected for a high-index surface, it is surprisingly elementary. The (2x1) unit cell contains two As dimers and two rebonded Ga atoms. The surface energy is calculated as 53 meV/Å(2), which falls well within the range of low-index GaAs surface energies.

  13. High efficiency thin-film GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Stirn, R. J.

    1977-01-01

    Several oxidation techniques are discussed which have been found to increase the open circuit (V sub oc) of metal-GaAs Schottky barrier solar cells, the oxide chemistry, attempts to measure surface state parameters, the evolving characteristics of the solar cell as background contamination (has been decreased, but not eliminated), results of focused Nd/YAG laser beam recrystallization of Ge films evaporated onto tungsten, and studies of AMOS solar cells fabricated on sliced polycrystalline GaAs wafers. Also discussed are projected materials availability and costs for GaAs thin-film solar cells.

  14. Simple intrinsic defects in GaAs : numerical supplement.

    SciTech Connect

    Schultz, Peter Andrew

    2012-04-01

    This Report presents numerical tables summarizing properties of intrinsic defects in gallium arsenide, GaAs, as computed by density functional theory. This Report serves as a numerical supplement to the results published in: P.A. Schultz and O.A. von Lilienfeld, 'Simple intrinsic defects in GaAs', Modelling Simul. Mater. Sci Eng., Vol. 17, 084007 (2009), and intended for use as reference tables for a defect physics package in device models. The numerical results for density functional theory calculations of properties of simple intrinsic defects in gallium arsenide are presented.

  15. ICP etching of GaAs via hole contacts

    SciTech Connect

    Shul, R.J.; Baca, A.G.; Briggs, R.D.; McClellan, G.B.; Pearton, S.J.; Constantine, C.

    1996-09-01

    Deep etching of GaAs is a critical process step required for many device applications including fabrication of through-substrate via holes for monolithic microwave integrated circuits (MMICs). Use of high-density plasmas, including inductively coupled plasmas (ICP), offers an alternative approach to etching vias as compared to more conventional parallel plate reactive ion etch systems. This paper reports ICP etching of GaAs vias at etch rates of about 5.3 {mu}m/min with via profiles ranging from highly anistropic to conical.

  16. Electronic contribution to friction on GaAs

    SciTech Connect

    Applied Science and Technology Graduate Group, UC Berkeley; Dept. of Materials Sciences and Engineering, UC Berkeley; Salmeron, Miquel; Qi, Yabing; Park, J.Y.; Hendriksen, B.L.M.; Ogletree, D.F.; Salmeron, Miquel

    2008-04-15

    The electronic contribution to friction at semiconductor surfaces was investigated by using a Pt-coated tip with 50nm radius in an atomic force microscope sliding against an n-type GaAs(100) substrate. The GaAs surface was covered by an approximately 1 nm thick oxide layer. Charge accumulation or depletion was induced by the application of forward or reverse bias voltages. We observed a substantial increase in friction force in accumulation (forward bias) with respect to depletion (reverse bias). We propose a model based on the force exerted by the trapped charges that quantitatively explains the experimental observations of excess friction.

  17. Investigation of high efficiency GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Olsen, Larry C.; Dunham, Glen; Addis, F. W.; Huber, Dan; Linden, Kurt

    1989-01-01

    Investigations of basic mechanisms which limit the performance of high efficiency GaAs solar cells are discussed. P/N heteroface structures have been fabricated from MOCVD epiwafers. Typical AM1 efficiencies are in the 21 to 22 percent range, with a SERI measurement for one cell being 21.5 percent. The cells are nominally 1.5 x 1.5 cm in size. Studies have involved photoresponse, T-I-V analyses, and interpretation of data in terms of appropriate models to determine key cell parameters. Results of these studies are utilized to determine future approaches for increasing GaAs solar cell efficiencies.

  18. Inversion-mode GaAs wave-shaped field-effect transistor on GaAs (100) substrate

    SciTech Connect

    Zhang, Jingyun; Si, Mengwei; Wu, Heng; Ye, Peide D.; Lou, Xiabing; Gordon, Roy G.; Shao, Jiayi; Manfra, Michael J.

    2015-02-16

    Inversion-mode GaAs wave-shaped metal-oxide-semiconductor field-effect transistors (WaveFETs) are demonstrated using atomic-layer epitaxy of La{sub 2}O{sub 3} as gate dielectric on (111)A nano-facets formed on a GaAs (100) substrate. The wave-shaped nano-facets, which are desirable for the device on-state and off-state performance, are realized by lithographic patterning and anisotropic wet etching with optimized geometry. A well-behaved 1 μm gate length GaAs WaveFET shows a maximum drain current of 64 mA/mm, a subthreshold swing of 135 mV/dec, and an I{sub ON}/I{sub OFF} ratio of greater than 10{sup 7}.

  19. Structure of high-index GaAs surfaces - the discovery of the stable GaAs(2511) surface

    NASA Astrophysics Data System (ADS)

    Jacobi, K.; Geelhaar, L.; Márquez, J.

    We present a brief overview of surface structures of high-index GaAs surfaces, putting emphasis on recent progress in our own laboratory. By adapting a commercial scanning tunneling microscope (STM) to our molecular beam epitaxy and ultra high vacuum analysis chamber system, we have been able to atomically resolve the GaAs( {1} {1} {3})B(8 ×1), (114)Aα2(2×1), (137), (3715), and (2511) surface structures. In cooperation with P. Kratzer and M. Scheffler from the Theory Department of the Fritz-Haber Institute we determined the structure of some of these surfaces by comparing total-energy calculations and STM image simulations with the atomically resolved STM images. We present the results for the {112}, {113}, and {114} surfaces. Then we describe what led us to proceed into the inner parts of the stereographic triangle and to discover the hitherto unknown stable GaAs(2511) surface.

  20. Design and optimization of very high power density monochromatic GaAs photovoltaic cells

    SciTech Connect

    Algora, C.; Diaz, V.

    1998-09-01

    This paper deals with the structure optimization of very high power density monochromatic GaAs photovoltaic cells and the theoretical prediction of their performance at irradiances ranging from 0.1 to 100 W/cm{sup 2}. A multifaceted optimum design including the front metal grid, device size and the semiconductor layer structure is presented. The variation in efficiency depending on emitter thickness, base thickness, emitter doping and base doping is also addressed. The objective of this being the configuration of a structure suitable for working up to 100 W/cm{sup 2} without the detrimental influence of series resistance. For this, a detailed analysis of the effect of series resistance and the quantitative determination of its different components is carried out. The optimum wavelength is 830 nm at 300 K for all the analyzed light intensities, in which a 63% peak efficiency under an irradiance of 100 W/cm{sup 2} for a p/n structure is obtained. The temperature effect on device performance in the 273--350 K range is also studied. Finally, the influence of device processing is analyzed.

  1. Photoelectrical characteristics of as-grown highresistance GaAs single crystals

    NASA Astrophysics Data System (ADS)

    Budnitskii, D. L.; Koretskaya, O. B.; Tolbanov, O. P.; Tyazhev, A. V.

    2010-06-01

    The electrophysical and photoelectrical properties of high-resistance GaAs produced by single crystal growth are studied and analyzed. The electron (τ n ) and hole (τ p ) lifetimes are estimated. The charge-carrier lifetimes are compared in as-grown and diffusion high-resistance GaAs. The conclusion is made that in high-resistance GaAs produced by chromium diffusion, the charge-carrier recombination mechanism qualitatively differs from that in as-grown GaAs. The charge-carrier recombination in diffusion GaAs is determined by the occurrence of recombination barriers due to chromium diffusion.

  2. Irradiated foods

    MedlinePlus

    ... it reduces the risk for food poisoning . Food irradiation is used in many countries. It was first approved in the U.S. to prevent sprouts on white potatoes, and to control insects on wheat and in certain spices and seasonings.

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

    NASA Technical Reports Server (NTRS)

    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.

  4. III-nitride heterostructure field-effect transistors grown on semi-insulating GaN substrate without regrowth interface charge

    NASA Astrophysics Data System (ADS)

    Liu, J. P.; Ryou, J.-H.; Yoo, D.; Zhang, Y.; Limb, J.; Horne, C. A.; Shen, S.-C.; Dupuis, R. D.; Hanser, A. D.; Preble, E. A.; Evans, K. R.

    2008-03-01

    Charge is observed at the regrowth interface for heterostructure field-effect transistors (HFETs) grown on semi-insulating (SI) bulk GaN substrates, even with Fe doping in the regrown buffer layer for reduction of the interface charge. Ultraviolet photoenhanced chemical (PEC) etching is used to treat the surface of SI bulk GaN substrates. Employing optimized etching conditions, a very smooth surface is achieved for the bulk GaN substrate after the etching. The charge at the regrowth interface is eliminated for HFETs grown on etched SI GaN substrates. Secondary ion mass spectrometry measurements show that the Si impurity concentration at the regrowth interface for HFETs grown on etched SI GaN substrates is much lower than that for HFETs grown on unetched SI GaN substrates, which suggests that the charge-containing layer on the SI substrate is removed by PEC etching and that the effects of the reduced charge layer near the regrowth interface can be eliminated by Fe doping for HFETs grown on etched SI substrates.

  5. Gallium arsenide (GaAs) island growth under SiO(2) nanodisks patterned on GaAs substrates.

    PubMed

    Tjahjana, Liliana; Wang, Benzhong; Tanoto, Hendrix; Chua, Soo-Jin; Yoon, Soon Fatt

    2010-05-14

    We report a growth phenomenon where uniform gallium arsenide (GaAs) islands were found to grow underneath an ordered array of SiO(2) nanodisks on a GaAs(100) substrate. Each island eventually grows into a pyramidal shape resulting in the toppling of the supported SiO(2) nanodisk. This phenomenon occurred consistently for each nanodisk across a large patterned area of approximately 50 x 50 microm(2) (with nanodisks of 210 nm diameter and 280 nm spacing). The growth mechanism is attributed to a combination of 'catalytic' growth and facet formation.

  6. Present status of GaAs. [including space processing and solid state applications

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.; Jastrzebski, L.

    1979-01-01

    An extensive literature survey on GaAs was carried out for the period December 31, 1970, to December 31, 1977. The increasing interest in GaAs device structures increased steadily during that period. The leading research and development centers and the specific areas of interest were identified. A workshop on GaAs was held in November 1977 to assess the present status of melt-grown GaAs and the existing needs for reliable chemical, structural, and electronic characterization methods. It was concluded that the present available bulk GaAs crystals are of poor quality and that GaAs technology is lagging demonstrated or potentially feasible GaAs devices and systems.

  7. ZnSe Films in GaAs Solar Cells

    NASA Technical Reports Server (NTRS)

    Kachare, Ram H.

    1987-01-01

    ZnSe increases efficiency and conserves material. Two proposed uses of zinc selenide films promise to boost performance and reduce cost of gallium arsenide solar cells. Accordingly ZnSe serves as surface-passivation layer and as sacrificial layer enabling repeated use of costly GaAs substrate in fabrication.

  8. GaAs Photovoltaics on Polycrystalline Ge Substrates

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Pal, AnnaMaria T.; McNatt, Jeremiah S.; Wolford, David S.; Landis, Geoffrey A.; Smith, Mark A.; Scheiman, David; Jenkins, Phillip P.; McElroy Bruce

    2007-01-01

    High efficiency III-V multijunction solar cells deposited on metal foil or even polymer substrates can provide tremendous advantages in mass and stowage, particularly for planetary missions. As a first step towards that goal, poly-crystalline p/i/n GaAs solar cells are under development on polycrystalline Ge substrates. Organo Metallic Vapor Phase Epitaxy (OMVPE) parameters for pre-growth bake, nucleation and deposition have been examined. Single junction p/i/n GaAs photovoltaic devices, incorporating InGaP front and back window layers, have been grown and processed. Device performance has shown a dependence upon the thickness of a GaAs buffer layer deposited between the Ge substrate and the active device structure. A thick (2 m) GaAs buffer provides for both increased average device performance as well as reduced sensitivity to variations in grain size and orientation. Illumination under IR light (lambda > 1 micron), the cells showed a Voc, demonstrating the presence of an unintended photoactive junction at the GaAs/Ge interface. The presence of this junction limited the efficiency to approx.13% (estimated with an anti-refection coating) due to the current mismatch and lack of tunnel junction interconnect.

