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Sample records for lec semi-insulating gaas

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

    Science.gov (United States)

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

    1981-01-01

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

  2. Sub-bandgap photocurrent response and carrier transport properties of undoped semi-insulating LEC GaAs as a composite

    Institute of Scientific and Technical Information of China (English)

    YANG Ruixia; ZHAO Zhengping; LOU Jianzhong; LV Miao; YANG Yongjun; LIU Lihao

    2003-01-01

    Undoped (ND) semi-insulating (SI) liquid encapsulated Czochralski (LEC) GaAs crystals were investigated by photocurrent and temperature-dependent Hall measurements. It is indicated that strong nonuniformities in the distributions of impurities and defects can occur for the NDSILEC GaAs crystal grown under a condition with strong constitutional supercooling. In such case, the deep level that dominates Fermi level is spacial location dependent, and the GaAs crystal becomes a composite consisting of a large number of elementary domains with different conductivities. The sub-bandgap photocurrent response and the carrier transport properties for this kind of composite are quite different from those for homogeneous NDSILEC GaAs.

  3. Outer space grown semi-insulating GaAs and its applications

    Institute of Scientific and Technical Information of China (English)

    林兰英; 张绵; 钟兴儒; 陈诺夫; Masayoshi; Yamada

    1999-01-01

    GaAs single crystal has been grown in recoverable satellite. Hall measurements indicate that the GaAs shows semi-insulating behavior. The structural properties of the crystal have been improved obviously, and their uniformity has been improved as well. The stoichiometry and its distribution in space-grown GaAs are improved greatly compared with the GaAs single crystal grown terrestrially. The properties of integrated circuits made by direct ion-implantation on space-grown GaAs are better than those made on ground-grown materials. These results show that the stoichiometry in semi-insulating GaAs seriously affects the properties of related devices.

  4. Terahertz Radiation from Large Aperture Bulk Semi-insulating GaAs Photoconductive Dipole Antenna

    Institute of Scientific and Technical Information of China (English)

    施卫; 贾婉丽; 侯磊; 许景周; 张希成

    2004-01-01

    We report the experimental results of a large-aperture biased semi-insulating GaAs photoconductive dipole antenna, with a gap of 3mm between two Au/Ge/Ni electrodes, triggered by 800nm Ti-sapphire laser pulses with 82 MHz repetition rate. A direct comparison is made between insulated GaAs dipole antenna with a Si3N4 layer and bare GaAs dipole antenna. Both the current in the antenna and the radiation amplitude present as linear to the exciting power when the applied voltage is fixed. The Si3N4 insulated GaAs dipole antenna can hold higher biased voltage than a normal GaAs dipole antenna; its terahertz radiation generation efficiency is significantly higher than that of a normal GaAs dipole antenna.

  5. 20 THz broadband generation using semi-insulating GaAs interdigitated photoconductive antennas.

    Science.gov (United States)

    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.

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

    Science.gov (United States)

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

    2011-12-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Dreyer, W.; Duderstadt, F.

    2004-07-01

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

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

    CERN Document Server

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

    2000-01-01

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

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

    Science.gov (United States)

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

    2017-07-01

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

  10. High Gain Lateral Semi-Insulating GaAs Photoconductive Switch Triggered by 1064 nm Laser Pulses

    Institute of Scientific and Technical Information of China (English)

    施卫; 张显斌; 李琦; 陈二柱; 赵卫

    2002-01-01

    We report on the experimental results of a lateral semi-insulating GaAs photoconductive switch, with a gap of 8mm between two electrodes, triggered by 1064nm laser pulses at a wavelength beyond the GaAs absorption edge. Both the linear and nonlinear modes of the switch were observed when it was triggered by light pulses with an energy of l.9mJ and a pulse width of 60ns, and operated at high voltages of 3 and 5kV. The results show that when the semi-insulating GaAs photoconductive switch operates under an electrical field of 4.37 k V/cm, it will enter into the linear mode first, and then the switch will undergo the nonlinear mode (lock-on) after a delay of about 20 - 100 ns. It is worth noticing that the delay time under high light energy is longer than that in the low optical energy. The non-intrinsic absorption mechanism is discussed. EL2 deep level defects and double-photon absorption in GaAs may play a key part in the absorption process.

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

    Institute of Scientific and Technical Information of China (English)

    Ma Xiangrong; Shi Wei; Ji Weili; Xue Hong

    2011-01-01

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

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

    Science.gov (United States)

    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.

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

    CERN Document Server

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

    2014-01-01

    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. Scholl was not capable to generate the NNDC curve for SI-GaAs, in this work we 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 structu...

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

    CERN Document Server

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

    1999-01-01

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

  15. Current-voltage characteristics and charge DLTS spectra of proton-bombarded Schottky diodes on semi-insulating GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Thurzo, I. (Inst. of Physics, Slovak Academy of Sciences, Bratislava (Slovakia)); Hrubcin, L. (Inst. of Electrical Engineering, Slovak Academy of Sciences, Bratislava (Slovakia)); Bartos, J. (Inst. of Physics, Slovak Academy of Sciences, Bratislava (Slovakia)); Pincik, E. (Inst. of Physics, Slovak Academy of Sciences, Bratislava (Slovakia))

    1993-10-01

    Changes in the current-voltage characteristics and charge DLTS spectra of Schottky diodes on semi-insulating GaAs after irradiation by protons at different energies and doses are presented and discussed. Apart from a progressive degradation of the Schottky barriers with enhanced proton energy and dose, there is a threshold, positioned between 10[sup 14] and 10[sup 15] protons/cm[sup 2], for observing trap-limited transients. (orig.)

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

    Science.gov (United States)

    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.

