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Sample records for semiinsulating gaas irradiated

  1. 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.

  2. 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. PMID:26421576

  3. 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.

  4. The influence of high-energy electrons irradiation on the electrical properties of Schottky barrier detectors based on semi-insulating GaAs

    NASA Astrophysics Data System (ADS)

    Zatko, B.; Sagatova, A.; Bohacek, P.; Sedlackova, K.; Sekacová, M.; Arbet, J.; Necas, V.

    2016-01-01

    In this work we fabricated detectors based on semi-insulating GaAs and studied their electrical properties (current-voltage characteristics, galvanomagnetic measurements) after irradiation with 5 MeV electrons from a linear accelerator up to a dose of 104 kGy. A series of detectors were prepared using Ti/Pt/Au Schottky contact with 1 mm diameter. The thickness of the base material was about 230 μm. A whole area Ni/AuGe/Au ohmic contact was evaporated on the back side. For galvanomagnetic measurements we used three samples from the same wafer. All samples were irradiated by a pulse beam of 5 MeV electrons using the linear accelerator in 11 steps, where the accumulative dose increased from 1 kGy up to 104 kGy. Also different dose rates (20, 40 and 80 kGy/h) were applied to the samples. After each irradiation step we performed electrical measurement of each sample. We analyze the electron Hall mobility, resistivity, electron Hall concentration, breakdown voltage and reverse current of samples before and after irradiation using different dose rates.

  5. GaAs Semi-Insulating Layer for a GaAs Device

    NASA Technical Reports Server (NTRS)

    Sherrill, G.; Mattauch, R. J.

    1986-01-01

    Improved design for GaAs electronic device or integrated circuit designed to operate at cryogenic temperatures, customary SiO2 insulating layer replaced by semi-insulating layer of GaAs. Thermal expansions of device and covering layer therefore match closely, and thermal stresses caused by immersion in cryogenic chamber nearly eliminated.

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

    SciTech Connect

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

    2014-02-10

    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 (10{sup 14} ions/cm{sup 2}) 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.

  7. Micro-inhomogeneity effects and radiation damage in semi-insulating GaAs radiation detectors

    SciTech Connect

    Bates, R.; O`Shea, V.; Raine, C.; Smith, K.M.; Didziulis, R.; Kazukauskas, V.; Rinkevicius, V.; Storasta, J.; Vaitkus, J.

    1998-06-01

    Thermally-stimulated current (TSC) measurements and a detailed analysis of current-voltage (I-V) characteristics have been made on semi-insulating GaAs (SI-GaAs) Schottky diode particle detectors, fabricated on substrates from several supplies, before and after irradiation with 24 GeV protons and 300 MeV pions. The analysis of I-V characteristics allows the determination of the barrier height and bulk resistance in detectors. Changes observed in I-V characteristics and TSC spectra after irradiation are described and a dislocation-net model of radiation-damaged devices is proposed.

  8. 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. PMID:25401668

  9. 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).

  10. 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.

  11. 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.

  12. 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.

  13. Nonlinear transport of semi-insulating GaAs in a semiconductor gas discharge structure

    NASA Astrophysics Data System (ADS)

    Yücel Kurt, H.; Salamov, B. G.

    2007-12-01

    Nonlinear transport of a semi-insulating (SI) GaAs photodetector in a semiconductor gas discharge structure (SGDS) is studied experimentally for a wide range of gas pressures p, interelectrode distances d and different diameters D of the detector areas. While being driven with a stationary voltage, the system generates current and discharge light emission (DLE) instabilities with different amplitudes of the oscillations. The transformation of the profile and amplitude of the current density of the filaments in the different regions of the current-voltage characteristic (CVC) has been studied. Instabilities of spatially non-uniform distributions resulting in the formation of multiple current filaments with increasing voltages above the critical values have been observed. It is shown that the interelectrode distance only plays a passive role and is not responsible for the appearance of the DLE instability under the experimental conditions. At the same time, the expanded range of current and DLE oscillations are observed for different diameters D of the infrared (IR) photodetector areas. An SGDS with an N-shaped CVC is analysed using both the current and DLE data which show the electrical instability in the GaAs photodetector. It is found that the application of high feeding voltage to this photodetector gives rise to a non-uniform spatial distribution of the DLE, which disturbs the operation of the system. The experiment also presents a new method to study and visualize the electrical instabilities in a high-resistivity IR photodetector of large diameter.

  14. High resolution scanning photoluminescence characterization of semi-insulating GaAs using a laser scanning microscope

    NASA Astrophysics Data System (ADS)

    Marek, J.; Elliot, A. G.; Wilke, V.; Geiss, R.

    1986-12-01

    Spatially resolved photoluminescence properties of semi-insulating, liquid encapsulated Czochralski-grown GaAs substrates are analyzed with a laser scanning microscope. The improved resolution of the laser scanning microscope results in the observation of single dislocations within the subgrain boundaries of the polyganized dislocation cell network for the first time by photoluminescence. Both the cell structure and the Cottrell cloud are clearly resolved.

  15. 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.

  16. 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.

  17. 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. PMID:18264312

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    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 106 shots. The results show that this structure reduces the on-state resistance and extends the longevity of the GaAs PCSS.

  19. Photocurrent spectra of semi-insulating GaAs M-S-M diodes: Role of the contacts

    NASA Astrophysics Data System (ADS)

    Dubecký, František; Oswald, Jiří; Kindl, Dobroslav; Hubík, Pavel; Dubecký, Matúš; Gombia, Enos; Šagátová, Andrea; Boháček, Pavol; Sekáčová, Mária; Nečas, Vladimír

    2016-04-01

    Current-voltage (I-V) characteristics and photocurrent (PC) spectra (600-1000 nm) of the metal-semiconductor-metal (M-S-M) structures based on high-quality undoped semi-insulating (SI) GaAs with AuGeNi backside contact and different semitransparent top contacts (AuGeNi, Pt, Gd and Nd) are reported, and analysed with the help of a simple physical model. It is shown that the dominant peak in the PC spectra and the change of photocurrent sign can be explained by a presence of two Schottky-like barriers at the top and bottom surfaces. In addition, I-V and PC results show dependence on the bias and its polarity, and on the contact metal used. The possible origins of these effects are discussed.

  20. 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.

  1. 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.

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

    NASA Astrophysics Data System (ADS)

    Liu, Qiang; Ruda, Harry E.

    1997-04-01

    Dual-beam (bias and probe) transient surface photovoltage (SPV) measurements were made on undoped semi-insulating 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 nonexponential 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 preexponential constant of 1.9×1012 s-1 were obtained, and attributed to the thermal recovery rate for EL2.

  3. The contact and photoconductivity characteristics between Co doped amorphous carbon and GaAs: n-type low-resistivity and semi-insulated high-resistivity GaAs

    NASA Astrophysics Data System (ADS)

    Zhai, Zhangyin; Yu, Hualing; Zuo, Fen; Guo, Chunlian; Chen, Guibin; Zhang, Fengming; Wu, Xiaoshan; Gao, Ju

    2016-06-01

    The Co doped amorphous carbon films (a-C:Co), deposited by pulsed laser deposition, show p-n and ohmic contact characteristics with n-type low resistivity GaAs (L-GaAs) and semi-insulated high-resistivity GaAs (S-GaAs). The photosensitivity enhances for a-C:Co/L-GaAs, while inverse decreases for a-C:Co/S-GaAs heterojunction, respectively. Furthermore, the enhanced photosensitivity for the a-C:Co/L-GaAs/Ag heterojunction also shows deposition temperature dependence behavior, and the optimum deposition temperature is around 500 °C.

  4. 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.

  5. The reverse mode of the photo activated charge domain in high field biased semi-insulating GaAs

    NASA Astrophysics Data System (ADS)

    Qu, Guanghui; Shi, Wei

    2013-02-01

    The nonlinear accumulation of the photogenerated electrons in high field biased SI-GaAs has been defined as photo activated charge domain (PACD). The transient transport dynamics of the PACD is investigated. The result shows that the PACD, working as a reverse gun dipole domain when biased electric field much higher than 4 kV/cm, and the reverse mode of the PACD could dominate the electric field shielding by its main electric field ultrafast and exponential rising against the bias field. Such mechanisms could play an important role in GaAs THz antenna, GaAs photoconductive semiconductor switch, and the other ultrafast GaAs devices.

  6. 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.

  7. Implanted Si atoms shifting between Ga sites and As sites by thermal stress in conductive-layer GaAs crystals on semi-insulating substrates

    NASA Astrophysics Data System (ADS)

    Saito, Yasuyuki

    1992-04-01

    Large (0.8 V order) discrepancies of threshold voltage Vth between the predicted Vth values by the Lindhard-Scharff-Schio/tt Gaussian approximate calculation and the Vth of the tungsten nitride (WNx) self-alignment (SA) gate GaAs metal-semiconductor field-effect transistors (MESFETs) were observed. These discrepancies were confirmed by the comparison of the Vth of the WNx-SA-gate MESFETs and the Vth of the (N+: high carrier concentration layers self-aligned of source-drain electrodes)-less conventional MESFETs on 2-in.-diam semi-insulating substrates from liquid-encapsulated-Czochralski-technique-grown <100> boules. The discrepancy was also analyzed by the capacitance-voltage (C-V) measurement of large-diameter (440 μm) Schottky diodes which were built into the MESFET arrays. It was found that for obtained SA-process carrier depth profiles (Si, 150 keV, 3×1012 cm-2) the carrier concentration at a depth of 0.25 μm decreased from 5.3×1016 to 2.0×1016 cm-3, but, on the other hand, the peak carrier concentration slightly decreased from 12.8×1016 to 12.4×1016 cm-3. By the calculation for Vth on the basis of the actual C-V carrier depth profiles, it was found that the carrier concentration decrease was comparable to the Vth variation (0.8 V). Furthermore, the Vth variation of the shallow channel implantation (50 keV) was comparable to that of the deep channel implantation (150 keV). As a result of the experiment and analysis, it was found that the large Vth variation for the SA N+ process was caused by reoccupation (Ga sites to As sites) of implanted Si atoms in the channel active-layer crystal by tensile stress formed by the thermal-expansion coefficient difference between chemical-vapor deposition (CVD) phosphosilicate glass (or CVD SiO2) film and (100) GaAs substrate crystal. The Si atom reoccupation quantity was, for the first time, explained by the Si atom compensation ratio equation as a function of the bond length (Si-As and Si-Ga) variation, an equation

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  9. Lateral npn junction and semi-insulating GaAs current confinement structure for index-guided InGaAs/AlGaAs lasers by molecular beam epitaxy

    SciTech Connect

    Takamori, Takeshi; Watanabe, Kenji; Kamijoh, Takeshi )

    1993-06-01

    A novel current confinement structure with a lateral npn junction and a semi-insulating GaAs (SI-GaAs) is examined for an index-guided InGaAs/AlGaAs strained quantum-well laser. An amphoteric doping of Si in GaAs and AlGaAs is used to form the lateral npn structure grown over a channeled patterned low-temperature grown Si-GaAs layer. A threshold current of 7.4 mA and total external differential quantum efficiency of 59% under room-temperature continuous-wave operation are achieved with devices fabricated by a self-aligned process. The device with AR-HR coatings emitted the light output over 300 mW.

  10. Neutron irradiation effects in GaAs

    SciTech Connect

    Patel, J.U.

    1992-01-01

    Changes in electrical properties of n-GaAs as a result of irradiations with fast neutron have been studied, after epitaxial layers doped with Si at concentrations in the range 1.35 x 10[sup 15] to 1.60 x 10[sup 16] cm[sup [minus]3] were irradiated with reactor neutron fluences up to 1.31 x 10[sup 15] cm [sup [minus]2]. When the changes in carrier concentration, Hall mobility and resistivity were more than 25% of their initial values, nonlinear dependence on neutron fluence was apparent. New theory is proposed which explains the changes in electrical properties in terms of rates of trapping and release of charges. A theoretical relationship is derived for the change in carrier concentration as a function of neutron fluence and Fermi level shift was found to be consistent with the observed changes in carrier concentration. A correlation has been found between the changes in carrier concentration and mobility with neutron fluence using newly defined physically meaningful parameters in the case of two pairs of samples. The correlation has been explained in terms of the increased scattering of charge carriers from the defects created by neutrons that trap the free carriers. Mobility changes were measured at temperatures from 15 K to 305 K in n-GaAs van-der Pauw samples irradiated by fast reactor neutrons. The inverse mobility values obtain versus temperature, from the variable temperature Hall measurements, in the case of irradiated and in-irradiated samples were fitted using the relation [mu][sup [minus]1] = T[sup [minus]3/2] + B T[sup 3/2]. The inverse mobility increased as a result of neutron irradiations over the whole range of temperature, the increase being attributed to the increased scattering from neutron induced charged defects.

  11. High-resolution transmission electron microscopy study on the growth modes of GaSb islands grown on a semi-insulating GaAs (001) substrate

    NASA Astrophysics Data System (ADS)

    Kim, Y. H.; Lee, J. Y.; Noh, Y. G.; Kim, M. D.; Oh, J. E.

    2007-06-01

    The initial growth behaviors of GaSb on a GaAs substrate were studied using a high-resolution electron microscope (HRTEM). Four types of GaSb islands were observed by HRTEM. HRTEM micrographs showed that strain relaxation mechanisms were different in the four types of islands. Although 90° misfit dislocations relieve misfit strain in the islands, additional mechanisms are required to relax the remaining strain. The existence of elastic deformation near the surface related to dislocations and intermediate layers between GaSb and GaAs were demonstrated in island growths. Finally, the generation of planar defects to relieve strain was observed in a specific GaSb growth.

  12. SNMS characterization of ion irradiated GaAs surfaces

    NASA Astrophysics Data System (ADS)

    Scandurra, A.; Licciardello, A.; Torrisi, A.; Weigert, R.; Puglisi, O.

    1996-09-01

    This study deals with the phenomena that influence the relative intensity of the sputtered neutral yields when altered layers of GaAs are analysed by using sputtered neutral mass spectrometry (SNMS) technique. The altered layers were obtained by irradiation with He +, Ne +, Ar +, Kr +, Xe + and O 2+ ions of various energies, in order to explore different nuclear stopping power regimes. The main result is a considerable change both of the absolute and relative yields of As and Ga as a function of the bombarding time, type and energy of primary ions. The absolute variation in the sputtered neutral signal is probably related with the amorphization of the outer layers. The relative variation in the yield of As with respect to Ga is not due to true preferential sputtering but to surface segregation followed by removal of the segregated species during the bombardment.

  13. 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.

  14. Origins of ion irradiation-induced Ga nanoparticle motion on GaAs surfaces

    SciTech Connect

    Kang, M.; Wu, J. H.; Chen, H. Y.; Thornton, K.; Goldman, R. S.; Sofferman, D. L.; Beskin, I.

    2013-08-12

    We have examined the origins of ion irradiation-induced nanoparticle (NP) motion. Focused-ion-beam irradiation of GaAs surfaces induces random walks of Ga NPs, which are biased in the direction opposite to that of ion beam scanning. Although the instantaneous NP velocities are constant, the NP drift velocities are dependent on the off-normal irradiation angle, likely due to a difference in surface non-stoichiometry induced by the irradiation angle dependence of the sputtering yield. It is hypothesized that the random walks are initiated by ion irradiation-induced thermal fluctuations, with biasing driven by anisotropic mass transport.

  15. Performance and temperature dependencies of proton irradiated n/p GaAs and n/p silicon cells

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

    The n/p homojunction GaAs cell is found to be more radiation resistant than p/nheteroface GaAs under 10 MeV proton irradiation. Both GaAs cell types outperform conventional silicon n/p cells under the same conditions. An increase temperature dependency of maximum power for the GaAs n/p cells is attributed largely to differences in Voc between the two GaAs cell types. These results and diffusion length considerations are consistent with the conclusion that p-type GaAs is more radiation resistant than n-type and therefore that the n/p configuration is possibly favored for use in the space radiation environment. However, it is concluded that additional work is required in order to choose between the two GaAs cell configurations.

  16. Defects in electron-irradiated GaAs studied by positron lifetime spectroscopy

    SciTech Connect

    Polity, A.; Rudolf, F.; Nagel, C.; Eichler, S.; Krause-Rehberg, R.

    1997-04-01

    A systematic study of electron-irradiation-induced defects in GaAs was carried out. The irradiation was performed at low temperature (4 K) with an incident energy of 2 MeV. Both, the defect formation and annealing behavior were studied in dependence on the fluence (10{sup 15}--10{sup 19} cm{sup {minus}2}) in undoped, n-, and p-doped GaAs. Temperature-dependent positron lifetime measurements were performed between 20 and 600 K. The thermal stability of defects was studied by annealing experiments in the temperature range of 90--600 K. A defect complex, which anneals in a main stage at 300 K, was found in all GaAs samples after electron irradiation. A possible candidate for this defect is a complex of a vacancy connected with an intrinsic defect. A second vancancylike defect was observed in n-type material after annealing at 550 K. This defect was assumed to be in the As sublattice. {copyright} {ital 1997} {ital The American Physical Society}

  17. 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.

  18. 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.

  19. 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.

  20. Damage and coefficients and thermal annealing of irradiated silicon and GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Anspaugh, B. E.; Downing, R. G.

    1981-01-01

    Electron and proton damage coefficients have been measured for several types of silicon cells of recent manufacture using 1 MeV electrons and protons with energies of 8.3, 17.5 and 40 MeV. LPE (AlGa)As-GaAs cells were also irradiated and pseudodamage coefficients derived under the assumption that the irradiation changes the diffusion length in only one of the n- or p-type layers. After irradiation the cells were annealed isochronally up to 450 C. The damage coefficient and annealing data for silicon cells are in substantial agreement with previous work. The GaAs cells have pseudo-damage coefficients which are dependent on fluence, and have about the same energy dependence as Si damage coefficients.

  1. 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.

  2. A stress gettering mechanism in semi-insulating, copper-contaminated gallium arsenide

    NASA Astrophysics Data System (ADS)

    Kang, Nam Soo; Zirkle, Thomas E.; Schroder, Dieter K.

    1992-07-01

    We have demonstrated a stress gettering mechanism in semi-insulating, copper-contaminated gallium arsenide (GaAs) using cathodoluminescence (CL), thermally stimulated current spectroscopy (TSC), and low temperature Fourier transform infrared spectroscopy (FTIR). Cathodoluminescence shows a local gettering effect around dislocation cores in bulk semi-insulating GaAs qualitatively. This gettering result was confirmed by low temperature FTIR data, which show absorption features resulting from the transition of electrons from the valence band to copper levels. The energy level of each absorption shoulder corresponds to the various copper levels in GaAs. After gettering, the absorption depth at each shoulder decreases. Thermally stimulated current measurements show changes after copper doping. The characteristic returns to that of uncontaminated GaAs after gettering. On the basis of these qualitative and quantitative data, we conclude that copper was gettered, and we propose a stress gettering mechanism in semi-insulating, copper-contaminated GaAs on the basis of dislocation cores acting as localized gettering sites.

  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. Dielectric properties of semi-insulating silicon at microwave frequencies

    NASA Astrophysics Data System (ADS)

    Krupka, Jerzy; Kamiński, Paweł; Kozłowski, Roman; Surma, Barbara; Dierlamm, Alexander; Kwestarz, Michał

    2015-08-01

    The permittivity and dielectric loss tangent of high-purity silicon with semi-insulating properties achieved by the irradiation with 23-MeV protons have been measured at frequencies from 1 GHz to 15 GHz. The dielectric losses were separated from the conductor losses on the basis of the total loss tangent measurements versus frequency. The resistivity measurements of the material performed at radio frequencies (RF) by means of the capacitance spectroscopy method have shown the non-uniform resistivity distribution in the direction perpendicular to the surface of the semi-insulating wafer. The excellent agreement between the resistivity measurements results at RF and those obtained by using microwave methods have been achieved. It has been confirmed that high-purity, semi-insulating silicon is practically non-dispersive and possesses extremely low dielectric losses that are constant to within experimental errors in the frequency range from 1 GHz to 350 GHz. In this frequency range, the dielectric loss tangent of semi-insulating silicon is equal to 1.2 ×10-5 .

  5. 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.

  6. 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.

  7. The influence of electron irradiation on electron holography of focused ion beam milled GaAs p-n junctions

    SciTech Connect

    Cooper, David; Twitchett-Harrison, Alison C.; Midgley, Paul A.; Dunin-Borkowski, Rafal E.

    2007-05-01

    Electron beam irradiation is shown to significantly influence phase images recorded from focused ion beam milled GaAs p-n junction specimens examined using off-axis electron holography in the transmission electron microscope. Our results show that the use of improved electrical connections to the specimen overcomes this problem, and may allow the correct built in potential across the junction to be recovered.

  8. 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.

  9. 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.

  10. 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.

  11. Effects of electron and proton irradiations on n/p and p/n GaAs cells grown by MOCVD

    NASA Technical Reports Server (NTRS)

    Weinberg, Irving; Swartz, Clifford K.; Hart, Russell E., Jr.

    1987-01-01

    State-of-the-art n/p and p/n heteroface GaAs cells, processed by metal organic chemical vapor deposition, were irradiated by 1 MeV electrons and 37 MeV protons and their performance determined as a function of fluence. It was found that the p/n cells were more radiation resistant than the n/p cells. The increased loss in the n/p cells was attributed to increases in series resistance and losses in the p-region resulting from the irradiation. The greater loss in fill factor observed for the n/p cells introduces the possibility that the presently observed superiority of the p/n cells may not be an intrinsic property of this configuration in GaAs.

  12. Annealing results on low-energy proton-irradiated GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Kachare, R.; Anspaugh, B. E.; O'Meara, L.

    1988-01-01

    AlGaAs/GaAs solar cells with an approximately 0.5-micron-thick Al(0.85)Ga(0.15)As window layer were irradiated using normal and isotropic incident protons having energies between 50 and 500 keV with fluence up to 1 x 10 to the 12th protons/sq cm. The irradiated cells were annealed at temperatures between 150 and 300 C in nitrogen ambient. The annealing results reveal that significant recovery in spectral response at longer wavelengths occurred. However, the short-wavelength spectral response showed negligible annealing, irrespective of the irradiation energy and annealing conditions. This indicates that the damage produced near the AlGaAs/GaAs interface and the space-charge region anneals differently than damage produced in the bulk. This is explained by using a model in which the as-grown dislocations interact with irradiation-induced point defects to produce thermally stable defects.

  13. Annealing results on low-energy proton-irradiated GaAs solar cells

    SciTech Connect

    Kachare, R.; Anspaugh, B.E.; O'Meara, L.

    1988-11-01

    AlGaAs/GaAs solar cells with an approximately 0.5-..mu..m-thick Al/sub 0.85/Ga/sub 0.15/As window layer were irradiated using normal and isotropic incident protons having energies between 50 and 500 keV with fluence up to 1 x 10/sup 12/ protons/cm/sup 2/. The irradiated cells were annealed at temperatures between 150 and 300 /sup 0/C in nitrogen ambient. The annealing results reveal that significant recovery in spectral response at longer wavelengths occurred. However, the short-wavelength spectral response showed negligible annealing, irrespective of the irradiation energy and annealing conditions. This indicates that the damage produced near the AlGaAs/GaAs interface and the space-charge region anneals differently than damage produced in the bulk. This is explained by using a model in which the as-grown dislocations interact with irradiation-induced point defects to produce thermally stable defects.

  14. Design and fabrication of GaAs OMIST photodetector

    NASA Astrophysics Data System (ADS)

    Kang, Xuejun; Lin, ShiMing; Liao, Qiwei; Gao, Junhua; Liu, Shi'an; Cheng, Peng; Wang, Hongjie; Zhang, Chunhui; Wang, Qiming

    1998-08-01

    We designed and fabricated GaAs OMIST (Optical-controlled Metal-Insulator-Semiconductor Thyristor) device. Using oxidation of AlAs layer that is grown by MBE forms the Ultra- Thin semi-Insulating layer (UTI) of the GAAS OMIST. The accurate control and formation of high quality semi-insulating layer (AlxOy) are the key processes for fabricating GaAs OMIST. The device exhibits a current-controlled negative resistance region in its I-V characteristics. When illuminated, the major effect of optical excitation is the reduction of the switching voltage. If the GaAs OMIST device is biased at a voltage below its dark switching voltage Vs, sufficient incident light can switch OMIST from high impedance low current 'off' state to low impedance high current 'on' state. The absorbing material of OMIST is GaAS, so if the wavelength of incident light within 600 to approximately 850 nm can be detected effectively. It is suitable to be used as photodetector for digital optical data process. The other attractive features of GaAs OMIST device include suitable conducted current, switching voltage and power levels for OEIC, high switch speed and high sensitivity to light or current injection.

  15. Performance of GaAs and silicon concentrator cells under 37 MeV proton irradiation

    NASA Technical Reports Server (NTRS)

    Curtis, Henry B.; Swartz, Clifford K.

    1987-01-01

    Gallium arsenide concentrator cells from three sources and silicon concentrator cells from one source were exposed to 37 MeV protons at fluences up to 2.8 x 10 to the 12th protons/sq cm. Performance data were taken after several fluences, at two temperatures (25 and 80 C), and at concentration levels from 1 to about 150 x AMO. Data at one sun and 25 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 x 5 mm with a 4-mm diameter illuminated area.

  16. 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.

  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. High purity liquid phase epitaxial GaAs for radiation detectors

    SciTech Connect

    Wynne, D.I.; Haller, E.E.; Rossington Tull, C.S.

    1998-12-31

    The authors report on the growth of high purity n-GaAs using Liquid Phase Epitaxy (LPE) and the fabrication of room temperature p-i-n radiation detectors. The epilayers are grown from a Ga solvent in a graphite boat in a pure hydrogen atmosphere. Growth is started at a temperature of approximately 800 C. The best epilayers show a net-residual-donor concentration of 2 {times} 10{sup 13} cm{sup {minus}3}, confirmed by Hall effect measurements. The residual donors have been analyzed by far infrared spectroscopy and found to be sulfur and silicon. Epilayers with thicknesses of up to 120 {micro}m have been deposited on 650 {micro}m thick semi-insulating GaAs substrates and on 500 {micro}m thick n{sup +}-type GaAs substrates. The authors report the results obtained with Schottky barrier diodes fabricated from these high purity n-type GaAs epilayers and operated as X-ray detectors. The Schottky barrier contacts consisted of evaporated circular gold contacts on epilayers on n{sup +} substrates. The ohmic contacts were formed by evaporated and alloyed Ni-Ge-Au films on the back of the substrate. Several of the diodes exhibit currents of the order of 1 to 10 nA at reverse biases depleting approximately 50 {micro}m of the epilayer. This very encouraging result, demonstrating the possibility for fabricating GaAs p-i-n diodes with depletion layers in high purity GaAs instead of semi-insulating GaAs, is supported by similar results obtained by several other groups. The consequences of using high purity instead of semi-insulating GaAs will be much reduced charge carrier trapping. Diode electrical characteristics and detector performance results using {sup 55}Fe and {sup 241}Am radiation will be discussed.

  19. Efficient defect structure analysis in semi-insulating materials by support vector machine and relevance vector machine

    NASA Astrophysics Data System (ADS)

    Jankowski, Stanisław; Będkowski, Janusz; Danilewicz, Przemysław; Szymański, Zbigniew

    2008-01-01

    We propose new approach for defect centers parameters extraction in semi-insulating GaAs. The experimental data is obtained by high-resolution photoinduced transient spectroscopy (HR-PITS). Two algorithms have been introduced: support vector machine - sequential minimal optimization (SVM-SMO) and relevance vector machine (RVM). Those methods perform the approximation of the Laplace surface. The advantages of proposed methods are: good accuracy of approximation, low complexity, excellent generalization. We developed SVM-RVM-PITS system, which enables graphical representation of Laplace surface, defining local area for defect parameter extraction, choosing the SVM or RVM method for approximation, calculation of the Arrhenius line factors and finally the parameters of the defect centers.

  20. 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.

  1. Temperature effect on betavoltaic microbatteries based on Si and GaAs under 63Ni and 147Pm irradiation

    NASA Astrophysics Data System (ADS)

    Wang, Hao; Tang, Xiao-bin; Liu, Yun-Peng; Xu, Zhi-Heng; Liu, Min; Chen, Da

    2015-09-01

    The effect of temperature on the output performance of four different types of betavoltaic microbatteries was investigated experimental and theoretical. Si and GaAs were selected as the energy conversion devices in four types of betavoltaic microbatteries, and 63Ni and 147Pm were used as beta sources. Current density-voltage curves were determined at a temperature range of 213.15-333.15 K. A simplified method was used to calculate the theoretical parameters of the betavoltaic microbatteries considering the energy loss of beta particles for self-absorption of radioactive source, the electron backscatter effect of different types of semiconductor materials, and the absorption of dead layer. Both the experimental and theoretical results show that the short-circuit current density increases slightly and the open-circuit voltage (VOC) decreases evidently with the increase in temperature. Different combinations of energy conversion devices and beta sources cause different effects of temperature on the microbatteries. In the approximately linear range, the VOC sensitivities caused by temperature for 63Ni-Si, 63Ni-GaAs, 147Pm-Si, and 147Pm-GaAs betavoltaic microbatteries were -2.57, -5.30, -2.53, and -4.90 mV/K respectively. Both theoretical and experimental energy conversion efficiency decreased evidently with the increase in temperature.

  2. Spatial resolution and nature of defects produced by low-energy proton irradiation of GaAs solar cells

    SciTech Connect

    Kachare, R.; Anspaugh, B.E.

    1986-11-24

    AlGaAs/GaAs solar cells with --0.5-..mu..m-thick Al/sub 0.85/Ga/sub 0.15/As window layers were irradiated using isotropic and normal incidence protons having energies between 50 and 500 keV with fluences up to 1 x 10/sup 12/ protons/cm/sup 2/. Although the projected range for these protons varies from 0 to more than 4.5 ..mu..m, the recombination losses due to the irradiation-induced defects were observed to be maximum in the vicinity of the AlGaAs/GaAs interface and the space-charge region irrespective of the proton energy. This was found by analyzing spectral response measurements. The results are explained by using a model in which the interaction of as-grown dislocations with irradiation-induced point defects is considered.

  3. Spatial resolution and nature of defects produced by low-energy proton irradiation of GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Kachare, R.; Anspaugh, B. E.

    1986-01-01

    AlGaAs/GaAs solar cells with about 0.5-micron-thick Al(0.85)Ga(0.15)As window layers were irradiated using isotropic and normal incidence protons having energies between 50 and 500 keV with fluences up to 1 x 10 to the 12th protons/sq cm. Although the projected range for these protons varies from 0 to more than 4.5 microns, the recombination losses due to the irradiation-induced defects were observed to be maximum in the vicinity of the AlGaAs/GaAs interface and the space-charge region irrespective of the proton energy. This was found by analyzing spectral response measurements. The results are explained by using a model in which the interaction of as-grown dislocations with irradiation-induced point defects is considered.

  4. Deep level domain spectroscopy of low frequency oscillations in semi-insulating InP

    NASA Astrophysics Data System (ADS)

    Backhouse, C.; Young, L.

    1992-11-01

    It is known that low frequency current oscillations occur in semi-insulating GaAs due to the formation and transit of high field domains caused by enhanced trapping of hot electrons by deep levels and that power density spectra of the current show peaks whose temperature dependence gives information on deep levels. In the present work Fe-compensated InP was investigated. The peaks rose from an approximately {1}/{f}{3}/{2} background and by estimating and removing this and by averaging many spectra, no less than 14 frequency peaks were resolved which gave straight lines on an Arrhenius plot of log( {T 2}/{2f}) vs{1}/{T}. Although the amplitude of the current oscillations is not so large as to preclude multiple domain propagation, it seems more likely that the domains are caused by hot electron trapping by one level only, rather than that several traps should have the necessary characteristics to launch domains. The multiplicity of peaks could be partly due to harmonics of the basic high field domain oscillation and partly due to conductivity modulation by other levels whose occupancies are changed by the passage of the domains: the task, if so, is to determine which peaks are which. The activation energies from the Arrhenius plots fell into groups close to 0.30, 0.39, 0.41, 0.44 and 0.49 eV. The 14 peaks thus are believed to arise from 5 deep levels. Evidence was found that the 0.49 eV level is iron-related and is responsible for producing the high field domains and for drain current drift in InP metal-insulator-semiconductor field-effect transistors.

  5. Diffusion studies of Ra and Pb in GaAs by the alpha-particle energy loss method

    NASA Astrophysics Data System (ADS)

    Adamcyk, M.; Beaudoin, M.; Kelson, I.; Levy, Y.; Tiedje, T.

    1998-12-01

    The temperature dependence of the diffusion of lead in GaAs is determined by measuring the modification to the energy spectrum of emitted alpha particles from the decay chain of implanted 212Pb atoms. Diffusion rates are measured for temperatures up to 900 °C. Higher rates are observed for the diffusion in silicon-doped GaAs than in semi-insulating GaAs. An upper limit for the diffusion of radium in GaAs is similarly obtained from the decay of the 224Ra isotope. Implications for the use of implanted alpha sources for thickness monitoring during epitaxial film growth by the alpha-particle energy loss method are discussed.

  6. Evolution Of Surface Topography On GaAs(100) And GaAs(111) At Normal And Oblique Incidence Of Ar{sup +}-Ions

    SciTech Connect

    Venugopal, V.; Basu, T.; Garg, S.; Majumder, S.; Sarangi, S. N.; Som, T.; Das, P.; Bhattacharyya, S. R.; Chini, T. K.

    2010-10-04

    Nanoscale surface structures emerging from medium energy (50-60 keV)Ar{sup +}-ion sputtering of p-type GaAs(100) and semi-insulating GaAs(111) substrates have been investigated. For normally incident 50 keV Ar{sup +}-ions of fluence 1x10{sup 17} ions/cm{sup 2} on GaAs(100) and GaAs(111) features in the form of nanoscale pits/holes without short range ordering are observed with densities 5.2x10{sup 9} /cm{sup 2} and 5.9x10{sup 9} /cm{sup 2}, respectively along with irregularly shaped patches of islands. For GaAs(111) on increasing the influence to 5x10{sup 17} /cm{sup 2} the pit density increases marginally to 6.2x10{sup 9} /cm{sup 2}. For 60 deg. off-normal incidence of 60 keV Ar.{sup +}-ions of fluence 2x10{sup 17} ions/cm{sup 2} on GaAs(100) microscale wavelike surface topography is observed. In all cases well-defined nanodots are absent on the surface.

  7. Reversible electrical properties of LEC GaAs

    NASA Astrophysics Data System (ADS)

    Look, D. C.; Theis, W. M.; Yu, P. W.; Sizelove, J. R.; Ford, W.; Mathur, G.

    1987-01-01

    Undoped, low-pressure, liquid-encapsulated Czochralski GaAs can be reversibly changed from conducting ( ρ ˜ 1Ω-cm) to semi-insulating ( ρ ˜ 107Ω-cm) by either slow or fast cooling, respectively, after a 5 hr, 950° C soak in an evacuated quartz ampoule. The semi-insulating wafers are very uniform and lead to tight threshold-voltage control in direct-implant MESFET’s. We have studied crystals in both states by temperature-dependent Hall effect, photoluminescence, IR absorption, mass spectroscopy, and DLTS. It is shown that donor and acceptor concentrations are typically more than an order of magnitude greater than the C and Si concentrations, which are both less than 3 × 1014 cm-3. The EL2 concentration remains relatively constant at about 1.0 × 1016 cm-3. Thus, the normal EL2-Si-C compensation model does not apply. The most likely explanation for the reversibility involves a delicate balance between native-defect donors and acceptors in equilibrium at 950° C, but with the donors dominating after a slow cool, and the acceptors after a fast cool. A consistent model includes a dominant donor at Ec 0.13eV, probably VAs AsGa, and a dominant acceptor at Ev + 0.07eV, probably VGa GaAs. In this model, vacancy motion is very important during the slow cool. Such processes must be strongly considered in the growth of bulk, high-purity GaAs.

  8. 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.

  9. Optically Detected Electron-Nuclear Double Resonance of As-Antisite Defects in GaAs

    NASA Astrophysics Data System (ADS)

    Hofmann, D. M.; Meyer, B. K.; Lohse, F.; Spaeth, J.-M.

    1984-09-01

    This Letter reports on the first optically detected electron-nuclear double-resonance (ENDOR) measurements of a paramagnetic semiconductor defect in which ligand hyperfine interactions could be resolved. In semi-insulating GaAs: Cr the ENDOR lines of the first-shell 75As neighbors of the regular tetrahedral AsAs4-antisite defect could be detected and analyzed. The ENDOR investigation reveals that at least one other AsAs4-antisite complex contributes to the same ESR spectrum.

  10. Wafer-fused orientation-patterned GaAs

    NASA Astrophysics Data System (ADS)

    Li, Jin; Fenner, David B.; Termkoa, Krongtip; Allen, Mark G.; Moulton, Peter F.; Lynch, Candace; Bliss, David F.; Goodhue, William D.

    2008-02-01

    The fabrication of thick orientation-patterned GaAs (OP-GaAs) films is reported using a two-step process where an OP-GaAs template with the desired crystal domain pattern was prepared by wafer fusion bonding and then a thick film was grown over the template by low pressure hydride vapor phase epitaxy (HVPE). The OP template was fabricated using molecular beam epitaxy (MBE) followed by thermocompression wafer fusion, substrate removal, and lithographic patterning. On-axis (100) GaAs substrates were utilized for fabricating the template. An approximately 350 μm thick OP-GaAs film was grown on the template at an average rate of ~70 μm/hr by HVPE. The antiphase domain boundaries were observed to propagate vertically and with no defects visible by Nomarski microscopy in stain-etched cross sections. The optical loss at ~2 μm wavelength over an 8 mm long OP-GaAs grating was measured to be no more than that of the semi-insulating GaAs substrate. This template fabrication process can provide more flexibility in arranging the orientation of the crystal domains compared to the Ge growth process and is scalable to quasi-phase-matching (QPM) devices operating from the IR to terahertz frequencies utilizing existing industrial foundries.

  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. Influence of electron irradiation on the electronic transport mechanisms during the conductive AFM imaging of InAs/GaAs quantum dots capped with a thin GaAs layer.

    PubMed

    Troyon, M; Smaali, K

    2008-06-25

    We have used conductive atomic force microscopy (C-AFM) to study the electronic transport mechanisms through InAs quantum dots (QDs) grown by molecular beam epitaxy on an n-type GaAs(001) substrate and covered with a 5 nm thick GaAs cap layer. The study is performed with a conductive atomic force microscope working inside a scanning electron microscope. Electric images can be obtained only if the sample is preliminarily irradiated with an electron probe current sufficiently high to generate strong electron beam induced current. In these conditions holes are trapped in QDs and surface states, so allowing the release of the Fermi level pinning and thus conduction through the sample. The electronic transport mechanism depends on the type of AFM probe used; it is explained for a metal (Co/Cr) coated probe and p-doped diamond coated probe with the aid of energy band diagrams. The writing (charge trapping) and erasing (untrapping) phenomena is conditioned by the magnitude of the electron probe current. A strong memory effect is evidenced for the sample studied. PMID:21828669

  13. 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).