  9. CLEFT Process for GaAs Solar Cells

    NASA Technical Reports Server (NTRS)

    Fan, J. C. C.; Bozler, C. O.; Mcclelland, R. W.

    1983-01-01

    CLEFT (cleavage of lateral epitaxial films for transfer) process involves growing ultrathin gallium arsenide (GaAs solar cell on much thicker layer of same material). Growth method is completed solar cell easily separated by cleaving from much thicker substrate. Thick substrate is reusable in making additional cells, which reduces cell material cost.

  10. Ballistic thermal point contacts made of GaAs nanopillars

    SciTech Connect

    Bartsch, Th.; Wetzel, A.; Sonnenberg, D.; Schmidt, M.; Heyn, Ch.; Hansen, W.

    2013-12-04

    We measure the thermal conductance of GaAs pillars that are only a few nanometers long. Our observations can be understood with a simple model, in which the pillars constitute thermal point contacts between 3D phonon reservoirs. Moreover, first measurements of the electronic transport through these pillars are presented.

  11. The 20 GHz power GaAs FET development

    NASA Technical Reports Server (NTRS)

    Crandell, M.

    1986-01-01

    The development of power Field Effect Transistors (FET) operating in the 20 GHz frequency band is described. The major efforts include GaAs FET device development (both 1 W and 2 W devices), and the development of an amplifier module using these devices.

  12. High efficiency thin-film GaAs solar cells

    SciTech Connect

    Zwerdling, S.; Wang, K.L.; Yeh, Y.C.M.

    1981-01-01

    This research is directed toward demonstrating the feasibility of producing high-efficiency GaAs solar cells with high power-to-weight ratio by organo-metallic chemical vapor deposition (OM-CVD) growth of thin epi-layers on suitable substrates. 4 refs.

  13. V-Grooved GaAs Solar Cell

    NASA Technical Reports Server (NTRS)

    Bailey, S. G.; Landis, G. R.; Wilt, D. M.; Thomas, R. D.; Arrison, A.; Fatemi, N. S.

    1991-01-01

    V-grooved GaAs solar photovoltaic cells increase optical coupling and greater conversion of light into electricity. Increases both trapping of incident light and lengths of optical paths in cell material. Net effect increases in total absorptivity, tolerance to damage by energetic particles, and short-circuit current. These improvements expected to follow from similar improvements obtained in silicon solar cells.

  14. CLEFT Process for GaAs Solar Cells

    NASA Technical Reports Server (NTRS)

    Fan, J. C. C.; Bozler, C. O.; Mcclelland, R. W.

    1983-01-01

    CLEFT (cleavage of lateral epitaxial films for transfer) process involves growing ultrathin gallium arsenide (GaAs solar cell on much thicker layer of same material). Growth method is completed solar cell easily separated by cleaving from much thicker substrate. Thick substrate is reusable in making additional cells, which reduces cell material cost.

  15. Status of GaAs solar cell production

    NASA Technical Reports Server (NTRS)

    Yeh, Milton; Ho, Frank; Iles, Peter A.

    1989-01-01

    Recent experience in producing GaAs solar cells, to meet the full requirements of space-array manufacturers is reviewed. The main problems have been in extending MOCVD technology to provide high throughput of high quality epitaxial layers, and to integrate the other important factors needed to meet the full range of user requirements. Some discussion of evolutionary changes is also given.

  16. GaAs Surface Passivation for Device Applications.

    DTIC Science & Technology

    1982-03-01

    inter- face electrical properties as deduced by analysis of the capacitance- voltage and conductance-voltage behavior of GaAs metal-insulator...capacitance at 10 kHz. The pseudo- inversional level is substantially greater than Cin v . However, beyond -10 V, the capacitance actually drops slightly

  17. Ballistic thermal point contacts made of GaAs nanopillars

    NASA Astrophysics Data System (ADS)

    Bartsch, Th.; Wetzel, A.; Sonnenberg, D.; Schmidt, M.; Heyn, Ch.; Hansen, W.

    2013-12-01

    We measure the thermal conductance of GaAs pillars that are only a few nanometers long. Our observations can be understood with a simple model, in which the pillars constitute thermal point contacts between 3D phonon reservoirs. Moreover, first measurements of the electronic transport through these pillars are presented.

  18. Temperature dependent GaAs MMIC radiation effects

    SciTech Connect

    Anderson, W.T.; Roussos, J.A. ); Gerdes, J. )

    1993-12-01

    The temperature dependence of pulsed neutron and flash x-ray radiation effects was studied in GaAs MMICs. Above room temperature the long term current transients are dominated by electron trapping in previously existing defects. At low temperature in the range 126 to 259 K neutron induced lattice damage appears to play an increasingly important role in producing long term current transients.

  19. Fast GaAs MMIC attenuator has 5-b resolution

    NASA Astrophysics Data System (ADS)

    Bedard, Brian; Maoz, Barak

    1991-10-01

    Circuit approaches to the design of digital attenuators are compared, and a switched-resistor design technique is presented which combines with GaAs MMIC technology to produce accurate, high-speed performance. A linear-circuit simulation program is described which predicts attenuator performance.

  20. GaAs MESFET with lateral non-uniform doping

    NASA Technical Reports Server (NTRS)

    Wang, Y. C.; Bahrami, M.

    1983-01-01

    An analytical model of the GaAs MESFET with arbitrary non-uniform doping is presented. Numerical results for linear lateral doping profile are given as a special case. Theoretical considerations predict that better device linearity and improved F(T) can be obtained by using linear lateral doping when doping density increases from source to drain.

  1. High purity, low dislocation GaAs single crystals

    NASA Technical Reports Server (NTRS)

    Chen, R. T.; Holmes, D. E.; Kirkpatrick, C. G.

    1983-01-01

    Liquid encapsulated Czochralski crystal growth techniques for producing undoped, high resistivity, low dislocation material suitable for device applications is described. Technique development resulted in reduction of dislocation densities in 3 inch GaAs crystals. Control over the melt stoichiometry was determined to be of critical importance for the reduction of twinning and polycrystallinity during growth.

  2. GaAs solar cell development

    NASA Technical Reports Server (NTRS)

    1979-01-01

    The four (AlGa)As-GaAs solar cells were fabricated and will be delivered for radiation damage testing using 1 MeV electrons. These cells were LPE grown at 700 C for 4 minutes. The junction depth was measured to be 0.3 micron using a secondary electron microscope. The radiation model for the shallow junction cells was verified. Some mesa diodes were also fabricated and will be irradiated along with the cells for parallel evaluations of their electrical characteristics.

  3. Evaluation of the minority carrier diffusion length and surface-recombination velocity in GaAs p/n solar cells

    NASA Technical Reports Server (NTRS)

    Hakimzadeh, Roshanak; Moeller, Hans J.; Bailey, Sheila

    1991-01-01

    The minority carrier diffusion length (Lp) and the surface recombination velocity (Vs) were measured as a function of distance (x) from the p-n junction in GaAs p/n concentrator solar cells. The measured Vs values were used in a theoretical expression for the normalized electron-beam-induced current. A fitting procedure was then used to fit this expression with experimental values to obtain Lp. The results show that both Vs and Lp vary with x. Lp measured in irradiated cells showed a marked reduction. These values were compared to those measured previously which did not account for Vs.

  4. Evaluation of the minority carrier diffusion length and surface-recombination velocity in GaAs p/n solar cells

    NASA Technical Reports Server (NTRS)

    Hakimzadeh, Roshanak; Moeller, Hans J.; Bailey, Sheila

    1991-01-01

    The minority carrier diffusion length (Lp) and the surface recombination velocity (Vs) were measured as a function of distance (x) from the p-n junction in GaAs p/n concentrator solar cells. The measured Vs values were used in a theoretical expression for the normalized electron-beam-induced current. A fitting procedure was then used to fit this expression with experimental values to obtain Lp. The results show that both Vs and Lp vary with x. Lp measured in irradiated cells showed a marked reduction. These values were compared to those measured previously which did not account for Vs.

  5. Oxidation of the GaAs semiconductor at the Al2O3/GaAs junction.

    PubMed

    Tuominen, Marjukka; Yasir, Muhammad; Lång, Jouko; Dahl, Johnny; Kuzmin, Mikhail; Mäkelä, Jaakko; Punkkinen, Marko; Laukkanen, Pekka; Kokko, Kalevi; Schulte, Karina; Punkkinen, Risto; Korpijärvi, Ville-Markus; Polojärvi, Ville; Guina, Mircea

    2015-03-14

    Atomic-scale understanding and processing of the oxidation of III-V compound-semiconductor surfaces are essential for developing materials for various devices (e.g., transistors, solar cells, and light emitting diodes). The oxidation-induced defect-rich phases at the interfaces of oxide/III-V junctions significantly affect the electrical performance of devices. In this study, a method to control the GaAs oxidation and interfacial defect density at the prototypical Al2O3/GaAs junction grown via atomic layer deposition (ALD) is demonstrated. Namely, pre-oxidation of GaAs(100) with an In-induced c(8 × 2) surface reconstruction, leading to a crystalline c(4 × 2)-O interface oxide before ALD of Al2O3, decreases band-gap defect density at the Al2O3/GaAs interface. Concomitantly, X-ray photoelectron spectroscopy (XPS) from these Al2O3/GaAs interfaces shows that the high oxidation state of Ga (Ga2O3 type) decreases, and the corresponding In2O3 type phase forms when employing the c(4 × 2)-O interface layer. Detailed synchrotron-radiation XPS of the counterpart c(4 × 2)-O oxide of InAs(100) has been utilized to elucidate the atomic structure of the useful c(4 × 2)-O interface layer and its oxidation process. The spectral analysis reveals that three different oxygen sites, five oxidation-induced group-III atomic sites with core-level shifts between -0.2 eV and +1.0 eV, and hardly any oxygen-induced changes at the As sites form during the oxidation. These results, discussed within the current atomic model of the c(4 × 2)-O interface, provide insight into the atomic structures of oxide/III-V interfaces and a way to control the semiconductor oxidation.

  6. Droplet-mediated formation of embedded GaAs nanowires in MBE GaAs1-x Bi x films

    NASA Astrophysics Data System (ADS)

    Wood, Adam W.; Collar, Kristen; Li, Jincheng; Brown, April S.; Babcock, Susan E.

    2016-03-01

    We have examined the morphology and composition of embedded nanowires that can be formed during molecular beam epitaxy of GaAs1-x Bi x using high angle annular dark field (‘Z-contrast’) imaging in an aberration-corrected scanning transmission electron microscope. Samples were grown in Ga-rich growth conditions on a stationary GaAs substrate. Ga-rich droplets are observed on the surface with lateral trails extending from the droplet in the [110] direction. Cross-sectional scanning transmission electron microscopy of the film reveals epitaxial nanowire structures of composition ˜GaAs embedded in the GaAs1-x Bi x epitaxial layers. These nanowires extend from a surface droplet to the substrate at a shallow angle of inclination (˜4°). They typically are 4 μm long and have a lens-shaped cross section with major and minor axes dimensions of 800 and 120 nm. The top surface of the nanowires exhibits a linear trace in longitudinal cross-section, across which the composition change from ˜GaAs to GaAs1-x Bi x appears abrupt. The bottom surfaces of the nanowires appear wavy and the composition change appears to be graded over ˜25 nm. The droplets have phase separated into Ga- and Bi-rich components. A qualitative model is proposed in which Bi is gettered into Ga droplets, leaving Bi depleted nanowires in the wakes of the droplets as they migrate in one direction across the surface during GaAs1-x Bi x film growth.

  7. Performance degradation of InGaP solar cells due to 70 keV electron irradiation

    NASA Astrophysics Data System (ADS)

    Okuno, Yasuki; Okuda, Shuichi; Oka, Takashi; Kawakita, Shirou; Imaizumi, Mitsuru

    2017-08-01

    The performance of InGaP solar cells irradiated with electron beams at energies lower than the damage threshold is degraded. To investigate the irradiation effect, GaAs and InGaP solar cells are irradiated with 70 keV electron beams. Measurements of the electroluminescence and external quantum efficiency, in addition to the light current voltage measurement, are conducted. The results show that the performance of the InGaP solar cell, mainly open-circuit voltage, is degraded and affected by nonradiative recombination centers, while the performance of the GaAs solar cell is hardly degraded. The comparison of the experimental results with the prediction from the displacement damage dose model suggests that the non-ionizing energy loss of electrons is the main factor for evaluating the degradation of the InGaP cell caused by electron beams in a relatively low energy range.