  17. Peculiar Transmission Characteristics of the Large Gap Semi-Insulating GaAs Photoconductive Switch

    Institute of Scientific and Technical Information of China (English)

    施卫; 马湘蓉

    2011-01-01

    Unique experimental phenomena are discovered in a large gap semiinsulating(SI)GaAs photoconductive semiconductor switch(PCSS)and the peculiar transmission characteristics are exhibited in the experiment.The transmission characteristics for the large gap SI-GaAs PCSS are entirely different from the commonly designed PCSS.By analyzing the differences of the transmission characteristics between the common and the large gap SI-GaAs PCSS,a detailed statistical analysis and theoretical explanations are expounded.The large gap SI-GaAs PCSS works in the overvoltage relaxation limit space charge accumulation(LSA)mode when the conditions of 5 × 104 s·cm-3 ≤ no/f ≤ 3 × 105 s.cm-3 and noL ≥ 1013 cm-2 must be met in the switch,with no being carrier concentration and f the frequency.The large gap SI-GaAs PCSS we developed has not shown the nonlinear (lock-in)behavior at high bias voltage,so the withstand voltage and service life for PCSS are improved.%Unique experimental phenomena are discovered in a large gap semiinsulating (SI) GaAs photoconductive semiconductor switch (PCSS) and the peculiar transmission characteristics are exhibited in the experiment. The transmission characteristics for the large gap SI-GaAs PCSS are entirely different from the commonly designed PCSS. By analyzing the differences of the transmission characteristics between the common and the large gap SI-GaAs PCSS, a detailed statistical analysis and theoretical explanations are expounded. The large gap SI-GaAs PCSS works in the overvoltage relaxation limit space charge accumulation (LSA) mode when the conditions of 5 x 104 s-cm~3 1013 cm~2 must be met in the switch, with no being carrier concentration and f the frequency. The large gap SI-GaAs PCSS we developed has not shown the nonlinear (lock-in) behavior at high bias voltage, so the withstand voltage and service life for PCSS are improved.

  18. On the detection performance of semi-insulating GaAs detectors coupled to multichannel ASIC DX64 for X-ray imaging applications

    Energy Technology Data Exchange (ETDEWEB)

    Zat' ko, Bohumir [Institute of Electrical Engineering, Slovak Academy of Sciences, Dubravska cesta 9, SK-841 04 Bratislava (Slovakia)], E-mail: elekbzat@savba.sk; Dubecky, Frantisek [Institute of Electrical Engineering, Slovak Academy of Sciences, Dubravska cesta 9, SK-841 04 Bratislava (Slovakia); Scepko, Pavol [T and N System, Ltd., Severna 5, SK-974 01 Banska Bystrica (Slovakia); Grybos, Pawel [Department of Measurement and Instrumentation, AGH University of Science and Technology, Al. Mickiewicza 30, PL-30 059 Krakow (Poland); Mudron, Jan [MTC, a. s., Kuzmanyho 11, SK-031 01 Liptovsky Mikulas (Slovakia); Maj, Piotr; Szczygiel, Robert [Department of Measurement and Instrumentation, AGH University of Science and Technology, Al. Mickiewicza 30, PL-30 059 Krakow (Poland); Frollo, Ivan [Institute of Measurement Science, Slovak Academy of Sciences, Dubravska cesta 9, SK-841 04 Bratislava (Slovakia)

    2008-06-11

    Detectors based on semi-insulating (SI) GaAs show high detection efficiency and satisfactory energy resolution for modern X-ray digital imaging applications. This work deals with the performance of SI GaAs-based detectors coupled by wire bonding to the input of multichannel readout chip DX64 (technology CMOS 0.35 {mu}m). Detectors have circular Ti/Pt/Au multilayer Schottky blocking contacts with different diameters (0.75, 0.50, 0.30 and 0.20 mm). First results of operation of the used readout system in the single-photon counting regime are given.

  19. Frequency and intensity dependence of the sub-band-gap features observed in the surface photovoltage spectrum of semi-insulating GaAs

    Science.gov (United States)

    Sharma, T. K.; Kumar, Shailendra; Rustagi, K. C.

    2002-11-01

    Surface photovoltage spectroscopy studies on thick semi-insulating GaAs wafers are reported in the range 850-950 nm using the chopped light geometry. We observed some interesting sharp features in the sub-band-gap of SI-GaAs, which were reported recently [Appl. Phys. Lett. 79, 1715(2001); Rev. Sci. Instrum. 73, 1835 (2002)]. In this article, we present the dependence of these features on the chopping frequency and the source intensity. The intensity variation in the above-band-gap region and for the A peak (898 nm) in the sub-band-gap region could be fitted with single component while it is necessary to consider more than one component to fit the data for the Q peak (887 nm) in the sub-band-gap region. A model consistent with the observed features is also proposed.

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

    CERN Document Server

    Rogalla, M

    1999-01-01

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

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

    Science.gov (United States)

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

    1996-08-01

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

  2. Photoinduced transient spectroscopy and photoluminescence studies of copper contaminated liquid-encapsulated Czochralski-grown semi-insulating GaAs

    Science.gov (United States)

    Tin, C. C.; Teh, C. K.; Weichman, F. L.