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Photoluminescence fatigue and inhomogeneous line broadening in semi-insulating Tl6SeI4 single crystals

    NASA Astrophysics Data System (ADS)

    Kostina, S. S.; Peters, J. A.; Lin, W.; Chen, P.; Liu, Z.; Wang, P. L.; Kanatzidis, M. G.; Wessels, B. W.

    2016-06-01

    Photoluminescence (PL) properties of semi-insulating Tl6SeI4 have been investigated. A broad emission band centered at 1.63 ± 0.02 eV was observed in all samples. The PL emission band is excitonic in nature and is tentatively attributed to a bound exciton emission. PL fatigue (a reduction in PL intensity under prolonged laser excitation) was always observed. The amount of PL fatigue depended on excitation power and temperature. PL fatigue kinetics are described by a stretched exponential with nominal lifetimes in the 10–265 s range. The recovery of the PL occurred within a few seconds of light cessation. The magnitude of PL fatigue in different samples correlated with inhomogeneous line broadening of the 1.63 eV emission band, such that broader bands exhibited more fatigue. An additional luminescence band centered at 1.78 eV was observed which increased in intensity under prolonged laser irradiation. The fatigue phenomenon is tentatively attributed to two mechanisms—the formation of photo-induced defects and the formation of quasi-stable particles. Both of these mechanisms introduce additional radiative and non-radiative recombination channels that lead to a decrease in the PL intensity under prolonged laser irradiation. Since inhomogeneous line broadening and PL fatigue are related to the concentration of defects or impurities, the measurement of these two parameters is an effective method to screen sample quality.

  19. 2D-ACAR Studies on Swift Heavy Ion Si-Implanted GaAs

    NASA Astrophysics Data System (ADS)

    Sivaji, K.; Selvakumar, S.

    Material properties modification by high energy heavy ion implantation is a prospective technology leading to many device fabrications. This technique induces defects and hence the physical properties of the materials are modified. The effects of swift heavy ion implantation induced defects by 120 MeV 28+Si ion implantation and doping in SI-GaAs are presented from the electron momentum distribution (EMD) of vacancy-type defects studied by two-dimensional angular correlation of annihilation radiation (2D-ACAR). The positron trapping due to the influence of high-energy Si- implantation in GaAs (n-type) is compared with the corresponding spectra of SI- GaAs and with Si-doped (n-type) GaAs. The EMD of the implanted sample shows a distinct increased isotropic distribution with a characteristic transform of its structure as evident from the low momentum region compared to the pristine sample. The characteristics of defects created by Si doping and by 120 MeV 28+Si ion implantation of undoped semi-insulating (SI) GaAS are discussed. These results indicate the nature of positron trapping in open volume defects such as vacancy clusters created by implantation.

  20. 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.

  1. Characterization of production GaAs solar cells for space

    SciTech Connect

    Anspaugh, B.E.

    1988-12-01

    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.

  2. 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.

  3. 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.

  4. 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.

  5. Ferroelectric films of barium strontium titanate on semi-insulating silicon carbide substrates

    NASA Astrophysics Data System (ADS)

    Tumarkin, A. V.; Razumov, S. V.; Gagarin, A. G.; Odinets, A. A.; Mikhailov, A. K.; Pronin, I. P.; Stozharov, V. M.; Senkevich, S. V.; Travin, N. K.

    2016-04-01

    Thin ferroelectric Ba x Sr1- x TiO3 (BST) layers have been grown for the first time on semi-insulating silicon carbide substrates by RF magnetron sputtering of a ceramic target without using buffer sublayers. Results of investigation of the structure of obtained BST films and the electrical properties of related planar capacitors are presented. The obtained structures are characterized by high nonlinearity and low dielectric losses at microwave frequencies.

  6. Identification of As-vacancy complexes in Zn-diffused GaAs

    SciTech Connect

    Elsayed, M.; Krause-Rehberg, R.; Korff, B.; Richter, S.; Leipner, H. S.

    2013-03-07

    We have used positron annihilation spectroscopy to study the introduction of point defects in Zn-diffused semi-insulating GaAs. The diffusion was performed by annealing the samples for 2 h at 950 Degree-Sign C. The samples were etched in steps of 7 {mu}m. Both Doppler broadening using slow positron beam and lifetime spectroscopy studies were performed after each etching step. Both techniques showed the existence of vacancy-type defects in a layer of about 45 {mu}m. Secondary ion mass spectroscopy measurements illustrated the presence of Zn at high level in the sample almost up to the same depth. Vacancy-like defects as well as shallow positron traps were observed by lifetime measurements. We distinguish two kinds of defects: As vacancy belongs to defect complex, bound to most likely one Zn atom incorporated on Ga sublattice, and negative-ion-type positron traps. Zn acceptors explained the observation of shallow traps. The effect of Zn was evidenced by probing GaAs samples annealed under similar conditions but without Zn treatment. A defect-free bulk lifetime value is detected in this sample. Moreover, our positron annihilation spectroscopy measurements demonstrate that Zn diffusion in GaAs system is governed by kick-out mechanism.

  7. 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.

  8. 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.

  9. GaAs surface cleaning by thermal oxidation and sublimation in molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Saito, Junji; Nanbu, Kazuo; Ishikawa, Tomonori; Kondo, Kazuo

    1988-01-01

    GaAs surface cleaning by thermal oxidation and sublimation prior to molecular-beam-epitaxial growth has been investigated as a means of reducing the carrier depletion at the substrate and epitaxial layer interface. The carrier depletion between the substrate and epitaxial films, measured by a C-V carrier profiling technique, was shown to decrease significantly with an increase in the thickness of the thermal oxidation. The concentration of carbon contamination near the substrate-epitaxial interface was measured using secondary ion mass spectroscopy. The carbon concentration correlated very well with the carrier depletion. Therefore, the main origin of the carrier depletion is believed to be the carbon concentration of the initial growth surface. Based on these results, the thermal oxidation and sublimation of a semi-insulating GaAs substrate was successfully applied to improve the mobility and sheet concentration of the two-dimensional electron gas in selectively doped GaAs/N-Al0.3Ga0.7As heterostructures with very thin GaAs buffer layers.

  10. 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.

  11. 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.

  12. Steady State Properties of Lock-On Current Filaments in GaAs

    NASA Astrophysics Data System (ADS)

    Kambour, K.; Kang, Samsoo; Myles, Charles W.; Hjalmarson, Harold P.

    1999-10-01

    Collective impact ionization has been used by Hjalmarson et al.(H. Hjalmarson, F. Zutavern, G. Loubriel, A. Baca, and D. Wake, Sandia Report SAND93-3972(1996).) to explain the lock-on effect, observed in optically activated, semi-insulating GaAs switches. We have used this theory to study some of the steady state properties of the lock-on current filaments which accompany this effect. In steady state, the energy gained from the electric field is exactly compensated for by the the energy lost due to the phonon cooling of the hot carriers. In the simplest approximation, the carrier distribution approaches a quasi-equilibrium Maxwell-Boltzmann distribution. In this presentation we report preliminary results on the validity of this quasi-equilibrium approximation. We find that this approximation leads to a filament carrier density which is much lower than the high density needed to achieve a quasi-equilibrium distribution. Further work is in progress.

  13. Current Sharing Among Multiple Lock-On Filaments in GaAs

    NASA Astrophysics Data System (ADS)

    Hjalmarson, H. P.; Loubriel, G. M.; Zutavern, F. J.

    1998-03-01

    Optically-triggered, high-power photoconductive semiconductor switches (PCSS's) using semi-insulating GaAs are under development at Sandia. These switches carry current in high carrier-density filaments. A major problem is the increased electrode damage in high power applications. One method we use to increase switch longevity is to trigger multiple filaments which share the current. For this talk, a hydrodynamic implementation of the collective impact ionization theory is used to evaluate and refine this method. To be specific, the current-voltage characteristic for two filaments is compared with that for a single filament. An important issue is the interaction of the two filaments as a function of their distance separation.

  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. 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.

  16. Magnetron Sputtered Gold Contacts on N-gaas

    NASA Technical Reports Server (NTRS)

    Buonaquisti, A. D.; Matson, R. J.; Russell, P. E.; Holloway, P. H.

    1984-01-01

    Direct current planar magnetron sputtering was used to deposit gold Schottky barrier electrical contacts on n-type GaAs of varying doping densities. The electrical character of the contact was determined from current voltage and electron beam induced voltage data. Without reducing the surface concentration of carbon and oxide, the contacts were found to be rectifying. There is evidence that energetic neutral particles reflected from the magnetron target strike the GaAs and cause interfacial damage similar to that observed for ion sputtering. Particle irradiation of the surface during contact deposition is discussed.

  17. Microscopic defect level characterization of semi-insulating compound semiconductors by TSC and PICTS. Application to the effect of hydrogen in CdTe

    NASA Astrophysics Data System (ADS)

    Hage-Ali, M.; Yaacoub, B.; Mergui, S.; Samimi, M.; Biglari, B.; Siffert, P.

    1991-06-01

    Thermally stimulated current (TSC) and photo-induced current transient spectroscopy (PICTS) methods have been developed for the microscopic defect characterization in semi-insulating compound semiconductors. The capabilities of these methods are demonstrated by investigating the effects of hydrogen implantation or diffusion into semi-insulating cadmium telluride.

  18. 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.

  19. Structural and optical properties of Cr-doped semi-insulating GaN epilayers

    SciTech Connect

    Mei, F.; Wu, K. M.; Pan, Y.; Han, T.; Liu, C.; Gerlach, J. W.; Rauschenbach, B.

    2008-09-15

    The properties of Cr-doped GaN epilayers grown by rf-plasma-assisted molecular beam epitaxy were studied. The deep acceptor nature of Cr was used to grow semi-insulating GaN epilayers on sapphire substrates for electronic device applications. The room-temperature (RT) sheet resistivity of the epilayers reached 10{sup 10} {omega}/square. The activation energy of dark conductivity was about 0.48 eV. Step-graded Al{sub x}Ga{sub 1-x}N/GaN (x=0.3-0.2) superlattices (SLs) were designed to filter dislocations. Transmission electron microscopy images showed that the SLs can dramatically reduce dislocation density. Al{sub 0.35}Ga{sub 0.65}N/GaN heterostructure grown on Cr-doped semi-insulating GaN epilayer exhibited a RT mobility of 960 cm{sup 2}/V s and sheet carrier density of 2.1x10{sup 13} cm{sup -2}.

  20. Heteroepitaxial InP solar cells on Si and GaAs substrates

    NASA Technical Reports Server (NTRS)

    Weinberg, Irving; Swartz, Clifford K.; Brinker, David J.

    1990-01-01

    The characteristics of InP cells processed from thin layers of InP heteroepitaxially grown on GaAs, on silicon with an intervening GaAs layer, and on GaAs with intervening Ga(x)In(1-x)As layers are described, and the factors affecting cell efficiency are discussed. Under 10 MeV proton irradiations, the radiation resistances of the heteroepitaxial cells were superior to that of homoepitaxial InP cells. The superior radiation resistance is attributed to the high dislocation densities present in the heteroepitaxial cells.

  1. Performance of monolithic integrated series-connected GaAs solar cells under concentrated light

    NASA Astrophysics Data System (ADS)

    Seno, Minato; Watanabe, Kentaroh; Sugiyama, Masakazu; Nakano, Yoshiaki

    2013-09-01

    The concentrator photovoltaic (CPV) system provides excellent cost performance and conversion efficiency by increasing the concentration ratio. The problem is that concentration ratio is limited by short-circuit current density (Jsc) due to cell resistance loss. In order to achieve much larger concentration ratio, the monolithically integrated series-connected GaAs photovoltaic (PV) cells were fabricated. By dividing a cell into sub-cells on a chip and connecting them in series, the cell provides smaller short-circuit current (Isc) and larger open-circuit voltage (Voc). This approach can reduce joule energy loss inside a cell without decreasing electrical power output and allow much larger concentration ratio. In our design, 10 series-connected sub-cells, with bypass diodes in parallel with each sub-cell, were integrated monolithically on semi-insulating GaAs. When some sub-cells in the array were shaded, the bypass diodes prevented the shaded sub-cells from breakdown and reduced fluctuation of power output. The detection area of a unit cell was 1.73 mm2 and an entire detection area occupied over 68% of the whole chip area. The arrayed 10 cells exhibited Voc of 9.0 V under illumination (AM 1.5G). The series-connected cell achieved maximum efficiency at higher concentration ratio than non-series-connected cell.

  2. 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.

  3. Low-temperature growth of GaSb epilayers on GaAs (001) by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Benyahia, D.; Kubiszyn, Ł.; Michalczewski, K.; Kębłowski, A.; Martyniuk, P.; Piotrowski, J.; Rogalski, A.

    2016-01-01

    Non-intentionally doped GaSb epilayers were grown by molecular beam epitaxy (MBE) on highly mismatched semi-insulating GaAs substrate (001) with 2 offcut towards [110]. The effects of substrate temperature and the Sb/Ga flux ratio on the crystalline quality, surface morphology and electrical properties were investigated by Nomarski optical microscopy, X-ray diffraction (XRD) and Hall measurements, respectively. Besides, differential Hall was used to investigate the hole concentration behaviour along the GaSb epilayer. It is found that the crystal quality, electrical properties and surface morphology are markedly dependent on the growth temperature and the group V/III flux ratio. Under the optimized parameters, we demonstrate a low hole concentration at very low growth temperature. Unfortunately, the layers grown at low temperature are characterized by wide FWHM and low Hall mobility.

  4. Low-temperature growth of GaSb epilayers on GaAs (001) by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Benyahia, D.; Kubiszyn, Ł.; Michalczewski, K.; KĘbŁOwski, , A.; Martyniuk, P.; Piotrowski, J.; Rogalski, A.

    2016-01-01

    Non-intentionally doped GaSb epilayers were grown by molecular beam epitaxy (MBE) on highly mismatched semi-insulating GaAs substrate (001) with 2 offcut towards [110]. The effects of substrate temperature and the Sb/Gaflux ratio on the crystalline quality, surface morphology and electrical properties were investigated by Nomarski optical microscopy, X-ray diffraction (XRD) and Hall measurements, respectively. Besides, differential Hall was used to investigate the hole concentration behaviour along the GaSb epilayer. It is found that the crystal quality, electrical properties and surface morphology are markedly dependent on the growth temperature and the group V/III flux ratio. Under the optimized parameters, we demonstrate a low hole concentration at very low growth temperature. Unfortunately, the layers grown at low temperature are characterized by wide FWHM and low Hall mobility.

  5. 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.

  6. The role of hydrogen in semi-insulating InP

    SciTech Connect

    Han, Y.; Liu, X.; Jiao, J.; Qian, J.; Chen, Y.; Wang, Z.; Lin, L.

    1998-12-31

    Complexes of vacancy at indium site with one to four hydrogen atoms and isolated hydrogen or hydrogen dimer and other infrared absorption lines, tentatively be assigned to hydrogen related defects were investigated by FTIR. Hydrogen can passivate imperfections, thereby eliminating detrimental electronic states from the energy bandgap. Incorporated hydrogen can introduce extended defects and generate electrically-active defects. Hydrogen also can act as an actuator for creating antistructure defects. Isolated hydrogen related defects (e.g., H{sub 2}{sup *}) may play an important role in the conversion of the annealed wafers from semiconducting to the semi-insulating behavior. H{sub 2}{sup *} may be a deep donor, whose energy level is very near the iron deep acceptor level in the energy gap.

  7. Photo-induced changes of hydrogen bonding in semi-insulating iron-doped indium phosphide

    NASA Astrophysics Data System (ADS)

    Pajot, B.; Song, C.-Y.; Darwich, R.; Gendron, F.; Ewels, C.

    1995-09-01

    After illumination with 1-1.3 eV photons during cooling-down, metastable PH modes are observed by IR absorption at 5 K in semi-insulating InP:Fe. They correlate with the photo-injection of holes, but not with a change of the charge state of the H-related centres present at equilibrium. They are explained by a change of the bonding of H, induced by hole trapping, from IR-inactive centres to PH-containing centres, stable only below 80 K. One metastable centre has well-defined geometrical parameters and the other one could be located in a region near from the interface with (Fe,P) precipitates.

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

    NASA Astrophysics Data System (ADS)

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

    2009-01-01

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

  9. 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.

  10. 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.

  11. 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.

  12. Cathodoluminescence of Yellow and Blue Luminescence in Undoped Semi-insulating GaN and n-GaN

    NASA Astrophysics Data System (ADS)

    Hou, Qi-Feng; Wang, Xiao-Liang; Xiao, Hong-Ling; Wang, Cui-Mei; Yang, Cui-Bai; Yin, Hai-Bo; Li, Jin-Min; Wang, Zhan-Guo

    2011-03-01

    Yellow and blue luminescence in undoped GaN layers with different resistivities are studied by cathodoluminescence. Intense yellow and blue luminescence bands are observed in semi-insulating GaN, while in n-GaN the yellow luminescence and blue luminescence bands are very weak. The stronger yellow and blue luminescences in semi-insulating GaN are correlated to the higher edge-type dislocation density. The scanning cathodoluminescence image reveals strong defect-related luminescence at the grain boundaries where the dislocations accumulate. It is found that the relative intensity of the blue luminescence band to the yellow luminescence band increases with the cathodoluminescence beam energies and is larger in n-GaN with a lower density of edge-type dislocations. An approximately 3.35 eV shoulder next to the near-band-edge peak is observed in n-GaN but not in semi-insulating GaN. A redshift of the near-band-edge peak with cathodoluminescence beam energy is observed in both samples and is explained by internal absorption.

  13. Effect of electron flux on radiation damage in GaAs solar cells

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

    The objective of this work was to evaluate the effect of electron flux and temperature on radiation damage in GaAs solar cells. The defect levels and the power ratio of the GaAs solar cells under various irradiation conditions are compared. In a 200 C continuous annealing experiment, the GaAs solar cells which were irradiated at a flux of 2 x 10 to the 9th e/sq cm s suffered less power degradation than the cells which were irradiated at the same temperature at a higher flux of 4 x 10 to the 10th e/sq cm s. After the continuous annealing experiment, a single-step post annealing at 200 C was performed for 40 hr on these irradiated cells. An additional improvement in power recovery was observed only on those cells irradiated at the high flux of 4 x 10 to the 10th e/sq cm s. DLTS data indicate that the defect density decreases with lower electron flux. Both of these observations strongly suggest that the continuous annealing in GaAs cells can be effective at temperatures as low as 150 C, or even less in a space environment such as geosynchronous orbit.

  14. Small signal model parameters analysis of GaN and GaAs based HEMTs over temperature for microwave applications

    NASA Astrophysics Data System (ADS)

    Alim, Mohammad A.; Rezazadeh, Ali A.; Gaquiere, Christophe

    2016-05-01

    Thermal and small-signal model parameters analysis have been carried out on 0.5 μm × (2 × 100 μm) AlGaAs/GaAs HEMT grown on semi-insulating GaAs substrate and 0.25 μm × (2 × 100 μm) AlGaN/GaN HEMT grown on SiC substrate. Two different technologies are investigated in order to establish a detailed understanding of their capabilities in terms of frequency and temperature using on-wafer S-parameter measurement over the temperature range from -40 to 150 °C up to 50 GHz. The equivalent circuit parameters as well as their temperature-dependent behavior of the two technologies were analyzed and discussed for the first time. The principle elevation or degradation of transistor parameters with temperature demonstrates the great potential of GaN device for high frequency and high temperature applications. The result provides some valuable insights for future design optimizations of advanced GaN and a comparison of this with the GaAs technology.

  15. 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.

  16. 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.

  17. THz wave emission of GaAs induced by He+ ion implantation

    NASA Astrophysics Data System (ADS)

    Yang, Kang; Cao, Jianqing; Huang, Can; Ji, Te; Zhang, Zengyan; Liu, Qi; Wu, Shengwei; Lin, Jun; Zhao, Hongwei; Zhu, Zhiyong

    2013-07-01

    Semi-Insulating Gallium Arsenide (SI-GaAs) was implanted with 1.5 MeV He+ ions and THz photoconductive antenna (PCA) was prepared on the implanted SI-GaAs surface. The antenna was applied as the THz wave emission source of a terahertz time domain spectroscopy (THz-TDS) and the THz wave emission ability was studied as a function of the implantation dose. It is found that the THz signal intensity increases with increase of implantation dose, and after reaching to a peak value the THz signal intensity decreases with further implantation. The best THz emission ability was achieved at a dose value between 1 × 1015 and 1 × 1016 ions/cm2. It is believed that the implantation induced defects in the 1 μm-thick surface area are responsible for the enhanced THz emission ability. The work proved that better THz photoconductive antenna than that made by low-temperature-grown GaAs (LT-GaAs) can be produced through He-ion implantation at proper dose.

  18. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    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.

  20. Microwave properties of semi-insulating silicon carbide between 10 and 40 GHz and at cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Hartnett, John G.; Mouneyrac, David; Krupka, Jerzy; le Floch, Jean-Michel; Tobar, Michael E.; Cros, Dominique

    2011-03-01

    The complex permittivity of high-purity, semi-insulating, axis-aligned monocrystalline 4H-SiC has been determined over the frequency range 10-40 GHz and at temperatures from 40 up to 295 K using whispering gallery modes and quasi TE0, n , p modes in a dielectric resonator constructed from seven layers of a 375 μm thick wafer. The real part of the permittivity (in the plane of the wafers) was found to be nearly independent of frequency. The dielectric loss tangent of 4H-SiC increases with temperature above 100 K. All results were obtained for the semiconductor in darkness.

  1. Formation of Semi-Insulating Layers on Semiconducting β-Ga2O3 Single Crystals by Thermal Oxidation

    NASA Astrophysics Data System (ADS)

    Oshima, Takayoshi; Kaminaga, Kenichi; Mukai, Akira; Sasaki, Kohei; Masui, Takekazu; Kuramata, Akito; Yamakoshi, Shigenobu; Fujita, Shizuo; Ohtomo, Akira

    2013-05-01

    Semi-insulating layers (SIL) were formed on the surfaces of nominally undoped β-Ga2O3 (010) single crystals by thermal oxidation. Capacitance-voltage measurement with double Schottky configuration was performed to evaluate the increase in the thickness of the SIL as a function of annealing temperature and time. A SiO2 layer prepared on the surface prevented the extension of the SIL, indicating that oxygen incorporation from air and successive bulk diffusion dominated the carrier compensation process. The activation energy of oxygen diffusion coefficient was estimated to be 4.1 eV.

  2. Electron Beam Excited GaAs Maskless Etching Using C12 Nozzle Installed FIB/EB Combined System

    NASA Astrophysics Data System (ADS)

    Takado, Norikazu; Ide, Yuichi; Asakawa, Kiyoshi

    1990-02-01

    We have developed a new fine-beam assisted GaAs maskless etching system capable of nanofabrication; a focused ion beam (FIB) and electron beam (EB) combined etching system with a reactive gas nozzle. In this FIB/EB combined system, EB excited GaAs etching was successfully performed by irradiating Cl2 gas on a temperature-controlled substrate. 5KeV EB was raster-scanned in a 100pm X 20pm rectangular pattern on a GaAs surface. With special care to remove the native oxide layer, spatially selective etching was also confirmed on a cleaned GaAs surface by controlling the Cl2 pressure.

  3. Auger electron spectroscopy analysis of the first stages of thermally stimulated oxidation of GaAs(100)

    NASA Astrophysics Data System (ADS)

    Passeggi, M. C. G.; Vaquila, I.; Ferrón, J.

    1998-05-01

    The first stages (exposures <10 4 L) of thermally stimulated oxidation of GaAs(100) have been studied using Auger electron spectroscopy and principal component analysis. We compare the GaAs oxidation processes taking place at high (700 K) and room temperatures, and during simultaneous electron bombardment and oxygen exposure. We found that while at room temperature, GaAs oxidizes via a one-phase process involving the simultaneous oxidation of Ga and As, the high temperature process is characterized by the presence of two different GaAs oxide phases. The first phase involves the simultaneous oxidation of Ga and As while in the second, only Ga oxides are formed. On the other hand, under simultaneous oxygen exposure and electron irradiation, two different oxide phases appear, both of them exhibiting the same features of the room temperature process, i.e., the simultaneous oxidation of Ga and As.

  4. 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.

  5. 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.

  6. Structural and optical characterization of GaN nanostructures formed by using N+ implantation into GaAs at various temperature

    NASA Astrophysics Data System (ADS)

    Woo, Hyung-Joo; Kim, Gi-Dong; Choi, Han-Woo; Kim, Joon-Kon

    2012-02-01

    We have investigated the evolution of GaN phase nanocrystallite formation in a GaAs matrix by using nitrogen-ion implantation and subsequent rapid thermal annealing. A semi-insulating GaAs (100) wafer was implanted with 50-keV nitrogen ions at fluences in the range of 0.5 ˜ 4.0 × 1017 cm-2 at temperatures of room temperature, 500 °C and 700 °C, followed by post-implantation annealing at 500 ˜ 900 °C under a pure nitrogen gas flow. In the case of high-temperature implantation, there were no significant changes in the UV-VIS absorption spectra after high-temperature annealing compared with the spectra of the as-implanted sample. On the other hand, microscopic blistering and/or exfoliation is preferred after post-implantation annealing at high temperatures above 600 °C. As a consequence, low-temperature implantation (<200 °C is recommended in order to keep a morphologically-clean sample surfaces especially at an implantation fluence of 2 × 1017 cm-2 or more. Formation of nanometer-sized GaN crystallites was confirmed by using X-ray diffraction, cross-sectional transmission electron microscopy and low-temperature photoluminescence spectroscopy, and the effects of different annealing conditions on the evolution of the structures of the crystallites are described.

  7. Measured Propagation Characteristics of Coplanar Waveguide on Semi-Insulating 4H-SiC Through 800 K

    NASA Technical Reports Server (NTRS)

    Ponchak, George E.; Alterovitz, Samuel A.; Downey, Alan N.; Freeman, Jon C.; Schwartz, Zachary D.

    2003-01-01

    Wireless sensors for high temperature industrial applications and jet engines require RF transmission lines and RF integrated circuits (RFICs) on wide bandgap semiconductors such as SiC. In this paper, the complex propagation constant of coplanar waveguide fabricated on semiinsulating 4H-SiC has been measured through 813 K. It is shown that the attenuation increases 3.4 dB/cm at 50 GHz as the SiC temperature is increased from 300 K to 813 K. Above 500 K, the major contribution to loss is the decrease in SiC resistivity. The effective permittivity of the same line increases by approximately 5 percent at microwave frequencies and 20 percent at 1 GHz.

  8. 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.

  9. Visualization of electrical domains in semi-insulating GaAs:Cr and potential use for variable grating mode operation

    NASA Astrophysics Data System (ADS)

    Rajbenbach, H.; Verdiell, J. M.; Huignard, J. P.

    1988-08-01

    The results of an experimental optical technique for imaging the electrical domain repartition in semi-insulating GaAs:Cr are reported. The technique is based on the use of the crystal as the active component of a transverse electro-optic two-dimensional light modulator. Under dc applied voltage, the electrical domains are traveling from the cathode to the anode at a velocity that increases with the applied voltage and with the incident illumination (v≂10-100 mm/s). Results for ac applied voltages are also presented. In particular, the observation of stationary and periodically distributed high-field domains in GaAs:Cr is reported for sawtooth applied voltages (1 kV, 50-250 Hz). These high-field domains induce a phase structure whose period is shown to be electrically controllable. This is the first reported demonstration of the possibility of a variable grating mode operation in semiconductors.

  10. Initial stages of oxidation of GaAs(111)2 × 2-Ga surfaces

    NASA Astrophysics Data System (ADS)

    Alonso, M.; Soria, F.

    1987-04-01

    The initial interaction of oxygen at room temperature with GaAs(111)2 × 2-Ga surfaces has been studied by quantitative Auger analysis and low-energy electron diffraction, under different electron irradiation and gas ionization conditions. Oxygen fills first the non-vacancy overlayer sites with a preferential bond to the Ga atoms. This adsorption phase is characterized by the absence of chemical shifts in the Ga Auger peaks that involve core levels. The oxidation stage begins with the occupation of the underlayer sites below the first Ga-As bilayer. For coverages lower than 2 monolayers oxygen adsorption and incorporation takes place without any loss of Ga or As atoms of the surface layers. Electron irradiation and gas ionization of the oxygen-covered surface increase the kinetics up to two orders of magnitude, but no changes in the adsorption sites and/or occupation sequence have been detected.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Temporal analysis of SEU in SOI/GAA SRAMs

    SciTech Connect

    Francis, P.; Colinge, J.P.; Berger, G.

    1995-12-01

    This paper analyzes the very strong SEU hardness of a 1k static random-access memory fabricated using the SOI/GAA technology, irradiated with a xenon ion beam at various angles of incidence. The memory has been shown to operate with a supply voltage as low as 2V while still presenting excellent SEU hardness. Since the different physical charge collection mechanisms are particularly slow in SOI devices, it is shown that collected and critical charges must be dynamically compared in order to determine the SEU threshold. A new approach is then proposed to evaluate the time-variable critical charge independently of the pulse shape generated by the incident ion, and a general analytical model is derived. Finally, predictions in good agreement with experimental data are obtained.

  16. Ultra-Thin-Film GaAs Solar Cells

    NASA Technical Reports Server (NTRS)

    Wang, K. L.; Shin, B. K.; Yeh, Y. C. M.; Stirn, R. J.

    1982-01-01

    Process based on organo-metallic chemical vapor deposition (OM/CVD) of trimethyl gallium with arsine forms economical ultrathin GaAs epitaxial films. Process has higher potential for low manufacturing cost and large-scale production compared with more-conventional halide CVD and liquid-phase epitaxy processes. By reducing thickness of GaAs and substituting low-cost substrate for single-crystal GaAs wafer, process would make GaAs solar cells commercially more attractive.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. NMR Investigation of Optical Polarization of Nuclear Spins in GaAs

    NASA Astrophysics Data System (ADS)

    Paravastu, Anant; Hayes, Sophia; Schwickert, Birgit; Reimer, Jeffrey; Dinh, Long; Balooch, Mehdi

    2003-03-01

    Light-induced nuclear spin alignments have been measured in GaAs as a function of photon energy, irradiation time, and sample temperature using NMR spectroscopy at 9.4 Tesla and 10 to 50 K. Significant optical enhancements were observed at a range of photon energies, starting just below the band gap and persisting through 100 meV above the gap. Irradiation above the band gap resulted in thermally activated NMR signal enhancements while sub band gap irradiation did not. Short and long irradiation time dependencies revealed insights into the nature of cross relaxation between electronic nuclear spins, contradicting mechanisms based on either localized electron-nuclear contact at defect sites or cross relaxation between nuclei and free electrons. We propose that the presence of a mobile or delocalized enabling electronic species characterized by a long electron-nuclear correlation time, such as an exciton, is necessary in any mechanism which explains the data.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. UV laser activated digital etching of GaAs

    SciTech Connect

    Meguro, T.; Aoyagi, Y.

    1996-12-31

    The self-limited etching characteristics of digital etching employing an UV laser/Cl{sub 2}/GaAs system are presented. The self-limiting nature is the key mechanism and plays an important role in digital etching for obtaining etch rates independent of etching parameters. Surface processes based on photodissociation of physisorbed chlorine on GaAs with diffusion of negatively charged Cl into GaAs are also discussed.

  15. Neutron radiation effects in GaAs planar doped barrier diodes

    SciTech Connect

    Kearney, M.J.; Couch, N.R. ); Edwards, M. ); Dale, I. )

    1993-04-01

    The planar doped barrier (PDB) diode has recently been shown to be a very attractive alternative to the Schottky diode for many microwave and millimeter-wave mixer and detector applications. The authors have studied the degradation of GaAs planar doped barrier diodes subject to neutron irradiation. For fluences as high as 10[sup 15] cm[sup [minus]2] the diode characteristics are very well preserved, which strengthens the rationale for using these devices in place of Schottky diodes in harsh working environments such as nuclear instrumentation and space.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Linearity of photoconductive GaAs detectors to pulsed electrons

    SciTech Connect

    Ziegler, L.H.

    1995-12-31

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

  2. 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.

  3. 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.

  4. 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.

  5. 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; Centre for Microscopy and Microanalysis, The University of Queensland, St. Lucia, Queensland 4072

    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.

  6. 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.

  7. Implantation of carbon in GaAs

    SciTech Connect

    Moll, A.J.

    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.

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

    SciTech Connect

    Tiskumara, R.; Joshi, R. P. Mauch, D.; Dickens, J. C.; Neuber, A. A.

    2015-09-07

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

  9. Measured Attenuation of Coplanar Waveguide on 6H, p-type SiC and High Purity Semi-Insulating 4H SiC through 800 K

    NASA Technical Reports Server (NTRS)

    Ponchak, George E.; Schwartz, Zachary D.; Alterovitz, Samuel A.; Downey, Alan N.

    2004-01-01

    Wireless sensors for high temperature applications such as oil drilling and mining, automobiles, and jet engine performance monitoring require circuits built on wide bandgap semiconductors. In this paper, the characteristics of microwave transmission lines on 4H-High Purity Semi-Insulating SiC and 6H, p-type SiC is presented as a function of temperature and frequency. It is shown that the attenuation of 6H, p-type substrates is too high for microwave circuits, large leakage current will flow through the substrate, and that unusual attenuation characteristics are due to trapping in the SiC. The 4H-HPSI SiC is shown to have low attenuation and leakage currents over the entire temperature range.

  10. A comparative study of the defects in Fe-doped or undoped semi-insulating InP after high temperature annealing

    SciTech Connect

    Cherkaoui, K.; Kallel, S.; Marrakchi, G.; Karoui, A.

    1996-12-31

    Fe-doped or undoped semi-insulating InP samples submitted to high temperature annealing process have been studied by Photoinduced current transient spectroscopy (PICTS) in order to compare the traps observed. The PICTS spectra of these samples show separately the presence of a multitude of traps having activation energies ranging from 0.12 eV to 0.66 eV. The Fe{sub In} trap level has not been clearly observed in all the samples. The comparison of the thermal parameters of the observed traps allows to assign some of them to a same defect. However, the identification seems to be less evident concerning other traps and should be rather related to the properties of the starting material.

  11. 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.

  12. 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.

  13. 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.

  14. The development of integrated chemical microsensors in GaAs

    SciTech Connect

    CASALNUOVO,STEPHEN A.; ASON,GREGORY CHARLES; HELLER,EDWIN J.; HIETALA,VINCENT M.; BACA,ALBERT G.; HIETALA,S.L.

    1999-11-01

    Monolithic, integrated acoustic wave chemical microsensors are being developed on gallium arsenide (GaAs) substrates. With this approach, arrays of microsensors and the high frequency electronic components needed to operate them reside on a single substrate, increasing the range of detectable analytes, reducing overall system size, minimizing systematic errors, and simplifying assembly and packaging. GaAs is employed because it is both piezoelectric, a property required to produce the acoustic wave devices, and a semiconductor with a mature microelectronics fabrication technology. Many aspects of integrated GaAs chemical sensors have been investigated, including: surface acoustic wave (SAW) sensors; monolithic SAW delay line oscillators; GaAs application specific integrated circuits (ASIC) for sensor operation; a hybrid sensor array utilizing these ASICS; and the fully monolithic, integrated SAW array. Details of the design, fabrication, and performance of these devices are discussed. In addition, the ability to produce heteroepitaxial layers of GaAs and aluminum gallium arsenide (AlGaAs) makes possible micromachined membrane sensors with improved sensitivity compared to conventional SAW sensors. Micromachining techniques for fabricating flexural plate wave (FPW) and thickness shear mode (TSM) microsensors on thin GaAs membranes are presented and GaAs FPW delay line and TSM resonator performance is described.

  15. Modeling atomic hydrogen diffusion in GaAs

    NASA Astrophysics Data System (ADS)

    Kagadei, Valerii A.; Nefyodtsev, E.

    2004-05-01

    The hydrogen diffusion model in GaAs in conditions of an intense flow of penetrating atoms has been developed. It is shown that the formation undersurface diffusion barrier layer from immobile interstitial molecules of hydrogen reduce probability of atoms penetration into crystal and rate of their diffusion in GaAs, and influence on the process of shallow- and/or deep-centers passivation. It is exhibited that the influence of diffusion barrier should be taken into account at optimum mode selection of GaAs structure hydrogenation.

  16. Photocurrent Spectroscopy of Single Wurtzite GaAs Nanowires

    SciTech Connect

    Kim, D. C.; Ahtapodov, L.; Boe, A. B.; Moses, A. F.; Dheeraj, D. L.; Fimland, B. O.; Weman, H.; Choi, J. W.; Ji, H.; Kim, G. T.

    2011-12-23

    Photocurrent of single wurtzite GaAs nanowires grown by Au-assisted molecular beam epitaxy is measured at room and low temperature (10 K). At room temperature a high photo-response with more than two orders of magnitude increase of current is observed. The wavelength dependence of the photocurrent shows a sharp change near the zinc blende GaAs band gap. The absence of the free exciton peak in the low temperature photocurrent spectrum, and problems related to determining the exact position of the energy bandgap of wurtzite GaAs from the observed data are discussed.

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. Simulation of silicon diffusion in GaAs

    NASA Astrophysics Data System (ADS)

    Saad, A. M.; Velichko, O. I.

    2011-03-01

    The simulation of coupled diffusion of silicon atoms and point defects in GaAs has been carried out for diffusion at the temperatures of 1000 and 850 °C. The amphoteric behavior of silicon atoms in GaAs has been taken into account in the investigation of high concentration diffusion from silicon layer deposited on GaAs substrate. The calculated dopant profiles agree well with the experimental ones and they confirm the adequacy of the model of silicon diffusion used for simulation. A comparison with the experimental data has enabled this work to obtain the parameters of silicon effective diffusivity and other values describing high concentration silicon diffusion in GaAs.

  2. 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.

  3. 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.

  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. 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.

  6. Laser-assisted metalorganic molecular beam epitaxy of GaAs

    NASA Astrophysics Data System (ADS)

    Donnelly, V. M.; Tu, C. W.; Beggy, J. C.; McCrary, V. R.; Lamont, M. G.; Harris, T. D.; Baiocchi, F. A.; Farrow, R. C.

    1988-03-01

    We report preliminary studies of the growth of homoepitaxial GaAs by laser-assisted metalorganic molecular beam epitaxy, using triethylgallium (TEGa) and As4 sources and a 193 nm ArF excimer laser. Laser irradiation results in a high, selective-area growth rate at temperatures below 450 °C, where pyrolytic growth is very slow. The process is extremely efficient, with roughly unit probability for impinging TEGa molecules sticking and being dissociated by laser radiation to form GaAs. From the strong dependence on laser fluence, the growth enhancement process appears to be pyrolytic in nature (because of transient heating by the pulsed laser) and not photolytic. The cross section for photolysis must be at least ten times lower than the gas-phase value (9×10-18 cm2). The surface morphology of films grown at 400 °C is rough at threshold fluences (˜0.10 J/cm2), but becomes smooth at higher fluences (˜0.13 J/cm2). These regions with relatively smooth surfaces exhibit enhanced photoluminescence yields compared to areas receiving less intense laser radiation.