  8. Towards semi-insulating InGaAsP/InP layers by post-growth processing using Fe ion implantation and rapid thermal annealing

    NASA Astrophysics Data System (ADS)

    Fekecs, André; Chicoine, Martin; Ilahi, Bouraoui; Schiettekatte, François; Charette, Paul G.; Arès, Richard

    2013-04-01

    In this paper, we report on an effective post-growth processing technique for developing semi-insulating (SI) photonic thin films absorbing in 1.3 µm. For that purpose, we examined a 1 µm thick unintentionally n-doped In0.72Ga0.28As0.61P0.39 epilayer (0.95 eV bandgap) modified by multiple-energy MeV Fe ion implantation. Fe was chosen as a deep-level impurity. The ion beam processing was performed at room temperature, followed by rapid thermal annealing (RTA) at 800 °C for 15 s. We investigated the impact of ion fluence on electrical properties by Hall effect measurements. Channelling Rutherford backscattering spectrometry, x-ray diffraction and photoluminescence measurements were carried out to evaluate crystal quality after each fabrication step. Beyond the onset of amorphization, when the total Fe fluence was more than 4.8 × 1013 cm-2, the implanted InGaAsP layer showed evidence of a poor recrystallization after RTA, and its isolation was impaired. Maximum resistivity values were achieved below the onset of amorphization where annealing reduced ion de-channelling and recovered damage-induced strain. With a total Fe fluence of 1.6 × 1013 cm-2, the electrical resistivity and Hall mobility reached values of 1.4 × 104 Ω cm and 4 × 102 cm2 V-1 s-1. These results add important insights on the optimization of this process for the development of InP-based SI photoconductive films.

  9. Comparison of semi-insulating InAlAs and InP:Fe for InP-based buried-heterostructure QCLs

    NASA Astrophysics Data System (ADS)

    Flores, Y. V.; Aleksandrova, A.; Elagin, M.; Kischkat, J.; Kurlov, S. S.; Monastyrskyi, G.; Hellemann, J.; Golovynskyi, S. L.; Dacenko, O. I.; Kondratenko, S. V.; Tarasov, G. G.; Semtsiv, M. P.; Masselink, W. T.

    2015-09-01

    In a previous work [Flores et al., J. Cryst. Growth 398 (2014) 40] [3] we demonstrated the advantages of using a thin InAlAs spacer layer in the fabrication of buried-heterostructure quantum-cascade lasers (QCLs), as it improves the morphology of the interface between the laser core and the InP:Fe lateral cladding. In this paper we investigate aspects of InAlAs, which are relevant for its role as insulating lateral cladding of the laser sidewalls: carrier traps, electrical resistivity, and functionality as a sole lateral cladding. We find that a thin InAlAs spacer layer not only improves the regrowth interface morphology, but also eliminates interface-related shallow electronic states, thus improving the electrical resistivity of the interface. We further find that bulk InAlAs grown by gas-source molecular-beam epitaxy as well as InP:Fe are semi-insulating at room temperature, with specific resistivities of 3 ×107 Ω cm and 2 ×108 Ω cm, respectively. Both materials have also a high thermal activation energy for electrical conductivity (0.79 eV and 0.68 eV, respectively). In order to compare the performance of InP:Fe and InAlAs as a lateral cladding, lasers were fabricated from the same QCL wafer with differing stripe insulation materials. The resulting lasers differ mainly by the lateral insulation material: SiO2, InP:Fe (with InAlAs spacer), and pure InAlAs. All devices show a similar performance and similar temperature dependence, indicating insulating properties of InAlAs adequate for application in lateral regrowth of buried-heterostructure QCLs.

  10. Studies of molecular-beam epitaxy growth of GaAs on porous Si substrates

    NASA Technical Reports Server (NTRS)

    Mii, Y. J.; Kao, Y. C.; Wu, B. J.; Wang, K. L.; Lin, T. L.; Liu, J. K.

    1988-01-01

    GaAs has been grown on porous Si directly and on Si buffer layer-porous Si substrates by molecular-beam epitaxy. In the case of GaAs growth on porous Si, transmission electron microscopy (TEM) reveals that the dominant defects in GaAs layers grown on porous Si are microtwins and stacking faults, which originate from the GaAs/porous Si interface. GaAs is found to penetrate into the porous Si layers. By using a thin Si buffer layer (50 nm), GaAs penetration diminishes and the density of microtwins and stacking faults is largely reduced and localized at the GaAs/Si buffer interface. However, there is a high density of threading dislocations remaining. Both Si (100) aligned and four degree tilted substrates have been examined in this study. TEM results show no observable effect of the tilted substrates on the quality of the GaAs epitaxial layer.

  11. Fabrication of GaAs subwavelength structure (SWS) for solar cell applications.

    PubMed

    Kim, Byung-Jae; Kim, Jihyun

    2011-05-09

    We developed a novel GaAs subwavelength structure (SWS) as an antireflective layer for solar cell applications. The GaAs SWS patterns were fabricated by a combination of nanosphere lithography (NSL) and reactive ion etching (RIE). The shape and height of the GaAs SWS were controlled by the diameter of the SiO2 nanospheres and the etching time. Various GaAs SWS were characterized by the reflectance spectra. The average reflectance of the polished GaAs substrate from 200nm to 800nm was 35.1%. However, the average reflectance of the tapered GaAs SWS was reduced to 0.6% due to scattering and moth-eye effects.

  12. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Lagowski, J.

    1986-01-01

    It was established that the findings on elemental semiconductors Ge and Si regarding crystal growth, segregation, chemical composition, defect interactions, and materials properties-electronic properties relationships are not necessarily applicable to GaAs (and to other semiconductor compounds). In many instances totally unexpected relationships were found to prevail. It was further established that in compound semiconductors with a volatile constituent, control of stoichiometry is far more critical than any other crystal growth parameter. It was also shown that, due to suppression of nonstoichiometric fluctuations, the advantages of space for growth of semiconductor compounds extend far beyond those observed in elemental semiconductors. A novel configuration was discovered for partial confinement of GaAs melt in space which overcomes the two major problems associated with growth of semiconductors in total confinement. They are volume expansion during solidification and control of pressure of the volatile constituent. These problems are discussed in detail.

  13. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Gatos, Harry C.; Lagowski, Jacek

    1989-01-01

    The program on Crystal Growth of Device Quality GaAs in Space was initiated in 1977. The initial stage covering 1977 to 1984 was devoted strictly to ground-based research. By 1985 the program had evolved into its next logical stage aimed at space growth experiments; however, since the Challenger disaster, the program has been maintained as a ground-based program awaiting activation of experimentation in space. The overall prgram has produced some 80 original scientific publications on GaAs crystal growth, crystal characterization, and new approaches to space processing. Publication completed in the last three years are listed. Their key results are outlined and discussed in the twelve publications included as part of the report.

  14. Single Material Band Gap Engineering in GaAs Nanowires

    SciTech Connect

    Spirkoska, D.; Abstreiter, G.; Efros, A.; Conesa-Boj, S.; Morante, J. R.; Arbiol, J.; Fontcuberta i Morral, A.

    2011-12-23

    The structural and optical properties of GaAs nanowire with mixed zinc-blende/wurtzite structure are presented. High resolution transmission electron microscopy indicates the presence of a variety of shorter and longer segments of zinc-blende or wurtzite crystal phases. Sharp photoluminescence lines are observed with emission energies tuned from 1.515 eV down to 1.43 eV. The downward shift of the emission peaks can be understood by carrier confinement at the wurtzite/zinc-blende heterojunction, in quantum wells and in random short period superlattices existent in these nanowires, assuming the theoretical staggered band-offset between wurtzite and zinc-blende GaAs.

  15. Field Emission from Self-Catalyzed GaAs Nanowires.

    PubMed

    Giubileo, Filippo; Di Bartolomeo, Antonio; Iemmo, Laura; Luongo, Giuseppe; Passacantando, Maurizio; Koivusalo, Eero; Hakkarainen, Teemu V; Guina, Mircea

    2017-09-16

    We report observations of field emission from self-catalyzed GaAs nanowires grown on Si (111). The measurements were taken inside a scanning electron microscope chamber with a nano-controlled tungsten tip functioning as anode. Experimental data were analyzed in the framework of the Fowler-Nordheim theory. We demonstrate stable current up to 10(-7) A emitted from the tip of single nanowire, with a field enhancement factor β of up to 112 at anode-cathode distance d = 350 nm. A linear dependence of β on the anode-cathode distance was found. We also show that the presence of a Ga catalyst droplet suppresses the emission of current from the nanowire tip. This allowed for the detection of field emission from the nanowire sidewalls, which occurred with a reduced field enhancement factor and stability. This study further extends GaAs technology to vacuum electronics applications.

  16. Testing a GaAs cathode in SRF gun

    SciTech Connect

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

    2011-03-28

    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{sup -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 {approx}10{sup -9} Torr. This destroys the GaAs's NEA surface. The SRF guns combine the excellent vacuum conditions of DC guns and the high

  17. Structure and diffusion in simulated liquid GaAs

    NASA Astrophysics Data System (ADS)

    Hanh, T. T. T.; Hoang, V. V.

    2010-03-01

    Structure and diffusion of Ga and As ions in simulated liquid GaAs have been studied in a model containing 3000 ions under periodic boundary conditions via molecular dynamics simulation (MD). The microstructure of systems has been analyzed through partial radial distribution functions (PRDFs), coordination number distributions, bond-angle distributions and interatomic distances. We found that calculated data agree well with the experimental ones. Temperature dependence of these distributions was obtained. Caculations show that liquid GaAs model with a real density at 5.3176 g cm-3 has a distorted tetrahedral network structure with the mean coordination number ZAs-Ga ≈ 4. Diffusion constant D in system has been calculated over temperatures ranged from 5000 K down to 1500 K. Calculations show that the temperature dependence of the diffusion constant D shows an Arrhenius law at relatively low temperatures above the melting point and it shows a power law, D˜ (T - Tc)γ, at higher temperatures.

  18. Experimental examination of gaas dissolution in in-p melt

    NASA Astrophysics Data System (ADS)

    Bolkhovityanov, Yu. B.; Bolkhovityanova, R. I.; Chikichev, S. I.

    1983-05-01

    The “solubility” of GaAs crystals in quaternary In-Ga-As-P liquids (X{Ga/I} = X{As/I}) has been studied experi-mentally at 770°C using seed-dissolution technique. The location of the true liquidus isotherm has been established independently by means of the direct vi-sual observation technique. Comparison between the two data sets indicates that the first method can be successfully used only for those In-Ga-As-P melt compositions which have the corresponding solid InxGa1-xAsyP1-y alloys nearly lattice-matched to the GaAs substrate. In other cases the results obtained by this method are totally misleading although in-teresting as they are. The phenomenon of “catastro-phic” substrate erosion is investigated. The results of the present study are interpreted within the conceptual framework developed previously.

  19. Ultrafast Characterization of Nanostructures in GaAs

    NASA Astrophysics Data System (ADS)

    Gilbert, Stephanie; Kawasaki, Jason; Steigerwald, Andrew; Gregory, Justin; Palmstrøm, Chris; Tolk, Norman

    2012-02-01

    We combine ultrafast pump-probe and optoacoustic spectroscopy with magneto-optical Kerr rotation measurements to characterize embedded, self-assembled magnetically active nanostructures in a GaAs host matrix. We observe variations in the pump-probe and optoacoustic signals depending on the composition and growth characteristics of the embedded layers. Further, we observe (a) distinct behaviors in the femtosecond response of the composite structures when the probe photon energy is tuned near the GaAs band edge and (b) strong modulation of the optoacoustic signal inside the embedded layer. These results indicate an effective change in the transient femtosecond response of the composite structure, likely originating in strain effects due to the presence of nanoparticles within the host lattice. We additionally probe ultrafast magneto-optical interactions through time-resolved Kerr measurements. Finally, we present a potential method for high-resolution depth-dependent magnetic characterization by combining the Kerr rotation and optoacoustic experimental techniques.