    1987-09-01

    Photoinduced transient spectroscopy (PITS) studies of samples of copper contaminated annealed semi-insulating GaAs in the temperature range of 274-384 K show two dominant levels at about Ev +0.5 eV and about Ec -0.59 eV in addition to the EL2 levels at about Ec -0.80 eV. Depth profiling using chemical etching followed by PITS measurements shows a competing process between the defects responsible for the level at Ev +0.5 eV and that at Ec -0.59 eV. The former is predominantly found near the surface and the latter is dominant in the interior. From the depth profiling results, we have determined that the diffusion constants for these two types of defects are about 4.7×10-10 cm2 s-1 and 5.2×10-10 cm2 s-1, respectively. We propose that the level at Ev +0.50 eV is due to a copper related complex and the level at Ec -0.59 eV is due to native defects. The copper related level at about Ev +0.50 eV is different from the often seen copper related defect level at around Ev +0.40 eV. The presence of these two levels would explain the variety of results reported by different workers on the deep levels attributed to copper. Photoluminescence measurements on a copper contaminated sample at 4.2 K show a peak at 1.36 eV which is due to CuGa acceptor level. This peak appears even after repeated etching of the sample, showing the presence of copper throughout the sample. Comparison data were also obtained for both ``copper-free'' annealed and unannealed samples.

  3. Flow instability of buoyant-Marangoni convection in the LEC GaAs melt

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Flow transitions and instabilities have significant effects on the quality of the crystals. The flow and heat transfer in the LEC GaAs melt are numerically studied by a time-dependent and three-dimensional turbulent flow model. The effects of the change of the buoyancy and Marangoni force on the flow state are analyzed by changing the temperature difference between the crystal and the crucible walls. The results show that the flow will transform from axisymmetric steady flow to non-axisymmetric oscillatory flow when the temperature difference exceeds the critical value, and that the mechanism of the transition is attributed to the Marangoni instability. The critical temperature differences for the flow transitions corresponding to different melt depth H are numerically predicted. Several important characteristics of the non-axisymmetric buoyant-Marangoni convection are numerically observed and compared with that of the non-axisymmetric mixed convection coupled with crystal rotation.

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

    Science.gov (United States)

    1980-06-01

    capsulated Czochralski (LEC) growth methods to reduce the residual donor level and, thereby, produce semi-insulating GaAs without the intentional addition...fold: First, to provide an assessment of the incorporation of B into GaAs grown by the liquid encapsulated Czochralski methods and, secondly, to...insulating GaAs wafers or direct ion implantation and annealing of bulk insulating substrates. The latter method would appear to be straight forward process

  5. Multiple steady state current-voltage characteristics in drift-diffusion modelisation of N type and semi-insulating GaAs Gunn structures

    Science.gov (United States)

    Manifacier, J. C.

    2010-12-01

    Theoretical and numerical investigations of carriers transport in N-Semi-Insulating (SI)-N and P-SI-P diodes is extended to the case of extrinsic (N type) or SI samples with Gunn like electric field dependent mobilities. The results obtained in a preceding publication [1] are valid as long as the bulk electric field does not increase above a threshold field E th associated with the beginning of negative electron differential mobility values: μ n,diff = ( dv n/ dE) diodes. SI(N -) characterizes a SI layer which keeps, under applied bias, a free electron concentration close to its thermal equilibrium value up to the beginning of electron space charge injection. A systematic study has been made by varying the contact boundary properties: flat band, metallic, N + or P +; the length of the sample and the electric parameters of the deep compensating trap of the SI layers. We show that these steady state numerical instabilities are related to the existence of multiple current-voltage solutions when numerical modelisation is made using the drift-diffusion model.

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

    Directory of Open Access Journals (Sweden)

    Pranab Biswas

    2014-05-01

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

  7. Large volume production of large size GaAs substrates and epitaxial wafers for microwave devices

    OpenAIRE

    Otoki, Y.; Kamogawa, H.; Ohnishi, M.; Inada, T.; Kashiwa, M.; Sakaguchi, H.

    1999-01-01

    Recent mass production techniques for LEC substrates and MOVPE wafers for microwave devices are described. Huge GaAs semi-insulating ingots (150mm diam., 310mm long) was obtained by Multi-hot-zone very large size pullar. Three step boule annealing and fully-automated process enabled mass production of the large size substrates. Epitaxiial wafers with abrupt hetero interface, excellent uniformity and reproducibility are producing largely by face down horizontal flow type MOVPE system, which ca...

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

    Energy Technology Data Exchange (ETDEWEB)

    Zychowitz, G.

    2006-02-03

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

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

    Science.gov (United States)

    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.

  10. Effect of the Si-doped In0.49Ga0.51P barrier layer on the device performance of In0.4Ga0.6As MOSFETs grown on semi-insulating GaAs substrates

    Institute of Scientific and Technical Information of China (English)

    Chang Hu-Dong; Sun Bing; Xue Bai-Qing; Liu Gui-Ming; Zhao Wei; Wang Sheng-Kai; Liu Hong-Gang

    2013-01-01

    In0.4Ga0.6As channel metal-oxide-semiconductor field-effect transistors (MOSFETs) with and without an Si-doped In0.49Ga0.51P barrier layer grown on semi-insulating GaAs substrates have been investigated for the first time.Compared with the In0.4Ga0.6As MOSFETs without an In0.49Ga0.51P barrier layer,In0.4Ga0.6As MOSFETs with an In0.49Ga0.51P barrier layer show higher drive current,higher transconductance,lower gate leakage current,lower subthreshold swing,and higher effective channel mobility.These In0.4Ga0.6As MOSFETs (gate length 2 μm) with an In0.49Ga0.s1P barrier layer exhibit a high drive current of 117 mA/mm,a high transconductance of 71.9 mS/mm,and a maximum effective channel mobility of 1266 cm2/(V·s).