  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. Surface Science Analysis of GaAs Photocathodes Following Sustained Electron Beam Delivery

    SciTech Connect

    Shutthanandan, V.; Zhu, Zihua; Stutzman, Marcy L.; Hannon, Fay; Hernandez-Garcia, Carlos; Nandasiri, Manjula I.; Kuchibhatla, Satyanarayana V N T; Thevuthasan, Suntharampillai; Hess, Wayne P.

    2012-06-12

    Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power Free Electron Lasers (FEL). Several photocathode degradation processes are suspected, including defect formation by ion back bombardment, photochemistry of surface adsorbed species and irradiation-induced surface defect formation. To better understand the mechanisms of photocathode degradation, we have conducted surface and bulk analysis studies of two GaAs photocathodes removed from the FEL photoinjector after delivering electron beam for a few years. The analysis techniques include Helium Ion Microscopy (HIM), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Secondary Ion Mass Spectrometry (SIMS). In addition, strained super-lattice GaAs photocathode samples, removed from the CEBAF photoinjector were analyzed using Transmission Electron Microscopy (TEM) and SIMS. This analysis of photocathode degradation during nominal photoinjector operating conditions represents first steps towards developing robust new photocathode designs necessary for generating sub-micron emittance electron beams required for both fourth generation light sources and intense polarized CW electron beams for nuclear and high energy physics facilities.

  9. Phononic Crystal Waveguiding in GaAs

    NASA Astrophysics Data System (ADS)

    Azodi Aval, Golnaz

    Compared to the much more common photonic crystals that are used to manipulate light, phononic crystals (PnCs) with inclusions in a lattice can be used to manipulate sound. While trying to propagate in a periodically structured media, acoustic waves may experience geometries in which propagation forward is totally forbidden. Furthermore, defects in the periodicity can be used to confine acoustic waves to follow complicated routes on a wavelength scale. Using advanced fabrication methods, we aim to implement these structures to control surface acoustic wave (SAW) propagation on the piezoelectric surface and eventually interact SAWs with quantum structures. To investigate the interaction of SAWs with periodic elastic structures, SAW interdigital transducers (IDTs) and PnC fabrication procedures were developed. GaAs is chosen as a piezoelectric substrate for SAWs propagation. Lift-off photolithography processes were used to fabricate IDTs with finger widths as low as 1.5 microns. PnCs are periodic structures of shallow air holes created in GaAs substrate by means of a wet-etching process. The PnCs are square lattices with lattice constants of 8 and 4 microns. To predict the behavior of a SAW when interacting with the PnC structures, an FDTD simulator was used to calculate the band structures and SAW wave displacement on the crystal surface. The bandgap (BG) predicted for the 8 micron crystal ranges from 180 MHz to 220 MHz. Simulations show a shift in the BG position for 4 microns crystals ranging from 391 to 439 MHz. Two main waveguide geometries were considered in this work: a simple line waveguide and a funneling entrance line waveguide. Simulations indicated an increase in acoustic power density for the funneling waveguides. Fabricated device evaluated with electrical measurements. In addition, a scanning Sagnac interferometer is used to map the energy density of the SAWs. The Sagnac interferometer is designed to measure the outward displacement of a surface due to

  10. Electron-beam-induced reactions at O 2/GaAs(1 0 0) interfaces

    NASA Astrophysics Data System (ADS)

    Palomares, F. J.; Alonso, M.; Jiménez, I.; Avila, J.; Sacedón, J. L.; Soria, F.

    2001-06-01

    We present a high resolution core-level photoemission study with synchrotron radiation, which illustrates the induced chemical reactions at O 2/GaAs(1 0 0) interfaces upon irradiation with a 150 eV electron beam, for different current densities. A detailed line shape analysis of As(3d) and Ga(3d) levels allows us to identify the oxide phases formed, and to follow their evolution up to coverages of 10 Å. Equivalent amounts of Ga and As oxides are produced. The distribution of As oxides, in particular the As 2O 3/As 2O 5 oxide ratio, is found to depend on the electronic current density, whereas no differences are observed for Ga oxides. These changes are discussed in terms of the kinetic constraints introduced by the electron beam and the instability of the As 2O 5 species upon electron bombardment in vacuum.

  11. Polycrystal GaAs infrared windows

    NASA Astrophysics Data System (ADS)

    Wada, Hideo; Shibata, Ken-ichiro; Yamashita, Masashi; Nakayama, Shigeru; Fujii, Akihito

    2001-09-01

    There are difficult points such as lowering of the detection or recognition capability of some targets by aerodynamic heating with speedup of the aircraft and missile and restriction of the operation by the raindrop in rainfall time on the conventional ZnS infrared window application used for missile seeker and FLIR equipment. Therefore, in this study, the promising polycrystal GaAs which has low infrared radiations in high temperature was produced using HB method (Horizontal Boat method) and VG method (Vertical Boat method) as a new infrared window material expected the durability for rain erosion. As the result, 70mm2 windows by the HB method and 100mm diameter windows by VB method were realized. Moreover, their optical characteristics, mechanical properties and thermal shock durabilities were measured and they were confirmed to be about 56% in average transmittance in the wavelength of 10micrometers bands, 530~630kg/mm2 in their hardness and thermostable at 300 degree(s)C.

  12. 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.

  13. Confinement in thickness-controlled GaAs polytype nanodots.

    PubMed

    Vainorius, Neimantas; Lehmann, Sebastian; Jacobsson, Daniel; Samuelson, Lars; Dick, Kimberly A; Pistol, Mats-Erik

    2015-04-01

    Polytype nanodots are arguably the simplest nanodots than can be made, but their technological control was, up to now, challenging. We have developed a technique to produce nanowires containing exactly one polytype nanodot in GaAs with thickness control. These nanodots have been investigated by photoluminescence, which has been cross-correlated with transmission electron microscopy. We find that short (4-20 nm) zincblende GaAs segments/dots in wurtzite GaAs confine electrons and that the inverse system confines holes. By varying the thickness of the nanodots we find strong quantum confinement effects which allows us to extract the effective mass of the carriers. The holes at the top of the valence band have an effective mass of approximately 0.45 m0 in wurtzite GaAs. The thinnest wurtzite nanodot corresponds to a twin plane in zincblende GaAs and gives efficient photoluminescence. It binds an exciton with a binding energy of roughly 50 meV, including central cell corrections. PMID:25761051

  14. 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.

  15. Si surface preparation with Si beam irradiation on the growth on III-V on Si

    SciTech Connect

    Kawanami, H.; Baskar, K.; Sakata, I.; Sekigawa, T.

    1998-12-31

    The preliminary results of the effects of the Si beam irradiation for the Si surface preparation on the growth of GaAs on Si by MBE are reported. The effects are combined with thermal cyclic anneal (TCA). A slight improvement in the crystalline quality is observed on the photoluminescence spectra of the films grown with Si irradiation, In experimental conditions, Si irradiation during the Si surface preparation has not indicated large effects on the FWHM of XRD. It is also indicated that initial substrate surface treatment affects the quality of thicker film through TCA treatment. Higher substrate temperature during Si beam irradiation is expected to indicate positive Si beam irradiation effects.

  16. 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...

  17. Humidity effects on tribochemical removal of GaAs surfaces

    NASA Astrophysics Data System (ADS)

    Yu, Bingjun; Gao, Jian; Jin, Chenning; Xiao, Chen; Wu, Jiang; Liu, Huiyun; Jiang, Shulan; Chen, Lei; Qian, Linmao

    2016-06-01

    Defect-free tribochemical removal of gallium arsenide (GaAs) was demonstrated in vacuum, dry air, and various humidity environments by scratching with a SiO2 tip. The removal depth increases with increasing relative humidity (1–90%), and reaches its maximum value in water. A perfect crystal matrix without defects was observed in the cross section of the scratched groove using a transmission electron microscope. A model based on reactive tip scratching-induced oxidation, water solubility of debris, and adhesion effect was proposed to interpret tribochemical removal of GaAs surface. This study provides new insights into defect-free and site-controlled nanofabrication of GaAs.

  18. Recent developments in GaAs solar cells

    SciTech Connect

    Kamath, G.S.

    1983-08-01

    The higher efficiency, radiation hardness and greater survivability at higher temperatures give GaAs cells a distinct advantage in space applications over silicon cells. Recent progress in fabrication technology has demonstrated the feasibility of high yield mass production of GaAs cells at a cost low enough to warrant their use in satellite power systems. Small panels have been assembled for several preliminary flight tests with encouraging results. Additional developments in concentrator cells as well as in all (AlGa)As cells for future systems such as cascade cells are reviewed. The (AlGa)As cells, in combination with silicon or GaAs cells, could lead to a multijunction cell with an efficiency 50% higher than any single junction cell.

  19. 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.

  20. Unpinned GaAs MOS capacitors and transistors

    NASA Astrophysics Data System (ADS)

    Tiwari, Sandip; Wright, Steven L.; Batey, John

    1988-09-01

    Metal-oxide-semiconductor (MOS) capacitors and field-effect transistors (MOSFETs) in the GaAs semiconductor system using an unpinned interface are described. The structures utilize plasma-enhanced chemical-vapor deposition (PECVD) for the silicon-dioxide insulator on GaAs that has been terminated with a few monolayers of silicon during growth by molecular beam epitaxy. Interface densities in the structures have been reduced to about 10 to the 12th/sq cm-eV. High-frequency characteristics indicate strong inversion of both p-type and n-type GaAs. The excellent insulating quality of the oxide has allowed demonstration of quasi-static characteristics. MOSFETs operating in depletion mode with a transconductance of 60 mS/mm at 8.0-micron gate lengths have been fabricated.

  1. Atomic hydrogen cleaning of GaAS Photocathodes

    SciTech Connect

    M. Poelker; J. Price; C. Sinclair

    1997-01-01

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

  2. 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. PMID:26339987

  3. 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.

  4. 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.

  5. Temperature dependence of optical properties of GaAs

    NASA Technical Reports Server (NTRS)

    Yao, Huade; Snyder, Paul G.; Woollam, John A.

    1991-01-01

    The effect of temperature on the optical properties of GaAs was investigated using spectroscopic ellipsometry measurements, between room temperature and about 610 C in increments of 50 C, of pseudodielectric functions and related optical constants of GaAs. A quantitative analysis of the pseudodielectric function spectrum was carried out using a harmonic-oscillator approximation (HOA) to fit the measured dielectric functions. Good fits were obtained with this model, which provides a convenient means of reproducing the GaAs dielectric function at any temperature, by using the temperature-dependent oscillator parameters. The HOA analysis also provides information about band-gap variation with temperature. Using the measured optical constants at a number of fixed temperatures, an algorithm was developed for computing the dielectric function spectrum at an arbitrary temperature in the range 22-610 C.

  6. 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

  7. 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.

  8. GaAs MMICs for EHF SATCOM ground terminals

    NASA Astrophysics Data System (ADS)

    Hampel, Daniel; Upton, Alastair

    The authors address the potential use of GaAs, and their benefits, for EHF ground terminals. This assessment of GaAs MMICs (monoltihic microwave integrated circuits), while concentrating on the analog RF front end, also includes some associated critical digital functions. Performance requirements and specific application areas, such as 20-GHz low-noise amplifiers and 44-GHz power amplifiers, are discussed and current state-of-the-art performance in low-noise high-electron-mobility transistors (HEMTs) and high-efficiency pseudomorphic HEMTs is presented, along with projected performance improvements over the next five years.

  9. 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.

  10. Peeled film GaAs solar cells for space power

    SciTech Connect

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

    1990-05-01

    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.

  11. GaAs laser diode pumped Nd:YAG laser

    NASA Technical Reports Server (NTRS)

    Conant, L. C.; Reno, C. W.

    1974-01-01

    A 1.5-mm by 3-cm neodymium-ion doped YAG laser rod has been side pumped using a GaAs laser diode array tuned to the 8680-A absorption line, achieving a multimode average output power of 120 mW for a total input power of 20 W to the final-stage laser diode drivers. The pumped arrangement was designed to take advantage of the high brightness of a conventional GaAs array as a linear source by introducing the pump light through a slit into a close-wrapped gold coated pump cavity. This cavity forms an integrating chamber for the pump light.

  12. 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.

  13. 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.

  14. Epitaxial EuO thin films on GaAs

    SciTech Connect

    Swartz, A. G.; Ciraldo, J.; Wong, J. J. I.; Li Yan; Han Wei; Lin Tao; Shi, J.; Kawakami, R. K.; Mack, S.; Awschalom, D. D.

    2010-09-13

    We demonstrate the epitaxial growth of EuO on GaAs by reactive molecular beam epitaxy. Thin films are grown in an adsorption-controlled regime with the aid of an MgO diffusion barrier. Despite the large lattice mismatch, it is shown that EuO grows well on MgO(001) with excellent magnetic properties. Epitaxy on GaAs is cube-on-cube and longitudinal magneto-optic Kerr effect measurements demonstrate a large Kerr rotation of 0.57 deg., a significant remanent magnetization, and a Curie temperature of 69 K.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Photoluminescence of Si-doped GaAs epitaxial layers

    SciTech Connect

    Yaremenko, N. G. Karachevtseva, M. V.; Strakhov, V. A.; Galiev, G. B.; Mokerov, V. G.

    2008-12-15

    The effect of arsenic pressure on the amphoteric behavior of Si during the growth of the Si-doped (100)-, (111)Ga-, and (111)As-oriented GaAs layers is studied by photoluminescence spectroscopy. The edge luminescence band is examined, and the concentration and the degree of compensation as functions of the arsenic pressure are determined. Nonstoichiometry defects in GaAs layers grown with a deficit and an excess of arsenic are studied. It is shown that the defects formed in the (111)Ga- and (111)As-oriented layers are different in nature.

  1. Inversion-mode GaAs wave-shaped field-effect transistor on GaAs (100) substrate

    NASA Astrophysics Data System (ADS)

    Zhang, Jingyun; Lou, Xiabing; Si, Mengwei; Wu, Heng; Shao, Jiayi; Manfra, Michael J.; Gordon, Roy G.; Ye, Peide D.

    2015-02-01

    Inversion-mode GaAs wave-shaped metal-oxide-semiconductor field-effect transistors (WaveFETs) are demonstrated using atomic-layer epitaxy of La2O3 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 ION/IOFF ratio of greater than 107.

  2. 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}.

  3. Effect of gamma-ray irradiation on structural properties of GaAsN films grown by metal organic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Klangtakai, Pawinee; Sanorpim, Sakuntam; Wattanawareekul, Atiwat; Suwanyangyaun, Pattana; Srepusharawoot, Pornjuk; Onabe, Kentaro

    2015-05-01

    The effects of gamma-ray irradiation on the structural properties of GaAs1-xNx films (N concentration=1.9 and 5.1 at%) grown by metal organic vapor phase epitaxy on GaAs (001) substrates were investigated. The GaAs1-xNx films were irradiated by gamma rays with irradiation strength of 0-2.0 MGy. Scanning electron microscopy and atomic force microscopy results showed that a gamma ray with a strength of 0, 0.5, 1.0, 1.5, and 2.0 MGy formed holes with a density of 0.0, 8.8, 9.4, 11.5, and 11.9 μm-2, respectively, on the surface of a GaAs0.981N0.019 film with low N content. On the other hand, the irradiated high-N-content GaAs0.949N0.051 film exhibited a cross-hatch pattern, which was induced by partial strain relaxation at high N levels, with a line density of 0.0, 0.21, 0.37, 0.67, and 0.26 μm-1 corresponding to an irradiation strength of 0, 0.5, 1.0, 1.5, and 2.0 MGy, respectively. The high-resolution X-ray diffraction and Raman scattering results revealed an increase in N incorporation and strain relaxation after irradiation. In addition, the GaAs0.949N0.051 films exhibited phase separation, which took place via N out-diffusion across the interface when the irradiation strength exceeded 1.0 MGy. Based on these results, the main cause of structural change was determined to be the irradiation effects including displacement damage and gamma-ray heating.

  4. 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.

  5. Use of ZnSe as an interlayer for GaAs growth on Si

    NASA Astrophysics Data System (ADS)

    Bringans, R. D.; Biegelsen, D. K.; Swartz, L.-E.; Ponce, F. A.; Tramontana, J. C.

    1992-07-01

    ZnSe has been used as an interlayer between Si substrates and GaAs layers in molecular beam epitaxial growth of GaAs on Si. It is found that thin GaAs layers are much more uniform and have fewer defects when grown on ZnSe interlayers than when they are grown directly on Si. The growth of GaAs on ZnSe is much more difficult than the more usual reverse sequence, and different growth modes for the epitaxy of GaAs on ZnSe are compared. Deposition of GaAs on ZnSe at room temperature followed by solid phase regrowth led to an epitaxial layer plus a polycrystalline layer. A slow ramping of the substrate temperature during the GaAs epitaxial growth was found to give the best crystal quality.

  6. 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.

  7. The surface chemistry of GaAs atomic layer epitaxy

    SciTech Connect

    Creighton, J.R.; Banse, B.A.

    1991-01-01

    In this paper we review three proposed mechanisms for GaAs ALE and review or present data support or contradiction of these mechanisms. Surface chemistry results clearly demonstrated that TMGa irreversibly chemisorbs on the Ga-rich GaAs(100) surface. The reactive sticking coefficient (RSC) of TMGa on the adsorbate-free Ga-rich GaAs(100) surface was measured to be {approximately}0.5, conclusively demonstrating that the selective adsorption'' mechanism of ALE is not valid. We describe kinetic evidence for methyl radical desorption in support of the adsorbate inhibition'' mechanism. The methyl radical desorption rates determined by temperature programmed desorption (TPD) demonstrate that desorption is at least a factor of {approximately}10 faster from the As-rich c(2 {times} 8)/(2 {times} 4) surface than from the Ga-rich surface. It is disparity in CH{sub 3} desorption rates between the As-rich and Ga-rich surfaces that is largely responsible for GaAs ALE behavior. A gallium alkyl radical (e.g. MMGa) is also observed during TPD and molecular beam experiments, in partial support of the flux balance'' mechanism. Stoichiometry issues of ALE are also discussed. We have discovered that arsine exposures typical of atmospheric pressure and reduced pressure ALE lead to As coverages {ge} 1 ML, which provides the likely solution to the stoichiometry question regarding the arsine cycle. 32 refs., 6 figs.

  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. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Processing and characterization of epitaxial GaAs radiation detectors

    NASA Astrophysics Data System (ADS)

    Wu, X.; Peltola, T.; Arsenovich, T.; Gädda, A.; Härkönen, J.; Junkes, A.; Karadzhinova, A.; Kostamo, P.; Lipsanen, H.; Luukka, P.; Mattila, M.; Nenonen, S.; Riekkinen, T.; Tuominen, E.; Winkler, A.

    2015-10-01

    GaAs devices have relatively high atomic numbers (Z=31, 33) and thus extend the X-ray absorption edge beyond that of Si (Z=14) devices. In this study, radiation detectors were processed on GaAs substrates with 110 - 130 μm thick epitaxial absorption volume. Thick undoped and heavily doped p+ epitaxial layers were grown using a custom-made horizontal Chloride Vapor Phase Epitaxy (CVPE) reactor, the growth rate of which was about 10 μm / h. The GaAs p+/i/n+ detectors were characterized by Capacitance Voltage (CV), Current Voltage (IV), Transient Current Technique (TCT) and Deep Level Transient Spectroscopy (DLTS) measurements. The full depletion voltage (Vfd) of the detectors with 110 μm epi-layer thickness is in the range of 8-15 V and the leakage current density is about 10 nA/cm2. The signal transit time determined by TCT is about 5 ns when the bias voltage is well above the value that produces the peak saturation drift velocity of electrons in GaAs at a given thickness. Numerical simulations with an appropriate defect model agree with the experimental results.

  14. Effects of incident short wavelength (UV) light on the morphology of MBE grown GaAs

    NASA Astrophysics Data System (ADS)

    Beaton, Daniel A.; Sanders, Charlotte; Alberi, Kirstin

    2014-03-01

    The exploration of novel semiconductor materials increasingly relies on growth techniques that operate far from equilibrium in order to overcome thermodynamic limitations to synthesis. As one example, low temperature molecular beam epitaxy (MBE) offers a pathway to enhance substitutional dopant incorporation over surface segregation but adatom mobility suffers as a consequence and leads to higher concentrations of lattice defects. We explore the use of external stimuli, namely incident UV light, as a means to influence adatom kinetics; UV light is absorbed in the first few atomic layers of the as-growing epitaxial film and the effects of the incident radiation predominantly effect only the surface adatoms. GaAs homoepitaxy by MBE is studied as a model case as a function of illumination conditions under broadband Xe and KrF excimer laser irradiation. In-situ reflective high energy electron diffraction analysis paired with ex-situ atomic force microscopy measurements yields insight into the effects of photon irradiation on surface adatom mobility, morphology and smoothing processes. This work was supported by the DOE Office of Science, Basic Energy Sciences under contract DE-AC36-08GO28308.

  15. Structural and optical characterization of Mg-doped GaAs nanowires grown on GaAs and Si substrates

    SciTech Connect

    Falcão, B. P. Leitão, J. P.; Correia, M. R.; Soares, M. R.; Morales, F. M.; Mánuel, J. M.; Garcia, R.; Gustafsson, A.; Moreira, M. V. B.; Oliveira, A. G. de; González, J. C.

    2013-11-14

    We report an investigation on the morphological, structural, and optical properties of large size wurtzite GaAs nanowires, low doped with Mg, grown on GaAs(111)B and Si(111) substrates. A higher density of vertical nanowires was observed when grown upon GaAs(111)B. Very thin zinc-blende segments are observed along the axis of the nanowires with a slightly higher linear density being found on the nanowires grown on Si(111). Low temperature cathodoluminescence and photoluminescence measurements reveal an emission in the range 1.40–1.52 eV related with the spatial localization of the charge carriers at the interfaces of the two crystalline phases. Mg related emission is evidenced by cathodoluminescence performed on the GaAs epilayer. However, no direct evidence for a Mg related emission is found for the nanowires. The excitation power dependency on both peak energy and intensity of the photoluminescence gives a clear evidence for the type II nature of the radiative transitions. From the temperature dependence on the photoluminescence intensity, non-radiative de-excitation channels with different activation energies were found. The fact that the estimated energies for the escape of the electron are higher in the nanowires grown on Si(111) suggests the presence of wider zinc-blende segments.

  16. 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.

  17. 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. PMID:25686555

  18. 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.

  19. alloy lattice-matched to GaAs: a first-principles study

    NASA Astrophysics Data System (ADS)

    Ma, Xiaoyang; Li, Dechun; Zhao, Shengzhi; Li, Guiqiu; Yang, Kejian

    2014-10-01

    First-principles calculations based on density functional theory have been performed for the quaternary GaAs1- x- y N x Bi y alloy lattice-matched to GaAs. Using the state-of-the-art computational method with the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, electronic, and optical properties were obtained, including band structures, density of states (DOSs), dielectric function, absorption coefficient, refractive index, energy loss function, and reflectivity. It is found that the lattice constant of GaAs1- x- y N x Bi y alloy with y/ x =1.718 can match to GaAs. With the incorporation of N and Bi into GaAs, the band gap of GaAs1- x- y N x Bi y becomes small and remains direct. The calculated optical properties indicate that GaAs1- x- y N x Bi y has higher optical efficiency as it has less energy loss than GaAs. In addition, it is also found that the electronic and optical properties of GaAs1- x- y N x Bi y alloy can be further controlled by tuning the N and Bi compositions in this alloy. These results suggest promising applications of GaAs1- x- y N x Bi y quaternary alloys in optoelectronic devices.

  20. Femtosecond pulsed laser ablation of GaAs

    NASA Astrophysics Data System (ADS)

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

    2004-01-01

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

  1. Lateral epitaxial overgowth of GaAs by organometallic chemical vapor deposition

    NASA Technical Reports Server (NTRS)

    Gale, R. P.; Mcclelland, R. W.; Fan, J. C. C.; Bozler, C. O.

    1982-01-01

    Lateral epitaxial overgrowth of GaAs by organometallic chemical vapor deposition has been demonstrated. Pyrolytic decomposition of trimethylgallium and arsine, without the use of HCl, was used to deposit GaAs on substrates prepared by coating (110) GaAs wafers with SiO2, then using photolithography to open narrow stripes in the oxide. Lateral overgrowth was seeded by epitaxial deposits formed on the GaAs surfaces exposed by the stripe openings. The extent of lateral overgrowth was investigated as a function of stripe orientation and growth temperature. Ratios of lateral to vertical growth rates greater than five have been obtained. The lateral growth is due to surface-kinetic control for the two-dimensional growth geometry studied. A continuous epitaxial GaAs layer 3 microns thick has been grown over a patterned mask on a GaAs substrate and then cleaved from the substrate.

  2. 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.

  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. 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.

  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. 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.

  7. 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.

  8. 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.

  9. GaAs arrays for X-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    Owens, Alan; Andersson, Hans; Campbell, M.; Lumb, David H.; Nenonen, Seppo A. A.; Tlustos, Lukas

    2004-09-01

    We present results from our compound semiconductor laboratory program and describe the development of a large area GaAs imaging array for planetary remote sensing applications. The device is fabricated from ~150 micron thick epitaxial material, patterned into a 64 x 64 pixel array, back-thinned and contacted. It will be flip-chip bump bonded onto a custom designed, fully spectroscopic, low noise (< 20 e- rms) active pixel sensor ASIC. At present, the ASIC is still under development and so in order to validate and qualify the various technological steps, we have produced a GaAs imager based on the MEDIPIX-1 format using a MEDIPIX-1 readout chip. In X-ray tests, the device was found to work well with a bump yield of 99.9%. After flat field corrections, the spatial uniformity of the array was commensurate with Poisson noise.

  10. 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.

  11. Sub-additivity in Electron Emission from GaAs

    NASA Astrophysics Data System (ADS)

    Brunkow, Evan; Clayburn, Nathan; Becker, Maria; Jones, Eric; Batelaan, Herman; Gay, Timothy

    2016-05-01

    When two spatially-overlapped laser pulses (775 nm center wavelength, 75 fs duration) are incident on an untreated <100> GaAs crystal surface, the electron emission rate depends on the temporal separation between the two pulses. We have shown that for delays between 0.2 and 1000ps, the emission rate is ``sub-additive'', i.e., is lower than when the beams have separation >> 1 ns. We believe the cause of this sub-additivity is an increase in reflectance and transmittance due to electrons occupying the excited state of the GaAs. We are now able to manipulate the magnitude of the sub-additivity by changing the number of electrons that are in the excited state. Sub-additivity is not observed with tungsten tip surfaces which have no excited state. Funded by NSF PHY-1505794, EPSCoR IIIA-1430519, and NSF 1306565 (HB).

  12. 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.

  13. Oxygen-enhanced wet thermal oxidation of GaAs

    NASA Astrophysics Data System (ADS)

    Bauters, J. F.; Fenlon, R. E.; Seibert, C. S.; Yuan, W.; Plunkett, J. S. B.; Li, J.; Hall, D. C.

    2011-10-01

    An oxygen-enhanced wet thermal oxidation process is used to grow smooth, uniform, insulating native oxides of GaAs. At 420 °C, a maximum linear growth rate of 4.8 nm/min is observed for oxidation in water vapor with 2000 ppm O2 added relative to the N2 carrier gas, with growth ceasing by 7000 ppm. Films as thick as 800 nm with surface roughness as low as 0.2 nm are demonstrated. In fabricated metal-oxide-semiconductor capacitors, a 412 nm thick native oxide film exhibits a factor of ˜2700 reduction in leakage current density at 1 V relative to a direct metal (Au:Ti) to GaAs contact.

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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. PMID:26698787

  20. SEU design consideration for MESFETs on LT GaAs

    SciTech Connect

    Weatherford, T.R.; Radice, R.; Eskins, D.

    1997-12-01

    Computer simulation results are reported on transistor design and single-event charge collection modeling of metal-semiconductor field effect transistors (MESFETs) fabricated in the Vitesse H-GaAsIII{reg_sign} process on Low Temperature grown (LT) GaAs epitaxial layers. Tradeoffs in Single Event Upset (SEU) immunity and transistor design are discussed. Effects due to active loads and diffusion barriers are examined.

  1. Epitaxial Fe on free-standing GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Yang, Mingze; Darbandi, Ali; Majumder, Sarmita; Watkins, Simon; Kavanagh, Karen

    2016-07-01

    Epitaxial Fe contacts have been fabricated onto the top half of free-standing, Te-doped GaAs nanowires (NWs) via electrodeposition. Electrical isolation from the substrate via a polymeric layer enabled the measurement of electrical transport through individual wires. Using a fixed probe within a scanning electron microscope, an average metal-semiconductor diode barrier height of 0.69 ± 0.03 eV (ideality factor 1.48 ± 0.02) was found.

  2. 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.

  3. 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.

  4. 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.

  5. Lattice Distortion of GaAsBi Alloy Grown on GaAs by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Takehara, Yuji; Yoshimoto, Masahiro; Huang, Wei; Saraie, Junji; Oe, Kunishige; Chayahara, Akiyoshi; Horino, Yuji

    2006-01-01

    GaAs1-xBix alloys were grown on GaAs by molecular beam epitaxy (MBE). The lattice constants perpendicular and parallel to the surface of epilayers were estimated by high-resolution X-ray diffraction (XRD) analysis. The GaBi molar fraction was estimated by the Rutherford backscattering spectroscopy (RBS). GaAs1-xBix epilayers with GaBi molar fractions less than 5% were almost coherently grown on GaAs substrate with compressive strain. The lattice mismatch between GaAs1-xBix (x=5%) and GaAs was estimated to be approximately 0.5%.

  6. Observation and Measurement of Temperature Rise and Distribution on GaAs Photo-cathode Wafer with a 532nm Drive Laser and a Thermal Imaging Camera

    SciTech Connect

    Shukui Zhang, Stephen Benson, Carlos Hernandez-Garcia

    2011-03-01

    Significant temperature rise and gradient are observed from a GaAs photo-cathode wafer irradiated at various power levels with over 20W laser power at 532nm wavelength. The laser power absorption and dissipated thermal distribution are measured. The result shows a clear indication that proper removal of laser induced heat from the cathode needs to be considered seriously when designing a high average current or low quantum efficiency photo-cathode electron gun. The measurement method presented here provides a useful way to obtain information about both temperature and thermal profiles, it also applies to cathode heating study with other heating devices such as electrical heaters.

  7. 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.

  8. Cathodoluminescence characterization of ion implanted GaAs

    NASA Astrophysics Data System (ADS)

    Cone, M. L.

    1980-03-01

    The unique properties of GaAs make it possible to construct integrated circuit devices that are impossible in Si. The Air Force Avionics Laboratory/AADR has been developing this technology for a number of years. The difficulty of introducing dopants by diffusion has lead ion implantation to play an increasing role in the fabrication process. The present production technique for high performance devices is to fabricate large quantities and select those few that meet the desired specifications. Having a nondestructive technique that can be used to characterize the implantation process during fabrication of the device so as to reject faulty device structures can save valuable time as well as money. Depth-resolved cathodoluminescence is a process that can be used for this purpose. This research develops and verifies a model of cathodoluminescence in ion implanted GaAs. This model can now be used as a tool for further study of ion implanted GaAs. This is the first step in developing cathodoluminescence as a tool for deducing the shape of the ion implanted depth profile in semiconductor materials.

  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. PMID:25870287

  10. Preparation and characterization of pulse electrodeposited GaAs films

    NASA Astrophysics Data System (ADS)

    Murali, K. R.; Trivedi, D. C.

    2006-04-01

    GaAs is a III-V compound possessing high mobility and a direct band gap of 1.43 eV, making it a very suitable candidate for photovoltaic applications. Thin GaAs films were prepared by plating an aqueous solution containing GaCl3 and As2O3 at a pH of 2 and at room temperature. The current density was kept at 50 mA cm-2 and the duty cycle was varied in the range 10-50%. The films were deposited on titanium, nickel and tin oxide coated glass substrates. Films exhibited polycrystalline nature with peaks corresponding to single-phase GaAs. Optical absorption measurements indicated a direct band gap of 1.40 eV. Atomic force microscope measurements indicated uniform coverage with large crystallites for the films deposited at higher duty cycles. Photoelectrochemical cells were made using the films as photoelectrodes and graphite as counter electrode in 1 M polysulphide electrolyte. At 60 mW cm-2 illumination, an open-circuit voltage of 0.5 V and a short-circuit current density of 5.0 mA cm-2 were observed for the films deposited at a duty cycle of 50%.

  11. Integration of colossal magnetoresistors with GaAs

    NASA Astrophysics Data System (ADS)

    Khartsev, S. I.; Kim, J.-H.; Grishin, A. M.

    2005-10-01

    Colossal magnetoresistive (CMR) La 0.67Ca 0.33MnO 3 (LCMO) and La 0.67Sr 0.33MnO 3 (LSMO) films have been grown by pulsed laser deposition technique on GaAs(0 0 1) substrates buffered with epitaxial MgO layer. X-ray diffraction revealed strong c-axis out-of-plane orientation and strong in-plane texture of CMR/MgO bilayers on GaAs single crystal. The maximum temperature coefficient of resistivity TCR=9.0% K -1 at 223 K and 2.0% K -1 at 327 K, and the magnetoresistance Δ ρ/ ρ˜-7.95% kOe -1 and -1.47% kOe -1 have been achieved for LCMO/MgO/GaAs and LSMO/MgO/GaAs heteroepitaxial structures, respectively. Comparison with the test LCMO and LSMO films grown directly onto the bulk MgO(0 0 1) single crystal demonstrates the identity of LSMO/MgO/GaAs and LSMO/MgO films properties whereas the LCMO films grown on MgO buffered GaAs show lower transition temperature T=242 K compared to 253 K in LCMO/MgO.

  12. Photoluminescence of Be implanted Si-doped GaAs

    SciTech Connect

    Kroon, R.E.; Botha, J.R.; Neethling, J.H.; Drummond, T.J.

    1999-11-12

    Degenerately doped n-type GaAs produces band-to-band luminescence with the peak energy dependent on the carrier concentration. In this study the photoluminescence of Si-doped GaAs is examined after implantation with high energy Be ions and annealing. The band-to-band peak energy in the unimplanted (reference) material is shown to be smaller than reported values in Te-doped GaAs of the same carrier concentration. This is attributed to compensation in the Si doped material as a result of its amphoteric nature. For the implanted samples, no luminescence was recorded for the unannealed samples or those annealed at 400 C and 500 C. Comparing the relative peak intensities from material annealed at 600 C for 15 min and 30 min indicates an increase in the number of As vacancies with anneal time. For samples annealed at 700 C and 800 C, the dominant luminescence is associated with Ga{sub As} antisite defects. It is suggested that formation of these defects occurs predominantly only at these higher temperatures. Crystal recovery as measured by the luminescence intensity increased with both anneal temperature and time. For the implanted sample annealed at 800 C for 15 min, the dominant peak height was 25% of that from the reference sample.

  13. Selective photon-stimulated desorption of hydrogen from GaAs surfaces.

    PubMed

    Petravic, M; Deenapanray, P N; Comtet, G; Hellner, L; Dujardin, G; Usher, B F

    2000-03-01

    Photon-stimulated desorption of H(+) from hydrogenated GaAs (110) and (100) surfaces was studied as a function of photon energy. Distinct peaks, observed around As 3d core-level binding energy for desorption from the GaAs (100) surface and in the As 3d and Ga 3p region for desorption from the GaAs (110) surface, show a striking similarity with the fine structure (spin-orbit splitting) measured in the photoemission from As 3d and Ga 3p levels. These results provide clear evidence for direct desorption processes and represent a basis for selective modification of hydrogenated GaAs surfaces. PMID:11017257

  14. Recovery of gallium and arsenic from GaAs wafer manufacturing slurries

    SciTech Connect

    Jadvar, R.; McCoy, B.J. ); Ford, B.; Galt, J. )

    1991-11-01

    Lapping and polishing slurries from the gallium arsenide (GaAs) wafer manufacturing process were used to develop simple and inexpensive methods for separation and recovery of valuable gallium and toxic arsenic. The lapping slurry, containing GaAs, glycerol, alumina, iron oxide, and water, is treated by a process involving water addition, dissolution of GaAs, mixing, sedimentation, decantation, and evaporation. The polishing slurry, containing GaAs, silica, sodium bicarbonate, sodium hypochlorite and water, is treated simply by a repetitive cycle of adding water, mixing, settling, decanting, and evaporating. After treatment, the slurries contain less than 5 ppm of dissolved arsenic and are considered non-hazardous.

  15. GaAs thin films and methods of making and using the same

    DOEpatents

    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.

  16. 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.

  17. GaAs high-speed digital IC technology: An overview

    SciTech Connect

    Larson, L.E.; Jensen, J.F.; Greiling, P.T.

    1986-10-01

    Gallium arsenide integrated circuit technology has advanced to the stage where small-scale integration (SSI) and medium-scale integration (MSI) circuits are available for implementation in high-speed digital systems. The recent availability of GaAs wafer foundries for fabrication of custom designs, along with commercially available GaAs components, allows system designers for the first time to take advantage of the inherent high speed and low power capabilities of the technology. Large-scale integration (LSI) complexity circuits are already being fabricated in the United States and abroad, and higher levels of integration are expected. This will result in improved levels of performance for large digital systems. The advantages of higher levels of integration are clearly evident, although there appears to be an optimum level of integration for each GaAs logic family beyond which system speed actually degrades. In conjunction with the development of GaAs technology, an industry-standard GaAs production process is also evolving. This generic process is available (with minor variations) from most of the GaAs wafer foundries and IC manufacturers. Here the authors review digital GaAs IC device and circuit technology and analyze the performance of GaAs circuits fabricated by this production process. They also analyze the effect of the GaAs IC integration level on computer system speed.

  18. Nonlinear optical studies and CO2 laser-induced melting of Zn-doped GaAs

    NASA Astrophysics Data System (ADS)

    James, R. B.; Mills, B. E.; Christie, W. H.; Eby, R. E.; Darken, L. S., Jr.

    1986-02-01

    The intensity dependence of the free-hole absorption of CO2 laser radiation in GaAs:Zn crystals has been measured. Experimental results pertaining to nonlinear optical transmission measurements, the topography of the laser-irradiated surfaces, deviations from stoichiometry in the near-surface region, the incorporation of oxygen, and the pulsed laser annealing of ion-implanted GaAs are discussed. The intensity dependence of the nonlinear absorption is found to be closely approximated by an inhomogeneously broadened two-level model; the measured level for the saturation intensity is in good agreement with theoretical calculations. An energy-density 'window' exists for which the resolidified layer is both crystalline and maintains a high degree of surface planarity. Ga-rich regions remain after the solidification of the molten layer. The amount of arsenic loss increases with increasing laser-energy density and number of laser shots.

  19. Quantum dot solar cell tolerance to alpha-particle irradiation

    SciTech Connect

    Cress, Cory D.; Hubbard, Seth M.; Landi, Brian J.; Raffaelle, Ryne P.; Wilt, David M.

    2007-10-29

    The effects of alpha-particle irradiation on an InAs quantum dot (QD) array and GaAs-based InAs QD solar cells were investigated. Using photoluminescence (PL) mapping, the PL intensity at 872 and 1120 nm, corresponding to bulk GaAs and InAs QD emissions, respectively, were measured for a five-layer InAs QD array which had a spatially varying total alpha-particle dose. The spectral response and normalized current-voltage parameters of the solar cells, measured as a function of alpha-particle fluence, were used to investigate the change in device performance between GaAs solar cells with and without InAs QDs.