  20. GaAs solar cells for laser power beaming

    NASA Technical Reports Server (NTRS)

    Olsen, Larry C.; Dunham, Glen; Huber, Daniel A.; Addis, F. William; Anheier, Norman; Coomes, E. P.

    1991-01-01

    Efforts to develop GaAs solar cells for coupling to laser beams in the wavelength range of 800 to 840 nm are described. This work was motivated primarily by interests in space-tp-space power beaming applications. In particular, the Battelle Pacific Northwest Laboratories is conducting studies of the utilization of power beaming for several future space missions. Modeling calculations of GaAs cell performance were carried out using PC-1D to determine an appropriate design for a p/n cell structure. Epitaxial wafers were grown by MOCVD and cells fabricated at WSU Tri-Cities. Under simulated conditions, an efficiency of 53 percent was achieved for a cell coupled to 806 nm light at 400 mW/sq cm.

  1. A V-grooved GaAs solar cell

    NASA Technical Reports Server (NTRS)

    Bailey, S. G.; Fatemi, N. S.; Landis, G. A.; Wilt, D. M.; Thomas, R. D.; Arrison, A.

    1988-01-01

    V-grooved GaAs solar cells promise the benefits of improved optical coupling, higher short-circuit current, and increased tolerance to particle radiation compared to planar cells. A GaAs homojunction cell was fabricated by etching a V-groove pattern into an n epilayer (2.1 x 10 to the 17th power per cu cm) grown by metalorganic chemical vapor deposition (MOCVD) on an n+ substrate (2.8 x 10 to the 18th power per cu cm) and then depositing and MOCVD p epilayer (4.2 x 10 to the 18th power per cu cm). Reflectivity measurements on cells with and without an antireflective coating confirm the expected decrease in reluctance of the microgrooved cell compared to the planar structure. The short circuit current of the V-grooved solar cell was 13 percent higher than that of the planar control.

  2. A V-grooved GaAs solar cell

    NASA Technical Reports Server (NTRS)

    Bailey, S. G.; Fatemi, N.; Landis, G. A.; Wilt, D. M.; Thomas, R. D.; Arrison, A.

    1988-01-01

    V-grooved GaAs solar cells promise the benefits of improved optical coupling, higher short-circuit current, and incrased tolerance to particle radiation compared to planar cells. A GaAs homojunction cell was fabricated by etching a V-groove pattern into an n-epilayer (2.1 x 10 to the 17th power per cu cm) grown by metalorganic chemical vapor deposition (MOCVD) on an n+ substrate (2.8 x 10 to the 18th power per cu cm) and then depositing an MOCVD p epilayer (4.2 x 10 to the 18th power per cu cm). Reflectivity measurements on cells with and without an antireflective coating confirm the expected decrease in reflectance of the microgrooved cell compared to the planar structure. The short-circuit current of the V-grooved solar cell was 13 percent higher than that of the planar control.

  3. Cryogenic measurements of aerojet GaAs n-JFETs

    NASA Technical Reports Server (NTRS)

    Goebel, John H.; Weber, Theodore T.

    1993-01-01

    The spectral noise characteristics of Aerojet gallium arsenide (GaAs) junction field effect transistors (JFET's) have been investigated down to liquid-helium temperatures. Noise characterization was performed with the field effect transistor (FET) in the floating-gate mode, in the grounded-gate mode to determine the lowest noise readings possible, and with an extrinsic silicon photodetector at various detector bias voltages to determine optimum operating conditions. The measurements indicate that the Aerojet GaAs JFET is a quiet and stable device at liquid helium temperatures. Hence, it can be considered a readout line driver or infrared detector preamplifier as well as a host of other cryogenic applications. Its noise performance is superior to silicon (Si) metal oxide semiconductor field effect transistor (MOSFET's) operating at liquid helium temperatures, and is equal to the best Si n channel junction field effect transistor (n-JFET's) operating at 300 K.

  4. Formation and properties of porous GaAs

    SciTech Connect

    Schmuki, P.; Lockwood, D.J.; Fraser, J.W.; Graham, M.J.; Isaacs, H.S.

    1996-06-01

    Porous structures on n-type GaAs (100) can be grown electrochemically in chloride-containing solutions. Crystallographic etching of the sample is a precursor stage of the attack. Polarization curves reveal the existanece of a critical onset potential for por formation (PFP). PFP is strongly dependent on the doping level of the sample and presence of surface defects. Good agreement between PFP and breakdown voltage of the space charge layer is found. Surface analysis by EDX, AES, and XPS show that the porous structure consists mainly of GaAs and that anion uptake in the structure can only observed after attackhas been initiated. Photoluminescence measurements reveal (under certain conditions) visible light emission from the porous structure.

  5. Optical detectors for GaAs MMIC integration: Technology assessment

    NASA Technical Reports Server (NTRS)

    Claspy, P. C.; Bhasin, K. B.

    1989-01-01

    Fiber optic links are being considered to transmit digital and analog signals in phased array antenna feed networks in space communications systems. The radiating elements in these arrays will be GaAs monolithic microwave integrated circuits (MMIC's) in numbers ranging from a few hundred to several thousand. If such optical interconnects are to be practical it appears essential that the associated components, including detectors, be monolithically integrated on the same chip as the microwave circuitry. The general issue of monolithic integration of microwave and optoelectronic components is addressed from the point of view of fabrication technology and compatibility. Particular attention is given to the fabrication technology of various types of GaAs optical detectors that are designed to operate at a wavelength of 830 nm.

  6. Government systems and GaAs monolithic components

    NASA Astrophysics Data System (ADS)

    Sieger, K. J.

    1983-12-01

    The current state of monolithic GaAs technology and its current and future applications to government systems are reviewed, with attention given to the government investment strategy, commercial market impact, new technology, and challenges from silicon technology. Data obtained from a survey to determine the status of GaAs IC technology are presented. These contain the system type and acronym, a technical description of the system, the critical research and development needed to develop the particular IC, specific applications and functions of the IC in the system, the year of implementation, and the potential chip buyer. High volume applications, with chip counts of one million and more, are identified as phased arrays (radar and communication), expendable decoys, missile seekers, and satellite signal processors. Problem areas, future trends, and areas of uncertainty are discussed.

  7. High purity low dislocation GaAs single crystals

    NASA Technical Reports Server (NTRS)

    Chen, R. T.; Holmes, D. E.; Kirkpatrick, C. G.

    1982-01-01

    Recent advances in GaAs bulk crystal growth using the LEC (liquid encapsulated Czochralski) technique are described. The dependence of the background impurity concentration and the dislocation density distribution on the materials synthesis and growth conditions were investigated. Background impurity concentrations as low as 4 x 10 to the 15th power were observed in undoped LEC GaAs. The dislocation density in selected regions of individual ingots was very low, below the 3000 cm .3000/sq cm threshold. The average dislocation density over a large annular ring on the wafers fell below the 10000/sq cm level for 3 inch diameter ingots. The diameter control during the program advanced to a diameter variation along a 3 inch ingot less than 2 mm.

  8. Optical detectors for GaAs MMIC integration - Technology assessment

    NASA Technical Reports Server (NTRS)

    Claspy, P. C.; Bhasin, K. B.

    1989-01-01

    Fiber optic links are being considered to transmit digital and analog signals in phased array antenna feed networks in space communications systems. The radiating elements in these arrays will be GaAs monolithic microwave integrated circuits (MMIC's) in numbers ranging from a few hundred to several thousand. If such optical interconnects are to be practical it appears essential that the associated components, including detectors, be monolithically integrated on the same chip as the microwave circuitry. The general issue of monolithic integration of microwave and optoelectronic components is addressed from the point of view of fabrication technology and compatibility. Particular attention is given to the fabrication technology of various types of GaAs optical detectors that are designed to operate at a wavelength of 830 nm.

  9. Crystal growth of device quality GaAs in space

    NASA Technical Reports Server (NTRS)

    Lagowski, J.

    1981-01-01

    Experimental and theoretical efforts in the development of crystal growth approaches, effective techniques for electronic characterization on a macro and microscale, and in the discovery of phenomena and processes relevant to GaAs device applications are reported. The growth of electron trap-free bulk GaAS with extremely low density of dislocations is described. In electroepitaxy, growth configuration which eliminates the substrate back-contact was developed. This configuration can be extended to the simultaneous growth on many substrates with a thin solution layer sandwiched between any two of them. The significant reduction of Joule heating effects in the configuration made it possible to realize the in situ measurement of the layer thickness and the growth velocity. Utilizing the advantages of electroepitaxy in achieving abrupt acceleration (or deceleration) of the growth it was shown that recombination centers are formed as a result of growth acceleration.

  10. The GaAs solar cell research and development programs of the Air Force

    NASA Technical Reports Server (NTRS)

    Masloski, K. T.

    1980-01-01

    The compound GaAs is of interest for space application photovoltaics due to its inherent advantages over silicon. Higher efficiencies, superior radiation hardness, and a greater temperature resistance are the major advantages of GaAs over Si. Air Force programs look for ways of maximizing these advantages while minimizing disadvantages such as higher costs and weights. Four programs in GaAs photovoltaics are described and each program is discussed in terms of its objective, approach and status.

  11. Optically activated GaAs MMIC switch for microwave and millimeter wave applications

    NASA Astrophysics Data System (ADS)

    Paolella, Arthur C.; Madjar, Asher; Herczfeld, Peter R.; Sturzebecher, Dana

    1991-03-01

    Optical control of microwave devices particularly MMIC is a rapidly growing research area. The GaAs MESFET is the prime candidate as the optical detector for MMIC applications. In this paper a theoretical analysis is presented which predicts the photoresponse in the MESFET. The analysis includes both internal and external photovoltaic and photoconductive effects. The paper also describes the operation of an optically activated GaAs MMIC switch using GaAs MESFET as the optical detector.

  12. Raman-scattering probe of anharmonic effects in GaAs

    NASA Astrophysics Data System (ADS)

    Verma, Prabhat; Abbi, S. C.; Jain, K. P.

    1995-06-01

    A comparative study of anharmonic effects in various structural forms of GaAs, namely crystalline, disordered and ion-implanted, and pulse laser annealed (PLA), using temperature-dependent Raman scattering, is reported for various phonon modes over the temperature range 10-300 K. The disordered and PLA samples are found to have greater anharmonicity than crystalline GaAs. The localized vibrational mode in PLA GaAs shows shorter relaxation time than the LO-phonon mode.

  13. Improved GaAs solar cells with very thin junctions

    NASA Technical Reports Server (NTRS)

    Hovel, H. J.; Woodall, J. M.

    1976-01-01

    Violet cells with 500-1000 A junction depths have been made in GaAs by narrow junction diffusion followed by anodization. The best AM0 efficiencies obtained by this technique have been 10.5% (14% at AM1). GaAlAs-GaAs structures with very thin GaAlAs layers are much more promising, and efficiencies of over 18% at AM0 have been measured (21.9% at AM1).

  14. On the dissolution properties of GaAs in Ga

    NASA Technical Reports Server (NTRS)

    Davidson, M. C.; Moynahan, A. H.

    1977-01-01

    The dissolution of GaAs in Ga was studied to determine the nature and cause of faceting effects. Ga was allowed to dissolve single crystalline faces under isothermal conditions. Of the crystalline planes with low number indices, only the (100) surface showed a direct correlation of dissolution sites to dislocations. The type of dissolution experienced depended on temperature, and there were three distinct types of behavior.

  15. GaAs Optoelectronic Integrated-Circuit Neurons

    NASA Technical Reports Server (NTRS)

    Lin, Steven H.; Kim, Jae H.; Psaltis, Demetri

    1992-01-01

    Monolithic GaAs optoelectronic integrated circuits developed for use as artificial neurons. Neural-network computer contains planar arrays of optoelectronic neurons, and variable synaptic connections between neurons effected by diffraction of light from volume hologram in photorefractive material. Basic principles of neural-network computers explained more fully in "Optoelectronic Integrated Circuits For Neural Networks" (NPO-17652). In present circuits, devices replaced by metal/semiconductor field effect transistors (MESFET's), which consume less power.