  11. Epitaxial Growth of Semi-Insulating GaAs

    Science.gov (United States)

    1978-03-01

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

  12. Thermal cycling, DLTS, and PEC studies on LEC gallium arsenide. [GaAs:Si

    Energy Technology Data Exchange (ETDEWEB)

    Santhanaraghavan, P. (Anna Univ., Madras (India). Crystal Growth Centre); Sankaranarayanan, K. (Anna Univ., Madras (India). Crystal Growth Centre); Arokiaraj, J. (Anna Univ., Madras (India). Crystal Growth Centre); Anbukumar, S. (Anna Univ., Madras (India). Crystal Growth Centre); Kumar, J. (Anna Univ., Madras (India). Crystal Growth Centre); Ramasamy, P. (Anna Univ., Madras (India). Crystal Growth Centre)

    1994-01-01

    This paper discusses the growth of gallium arsenide single crystals using the LEC technique. The Semi-insulating gallium arsenide was studied. The defect investigations were made by DLTS and etching studies. The variation of deep level concentration along the wafer was estimated using DLTS. The fabrication and efficiency of the PEC Solar cells are also reported. (orig.)

  13. Undoped semi-insulating indium phosphide (InP) and its applications

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    @@ During the past several years, the research and development of InP material has made great progress due to serving as the substrate for most optoelectronic devices operating at the communications wavelength of 1.31 and 1.55 (m. At present, InP has become an important semiconductor material together with Si and GaAs. When compared to GaAs, InP has higher electron velocity, higher radiation hardness and better heat-conducting property. The advantage of InP crystal material allows higher frequency operation and lower power requirements. Therefore, InPis widely being used for the manufacture of microwave devices, high-frequency devices and optoelectronic integrated circuits (OEICs) which are indispensable for wireless technology, satellite communications[1-3]. Although n-type and p-type InP can meet actual needs, semi-insulating InP substrates remain to be improved due to their poor uniformity and consistency. For this reason, several possible approaches have been reported to the preparation of SI InP by wafer annealing under different conditions[4-9].

  14. Conductivity, Hall and magnetoresistance effect measurements on SI GaAs and InP

    Energy Technology Data Exchange (ETDEWEB)

    Acar, S.; Kasap, M. [Department of Physics, Faculty of Science and Arts, University of Gazi, Teknikokullar, 06500 Ankara (Turkey)

    2004-05-01

    The conductivity, Hall effect and magnetoresistance quantities in semi-insulating undoped GaAs and Fe-doped GaAs and InP grown by the LEC technique have been measured in the temperature range 300-420 K. It is shown that mixed conductivity is present in all samples. The experimental data were analyzed using a two-band model including electron and hole transport. A good fit has been obtained self-consistently to both conductivity and mobility. The single-band parameters have been extracted from the measured data in the studied temperature range. From ln (vertical stroke R{sub H,} {sub 0} vertical stroke T {sup 3/2}) and {sigma} vs T {sup -1} plots, activation energies of 0.77 and 0.65 eV have also been observed for GaAs and InP, respectively. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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

    CERN Document Server

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

    1999-01-01

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

  16. Semi-insulating GaAs-based Schottky contacts in the role of detectors of ionising radiation: An effect of the interface treatment

    CERN Document Server

    Ivanco, J; Darmo, J; Krempasky, M; Besse, I; Senderak, R

    1999-01-01

    It is generally agreed that the substrate material quality plays a key role in the performance of back-to-back detectors of ionising radiation based on semi-insulating (SI) material. The aim of this paper is to evaluate usually overlooked problem, namely the influence of the Schottky contact preparation on detector performance. We report on different approaches to modify and control the quality of the metal/SI GaAs interface via a treatment of the SI-GaAs surface by means of low-temperature hydrogen plasma and wet etching. The measured electrical and detecting properties of such structures display a strong dependence on the history and the way the GaAs surface is treated prior to the metal evaporation. We point out, therefore, that the semiconductor surface treatment before the Schottky metallization plays a role of comparable importance to the influence of the SI-GaAs substrate properties on detector performances. (author)

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

    Science.gov (United States)

    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).

  18. Radiation damage to neutron and proton irradiated GaAs particle detectors

    CERN Document Server

    Rogalla, M; Evans, N; Joost, S; Kienzle-Focacci, M N; Geppert, R; Göppert, R; Irsigler, R; Ludwig, J; Runge, K; Schmid, T; Eich, Th.; Schmid, Th.

    1997-01-01

    The radiation damage in 200 um thick Schottky diodes made on semi-insulating (SI) undoped GaAs Liquid Encapsulated Czochralski (LEC) bulk material with resistivities between 0.4 and 8.9*10E7 Ohm*cm were studied using alpha-spectroscopy, signal response to minimum ionising particles (MIP), I-V and CV-measurements. The results have been analysed to investigate the influence of the substrate resistivity on the detector performance after neutron and proton irradiation. The leakage current density, signal response to alpha-particles and MIPs show a strong dependence on the resistivity before and after irradiation. An observed decrease of the electron mean free drift length before and after irradiation with increasing substrate resistivity can be explained by a model involving the different ionisation ratios of defects, which are introduced by the irradiation. Comparison of the radiation damage due to neutrons and protons gives a hardness factor of 7+-0.9 for 24 GeV/c protons. The best detectors show a response to ...

  19. Comprehensive measurements of GaAs pixel detectors capacitance

    CERN Document Server

    Caria, M; D'Auria, S; Lai, A; Randaccio, P; Cadeddu, S

    2002-01-01

    We have studied GaAs pixel detectors on semi-insulating wafers with Schottky contacts. We performed comprehensive measurements on the inter-pixel and capacitance to back plane. Being semi-insulating, the behaviour is totally different with respect to other common semiconductors, such as high resistivity silicon. Non-homogeneities are also an issue, due to both the contacts and the crystal bulk. In order to detect them and their influence on capacitance, we undertook systematic measurements with different configurations of the measuring electrodes.