  20. 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.

  1. 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...

  2. 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...

  3. 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...

  4. 46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 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...

  5. 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.

  6. Optically Pumped NMR Studies of Mechanically Induced Strain in GaAs Films

    NASA Astrophysics Data System (ADS)

    Bowers, Clifford; Wood, Ryan; Tokarski, John, III; McCarthy, Lauren; Saha, Dipta; Stanton, Christopher; Moreno, Jesus

    2015-03-01

    We present a new methodology for measuring strain in semiconductor films based on optically pumped NMR (OPNMR). Single crystals of GaAs were epoxy bonded to Si wafers at 100 °C. The GaAs is then variably thinned by selective chemical etching. Upon cooling, biaxial tensile strains are induced in the GaAs films since the coefficient of thermal expansion in GaAs is different than in the Si support. OPNMR experiments were carried out at 6-10 K. The OPNMR spectra are selective to nuclei within a photon penetration depth from the surface. When mounted on a 0.635 mm thick Si support, the strain, which is proportional to the observed quadrupole splitting, is found to decrease with increasing thickness of the GaAs films and appears to approach a residual value. When the same GaAs film is mounted on a thicker 5mm Si block, the strain increased. To explain the observations, we consider effects of dislocation relaxation of strain and bending of the composite. The interface strain extracted from the measurements is 5.5 × 10-4, in good agreement with the value estimated using the differential thermal contraction of Si and GaAs. The strain resolution of the technique is about 10-5 in GaAs.

  7. Prediction of dislocation generation during Bridgman growth of GaAs crystals

    NASA Technical Reports Server (NTRS)

    Tsai, C. T.; Yao, M. W.; Chait, Arnon

    1992-01-01

    Dislocation densities are generated in GaAs single crystals due to the excessive thermal stresses induced by temperature variations during growth. A viscoplastic material model for GaAs, which takes into account the movement and multiplication of dislocations in the plastic deformation, is developed according to Haasen's theory. The dislocation density is expressed as an internal state variable in this dynamic viscoplastic model. The deformation process is a nonlinear function of stress, strain rate, dislocation density and temperature. The dislocation density in the GaAs crystal during vertical Bridgman growth is calculated using a nonlinear finite element model. The dislocation multiplication in GaAs crystals for several temperature fields obtained from thermal modeling of both the GTE GaAs experimental data and artificially designed data are investigated.

  8. Heterogeneous integration of GaAs pHEMT and Si CMOS on the same chip

    NASA Astrophysics Data System (ADS)

    Li-Shu, Wu; Yan, Zhao; Hong-Chang, Shen; You-Tao, Zhang; Tang-Sheng, Chen

    2016-06-01

    In this work, we demonstrate the technology of wafer-scale transistor-level heterogeneous integration of GaAs pseudomorphic high electron mobility transistors (pHEMTs) and Si complementary metal–oxide semiconductor (CMOS) on the same Silicon substrate. GaAs pHEMTs are vertical stacked at the top of the Si CMOS wafer using a wafer bonding technique, and the best alignment accuracy of 5 μm is obtained. As a circuit example, a wide band GaAs digital controlled switch is fabricated, which features the technologies of a digital control circuit in Si CMOS and a switch circuit in GaAs pHEMT, 15% smaller than the area of normal GaAs and Si CMOS circuits.

  9. Stalled DNA Replication Forks at the Endogenous GAA Repeats Drive Repeat Expansion in Friedreich's Ataxia Cells.

    PubMed

    Gerhardt, Jeannine; Bhalla, Angela D; Butler, Jill Sergesketter; Puckett, James W; Dervan, Peter B; Rosenwaks, Zev; Napierala, Marek

    2016-08-01

    Friedreich's ataxia (FRDA) is caused by the expansion of GAA repeats located in the Frataxin (FXN) gene. The GAA repeats continue to expand in FRDA patients, aggravating symptoms and contributing to disease progression. The mechanism leading to repeat expansion and decreased FXN transcription remains unclear. Using single-molecule analysis of replicated DNA, we detected that expanded GAA repeats present a substantial obstacle for the replication machinery at the FXN locus in FRDA cells. Furthermore, aberrant origin activation and lack of a proper stress response to rescue the stalled forks in FRDA cells cause an increase in 3'-5' progressing forks, which could enhance repeat expansion and hinder FXN transcription by head-on collision with RNA polymerases. Treatment of FRDA cells with GAA-specific polyamides rescues DNA replication fork stalling and alleviates expansion of the GAA repeats, implicating DNA triplexes as a replication impediment and suggesting that fork stalling might be a therapeutic target for FRDA. PMID:27425605

  10. A study of binding biotinylated nano-beads to the surface of (001) GaAs

    NASA Astrophysics Data System (ADS)

    Ding, Ximing; Moumanis, Khalid; Dubowski, Jan J.; Frost, Eric H.

    2006-02-01

    We have investigated the deposition of biotinylated nano-beads on the surface of GaAs. The deposition procedure involved either direct coating of (001) GaAs with nano-beads, or binding the nano-beads with avidin immobilized on the surface of (001) GaAs through the interface of biotin and the NH II terminal group of 11-amino-1-undecanethiol (HS(CH II) 11NH II). The efficiency of binding was tested by washing the samples in a solution of a commercial detergent and by subjecting them to a deionized water ultrasonic bath. The results indicate that nano-beads deposited directly on the surface of (001) GaAs withstand the detergent washing test but they are easily removed by ultrasonic washing. In contrast, the nano-beads attached to (001) GaAs through the avidin-biotin-thiol interface survive the ultrasonic washing tests.

  11. Micromechanical Switches on GaAs for Microwave Applications

    NASA Technical Reports Server (NTRS)

    Randall, John N.; Goldsmith, Chuck; Denniston, David; Lin, Tsen-Hwang

    1995-01-01

    In this presentation, we describe the fabrication of micro-electro-mechanical system (MEMS) devices, in particular, of low-frequency multi-element electrical switches using SiO2 cantilevers. The switches discussed are related to micromechanical membrane structures used to perform switching of optical signals on silicon substrates. These switches use a thin metal membrane which is actuated by an electrostatic potential, causing the switch to make or break contact. The advantages include: superior isolation, high power handling capabilities, high radiation hardening, very low power operations, and the ability to integrate onto GaAs monolithic microwave integrated circuit (MMIC) chips.

  12. Molecular dynamics simulations of displacement cascades in GaAs.

    SciTech Connect

    Foiles, Stephen Martin

    2010-04-01

    The quantification of the production of primary defects via displacement cascades is an important ingredient in the prediction of the influence of radiation on the performance of electronic components in radiation environments. Molecular dynamics simulations of displacement cascades are performed for GaAs The interatomic interactions are described using a recently proposed Bond Order Potential, and a simple model of electronic stopping is incorporated. The production of point defects is quantified as a function of recoil energy and recoil species. Correlations in the point defects are examined. There are a large number of anti-site defects nearest-neighbor pairs as well as di-vacancies and larger order vacancy clusters. Radiation damage and ion implantation in materials have been studied via molecular dynamics for many years. A significant challenge in these simulations is the detailed identification and quantification of the primary defect production. For the present case of a compound semiconductor, GaAs, there are a larger number of possible point defects compared to elemental materials; two types of vacancies, two types of interstitials and antisite defects. This is further complicated by the fact that, in addition to the formation of point defects, amorphous zones may also be created. The goal of the current work is to quantify the production of primary defects in GaAs due to radiation exposures. This information will be used as part of an effort to predict the influence of radiation environments on the performance of electronic components and circuits. The data provide the initial state for continuum-level analysis of the temporal evolution of defect populations. For this initial state, it is important to know both the number of the various point defects that may be produced as well as the initial spatial correlations between the primary defects. The molecular dynamics simulations employ a recently developed Bond Order Potential (BOP) for GaAs. The analysis

  13. Optical modulator based on GaAs photonic crystals

    NASA Astrophysics Data System (ADS)

    Li, Jiusheng

    2005-11-01

    In this letter, we propose a novel optical modulator based on GaAs photonic crystals and investigate its optically properties numerically by using the finite-difference time-domain method. The position of the cutoff frequency can be varied by free carriers injection, and the band gap shift can be observed. Band gap shift is used to modulate light. Bing several micrometers length, low insertion loss, and large extinction ratios, the modulator can be used in ultra-small and ultra-dense photonic integrated circuits.

  14. 17 GHz low noise GaAs FET amplifier

    NASA Astrophysics Data System (ADS)

    Bharj, J. S.

    1984-10-01

    The considered amplifier is suitable for use as the first stage in a direct broadcast TV satellite receiver, and it was specifically designed for the Unisat spacecraft. Attention is given to RF device characterization, the design of the low-noise FET amplifier, the very significant dispersion effects at 17 GHz, the noise figure, and questions of DC bias. Balanced stages are used for low-noise and high-gain amplifiers to enhance the reliability. The noise figure of the amplifier is approximately 3.75 dB in the frequency band of interest. A low-noise microstrip GaAs FET amplifier circuit is shown.

  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. Quantum effects in electron beam pumped GaAs

    SciTech Connect

    Yahia, M. E.; Azzouz, I. M.; Moslem, W. M.

    2013-08-19

    Propagation of waves in nano-sized GaAs semiconductor induced by electron beam are investigated. A dispersion relation is derived by using quantum hydrodynamics equations including the electrons and holes quantum recoil effects, exchange-correlation potentials, and degenerate pressures. It is found that the propagating modes are instable and strongly depend on the electron beam parameters, as well as the quantum recoil effects and degenerate pressures. The instability region shrinks with the increase of the semiconductor number density. The instability arises because of the energetic electron beam produces electron-hole pairs, which do not keep in phase with the electrostatic potential arising from the pair plasma.

  17. 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.

  18. High-efficiency nanostructured window GaAs solar cells.

    PubMed

    Liang, Dong; Kang, Yangsen; Huo, Yijie; Chen, Yusi; Cui, Yi; Harris, James S

    2013-10-01

    Nanostructures have been widely used in solar cells due to their extraordinary optical properties. In most nanostructured cells, high short circuit current has been obtained due to enhanced light absorption. However, most of them suffer from lowered open circuit voltage and fill factor. One of the main challenges is formation of good junction and electrical contact. In particular, nanostructures in GaAs only have shown unsatisfactory performances (below 5% in energy conversion efficiency) which cannot match their ideal material properties and the record photovoltaic performances in industry. Here we demonstrate a completely new design for nanostructured solar cells that combines nanostructured window layer, metal mesa bar contact with small area, high quality planar junction. In this way, we not only keep the advanced optical properties of nanostructures such as broadband and wide angle antireflection, but also minimize its negative impact on electrical properties. High light absorption, efficient carrier collection, leakage elimination, and good lateral conductance can be simultaneously obtained. A nanostructured window cell using GaAs junction and AlGaAs nanocone window demonstrates 17% energy conversion efficiency and 0.982 V high open circuit voltage. PMID:24021024

  19. Sn-seeded GaAs nanowires grown by MOVPE.

    PubMed

    Sun, Rong; Vainorius, Neimantas; Jacobsson, Daniel; Pistol, Mats-Erik; Lehmann, Sebastian; Dick, Kimberly A

    2016-05-27

    It has previously been reported that in situ formed Sn nanoparticles can successfully initiate GaAs nanowire growth with a self-assembled radial p-n junction composed of a Sn-doped n-type core and a C-doped p-type shell. In this paper, we investigate the effect of fundamental growth parameters on the morphology and crystal structure of Sn-seeded GaAs nanowires. We show that growth can be achieved in a broad temperature window by changing the TMGa precursor flow simultaneously with decreasing temperature to prevent nanowire kinking at low temperatures. We find that changes in the supply of both AsH3 and TMGa can lead to nanowire kinking and that the formation of twin planes is closely related to a low V/III ratio. From PL results, we observe an increase of the average luminescence energy induced by heavy doping which shifts the Fermi level into the conduction band. Furthermore, the doping level of Sn and C is dependent on both the temperature and the V/III ratio. These results indicate that using Sn as the seed particle for nanowire growth is quite different from traditionally used Au in for example growth conditions and resulting nanowire properties. Thus, it is very interesting to explore alternative metal seed particles with controllable introduction of other impurities. PMID:27087548

  20. 28 percent efficient GaAs concentrator solar cells

    NASA Technical Reports Server (NTRS)

    Macmillan, H. F.; Hamaker, H. C.; Kaminar, N. R.; Kuryla, M. S.; Ladle Ristow, M.

    1988-01-01

    AlGaAs/GaAs heteroface solar concentrator cells which exhibit efficiencies in excess of 27 percent at high solar concentrations (over 400 suns, AM1.5D, 100 mW/sq cm) have been fabricated with both n/p and p/n configurations. The best n/p cell achieved an efficiency of 28.1 percent around 400 suns, and the best p/n cell achieved an efficiency of 27.5 percent around 1000 suns. The high performance of these GaAs concentrator cells compared to earlier high-efficiency cells was due to improved control of the metal-organic chemical vapor deposition growth conditions and improved cell fabrication procedures (gridline definition and edge passivation). The design parameters of the solar cell structures and optimized grid pattern were determined with a realistic computer modeling program. An evaluation of the device characteristics and a discussion of future GaAs concentrator cell development are presented.

  1. Step-step interactions on GaAs (110) nanopatterns

    SciTech Connect

    Galiana, B.; Benedicto, M.; Tejedor, P.

    2013-01-14

    The step-step interactions on vicinal GaAs (110) surface patterns have been extracted from the quantitative analysis of the terrace width distribution (TWD). We have specifically studied the interactions in near-equilibrium faceting and kinetics-driven step bunching and meandering formed by spontaneous self-organization or through the modification of GaAs growth kinetics by atomic hydrogen. We show that the experimental TWDs determined from atomic force microscopy measurements can be accurately described by a weighed sum of a generalized Wigner distribution and several Gaussians. The results of our calculations indicate that straight facets are formed during high temperature homoepitaxy due to attractive interactions between [110] steps. At low temperatures, steady state attractive interactions in [110] step bunches are preceded by a transition regime dominated by entropic and energetic repulsions between meandering [11n]-type steps (n {>=} 2), whose population density exceeds that of the [110] bunched steps. In addition, it has been found that atomic H reduces the attractive interactions between [110] bunched steps and enhances entropic and dipole-induced energetic repulsions between H-terminated [11n] steps through the inhibition of As-As bond formation at step edges. Our analysis has evidenced a correlation between the value of the adjustable parameter that accounts in our model for the specific weight of the secondary peaks in the TWD ({beta}) and the extent of transverse meandering on the vicinal surface.

  2. Phase Transformation in Radially Merged Wurtzite GaAs Nanowires

    PubMed Central

    2015-01-01

    III–V Nanowires (NWs) grown with metal–organic chemical vapor deposition commonly show a polytypic crystal structure, allowing growth of structures not found in the bulk counterpart. In this paper we studied the radial overgrowth of pure wurtzite (WZ) GaAs nanowires and characterized the samples with high resolution X-ray diffraction (XRD) to reveal the crystal structure of the grown material. In particular, we investigated what happens when adjacent WZ NWs radially merge with each other by analyzing the evolution of XRD peaks for different amounts of radial overgrowth and merging. By preparing cross-sectional lamella samples we also analyzed the local crystal structure of partly merged NWs by transmission electron microscopy. Once individual NWs start to merge, the crystal structure of the merged segments is transformed progressively from initial pure WZ to a mixed WZ/ZB structure. The merging process is then modeled using a simple combinatorial approach, which predicts that merging of two or more WZ NWs will result in a mixed crystal structure containing WZ, ZB, and 4H. The existence large and relaxed segments of 4H structure within the merged NWs was confirmed by XRD, allowing us to accurately determine the lattice parameters of GaAs 4H. We compare the measured WZ and 4H unit cells with an ideal tetrahedron and find that both the polytypes are elongated in the c-axis and compressed in the a-axis compared to the geometrically converted cubic ZB unit cell. PMID:26494983

  3. Sn-seeded GaAs nanowires grown by MOVPE

    NASA Astrophysics Data System (ADS)

    Sun, Rong; Vainorius, Neimantas; Jacobsson, Daniel; Pistol, Mats-Erik; Lehmann, Sebastian; Dick, Kimberly A.

    2016-05-01

    It has previously been reported that in situ formed Sn nanoparticles can successfully initiate GaAs nanowire growth with a self-assembled radial p–n junction composed of a Sn-doped n-type core and a C-doped p-type shell. In this paper, we investigate the effect of fundamental growth parameters on the morphology and crystal structure of Sn-seeded GaAs nanowires. We show that growth can be achieved in a broad temperature window by changing the TMGa precursor flow simultaneously with decreasing temperature to prevent nanowire kinking at low temperatures. We find that changes in the supply of both AsH3 and TMGa can lead to nanowire kinking and that the formation of twin planes is closely related to a low V/III ratio. From PL results, we observe an increase of the average luminescence energy induced by heavy doping which shifts the Fermi level into the conduction band. Furthermore, the doping level of Sn and C is dependent on both the temperature and the V/III ratio. These results indicate that using Sn as the seed particle for nanowire growth is quite different from traditionally used Au in for example growth conditions and resulting nanowire properties. Thus, it is very interesting to explore alternative metal seed particles with controllable introduction of other impurities.

  4. Image processing using Gallium Arsenide (GaAs) technology

    NASA Technical Reports Server (NTRS)

    Miller, Warner H.

    1989-01-01

    The need to increase the information return from space-borne imaging systems has increased in the past decade. The use of multi-spectral data has resulted in the need for finer spatial resolution and greater spectral coverage. Onboard signal processing will be necessary in order to utilize the available Tracking and Data Relay Satellite System (TDRSS) communication channel at high efficiency. A generally recognized approach to the increased efficiency of channel usage is through data compression techniques. The compression technique implemented is a differential pulse code modulation (DPCM) scheme with a non-uniform quantizer. The need to advance the state-of-the-art of onboard processing was recognized and a GaAs integrated circuit technology was chosen. An Adaptive Programmable Processor (APP) chip set was developed which is based on an 8-bit slice general processor. The reason for choosing the compression technique for the Multi-spectral Linear Array (MLA) instrument is described. Also a description is given of the GaAs integrated circuit chip set which will demonstrate that data compression can be performed onboard in real time at data rate in the order of 500 Mb/s.

  5. GaAs clean up studied with synchrotron radiation photoemission

    NASA Astrophysics Data System (ADS)

    Tallarida, Massimo; Adelmann, Christoph; Delabie, Annelies; van Elshocht, Sven; Caymax, Matty; Schmeisser, Dieter

    2012-12-01

    In this contribution we describe the chemical changes at the surface of GaAs upon adsorption of tri-methyl-aluminum (TMA). TMA is used to grow Al2O3 with atomic layer deposition (ALD) usually using H2O as oxygen source. Recently, it was pointed out that the adsorption of TMA on various III-V surfaces reduces the native oxide, allowing the growth of an abrupt III-V/High-K interface with reduced density of defects. Synchrotron radiation photoemission spectroscopy (SR-PES) is a powerful method to characterize surfaces and interfaces of many materials, as it is capable to determine their chemical composition as well as the electronic properties. We performed in-situ SR-PES measurements after exposing a GaAs surface to TMA pulses at about 250°C. Upon using the possibility of tuning the incident photon energy we compared the Ga3d spectra at 41 eV, 71 eV, 91 eV and 121 eV, as well as the As3d at 71 eV and 91 eV. Finally, we show that using SR-PES allows a further understanding of the surface composition, which is usually not accessible with other techniques.

  6. Bismuth alloying properties in GaAs nanowires

    SciTech Connect

    Ding, Lu; Lu, Pengfei; Cao, Huawei; Cai, Ningning; Yu, Zhongyuan; Gao, Tao; Wang, Shumin

    2013-09-15

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

  7. Sol-gel derived ? thin films on GaAs

    NASA Astrophysics Data System (ADS)

    Arscott, S.; Smith, N.; Kurchania, R.; Milne, S. J.; Miles, R. E.

    1998-02-01

    Sol-gel derived thin films of lead zirconate titanate (PZT) have been fabricated on a platinized GaAs substrate using a propane-1,3-diol based sol-gel route. PZT can be used as the piezoelectric component in bulk acoustic wave devices for monolithic microwave integrated circuit applications. A 100 nm silicon nitride buffer layer was deposited onto the GaAs by plasma-enhanced chemical vapour deposition in order to prevent gallium and arsenic outdiffusion during film fabrication. Rapid thermal processing (RTP) techniques were employed to decompose thermally the sol-gel layer to PZT in a further effort to minimize problems of gallium and arsenic outdiffusion. Adhesion between the bottom electrode and substrate was found to improve when an intermediate titanium layer deposited between the platinum and silicon nitride was oxidized prior to deposition of the platinum electrode. A crystalline PZT film was produced on the 0268-1242/13/2/016/img9 substrate configuration by firing the sol-gel coating at 0268-1242/13/2/016/img10C for 10 s using RTP. A single deposition of sol resulted in a film having a thickness of 0268-1242/13/2/016/img11. Ferroelectric hysteresis measurements yielded average values of remanant polarization and coercive field of 0268-1242/13/2/016/img12 and 0268-1242/13/2/016/img13 respectively.

  8. Thermal stress cycling of GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Janousek, B. K.; Francis, R. W.; Wendt, J. P.

    1985-01-01

    A thermal cycling experiment was performed on GaAs solar cells to establish the electrical and structural integrity of these cells under the temperature conditions of a simulated low-Earth orbit of 3-year duration. Thirty single junction GaAs cells were obtained and tests were performed to establish the beginning-of-life characteristics of these cells. The tests consisted of cell I-V power output curves, from which were obtained short-circuit current, open circuit voltage, fill factor, and cell efficiency, and optical micrographs, spectral response, and ion microprobe mass analysis (IMMA) depth profiles on both the front surfaces and the front metallic contacts of the cells. Following 5,000 thermal cycles, the performance of the cells was reexamined in addition to any factors which might contribute to performance degradation. It is established that, after 5,000 thermal cycles, the cells retain their power output with no loss of structural integrity or change in physical appearance.

  9. Preparation of pulse plated GaAs films

    NASA Astrophysics Data System (ADS)

    Murali, K. R.; Trivedi, D. C.

    2006-07-01

    Thin GaAs films were prepared by pulse plating from an aqueous solution containing 0.20 M GaCl3 and 0.15 M As2O3 at a pH of 2 and at room temperature. The current density was kept as 50 mA cm-2 the duty cycle was varied in the range 10 50%. The films were deposited on titanium, nickel and tin oxide coated glass substrates. Films exhibited polycrystalline nature with peaks corresponding to single phase GaAs. Optical absorption measurements indicated a direct band gap of 1.40 eV. Photoelectrochemical cells were made using the films as photoelectrodes and graphite as counter electrode in 1 M polysulphide electrolyte. At 60 mW cm-2 illumination, an open circuit voltage of 0.5 V and a short circuit current density of 5.0 mA cm-2 were observed for the films deposited at a duty cycle of 50%.

  10. Cryogenic measurements of aerojet GaAs n-JFETs

    NASA Technical Reports Server (NTRS)

    Goebel, John H.; Weber, Theodore T.; Van Rheenen, Arthur D.; Jostad, Leon; Kim, Joo-Young; Gable, Ben

    1992-01-01

    The spectral noise characteristics of Aerojet GaAs n-JFETs have been investigated down to liquid helium temperatures. Voltage noise characterization was performed with the FET in 1) the floating gate mode, 2) the grounded gate mode to determine the lowest noise readings possible and 3) with an extrinsic silicon photodetector at various detector bias voltages, to determine optimum operating conditions. Current noise characterization was measured at the drain in the temperature range 300 to 77 K. Device design and MBE processing are described. Static I-V characterization is done at 300, 77 and 6 K. The measurements indicate that the Aerojet GaAs n-JFET is a quiet and stable device at liquid helium temperatures. Hence, it can be considered as a readout line driver or infrared detector preamplifier as well as a host of other cryogenic applications. Its noise performance is superior to that of Si MOSFETs operating at liquid helium temperatures, and is equal to the best Si n-JFETs operating at 300 K.

  11. [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. PMID:8619113

  12. 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.

  13. Relationship between planar GaAs nanowire growth direction and substrate orientation

    NASA Astrophysics Data System (ADS)

    Dowdy, Ryan S.; Walko, Donald A.; Li, Xiuling

    2013-01-01

    Planar GaAs nanowires are epitaxially grown on GaAs substrates of various orientations, via the Au-catalyzed vapor-liquid-solid mechanism using metal organic chemical vapor deposition. The nanowire geometry and growth direction are examined using scanning electron microscopy and x-ray microdiffraction. A hypothesis relating the planar nanowire growth direction to the surface projections of <111> B crystal directions is proposed. GaAs planar nanowire growth on vicinal substrates is performed to test this hypothesis. Good agreement between the experimental results and the projection model is found.

  14. Photonic crystal thin films of GaAs prepared by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Povey, I. M.; Whitehead, D.; Thomas, K.; Pemble, M. E.; Bardosova, M.; Renard, J.

    2006-09-01

    Photonic crystal thin films were fabricated via the self-assembly of a lattice of silica spheres on silicon (100) substrates. Progressive infilling of the air spaces within the structure with GaAs was achieved using trimethylgallium and arsine under atomic-layer-deposition conditions. Samples with the highest levels of GaAs infill were subsequently inverted using selective etching. Reflectance spectra are interpreted via the Bragg expression and calculated photonic band structure diagrams. For GaAs infilled and inverted samples, the relative positions of the first and second order Bragg reflections are strongly influenced by the wavelength dependent refractive index.

  15. Arsenic ambient conditions preventing surface degradation of GaAs during capless annealing at high temperatures

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

    Changes in surface morphology and composition caused by capless annealing of GaAs were studied as a function of annealing temperature, T(GaAs), and the ambient arsenic pressure controlled by the temperature, T(As), of an arsenic source in the annealing ampul. It was established that any degradation of the GaAs surface morphology could be completely prevented, providing that T(As) was more than about 0.315T(GaAs) + 227 C. This empirical relationship is valid up to the melting point temperature of GaAs (1238 C), and it may be useful in some device-processing steps.

  16. High resolution electron microscopy of GaAs capped GaSb nanostructures

    SciTech Connect

    Molina Rubio, Sergio I; Beltran, AM; Ben, Teresa; Galindo, P.L.; Taboada, Alfonso G; Chisholm, Matthew F

    2012-01-01

    We show in this work that GaAs capping of 2 ML of GaSb grown by molecular beam epitaxy results in the formation of very small (with heights of about 1 nm) GaAsxSb1 x nanostructures surrounded by a GaAs rich layer. This conclusion is obtained by analyzing the morphology of the GaAsxSb1 x nanostructures by high resolution scanning transmission electron microscopy in Z-contrast mode. This result shows that a significant fraction of the Sb atoms must segregate along the growth direction during the GaAs capping process.

  17. Epitaxial and polycrystalline GaAs solar cells using OM-CVD techniques

    NASA Technical Reports Server (NTRS)

    Yeh, Y. C. M.; Wang, K. L.; Shin, B. K.; Stirn, R. J.

    1980-01-01

    GaAs epitaxial films were grown by chemical vapor deposition using organo-metallic sources (OM-CVD) on single crystal and polycrystalline bulk GaAs, as well as on bulk polycrystalline and recrystallized thin-film Ge substrates. Details of Antireflecting Metal-Oxide-Semiconductor (AMOS) solar cells fabricated on GaAs films grown on bulk polycrystalline Ge and recrystallized Ge thin-film substrates will be discussed, as well as preliminary photovoltaic results obtained for n(+)/p homojunction structures.

  18. Assembly of Submicron Ferromagnets in GaAs Semiconductors*

    NASA Astrophysics Data System (ADS)

    Shi, Jing

    1996-03-01

    Spin-dependent electronic phenomena discovered in nanoscale metallic systems have raised interesting scientific questions regarding spin interactions and are currently finding technological applications. In particular, incorporating microscopic magnets within semiconducting compounds offers the exciting possibility of combining local magnetism with the flexibility of semiconductor-based quantum electronic structures. This work demonstrates that submicron room-temperature ferromagnets have been successfully formed in GaAs semiconductors through a simple process of ion implantation and subsequent heat treatment (J. Shi et al), Nature 377, 707 (1995); J. Shi et al, J. Appl. Phys. (accepted for publication, 1996).. A combination of transmission electron, atomic force, and magnetic force microscopies have been used in conjunction with magnetization measurements to directly examine the structural and magnetic properties of this new system. After Mn^+-implantation at various doses, rapid thermal annealing crystallizes in situ submicron GaMn ferromagnetic particles ( ~ 200 nm) at the GaAs surface. These GaMn particles are crystalline, some with quasicrystalline-like order. Bulk magnetization measurements show that the GaMn particles are room temperature ferromagnets with a Curie temperature far exceeding room temperature. Both the particle size and coercivity can be varied by controlling the implantation and annealing conditions. High resolution magnetic force microscopy images on single GaMn ferromagnets reveal that unmagnetized samples contain both magnetic single- and multi-domain particles, but after initial magnetization, the single-domain state predominates, with magnetic moments aligned preferentially along the [001] directions of the GaAs substrate. In particular, magnetic force imaging has been performed in a changing magnetic field (up to 8 kOe) to directly study and image magnetization reversal of single-domain particles. *Work done in collaboration with D

  19. The electronic and optical properties of quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs: a first-principles study

    PubMed Central

    2014-01-01

    First-principles calculations based on density functional theory have been performed for the quaternary GaAs1-x-y N x Bi y alloy lattice-matched to GaAs. Using the state-of-the-art computational method with the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, electronic, and optical properties were obtained, including band structures, density of states (DOSs), dielectric function, absorption coefficient, refractive index, energy loss function, and reflectivity. It is found that the lattice constant of GaAs1-x-y N x Bi y alloy with y/x =1.718 can match to GaAs. With the incorporation of N and Bi into GaAs, the band gap of GaAs1-x-y N x Bi y becomes small and remains direct. The calculated optical properties indicate that GaAs1-x-y N x Bi y has higher optical efficiency as it has less energy loss than GaAs. In addition, it is also found that the electronic and optical properties of GaAs1-x-y N x Bi y alloy can be further controlled by tuning the N and Bi compositions in this alloy. These results suggest promising applications of GaAs1-x-y N x Bi y quaternary alloys in optoelectronic devices. PMID:25337061

  20. A photoconductive model for superior GaAs THz photomixers

    NASA Astrophysics Data System (ADS)

    Brown, E. R.

    1999-08-01

    Theoretical methods are used to evaluate the THz output from photomixer structures consisting of interdigitated electrodes and planar antennas on top of a low-temperature-grown GaAs layer. Consistent with experiment, the THz power from a standard photomixer is found to be limited by low external quantum efficiency (˜1%). This arises primarily from low photoconductive gain, which is attributed to a long transit time (between electrodes) for the majority of photocarriers generated in the structure. The modeling is then applied to an improved structure containing a thinner absorbing layer (≈0.34 μm for λ=0.85 μm pump) with a dielectric mirror below it to induce resonant-cavity absorption near the surface where the gain is higher. Through increased gain and absorptivity, the model predicts ≈7× greater THz output for the same optical pump power.

  1. Artificial graphene in nanopatterned GaAs Quantum Wells

    NASA Astrophysics Data System (ADS)

    Wang, Sheng; Scarabelli, Diego; Levy, Antonio; Pfeiffer, Loren; West, Ken; Pellegrini, Vittorio; Manfra, Michael J.; Wind, Shalom; Pinczuk, Aron

    2015-03-01

    Electrons in graphene have linear energy-momentum dispersion, making them massless Dirac fermions. An alternative way to achieve massless Dirac-fermions in a controlled and tunable manner is to construct a honeycomb lattice potential for a 2D electron gas in a semiconductor quantum well. We report realization of very short period (as small as 40 nm) honeycomb lattice pattern using e-beam lithography and drying etching on a GaAs quantum well and spectroscopy data of electron states under this potential modulation. The study is carried out using photoluminescence and light scattering at low temperature (about 4K). Inter mini-band transitions are observed by resonant inelastic light scattering and interpreted with calculated mini-band structure. Control over parameters such as Fermi level should permit manipulation of massless fermions. This will provide a platform for novel behavior such as topological states in a semiconductor quantum simulator. Supported by DOE-BES Award DE-SC0010695.

  2. Surface Stoichiometry, Structure, and Kinetics of GaAs MOCVD

    SciTech Connect

    Baucom, K.C.; Creighton, J.R.; Moffat, H.K.

    1999-01-29

    We have used reflectance-difference spectroscopy (RDS) to examine the surface phases of GaAs(100) during metalorganic chemical vapor deposition (MOCVD). Since the identities of two important surface phases were unknown, we determined their structure and stoichiometry using a variety of surface science techniques. The Type III phase is a newly characterized As-rich (1 X 2)-CH{sub 3} reconstruction. The Type II phase is a metastable derivative of the Type I phase. RDS also indicates that the surface during MOCVD has a considerable degree of heterogeneity. Deposition rates were measured over a similar range of conditions and the kinetically-limited regime was found to correlate with the Type III phase. A simple kinetic model was found to quantitatively describe the deposition rates.

  3. Surface defects in GaAs wafer processes

    NASA Astrophysics Data System (ADS)

    Matsushita, H.; Ishida, M.; Kikawa, J.

    1990-06-01

    The causes of micro- and macro-irregularities observed on GaAs(100) polished wafers were investigated. From the results, the wafer processes were improved so that a high-quality surface was obtained without orange peel, haze, or pits. For 3-inch wafers the flatness was improved to less than 2 μm in TTV and the warp to less than 5 μm. Improvements in the wafer processes were: development of a better polishing solution, filtering of this solution with maintenance of the pad conditions, thereby eliminating scratches, annealing at high temperature to eliminate pits, advances in slicing and lapping to reduce warp, and three-stage double-sided polishing to eliminate dimples and to improve TTV.

  4. Computational study of ridge states in GaAs nanopillars

    NASA Astrophysics Data System (ADS)

    Yu, Ted H.; Ratsch, Christian

    2015-08-01

    Semiconductor nanopillars have unique geometries that make them very promising materials for a variety of devices. In order to improve their performance, we need to understand how they are affected by ridge states that lie on the six corners of the nanopillar hexagon. Although the GaAs nanopillars are primarily zinc blende (ABC), stacking faults of wurtzite (AB) stacking occur. We use density-functional theory to study stacking faults using one-dimensional periodic geometries that have a combination of zinc blende and wurtzite stacking. In contrast to perfect zinc blende nanopillars, energetically favorable midgap ridge states created by stacking faults are found in these geometries using density-functional theory. The calculated band diagrams and densities of state help us to understand how these midgap states lead to a reduced mobility and carrier localization. We also study how sulfur passivation affects and potentially improves the performance by modifying the ridges.

  5. A Ka-band GaAs monolithic phase shifter

    NASA Technical Reports Server (NTRS)

    Sokolov, V.; Geddes, J. J.; Contolatis, A.; Bauhahn, P. E.; Chao, C.

    1983-01-01

    The design and performance of a GaAs monolithic 180-degree one-bit switched line phase shifter test circuit for Ka-band operation is presented. A self-aligned gate (SAG) fabrication technique is also described that reduces resistive parasitics in the switching FET's. Over the 27.5-30 GHz band, typical measured differential insertion phase is within 10-20 deg of the ideal time delay characteristic. Over the same band, the insertion loss for the SAG phase shifter is about 2.5-3 dB per bit. The SAG fabrication technique holds promise in reducing phase shifter insertion loss to about 1.5 dB/bit for 30-GHz operation.

  6. The binding energies of a bulged GaAs nanowire

    NASA Astrophysics Data System (ADS)

    Zamani, A.; Estabar, Th.; Safarpour, Gh.; Moradi, M.

    2014-12-01

    As it is well-known the electronic structure of the semiconductor nanostructures are so sensitive to alteration of confinement while the nanostructure morphology often determines the confinement. Accordingly existence of a bulge on the wire surface will affect the features of the nanowire. In the present work we consider an on-center hydrogenic donor impurity in a GaAs nanowire with bulge. The ground and first excited states energy levels as well as their binding energies are calculated as functions of bulge and nanowire radius. It is found that both the energy levels and binding energies are strongly influenced by the bulge size for ultrafine nanowires. For large wire radii the effects of bulge existence is trivial and the electronic properties of the system approach to those of the simple nanowire.

  7. Morphology of thermal oxide layers on GaAs

    NASA Astrophysics Data System (ADS)

    Beserman, R.; Schwarz, S. A.; Hwang, D. M.; Chen, C. Y.

    1991-08-01

    The oxidation process of pure GaAs has been studied with use of several complementary experimental techniques: Raman scattering, electrical conductivity, transmission electron microscopy, and secondary-ion mass spectrometry. The morphology of the oxide layer and the oxide-GaAs interface evolve as a function of oxidation time. A high density of well-oriented As microcrystallites penetrates into the substrate, forming a conductive interfacial layer in the early stages of the oxidation process. After longer oxidation times, when the Raman As intensity and the interfacial conductivity are reduced, As is distributed into the oxide layer, forming crystallites that are no longer well oriented. Simultaneously, the crystalline gallium oxide breaks up to into microcrystallites that could provide channels for the outdiffusion of As. From the experimental evidence, we deduce that the interfacial density of crystalline As is reduced for long oxidation times.

  8. High gain GaAs photoconductive semiconductor switches: Switch longevity

    SciTech Connect

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

    1998-07-01

    Optically activated, high gain GaAs switches are being tested for many different pulsed power applications that require long lifetime (longevity). The switches have p and n contact metallization (with intentional or unintentional dopants) configured in such a way as to produce p-i-n or n-i-n switches. The longevity of the switches is determined by circuit parameters and by the ability of the contacts to resist erosion. This paper will describe how the switches performed in test-beds designed to measure switch longevity. The best longevity was achieved with switches made with diffused contacts, achieving over 50 million pulses at 10 A and over 2 million pulses at 80 A.

  9. The kinetics of parasitic growth in GaAs MOVPE

    NASA Astrophysics Data System (ADS)

    Clayton, A. J.; Irvine, S. J. C.

    2007-03-01

    Gallium arsenide (GaAs) deposition was carried out in a horizontal quartz reactor tube with trimethylgallium (TMGa) and arsine (AsH 3) as precursors, using a hydrogen (H 2) carrier gas. Temperatures were in the range 400-500 °C, where surface reactions limit deposition rate. Nucleation time and deposition rate were monitored using laser interferometry, optimum reflectance was gained by aligning a quartz wafer to back reflect the incident beam. The 980 nm infrared laser beam was sufficiently long in wavelength to be able to penetrate the wall deposit. Results showing the effect of temperature and V/III ratio on the nucleation time and deposition rate are presented, where with temperature the nucleation delay was observed to reduce and the growth rate to increase. The nucleation delay is consistent with a thermally activated surface nucleation for the parasitic GaAs. A theoretical growth rate model, based on a restricted set of reaction steps was used to compare with the experimental growth rates. Without any free parameters, the growth rates from theoretical calculation and experiment agreed within a factor of two and showed the same trends with V/III ratio and temperature. The non-linearity of the theoretical growth rates on an Arrhenius plot indicates that there is more than one dominant reaction step over the temperature range investigated. The range of experimental activation energies, calculated from Arrhenius plots, was 17.56-23.59 kJ mol -1. A comparison of these activation energies and minimum deposition temperature with the literature indicates that the wall temperature measurement on an Aixtron reactor is over 100 °C higher than previously reported.