  16. A high-speed GaAs MESFET optical controller

    NASA Technical Reports Server (NTRS)

    Claspy, P. C.; Bhasin, K. B.; Richard, M.; Bendett, M.; Gustafson, G.

    1989-01-01

    Optical interconnects are being considered for control signal distribution in phased array antennas. A packaged hybrid GaAs optical controller with a 1:16 demultiplexed output that is suitable for this application is described. The controller, which was fabricated using enhancement/depletion mode MESFET technology, operates at demultiplexer-limited input data rates up to 305 Mb/s and requires less than 200 microW optical input power.

  17. Diboride diffusion barriers in silicon and GaAs technology

    NASA Astrophysics Data System (ADS)

    Shappirio, J. R.; Finnegan, J. J.; Lux, R. A.

    1986-12-01

    The synthesis and properties of a new class of contact compounds, the transition metal borides, are described. The effectiveness of the contact compounds as diffusion barriers when used to separate silicon from second level aluminum metallization is evaluated. Bulk and thin film resistivity and melting point data for disilicides and diborides are compared. The application of ZrB2 and TiB2 diffusion barriers to achieve stable ohmic contacts to n-type GaAs is discussed.

  18. Scalable high-power optically pumped GaAs laser

    NASA Astrophysics Data System (ADS)

    Le, H. Q.; di Cecca, S.; Mooradian, A.

    1991-05-01

    The use of disk geometry, optically pumped semiconductor gain elements for high-power scalability and good transverse mode quality has been studied. A room-temperature TEM00 transverse mode, external-cavity GaAs disk laser has been demonstrated with 500 W peak-power output and 40-percent slope efficiency, when pumped by a Ti:Al2O3 laser. The conditions for diode laser pumping are shown to be consistent with available power level.

  19. A high-speed GaAs MESFET optical controller

    NASA Technical Reports Server (NTRS)

    Claspy, P. C.; Bhasin, K. B.; Richard, M.; Bendett, M.; Gustafson, G.

    1989-01-01

    Optical interconnects are being considered for control signal distribution in phased array antennas. A packaged hybrid GaAs optical controller with a 1:16 demultiplexed output that is suitable for this application is described. The controller, which was fabricated using enhancement/depletion mode MESFET technology, operates at demultiplexer-limited input data rates up to 305 Mb/s and requires less than 200 microW optical input power.

  20. Vacancy-associated Te sites in GaAs

    NASA Astrophysics Data System (ADS)

    Wuyts, K.; Langouche, G.; van Rossum, M.; Silverans, R. E.

    1992-03-01

    Defect structures, observed by 129I Mössbauer spectroscopy in high-dose Te-doped GaAs, are identified by a reference study of the semiconducting compound Ga2Te3. The formation of TeAs-VGa complexes (tellurium atoms quasisubstitutional on an As site with a gallium vacancy in the first-neighbor shell) is proposed, in agreement with theoretical predictions. The relevance of this assignment in relation to the earlier proposed Te DX configuration is also discussed.

  1. Monolithic GaAs surface acoustic wave chemical microsensor array

    SciTech Connect

    HIETALA,VINCENT M.; CASALNUOVO,STEPHEN A.; HELLER,EDWIN J.; WENDT,JOEL R.; FRYE-MASON,GREGORY CHARLES; BACA,ALBERT G.

    2000-03-09

    A four-channel surface acoustic wave (SAW) chemical sensor array with associated RF electronics is monolithically integrated onto one GaAs IC. The sensor operates at 690 MHz from an on-chip SAW based oscillator and provides simple DC voltage outputs by using integrated phase detectors. This sensor array represents a significant advance in microsensor technology offering miniaturization, increased chemical selectivity, simplified system assembly, improved sensitivity, and inherent temperature compensation.

  2. GaAs Optoelectronic Integrated-Circuit Neurons

    NASA Technical Reports Server (NTRS)

    Lin, Steven H.; Kim, Jae H.; Psaltis, Demetri

    1992-01-01

    Monolithic GaAs optoelectronic integrated circuits developed for use as artificial neurons. Neural-network computer contains planar arrays of optoelectronic neurons, and variable synaptic connections between neurons effected by diffraction of light from volume hologram in photorefractive material. Basic principles of neural-network computers explained more fully in "Optoelectronic Integrated Circuits For Neural Networks" (NPO-17652). In present circuits, devices replaced by metal/semiconductor field effect transistors (MESFET's), which consume less power.

  3. Gallium arsenide (GaAs) solar cell modeling studies

    NASA Technical Reports Server (NTRS)

    Heinbockel, J. H.

    1980-01-01

    Various models were constructed which will allow for the variation of system components. Computer studies were then performed using the models constructed in order to study the effects of various system changes. In particular, GaAs and Si flat plate solar power arrays were studied and compared. Series and shunt resistance models were constructed. Models for the chemical kinetics of the annealing process were prepared. For all models constructed, various parametric studies were performed.

  4. Solar heating of GaAs nanowire solar cells

    SciTech Connect

    Wu, Shao-Hua; Povinelli, Michelle L.

    2015-09-25

    We use a coupled thermal-optical approach to model the operating temperature rise in GaAs nanowire solar cells. Our findings show 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.

  5. GaAs Concentrator Photovoltaic Power System Feasibility Investigation.

    DTIC Science & Technology

    1977-12-01

    cells at high intensity levels by permitting testing in a controlled thermal environment without the thermal problems ( heat flux) inherent with...multisun steady state simulation; i.e., the bulk cell temperature is constant and controlled by the backs de- heating /cooling block of the test fixture...determine the efficiency of the GaAs cells at various temperatures. Thus, the cells will be mounted on a small, thermocouple-equipped heat sink block

  6. Solar heating of GaAs nanowire solar cells.

    PubMed

    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.

  7. Transient GaAs plasmonic metasurfaces at terahertz frequencies

    DOE PAGES

    Yang, Yuanmu; Kamaraju, N.; Campione, Salvatore; ...

    2016-12-09

    Here we demonstrate the ultrafast formation of terahertz (THz) metasurfaces through all-optical creation of spatially modulated carrier density profiles in a deep-subwavelength GaAs film. The switch-on of the transient plasmon mode, governed by the GaAs effective electron mass and electron–phonon interactions, is revealed by structured-optical pump THz probe spectroscopy, on a time scale of 500 fs. By modulating the carrier density using different pump fluences, we observe a wide tuning of the electric dipole resonance of the transient GaAs metasurface from 0.5 THz to 1.7 THz. Furthermore, we numerically demonstrate that the metasurface presented here can be generalized to moremore » complex architectures for realizing functionalities such as perfect absorption, leading to a 30 dB modulation depth. In conclusion, the platform also provides a pathway to achieve ultrafast manipulation of infrared beams in the linear and, potentially, nonlinear regime.« less

  8. Analysis of optical absorption in GaAs nanowire arrays.

    PubMed

    Guo, Haomin; Wen, Long; Li, Xinhua; Zhao, Zhifei; Wang, Yuqi

    2011-12-06

    In this study, the influence of the geometric parameters on the optical absorption of gallium arsenide [GaAs] nanowire arrays [NWAs] has been systematically analyzed using finite-difference time-domain simulations. The calculations reveal that the optical absorption is sensitive to the geometric parameters such as diameter [D], length [L], and filling ratio [D/P], and more efficient light absorption can be obtained in GaAs NWAs than in thin films with the same thickness due to the combined effects of intrinsic antireflection and efficient excitation of resonant modes. Optimized geometric parameters are obtained as follows: D = 180 nm, L = 2 μm, and D/P = 0.5. Meanwhile, the simulation on the absorption of GaAs NWAs for oblique incidence has also been carried out. The underlying physics is discussed in this work.PACS: 81.07.Gf nanowires; 81.05.Ea III-V semiconductors; 88.40.hj efficiency and performance of solar cells; 73.50.Pz photoconduction and photovoltaic effects.

  9. Ab initio study of hot electrons in GaAs.

    PubMed

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

    2015-04-28

    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 theory. Our computed electron-phonon relaxation times at the onset of the Γ, L, and X valleys are in excellent agreement with ultrafast optical experiments and show that the ultrafast (tens of femtoseconds) hot electron decay times observed experimentally arise from electron-phonon scattering. This result is an important advance to resolve a controversy on hot electron cooling in GaAs. We further find that, contrary to common notions, all optical and acoustic modes contribute substantially to electron-phonon scattering, with a dominant contribution from transverse acoustic modes. This work provides definitive microscopic insight into hot electrons in GaAs and enables accurate ab initio computation of hot carriers in advanced materials.

  10. Selective Nucleation of GaAs on Si Nanofacets.

    PubMed

    Prieto, Ivan; Kozak, Roksolana; Skibitzki, Oliver; Rossell, Marta D; Schroeder, Thomas; Erni, Rolf; von Känel, Hans

    2017-06-01

    The early growth stage of GaAs by metal organic vapor phase epitaxy on a novel kind of Si substrate is investigated. The substrate consists of nanotips (NTs) fabricated on a Si(001) wafer by means of lithography and reactive ion etching. 3D GaAs nanocrystals are found to nucleate with a probability of 90% on the (n0m), (-n0m), (0nm), and (0-nm) facets (n, m integers) of these NTs. Additionally, in terms of nucleation yield, an average of 2 GaAs nanocrystals in each of those facets is observed. By contrast, facets of type {±nnm} remain virtually free of any 3D nuclei. A simple model based on the kinetics of the growth is used to explain the facet selective 3D nucleation. The model is consistent with a similar selectivity observed on micrometer-sized substrate features. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Carrier dynamics in GaAs photonic crystal cavities near the material band edge.

    PubMed

    Bose, Ranojoy; Pelc, Jason S; Vo, Sonny; Santori, Charles M; Beausoleil, Raymond G

    2015-05-18

    We measure fast carrier decay rates (6 ps) in GaAs photonic crystal cavities with resonances near the GaAs bandgap energy at room temperature using a pump-probe measurement. Carriers generated via photoexcitation using an above-band femtosecond pulse cause a substantial blue-shift of three time the cavity linewidth for the cavity peak. The experimental results are compared to theoretical models based on free carrier effects near the GaAs band edge. The probe transmission is modified by nearly 30% for an estimated above-band pump energy of 4.2 fJ absorbed in the GaAs slab.

  12. Advances in large-diameter liquid encapsulated Czochralski GaAs

    NASA Technical Reports Server (NTRS)

    Chen, R. T.; Holmes, D. E.; Kirkpatrick, C. G.

    1982-01-01

    The purity, crystalline perfection, and electrical properties of n- and p-type GaAs crystals grown by the liquid encapsulated Czochralski (LEC) technique are evaluated. The determination of the dislocation density, incidence of twinning, microstructure, background purity, mobility, and minority carrier diffusion length is included. The properties of the LEC GaAs crystals are generally comparable to, if not superior to those of small-diameter GaAs material grown by conventional bulk growth techniques. As a result, LEC GaAs is suitable for application to minority carrier devices requiring high-quality and large-area substrates.

  13. A 32-bit RISC Implemented in Enhancement-Mode JFET GaAs

    SciTech Connect

    Rasset, L.; Niederland, A.; Lane, J. A.; Geideman, W. A.

    1986-10-01

    Recently, considerable attention has been focused on gallium arsenide (GaAs) semiconductor process technologies for very high speed digital integrated circuits. This attention is motivated primarily by the ability of GaAs transistors to switch much faster with lower power consumption than transistors in silicon technologies. Soon to be available with higher switching speed and more transistors than the fastest silicon technology (emitter-coupled logic), GaAs digital ICs will be a boon to developers of super-computers and specialized high-speed microprocessors, such as digital signal processors. GaAs transistors are also much more resistant to temperature extremes and to ionizing radiation than silicon, important features for applications requiring operation in harsh environments. This does not mean that GaAs will replace silicon; rather, where the higher cost of GaAs is warranted by application requirements that only GaAs can satisfy, it will augment silicon. The high cost of GaAs chips is due mainly to the scarcity of gallium and the inferior quality and difficulty in manufacturing the gallium arsenide compound. Unlike silicon, which is very uniform and pure, GaAs has many defects and its characteristics may vary considerably from ingot to ingot, affecting yield. Also, the wafers have a tendency to break during processing.