  20. Vanadium-Doped Semi-Insulating 6H-SiC for Microwave Power Device Applications

    Institute of Scientific and Technical Information of China (English)

    Li'na Ning; Zhihong Feng; Yingmin Wang; Kai Zhang; Zhen Feng; Xiangang Xu

    2009-01-01

    Two-inch semi-insulating SiC bulk crystals with resistivity higher than 1×106 Ωcm were achieved by vanadium doping during sublimation. Secondary-ion-mass-spectrometry (SIMS) was employed to determine the concen-tration of impurities in the crystals, such as B, Al, V and N. These results indicated that the concentration of nitrogen and aluminum kept on decreasing and the concentration of B and V was almost constant during the whole growth. An inner crucible was used to control the exhausting of vanadium, which made the uniformity of the high resistivity (1×106 Ωcm) in the wafer up to 80%. High-performance AlGaN/GaN high-electron-mobility-transistor (HEMT) materials and devices were grown and fabricated on semi-insulating 6H-SiC sub-strates. The two-dimensional electron gas (2DEG) mobility at room-temperature was 1795 cm2/V·s. The charge carrier concentration of the substrate determined by capacitance-voltage (C-V) test was 7.3 × 1015 cm-3. The device with a gate width of 1 mm exhibits a maximum output power of 5.5 W at 8 GHz, which proves the semi-insulating property of the substrates indirectly.

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

    Science.gov (United States)

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

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

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

    Science.gov (United States)

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

    2016-12-01

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

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

    CERN Document Server

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

    2002-01-01

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

  4. Influence of Zn Diffusion on Bandwidth and Extinction in MQW Electroabsorption Modulators Buried with Semi-Insulating InP

    Institute of Scientific and Technical Information of China (English)

    Takayuki; Yamanaka; Hideki; Fukano; Ken; Tsuzuki; Munehisa; Tamura; Ryuzo; Iga; Matsuyuki; Ogasawara; Yasuhiro; Kondo; Tadashi; Saitoh

    2003-01-01

    A comprehensive analysis of multi-quantum-well electroabsorption modulators buried with semi-insulating (SI)-InP is presented. We quantitatively demonstrate that suppression of Zn diffusion into the burying and optical core layers plays a key role in high-speed and high-extinction operation.

  5. Accrual of ROCs LECs and REGOs

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2005-07-01

    This report summarises the findings of a project to identify the technical and administrative difficulties experienced by microgenerators in accessing the benefits of Renewables Obligation Certificates (ROCs), Levy Exemption Certificates (LECs) and Renewable Electricity Guarantees of Origin (REGO). These include cost, administrative complexity and financial risk. Changes allowing bulk processing, meter data provision, sell and buyback contracts, and alignment of ROCs, LECs and REGOs are discussed as well as making the schemes more customer friendly. The background to the project is traced, and an overview of the processes associated with gaining ROCs, LECs and REGOs is presented.

  6. Raman investigations on nitrogen ion implantation effects on semi-insulating InP

    CERN Document Server

    Santhakumar, K; Kesavamoorthy, R; Magudapathy, P; Nair, K G M; Ravichandran, V

    2002-01-01

    Raman scattering measurements on liquid-encapsulated Czochralski-grown Fe-doped semi-insulating InP(1 0 0) single crystal substrates have been carried out before and after 120 keV N sup + implantation for various doses from 10 sup 1 sup 3 to 10 sup 1 sup 5 cm sup - sup 2 and also after post-implantation rapid thermal annealing of these samples. It is observed that LO phonon mode frequency decreases and full width at half maximum (FWHM) increases with fluence due to implantation-induced lattice damage. Forbidden Raman TO mode in (1 0 0) cut InP is observed at the doses of 5x10 sup 1 sup 3 and 5x10 sup 1 sup 4 cm sup - sup 2. This might have appeared due to the polycrystalline and/or misoriented regions created during implantation. TO mode is not observed for high doses in as-implanted samples due to excessive lattice damage induced by the implantation. On rapid thermal annealing at 573 K for 30 s, the implanted samples show a partial recovery of LO phonon mode frequency and FWHM due to partial annealing of the...

  7. The effect of nitrogen implantation on structural changes in semi-insulating InP

    Energy Technology Data Exchange (ETDEWEB)

    Santhakumar, K.; Jayavel, P.; Reddy, G.L.N.; Sastry, V.S.; Nair, K.G.M.; Ravichandran, V. E-mail: vravichandran@vsnl.com

    2003-12-01

    110 keV nitrogen ions (N{sup +}) of fluences 1 x 10{sup 14}-1 x 10{sup 17} cm{sup -2} have been implanted in liquid encapsulated Czochralski grown Fe-doped semi-insulating indium phosphide (InP) single crystal substrates. Grazing incidence X-ray diffraction measurements on as-grown and implanted samples have been carried out and analyzed. At all above fluences, a broad hump in the region of InP(1 1 1) peaks is observed. It might have resulted from implantation-induced misoriented grains along certain preferred orientations. The peak observed at a d-value of 1.77 A for all the fluences becomes more pronounced as the implantation fluence increases up to 1 x 10{sup 16} cm{sup -2}. This could indicate formation of an Indium phosphide nitride alloy. Post-implantation annealing reduces the structural defects and assists in the growth of the nitride phase.