  10. XPS and AFM Study of GaAs Surface Treatment

    SciTech Connect

    Contreras-Guerrero, R.; Wallace, R. M.; Aguirre-Francisco, S.; Herrera-Gomez, A.; Lopez-Lopez, M.

    2008-11-13

    Obtaining smooth and atomically clean surfaces is an important step in the preparation of a surface for device manufacturing. In this work different processes are evaluated for cleaning a GaAs surface. A good surface cleaning treatment is that which provides a high level of uniformity and controllability of the surface. Different techniques are useful as cleaning treatments depending on the growth process to be used. The goal is to remove the oxygen and carbon contaminants and then form a thin oxide film to protect the surface, which is easy to remove later with thermal desorption mechanism like molecular beam epitaxy (MBE) with minimal impact to the surface. In this study, atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) were used to characterize the structure of the surface, the composition, as well as detect oxygen and carbon contaminant on the GaAs surface. This study consists in two parts. The first part the surface was subjected to different chemical treatments. The chemical solutions were: (a)H{sub 2}SO{sub 4}:H{sub 2}O{sub 2}:H{sub 2}O(4:1:100), (b) HCl: H{sub 2}O(1:3), (c)NH{sub 4}OH 29%. The treatments (a) and (b) reduced the oxygen on the surface. Treatment (c) reduces carbon contamination. In the second part we made MOS devices on the surfaces treated. They were characterized by CV and IV electrical measurements. They show frequency dispersion.

  11. Oxygen defects in GaAs: A hybrid functional study

    NASA Astrophysics Data System (ADS)

    Colleoni, Davide; Pasquarello, Alfredo

    2016-03-01

    Using hybrid density functional calculations, we address the structural properties, formation energies, and charge transition levels of a variety of oxygen defects in GaAs. The set of considered defects comprises the bridging O atom in a As-O-Ga configuration, interstitial O atoms in tetrahedral sites, and O atoms substitutional to either Ga (OGa) or As atoms (OAs). In addition, we consider an As vacancy containing two O atoms, for which the most stable configurations are found through the use of molecular dynamics simulations, and defect complexes involving a OAs defect bound to either one or two AsGa antisites, denoted AsGa-OAs and (AsGa)2-OAs , respectively. We find that the bridging O defect and the AsGa-OAs and (AsGa)2-OAs complexes are the most stable oxygen defects in GaAs. The actual occurrence of these defects is examined against two criteria. The first criterion concerns the stability against O dissociation and is evaluated via the calculation of dissociation energies. The second criterion involves the defect formation at thermodynamic equilibrium and is inferred from the comparison between the formation energy of the oxygen defect and that of its O-related dissociation product (bridging O defect). Both the AsGa-OAs and (AsGa)2-OAs complexes satisfy these criteria and are stable against O dissociation. Further analysis in cooled-down conditions leads us to dismiss the AsGa-OAs defect due to the more favorable bonding of two rather than one AsGa antisites. The conclusion that only the bridging O defect and the (AsGa)2-OAs complex are expected to occur is in accord with experimental observations.

  12. 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)

  13. Anharmonicity in light scattering by optical phonons in GaAs1-xBix

    NASA Astrophysics Data System (ADS)

    Joshya, R. S.; Rajaji, V.; Narayana, Chandrabhas; Mascarenhas, A.; Kini, R. N.

    2016-05-01

    We present a Raman spectroscopic study of GaAs1-xBix epilayers grown by molecular beam epitaxy. We have investigated the anharmonic effect on the GaAs-like longitudinal optical phonon mode ( LOGaAs' ) of GaAs1-xBix for different Bi concentrations at various temperatures. The results are analyzed in terms of the anharmonic damping effect induced by thermal and compositional disorder. We have observed that the anharmonicity increases with Bi concentration in GaAs1-xBix as evident from the increase in the anharmonicity constants. In addition, the anharmonic lifetime of the optical phonon decreases with increasing Bi concentration in GaAs1-xBix.

  14. High-voltage picosecond photoconductor switch based on low-temperature-grown GaAs

    NASA Technical Reports Server (NTRS)

    Frankel, Michael Y.; Whitaker, John F.; Mourou, Gerard A.; Smith, Frank W.; Calawa, Arthur R.

    1990-01-01

    A GaAs material grown by molecular beam epitaxy at a low substrate temperature was used to fabricate a photoconductor switch that produces 6-V picosecond electrical pulses. The pulses were produced on a microwave coplanar-strip transmission line lithographically patterned on the low-temperature (LT) GaAs. A 150-fs laser pulse was used to generate carriers in the LT GaAs gap between the metal strips, partially shorting a high DC voltage placed across the lines. The 6-V magnitude of the electrical pulses obtained is believed to be limited by the laser pulse power and not by the properties of the LT GaAs. Experiments were also performed on a picosecond photoconductor switch fabricated on a conventional ion-damaged silicon-on-sapphire substrate. Although comparable pulse durations were obtained, the highest pulse voltage achieved with the latter device was 0.6 V.

  15. Long-term radiation effects on GaAs solar cell characteristics

    NASA Technical Reports Server (NTRS)

    Heinbockel, J. H.; Doviak, M. J.

    1978-01-01

    This report investigates preliminary design considerations which should be considered for a space experiment involving Gallium Arsenide (GaAs) solar cells. The electron radiation effects on GaAs solar cells were conducted in a laboratory environment, and a statistical analysis of the data is presented. In order to augment the limited laboratory data, a theoretical investigation of the effect of radiation on GaAs solar cells is also developed. The results of this study are empirical prediction equations which can be used to estimate the actual damage of electrical characteristics in a space environment. The experimental and theoretical studies also indicate how GaAs solar cell parameters should be designed in order to withstand the effects of electron radiation damage.

  16. Free-standing GaAs nanowires growth on ITO glass by MOCVD

    NASA Astrophysics Data System (ADS)

    Wu, D.; Tang, X. H.; Olivier, A.; Li, X. Q.

    2015-04-01

    GaAs nanowires (NWs) are directly grown on indium tin oxide (ITO) glass substrate by metalorganic chemical vapour deposition (MOCVD), using Au nanoparticles (NPs) as catalyst. By functionalization of the ITO glass and optimization of the Au NPs deposition time, the Au NPs area density deposited on the ITO glass reaches 92 NP μm-2. Uniform and free-standing GaAs NWs without kinking or worm-shape defects have been grown at 430 °C. More than 96% of the NWs have tilt angles larger than 45° with respect of the substrate. The effects of the growth temperature and the Au NPs size on the GaAs NWs growth rate, the NW diameter, and tapering effect are investigated. These results of GaAs NWs growth are the essential step for understanding III-V NWs integration on transparent conductive oxide coated low cost substrate and developing high efficiencyhybrid solar cells.

  17. Accelerated life testing and temperature dependence of device characteristics in GaAs CHFET devices

    NASA Technical Reports Server (NTRS)

    Gallegos, M.; Leon, R.; Vu, D. T.; Okuno, J.; Johnson, A. S.

    2002-01-01

    Accelerated life testing of GaAs complementary heterojunction field effect transistors (CHFET) was carried out. Temperature dependence of single and synchronous rectifier CHFET device characteristics were also obtained.

  18. Growth and characterization of molecular beam epitaxial GaAs layers on porous silicon

    NASA Technical Reports Server (NTRS)

    Lin, T. L.; Liu, J. K.; Sadwick, L.; Wang, K. L.; Kao, Y. C.

    1987-01-01

    GaAs layers have been grown on porous silicon (PS) substrates with good crystallinity by molecular beam epitaxy. In spite of the surface irregularity of PS substrates, no surface morphology deterioration was observed on epitaxial GaAs overlayers. A 10-percent Rutherford backscattering spectroscopy minimum channeling yield for GaAs-on-PS layers as compared to 16 percent for GaAs-on-Si layers grown under the same condition indicates a possible improvement of crystallinity when GaAs is grown on PS. Transmission electron microscopy reveals that the dominant defects in the GaAs-on-PS layers are microtwins and stacking faults, which originate from the GaAs/PS interface. GaAs is found to penetrate into the PS layers. n-type GaAs/p-type PS heterojunction diodes were fabricated with good rectifying characteristics.

  19. High-power question - will diamonds be the next GaAs

    SciTech Connect

    Manz, B.

    1988-05-01

    It is shown that, due to the outstanding properties of diamond material, diamond technology offers much promise for microwave power generation. For example, diamond exhibits high dielectric breakdown voltage (10 to the 7th V, 50 times that of conventional semiconductors such as GaAs), high thermal conductivity (20 W/cm per C, which is about four times that of Cu), a low dielectric constant (5.5, half that of GaAs), and high saturated carrier velocity (2.7 times that of GaAs, Si, or InP). Moreover, unlike GaAs, Si, or InP, the saturated carrier velocity of diamond maintains its high rate in electric fields of increasing intensity. However, the process of growing pure thin-film material is still at experimental stages. The approaches used in growing diamond by the laboratories in the U.S, USSR, and Japan are discussed.

  20. Fracture strength of GaAs solar cells as a function of manufacturing process steps

    NASA Technical Reports Server (NTRS)

    Chen, C. P.; Leipold, M. H.

    1985-01-01

    Fracture of single crystal GaAs substrate during the solar cell processing is an important factor in solar cell yield and cost. Fracture mechanics technique was utilized to evaluate cell cracking characteristics and changes in fracture strength of GaAs solar cells in a present state-of-the-art of manufacturing process for GaAs solar cells from wafer to complete cell of a typical production line. Considerable change in the fracture strength of GaAs solar cells as a function of cell processing was found. The strength data were described by Weibull statistical analysis and can be interpreted with the change of flaw distribution of each of the manufacturing process steps.

  1. Cubic GaS: A Surface Passivator For GaAs

    NASA Technical Reports Server (NTRS)

    Hepp, Aloysius F.; Barron, Andrew R.; Power, Michael B.; Jenkins, Phillip P.; Macinnes, Andrew N.

    1994-01-01

    Thin films of cubic form of gallium sulfide (GaS) formed on surfaces of gallium arsenide (GaAs) substrates via metal/organic chemical vapor deposition (MOCVD). Deposited cubic GaS, crystalline lattice matched to substrate GaAs, neutralizes electrically active defects on surfaces of both n-doped and p-doped GaAs. Enabling important GaAs-based semiconducting materials to serve as substrates for metal/insulator/semiconductor (MIS) capacitors. Cubic GaS enables fabrication of ZnSe-based blue lasers and light-emitting diodes. Because GaS is optically transparent, deposited to form window layers for such optoelectronic devices as light-emitting diodes, solar optical cells, and semiconductor lasers. Its transparency makes it useful as interconnection material in optoelectronic integrated circuits. Also useful in peeled-film technology because selectively etched from GaAs.

  2. Advances in Discrete GaAs JFETs and Simple Amplifiers for Deep Cryogenic Readouts

    NASA Technical Reports Server (NTRS)

    Cunningham, T. J.; Fitzsimmons, M.

    1998-01-01

    The progress of the Jet Propulsion Laboratory in developing gallium arsenide junction field-effect transistors (GaAs JFETs) for application in infrared readout electronics operating below 10 Kelvin is discussed.

  3. Direct Observation of the E_ Resonant State in GaAs1-xBix

    SciTech Connect

    Alberi, Kirstin; Beaton, Daniel A.; Mascarenhas, Angelo

    2015-12-15

    Bismuth-derived resonant states with T2 symmetry are detected in the valence band of GaAs1-xBix using electromodulated reflectance. A doublet is located 42 meV below the valence band edge of GaAs that is split by local strain around isolated Bi impurity atoms. A transition associated with a singlet is also observed just above the GaAs spin orbit split-off band. These states move deeper into the valence band with increasing Bi concentration but at a much slower rate than the well-known giant upward movement of the valence band edge in GaAs1-xBix. Our results provide key new insights for clarifying the mechanisms by which isovalent impurities alter the bandstructure of the host semiconductor.

  4. Cooperative chemisorption of K and O elements on cleaved GaAs(110) surface

    NASA Astrophysics Data System (ADS)

    Ren, Bin; Miao, Zhuang; Hou, Zhi-Peng; Cheng, Hong-Chang; Shi, Feng; Jiao, Gang-Cheng; Bai, Xiao-Feng; Niu, Sen; Wang, Long; Fu, Ling-Yun

    2014-09-01

    Using the projected augmented wave potential by the density functional theory based upon gradual gradient approach method and the slab model, from the calculated surface, we identify the relaxed atoms sites of GaAs(110) surface, the electronic structure of elements K and O adsorpted on binding sites of ideal GaAs(110) surface have also been calculated, especially the total energy of the adsorption system. The comparison results of calculated total energy showed: for K and O elements at highest coverage of Θ=1ML on GaAs(110) surface, they were not formed to local domain of competitive chemical adsorption, while they were formed to a compound uniformity phase of cooperative chemical adsorption. Our calculated results providing theoretical basis and reference for the application of alkali oxidation adsorpted on GaAs surface to form a negative electron affinity photocathode.

  5. Epitaxial thin film GaAs solar cells using OM-CVD techniques. [Organometallics

    NASA Technical Reports Server (NTRS)

    Stirn, R. J.; Wang, K. L.; Yeh, Y. C. M.

    1981-01-01

    A new approach has been initiated at JPL to fabricate thin-film, high efficiency GaAs solar cells on low-cost, single-crystal Si substrates having a thin CVD interlayer of Ge to minimize the lattice and thermal expansion mismatch. For initial experiments, n(+)/p GaAs cells were grown by OM-CVD on single-crystal GaAs and Ge wafers. Details of the growths and performance results will be presented. Subsequently, a combined epitaxial structure of OM-CVD GaAs on a strongly adherent Ge interlayer on (100) Si was grown. This is the first report of the successful growth of this composite structure. Low module costs projected by JPL SAMICS methodology calculations and the potential for 400-600W/kg space solar arrays will be discussed.

  6. Quantitative study of GaAs nanowires catalyzed by Au film of different thicknesses

    PubMed Central

    2012-01-01

    In this letter, we quantitatively investigated epitaxial GaAs nanowires catalyzed by thin Au films of different thicknesses on GaAs (111)B substrates in a metal-organic chemical vapor deposition reactor. Prior to nanowire growth, the de-wetting of Au thin films to form Au nanoparticles on GaAs (111)B in AsH3 ambient at different temperatures is investigated. It is found that with increasing film thickness, the size of the Au nanoparticles increases while the density of the nanoparticles reduces. Furthermore, higher annealing temperature produces larger Au nanoparticles for a fixed film thickness. As expected, the diameters and densities of the as-grown GaAs nanowires catalyzed by these thin Au films reflect these trends. PMID:23095345

  7. Inversion of spin dependent photocurrent at Fe3O4/modulation doped GaAs heterointerfaces

    NASA Astrophysics Data System (ADS)

    Shirahata, Y.; Wada, E.; Itoh, M.; Taniyama, T.

    2011-04-01

    We demonstrate inversion of the spin dependent photocurrent across an Fe3O4/modulation doped GaAs interface under optical spin orientation condition. The spin dependent photocurrent for fully epitaxial Fe3O4/GaAs and Fe/GaAs interfaces clearly show the opposite magnetic field dependence, where the spin filtering efficiency for the Fe3O4/GaAs decreases with increasing magnetic field. The results clearly indicate that the spin polarization of the Fe3O4 layer has the opposite sign to that of Fe at the Fermi energy, consistent with theoretical predictions, and the result is a consequence of the atomically flat Fe3O4/GaAs interface we obtained.

  8. Performance analysis of undoped cylindrical gate all around (GAA) MOSFET at subthreshold regime

    NASA Astrophysics Data System (ADS)

    Jena, B.; Pradhan, K. P.; Dash, S.; Mishra, G. P.; Sahu, P. K.; Mohapatra, S. K.

    2015-09-01

    In this work the sensitivity of process parameters like channel length (L), channel thickness (tSi), and gate work function (φM) on various performance metrics of an undoped cylindrical gate all around (GAA) metal-oxide-semiconductor field effect transistor (MOSFET) are systematically analyzed. Undoped GAA MOSFET is a radical invention as it introduces a new direction for transistor scaling. In conventional MOSFET, generally the channel doping concentration is very high to provide high on-state current, but in contrary it causes random dopant fluctuation and threshold voltage variation. So, the undoped nature of GAA MOSFET solves the above complications. Hence, we have analyzed the electrical characteristics as well as the analog/RF performances of undoped GAA MOSFET through Sentaurus device simulator.

  9. Neuropathology in respiratory-related motoneurons in young Pompe (Gaa(-/-)) mice.

    PubMed

    Turner, Sara M F; Hoyt, Aaron K; ElMallah, Mai K; Falk, Darin J; Byrne, Barry J; Fuller, David D

    2016-06-15

    Respiratory and/or lingual dysfunction are among the first motor symptoms in Pompe disease, a disorder resulting from absence or dysfunction of the lysosomal enzyme acid α-glucosidase (GAA). Here, we histologically evaluated the medulla, cervical and thoracic spinal cords in 6 weeks old asymptomatic Pompe (Gaa(-/-)) mice to determine if neuropathology in respiratory motor regions has an early onset. Periodic acid-Schiff (PAS) staining indicated glycogen accumulation was exclusively occurring in Gaa(-/-) hypoglossal, mid-cervical and upper thoracic motoneurons. Markers of DNA damage (Tunel) and ongoing apoptosis (Cleaved Caspase 3) did not co-localize with PAS staining, but were prominent in a medullary region which included the nucleus tractus solitarius, and also in the thoracic spinal dorsal horn. We conclude that respiratory-related motoneurons are particularly susceptible to GAA deficiency and that neuronal glycogen accumulation and neurodegeneration may occur independently in early stage disease. The data support early therapeutic intervention in Pompe disease. PMID:26921786

  10. GaAs monolithic R.F. 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.

  11. Irradiance gradients

    SciTech Connect

    Ward, G.J. Ecole Polytechnique Federale, Lausanne ); Heckbert, P.S. . School of Computer Science Technische Hogeschool Delft . Dept. of Technical Mathematics and Informatics)

    1992-04-01

    A new method for improving the accuracy of a diffuse interreflection calculation is introduced in a ray tracing context. The information from a hemispherical sampling of the luminous environment is interpreted in a new way to predict the change in irradiance as a function of position and surface orientation. The additional computation involved is modest and the benefit is substantial. An improved interpolation of irradiance resulting from the gradient calculation produces smoother, more accurate renderings. This result is achieved through better utilization of ray samples rather than additional samples or alternate sampling strategies. Thus, the technique is applicable to a variety of global illumination algorithms that use hemicubes or Monte Carlo sampling techniques.

  12. A novel GAA-repeat-expansion-based mouse model of Friedreich’s ataxia

    PubMed Central

    Anjomani Virmouni, Sara; Ezzatizadeh, Vahid; Sandi, Chiranjeevi; Sandi, Madhavi; Al-Mahdawi, Sahar; Chutake, Yogesh; Pook, Mark A.

    2015-01-01

    Friedreich’s ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by a GAA repeat expansion mutation within intron 1 of the FXN gene, resulting in reduced levels of frataxin protein. We have previously reported the generation of human FXN yeast artificial chromosome (YAC) transgenic FRDA mouse models containing 90–190 GAA repeats, but the presence of multiple GAA repeats within these mice is considered suboptimal. We now describe the cellular, molecular and behavioural characterisation of a newly developed YAC transgenic FRDA mouse model, designated YG8sR, which we have shown by DNA sequencing to contain a single pure GAA repeat expansion. The founder YG8sR mouse contained 120 GAA repeats but, due to intergenerational expansion, we have now established a colony of YG8sR mice that contain ~200 GAA repeats. We show that YG8sR mice have a single copy of the FXN transgene, which is integrated at a single site as confirmed by fluorescence in situ hybridisation (FISH) analysis of metaphase and interphase chromosomes. We have identified significant behavioural deficits, together with a degree of glucose intolerance and insulin hypersensitivity, in YG8sR FRDA mice compared with control Y47R and wild-type (WT) mice. We have also detected increased somatic GAA repeat instability in the brain and cerebellum of YG8sR mice, together with significantly reduced expression of FXN, FAST-1 and frataxin, and reduced aconitase activity, compared with Y47R mice. Furthermore, we have confirmed the presence of pathological vacuoles within neurons of the dorsal root ganglia (DRG) of YG8sR mice. These novel GAA-repeat-expansion-based YAC transgenic FRDA mice, which exhibit progressive FRDA-like pathology, represent an excellent model for the investigation of FRDA disease mechanisms and therapy. PMID:25681319

  13. Enhancing optical absorption in InP and GaAs utilizing profile etching

    NASA Technical Reports Server (NTRS)

    Bailey, Sheila G.; Fatemi, Navid S.; Landis, Geoffrey A.

    1991-01-01

    The current state of profile etching in GaAs and InP is summarized, including data on novel geometries attainable as a function of etchant temperature, composition, and rate; substrate orientation; carrier concentration; and oxide thickness between substrate and photoresist. V-grooved solar cells were manufactured with both GaAs and InP, and the improved optical absorption was demonstrated. Preferred parameters for various applications are listed and discussed.

  14. Enhancing optical absorption in InP and GaAs utilizing profile etching

    NASA Technical Reports Server (NTRS)

    Bailey, Sheila G.; Fatemi, Navid S.; Landis, Geoffrey A.

    1991-01-01

    The current state of profile etching in GaAs and InP is summarized, including data on novel geometries attainable as a function of etchant temperature, composition, and rate; substrate orientation; carrier concentration; and oxide thickness between substrate and photoresist. V-grooved solar cells have been manufactured with both GaAs and InP, and the improved optical absorption demonstrated. Preferred parameters for various applications are listed and discussed.

  15. Landau level spin diode in a GaAs two dimensional hole system

    NASA Astrophysics Data System (ADS)

    Klochan, O.; Hamilton, A. R.; das Gupta, K.; Sfigakis, F.; Beere, H. E.; Ritchie, D. A.

    2015-03-01

    We have fabricated and characterized a Landau level spin diode in a GaAs two-dimensional hole system. We used the spin diode to probe the hyperfine coupling between hole and nuclear spins and found no detectable net nuclear spin polarization, indicating that hole-nuclear spin flip-flop processes are suppressed by at least factor of 50 compared to GaAs electron systems.

  16. Basic mechanisms study for MIS solar cell structures on GaAs

    NASA Technical Reports Server (NTRS)

    Fonash, S. J.

    1978-01-01

    The solar cell structure examined is the MIS configuration on (n) GaAs. The metal room temperature oxide/(n) GaAs materials system was studied. Metals with electronegativities varying from 2.4 (Au) to 1.5 (Al) were used as the upper electrode. The thinnest metallization that did not interfere with the measurement techniques (by introducing essentially transmission line series resistance problems across a device) was used. Photovoltaic response was not optimized.

  17. Electron transfer and capture dynamics in ZnSe quantum wells grown on GaAs

    SciTech Connect

    Dongol, A.; Wagner, H. P.

    2013-12-04

    We investigate the transfer and capture dynamics of electrons in phase coherent photorefractive ZnSe quantum wells grown on GaAs using degenerate three-beam four-wave-mixing. The measurements reveal electron capture times by the quantum well in the order of several tens of picoseconds and a transit time of approximately 5 picoseconds from the GaAs substrate through the ZnMgSe barrier.

  18. Etching Technique to Reveal Dislocations in Thin GaAs Films Grown on Si Substrates

    NASA Astrophysics Data System (ADS)

    Nishikawa, Hironobu; Soga, Tetsuo; Mikuriya, Nobuo; Jimbo, Takashi; Umeno, Masayoshi

    1988-02-01

    Dislocations in GaAs and GaAs/Si are revealed by the etching technique at room temperature. The etchant is composed of H2O, K2Cr2O7, HNO3, HCl and H2SO4. The dislocation density of GaAs grown on Si by MOCVD using GaP and strained layer superlattices is about 1× 106 cm-2.

  19. GaAs transistors formed by Be or Mg ion implantation

    NASA Technical Reports Server (NTRS)

    Hunsperger, R. G.; Marsh, O. J.

    1974-01-01

    N-p-n transistor structures have been formed in GaAs by implanting n-type substrates with Be ions to form base regions and then implanting them with 20-keV Si ions to form emitters. P-type layers have been produced in GaAs by implantation of either Mg or Be ions, with substrate at room temperature, followed by annealing at higher temperatures.

  20. Enhanced light absorption in GaAs solar cells with internal Bragg reflectors

    NASA Astrophysics Data System (ADS)

    Tobin, S. P.; Vernon, S. M.; Sanfacon, M. M.; Mastrovito, A.

    The use of epitaxial multilayer dielectric mirrors (Bragg reflectors) as back-surface reflectors in thin-film GaAs solar cells on GaAs and silicon substrates is investigated. Al0.3Ga0.9As/Al0.85Ga0.15As Bragg reflectors were grown by low-pressure MOCVD on GaAs substrates and shown to exhibit near-ideal optical reflectance and structural perfection. Thin GaAs solar cells grown on Bragg reflectors showed increases in short-circuit current (0.5 to 1.0 mA/sq cm) and efficiency (0.7 percentage points) relative to cells without back reflectors. Efficiencies of 24.7 percent at one sun AM1.5 were measured for GaAs cells only 2 microns thick on Bragg reflectors. In addition to the optical enhancements, Bragg reflectors also appear to improve the defect structure of GaAs-on-Si solar cells. This approach should lead to improved efficiency for GaAs-on-Si solar cells and improved radiation resistance on GaAs cells.

  1. Single-event phenomena in GaAs devices and circuits

    SciTech Connect

    McMorrow, D.; Melinger, J.S.; Campbell, A.B. III; Weatherford, T.R.; Buchner, S.; Knudson, A.R.; Tran, L.H.

    1996-04-01

    The single-event upset (SEU) characteristics of GaAs devices and circuits are reviewed. GaAs FET-based integrated circuits (IC`s) are susceptible to upsets from both cosmic-ray heavy ions and protons trapped in the Earth`s radiation belts. The origin of the SEU sensitivity of GaAs IC`s is discussed in terms of both device-level and circuit-level considerations. At the device level, efficient charge-enhancement mechanisms through which more charge can be collected than is deposited by the ion have a significant negative impact on the SEU characteristics of GaAs IC`s. At the circuit level, different GaAs digital logic topologies exhibit different levels of sensitivity to SEU because of variations in parameters, including logic levels, capacitances, and the degree of gate or peripheral isolation. The operational and SEU characteristics of several different GaAs logic families are discussed. Recent advances in materials and processing that provide possible solutions to the SEU problem are addressed.

  2. Investigation of the optical and electrical properties of p-type porous GaAs structure

    NASA Astrophysics Data System (ADS)

    Saghrouni, H.; Missaoui, A.; Hannachi, R.; Beji, L.

    2013-12-01

    Porous GaAs layers have been formed by electrochemical anodic etching of (1 0 0) heavily doped p-type GaAs substrate in a HF:C2H5OH solution. The surface morphology of porous GaAs has been studied using atomic force microscopy (AFM). Nano-structural nature of the porous layer has been demonstrated by X-ray diffraction analysis (XRD) and confirmed by AFM. An estimation of the main size of the GaAs crystallites obtained from effective mass theory and based on PL data was close to the lowest value obtained from the AFM results. The porous p-GaAs samples are characterised by spectroscopic ellipsometry and modulation spectroscopy techniques. The objective of this study is to determine the porosity, refractive index, and thickness. The porosity of GaAs determined by atomic force microscopy confirmed by the value obtained from the spectroscopic ellipsometry. In fact the current-voltage I(V) characteristics of metal-semiconductor Au/p-GaAs are investigated and compared with Au/p-porous GaAs structures. From the forward bias I(V) characteristics of these devices, the main electrical parameters such as ideality factor, barrier height, and series resistance have been determined.

  3. Irradiated foods

    MedlinePlus

    ... it reduces the risk of 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.

  4. Structural Evolution During Formation and Filling of Self-patterned Nanoholes on GaAs (100) Surfaces

    PubMed Central

    2008-01-01

    Nanohole formation on an AlAs/GaAs superlattice gives insight to both the “drilling” effect of Ga droplets on AlAs as compared to GaAs and the hole-filling process. The shape and depth of the nanoholes formed on GaAs (100) substrates has been studied by the cross-section transmission electron microscopy. The Ga droplets “drill” through the AlAs layer at a much slower rate than through GaAs due to differences in activation energy. Refill of the nanohole results in elongated GaAs mounds along the [01−1] direction. As a result of capillarity-induced diffusion, GaAs favors growth inside the nanoholes, which provides the possibility to fabricate GaAs and AlAs nanostructures. PMID:20596345

  5. Terahertz generation from electron- and neutron-irradiated semiconductor crystal surfaces

    NASA Astrophysics Data System (ADS)

    Bereznaya, S. A.; Korotchenko, Z. V.; Redkin, R. A.; Sarkisov, S. Yu.; Brudnyi, V. N.; Kosobutsky, A. V.; Atuchin, V. V.

    2016-07-01

    Terahertz generation from the InP, InSb, GaAs and GaSe crystal surfaces excitated by femtosecond laser pulses has been studied. The terahertz spectra emitted from the native crystals and the crystals previously irradiated by high-energy neutrons or electrons have been recorded. Also, a simulation of the terahertz emission process has been performed. A weak terahertz signal generated from the GaSe native surface has been registered. In the case of electron-irradiated GaSe, the signal is increased several fold because of increased laser radiation absorption.

  6. Study of strain boundary conditions and GaAs buffer sizes in InGaAs quantum dots

    NASA Technical Reports Server (NTRS)

    Oyafuso, F.; Klimeck, G.; Boykin, T. B.; Bowen, R. C.; Allmen, P. von

    2003-01-01

    NEMO 3-D has been developed for the simulation of electronic structure in self-assembled InGaAs quantum dots on GaAs substrates. Typical self-assembled quantum dots in that material system contain about 0.5 to 1 million atoms. Effects of strain by the surrounding GaAs buffer modify the electronic structure inside the quantum dot significantly and a large GaAs buffer must be included in the strain and electronic structure.

  7. Enhanced thermoelectric figure of merit in thin GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Zou, Xiaolong; Chen, Xiaobin; Huang, Huaqing; Xu, Yong; Duan, Wenhui

    2015-05-01

    Combining density functional theory and the nonequilibrium Green's function method, we investigate the thermoelectric properties of thin GaAs nanowires (NWs). After identifying the most stable structures for GaAs NWs, either in wurtzite (wz) or zinc blende (zb) stacking, we present a systematic analysis on the thermoelectric properties of these NWs and their dependence on stacking type (wz or zb), size of NWs, and temperature. Although bulk GaAs is a well-known poor thermoelectric material, the thermoelectric figure of merit, ZT, is significantly enhanced in thin GaAs NWs. Typically, the room temperature ZT of a 1.1 nm-diameter GaAs NW reaches as high as 1.34, exhibiting more than 100-fold improvement over the bulk counterpart, which is attributed to both the reduced thermal conduction and enhanced power factor in thin NWs. Adopting their unique electronic characteristics, further enhancement is possible through surface engineering, for example, the introduction of surface roughness or dopants.Combining density functional theory and the nonequilibrium Green's function method, we investigate the thermoelectric properties of thin GaAs nanowires (NWs). After identifying the most stable structures for GaAs NWs, either in wurtzite (wz) or zinc blende (zb) stacking, we present a systematic analysis on the thermoelectric properties of these NWs and their dependence on stacking type (wz or zb), size of NWs, and temperature. Although bulk GaAs is a well-known poor thermoelectric material, the thermoelectric figure of merit, ZT, is significantly enhanced in thin GaAs NWs. Typically, the room temperature ZT of a 1.1 nm-diameter GaAs NW reaches as high as 1.34, exhibiting more than 100-fold improvement over the bulk counterpart, which is attributed to both the reduced thermal conduction and enhanced power factor in thin NWs. Adopting their unique electronic characteristics, further enhancement is possible through surface engineering, for example, the introduction of surface

  8. Aging and detergent washing effects of the surface of (001) and (110) GaAs passivated with hexadecanethiol

    NASA Astrophysics Data System (ADS)

    Moumanis, Kh.; Ding, X.; Dubowski, J. J.; Frost, E. H.

    2006-08-01

    We report on aging and detergent washing effects in GaAs wafers passivated with hexadecanethiol (HDT) [HS(CH2)15CH3]. The evolution of the photoluminescence (PL) signal from GaAs was measured at room temperature as a function of time, up to 1000h, for thiolated (001) GaAs that was solvent cleaned and etched using standard procedures, and for thiolated (110) GaAs that was obtained by cleaving in air. For 2h of thiolation time, the decay of the PL signal from (001) GaAs and (110) GaAs could be fitted, respectively, with double and single exponential functions. This indicates that at least two different types of non-adiative recombination centers (NRRC) form on the (001) surface. The overall density of surface states formed on (110) GaAs is significantly lower than those on (001) GaAs. A single exponential decay of the PL signal has been observed for 18h thiolated samples. The strong increase of the PL signal after detergent washing of (001) GaAs suggests that this treatment is effective in removal of some of the NRRC. The 19-fold enhancement of the PL signal, in comparison to that of the oxidized sample, has been obtained using the sample that, following the etching and detergent washing procedures, was thiolated with HDT.

  9. GaAs Substrates for High-Power Diode Lasers

    NASA Astrophysics Data System (ADS)

    Mueller, Georg; Berwian, Patrick; Buhrig, Eberhard; Weinert, Berndt

    GaAs substrate crystals with low dislocation density (Etch-Pit Density (EPD) < 500,^-2) and Si-doping ( ~10^18,^-3) are required for the epitaxial production of high-power diode-lasers. Large-size wafers (= 3 mathrm{in} -> >=3,) are needed for reducing the manufacturing costs. These requirements can be fulfilled by the Vertical Bridgman (VB) and Vertical Gradient Freeze (VGF) techniques. For that purpose we have developed proper VB/VGF furnaces and optimized the thermal as well as the physico-chemical process conditions. This was strongly supported by extensive numerical process simulation. The modeling of the VGF furnaces and processes was made by using a new computer code called CrysVUN++, which was recently developed in the Crystal Growth Laboratory in Erlangen.GaAs crystals with diameters of 2 and 3in were grown in pyrolytic Boron Nitride (pBN) crucibles having a small-diameter seed section and a conical part. Boric oxide was used to fully encapsulate the crystal and the melt. An initial silicon content in the GaAs melt of c (melt) = 3 x10^19,^-3 has to be used in order to achieve a carrier concentration of n = (0.8- 2) x10^18,^-3, which is the substrate specification of the device manufacturer of the diode-laser. The EPD could be reduced to values between 500,^-2 and 50,^-2 with a Si-doping level of 8 x10^17 to 1 x10^18,^-3. Even the 3in wafers have rather large dislocation-free areas. The lowest EPDs ( <100,^-2) are achieved for long seed wells of the crucible.

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  11. Current-voltage characteristics of silicon-doped GaAs nanowhiskers with a protecting AlGaAs coating overgrown with an undoped GaAs layer

    SciTech Connect

    Dementyev, P. A.; Dunaevskii, M. S. Samsonenko, Yu. B.; Cirlin, G. E.; Titkov, A. N.

    2010-05-15

    A technique for measurement of longitudinal current-voltage characteristics of semiconductor nanowhiskers remaining in contact with the growth surface is suggested. The technique is based on setting up a stable conductive contact between the top of a nanowhisker and the probe of an atomic-force microscope. It is demonstrated that, as the force pressing the probe against the top of the nanowhisker increases, the natural oxide layer covering the top is punctured and a direct contact between the probe and the nanowhisker body is established. In order to prevent nanowhiskers from bending and, ultimately, breaking, they need to be somehow fixed in space. In this study, GaAs nanowhiskers were kept fixed by partially overgrowing them with a GaAs layer. To isolate nanowhiskers from the matrix they were embedded in, they were coated by a nanometer layer of AlGaAs. Doping of GaAs nanowhiskers with silicon was investigated. The shape of the current-voltage characteristics obtained indicates that introduction of silicon leads to p-type conduction in nanowhiskers, in contrast to n-type conduction in bulk GaAs crystals grown by molecular-beam epitaxy. This difference is attributed to the fact that the vapor-liquid-solid process used to obtain nanowhiskers includes a final stage of liquid-phase epitaxy, a characteristic of the latter being p-type conduction obtained in bulk GaAs(Si) crystals.

  12. 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.

  13. Strain-induced birefringence in GaAs

    SciTech Connect

    Raynolds, J.E.; Levine, Z.H.; Wilkins, J.W.

    1995-04-15

    We present the results of density-functional calculations of the dielectric function and the photoelastic tensor---the susceptibility for strain-induced birefringence---in GaAs for photon frequencies below the direct band gap. These calculations were performed in the Kohn-Sham local-density approximation in a pseudopotential/plane-wave scheme which includes local-field effects and self-energy corrections. We find that traditional special-points integration methods are inadequate for performing the Brillouin-zone integrals involved in computing the photoelastic tensor. Very high resolution of the critical point at {ital k}=0 is needed to obtain even the correct {ital qualitative} behavior of the photoelastic tensor. Accurate expansions of the integrand in spherical harmonics for small {ital k} and plane waves elsewhere in the Brillouin zone were obtained and an integration approach which correctly integrates the expansions was used. Dramatic improvement in the qualitative frequency dispersion of the photoelastic tensor, in comparison with experiments, is obtained despite a large (50%) shift of the static value away from the measurement. We also present the result of a calculation of the internal strain relaxation associated with strains along the bonding [111] direction. These results are in excellent agreement with two previous {ital ab} {ital initio} calculations and with recent measurements.

  14. Fine structure of the Mn acceptor in GaAs

    NASA Astrophysics Data System (ADS)

    Krainov, I. V.; Debus, J.; Averkiev, N. S.; Dimitriev, G. S.; Sapega, V. F.; Lähderanta, E.

    2016-06-01

    We reveal the electronic level structure of the Mn acceptor, which consists of a valence-band hole bound to an Mn2 + ion, in presence of applied uniaxial stress and an external magnetic field in bulk GaAs. Resonant spin-flip Raman scattering is used to measure the g factor of the AMn0 center in the ground and excited states with the total angular momenta F =1 and F =2 and characterize the optical selection rules of the spin-flip transitions between these Mn-acceptor states. We determine the random stress fields near the Mn acceptor, the constant of the antiferromagnetic exchange interaction between the valence-band holes and the electrons of the inner Mn2 + shell as well as the deformation potential for the exchange energy. The p -d exchange energy, in particular, decreases significantly with increasing compressive stress. By combining the experimental Raman study with the developed theoretical model on the scattering efficiency, in which also the random local and external uniaxial stresses and magnetic field are considered, the fine structure of the Mn acceptor is determined in full detail.