  14. GAA triplet-repeats cause nucleosome depletion in the human genome.

    PubMed

    Zhao, Hongyu; Xing, Yongqiang; Liu, Guoqing; Chen, Ping; Zhao, Xiujuan; Li, Guohong; Cai, Lu

    2015-08-01

    Although there have been many investigations into how trinucleotide repeats affect nucleosome formation and local chromatin structure, the nucleosome positioning of GAA triplet-repeats in the human genome has remained elusive. In this work, the nucleosome occupancy around GAA triplet-repeats across the human genome was computed statistically. The results showed a nucleosome-depleted region in the vicinity of GAA triplet-repeats in activated and resting CD4(+) T cells. Furthermore, the A-tract was frequently adjacent to the upstream region of GAA triplet-repeats and could enhance the depletion surrounding GAA triplet-repeats. In vitro chromatin reconstitution assays with GAA-containing plasmids also demonstrated that the inserted GAA triplet-repeats destabilized the ability of recombinant plasmids to assemble nucleosomes. Our results suggested that GAA triplet-repeats have lower affinity to histones and can change local nucleosome positioning. These findings may be helpful for understanding the mechanism of Friedreich's ataxia, which is associated with GAA triplet-repeats at the chromatin level.

  15. Gate Drain Underlapped-PNIN-GAA-TFET for Comprehensively Upgraded Analog/RF Performance

    NASA Astrophysics Data System (ADS)

    Madan, Jaya; Chaujar, Rishu

    2017-02-01

    This work integrates the merits of gate-drain underlapping (GDU) and N+ source pocket on cylindrical gate all around tunnel FET (GAA-TFET) to form GDU-PNIN-GAA-TFET. It is analysed that the source pocket located at the source-channel junction narrows the tunneling barrier width at the tunneling junction and thereby enhances the ON-state current of GAA-TFET. Further, it is obtained that the GDU resists the extension of carrier density (built-up under the gated region) towards the drain side (under the underlapped length), thereby suppressing the ambipolar current and reducing the parasitic capacitances of GAA-TFET. Consequently, the amalgamated merits of both engineering schemes are obtained in GDU-PNIN-GAA-TFET that thus conquers the greatest challenges faced by TFET. Thus, GDU-PNIN-GAA-TFET results in an up-gradation in the overall performance of GAA-TFET. Moreover, it is realised that the RF figure of merits FOMs such as cut-off frequency (fT) and maximum oscillation frequency (fMAX) are also considerably improved with integration of source pocket on GAA-TFET. Thus, the improved analog and RF performance of GDU-PNIN-GAA-TFET makes it ideal for low power and high-speed applications.

  16. GaAs thin films and methods of making and using the same

    SciTech Connect

    Boettcher, Shannon; Ritenour, Andrew; Boucher, Jason; Greenaway, Ann

    2016-06-14

    Disclosed herein are embodiments of methods for making GaAs thin films, such as photovoltaic GaAs thin films. The methods disclosed herein utilize sources, precursors, and reagents that do not produce (or require) toxic gas and that are readily available and relatively low in cost. In some embodiments, the methods are readily scalable for industrial applications and can provide GaAs thin films having properties that are at least comparable to or potentially superior to GaAs films obtained from conventional methods.

  17. Phytosanitary Irradiation

    PubMed Central

    Hallman, Guy J.; Blackburn, Carl M.

    2016-01-01

    Phytosanitary treatments disinfest traded commodities of potential quarantine pests. Phytosanitary irradiation (PI) treatments use ionizing radiation to accomplish this, and, since their international commercial debut in 2004, the use of this technology has increased by ~10% annually. Generic PI treatments (one dose is used for a group of pests and/or commodities, although not all have been tested for efficacy) are used in virtually all commercial PI treatments, and new generic PI doses are proposed, such as 300 Gy, for all insects except pupae and adult Lepidoptera (moths). Fresh fruits and vegetables tolerate PI better than any other broadly used treatment. Advances that would help facilitate the use of PI include streamlining the approval process, making the technology more accessible to potential users, lowering doses and broadening their coverage, and solving potential issues related to factors that might affect efficacy. PMID:28231103

  18. Hopping conduction and its photoquenching in molecular beam epitaxial GaAs grown at low temperatures

    SciTech Connect

    Fang, Z.Q.; Look, D.C.

    1993-12-01

    As the growth temperature of molecular beam epitaxial GaAs is increased from 250 to 400{degrees}C, the dominant conduction changes from hopping conduction to band conduction with a donor activation energy of 0.65 eV. A 300{degrees}C grown layer is especially interesting because each conduction mechanism is dominant in a particular temperature range, hopping below 300K and band conduction above. Below 140K, the hopping conduction is greatly diminished (quenched) by irradiation with either infrared (hv {le} 1.12 eV) or 1.46 eV light, but then recovers above 140K with exactly the same thermal kinetics as are found for the famous EL2. Thus, the 0.65 eV donor, which is responsible for both the hopping and band conduction, is very similar to EL2, but not identical because of the different activation energy (0.65 eV vs 0.75 eV for EL2). 12 refs., 4 figs.

  19. Electrical and structural characterization of GaAs on InP grown by OMCVD; application to GaAs MESFETs

    NASA Astrophysics Data System (ADS)

    Azoulay, R.; Clei, A.; Dugrand, L.; Draïdia, auN.; Leroux, G.; Biblemont, S.

    1991-01-01

    The growth of GaAs on InP has attracted considerable interest recently because of the possibility of integration of GaAs electronic devices and 1.3 μm optical devices on the same wafer. In this work, we have investigated the growth of GaAs MESFETs and doped channel MIS-like FETs on InP by atmospheric pressure OMCVD. Because of the difference between the thermal expansion coefficient of GaAs and InP, the layers are under biaxial strain. The lowest FWHM of the (004) reflection curve of the double crystal X-ray diffraction spectra is 110 arc sec for a 12 μm thick layer. We have investigated the influence of the substrate temperature and of the arsine molar fraction on the residual carrier concentration of layers grown side by side on GaAs and on InP. The GaAs layers grown on InP are much more compensated than the layers grown on GaAs, indicating a higher incorporation of impurities. On MESFETs grown on InP, gm = 200mS/mm with Fmax higher than 30 GHz. On doped-channel MIS-like FETs on InP, we have measured gm = 145mS/mm.

  20. Laser diodes employing GaAs1-x Bi x /GaAs1-y P y quantum well active regions

    NASA Astrophysics Data System (ADS)

    Kim, Honghyuk; Guan, Yingxin; Forghani, Kamran; Kuech, Thomas F.; Mawst, Luke J.

    2017-07-01

    Laser diodes employing strain-compensated GaAs1-x Bi x /GaAs1-y P y quantum well (QW) active regions were grown by metalorganic vapor phase epitaxy (MOVPE). High resolution x-ray diffraction, room temperature photoluminescence, and in situ optical reflectance monitoring during the MOVPE growth provided valuable feedback for the optimization of the material growth conditions. In addition, the post-growth in situ thermal annealing was employed to improve the radiative efficiency of the GaAs1-x Bi x /GaAs1-y P y QW structures. Wide ridge waveguide lasers with GaAs barriers exhibited high threshold current densities (J th ˜ 8 kA cm-2), excessive band-filling, and carrier leakage at room temperature, resulting in the lasing from a high energy transition. By contrast, devices employing GaAs1-y P y barriers exhibited significantly lower threshold current densities (J th ˜ 5.9 kA cm-2), and longer wavelength QW emission, presumably as a result of improved active region carrier confinement. Devices with GaAs0.8P0.2 barriers after the post-growth thermal annealing exhibited further reduced threshold current density (J th ˜ 4.1 kA cm-2).

  1. DLTS Measurement on Electron-Irradiated GaAs-on-Si

    NASA Astrophysics Data System (ADS)

    Okamoto, Hiroshi; Oh'hara, Takahiko; Kadota, Yoshiaki; Ohmachi, Yoshiro

    1990-06-01

    Three electron traps, E3*, E4*, and E5*, are observed in 1 MeV-electron-irradiated GaAs-on-Si by using DLTS measurement. The characteristics of these traps are similar to those of E3, E4, and E5 in irradiated GaAs-on-GaAs. The slightly lower activation energies and broader DLTS peaks of the traps in GaAs-on-Si than those in GaAs-on-GaAs might be caused by band-gap decrease and valence-band splitting of biaxially strained GaAs on Si.

  2. Laser biostimulation (Ne-He and Ga-As) effects as compared to the conventional therapy in several pelvic inflammatory diseases

    NASA Astrophysics Data System (ADS)

    Antipa, Ciprian; Dona, Dumitru; Podoleanu, Adrian Gh.; Crisan, Nicolae; Constantinescu, Camelia

    1993-05-01

    We studied the effects of the very low-power Gallium-Arsenic infrared semiconductor laser and low-power Helium-Neon laser irradiation, single or in combination, compared to the placebo and conventional therapy on the recovery of 118 female patients from our hospital with the diagnosis of chronic pelvic inflammatory disorders. Laser biostimulation therapy proved to be significantly more efficient as compared with placebo or conventional therapy. The most efficient of all kinds of irradiations was the combination between He-Ne and Ga-As (laserpuncture and scanning). After laser treatments we didn't find any significant local genital changes both at the bimanual examination (except provoked pain), and at the echographical examination. Soft and very low-power laser therapy can be a useful alternative to the conventional treatments for pelvic inflammatory diseases.

  3. (AlAs) {1}/{2}(GaAs) {1}/{2} Fractional-layer superlattices grown on (001) vicinal GaAs substrates by MOCVD

    NASA Astrophysics Data System (ADS)

    Fukui, T.; Saito, H.; Tokura, Y.; Tsubaki, K.; Susa, N.

    1990-04-01

    (AlAs) {1}/{2}(GaAs) {1}/{2} fractional-layer superlattices (FLSs) with a new periodicity perpendicular to the growth direction are successfully grown by metal-organic chemical vapor deposition on GaAs(001) substrates slightly misoriented towards [1¯10]. The superlattice images are clearly observed by transmission electron microscopy, which shows that the superlattice periods are almost uniform everywhere. Optical properties of GaAs quantum well wire arrays using FLSs are also studied, and the interface mixing layer thicknesses arc estimated.

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

    NASA Astrophysics Data System (ADS)

    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.

  5. THz conductivity of semi-insulating and magnetic CoFe2O4 nano-hollow structures through thermally activated polaron

    NASA Astrophysics Data System (ADS)

    Rakshit, Rupali; Serita, Kazunori; Tonouchi, Masayoshi; Mandal, Kalyan

    2016-11-01

    Herein, terahertz (THz) time domain spectroscopy is used to measure the complex conductivity of semi-insulating CoFe2O4 nanoparticles (NPs) and nano-hollow spheres (NHSs) with different diameters ranging from 100 to 350 nm having a nanocrystalline shell thickness of 19 to 90 nm, respectively. Interestingly, the magnitude of conductivity for CoFe2O4 NPs and NHSs of same average diameter (˜100 nm) for a given frequency of 0.3 THz is found to be 0.33 S/m and 9.08 S/m, respectively, indicating that the hollow structure exhibits greater THz conduction in comparison to its solid counterpart. Moreover, THz conductivity can be tailored by varying the nano-shell thickness of NHSs, and a maximum conductivity of 15.61 S/m is observed at 0.3 THz for NHSs of average diameter 250 nm. A detailed study reveals that thermally activated polaronic hopping plays the key role in determining the electrical transport property of CoFe2O4 nanostructures, which is found to solely depend on their magnitude of THz absorptivity. The non-Drude conductivity of all CoFe2O4 nanostructures is well described by the Polaron model instead of the Drude-Smith model, which is relevant for backscattering of free electrons in a nanostructured material. The Polaron model includes intra-particle and interparticle polaronic conductivities for closely spaced magnetic nanostructures and provides a mean free path of 29 nm for CoFe2O4 NPs of diameter 100 nm, which is comparable with its average crystallite size, indicating the applicability of the developed model for nanomaterials where charge transport is determined by polaronic hopping. Finally, we have demonstrated the morphology and size dependent magnetic measurements of ferrimagnetically aligned CoFe2O4 nanostructures through a vibrating sample magnetometer in the temperature range of 80-250 K, revealing that the disordered surface spin layer of nanostructures significantly controls their magnetism.