  8. Properties and annealing stability of Fe doped semi-insulating GaN structures

    Energy Technology Data Exchange (ETDEWEB)

    Polyakov, A.Y.; Smirnov, N.B.; Govorkov, A.V.; Shlensky, A.A. [Institute of Rare Metals, B. Tolmachevsky 5, Moscow 119017 (Russian Federation); McGuire, Kris; Harley, E.; McNeil, L.E. [Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC (United States); Khanna, Rohit; Pearton, S.J. [Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611 (United States); Zavada, J.M. [US Army Research Office, Research Triangle Park, NC 27709 (United States)

    2005-05-01

    The properties of semi-insulating GaN films doped with Fe are reported. The 300 K sheet resistivity of the films is 2 x 10{sup 10} {omega}/square with an activation energy of the dark conductivity of 0.5 eV. The Fermi level is also pinned at E{sub C}-0.5 eV. The concentration of the 0.5 eV traps in the Fe doped portion of the films was 3 x 10{sup 16} cm{sup -3}. Also present is a high concentration of deeper electron traps with the level near E{sub C}-0.9 eV and of hole traps with level near E{sub V}+0.9 eV. Intra-center transitions of the Fe{sup 3+} center are observed in the photoluminescence spectra. The stability of the films were studied after rapid thermal annealing (RTA) at temperatures 750-1050 C and furnace annealing in hydrogen at temperatures up to 850 C. The Fe is distributed nonuniformly, with a minimum near 0.5-1 {mu}m from the surface. RTA at 850 C leads to roughness of the surface and decreases of the sheet resistivity and the cathodoluminescence intensity. The density of deep traps also greatly decreases. The effect becomes much more pronounced for furnace annealing in hydrogen for times on the order of 15 minutes and 850 C is the highest practicable under these conditions without destroying the surface morphology. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Raman Back-scattering study of Damaged and Strain Subsurface Layers in GaAs Wafers

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The damaged and strain subsurface layers of semi-insulating(SI) GaAs substrate were characterized non-destructively by Raman back-scattering.The study shows that the thicknesses of the damaged and strain layers are less than 3μm.The damaged and strain layer can be removed after being etched in H2SO4·H2O2·H2O for 1.5 min.

  10. Poole-Frenkel Effect and Phonon-Assisted Tunneling in GaAs Nanowires

    OpenAIRE

    2010-01-01

    We present electronic transport measurements of GaAs nanowires grown by catalyst-free metal-organic chemical vapor deposition. Despite the nanowires being doped with a relatively high concentration of substitutional impurities, we find them inordinately resistive. By measuring sufficiently high aspect-ratio nanowires individually in situ, we decouple the role of the contacts and show that this semi-insulating electrical behavior is the result of trap-mediated carrier transport. We observe Poo...

  11. MEMBRANE LEc EXPRESSION IN BREAST CANCER CELLS

    Directory of Open Access Journals (Sweden)

    Ya. A. Udalova

    2009-01-01

    Full Text Available Affine chromatography was used to isolate Lec antibodies from the sera of a healthy female donor with the high titers of these anti- bodies, which were labeled with biotin. The study enrolled 51 patients with primary breast cancer (BC. Antigen expression was found by immunohistochemistry and flow cytometry. With these two techniques being used, the detection rate of Lec expression in BC cells was 65% (33/51; the antigen was most frequently found by flow cytometry as compared with immunohistochemistry: 72 and 58% of cases, respectively.

  12. Comparison of Geant4 with EGSnrc for Simulation of Gamma-Radiation Detectors Based on Semi-Insulating Materials

    CERN Document Server

    Skrypnyk, A I; Khazhmuradov, M A

    2011-01-01

    We considered GEANT4 version 4.9.4 with different Electromagnetic Physics Package for calculation of response functions of detectors based on semi-insulating materials. Computer simulations with GEANT4 packages were run in order to determine the energy deposition of gamma-quanta in detectors of specified composition (Mercuric (II) Iodide and Thallium Bromide) at various energies from 0.026 to 3 MeV. The uncertainty in these predictions is estimated by comparison of their results with EGSnrc simulations. A general good agreement is found for EGSnrc and GEANT4 with Penelope 2008 model of LowEnergy Electromagnetic package.

  13. Integratable and High Speed Complex-Coupled MQW-DFB Lasers Fabricated on Semi-Insulating Substrates

    Institute of Scientific and Technical Information of China (English)

    CHENG Yuan-Bing; WANG Yang; SUN Yu; PAN Jiao-Qing; BIAN Jing; AN Xin; ZHAO ling-juan; WANG Wei

    2009-01-01

    A novel integratable and high speed InGaAsP multi-quantum well (MQW) complex-coupled distributed feedback (DFB) laser is successfully fabricated on a semi-insulating substrate. The fabricated ridge DFB laser exhibits a threshold current of 26 mA, a slope efficiency of 0. 14 W.A-1 and a side mode suppression ratio of 40 dB together with a 3 dB bandwidth of more than 8 GHz. The device is suitable for 10 Gbit/s optical fiber communication.

  14. Impurities interactions in the crytal growth of LEC gallium arsenides

    Energy Technology Data Exchange (ETDEWEB)

    Mucchino, C. [Consiglio Nazionale delle Ricerche, Parma (Italy). Lab. MASPEC; Goeroeg, T. [Consiglio Nazionale delle Ricerche, Parma (Italy). Lab. MASPEC; Zanotti, L. [Consiglio Nazionale delle Ricerche, Parma (Italy). Lab. MASPEC; Mignoni, G. [Consiglio Nazionale delle Ricerche, Parma (Italy). Lab. MASPEC; Catellani, A. [Consiglio Nazionale delle Ricerche, Parma (Italy). Lab. MASPEC

    1996-06-01

    The control of low level impurities is still considered to play a key role in obtaining GaAs based devices with an high degree of uniformity and reproducibility. Although in the recent years the importance of appropriate post growth thermal treatments has been recognized as the most relevant step in achieving homogeneous material, the contamination reduction of the melt is a fundamental requisite for growing crystals with good electric characteristics and morphology. In this work we report on new results obtained from boron and silicon doped gallium arsenide crystals grown by LEC technique in a high pressure puller: different doping procedures for heavily Si doped crystals are described and interactions between silicon and boron in the liquid, are discussed together with the analysis of their distribution in the ingot. On the basis of our experimental data from crystals doped with either B or B and Si together, a tentative explanation of the incorporation mechanism of such elements is given and a comparison with previously reported results is made. (orig.)