  15. Solid phase epitaxial regrowth of (100)GaAs

    SciTech Connect

    Almonte, M I

    1996-02-01

    This thesis showed that low temperature (250 C) SPE of stoichiometrically balanced ion implanted GaAs layers can yield good epitaxial recovery for doses near the amorphization threshold. For 250 C anneals, most of the regrowth occurred in the first 10 min. HRTEM revealed much lower stacking fault density in the co-implanted sample than in the As-only and Ga-only samples with comparable doses. After low temp annealing, the nonstoichiometric samples had a large number of residual defects. For higher dose implants, very high temperatures (700 C) were needed to remove residual defects for all samples. The stoichiometrically balanced layer did not regrow better than the Ga-only and As-only samples. The co-implanted sample exhibited a thinner amorphous layer and a room temperature (RT) annealing effect. The amorphous layer regrew about 5 nm, suggesting that stoichiometrically balanced amorphous layers can regrow even at RT. Mechanisms for solid phase crystallization in (100)GasAs is discussed: nucleation and growth of randomly oriented crystallites and SPE. These two mechanisms compete in compound semiconductors at much lower temperatures than in Si. For the low dose As-only and Ga-only samples with low-temp anneals, both mechanisms are active. For this amorphization threshold dose, crystallites remain in the amorphous layer for all as-implants. 250 C annealing showed recrystallization from the surface and bulk for these samples; for the co-implant, the mechanism is not evident.

  16. Si and GaAs photocapacitive MIS infrared detectors

    NASA Technical Reports Server (NTRS)

    Sher, A.; Tsuo, Y. H.; Moriarty, J. A.; Miller, W. E.; Crouch, R. K.

    1980-01-01

    Improvement of the previously reported photocapacitive MIS infrared detectors has led to the development of exceptional room-temperature devices. Unoptimized peak detectivities on the order of 10 to the 13th cm sq rt Hz/W, a value which exceeds the best obtainable from existing solid-state detectors, have now been consistently obtained in Si and GaAs devices using high-capacitance LaF3 or composite LaF3/native-oxide insulating layers. The measured spectral response of representative samples is presented and discussed in detail together with a simple theory which accounts for the observed behavior. The response of an ideal MIS photocapacitor is also contrasted with that of both a conventional photoconductor and a p-i-n photodiode, and reasons for the superior performance of the MIS detectors are given. Finally, fundamental studies on the electrical, optical, and noise characteristics of the MIS structures are analyzed and discussed in the context of infrared-detector applications.

  17. GaAs quantum dot solar cell under concentrated radiation

    SciTech Connect

    Sablon, K.; Little, J. W.; Hier, H.; Li, Y.; Mitin, V.; Vagidov, N.; Sergeev, A.

    2015-08-17

    Effects of concentrated solar radiation on photovoltaic performance are investigated in well-developed GaAs quantum dot (QD) solar cells with 1-Sun efficiencies of 18%–19%. In these devices, the conversion processes are enhanced by nanoscale potential barriers and/or AlGaAs atomically thin barriers around QDs, which prevent photoelectron capture to QDs. Under concentrated radiation, the short circuit current increases proportionally to the concentration and the open circuit voltage shows the logarithmic increase. In the range up to hundred Suns, the contributions of QDs to the photocurrent are proportional to the light concentration. The ideality factors of 1.1–1.3 found from the V{sub OC}-Sun characteristics demonstrate effective suppression of recombination processes in barrier-separated QDs. The conversion efficiency shows the wide maximum in the range of 40–90 Suns and reaches 21.6%. Detailed analysis of I-V-Sun characteristics shows that at low intensities, the series resistance decreases inversely proportional to the concentration and, at ∼40 Suns, reaches the plateau determined mainly by the front contact resistance. Improvement of contact resistance would increase efficiency to above 24% at thousand Suns.

  18. Ultrafast terahertz emission properties in GaAs semiconductor

    NASA Astrophysics Data System (ADS)

    Wang, Aihua; Shi, Yulei; Zhou, Qingli

    2015-08-01

    Ultrafast carrier dynamics in Schottky barriers is an extremely active area of research in recent years. The observation of the generation of terahertz pulses from metal/semiconductor interfaces provides a technique to characterize electronic properties of these materials. However, a detailed analysis of these phenomena has not been performed satisfactorily. In this work, the measurements of optically generated terahertz emission from Au/GaAs interfaces are investigated in detail. We observe that, under high laser power excitation, terahertz signals from bare GaAs wafers and Au/GaAs samples exhibit an opposite polarity. The polarity-flip behaviors in the terahertz beams are also observed in the temperature-dependent measurements and the femtosecond pump-generation studies of the Au/GaAs interfaces. These effects can be fully explained in terms of the dynamics of carrier transfer in the Au/GaAs Schottky barriers, which involves the internal photoelectric emission and the electron tunneling effect, and picosecond time constants are found for these processes.

  19. Droplet-mediated formation of embedded GaAs nanowires in MBE GaAs(1-x)Bi(x) films.

    PubMed

    Wood, Adam W; Collar, Kristen; Li, Jincheng; Brown, April S; Babcock, Susan E

    2016-03-18

    We have examined the morphology and composition of embedded nanowires that can be formed during molecular beam epitaxy of GaAs(1-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 GaAs(1-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 GaAs(1-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 GaAs(1-x)Bi(x) film growth. PMID:26876494

  20. Ab initio structural and vibrational properties of GaAs diamondoids and nanocrystals

    SciTech Connect

    Abdulsattar, Mudar Ahmed; Hussein, Mohammed T.; Hameed, Hadeel Ali

    2014-12-15

    Gallium arsenide diamondoids structural and vibrational properties are investigated using density functional theory at the PBE/6-31(d) level and basis including polarization functions. Variation of energy gap as these diamondoids increase in size is seen to follow confinement theory for diamondoids having nearly equiaxed dimensions. Density of energy states transforms from nearly single levels to band structure as we reach larger diamondoids. Bonds of surface hydrogen with As atoms are relatively localized and shorter than that bonded to Ga atoms. Ga-As bonds have a distribution range of values due to surface reconstruction and effect of bonding to hydrogen atoms. Experimental bulk Ga-As bond length (2.45 Å) is within this distribution range. Tetrahedral and dihedral angles approach values of bulk as we go to higher diamondoids. Optical-phonon energy of larger diamondoids stabilizes at 0.037 eV (297 cm{sup -1}) compared to experimental 0.035 eV (285.2 cm{sup -1}). Ga-As force constant reaches 1.7 mDyne/Å which is comparable to Ga-Ge force constant (1.74 mDyne/Å). Hydrogen related vibrations are nearly constant and serve as a fingerprint of GaAs diamondoids while Ga-As vibrations vary with size of diamondoids.

  1. Highly efficient single-junction GaAs thin-film solar cell on flexible substrate.

    PubMed

    Moon, Sunghyun; Kim, Kangho; Kim, Youngjo; Heo, Junseok; Lee, Jaejin

    2016-01-01

    There has been much interest in developing a thin-film solar cell because it is lightweight and flexible. The GaAs thin-film solar cell is a top contender in the thin-film solar cell market in that it has a high power conversion efficiency (PCE) compared to that of other thin-film solar cells. There are two common structures for the GaAs solar cell: n (emitter)-on-p (base) and p-on-n. The former performs better due to its high collection efficiency because the electron diffusion length of the p-type base region is much longer than the hole diffusion length of the n-type base region. However, it has been limited to fabricate highly efficient n-on-p single-junction GaAs thin film solar cell on a flexible substrate due to technical obstacles. We investigated a simple and fast epitaxial lift-off (ELO) method that uses a stress originating from a Cr/Au bilayer on a 125-μm-thick flexible substrate. A metal combination of AuBe/Pt/Au is employed as a new p-type ohmic contact with which an n-on-p single-junction GaAs thin-film solar cell on flexible substrate was successfully fabricated. The PCE of the fabricated single-junction GaAs thin-film solar cells reached 22.08% under air mass 1.5 global illumination. PMID:27435899

  2. Measurement of electron beam polarization produced by photoemission from bulk GaAs using twisted light

    NASA Astrophysics Data System (ADS)

    Clayburn, Nathan; Dreiling, Joan; McCarter, James; Ryan, Dominic; Poelker, Matt; Gay, Timothy

    2012-06-01

    GaAs photocathodes produce spin polarized electron beams when illuminated with circularly polarized light with photon energy approximately equal to the bandgap energy [1, 2]. A typical polarization value obtained with bulk GaAs and conventional circularly polarized light is 35%. This study investigated the spin polarization of electron beams emitted from GaAs illuminated with ``twisted light,'' an expression that describes a beam of light having orbital angular momentum (OAM). In the experiment, 790nm laser light was focused to a near diffraction-limited spot size on the surface of the GaAs photocathode to determine if OAM might couple to valence band electron spin mediated by the GaAs lattice. Our polarization measurements using a compact retarding-field micro-Mott polarimeter [3] have established an upper bound on the polarization of the emitted electron beam of 2.5%. [4pt] [1] D.T. Pierce, F. Meier, P. Zurcher, Appl. Phys. Lett. 26 670 (1975).[0pt] [2] C.K. Sinclair, et al., PRSTAB 10 023501 (2007).[0pt] [3] J.L. McCarter, M.L. Stutzman, K.W. Trantham, T.G. Anderson, A.M. Cook, and T.J. Gay Nucl. Instrum. and Meth. A (2010).

  3. High Performance Ultrathin GaAs Solar Cells Enabled with Heterogeneously Integrated Dielectric Periodic Nanostructures.

    PubMed

    Lee, Sung-Min; Kwong, Anthony; Jung, Daehwan; Faucher, Joseph; Biswas, Roshni; Shen, Lang; Kang, Dongseok; Lee, Minjoo Larry; Yoon, Jongseung

    2015-10-27

    Due to their favorable materials properties including direct bandgap and high electron mobilities, epitaxially grown III-V compound semiconductors such as gallium arsenide (GaAs) provide unmatched performance over silicon in solar energy harvesting. Nonetheless, their large-scale deployment in terrestrial photovoltaics remains challenging mainly due to the high cost of growing device quality epitaxial materials. In this regard, reducing the thickness of constituent active materials under appropriate light management schemes is a conceptually viable option to lower the cost of GaAs solar cells. Here, we present a type of high efficiency, ultrathin GaAs solar cell that incorporates bifacial photon management enabled by techniques of transfer printing to maximize the absorption and photovoltaic performance without compromising the optimized electronic configuration of planar devices. Nanoimprint lithography and dry etching of titanium dioxide (TiO2) deposited directly on the window layer of GaAs solar cells formed hexagonal arrays of nanoscale posts that serve as lossless photonic nanostructures for antireflection, diffraction, and light trapping in conjunction with a co-integrated rear-surface reflector. Systematic studies on optical and electrical properties and photovoltaic performance in experiments, as well as numerical modeling, quantitatively describe the optimal design rules for ultrathin, nanostructured GaAs solar cells and their integrated modules. PMID:26376087

  4. Development of a 1K x 1K GaAs QWIP Far IR Imaging Array

    NASA Technical Reports Server (NTRS)

    Jhabvala, M.; Choi, K.; Goldberg, A.; La, A.; Gunapala, S.

    2003-01-01

    In the on-going evolution of GaAs Quantum Well Infrared Photodetectors (QWIPs) we have developed a 1,024 x 1,024 (1K x1K), 8.4-9 microns infrared focal plane array (FPA). This 1 megapixel detector array is a hybrid using the Rockwell TCM 8050 silicon readout integrated circuit (ROIC) bump bonded to a GaAs QWIP array fabricated jointly by engineers at the Goddard Space Flight Center (GSFC) and the Army Research Laboratory (ARL). The finished hybrid is thinned at the Jet Propulsion Lab. Prior to this development the largest format array was a 512 x 640 FPA. We have integrated the 1K x 1K array into an imaging camera system and performed tests over the 40K-90K temperature range achieving BLIP performance at an operating temperature of 76K (f/2 camera system). The GaAs array is relatively easy to fabricate once the superlattice structure of the quantum wells has been defined and grown. The overall arrays costs are currently dominated by the costs associated with the silicon readout since the GaAs array fabrication is based on high yield, well-established GaAs processing capabilities. In this paper we will present the first results of our 1K x 1K QWIP array development including fabrication methodology, test data and our imaging results.

  5. Highly efficient single-junction GaAs thin-film solar cell on flexible substrate

    PubMed Central

    Moon, Sunghyun; Kim, Kangho; Kim, Youngjo; Heo, Junseok; Lee, Jaejin

    2016-01-01

    There has been much interest in developing a thin-film solar cell because it is lightweight and flexible. The GaAs thin-film solar cell is a top contender in the thin-film solar cell market in that it has a high power conversion efficiency (PCE) compared to that of other thin-film solar cells. There are two common structures for the GaAs solar cell: n (emitter)-on-p (base) and p-on-n. The former performs better due to its high collection efficiency because the electron diffusion length of the p-type base region is much longer than the hole diffusion length of the n-type base region. However, it has been limited to fabricate highly efficient n-on-p single-junction GaAs thin film solar cell on a flexible substrate due to technical obstacles. We investigated a simple and fast epitaxial lift-off (ELO) method that uses a stress originating from a Cr/Au bilayer on a 125-μm-thick flexible substrate. A metal combination of AuBe/Pt/Au is employed as a new p-type ohmic contact with which an n-on-p single-junction GaAs thin-film solar cell on flexible substrate was successfully fabricated. The PCE of the fabricated single-junction GaAs thin-film solar cells reached 22.08% under air mass 1.5 global illumination. PMID:27435899

  6. GaAs Blocked-Impurity-Band Detectors for Far-Infrared Astronomy

    SciTech Connect

    Cardozo, Benjamin Lewin

    2004-12-21

    High-purity and doped GaAs films have been grown by Liquid-phase epitaxy (LPE) for development of a blocked impurity band (BIB) detector for far-infrared radiation. The film growth process developed has resulted in the capability to grow GaAs with a net active impurity concentration below 1 x 10{sup 13} cm{sup -3}, ideal for the blocking layer of the BIB detector. The growth of n-type LPE GaAs films with donor concentrations below the metal-insulator transition, as required for the absorbing layer of a BIB detector, has been achieved. The control of the donor concentration, however, was found to be insufficient for detector production. The growth by LPE of a high-purity film onto a commercially grown vapor-phase epitaxial (VPE) n-type GaAs doped absorbing layer resulted in a BIB device that showed a significant reduction in the low-temperature dark current compared to the absorbing layer only. Extended optical response was not detected, most likely due to the high compensation of the commercially grown GaAs absorbing layer, which restricts the depletion width of the device.

  7. High-efficiency thin-film GaAs solar cells, phase2

    NASA Technical Reports Server (NTRS)

    Yeh, Y. C. M.

    1981-01-01

    Thin GaAs epi-layers with good crystallographic quality were grown using a (100) Si-substrate on which a thin Ge epi-interlayer was grown by CVD from germane. Both antireflection-coated metal oxide semiconductor (AMOS) and n(+)/p homojunction structures were studied. The AMOS cells were fabricated on undoped-GaAs epi-layers deposited on bulk poly-Ge substrates using organo-metallic CVD film-growth, with the best achieved AM1 conversion efficiency being 9.1%. Both p-type and n(+)-type GaAs growth were optimized using 50 ppm dimethyl zinc and 1% hydrogen sulfide, respectively. A direct GaAs deposition method in fabricating ultra-thin top layer, epitaxial n(+)/p shallow homojunction solar cells on (100) GaAs substrates (without anodic thinning) was developed to produce large area (1 sq/cm) cells, with 19.4% AM1 conversion efficiency achieved. Additionally, an AM1 conversion efficiency of 18.4% (17.5% with 5% grid coverage) was achieved for a single crystal GaAs n(+)/p cell grown by OM-CVD on a Ge wafer.

  8. GaAs Refractive Index Dependence On Carrier Density and Optimizing Terahertz Devices

    NASA Astrophysics Data System (ADS)

    Kim, Christopher; Wu, Dong Ho; Graber, Benjamin

    GaAs is used for various applications, including high speed transistors, high-efficiency photovoltaic cells, electro-optics and terahertz (THz) emitters and detectors. To date, information on the refractive index of GaAs is available only over a limited wave spectrum of 0.2-17um, where the refractive index varies from 1.3 to 5.0. As detailed information on the refractive index of GaAs at THz frequencies is not available or inadequate for our effort to develop an improved GaAs-based THz emitter, we experimentally investigated the behavior of the refractive index of GaAs for different charge carrier densities, especially with or without the presence of surface plasma. Using a Time Domain THz Spectrometer, which is capable of measuring THz pulses containing a wave spectrum over 100-3000um with a time accuracy better than 6 femtoseconds, we measured the delay of THz pulses traversing through a GaAs substrate of known thickness while modulating the charge carrier concentration. From the experimental data we estimated the refractive index for THz frequencies to vary from 3.5 to 3.8 for different charge carrier concentrations. We will discuss details of our experiments and implications of our experimental results, especially for our GaAs-based THz devices.

  9. Highly efficient single-junction GaAs thin-film solar cell on flexible substrate

    NASA Astrophysics Data System (ADS)

    Moon, Sunghyun; Kim, Kangho; Kim, Youngjo; Heo, Junseok; Lee, Jaejin

    2016-07-01

    There has been much interest in developing a thin-film solar cell because it is lightweight and flexible. The GaAs thin-film solar cell is a top contender in the thin-film solar cell market in that it has a high power conversion efficiency (PCE) compared to that of other thin-film solar cells. There are two common structures for the GaAs solar cell: n (emitter)-on-p (base) and p-on-n. The former performs better due to its high collection efficiency because the electron diffusion length of the p-type base region is much longer than the hole diffusion length of the n-type base region. However, it has been limited to fabricate highly efficient n-on-p single-junction GaAs thin film solar cell on a flexible substrate due to technical obstacles. We investigated a simple and fast epitaxial lift-off (ELO) method that uses a stress originating from a Cr/Au bilayer on a 125-μm-thick flexible substrate. A metal combination of AuBe/Pt/Au is employed as a new p-type ohmic contact with which an n-on-p single-junction GaAs thin-film solar cell on flexible substrate was successfully fabricated. The PCE of the fabricated single-junction GaAs thin-film solar cells reached 22.08% under air mass 1.5 global illumination.

  10. Superpulsed (Ga-As, 904 nm) low-level laser therapy (LLLT) attenuates inflammatory response and enhances healing of burn wounds.

    PubMed

    Gupta, Asheesh; Keshri, Gaurav K; Yadav, Anju; Gola, Shefali; Chauhan, Satish; Salhan, Ashok K; Bala Singh, Shashi

    2015-06-01

    Low-level laser therapy (LLLT) using superpulsed near-infrared light can penetrate deeper in the injured tissue and could allow non-pharmacological treatment for chronic wound healing. This study investigated the effects of superpulsed laser (Ga-As 904 nm, 200 ns pulse width; 100 Hz; 0.7 mW mean output power; 0.4 mW/cm(2) average irradiance; 0.2 J/cm(2) total fluence) on the healing of burn wounds in rats, and further explored the probable associated mechanisms of action. Irradiated group exhibited enhanced DNA, total protein, hydroxyproline and hexosamine contents compared to the control and silver sulfadiazine (reference care) treated groups. LLLT exhibited decreased TNF-α level and NF-kB, and up-regulated protein levels of VEGF, FGFR-1, HSP-60, HSP-90, HIF-1α and matrix metalloproteinases-2 and 9 compared to the controls. In conclusion, LLLT using superpulsed 904 nm laser reduced the inflammatory response and was able to enhance cellular proliferation, collagen deposition and wound contraction in the repair process of burn wounds. Photomicrographs showing no, absence inflammation and faster wound contraction in LLLT superpulsed (904 nm) laser treated burn wounds as compared to the non-irradiated control and silver sulfadiazine (SSD) ointment (reference care) treated wounds. PMID:25207838

  11. Electronic properties of deep-level defects in proton irradiated AlGaAs-GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Li, S. S.

    1981-01-01

    Deep level transient spectroscopy and capacitance voltage techniques as well as analysis of the forward current voltage (I-V) characteristics and SEM-EIC data were carried out for proton irradiated GaAs solar cells over a wide range of proton energies and proton fluences. Defect and recombination parameters such as defect energy levels and density, carrier capture cross sections and lifetimes as well as diffusion lengths in the undoped n-GaAs LPE layers were determined. Good correlation between these defect parameters and solar cell performance parameters was obtained for GaAs solar cells irradiated by 200 and 290 KeV protons. It was found that 200 to 290 KeV protons will produce the most defects and damages to the GaAs solar cell structure used. The influence of the low temperature (200 to 400 C) periodic thermal annealing on the deep level defects and the performance of the 200 KeV proton irradiated cells is discussed.

  12. Interpolative modeling of GaAs FET S-parameter data bases for use in Monte Carlo simulations

    NASA Technical Reports Server (NTRS)

    Campbell, L.; Purviance, J.

    1992-01-01

    A statistical interpolation technique is presented for modeling GaAs FET S-parameter measurements for use in the statistical analysis and design of circuits. This is accomplished by interpolating among the measurements in a GaAs FET S-parameter data base in a statistically valid manner.

  13. Micro-Photoluminescence Characterization of Low Density Droplet GaAs Quantum Dots for Single Photon Sources

    SciTech Connect

    Ha, S.-K.; Song, J. D.; Lim, J. Y.; Choi, W. J.; Han, I. K.; Lee, J. I.; Bounouar, S.; Donatini, F.; Dang, L. S.; Poizat, J. P.

    2011-12-23

    The GaAs quantum dots in AlGaAs barriers were grown by droplet epitaxy, emitting around 700 nm in wavelength which is compatible with low cost Si based detectors. The excitation power dependent and time resolved micro-photoluminescence measurements identified optical characteristics of exciton and biexciton states which are attributed to good quantum confinements in GaAs QDs.

  14. GaSb thermophotovoltaic cells grown on GaAs by molecular beam epitaxy using interfacial misfit arrays

    NASA Astrophysics Data System (ADS)

    Juang, Bor-Chau; Laghumavarapu, Ramesh B.; Foggo, Brandon J.; Simmonds, Paul J.; Lin, Andrew; Liang, Baolai; Huffaker, Diana L.

    2015-03-01

    There exists a long-term need for foreign substrates on which to grow GaSb-based optoelectronic devices. We address this need by using interfacial misfit arrays to grow GaSb-based thermophotovoltaic cells directly on GaAs (001) substrates and demonstrate promising performance. We compare these cells to control devices grown on GaSb substrates to assess device properties and material quality. The room temperature dark current densities show similar characteristics for both cells on GaAs and on GaSb. Under solar simulation the cells on GaAs exhibit an open-circuit voltage of 0.121 V and a short-circuit current density of 15.5 mA/cm2. In addition, the cells on GaAs substrates maintain 10% difference in spectral response to those of the control cells over a large range of wavelengths. While the cells on GaSb substrates in general offer better performance than the cells on GaAs substrates, the cost-savings and scalability offered by GaAs substrates could potentially outweigh the reduction in performance. By further optimizing GaSb buffer growth on GaAs substrates, Sb-based compound semiconductors grown on GaAs substrates with similar performance to devices grown directly on GaSb substrates could be realized.

  15. GaSb thermophotovoltaic cells grown on GaAs by molecular beam epitaxy using interfacial misfit arrays

    SciTech Connect

    Juang, Bor-Chau Laghumavarapu, Ramesh B.; Foggo, Brandon J.; Lin, Andrew; Simmonds, Paul J.; Liang, Baolai; Huffaker, Diana L.

    2015-03-16

    There exists a long-term need for foreign substrates on which to grow GaSb-based optoelectronic devices. We address this need by using interfacial misfit arrays to grow GaSb-based thermophotovoltaic cells directly on GaAs (001) substrates and demonstrate promising performance. We compare these cells to control devices grown on GaSb substrates to assess device properties and material quality. The room temperature dark current densities show similar characteristics for both cells on GaAs and on GaSb. Under solar simulation the cells on GaAs exhibit an open-circuit voltage of 0.121 V and a short-circuit current density of 15.5 mA/cm{sup 2}. In addition, the cells on GaAs substrates maintain 10% difference in spectral response to those of the control cells over a large range of wavelengths. While the cells on GaSb substrates in general offer better performance than the cells on GaAs substrates, the cost-savings and scalability offered by GaAs substrates could potentially outweigh the reduction in performance. By further optimizing GaSb buffer growth on GaAs substrates, Sb-based compound semiconductors grown on GaAs substrates with similar performance to devices grown directly on GaSb substrates could be realized.

  16. Effects of low-temperature buffer-layer thickness and growth temperature on the SEE sensitivity of GaAs HIGFET circuits

    SciTech Connect

    Weatherford, T.R.; Fouts, D.J.; Marshall, P.W. |; Marshall, C.J.; Mathes, B.; LaMacchia, M.

    1997-12-01

    Heavy-ion Single Event Effects (SEE) test results reveal the role of growth temperature and buffer layer thickness in the use of a low-temperature grown GaAs (LT GaAs) buffer layer for suppressing SEE sensitivity in GaAs HIGFET circuits.

  17. Bismuth-induced phase control of GaAs nanowires grown by molecular beam epitaxy

    SciTech Connect

    Lu, Zhenyu; Chen, Pingping E-mail: luwei@mail.sitp.ac.cn; Shi, Suixing; Yao, Luchi; Zhou, Xiaohao; Lu, Wei E-mail: luwei@mail.sitp.ac.cn; Zhang, Zhi; Zhou, Chen; Zou, Jin

    2014-10-20

    In this work, the crystal structure of GaAs nanowires grown by molecular beam epitaxy has been tailored only by bismuth without changing the growth temperature and V/III flux ratio. The introduction of bismuth can lead to the formation of zinc-blende GaAs nanowires, while the removal of bismuth changes the structure into a 4H polytypism before it turns back to the wurtzite phase eventually. The theoretical calculation shows that it is the steadiest for bismuth to adsorb on the GaAs(111){sub B} surface compared to the liquid gold catalyst surface and the interface between the gold catalyst droplet and the nanowire, and these adsorbed bismuth could decrease the diffusion length of adsorbed Ga and hence the supersaturation of Ga in the gold catalyst droplet.

  18. Frequency-tunable continuous-wave terahertz sources based on GaAs plasmonic photomixers

    NASA Astrophysics Data System (ADS)

    Yang, Shang-Hua; Jarrahi, Mona

    2015-09-01

    We present frequency-tunable, continuous-wave terahertz sources based on GaAs plasmonic photomixers, which offer high terahertz radiation power levels at 50% radiation duty cycle. The use of plasmonic contact electrodes enhances photomixer quantum efficiency while maintaining its ultrafast operation by concentrating a large number of photocarriers in close proximity to the device contact electrodes. Additionally, the relatively high thermal conductivity and high resistivity of GaAs allow operation under high optical pump power levels and long duty cycles without reaching the thermal breakdown limit of the photomixer. We experimentally demonstrate continuous-wave terahertz radiation with a radiation frequency tuning range of more than 2 THz and a record-high radiation power of 17 μW at 1 THz through plasmonic photomixers fabricated on a low temperature grown GaAs substrate at 50% radiation duty cycle.

  19. GaAs Core/SrTiO3 Shell Nanowires Grown by Molecular Beam Epitaxy.

    PubMed

    Guan, X; Becdelievre, J; Meunier, B; Benali, A; Saint-Girons, G; Bachelet, R; Regreny, P; Botella, C; Grenet, G; Blanchard, N P; Jaurand, X; Silly, M G; Sirotti, F; Chauvin, N; Gendry, M; Penuelas, J

    2016-04-13

    We have studied the growth of a SrTiO3 shell on self-catalyzed GaAs nanowires grown by vapor-liquid-solid assisted molecular beam epitaxy on Si(111) substrates. To control the growth of the SrTiO3 shell, the GaAs nanowires were protected using an arsenic capping/decapping procedure in order to prevent uncontrolled oxidation and/or contamination of the nanowire facets. Reflection high energy electron diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy were performed to determine the structural, chemical, and morphological properties of the heterostructured nanowires. Using adapted oxide growth conditions, it is shown that most of the perovskite structure SrTiO3 shell appears to be oriented with respect to the GaAs lattice. These results are promising for achieving one-dimensional epitaxial semiconductor core/functional oxide shell nanostructures. PMID:27008537

  20. Monolithic optical integrated control circuitry for GaAs MMIC-based phased arrays

    NASA Technical Reports Server (NTRS)

    Bhasin, K. B.; Ponchak, G. E.; Kascak, T. J.

    1985-01-01

    Gallium arsenide (GaAs) monolithic microwave integrated circuits (MMIC's) show promise in phased-array antenna applications for future space communications systems. Their efficient usage will depend on the control of amplitude and phase signals for each MMIC element in the phased array and in the low-loss radiofrequency feed. For a phased array contining several MMIC elements a complex system is required to control and feed each element. The characteristics of GaAs MMIC's for 20/30-GHz phased-array systems are discussed. The optical/MMIC interface and the desired characteristics of optical integrated circuits (OIC's) for such an interface are described. Anticipated fabrication considerations for eventual full monolithic integration of optical integrated circuits with MMIC's on a GaAs substrate are presented.

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

    SciTech Connect

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

    1994-06-01

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

  2. GaAs Industry in Europe-Technologies, Trends and New Developments

    NASA Astrophysics Data System (ADS)

    Jung, Helmut; Blanck, Hervé; Bösch, Wolfgang; Mayock, Jim

    The GaAs industry has been growing immensely during recent years. This is mainly driven by the tremendous growth of the wireless communication market, which is still continuously growing. Additionally, an emerging mmW market with applications in automotive, defense and optoelectronics is further driving the demand for GaAs components. The two largest European GaAs fabrication companies, UMS and Filtronic are very well positioned to address the complete frequency range from 1GHz up to 100GHz for commercial, high volume low cost markets, as well as individual niche applications. An overview of the companies' structures, their processes and design capabilities and also their new product developments will be presented in this paper.

  3. Strong carrier lifetime enhancement in GaAs nanowires coated with semiconducting polymer.

    PubMed

    Yong, Chaw Keong; Noori, Keian; Gao, Qiang; Joyce, Hannah J; Tan, H Hoe; Jagadish, Chennupati; Giustino, Feliciano; Johnston, Michael B; Herz, Laura M

    2012-12-12

    The ultrafast charge carrier dynamics in GaAs/conjugated polymer type II heterojunctions are investigated using time-resolved photoluminescence spectroscopy at 10 K. By probing the photoluminescence at the band edge of GaAs, we observe strong carrier lifetime enhancement for nanowires blended with semiconducting polymers. The enhancement is found to depend crucially on the ionization potential of the polymers with respect to the Fermi energy level at the surface of the GaAs nanowires. We attribute these effects to electron doping by the polymer which reduces the unsaturated surface-state density in GaAs. We find that when the surface of nanowires is terminated by native oxide, the electron injection across the interface is greatly reduced and such surface doping is absent. Our results suggest that surface engineering via π-conjugated polymers can substantially improve the carrier lifetime in nanowire hybrid heterojunctions with applications in photovoltaics and nanoscale photodetectors. PMID:23171081

  4. Vibrational, electronic and structural properties of wurtzite GaAs nanowires under hydrostatic pressure

    PubMed Central

    Zhou, Wei; Chen, Xiao-Jia; Zhang, Jian-Bo; Li, Xin-Hua; Wang, Yu-Qi; Goncharov, Alexander F.

    2014-01-01

    The structural, vibrational, and electronic properties of GaAs nanowires have been studied in the metastable wurtzite phase via Resonant Raman spectroscopy and synchrotron X-ray diffraction measurements in diamond anvil cells under hydrostatic conditions between 0 and 23 GPa. The direct band gap E0 and the crystal field split-off gap E0 + Δ of wurtzite GaAs increase with pressure and their values become close to those of zinc-blende GaAs at 5 GPa, while being reported slightly larger at lower pressures. Above 21 GPa, a complete structural transition from the wurtzite to an orthorhombic phase is observed in both Raman and X-ray diffraction experiments. PMID:25253566

  5. Vapor phase epitaxy of CdTe on sapphire and GaAs

    NASA Astrophysics Data System (ADS)

    Kasuga, Masanobu; Futami, Hiroyuki; Iba, Yoshihiro

    1991-12-01

    CdTe films were deposited on three kinds of sapphire substrate and two kinds of GaAs substrate by open tube vapor transport. X-ray Laue diffraction study showed that CdTe(111) film grew on every kind of sapphire substrate used, i.e. on the (0001) basal plane, the (11 overline20)A plane and the (1 overline102)R plane, and that there exist a few degrees of tilt angel between CdTe(111) and the lattice plane of each substrate. The process of making the tilt angle may be explained by the atomistic mismatch model of the Cd and Al arrangement which is projected on the film-substrate interface. On GaAs(100), either CdTe(111) or CdTe(100) was obtained, whereas only a twin crystalline film was obtained on GaAs(111). These results are also consistent with the mismatch model of Cd and Ga atoms.

  6. Radiation detectors fabricated on high-purity GaAs epitaxial materials

    NASA Astrophysics Data System (ADS)

    Wu, X.; Kostamo, P.; Gädda, A.; Nenonen, S.; Riekkinen, T.; Härkönen, J.; Salonen, J.; Andersson, H.; Zhilyaev, Y.; Fedorov, L.; Eränen, S.; Mattila, M.; Lipsanen, H.; Prunnila, M.; Kalliopuska, J.; Oja, A.

    2014-12-01

    Epitaxial GaAs material shows a great potential in X-ray spectroscopy and radiography applications due to its high absorption efficiency and low defect density. Fabrication of pixel radiation detectors from high-purtity epitaxial GaAs has been developed further. The process is based on mesa etching for pixellisation and sputtering for metallization. The leakage currents of processed pad detectors are below 10 nA/cm2 at a reverse bias of 100 V and decrease exponentially with the temperature. Measurement with transient current technique (TCT) shows that electrons have a trapping time of 8 ns. Good spectroscopic result were obtained from both a pad detector and a hybridized Medipix GaAs detector.

  7. Observation of free exciton photoluminescence emission from single wurtzite GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Hoang, Thang B.; Moses, A. F.; Zhou, H. L.; Dheeraj, D. L.; Fimland, B. O.; Weman, H.

    2009-03-01

    Microphotoluminescence measurements are used to investigate the optical properties of single wurtzite GaAs nanowires grown by molecular beam epitaxy. The wurtzite GaAs nanowires exhibit a photoluminescence emission peak at 1.544 eV, 29 meV higher than the zinc blende GaAs free exciton energy. Temperature dependent photoluminescence measurements (4.4-70 K) show indications of defect and impurity related emissions at lower energies (1.53-1.54 eV) and the presence of nonradiative defects. High resolution transmission electron microscopy images show a low density of short zinc blende segments sandwiched in between a dominating wurtzite structure and weak photoluminescence emission related to such zinc blende segments is also observed.

  8. Frequency-tunable continuous-wave terahertz sources based on GaAs plasmonic photomixers

    SciTech Connect

    Yang, Shang-Hua; Jarrahi, Mona

    2015-09-28

    We present frequency-tunable, continuous-wave terahertz sources based on GaAs plasmonic photomixers, which offer high terahertz radiation power levels at 50% radiation duty cycle. The use of plasmonic contact electrodes enhances photomixer quantum efficiency while maintaining its ultrafast operation by concentrating a large number of photocarriers in close proximity to the device contact electrodes. Additionally, the relatively high thermal conductivity and high resistivity of GaAs allow operation under high optical pump power levels and long duty cycles without reaching the thermal breakdown limit of the photomixer. We experimentally demonstrate continuous-wave terahertz radiation with a radiation frequency tuning range of more than 2 THz and a record-high radiation power of 17 μW at 1 THz through plasmonic photomixers fabricated on a low temperature grown GaAs substrate at 50% radiation duty cycle.

  9. Growth of GaAs crystals from the melt in a partially confined configuration

    NASA Technical Reports Server (NTRS)

    Gatos, Harry C.; Lagowski, Jacek

    1988-01-01

    The experimental approach was directed along two main goals: (1) the implementation of an approach to melt growth in a partially confined configuration; and (2) the investigation of point defect interaction and electronic characteristics as related to thermal treatment following solidification and stoichiometry. Significant progress was made along both fronts. Crystal growth of GaAs in triangular ampuls was already carried out successfully and consistent with the model. In fact, pronounced surface tension phenomena which cannot be observed in ordinary confinement system were identified and should premit the assessment of Maragoni effects prior to space processing. Regarding thermal treatment, it was discovered that the rate of cooling from elevated temperatures is primarily responsible for a whole class of defect interactions affecting the electronic characteristics of GaAs and that stoichiometry plays a critical role in the quality of GaAs.

  10. Molecular beam epitaxy growth of GaAs1-xBix

    NASA Astrophysics Data System (ADS)

    Tixier, S.; Adamcyk, M.; Tiedje, T.; Francoeur, S.; Mascarenhas, A.; Wei, Peng; Schiettekatte, F.

    2003-04-01

    GaAs1-xBix epilayers with bismuth concentrations up to x=3.1% were grown on GaAs by molecular beam epitaxy. The Bi content in the films was measured by Rutherford backscattering spectroscopy. X-ray diffraction shows that GaAsBi is pseudomorphically strained to GaAs but that some structural disorder is present in the thick films. The extrapolation of the lattice constant of GaAsBi to the hypothetical zincblende GaBi alloy gives 6.33±0.06 Å. Room-temperature photoluminescence of the GaAsBi epilayers is obtained and a significant redshift in the emission of GaAsBi of ˜84 meV per percent Bi is observed.

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    We observed visible-light electroluminescence (EL) due to d-d transitions in light-emitting diodes with Mn-doped GaAs layers (here, referred to as GaAs:Mn). Besides the band-gap emission of GaAs, the EL spectra show two peaks at 1.89 eV and 2.16 eV, which are exactly the same as 4A2(4F) → 4T1(4G) and 4T1(4G) → 6A1(6S) transitions of Mn atoms doped in ZnS. The temperature dependence and the current-density dependence are consistent with the characteristics of d-d transitions. We explain the observed EL spectra by the p-d hybridized orbitals of the Mn d electrons in GaAs.

  12. Vibrational, electronic and structural properties of wurtzite GaAs nanowires under hydrostatic pressure.

    PubMed

    Zhou, Wei; Chen, Xiao-Jia; Zhang, Jian-Bo; Li, Xin-Hua; Wang, Yu-Qi; Goncharov, Alexander F

    2014-01-01

    The structural, vibrational, and electronic properties of GaAs nanowires have been studied in the metastable wurtzite phase via Resonant Raman spectroscopy and synchrotron X-ray diffraction measurements in diamond anvil cells under hydrostatic conditions between 0 and 23 GPa. The direct band gap E0 and the crystal field split-off gap E0 + Δ of wurtzite GaAs increase with pressure and their values become close to those of zinc-blende GaAs at 5 GPa, while being reported slightly larger at lower pressures. Above 21 GPa, a complete structural transition from the wurtzite to an orthorhombic phase is observed in both Raman and X-ray diffraction experiments. PMID:25253566

  13. Effects of ultrathin oxides in conducting MIS structures on GaAs

    NASA Technical Reports Server (NTRS)

    Childs, R. B.; Ruths, J. M.; Sullivan, T. E.; Fonash, S. J.

    1978-01-01

    Schottky barrier-type GaAs baseline devices (semiconductor surface etched and then immediately metalized) and GaAs conducting metal oxide-semiconductor devices are fabricated and characterized. The baseline surfaces (no purposeful oxide) are prepared by a basic or an acidic etch, while the surface for the MIS devices are prepared by oxidizing after the etch step. The metallizations used are thin-film Au, Ag, Pd, and Al. It is shown that the introduction of purposeful oxide into these Schottky barrier-type structures examined on n-type GaAs modifies the barrier formation, and that thin interfacial layers can modify barrier formation through trapping and perhaps chemical reactions. For Au- and Pd-devices, enhanced photovoltaic performance of the MIS configuration is due to increased barrier height.