  6. The Automated DC Parameter Testing of GaAs MESFETs Using the Singer Automatic Integrated Circuit Test System.

    DTIC Science & Technology

    1980-09-01

    Equivalent GaAs MESFET Circuit Model 37 11 Hower’s Equivalent GaAs MESFET Circuit Model 38 12 Modified DC Equivalent Circuit Model of...I Truth Table for the GaAs MESFET Logic Gate of Figure 1 29 II Equivalent - Circuit Parameters of a GaAs MESFET with a 1 micron x 500 micron Gate 39...using Schottky diodes in the output buffer circuit . The number of diodes required is determined by the pinchoff voltage of the

  7. Effect of high energy proton irradiation on InAs/GaAs quantum dots: Enhancement of photoluminescence efficiency (up to {approx}7 times) with minimum spectral signature shift

    SciTech Connect

    Sreekumar, R.; Mandal, A.; Gupta, S.K.; Chakrabarti, S.

    2011-11-15

    Graphical abstract: Authors demonstrate enhancement in photoluminescence efficiency (7 times) in single layer InAs/GaAs quantum dots using proton irradiation without any post-annealing treatment via either varying proton energy (a) or fluence (b). The increase in PL efficiency is explained by a proposed model before (c) and after irradiation (d). Highlights: {yields} Proton irradiation improved PL efficiency in InAs/GaAs quantum dots (QDs). {yields} Proton irradiation favoured defect and strain annihilation in InAs/GaAs QDs. {yields} Reduction in defects/non-radiative recombination improved PL efficiency. {yields} Protons could be used to improve PL efficiency without spectral shift. {yields} QD based devices will be benefited by this technique to improve device performance. -- Abstract: We demonstrate 7-fold increase of photoluminescence efficiency in GaAs/(InAs/GaAs) quantum dot hetero-structure, employing high energy proton irradiation, without any post-annealing treatment. Protons of energy 3-5 MeV with fluence in the range (1.2-7.04) x 10{sup 12} ions/cm{sup 2} were used for irradiation. X-ray diffraction analysis revealed crystalline quality of the GaAs cap layer improves on proton irradiation. Photoluminescence study conducted at low temperature and low laser excitation density proved the presence of non-radiative recombination centers in the system which gets eliminated on proton irradiation. Shift in photoluminescence emission towards higher wavelength upon irradiation substantiated the reduction in strain field existed between GaAs cap layer and InAs/GaAs quantum dots. The enhancement in PL efficiency is thus attributed to the annihilation of defects/non-radiative recombination centers present in GaAs cap layer as well as in InAs/GaAs quantum dots induced by proton irradiation.

  8. Implementation and Performance of GaAs Digital Signal Processing ASICs

    NASA Technical Reports Server (NTRS)

    Whitaker, William D.; Buchanan, Jeffrey R.; Burke, Gary R.; Chow, Terrance W.; Graham, J. Scott; Kowalski, James E.; Lam, Barbara; Siavoshi, Fardad; Thompson, Matthew S.; Johnson, Robert A.

    1993-01-01

    The feasibility of performing high speed digital signal processing in GaAs gate array technology has been demonstrated with the successful implementation of a VLSI communications chip set for NASA's Deep Space Network. This paper describes the techniques developed to solve some of the technology and implementation problems associated with large scale integration of GaAs gate arrays.

  9. Effect of melt stoichiometry on twin formation in LEC GaAs. [Liquid Encapsulated Czochralski technique

    NASA Technical Reports Server (NTRS)

    Chen, R. T.; Holmes, D. E.

    1982-01-01

    It is shown that the incidence of twin formation in large diameter, undoped, (100) LEC GaAs is reduced when the melt composition is slightly As-rich. Twenty GaAs crystals were grown from stoichiometric and nonstoichiometric melts. The results suggest that the barrier to twin formation is related to the stoichiometry of the solid at the solidification front.

  10. Diffused P+-N solar cells in bulk GaAs

    NASA Technical Reports Server (NTRS)

    Borrego, J. M.; Ghandhi, S. K.

    1982-01-01

    Recently melt grown GaAs, made by liquid encapsulation techniques, has become available. This material is of sufficiently good quality to allow the fabrication of solar cells by direct diffusion. Results obtained with p(+)/n junction solar cells made by zinc diffusion are described. The quality of bulk GaAs for this application is evaluated.

  11. Matrix-vector multiplication in thin photorefractive GaAs crystals

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Gheen, Gregory

    1988-01-01

    Optical matrix-vector multiplication using four-wave mixing in a thin photorefractive GaAs crystal is demonstrated. Using a thin wafer of GaAs offers the potential to integrate the encoding spatial light modulators directly on the wave-mixing medium.

  12. Measurement of charge limit in a strained lattice GaAs photocathode

    SciTech Connect

    Saez, P.; Alley, R.; Aoyagi, H.

    1993-04-01

    The SLAC Linear Collider (SLC) Polarized Electron Source (PES) photocathodes have shown a charge saturation when illuminated with a high intensity laser pulse. This charge limit in the cesium-activated GaAs crystal seems to be strongly dependent on its surface condition and on the incident light wavelength. Charge limit studies with highly polarized strained lattice GaAs materials are presented.

  13. Optical processing using photorefractive GaAs and InP

    NASA Technical Reports Server (NTRS)

    Liu, Duncan T. H.; Cheng, Li-Jen; Luke, Keung L.

    1991-01-01

    The unique features of photorefractive compound semiconductors are presented. The advantages of this class of nonlinear optical materials for optical processing are illustrated with examples using GaAs and InP. The difference between GaAs and InP in the laser power density requirement is discussed.

  14. Ka-band propagation characteristics of microstrip lines on GaAs substrates at cryogenic temperatures

    NASA Technical Reports Server (NTRS)

    Romanofsky, R. R.; Martinez, J. C.; Viergutz, B. J.; Bhasin, K. B.

    1990-01-01

    Effective permitivity and loss characteristics of gold microstrip lines on GaAs substrates were obtained by characterizing GaAs linear resonators at cryogenic temperatures (300 to 20 K) from 30-40 GHz. A slight decrease in effective permittivity and a significant reduction in loss were observed with lower temperatures.

  15. 46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

  16. 46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

  17. 46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia... General Agency operations not related to the current GAA/MSTS Southeast Asia Program, NSA Order 35 (OPR-2... lieu of those appearing in sections 3 and 4 of NSA Order 35 (OPR-2). Continental United States ports do...

  18. Implementation and Performance of GaAs Digital Signal Processing ASICs

    NASA Technical Reports Server (NTRS)

    Whitaker, William D.; Buchanan, Jeffrey R.; Burke, Gary R.; Chow, Terrance W.; Graham, J. Scott; Kowalski, James E.; Lam, Barbara; Siavoshi, Fardad; Thompson, Matthew S.; Johnson, Robert A.

    1993-01-01

    The feasibility of performing high speed digital signal processing in GaAs gate array technology has been demonstrated with the successful implementation of a VLSI communications chip set for NASA's Deep Space Network. This paper describes the techniques developed to solve some of the technology and implementation problems associated with large scale integration of GaAs gate arrays.

  19. Matrix-vector multiplication in thin photorefractive GaAs crystals

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Gheen, Gregory

    1988-01-01

    Optical matrix-vector multiplication using four-wave mixing in a thin photorefractive GaAs crystal is demonstrated. Using a thin wafer of GaAs offers the potential to integrate the encoding spatial light modulators directly on the wave-mixing medium.

  20. Optical processing using photorefractive GaAs and InP

    NASA Technical Reports Server (NTRS)

    Liu, Duncan T. H.; Cheng, Li-Jen; Luke, Keung L.

    1991-01-01

    The unique features of photorefractive compound semiconductors are presented. The advantages of this class of nonlinear optical materials for optical processing are illustrated with examples using GaAs and InP. The difference between GaAs and InP in the laser power density requirement is discussed.

  1. Spatial light modulation by beam coupling in GaAs crystals

    NASA Technical Reports Server (NTRS)

    Cheng, Li-Jen; Gheen, Gregory; Chao, Tien-Hsin; Liu, Hua-Kuang; Partovi, Ashfin

    1987-01-01

    The first demonstration of spatial light modulation in GaAs using the photorefractive effect is reported. A special configuration was employed in which polarization rotation created by beam coupling was utilized. The ability to obtain these results despite a small coupling gain coefficient demonstrates the usefulness of the polarization technique presented here for optical processing with GaAs crystals.

  2. Use of Irradiated Foods

    NASA Technical Reports Server (NTRS)

    Brynjolfsson, A.

    1985-01-01

    The safety of irradiated foods is reviewed. Guidelines and regulations for processing irradiated foods are considered. The radiolytic products formed in food when it is irradiated and its wholesomeness is discussed. It is concluded that food irradiation processing is not a panacea for all problems in food processing but when properly used will serve the space station well.

  3. Use of Irradiated Foods

    NASA Technical Reports Server (NTRS)

    Brynjolfsson, A.

    1985-01-01

    The safety of irradiated foods is reviewed. Guidelines and regulations for processing irradiated foods are considered. The radiolytic products formed in food when it is irradiated and its wholesomeness is discussed. It is concluded that food irradiation processing is not a panacea for all problems in food processing but when properly used will serve the space station well.

  4. Perpendicular magnetic properties of CoCr films on GaAs

    NASA Astrophysics Data System (ADS)

    Manago, T.; Kuramochi, H.; Akinaga, H.

    2005-01-01

    CoCr films were deposited on three types of GaAs substrates, GaAs(001), GaAs(111), and Al oxide/GaAs(001). The perpendicular magnetic properties were investigated by magneto-optical Kerr-effect measurements. The direct deposition of the CoCr film on the GaAs substrate did not show any perpendicular magnetic properties. This fact indicates that the lattice distortion influenced by the GaAs lattice suppresses the perpendicular magnetism. The CoCr film on the Al oxide layer showed a tilted squarelike hysteresis loop. The thickness dependence of the hysteresis loop and the magnetic force microscopy showed that the onset thickness of ferromagnetism was 6.5nm. The domain size of the CoCr films monotonously decreases with the increasing thickness (6.5-75nm).

  5. GaAs nanowires on Si substrates grown by a solid source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Ihn, Soo-Ghang; Song, Jong-In; Kim, Young-Hun; Lee, Jeong Yong

    2006-07-01

    High-quality Au-catalyzed GaAs nanowires were grown on Si substrates by vapor-liquid-solid growth in a solid source molecular beam epitaxy system. X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy reveal that the GaAs nanowires were epitaxially grown on Si substrates with uniform diameters along the nanowires. While GaAs nanowires on Si(111) and (001) substrates were mainly grown along the ⟨111⟩ direction with zinc-blende and wurtzite structures, unusual GaAs nanowires grown along ⟨001⟩ with a pure zinc-blende structure were also observed. Strong photoluminescence was observed from GaAs nanowires grown on a Si(001) substrate at room temperature.

  6. Controlling crystal phases in GaAs nanowires grown by Au-assisted molecular beam epitaxy.

    PubMed

    Dheeraj, D L; Munshi, A M; Scheffler, M; van Helvoort, A T J; Weman, H; Fimland, B O

    2013-01-11

    Control of the crystal phases of GaAs nanowires (NWs) is essential to eliminate the formation of stacking faults which deteriorate the optical and electronic properties of the NWs. In addition, the ability to control the crystal phase of NWs provides an opportunity to engineer the band gap without changing the crystal material. We show that the crystal phase of GaAs NWs grown on GaAs(111)B substrates by molecular beam epitaxy using the Au-assisted vapor-liquid-solid growth mechanism can be tuned between wurtzite (WZ) and zinc blende (ZB) by changing the V/III flux ratio. As an example we demonstrate the realization of WZ GaAs NWs with a ZB GaAs insert that has been grown without changing the substrate temperature.