  15. Polytype Stabilization of High-purity Semi-insulating 4H-SiC Crystal via the PVT Method

    Directory of Open Access Journals (Sweden)

    Kai-li MAO

    2016-05-01

    Full Text Available Because the conditions under which semi-insulating 4H-SiC crystals can grow are so specific, other polytypes such as 15R and 6H can easily emerge during the growth process. In this work, a polytype stabilization technology was developed by altering the following parameters: growth temperature, temperature field distribution, and C/Si ratio. In the growth process of high-purity semi-insulating 4H-SiC crystals, the generation of undesirable polytypes was prevented, and a crystal 100 % 4H-SiC polytype was obtained. A high C/Si ratio in powder source was shown to be advantageous for the stabilization of the 4H polytype. Several methods were applied to evaluate the quality of crystals precisely; these methods include Raman mapping, X-ray diffraction, and resistivity mapping. Results showed that the 3inch-wafer was entirely made of 4H polytype, the mean value of FWHM was approximately 40 arcsec, and the distribution of the resistivity value was between 106 Ω×cm and 107 Ω×cm.DOI: http://dx.doi.org/10.5755/j01.ms.22.2.12914

  16. Growth of Semi-Insulating GaN by Using Two-Step A1N Buffer Layer

    Institute of Scientific and Technical Information of China (English)

    ZHOU Zhong-Tang; QUO Li-Wei; XING Zhi-Gang; DING Guo-Jian; ZHANG Jie; PENG Ming-Zeng; JIA Hai-Qiang; CHEN Hong; ZHOU Jun-Ming

    2007-01-01

    Semi-insulating GaN is grown by using a two-step A1N buffer layer by metalorganic chemical vapour deposition. The sheet resistance of as-grown semi-insulating GaN is dramatically increased to 1013 Ω/sq by using two-step A1N buffer instead of the traditional low-temperature GaN buffer. The high sheet resistance of as-grown GaN over 10 Ωfi/sq is due to inserting an insulating buffer layer (two-step A1N buffer) between the high-temperature GaN layer and a sapphire substrate which blocks diffusion of oxygen and overcomes the weakness of generating high density carrier near interface of GaN and sapphire when a low-temperature GaN buffer is used. The result suggests that the high conductive feature of unintentionally doped GaN is mainly contributed from the highly conductive channel near interface between GaN and the sapphire substrate, which is indirectly manifested by room-temperature photoluminescence excited by an incident laser beam radiating on growth surface and on the substrate. The functions of the two-step A1N buffer layer in reducing screw dislocation and improving crystal quality of GaN are also discussed.

  17. Lateral IBIC analysis of GaAs Schottky diodes

    Energy Technology Data Exchange (ETDEWEB)

    Vittone, E. [Experimental Physics Department, ' Nanostructured interfaces and surfaces' (NIS) Centre of Excellence of the University of Torino, and INFN - Torino (Italy) and INFM, Research Unit of Torino-University, Via P. Giuria 1, 10125 Torino (Italy)]. E-mail: vittone@to.infn.it; Olivero, P. [Experimental Physics Department, ' Nanostructured interfaces and surfaces' (NIS) Centre of Excellence of the University of Torino, and INFN - Torino (Italy) and INFM, Research Unit of Torino-University, Via P. Giuria 1, 10125 Torino (Italy)]. E-mail: p.olivero@physics.unimelb.edu.au; Nava, F. [INFN and Departimento di Fisica, Universita di Modena e Reggio Emilia, Via Campi, 213/A - 41100 Modena (Italy); Manfredotti, C. [Experimental Physics Department, ' Nanostructured interfaces and surfaces' (NIS) Centre of Excellence of the University of Torino, and INFN - Torino (Italy); INFM, Research Unit of Torino-University, Via P. Giuria 1, 10125 Torino (Italy); Lo Giudice, A. [INFM, Research Unit of Torino-University, Via P. Giuria 1, 10125 Torino (Italy); Fizzotti, F. [Experimental Physics Department, ' Nanostructured interfaces and surfaces' (NIS) Centre of Excellence of the University of Torino, and INFN - Torino (Italy); INFM, Research Unit of Torino-University, Via P. Giuria 1, 10125 Torino (Italy); Egeni, G. [INFN - Laboratori Nazionali di Legnaro, Viale dell' Universita 2, 35020 Legnaro (Pd) (Italy)

    2005-04-01

    Charge collection efficiency (CCE) profiles of a semi-insulating (SI) gallium arsenide LEC (Liquid Encapsulated Czochralski) Schottky diode have been investigated by lateral Ion Beam Induced Charge collection (IBIC) technique. A focussed 2.4 MeV proton microbeam was scanned over the cleaved surface of a SI-GaAs diode and the charge collection efficiency was evaluated as a function of the ion beam position at different bias voltages. By fitting the CCE profiles with the equations derived by the Shockley-Ramo-Gunn's theorem, drift lengths of electrons and holes were obtained. Experimental results are consistent with previous OBIC (Optical Beam Induced Current) and SP (Surface Potential) measurements and confirm the model based on the formation of a Mott barrier due to the enhanced electron capture cross section in high field conditions.