  14. Surface modifications induced by bismuth on (0 0 1) GaAs surfaces

    NASA Astrophysics Data System (ADS)

    Jiang, W. Y.; Liu, J. Q.; So, M. G.; Myrtle, K.; Kavanagh, K. L.; Watkins, S. P.

    2005-04-01

    We report the identification of reflectance difference (RD) spectra for GaAs (0 0 1) surfaces in the presence of small quantities of trimethylbismuth (TMBi) vapor under organometallic vapor phase epitaxy (OMVPE) conditions. An RD spectrum similar to that observed from the previously reported ( 3×8) Sb-terminated surface of GaAs is reported, suggesting strong similarities between the Bi and Sb terminated surfaces. Because of the low vapor pressure of Bi, it is stable under extended hydrogen purges at growth temperatures of 450C. Whereas As or Sb coverage typically saturates at 1-2 monolayers on the GaAs (0 0 1) surface under OMVPE conditions, no saturation of the Bi coverage is observed in this work. Extended exposure to TMBi results in the formation of Bi islands whose size increase with exposure time and TMBi concentration.

  15. A GaAs DETECTOR FOR DARK MATTER AND SOLAR NEUTRINO RESEARCH

    SciTech Connect

    T. BOWLES; ET AL

    2000-08-01

    The ability to produce large GaAs crystals with the requisite electronic properties to be fabricated into charged particle and photon detectors would provide a detector medium that would find numerous applications in both applied and fundamental research. Various applications would likely include x-ray detectors on satellites, environmental monitoring, medical imaging, bore hole mining spectroscopy, searches for dark matter, and solar neutrino research. We have carried out the development of GaAs detectors using two commercial crystal growing techniques. We have shown it should be able to grow detectors with 20 cm{sup 2} area and a depletion depth of 1 mm. Detectors of this size would find immediate applications in high-resolution, room temperature, low energy gamma ray measurements. We have also arrived at an understanding of the limitations of the common techniques used to grow GaAs and have determined that it should be possible to produce larger detectors using proprietary methods.

  16. Gallium loading of gold seed for high yield of patterned GaAs nanowires

    SciTech Connect

    Boulanger, J. P.; Chia, A. C. E.; LaPierre, R. R.

    2014-08-25

    A method is presented for maximizing the yield and crystal phase purity of vertically aligned Au-assisted GaAs nanowires grown with an SiO{sub x} selective area epitaxy mask on GaAs (111)B substrates. The nanowires were grown by the vapor-liquid-solid (VLS) method in a gas source molecular beam epitaxy system. During annealing, Au VLS seeds will alloy with the underlying GaAs substrate and collect beneath the SiO{sub x} mask layer. This behavior is detrimental to obtaining vertically aligned, epitaxial nanowire growth. To circumvent this issue, Au droplets were pre-filled with Ga assuring vertical yields in excess of 99%.

  17. Optical Response in Amorphous GaAs Thin Films Prepared by Pulsed Laser Deposition

    NASA Astrophysics Data System (ADS)

    Kiwa, Toshihiko; Kawashima, Ichiro; Nashima, Shigeki; Hangyo, Masanori; Tonouchi, Masayoshi

    2000-11-01

    Femtosecond optical response in GaAs thin films has been studied. We prepared GaAs thin films on MgO substrates and on YBa2Cu3O7-δ (YBCO) thin films using pulsed laser deposition (PLD) at temperatures below 250^\\circC@. A photocarrier lifetime of less than 1 ps is measured for the prepared GaAs thin films using femtosecond time-domain reflectivity change measurements. Pulsed electromagnetic wave [terahertz (THz) radiaiton] containing a frequency component of up to 1 THz is emitted from fabricated photoconductive switches using the prepared thin films. We also evaluated the THz radiation properties emitted from the photoswitches on the YBCO thin films.

  18. Ion implantation processing for high-speed GaAs JFETs

    SciTech Connect

    Zolper, J.C.; Baca, A.G.; Sherwin, M.E.; Shul, R.J.

    1995-07-01

    GaAs Junction Field Effect Transistors (JFETs) offer a higher gate turn-on voltage, resulting in a better noise margin and reduced power dissipation, than the more widely employed GaAs MESFET. The primary reason the JFET has not been more widely used is the speed penalty associated with the gate/channel junction and corresponding gate length broadening. We present the ion implantation processes used for a self-aligned, all ion-implanted, GaAs JFET that minimizes the speed penalty for the JFET while maintaining the advantageous higher gate turn-on voltage. Process characterization of the p{sub +}-gate implant done with either Mg, Zn, or Cd along with the co-implantation of P is presented. In addition, a novel backside channel confinement technology employing ion-implanted carbon is discussed. Complete JFET device results are reported.

  19. The ZnSe(110) puzzle - Comparison with GaAs(110)

    NASA Technical Reports Server (NTRS)

    Duke, C. B.; Paton, A.; Kahn, A.; Tu, D.-W.

    1984-01-01

    The surface structure of monocrystalline ZnSe(110) and of 4-5-nm-thick ZnSe(110) layers epitaxially grown on GaAs(110) is investigated by means of elastic LEED and AES; the results are analyzed using the computer programs and R-factor methods of Duke et al. (1981 and 1983), presented in graphs and tables, and compared to those for GaAs(110). Significant differences are attributed to bond-length-conserving outward rotation of Se and inward rotation of Zn in the top layer, with an angle of 4 deg between the actual plane of the cation-anion chain and the truncated bulk surface. The R intensities measured for ZnSe(110) and GaAs(110) are given as Rx = 0.22 and RI = 0.21 and Rx = 0.24 and RI = 0.16, respectively.

  20. Growth of Inclined GaAs Nanowires by Molecular Beam Epitaxy: Theory and Experiment

    PubMed Central

    2010-01-01

    The growth of inclined GaAs nanowires (NWs) during molecular beam epitaxy (MBE) on the rotating substrates is studied. The growth model provides explicitly the NW length as a function of radius, supersaturations, diffusion lengths and the tilt angle. Growth experiments are carried out on the GaAs(211)A and GaAs(111)B substrates. It is found that 20° inclined NWs are two times longer in average, which is explained by a larger impingement rate on their sidewalls. We find that the effective diffusion length at 550°C amounts to 12 nm for the surface adatoms and is more than 5,000 nm for the sidewall adatoms. Supersaturations of surface and sidewall adatoms are also estimated. The obtained results show the importance of sidewall adatoms in the MBE growth of NWs, neglected in a number of earlier studies. PMID:21076695

  1. The chemistry of O in reduction processes of the GaAs native oxides

    NASA Astrophysics Data System (ADS)

    Cuberes, M. T.; Sacedon, J. L.

    1992-05-01

    We present an X-ray photoelectron spectroscopy (XPS) study of the interfacial chemical reactions during the total reduction of a 5 Å thick GaAs native oxide layer accomplished in two separate stages. First, the As2O3 has been selectively reduced by annealing the oxidized surface at increasing temperatures. In the second stage, the reduction of the Ga oxides has been completed at room temperature by Si deposition. The total amount of O at the GaAs interface remains constant during both processes. During the As2O3 thermal reduction, the analysis of the Ga2p{3}/{2} and Ga LMM spectra shows that, depending on the annealing temperature, GaOx (x < {3}/{2}) or Ga2O3 growth occurs. The Si promoted of the Ga oxides results in the formation of Si oxides of different stoichiometry at the GaAs surface.

  2. Application of pulsed GaAs diode lasers to spectral atmospheric monitoring and remote sensing

    NASA Astrophysics Data System (ADS)

    Pencheva, Vasilka H.; Penchev, S.; Naboko, Vassily N.; Naboko, Sergei V.

    1999-05-01

    We report new aspects of application of pulsed GaAs diode lasers, concerning absorption spectroscopy of water vapor of third oscillatory molecular overtone 8990 - 9012 angstroms, and Mie-scattering lidar signal in the 15 km range. It is accessible by the power characteristics of a system utilizing the powerful `chip-stack' GaAs diode lasers, employing optimal photodetection technique based on an analyzing system with computer operated boxcar. Data on atmospheric aerosol backscatter signal acquired by DL lidar are presented with relevance to the potential of complex atmospheric remote sensing. GaAs diode lasers, with radiation matching water vapor spectrum of absorption- coefficients of 0.5 - 5 km-1 in Beer's law, are shown feasible for DIAL monitoring of atmospheric humidity.

  3. Effect of gate engineering in submicron GaAs MESFET for microwave frequency applications

    NASA Astrophysics Data System (ADS)

    Lakhdar, Nacereddine; Lakehal, Brahim

    2016-04-01

    We present an approach of GaAs MESFET incorporating the gate engineering effect to improve immunity against the short channel effects in order to enhance the scaling capability and the device performance for microwave frequency applications. In this context, a physics-based model for I–V characteristics and various microwave characteristics such as transconductance, cut-off frequency and maximum frequency of oscillation of submicron triple material gate (TM) GaAs MESFET are developed. The reduced short channel effects have also been discussed in combined designs i.e. TM, DM and SM in order to show the impact of our approach on the GaAs MESFETs-based device design. The proposed analytical models have been verified by their good agreement with 2D numerical simulations. The models developed in this paper will be useful for submicron and microwave analysis for circuit design.

  4. Influence of substrate orientation on the structural properties of GaAs nanowires in MOCVD

    NASA Astrophysics Data System (ADS)

    Muhammad, R.; Othaman, Z.; Wahab, Y.; Ibrahim, Z.; Sakrani, S.

    2016-04-01

    In this study, the effect of substrate orientation on the structural properties of GaAs nanowires grown by a metal organic chemical vapor deposition has been investigated. Gold colloids were used as catalyst to initiate the growth of nanowiresby the vapour-liquid-solid (VLS) mechanism. From the field-emission scanning electron microscopy (FE-SEM), the growth of the nanowires were at an elevation angle of 90°, 60°, 65° and 35° with respect to the GaAs substrate for (111)B, (311)B, (110) and (100) orientations respectively. The preferential NW growth direction is always <111>B. High-resolution transmission electron microscope (HRTEM) micrograph showed the NWs that grew on the GaAs(111)B has more structural defects when compared to others. Energy dispersive X-ray analysis (EDX) indicated the presence of Au, Ga and As. The bigger diameter NWs dominates the (111)B substrate surface.

  5. Origin of Fermi-level pinning at GaAs surfaces and interfaces

    NASA Astrophysics Data System (ADS)

    Colleoni, Davide; Miceli, Giacomo; Pasquarello, Alfredo

    2014-12-01

    Through first-principles simulation methods, we assign the origin of Fermi-level pinning at GaAs surfaces and interfaces to the bistability between the As-As dimer and two As dangling bonds, which transform into each other upon charge trapping. This defect is shown to be naturally formed both at GaAs surfaces upon oxygen deposition and in the near-interface substoichiometric oxide. Using electron-counting arguments, we infer that the identified defect occurs in opposite charge states. The Fermi-level pinning then results from the amphoteric nature of this defect which drives the Fermi level to its defect level. These results account for the experimental characterization at both GaAs surfaces and interfaces within a unified picture, wherein the role of As antisites is elucidated.

  6. Origin of Fermi-level pinning at GaAs surfaces and interfaces.

    PubMed

    Colleoni, Davide; Miceli, Giacomo; Pasquarello, Alfredo

    2014-12-10

    Through first-principles simulation methods, we assign the origin of Fermi-level pinning at GaAs surfaces and interfaces to the bistability between the As-As dimer and two As dangling bonds, which transform into each other upon charge trapping. This defect is shown to be naturally formed both at GaAs surfaces upon oxygen deposition and in the near-interface substoichiometric oxide. Using electron-counting arguments, we infer that the identified defect occurs in opposite charge states. The Fermi-level pinning then results from the amphoteric nature of this defect which drives the Fermi level to its defect level. These results account for the experimental characterization at both GaAs surfaces and interfaces within a unified picture, wherein the role of As antisites is elucidated. PMID:25372411

  7. Carbon and group II acceptor coimplantation in GaAs

    SciTech Connect

    Morton, R.; Lau, S.S.; Poker, D.B.; Chu, P.K.; Fung, K.K.; Wang, N.

    1998-11-01

    Coimplantations of carbon and one of the group II acceptors, Mg, Zn, or Cd, were performed and compared to implantations involving only a single element (Mg, Zn, or Cd) or Ga and C coimplanted into GaAs substrates. The group II and C (II/C) coimplantations act to balance the crystal stoichiometry since group II atoms prefer to reside in the Ga sublattice and C prefers to reside in the As sublattice. The electrical characteristics of the various implantations were obtained from sheet and differential Hall measurements. Rutherford backscattering spectrometry was employed to determine the amount of implantation-induced damage which was then correlated to the amount of C activation in the group II/C coimplanted samples. It was found that coimplantation of the heavier group II acceptors, Zn and Cd, resulted in layers with larger peak hole concentrations. This is a result of the large amount of lattice damage created by these elements which is thought to provide the necessary abundance of As vacancies for C activation. Secondary ion mass spectroscopy measurements of the samples after implant activation indicate that C coimplantation significantly reduces the diffusivity of the group II acceptors. Cross-sectional transmission electron microscopy indicated a unique defect structure (extrinsic dislocation loops) for the cases of group II/C coimplantation. These dislocation loops are located at the diffusion front of the group II element in the samples and therefore have a rather profound influence on the diffusion of the group II elements. A rationalization of the defect structure and the effect it has on the diffusion of group II elements is given. {copyright} {ital 1998 American Institute of Physics.}

  8. Basic properties of GaAs oxide generated by scanning probe microscope tip-induced nano-oxidation process

    NASA Astrophysics Data System (ADS)

    Okada, Yoshitaka; Iuchi, Yoshimasa; Kawabe, Mitsuo; Harris, James S.

    2000-07-01

    The basic properties of GaAs oxide generated by atomic force microscope (AFM) tip-induced nano-oxidation process have been investigated. The chemical analysis of the AFM tip-generated GaAs oxide was performed by using scanning microprobe x-ray photoelectron spectroscopy, and the main constituents of GaAs anodic oxide were determined to be Ga2O3 and As2O3. The electrical characterization showed that the electron transport across a GaAs oxide nanodot of ˜5.7 nm thickness, from a doped n+-Si tip into the n+-GaAs substrate follows the Fowler-Nordheim tunneling mechanism over a range of applied bias. Further, the tip-generated GaAs oxide nanodots were found to withstand moderate thermal treatments, but some volume reduction was observed.

  9. GaAs QWIP Array Containing More Than a Million Pixels

    NASA Technical Reports Server (NTRS)

    Jhabvala, Murzy; Choi, K. K.; Gunapala, Sarath

    2005-01-01

    A 1,024 x 1,024-pixel array of quantum-well infrared photodetectors (QWIPs) has been built on a 1.8 x 1.8- cm GaAs chip. In tests, the array was found to perform well in detecting images at wavelengths from 8 to 9 m in operation at temperatures between 60 and 70 K. The largest-format QWIP prior array that performed successfully in tests contained 512 x 640 pixels. There is continuing development effort directed toward satisfying actual and anticipated demands to increase numbers of pixels and pixel sizes in order to increase the imaging resolution of infrared photodetector arrays. A 1,024 x 1,024-pixel and even larger formats have been achieved in the InSb and HgCdTe material systems, but photodetector arrays in these material systems are very expensive and manufactured by fewer than half a dozen large companies. In contrast, GaAs-photodetector-array technology is very mature, and photodetectors in the GaAs material system can be readily manufactured by a wide range of industrial technologists, by universities, and government laboratories. There is much similarity between processing in the GaAs industry and processing in the pervasive silicon industry. With respect to yield and cost, the performance of GaAs technology substantially exceeds that of InSb and HgCdTe technologies. In addition, GaAs detectors can be designed to respond to any portion of the wavelength range from 3 to about 16 micrometers - a feature that is very desirable for infrared imaging. GaAs QWIP arrays, like the present one, have potential for use as imaging sensors in infrared measuring instruments, infrared medical imaging systems, and infrared cameras.

  10. Second harmonic generation in photonic crystal cavities in (111)-oriented GaAs

    SciTech Connect

    Buckley, Sonia Radulaski, Marina; Vučković, Jelena; Biermann, Klaus

    2013-11-18

    We demonstrate second harmonic generation at telecommunications wavelengths in photonic crystal cavities in (111)-oriented GaAs. We fabricate 30 photonic crystal structures in both (111)- and (100)-oriented GaAs and observe an increase in generated second harmonic power in the (111) orientation, with the mean power increased by a factor of 3, although there is a large scatter in the measured values. We discuss possible reasons for this increase, in particular, the reduced two photon absorption for transverse electric modes in (111) orientation, as well as a potential increase due to improved mode overlap.

  11. Fabrication of p(+)-n junction GaAs solar cells by a novel method

    NASA Technical Reports Server (NTRS)

    Ghandhi, S. K.; Mathur, G.; Rode, H.; Borrego, J. M.

    1984-01-01

    A novel method for making p(+)-n diffused junction GaAs solar cells, with the formation of a diffusion source, an anti-reflective coating, and a protective cover glass in a single chemical-vapor deposition operation is discussed. Consideration is given to device fabrication and to solar-cell characteristics. The advantages of the technique are that the number of process steps is kept to an absolute minimum, the fabrication procedure is low-cost, and the GaAs surface is protected during the entire operation.

  12. Pseudo-Rhombus-Shaped Subwavelength Crossed Gratings of GaAs for Broadband Antireflection

    NASA Astrophysics Data System (ADS)

    Chen, Xi; Fan, Zhong-Chao; Zhang, Jing; Song, Guo-Feng; Chen, Liang-Hui

    2010-12-01

    Holographic lithography coupled with the nonlinear response of photoresist to the exposure is adopted to fabricate porous photoresist (PR) mask. Conventional dot PR mask is also generated, and both patterns are transferred into a underlying GaAs substrate by the optimal dry etching process to obtain tapered subwavelength crossed gratings (SWCGs) to mimic the moth-eye structure. In comparison of the experiment and simulation, the closely-packed pseudo-rhombus-shaped GaAs SWCGs resulting from the porous mask outperforms the conical counterpart which comes from the dot mask, and achieves a reported lowest mean spectral reflectance of 1.1%.

  13. Fabrication of ordered GaAs nanowhiskers using electron-beam lithography

    SciTech Connect

    Soshnikov, I. P.; Afanas'ev, D. E.; Cirlin, G. E.; Petrov, V. A.; Tanklevskaya, E. M.; Samsonenko, Yu. B.; Bouravlev, A. D.; Khrebtov, A. I.; Ustinov, V. M.

    2011-06-15

    The formation of ordered GaAs nanowhiskers obtained on GaAs (111)As substrates using electron-beam lithography and catalytic molecular-beam epitaxy (MBE) growth is studied experimentally. The main parameters of the e-beam lithographic process necessary for obtaining Au catalyst droplets 10-150 nm in size are determined. It is established that subsequent MBE growth proceeds predominantly by the diffusion mechanism. In the regions subjected to a repeated e-beam exposure after the lift-off process, suppression of nanowhisker growth can take place.

  14. Lasing of TM modes in a two-dimensional GaAs microlaser.

    PubMed

    Fukushima, Takehiro; Shinohara, Susumu; Sunada, Satoshi; Harayama, Takahisa; Sakaguchi, Koichiro; Tokuda, Yasunori

    2014-05-19

    We fabricated and tested an unstrained GaAs single-quantum-well microlaser which has a two-dimensional cavity shape known as the Penrose unilluminable room. The cavity exhibits quasi-one-dimensional modes, namely axial, diamond-shaped, and V-shaped modes. In contrast to previous observations of TE-polarized emission in GaAs microlasers, we observed TM-polarized emission. We explain this observation as being the result of lasing of the diamond-shaped modes whose incident angle at the cavity interface is very close to the Brewster angle. PMID:24921312

  15. CBr4-based in-situ etching of GaAs, assisted with TMAl and TMGa

    NASA Astrophysics Data System (ADS)

    Della Casa, Pietro; Maaßdorf, Andre; Zeimer, Ute; Weyers, Markus

    2016-01-01

    In-situ etching of GaAs with CBr4 in metalorganic vapor phase epitaxy has been investigated at different temperatures using in-situ reflectivity to measure the etch rates. Deep (150 nm) etching of epitaxially-grown GaAs leads to the development of etch pits on the surface, corresponding to the emerging points of threading dislocations. Addition of trimethylgallium (TMGa) leads to a linear superposition of growth and etching. Trimethylaluminium (TMAl) added in moderate quantity enhances the etch rate and inhibits the development of etch pits. A model description for the enhanced etch rate is presented.

  16. A diffusion model for picosecond electron bunches from negative electron affinity GaAs photo cathodes

    SciTech Connect

    P. Hartmann; J. Bermuth; D. v. Harrach; J. Hoffmann; S. Kobis; E. Reichert; K. Aulenbacher; J. Schuler; M. Steigerwald

    1998-10-27

    Even though theoretical estimates predict response times for the photo emission process of electrons from a negative electron affinity GaAs photo emitter in excess of hundreds of picoseconds, recent measurements found electron bunch durations of 40 ps or less. This work presents precise measurements of picosecond electron bunches from a negative affinity bulk GaAs photo cathode and develops a model which explains the measured bunch durations as well as the observed bunch shapes. The bunch shape turns out to be independent from the quantum efficiency of the photo emitter.

  17. Ion back-bombardment of GaAs photocathodes inside dc high voltage electron guns

    SciTech Connect

    Joseph Grames; Philip Adderley; Joshua Brittian; Daniel Charles; James Clark; John Hansknecht; Benard Poelker; Marcy Stutzman; Kenneth Surles-law

    2005-05-01

    DC high voltage GaAs photoguns are key components at accelerator facilities worldwide. New experiments and new accelerator facilities demand improved performance from these guns, in particular higher current operation and longer photocathode operating lifetime. This conference submission explores bulk GaAs photocathode lifetime as a function of beam current, active photocathode area, laser spot size and the vacuum of the gun and beam line. Lifetime measurements were made at 100 microamps, a beam current relevant for accelerators like CEBAF, and at beam currents of 1 milliamps and 5 milliamps, a regime that is interesting for high current Free Electron Laser (FEL) and Energy Recovery Linac (ERL) operation.

  18. 6 to 18 GHz GaAs FET/MMIC amplifiers provide 1 W saturated output

    NASA Astrophysics Data System (ADS)

    Bybokas, Jim

    1987-05-01

    The paper describes the construction and performance characteristics of three amplifiers that combine GaAs FETs, GaAs MMICs, and thin-film hybrid construction and can provide more than 1 W of saturated output power over the 6 to 18 GHz frequency range. These amplifiers feature minimum gains of 26, 34, and 42 dB and noise figures of 13, 10, and 9 dB, respectively, and are specified for operation over the 0 to +50 C temperature range. Amplifier block diagram is included.

  19. Behavior of Cu and Zn Impurities on GaAs Wafer Surfaces

    NASA Astrophysics Data System (ADS)

    Shibaya, Hiroshi

    1995-08-01

    Surface Cu and Zn contamination levels of intentionally contaminated GaAs wafers were measured by total reflection X-ray fluorescence (TXRF). Cu and Zn are both major metallic impurities on GaAs wafer surfaces, but their adsorption behaviors in an organic base solution were quite different. Surface concentration of Cu was much higher than that of Zn when concentrations of Cu and Zn in the organic base solution were the same. Cleaning effects of running deionized water rinse in an ultrasonic bath (U-RDIW) were also studied. Surface concentrations of Cu and Zn were drastically reduced by U-RDIW rinse.

  20. Multilayers of InGaAs Nanostructures Grown on GaAs(210) Substrates

    PubMed Central

    2010-01-01

    Multilayers of InGaAs nanostructures are grown on GaAs(210) by molecular beam epitaxy. With reducing the thickness of GaAs interlayer spacer, a transition from InGaAs quantum dashes to arrow-like nanostructures is observed by atomic force microscopy. Photoluminescence measurements reveal all the samples of different spacers with good optical properties. By adjusting the InGaAs coverage, both one-dimensional and two-dimensional lateral ordering of InGaAs/GaAs(210) nanostructures are achieved. PMID:20676193

  1. Single crystal and polycrystalline GaAs solar cells using AMOS technology

    NASA Technical Reports Server (NTRS)

    Stirn, R. J.; Yeh, Y. C. M.

    1976-01-01

    A description is given of current technology for fabricating single AMOS (antireflection-coated metal oxide semiconductor) solar cells, with attention given to thermal, plasma, and anodic oxidation, native oxide stripping, and X-ray photoelectron spectroscopy results. Some preliminary results are presented on the chemistry and electrical characterization of such cells, and the characteristics of cells fabricated on sliced polycrystalline GaAs wafers are examined. Consideration is also given to the recrystallization of evaporated Ge films for use as low-cost substrates for polycrystalline GaAs solar cells.

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

    SciTech Connect

    Takamiya, Kengo; Fukushima, Toshiyuki; Yagi, Shuhei; Hijikata, Yasuto; Yaguchi, Hiroyuki; Mochizuki, Toshimitsu; Yoshita, Masahiro; Akiyama, Hidefumi; Kuboya, Shigeyuki; Onabe, Kentaro; Katayama, Ryuji

    2013-12-04

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

  3. Sulfidic photochemical passivation of GaAs surfaces in alcoholic solutions

    SciTech Connect

    Simonsmeier, T.; Ivankov, A.; Bauhofer, W.

    2005-04-15

    We report on a remarkable enhancement of the passivation effect of sulfidic solutions through illumination with above band gap light. Luminescence measurements on GaAs surfaces which have been illuminated during chemical passivation reveal in comparison to nonilluminated samples a further reduction of their surface density of states as well as a significantly increased stability of the passivation. Investigations with photoelectron spectroscopy show that illumination leads to a nearly complete removal of oxides on the surface. Measurements on Schottky diodes which have been manufactured with photochemically passivated GaAs indicate a noticeable decrease in band bending and a depinning of the Fermi level.

  4. A thermochemical model of radiation damage and annealing applied to GaAs solar cells

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

    Calculations of the equilibrium conditions for continuous radiation damage and thermal annealing are reported. The calculations are based on a thermochemical model developed to analyze the incorporation of point imperfections in GaAs, and modified by introducing the radiation to produce native lattice defects rather than high-temperature and arsenic atmospheric pressure. The concentration of a set of defects, including vacancies, divacancies, and impurity vacancy complexes, are calculated as a function of temperature. Minority carrier lifetimes, short circuit current, and efficiency are deduced for a range of equilibrium temperatures. The results indicate that GaAs solar cells could have a mission life which is not greatly limited by radiation damage.

  5. Ferroelectric Pb(Zr,Ti)O{sub 3} epitaxial layers on GaAs

    SciTech Connect

    Louahadj, L.; Le Bourdais, D.; Agnus, G.; Pillard, V.; Lecoeur, P.; Largeau, L.; Mazet, L.; Bachelet, R.; Regreny, P.; Dubourdieu, C.; Gautier, B.; Saint-Girons, G.; Albertini, D.

    2013-11-18

    Ferroelectric epitaxial Pb(Zr,Ti)O{sub 3} (PZT) layers were grown by pulsed laser deposition on SrTiO{sub 3}/GaAs templates fabricated by molecular beam epitaxy. The templates present an excellent structural quality and the SrTiO{sub 3}/GaAs is abrupt at the atomic scale. The PZT layers contain a- and c-domains, as shown by X-Ray diffraction analyses. Piezoforce microscopy experiments and macroscopic electrical characterizations indicate that PZT is ferroelectric. A relative dielectric permittivity of 164 is extracted from these measurements.

  6. Comparison of triethylaluminum, triethylgallium, triethylindium, and triethylantimony on GaAs(100)

    NASA Astrophysics Data System (ADS)

    Heitzinger, John M.; Jackson, M. S.; Ekerdt, J. G.

    1995-01-01

    The surface chemistry of triethylaluminum, triethylgallium, triethylindium, and triethylantimony was studied on GaAs(100) using thermal desorption spectroscopy, static secondary ion mass spectroscopy, and x-ray photoelectron spectroscopy. Ethylene, the major hydrocarbon reaction product, desorbs from the GaAs(100) surface during thermal desorption spectroscopy experiments at 565 K for all four molecules. This indicates an identical rate limiting step for the elimination of ethyl groups from the surface following adsorption of these molecules. We propose that ethyl groups migrate to Ga sites and then undergo reaction at these sites.

  7. GaAs Schottky barrier varactor diodes for submillimeter wavelength power generation

    NASA Technical Reports Server (NTRS)

    Crowe, T. W.; Peatman, W. C. B.; Winkler, E.

    1991-01-01

    The development of GaAs Schottky barrier diodes for frequencies well into the submillimeter wavelength range is discussed. These devices have the highest cutoff frequencies yet obtained for varactor diodes and have produced sufficient output power to drive Schottky mixers at frequencies as high as 640 GHz. The fundamental design tradeoff between cutoff frequency and capacitance modulation is explored. As the doping density is increased and the anode diameter is reduced, the dynamic cutoff frequency increases, reaching a maximum of roughly 5 THz. It is concluded that the maximum output frequency from harmonic multipliers based on standard GaAs varactor diodes will be about 1 THz.

  8. InGaAs quantum dot molecules around self-assembled GaAs nanomound templates

    SciTech Connect

    Lee, J. H.; Wang, Zh. M.; Strom, N. W.; Mazur, Yu. I.; Salamo, G. J.

    2006-11-13

    Several distinctive self-assembled InGaAs quantum dot molecules (QDMs) are studied. The QDMs self-assemble around nanoscale-sized GaAs moundlike templates fabricated by droplet homoepitaxy. Depending on the specific InAs monolayer coverage, the number of QDs per GaAs mound ranges from two to six (bi-QDMs to hexa-QDMs). The Ga contribution from the mounds is analyzed in determining the morphologies of the QDMs, with respect to the InAs coverages ranging between 0.8 and 2.4 ML. Optical characterization shows that the resulting nanostructures are high-quality nanocrystals.

  9. Some Aspects of the RHEED Behavior of Low-Temperature GaAs Growth

    SciTech Connect

    Nemcsics, A.

    2005-11-15

    The reflection high-energy electron diffraction (RHEED) behavior manifested during MBE growth on a GaAs(001) surface under low-temperature (LT) growth conditions is examined in this study. RHEED and its intensity oscillations during LT GaAs growth exhibit some particular behavior. The intensity, phase, and decay of the oscillations depend on the beam equivalent pressure (BEP) ratio and substrate temperature, etc. Here, the intensity dependence of RHEED behavior on the BEP ratio, substrate temperature, and excess of As content in the layer are examined. The change in the decay constant of the RHEED oscillations is also discussed.

  10. Helicity-dependent photocurrent in a (110) GaAs quantum well stack

    NASA Astrophysics Data System (ADS)

    Schmadel, D. C.; Kim, M.-H.; Sushkov, A. B.; Jenkins, G. S.; Koralek, J. D.; Moore, J. E.; Orenstein, J.; Ohno, Yuzo; Ohno, Hideo; Drew, H. D.

    2013-03-01

    There have been many reports on the circular photogalvanic effect (CPGE) in GaAs quantum wells. A recent theoretical study suggests that the CPGE can be governed by a quantum confinement-induced Berry phase effect that depends only on the quantum-well width and crystal orientation (J.E. Moore, Phys. Rev. Lett. 2010). We have measured the photocurrent in a (110)-oriented GaAs quantum well stack under illumination of circularly polarized THz radiation. We will report measurements of the helicity-driven photocurrent as a function of frequency, polarization, angle of incident, and temperature, and compare with theoretical predictions of the Berry phase contribution.

  11. The OAs defect in GaAs: A hybrid density functional study

    NASA Astrophysics Data System (ADS)

    Colleoni, Davide; Pasquarello, Alfredo

    2014-02-01

    The O center substitutional to As (OAs) is addressed through hybrid functional calculations as a candidate defect to explain the Fermi-level pinning in oxygen-doped GaAs. The defect center shows amphoteric behavior which could lead to Fermi-level pinning. However, the calculated charge transition levels only moderately agree with the experimental pinning level. Furthermore, the first-neighbor shell of the O atom and the absence of negative-U behavior clearly contrast with the experimental characterization. Thus, the present results do not support the OAs center as origin of the observed Fermi-level pinning in oxygen-doped GaAs.

  12. Low-temperature-grown GaAs enhanced wet thermal oxidation of Al0.98Ga0.02As

    NASA Astrophysics Data System (ADS)

    Reese, H.; Chiu, Y. J.; Hu, E.

    1998-11-01

    The effects of incorporating low-temperature-grown GaAs (LT GaAs) into the layer structure of Al0.98Ga0.02As/GaAs are studied. Results show that the structures containing a 300 nm layer of LT GaAs have faster oxidation rates and lower oxidation temperatures compared to reference samples without the LT GaAs layer. This letter will discuss the mechanisms involved in the oxidation rate increase, attributed to the LT GaAs enhancing the transport of As species during the oxidation process.

  13. Fabrication and characterization of GaAs/A1GaAs quantum-well lasers using thermally oxidized A1GaAs

    NASA Astrophysics Data System (ADS)

    Homan, Otte J.; Epler, John E.; Patterson, Bruce D.; Lehmann, Hans W.

    1994-07-01

    Aluminum-oxide thermally grown into high Al-concentration AlxGa1-xAs layers has recently been studied extensively. The material shows electrical and optical properties that make it useful in a semiconductor laser fabrication process where it can provide electrical isolation and optical guiding, as well as simplify the fabrication and integration process considerably. We use this thermal oxide to produce GaAs/AlGaAs semiconductor lasers that can be integrated with other devices. The GaAs cap- layer is masked with photoresist and the exposed GaAs areas are etched away, leaving a GaAs oxidation mask on the AlGaAs upper cladding layer. Using N2 carrier gas saturated with H2O vapor, the uncovered Al0.8Ga0.2As material is converted into a stable aluminum-oxide at temperatures around 450 degree(s)C. Due to the near-isotropic oxidation an `ellipsoidal' diffusion front is created, which is in strong contrast to the well-known mesa cross-section in conventional dry-etched ridge-waveguides but is more similar to e.g. wet-etched buried heterostruture lasers.

  14. Bandgap and optical absorption edge of GaAs1-xBix alloys with 0 < x < 17.8%

    NASA Astrophysics Data System (ADS)

    Masnadi-Shirazi, M.; Lewis, R. B.; Bahrami-Yekta, V.; Tiedje, T.; Chicoine, M.; Servati, P.

    2014-12-01

    The compositional dependence of the fundamental bandgap of pseudomorphic GaAs1-xBix layers on GaAs substrates is studied at room temperature by optical transmission and photoluminescence spectroscopies. All GaAs1-xBix films (0 ≤ x ≤ 17.8%) show direct optical bandgaps, which decrease with increasing Bi content, closely following density functional theory predictions. The smallest measured bandgap is 0.52 eV (˜2.4 μm) at 17.8% Bi. Extrapolating a fit to the data, the GaAs1-xBix bandgap is predicted to reach 0 eV at 35% Bi. Below the GaAs1-xBix bandgap, exponential absorption band tails are observed with Urbach energies 3-6 times larger than that of bulk GaAs. The Urbach parameter increases with Bi content up to 5.5% Bi, and remains constant at higher concentrations. The lattice constant and Bi content of GaAs1-xBix layers (0 < x ≤ 19.4%) are studied using high resolution x-ray diffraction and Rutherford backscattering spectroscopy. The relaxed lattice constant of hypothetical zincblende GaBi is estimated to be 6.33 ± 0.05 Å, from extrapolation of the Rutherford backscattering spectrometry and x-ray diffraction data.

  15. Direct electron beam writing of gallium oxide on GaAs(111) As surfaces

    NASA Astrophysics Data System (ADS)

    Alonso, M.; Sacedón, J. L.; Soria, F.

    1984-07-01

    In this letter we show the possibility of a direct electron beam writing on GaAs (111) As by electron stimulated oxidation. An estimate of the writing velocity is also given. The analysis of the profiles of the oxide spots by Auger spectroscopy indicates the stability of the gallium oxide formed, and the post-oxidation formation of an As-rich interface.

  16. DFT algorithms for bit-serial GaAs array processor architectures

    NASA Technical Reports Server (NTRS)

    Mcmillan, Gary B.

    1988-01-01

    Systems and Processes Engineering Corporation (SPEC) has developed an innovative array processor architecture for computing Fourier transforms and other commonly used signal processing algorithms. This architecture is designed to extract the highest possible array performance from state-of-the-art GaAs technology. SPEC's architectural design includes a high performance RISC processor implemented in GaAs, along with a Floating Point Coprocessor and a unique Array Communications Coprocessor, also implemented in GaAs technology. Together, these data processors represent the latest in technology, both from an architectural and implementation viewpoint. SPEC has examined numerous algorithms and parallel processing architectures to determine the optimum array processor architecture. SPEC has developed an array processor architecture with integral communications ability to provide maximum node connectivity. The Array Communications Coprocessor embeds communications operations directly in the core of the processor architecture. A Floating Point Coprocessor architecture has been defined that utilizes Bit-Serial arithmetic units, operating at very high frequency, to perform floating point operations. These Bit-Serial devices reduce the device integration level and complexity to a level compatible with state-of-the-art GaAs device technology.

  17. Modified energetics and growth kinetics on H-terminated GaAs (110)

    NASA Astrophysics Data System (ADS)

    Galiana, B.; Benedicto, M.; Díez-Merino, L.; Lorbek, S.; Hlawacek, G.; Teichert, C.; Tejedor, P.

    2013-10-01

    Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As4, has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å2 measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As4 molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed.

  18. Investigation of spectral responsivity of InAs QD-embedded GaAs solar cells

    NASA Astrophysics Data System (ADS)

    Bailey, Christopher G.; Forbes, David V.; Raffaelle, Ryne P.; Hubbard, Seth M.

    2011-02-01

    GaAs p-i-n solar cells embedded with varying number of QD layers (0-60) were grown by OMVPE. 1x1 cm2 cells were fabricated and standard solar cell testing was performed. Illuminated AM0 current-voltage characteristics were measured of both a baseline and 10-layer quantum dot (QD) embedded GaAs p-i-n. The QD solar cell (QDSC) gave an short circuit current of 23.1 mA/cm2 increase in of 0.7mA/cm2 above the baseline with no QDs. The QD embedded cell also showed limited loss in open circuit voltage characteristics of 0.99 V compared to 1.04 V of the baseline. Conversion efficiencies were 13.4 and 13.8 for the QDSC and baseline solar cell, respectively. Spectral responsivity measurements revealed equivalent GaAs response in the visible for the baseline, 10x and 20x layer QD samples, while systematically degraded emitter lifetime was found to be responsible for loss in visible responsivities for the 60x QDSC. Sub-GaAs bandgap response gave a systematic increase of 0.25 mA/QD layer. Spectral responsivity modeling was used and found that bulk GaAs emitter and i-region lifetimes degraded from 102 ns to 102 ps, with increasing number of QD layers.