  7. Comparative research on activation technique for GaAs photocathodes

    NASA Astrophysics Data System (ADS)

    Chen, Liang; Qian, Yunsheng; Chang, Benkang; Chen, Xinlong; Yang, Rui

    2012-03-01

    The properties of GaAs photocathodes mainly depend on the material design and activation technique. In early researches, high-low temperature two-step activation has been proved to get more quantum efficiency than high-temperature single-step activation. But the variations of surface barriers for two activation techniques have not been well studied, thus the best activation temperature, best Cs-O ratio and best activation time for two-step activation technique have not been well found. Because the surface photovoltage spectroscopy (SPS) before activation is only in connection with the body parameters for GaAs photocathode such as electron diffusion length and the spectral response current (SRC) after activation is in connection with not only body parameters but also surface barriers, thus the surface escape probability (SEP) can be well fitted through the comparative research between SPS before activation and SEP after activation. Through deduction for the tunneling process of surface barriers by Schrödinger equation, the width and height for surface barrier I and II can be well fitted through the curves of SEP. The fitting results were well proved and analyzed by quantitative analysis of angle-dependent X-ray photoelectron spectroscopy (ADXPS) which can also study the surface chemical compositions, atomic concentration percentage and layer thickness for GaAs photocathodes. This comparative research method for fitting parameters of surface barriers through SPS before activation and SRC after activation shows a better real-time in system method for the researches of activation techniques.

  8. High-gain GaAs MSM photodetector

    NASA Astrophysics Data System (ADS)

    Karulkar, V. T.; Purandare, S. C.; Srivastava, Atul K.; Arora, B. M.

    1992-12-01

    Photodetectors with metal-semiconductor -metal (MSM) structures having very high quan turn efficiency are investigated to identify the gain mechanism. From the temperature dependence studies impact ionisation of carriers in a region under the edge of the cathode is shown to be the predominant gain mechanism. Metal-Semiconductors-Metal (MSM) structure has recently emerged" 2 as an attractive device for photodetection due to its simple planar tech nology which can be easily adapted to optoelec tronic integration. The other features of MSM photodetector are their high sensitivity, low capacitance, low dark current and high speed. Substatial amount of work has been done on GaAs MSM photodiodes which are useful in near infrared wavelength regime. Devices with very low dark current (lOOpA at 1OV for 200x200pm geometry) and low rise and fall times (23 and 55 ps respecti vely) have been recently fabricated on semi-insu lating (SI) GaAs substrates1. The other interest ing feature of MSM structure is that it has in ternal gain. Despite intensive study of these devices there is still confusion about the physi cal origin of the gain in these devices. Ito et a13 attribute the gain to hole injection at the forward biased anode contact. Measurements of Zirngibl et al however, point to avalanche mechanism of gain in these devices. In this paper we report the results of experimental in vestigation of gain mechanism in GaAs MSM struc tures which have extremely high gain (100).

  9. Chemical investigations of GaAs wafer bonded interfaces

    NASA Astrophysics Data System (ADS)

    Hansen, D. M.; Albaugh, C. E.; Moran, P. D.; Kuech, T. F.

    2001-12-01

    The bonding chemistry of various GaAs-to-oxide/GaAs bonded samples was investigated using multiple internal transmission Fourier transform infrared spectroscopy for thermally annealed and thermocompression annealed samples. The oxides used in these investigations included a native GaAs oxide as well as two compositions of borosilicate glass (BSG) deposited by low-pressure chemical vapor deposition (LPCVD). For the thermally annealed samples, the hydrogen-bonded H2O/OH groups on the hydrophilic surface form a room temperature bond without the application of pressure. Chemical changes at the wafer-bonded interface occur in two temperature regions. For anneals between 200 and 400 °C for 1 h in N2, the H2O/OH groups react and evolve H that becomes absorbed within the oxide. The LPCVD BSG oxide was chemically unaltered during anneals in this temperature range, however, the GaAs native oxide underwent chemical modification. Initially, the GaAs oxide consisted of As(III)-O and Ga-O related oxides. The As(III)-O oxides react to form free As and Ga-O during annealing between 200 and 400 °C. For anneals between 500 and 600 °C, the reaction of H2O/OH groups continue and the H becomes infrared inactive, most likely forming H2 voids at the bonded interface. In addition, As(V)-O related oxides were observed during thermal annealing in this temperature range. No detectable chemical changes in the BSG were observed over the temperature range investigated. Samples that were annealed under an estimated 1-10 MPa of pressure had similar chemical changes to thermally annealed samples.

  10. Detection of irradiated liquor

    NASA Astrophysics Data System (ADS)

    Shengchu, Qi; Jilan, Wu; Rongyao, Yuan

    D-2,3-butanediol is formed by irradiation processes in irradiated liquors. This radiolytic product is not formed in unirradiated liquors and its presence can therefore be used to identify whether a liquor has been irradiated or not. The relation meso/dl≈1 for 2,3-butanediol and the amount present in irradiated liquors may therefore be used as an indication of the dose used in the irradiation.

  11. A first principles study of the lattice stability of diamond-structure semiconductors under intense laser irradiation

    SciTech Connect

    Feng Shiquan; Zhao Jianling; Cheng Xinlu

    2013-01-14

    Using density-functional linear-response theory, we calculated the phonon dispersion curves for the diamond structural elemental semiconductors of Ge, C and zinc-blende structure semiconductors of GaAs, InSb at different electronic temperatures. We found that the transverse-acoustic phonon frequencies of C and Ge become imaginary as the electron temperature is elevated, which means the lattices of C and Ge become unstable under intense laser irradiation. These results are very similar with previous theoretical and experimental results for Si. For GaAs and InSb, not only can be obtained the similar results for their transverse-acoustic modes, but also their LO-TO splitting gradually decreases as the electronic temperature is increased. It means that the electronic excitation weakens the strength of the ionicity of ionic crystal under intense laser irradiation.

  12. Regrowth mechanism for oxide isolation of GaAs nanowires.

    PubMed

    Dvorak, David; Darbandi, Ali; Kavanagh, Karen L; Watkins, Simon P

    2017-09-20

    Oxide-isolated GaAs nanowires (NWs) were obtained through a lithography-free method in which axial growth of NWs coated in aluminum oxide (Al2O3) is restarted using an annealing step. NWs are grown using the vapor-liquid-solid method and coated in nanometer thin oxide films using atomic layer deposition. Continued growth at the oxide-coated nanoparticle (NP) occurs after the thermally-induced fracture of the oxide during annealing. This oxide fracture is observed to depend on NP diameter, oxide thickness and annealing temperature. A thermal expansion mismatch model for stresses on the oxide shell is put forward to explain these results.

  13. Regrowth mechanism for oxide isolation of GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Dvorak, David; Darbandi, Ali; Kavanagh, Karen L.; Watkins, Simon P.

    2017-09-01

    Oxide-isolated GaAs nanowires (NWs) were obtained through a lithography-free method in which axial growth of NWs coated in aluminum oxide (Al2O3) is restarted using an annealing step. NWs are grown using the vapor–liquid–solid method and coated in nanometer thin oxide films using atomic layer deposition. Continued growth at the oxide-coated nanoparticle (NP) occurs after the thermally-induced fracture of the oxide during annealing. This oxide fracture is observed to depend on NP diameter, oxide thickness and annealing temperature. A thermal expansion mismatch model for stresses on the oxide shell is put forward to explain these results.

  14. Investigation of Optically Induced Avalanching in GaAs

    DTIC Science & Technology

    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

  15. Coupling reactions of trifluoroethyl iodide on GaAs(100)

    NASA Astrophysics Data System (ADS)

    Singh, N. K.; Kemp, N. T.; Paris, N.; Balan, V.

    2004-07-01

    We report on the reactions of 2-iodo-1,1,1-trifluoroethane (CF3CH2I) on gallium-rich GaAs(100)-(4×1), studied using the techniques of temperature programmed desorption and x-ray photoelectron spectroscopy. The study is to provide evidence for the formation of a higher fluorinated alkene, 1,1,4,4,4-pentafluoro-1-butene (CF2=CHCH2CF3) and alkane, 1,1,1,4,4,4-hexafluorobutane (CF3CH2CH2CF3) from the coupling reactions of covalently bonded surface alkyl (CF3CH2•) moieties. CF3CH2I adsorbs nondissociatively at 150 K. Thermal dissociation of this weakly chemisorbed state occurs below room temperature to form adsorbed CF3CH2• and I• species. The surface CF3CH2• species undergoes β-fluoride elimination to form gaseous CF2=CH2 and this represents the major pathway for the removal of CF3CH2• species from the surface. In competition with the β-fluoride elimination process the adsorbed CF3CH2• species also undergoes, recombination with surface iodine atoms to form recombinative molecular CF3CH2I, olefin insertion reaction with CF2=CH2 to form gaseous CF2=CHCH2CF3, and last self-coupling reaction to form CF3CH2CH2CF3. The adsorbed surface iodine atoms, formed by the dissociation of the molecularly chemisorbed CF3CH2I, and fluorine atoms formed during the β-fluoride elimination reaction, both form etch products (GaI, GaF, AsI, AsF, and As2) by their reactions with the surface layer Ga atoms, subsurface As atoms, and GaAs substrate. In this article we discuss the mechanisms by which these products form from the adsorbed CF3CH2• and I• species, and the role that the GaAs surface plays in the proposed reaction pathways. We compare the reactivity of the GaAs surface with transition metals in its ability to facilitate dehydrogenation and coupling reactions in adsorbed alkyl species. .

  16. GaAs vapor-grown bipolar transistors.

    NASA Technical Reports Server (NTRS)

    Nuese, C. J.; Gannon, J. J.; Dean, R. H.; Gossenberger, H. F.; Enstrom, R. E.

    1972-01-01

    Discussion of an approach for the fabrication of high-temperature GaAs transistors which is centered on the preparation of n-p-n three-layered structures entirely by a vapor-phase growth technique, as described by Tietjen and Amick (1966). The low growth temperature of approximately 750 C is thought to reduce contamination during crystal growth and to contribute to the reasonably high minority-carrier lifetimes obtained for the vapor-grown p-n junctions. The fact that impurity concentrations and layer thicknesses can be precisely controlled for epitaxial layers as thin as 1 micrometer is an important feature of this growth technique.

  17. CO2 laser waveguiding in proton implanted GaAs

    NASA Technical Reports Server (NTRS)

    Jenkinson, H. A.; Larson, D. C.

    1981-01-01

    Surface layers capable of supporting optical modes at 10.6 microns have been produced in n-type GaAs wafers through 300 keV proton implantation. The dominant mechanism for this effect appears to be free carrier compensation. Characterization of the implanted layers by analysis of infrared reflectivity spectra and synchronous coupling at 10.6 microns produced results in good agreement with elementary models. These results of sample characterization by infrared reflectivity and by CO2 laser waveguiding as implanted are presented and evaluated.

  18. New shallow acceptor levels in GaAs

    NASA Astrophysics Data System (ADS)

    Skromme, B. J.; Bose, S. S.; Stillman, G. E.

    1986-11-01

    Two previously unreported shallow acceptor levels with ionization energies of 25.2 and 43.2 meV, respectively, have been observed in a number of vapor phase epitaxial and metalorganic chemical vapor deposited GaAs samples grown in several different laboratories. The corresponding donor-to-acceptor and conduction band-to-acceptor transitions are identified in low temperature photoluminescence spectra by means of their temperature and excitation intensity-dependence. These levels are present as residual acceptors in high purity material, but their chemical and/or metallurgical nature has not yet been determined.

  19. Electronic properties of delta -doped GaAs

    NASA Astrophysics Data System (ADS)

    Gold, A.; Ghazali, A.; Serre, J.

    1992-07-01

    For temperature zero the authors study the effects of disorder on the electronic properties of the two-dimensional electron gas which exists in planar-doped ( delta -doped) GaAs. The density of states, the Fermi level, the single-particle relaxation time and the electron mobility are calculated as functions of the dopant concentration. The transition from a band tail to an impurity band and the nature of the metal-insulator transition are discussed. The authors compare the theoretical results on the mobility with some available experimental data.

  20. High-Speed GaAs MESFET Memory Study.

    DTIC Science & Technology

    1981-07-01

    ne .. ’ a-d Id,devt h ,, 1 nu-.4511) Semiconductor Memory Enhancement-Mode MESFET Random Access Memory (RAM) GaAs Integrated Circuits (ICs) 4aAs...differential is reached. Figure 2-5 is a differential amplifier with a gain of %20 ( determined bv the gm.R 0 product of the FETs). This circuit has been...Write Mode Figure 2-9 shows the circuit that was Simulated to determine the transient write-mode reset response. The capacitors CB and CBB (0.2 pF each