  19. Generation of terahertz radiation in ordered arrays of GaAs nanowires

    SciTech Connect

    Trukhin, V. N.; Mustafin, I. A.; Bouravleuv, A. D.; Cirlin, G. E.; Kakko, J. P.; Huhtio, T.; Lipsanen, H.

    2015-06-22

    THz generation under excitation by ultrashort optical pulses in ordered arrays of GaAs nanowires is reported. It was found that the efficiency of THz radiation generation increases due to the resonant leaky mode excitation in nanowires. The maximum value of the THz field is achieved when the distance between the nanowires is of the order of the wavelength of exciting light.

  20. Macromodel for exact computation of propagation delay time in GaAs and CMOS technologies

    NASA Astrophysics Data System (ADS)

    Garcia, Jose C.; Montiel-Nelson, Juan A.; Sosa, Javier; Navarro, Hector; Sarmiento, Roberto

    2003-04-01

    A new transient macromodel for the cells used in DCFL GaAs and CMOS digital design is introduced in this paper. The numerical solution determines accurate propagation delay times. The macromodel is based on the differential equation for the output voltage in terms of currents and capacitances. An straightforward treatment of the differential equation for an inverter in DCFL GaAs and CMOS has been obtained. It could be resolved numerically by a 4th order Runge Kutta method. Good agreement is obtained between the HSPICE simulation and the computation of the propagation delays for DCFL GaAs and CMOS basic gates: INV, NOR, OR and NAND. There is no error between HSPICE and our computation of propagation delay time for the high to low (tphl) and low to high (tplh) transitions. The propagation delay times for two types of transition were measured and compared with HSPICE. The results demonstrate that our approach matches with HSPICE with no error. The numerical method was programmed in C language. In addition, computation time analysis is provided and numerical solution is several orders of magnitude faster than HSPICE. Work is in progress to obtain the macromodel of a standard cell library for digital application both for a 0.6 microns E/D GaAs process (H-GaAsIV) from Vitesse Semiconductor and for a 0.18 microns logic/mixed-signal CMOS process (1P6M) from TSMC Corp.

  1. Performance of a wideband GaAs low-noise amplifier at cryogenic temperatures

    NASA Technical Reports Server (NTRS)

    Toncich, S. S.; Bhasin, K. B.; Chen, T. K.; Claspy, P. C.

    1992-01-01

    The gain and noise figure performance of a GaAs amplifier at cryogenic temperatures has been studied. Results obtained indicate that a lower noise figure and a higher gain are induced by decreasing the temperature, while no significant change in the input 1-dB compression point is observed. Repeated temperature cycling had no adverse effect on the amplifier performance.

  2. Maskless micro/nanofabrication on GaAs surface by friction-induced selective etching

    NASA Astrophysics Data System (ADS)

    Tang, Peng; Yu, Bingjun; Guo, Jian; Song, Chenfei; Qian, Linmao

    2014-02-01

    In the present study, a friction-induced selective etching method was developed to produce nanostructures on GaAs surface. Without any resist mask, the nanofabrication can be achieved by scratching and post-etching in sulfuric acid solution. The effects of the applied normal load and etching period on the formation of the nanostructure were studied. Results showed that the height of the nanostructure increased with the normal load or the etching period. XPS and Raman detection demonstrated that residual compressive stress and lattice densification were probably the main reason for selective etching, which eventually led to the protrusive nanostructures from the scratched area on the GaAs surface. Through a homemade multi-probe instrument, the capability of this fabrication method was demonstrated by producing various nanostructures on the GaAs surface, such as linear array, intersecting parallel, surface mesas, and special letters. In summary, the proposed method provided a straightforward and more maneuverable micro/nanofabrication method on the GaAs surface.

  3. Maskless micro/nanofabrication on GaAs surface by friction-induced selective etching.

    PubMed

    Tang, Peng; Yu, Bingjun; Guo, Jian; Song, Chenfei; Qian, Linmao

    2014-01-01

    In the present study, a friction-induced selective etching method was developed to produce nanostructures on GaAs surface. Without any resist mask, the nanofabrication can be achieved by scratching and post-etching in sulfuric acid solution. The effects of the applied normal load and etching period on the formation of the nanostructure were studied. Results showed that the height of the nanostructure increased with the normal load or the etching period. XPS and Raman detection demonstrated that residual compressive stress and lattice densification were probably the main reason for selective etching, which eventually led to the protrusive nanostructures from the scratched area on the GaAs surface. Through a homemade multi-probe instrument, the capability of this fabrication method was demonstrated by producing various nanostructures on the GaAs surface, such as linear array, intersecting parallel, surface mesas, and special letters. In summary, the proposed method provided a straightforward and more maneuverable micro/nanofabrication method on the GaAs surface. PMID:24495647

  4. Amphoteric behavior of Ge in GaAs: an LDA analysis

    NASA Astrophysics Data System (ADS)

    Giorgi, G.; Yamashita, K.

    2011-04-01

    We have studied the stability of neutral and charged Ge substitutional defects (donor, acceptor and molecular) in bulk GaAs host. To correct the severe underestimation given by the local density approximation (LDA) in predicting bandgaps, we have applied the LDA + U scheme (Dudarev et al 1998 Phys. Rev. B 57 1505) to the gallium d orbitals. We have aligned the LDA calculated band edges of GaAs to those calculated at LDA + U level. Then, we have corrected the thermal ionization energies (LDA derived) for the defects considered. The effect of atomic distance in the self-compensation mechanism in the case of Ge2 donor-acceptor defective cells was evaluated. Our results are compared with previous results on IV-doped III-V alloys. We found that self-passivation is the main mechanism for the thermodynamic stabilization of both defective cells and alloys. We have established a relationship between the energy of stabilization versus (1) the amount of molecular Ge2 in the alloys and (2) the distance between Ge donor-acceptor atoms in the supercells, finding an almost linear relationship. We conclude that Ge2-doped GaAs defective systems behave as extremely diluted (GaAs)1-xGe2x alloys (x → 0).

  5. Does Bi form clusters in GaAs1 - xBi x alloys?

    NASA Astrophysics Data System (ADS)

    Punkkinen, M. P. J.; Laukkanen, P.; Kuzmin, M.; Levämäki, H.; Lång, J.; Tuominen, M.; Yasir, M.; Dahl, J.; Lu, S.; Delczeg-Czirjak, E. K.; Vitos, L.; Kokko, K.

    2014-11-01

    GaAs1 - xBi x alloys attract significant interest due to their potentiality for several applications, including solar cells. Recent experiments link the crucial optical properties of these alloys to Bi clustering at certain Bi compositions. Using ab initio calculations, we show that there is no thermodynamical driving force for the formation of small GaBi clusters incorporating As substitutional sites. However, the Ga vacancies should gather Bi atoms leading to small Bi clusters, and the Ga vacancies can act as nucleation centers for phase separation. The formation energy of the GaAs1 - xBi x with respect to GaAs and GaBi shows a maximum at intermediate Bi concentrations. Thermodynamics and kinetics of the GaAs1 - xBi x film growth is discussed. High Bi solubility is obtained, if the Bi atoms on the energetically favorable atom positions in the subsurface layer are relatively frozen. The Ga vacancy concentration may be increased by the incorporation of Bi. The Bi atoms can also prevent the out diffusion of Ga vacancies.

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

    PubMed

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

    2015-09-16

    Among many available photovoltaic technologies at present, gallium arsenide (GaAs) is one of the recognized leaders for performance and reliability; however, it is still a great challenge to achieve cost-effective GaAs solar cells for smart systems such as transparent and flexible photovoltaics. In this study, highly crystalline long GaAs nanowires (NWs) with minimal crystal defects are synthesized economically by chemical vapor deposition and configured into novel Schottky photovoltaic structures by simply using asymmetric Au-Al contacts. Without any doping profiles such as p-n junction and complicated coaxial junction structures, the single NW Schottky device shows a record high apparent energy conversion efficiency of 16% under air mass 1.5 global illumination by normalizing to the projection area of the NW. The corresponding photovoltaic output can be further enhanced by connecting individual cells in series and in parallel as well as by fabricating NW array solar cells via contact printing showing an overall efficiency of 1.6%. Importantly, these Schottky cells can be easily integrated on the glass and plastic substrates for transparent and flexible photovoltaics, which explicitly demonstrate the outstanding versatility and promising perspective of these GaAs NW Schottky photovoltaics for next-generation smart solar energy harvesting devices. PMID:26284305

  7. SEU of complementary GaAs static RAMs due to heavy ions

    NASA Technical Reports Server (NTRS)

    Zuleeg, R.; Notthoff, J. K.; Nichols, D. K.

    1984-01-01

    The first measurement of single event upset (SEU) for complementary GaAs static RAMs caused by heavy ions is reported. Upset cross-sections of the circuits for 28 MeV oxygen ions are reported as well as the linear energy transfer (LET) threshold established by using 170 MeV oxygen ions at various angles of beam incidence.

  8. Optimum doping achieves high quantum yields in GaAs photoemitters

    NASA Technical Reports Server (NTRS)

    Sonnenberg, H.

    1971-01-01

    Experimental data indicate that optimum doping exists. Measured quantum yield curves indicate optimum overall response is obtained in GaAs emitters with doping in high 10 to the 18th power per cu cm range. Doping for optimum response is not necessarily in this range.

  9. Modified energetics and growth kinetics on H-terminated GaAs (110)

    SciTech Connect

    Galiana, B.; Benedicto, M.; Díez-Merino, L.; Tejedor, P.; Lorbek, S.; Hlawacek, G.; Teichert, C.

    2013-10-28

    Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As{sub 4}, has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å{sup 2} measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As{sub 4} molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed.

  10. Surface analysis of different oriented GaAs substrates annealed under bismuth flow

    NASA Astrophysics Data System (ADS)

    Fitouri, H.; Moussa, I.; Rebey, A.; El Jani, B.

    2007-03-01

    Several orientations of GaAs substrates, including (1 0 0), (4 1 1), (1 1 1) and (5 1 1) have been annealed in a metalorganic vapour phase epitaxy (MOVPE) horizontal reactor at different annealing temperatures and under different trimethyl-bismuth (TMBi) flux. Surface morphology of the annealed GaAs substrates was investigated by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show islands formation on all the studied samples. The density and size of Bi islands vary greatly with annealing temperature and TMBi flow. For different substrate orientations, the activation energies were deduced from Arrhenius plot of island density. Except for (5 1 1) oriented GaAs, all the studied orientations show the same activation energy of 1.8 eV. For low annealing temperature 420 °C, and under different Bi flux, each oriented substrate shows a specific behaviour. For higher temperatures 700 °C and above Bi islands are totally removed and the substrates are smooth. Surface change of (1 0 0) oriented GaAs substrate was in situ monitored by laser reflectometry.

  11. Measurement of Young's modulus of GaAs nanowires growing obliquely on a substrate

    SciTech Connect

    Alekseev, P. A. Dunaevskii, M. S.; Stovpyaga, A. V.; Lepsa, M.; Titkov, A. N.

    2012-05-15

    A convenient and fast method for measuring Young's modulus of semiconductor nanowires obliquely standing on the growth substrate is presented. In this method, the nanowire is elastically bent under the force exerted by the probe of an atomic-force microscope, and the load-unload dependences for the bending of the probe cantilever are recorded. Next, these curves are used to find the bending stiffness of the tilted nanowires, after which, taking into account the nanowire dimensions, Young's modulus is obtained. The implementation of this method is demonstrated for tilted GaAs nanowires growing on a GaAs (111) substrate. Young's modulus is determined by applying finite-element analysis to the problem of the stationary elastic bending of a nanowire taking into account the actual nanowire shape and faceting. It proves that a fairly accurate estimate of Young's modulus can be obtained even if the nanowire shape is approximated by a circular cylinder with a single cross-sectional area. The values of Young's modulus obtained for GaAs nanowires of cubic lattice symmetry are 2 to 3 times smaller than its value for bulk GaAs. This difference is attributed to the presence of stacking faults in the central part of the nanowires.

  12. Langley program of GaAs solar cells. [emphasizing energy conversion efficiency and radiation resistance

    NASA Technical Reports Server (NTRS)

    Conway, E. J.

    1979-01-01

    A brief overview of the development of GaAs solar cell technology is provided. An 18 to 20 percent AMO efficiency, stability under radiation and elevated-temperature operation, and high power-to-weight ratio are among the factors studied. Cell cost and availability are also examined.

  13. Enhanced charge recombination due to surfaces and twin defects in GaAs nanostructures

    SciTech Connect

    Brown, Evan; Sheng, Chunyang; Nakano, Aiichiro; Shimamura, Kohei; Shimojo, Fuyuki

    2015-02-07

    Power conversion efficiency of gallium arsenide (GaAs) nanowire (NW) solar cells is severely limited by enhanced charge recombination (CR) at sidewall surfaces, but its atomistic mechanisms are not well understood. In addition, GaAs NWs usually contain a high density of twin defects that form a twin superlattice, but its effects on CR dynamics are largely unknown. Here, quantum molecular dynamics (QMD) simulations reveal the existence of an intrinsic type-II heterostructure at the (110) GaAs surface. Nonadiabatic quantum molecular dynamics (NAQMD) simulations show that the resulting staggered band alignment causes a photoexcited electron in the bulk to rapidly transfer to the surface. We have found orders-of-magnitude enhancement of the CR rate at the surface compared with the bulk value. Furthermore, QMD and NAQMD simulations show unique surface electronic states at alternating (111)A and (111)B sidewall surfaces of a twinned [111]-oriented GaAs NW, which act as effective CR centers. The calculated large surface recombination velocity quantitatively explains recent experimental observations and provides microscopic understanding of the underlying CR processes.

  14. Cryogenic operation of GaAs based multiplier chains to 400 GHz

    NASA Technical Reports Server (NTRS)

    Maestrini, A.; Pukala, D.; Maiwald, F.; Schlecht, E.; Chattopadhyay, G.; Mehdi, I.

    2000-01-01

    The FIRST/HIFI mission allows for the local oscillator frequency multiplier chains to be cooled to 120 - 150 K in order to increase available output power. This paper will discuss the implication of cooling on GaAs based planar Schottky diode varactors for flight applications.

  15. Maskless micro/nanofabrication on GaAs surface by friction-induced selective etching

    PubMed Central

    2014-01-01

    In the present study, a friction-induced selective etching method was developed to produce nanostructures on GaAs surface. Without any resist mask, the nanofabrication can be achieved by scratching and post-etching in sulfuric acid solution. The effects of the applied normal load and etching period on the formation of the nanostructure were studied. Results showed that the height of the nanostructure increased with the normal load or the etching period. XPS and Raman detection demonstrated that residual compressive stress and lattice densification were probably the main reason for selective etching, which eventually led to the protrusive nanostructures from the scratched area on the GaAs surface. Through a homemade multi-probe instrument, the capability of this fabrication method was demonstrated by producing various nanostructures on the GaAs surface, such as linear array, intersecting parallel, surface mesas, and special letters. In summary, the proposed method provided a straightforward and more maneuverable micro/nanofabrication method on the GaAs surface. PMID:24495647

  16. Design of quantum efficiency measurement system for variable doping GaAs photocathode

    NASA Astrophysics Data System (ADS)

    Chen, Liang; Yang, Kai; Liu, HongLin; Chang, Benkang

    2008-03-01

    To achieve high quantum efficiency and good stability has been a main direction to develop GaAs photocathode recently. Through early research, we proved that variable doping structure is executable and practical, and has great potential. In order to optimize variable doping GaAs photocathode preparation techniques and study the variable doping theory deeply, a real-time quantum efficiency measurement system for GaAs Photocathode has been designed. The system uses FPGA (Field-programmable gate array) device, and high speed A/D converter to design a high signal noise ratio and high speed data acquisition card. ARM (Advanced RISC Machines) core processor s3c2410 and real-time embedded system are used to obtain and show measurement results. The measurement precision of photocurrent could reach 1nA, and measurement range of spectral response curve is within 400~1000nm. GaAs photocathode preparation process can be real-time monitored by using this system. This system could easily be added other functions to show the physic variation of photocathode during the preparation process more roundly in the future.

  17. Electrophilic surface sites as precondition for the chemisorption of pyrrole on GaAs(001) surfaces

    SciTech Connect

    Bruhn, Thomas; Fimland, Bjørn-Ove; Vogt, Patrick

    2015-03-14

    We report how the presence of electrophilic surface sites influences the adsorption mechanism of pyrrole on GaAs(001) surfaces. For this purpose, we have investigated the adsorption behavior of pyrrole on different GaAs(001) reconstructions with different stoichiometries and thus different surface chemistries. The interfaces were characterized by x-ray photoelectron spectroscopy, scanning tunneling microscopy, and by reflectance anisotropy spectroscopy in a spectral range between 1.5 and 5 eV. On the As-rich c(4 × 4) reconstruction that exhibits only nucleophilic surface sites, pyrrole was found to physisorb on the surface without any significant modification of the structural and electronic properties of the surface. On the Ga-rich GaAs(001)-(4 × 2)/(6 × 6) reconstructions which exhibit nucleophilic as well as electrophilic surface sites, pyrrole was found to form stable covalent bonds mainly to the electrophilic (charge deficient) Ga atoms of the surface. These results clearly demonstrate that the existence of electrophilic surface sites is a crucial precondition for the chemisorption of pyrrole on GaAs(001) surfaces.

  18. The role of proximity caps during the annealing of UV-ozone oxidized GaAs

    SciTech Connect

    Ghosh, S. C.; Biesinger, M. C.; LaPierre, R. R.; Kruse, P.

    2007-06-01

    This study provides a deeper insight into the chemistry and physics of the common engineering practice of using a proximity cap, while annealing compound semiconductors such as GaAs. We have studied the cases of a GaAs proximity cap, a Si proximity cap, and no proximity cap. Using x-ray photoelectron spectroscopy, it has been found that annealing increases the gallium to arsenic ratio in the oxide layer in all cases. During the annealing of UV-ozone oxidized GaAs, it has been observed that GaAs proximity caps also serve as a sacrificial layer to accelerate the desorption of oxide species. In all cases surface deterioration due to pit formation has been observed, and the depth of pits is found to depend on the effective role played by the capping material. Energy dispersive x-ray analysis provides additional evidence that pits mainly consist of elemental As and gallium oxide, with most of the elemental As situated at the pit-substrate interface. Deposition of a thin layer of gold and subsequent annealing to 500 deg. C for 300 s under different capping conditions shows the use of a proximate cap to be practically insignificant in annealing Au deposited films.

  19. Internal Photoemission and X-Ray Photoelectron Spectroscopic Studies of Sulfur-Passivated GaAs

    NASA Astrophysics Data System (ADS)

    Sato, Kenji; Ikoma, Hideaki

    1993-02-01

    Internal photoemission and X-ray photoelectron spectroscopic (XPS) measurements were performed to investigate the effect of sulfur passivation on the GaAs surface and the degradation of the GaAs surface exposed to air ambient after the passivation. The reverse bias dependence of the Schottky barrier height was very small in the as-sulfur-treated sample and was mainly explained by the image force lowering effect. However, it increased as this sample was exposed to air, indicating an increase in the interface state density. The XPS studies showed that both the Ga and As oxides were hardly observed in the sulfur-passivated samples. This indicates that sulfur passivation strongly suppresses oxidation of GaAs. However, a small amount of elemental arsenic was observed with a trace of the As suboxides (such as AsO) after exposure to air and it increased as the exposure time was increased. These results were probably correlated with the increase in the bias dependence of the Schottky barrier height in samples exposed to air after the passivation. Thermal oxidation of GaAs was found to be retarded by sulfur passivation until oxidation time was about 10 min at 300°C. A possible model of suppression of oxidation by sulfur passivation was also discussed.

  20. A new structure for comparing surface passivation materials of GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Desalvo, Gregory C.; Barnett, Allen M.

    1989-01-01

    The surface recombination velocity (S sub rec) for bare GaAs is typically as high as 10 to the 6th power to 10 to the 7th power cm/sec, which dramatically lowers the efficiency of GaAs solar cells. Early attempts to circumvent this problem by making an ultra thin junction (xj less than .1 micron) proved unsuccessful when compared to lowering S sub rec by surface passivation. Present day GaAs solar cells use an GaAlAs window layer to passivate the top surface. The advantages of GaAlAs in surface passivation are its high bandgap energy and lattice matching to GaAs. Although GaAlAs is successful in reducing the surface recombination velocity, it has other inherent problems of chemical instability (Al readily oxidizes) and ohmic contact formation. The search for new, more stable window layer materials requires a means to compare their surface passivation ability. Therefore, a device structure is needed to easily test the performance of different passivating candidates. Such a test device is described.

  1. Thermal oxidation of In/sub 2/S/sub 3//GaAs structures

    SciTech Connect

    Mittova, Ya.; Pukhova, V.V.

    1986-11-01

    The purpose of this work is to investigate the effect of indium sulfide, deposited on the surface of GaAs, on the process of oxidation of gallium arsenide, as well as on the composition and some properties of the oxide layers formed.

  2. Neutron damage equivalence for silicon, silicon dioxide, and GaAs

    NASA Astrophysics Data System (ADS)

    Luera, Theodore F.; Kelly, John G.; Stein, Herman J.; Lazo, Maximo S.; Lee, Clarence E.

    1987-12-01

    Displacement-energy and ionization-energy transfers to Si, SiO2, and GaAs as functions of incident neutron energy were calculated using cross-section data and fine group structure in the NJOY code system. Neutron spectra determinations for several reactor neutron environments were made using activation cross sections and a novel technique with the SAND II code. Measurements of carrier-removal rates in GaAs and of Si transistor gain degradation were made in representative neutron environments. Experimental results are compared to damage ratios predicted with the spectra and NJOY displacement functions. For fission-like spectra, calculated Si damage ratios are in good agreement with those determined with ASTM E722-85 and with measured transistor damage ratios. Significant differences are found between Si NJOY and ASTM E722-85 for 14-MeV-to-reactor neutron damage ratios; NJOY gives better agreement with experimental data reported in the literature. In GaAs, 14-MeV-to-reactor experimental damage ratios are smaller than predicted by calculated displacement ratios. This suggests that a more complex model of damage for majority carrier removal in GaAs is required. The use of incorrect damage functions is shown to adversely affect simulation fidelity in some representative neutron environments.

  3. Design and optimization of GaAs photovoltaic converter for laser power beaming

    NASA Astrophysics Data System (ADS)

    Shan, Tiqiang; Qi, Xinglin

    2015-07-01

    GaAs photovoltaic (PV) converters are useful for the conversion of monochromatic light into electrical power in numerous military and industrial applications. The work of this paper is to design a monochromatic GaAs PV converter for coupling to laser beams in the wavelength of 790-840 nm and optimize its structure, layer thicknesses, doping levels of the emitter and base, and antireflection coating. Modeling calculations of the GaAs PV converter optimization are carried out using PC-1D. From the highest efficiency point of view, the best wavelength is 840 nm at which the optimized structure gives an efficiency of 61.8% theoretically. Experiment results under 808 nm laser power beaming show that high optical-to-electrical conversion efficiency of 53.23% at 5 W/cm2 is achieved using the optimized GaAs PV laser converter. Finally, accurate extraction of the key parameters, viz. the ideality factor, reverse saturation current, series resistance and shunt resistance is introduced. Variations of these parameters with illumination intensity are also investigated analytically based on the one diode model, which are necessary for the design of a high performance PV generation system.

  4. An observation of direct-gap electroluminescence in GaAs structures with Ge quantum wells

    SciTech Connect

    Aleshkin, V. Ya.; Dikareva, N. V.; Dubinov, A. A.; Zvonkov, B. N.; Kudryavtsev, K. E.; Nekorkin, S. M.

    2015-02-15

    A light-emitting diode structure based on GaAs with eight narrow Ge quantum wells is grown by laser sputtering. An electroluminescence line polarized predominately in the plane parallel to the constituent layers of the structure is revealed. The line corresponds to the direct optical transitions in momentum space in the Ge quantum wells.

  5. The temporal dynamics of impurity photoconductivity in quantum wells in GaAs

    SciTech Connect

    Aleshkin, V. Ya. E-mail: aleshkin@ipm.sci-nnov.ru

    2015-10-15

    A theory of cascade capture at charged donors in quantum wells (QWs) is developed without using the Fokker-Planck approximation, which is not valid in QWs. The time dependences of impurity photoconductivity and photoelectron concentration in GaAs QWs are determined. The cascade capture time as a function of the charge donor concentration is calculated.

  6. On the cascade capture of electrons at donors in GaAs quantum wells

    SciTech Connect

    Aleshkin, V. Ya.

    2015-09-15

    The impact parameter for the cascade capture of electrons at a charged donor in a GaAs quantum well is calculated. A simple approximate analytical expression for the impact parameter is suggested. The temperature dependence of the impact parameter for the case of electron scattering by the piezoelectric potential of acoustic phonons is determined.

  7. Effects of surface passivation on twin-free GaAs nanosheets.

    PubMed

    Arab, Shermin; Chi, Chun-Yung; Shi, Teng; Wang, Yuda; Dapkus, Daniel P; Jackson, Howard E; Smith, Leigh M; Cronin, Stephen B

    2015-02-24

    Unlike nanowires, GaAs nanosheets exhibit no twin defects, stacking faults, or dislocations even when grown on lattice mismatched substrates. As such, they are excellent candidates for optoelectronic applications, including LEDs and solar cells. We report substantial enhancements in the photoluminescence efficiency and the lifetime of passivated GaAs nanosheets produced using the selected area growth (SAG) method with metal organic chemical vapor deposition (MOCVD). Measurements are performed on individual GaAs nanosheets with and without an AlGaAs passivation layer. Both steady-state photoluminescence and time-resolved photoluminescence spectroscopy are performed to study the optoelectronic performance of these nanostructures. Our results show that AlGaAs passivation of GaAs nanosheets leads to a 30- to 40-fold enhancement in the photoluminescence intensity. The photoluminescence lifetime increases from less than 30 to 300 ps with passivation, indicating an order of magnitude improvement in the minority carrier lifetime. We attribute these enhancements to the reduction of nonradiative recombination due to the compensation of surface states after passivation. The surface recombination velocity decreases from an initial value of 2.5 × 10(5) to 2.7 × 10(4) cm/s with passivation. PMID:25565000

  8. Low Temperature Photoluminescence Kinetics of Double-Ring Structured GaAs Quantum Dots.

    PubMed

    Myoung, Soung; Mun, Ok Mi; Yim, Sang-Youp; Kim, Jong Su

    2015-11-01

    This work is focused on spectroscopically characterizing kinetic properties of concentric quantum-ring complexes of GaAs quantum dots. Quantum-ring (or double-ring) GaAs quantum dots, embedded in an Al0.3Ga0.7As barrier layer, were grown by a droplet epitaxy method during molecular beam epitaxy on a GaAs (001) substrate. Emission peaks of photoluminescence spectra with different excitation power, were measured as 702 nm at 0.17 mW and 690 nm at 400 mW, were blue-shifted as the excitation power increased. In addition, excitation laser power dependence of time-resolved photoluminescence of double-ring GaAs quantum dots at 10 K under 400 nm excitation wavelength was performed, revealing that photoluminescence lifetime slowly decreased in comparison to that of single disc-like quantum dots as excitation power increased, implying that carrier transfer between inner ring and outer ring could slow down the decay process. The luminescence lifetime at 10 K increased from 245 to 409 ps in the range from 0.17 to 400 mW of excitation power. PMID:26726575

  9. Ab initio study of the strain dependent thermodynamics of Bi doping in GaAs

    NASA Astrophysics Data System (ADS)

    Jacobsen, Heather; Puchala, Brian; Kuech, Thomas F.; Morgan, Dane

    2012-08-01

    The thermodynamics of Bi incorporation into bulk and epitaxial GaAs was studied using density functional theory (DFT) and anharmonic elasticity calculations. The equilibrium concentration of Bi was determined as a function of epitaxial strain state, temperature, and growth conditions. For a bulk, unstrained system, Bi in GaAs under typical growth conditions (Ga-rich and Bi-metal-rich at 400 °C) has a dilute heat of solution of 572 meV/Bi and a solubility of x=5.2×10-5 in GaAs1-xBix. However, epitaxial strain can greatly enhance this solubility, and under the same conditions an epitaxial film of GaAs1-xBix with 5% in-plane tensile strain is predicted to have a Bi solubility of x=7.3×10-3, representing approximately a hundred times increase in solubility over the unstrained bulk case. Despite these potentially large increases in solubility, the equilibrium solubility is still very low compared to values that have been achieved experimentally through nonequilibrium growth. These values of solubility are also sensitive to the choice of the Bi reference state. If the primary route for phase separation is the formation of GaBi within the same structure, rather than Bi metal, GaBi would serve as the source/sink for Bi. If GaBi is used as the Bi reference state, the epitaxial formation energy on a bulk unstrained GaAs substrate is reduced dramatically to 144 meV/Bi, yielding a Bi solubility of x=0.083 in GaAs1-xBix. These calculations suggest that Bi solubility could be greatly enhanced if Bi metal formation is inhibited and the system is forced to remain constrained to the GaAs1-xBix structure. Although GaBi is not a naturally stable compound, it could potentially be stabilized through a combination of kinetic limitations and alloying.

  10. 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.

  11. InAs quantum dots in a single-crystal GaAs matrix

    NASA Astrophysics Data System (ADS)

    Brandt, O.; Tapfer, L.; Ploog, K.; Bierwolf, R.; Hohenstein, M.; Phillipp, F.; Lage, H.; Heberle, A.

    1991-10-01

    We directly synthesize InAs microclusters embedded in a single-crystal GaAs matrix by molecular-beam epitaxy. Fractional monolayers of InAs are deposited on terraced (001) GaAs surfaces and subsequently overgrown with GaAs. Growth conditions are adjusted in situ by reflection high-energy electron diffraction to those favoring step-flow nucleation of both Ga and In adatoms. The resulting microscopic structural configuration is studied by double-crystal x-ray diffractometry and high-resolution electron microscopy. These experiments reveal that InAs growth takes place in fact by nucleation of In adatoms on step edges. An array of isolated InAs clusters of subnanometer size (quantum dots) is thereby formed within the GaAs matrix. The interface of the InAs clusters is in registry with the surrounding GaAs matrix and is thus defect-free. Several spectroscopic techniques, such as transmission, cw photoluminescence, photoluminescence excitation, and picosecond photoluminescence, are applied to get insight into the optical properties of this system. We show that the optical response of excitons attached to the InAs dots is determined by the zero-dimensional symmetry of the system. This effect is most evident when comparing the spontaneous emission of InAs dots and InAs planes, which in either case results from the relaxation of excitons to the emitting state followed by their radiative recombination. The reduced translational symmetry causes a progressive release of wave-vector conservation, thus modifying the selection rules that uniquely determine the interaction of excitons with phonons (relaxation) and photons (recombination).

  12. Surface science analysis of GaAs photocathodes following sustained electron beam delivery

    NASA Astrophysics Data System (ADS)

    Shutthanandan, V.; Zhu, Z.; Stutzman, M. L.; Hannon, F. E.; Hernandez-Garcia, C.; Nandasiri, M. I.; Kuchibhatla, S. V. N. T.; Thevuthasan, S.; Hess, W. P.

    2012-06-01

    Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power free electron lasers (FEL). Photocathode quantum efficiency degradation is due to residual gases in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes, which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include helium ion microscopy, Rutherford backscattering spectrometry (RBS), atomic force microscopy, and secondary ion mass spectrometry (SIMS). In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the continuous electron beam accelerator facility (CEBAF) photoinjector and one unused, were also analyzed using transmission electron microscopy (TEM) and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but show evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements, the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.

  13. XPS investigation on vacuum thermal desorption of UV/ozone treated GaAs(100) surfaces

    NASA Astrophysics Data System (ADS)

    Cossu, G.; Ingo, G. M.; Mattogno, G.; Padeletti, G.; Proietti, G. M.

    In order to prepare suitable surfaces for molecular beam epitaxy (MBE), sacrificial thin oxide layers on HCl etched GaAs(100) surfaces were grown by both air and UV/ozone exposure. Passive films were subsequently removed by vacuum thermal desorption to achieve surfaces that were smooth and clean on an atomic scale. The evolution of the surface chemical composition, as a function of vacuum desorption temperature, has been studied by means of X-ray photoelectron spectroscopy (XPS). XPS results have evidenced for air and UV/ozone exposed GaAs(100) surfaces a relationship between desorption temperature and surface chemical composition; indeed, the oxide removal is temperature dependent and sequentially selective as follows: As 2O 3. AsO and Ga 2O 3. Furthermore, XPS results have shown that air-grown films have a chemical composition and thermal desorption behaviour different from UV/ozone treated materials. Indeed, these latter have an As 2O 3/Ga 2O 3 and an unoxidized As/Ga ratio close to unity for as grown and thermal treated at 580°C surfaces, respectively. By contrast, air-exposed GaAs(100) materials are Ga 2O 3-enriched and after vacuum thermal desorption treatments have never a stoichiometric composition(As (GaAs)/Ga (GaAs)= 1). Furthermore UV/ozone treated GaAs(100) surfaces subjected to a vacuum thermal treatment at 580°C, have a troublesome organic contamination level below XPS detectability, whereas from air-exposed surfaces, carbon is not completely thermally removable

  14. Surface science analysis of GaAs photocathodes following sustained electron beam delivery

    SciTech Connect

    Carlos Hernandez-Garcia, Fay Hannon, Marcy Stutzman, V. Shutthanandan, Z. Zhu, M. Nandasri, S. V. Kuchibhatla, S. Thevuthasan, W. P. Hess

    2012-06-01

    Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power Free Electron Lasers (FEL). Photocathode quantum efficiency (QE) degradation is due to residual gasses in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes, which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include Helium Ion Microscopy (HIM), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Secondary Ion Mass Spectrometry (SIMS). In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the Continuous Electron Beam Accelerator Facility (CEBAF) photoinjector and one unused, were also analyzed using Transmission Electron Microscopy (TEM) and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but shows evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.

  15. Formation of a pn junction on an anisotropically etched GaAs surface using metalorganic chemical vapor deposition

    NASA Technical Reports Server (NTRS)

    Leon, R. P.; Bailey, S. G.; Mazaris, G. A.; Williams, W. D.

    1986-01-01

    A continuous p-type GaAs epilayer has been deposited on an n-type sawtooth GaAs surface using MOCVD. A wet chemical etching process was used to expose the intersecting (111)Ga and (-1 -1 1)Ga planes with 6-micron periodicity. Charge-collection microscopy was used to verify the presence of the pn junction thus formed and to measure its depth. The ultimate goal of this work is to fabricate a V-groove GaAs cell with improved absorptivity, high short-circuit current, and tolerance to particle radiation.

  16. Formation of a pn junction on an anisotropically etched GaAs surface using metalorganic chemical vapor deposition

    SciTech Connect

    Leon, R.P.; Bailey, S.G.; Mazaris, G.A.; Williams, W.D.

    1986-10-13

    A continuous p-type GaAs epilayer has been deposited on an n-type sawtooth GaAs surface using metalorganic chemical vapor deposition. A wet chemical etching process was used to expose the intersecting (111)Ga and (1-bar1-bar1)Ga planes with 6 ..mu..m periodicity. Charge collection microscopy was used to verify the presence of the pn junction thus formed and to measure its depth. The ultimate goal of this work is to fabricate a V-groove GaAs cell with improved absorptivity, high short-circuit current, and tolerance to particle radiation.

  17. Structural and electronic properties of zinc blend GaAs 1-xBi x solid solutions

    NASA Astrophysics Data System (ADS)

    Abdiche, A.; Abid, H.; Riane, R.; Bouaza, A.

    2010-05-01

    First principles total energy calculations were carried out to investigate structural and electronic properties of zinc-blend (ZB) GaAs, GaBi and GaAs 1-xBi x solid solutions. We have calculated lattice parameters, bulk modulus, pressure derivative and GaAs 1-xBi x band-gap energy for zinc blend-type crystals of the compositions x=0, 0.25, 0.5, 0.75, 1. Discussions will be given in comparison with results obtained with other available theoretical and experimental results.

  18. A search for spin-polarized photoemission from GaAs using light with orbital angular momentum

    SciTech Connect

    Nathan Clayburn, James McCarter, Joan Dreiling, Bernard Poelker, Dominic Ryan, Timothy Gay

    2013-01-01

    Laser light with photon energy near the bandgap of GaAs and with different amounts of orbital angular momentum was used to produce photoemission from unstrained GaAs. The degree of electron spin polarization was measured using a micro-Mott polarimeter and found to be consistent with zero with an upper limit of ~3% for light with up to ±5{bar h} of orbital angular momentum. In contrast, the degree of spin polarization was 32.32 ± 1.35% using circularly-polarized laser light at the same wavelength, which is typical of bulk GaAs.

  19. Monolithic integration of optical grade GaAs on Si (001) substrates deeply patterned at a micron scale

    SciTech Connect

    Bietti, Sergio; Scaccabarozzi, Andrea; Bonera, Emiliano; Miglio, Leo; Sanguinetti, Stefano; Frigeri, Cesare; Falub, Claudiu V.; Känel, Hans von

    2013-12-23

    Dense arrays of micrometric crystals, with areal filling up to 93%, are obtained by depositing GaAs in a mask-less molecular beam epitaxy process onto Si substrates. The substrates are patterned into tall, micron sized pillars. Faceted high aspect ratio GaAs crystals are achieved by tuning the Ga adatom for short surface diffusion lengths. The crystals exhibit bulk-like optical quality due to defect termination at the sidewalls. Simultaneously, the thermal strain induced by different thermal expansion parameters of GaAs and Si is fully relieved. This opens the route to thick film applications without crack formation and wafer bowing.

  20. Current flow and potential efficiency of solar cells based on GaAs and GaSb p-n junctions

    SciTech Connect

    Andreev, V. M.; Evstropov, V. V.; Kalinovsky, V. S. Lantratov, V. M.; Khvostikov, V. P.

    2009-05-15

    Dependence of the efficiency of single-junction and multijunction solar cells on the mechanisms of current flow in photoactive p-n junctions, specifically on the form of the dark current-voltage characteristic J-V, has been studied. The resistanceless J-V{sub j} characteristic (with the series resistance disregarded) of a multijunction solar cell has the same shape as the characteristic of a single-junction cell: both feature a set of exponential portions. This made it possible to develop a unified analytical method for calculating the efficiency of singlejunction and multijunction solar cells. The equation relating the efficiency to the photogenerated current at each portion of the J-V{sub j} characteristic is derived. For p-n junctions in GaAs and GaSb, the following characteristics were measured: the dark J-V characteristic, the dependence of the open-circuit voltage on the illumination intensity P-V{sub OC}, and the dependence of the luminescence intensity on the forward current L-J. Calculated dependences of potential efficiency (under idealized condition for equality to unity of external quantum yield) on the photogenerated current for single-junction GaAs and GaSb solar cells and a GaAs/GaSb tandem are plotted. The form of these dependences corresponds to the shape of J-V{sub j} characteristics: there are the diffusion- and recombination-related portions; in some cases, the tunneling-trapping portion is also observed. At low degrees of concentration of solar radiation (C < 10), an appreciable contribution to photogenerated current is made by recombination component. It is an increase in this component in the case of irradiation with 6.78-MeV protons or 1-MeV electrons that brings about a decrease in the efficiency of conversion of unconcentrated solar radiation.