  18. Study of GaAs as a material for solar neutrino detectors

    CERN Document Server

    Markov, A V; Smirnov, N B; Govorkov, A V; Eremin, V K; Verbitskaya, E; Gavrin, V N; Kozlova, Y P; Veretenkin, Y P; Bowles, T J

    2000-01-01

    Semi-insulating GaAs crystals grown by liquid encapsulated Czochralski technique from Ga-rich melts were evaluated as a possible material for radiation detectors with a high active layer thickness. The density of deep traps, particularly the midgap EL2 donors pinning the Fermi level, was measured by various techniques in conducting and semi-insulating samples. For EL2 traps, a direct evidence of their partial neutralization in the space charge region of reverse biased Schottky diodes due to nonequilibrium capture of electrons is presented for the first time. It is shown that the density of EL2 centers decreases with decreased As composition of the melt very gradually, especially for post-growth annealed samples. Subsequently, if one aims to decrease the EL2 density to such an extent that it would make a serious impact on the depletion layer width in GaAs-based detectors one has to grow semi-insulating GaAs crystals from melts with As composition below about 43% which poses a problem for the preservation of hi...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-03-14

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

  20. 4H-SiC Schottky barrier diodes with semi-insulating polycrystalline silicon field plate termination

    Science.gov (United States)

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

    2014-05-01

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

  1. ESR characters of intrinsic defects in epitaxial semi-insulating 4H-SiC illuminated by Xe light

    Energy Technology Data Exchange (ETDEWEB)

    Cheng Ping; Zhang Yuming; Zhang Yimen; Guo Hui, E-mail: chpzmm@yahoo.com.c [Key Laboratory of Ministry of Education for Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi' an 710071 (China)

    2009-12-15

    The intrinsic defects in epitaxial semi-insulating 4H-SiC prepared by low pressure chemical vapor deposition (LPCVD) are studied by electron spin resonance (ESR) with different illumination times. The results show that the intrinsic defects in as-grown 4H-SiC consist of carbon vacancy (V{sub C}) and complex-compounds-related V{sub C}. There are two other apexes presented in the ESR spectra after illumination by Xe light, which are likely to be V{sub Si} and V{sub C}C{sub Si}. Illumination time changes the relative density of intrinsic defects in 4H-SiC; the relative density of intrinsic defects reaches a maximum when the illumination time is 2.5 min, and the ratio of V{sub C} to complex compounds is minimized simultaneously. It can be deduced that some V{sub Si} may be transformed to the complex-compounds-related V{sub C} because of the illumination. (semiconductor materials)

  2. Growth and characterization of Czochralski-grown n and p-type GaAs for space solar cell substrates

    Science.gov (United States)

    Chen, R. T.

    1983-01-01

    Progress in LEC (liquid encapsulated Czochralski) crystal growth techniques for producing high-quality, 3-inch-diameter, n- and p-type GaAs crystals suitable for solar cell applications is described. The LEC crystals with low dislocation densities and background impurities, high electrical mobilities, good dopant uniformity, and long diffusion lengths were reproducibly grown through control of the material synthesis, growth and doping conditions. The capability for producing these large-area, high-quality substrates should positively impact the manufacturability of highly efficiency, low cost, radiation-hard GaAs solar cells.

  3. The BABY BOOM Transcription Factor Activates the LEC1-ABI3-FUS3-LEC2 Network to Induce Somatic Embryogenesis.

    Science.gov (United States)

    Horstman, Anneke; Li, Mengfan; Heidmann, Iris; Weemen, Mieke; Chen, Baojian; Muino, Jose M; Angenent, Gerco C; Boutilier, Kim

    2017-10-01

    Somatic embryogenesis is an example of induced cellular totipotency, where embryos develop from vegetative cells rather than from gamete fusion. Somatic embryogenesis can be induced in vitro by exposing explants to growth regulators and/or stress treatments. The BABY BOOM (BBM) and LEAFY COTYLEDON1 (LEC1) and LEC2 transcription factors are key regulators of plant cell totipotency, as ectopic overexpression of either transcription factor induces somatic embryo formation from Arabidopsis (Arabidopsis thaliana) seedlings without exogenous growth regulators or stress treatments. Although LEC and BBM proteins regulate the same developmental process, it is not known whether they function in the same molecular pathway. We show that BBM transcriptionally regulates LEC1 and LEC2, as well as the two other LAFL genes, FUSCA3 (FUS3) and ABSCISIC ACIDINSENSITIVE3 (ABI3). LEC2 and ABI3 quantitatively regulate BBM-mediated somatic embryogenesis, while FUS3 and LEC1 are essential for this process. BBM-mediated somatic embryogenesis is dose and context dependent, and the context-dependent phenotypes are associated with differential LAFL expression. We also uncover functional redundancy for somatic embryogenesis among other Arabidopsis BBM-like proteins and show that one of these proteins, PLETHORA2, also regulates LAFL gene expression. Our data place BBM upstream of other major regulators of plant embryo identity and totipotency. © 2017 American Society of Plant Biologists. All Rights Reserved.

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

    Science.gov (United States)

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

    2017-02-01

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

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

    Science.gov (United States)

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

    2016-12-01

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

  6. Genomic rearrangements and functional diversification of lecA and lecB lectin-coding regions impacting the efficacy of glycomimetics directed against Pseudomonas aeruginosa

    Directory of Open Access Journals (Sweden)

    Amine M Boukerb

    2016-05-01

    Full Text Available LecA and LecB tetrameric lectins take part in oligosaccharide-mediated adhesion-processes of Pseudomonas aeruginosa. Glycomimetics have been designed to block these interactions. The great versatility of P. aeruginosa suggests that the range of application of these glycomimetics could be restricted to genotypes with particular lectin types. The likelihood of having genomic and genetic changes impacting LecA and LecB interactions with glycomimetics such as galactosylated and fucosylated calix[4]arene was investigated over a collection of strains from the main clades of P. aeruginosa. Lectin types were defined, and their ligand specificities were inferred. These analyses showed a loss of lecA among the PA7 clade. Genomic changes impacting lec loci were thus assessed using strains of this clade, and by making comparisons with the PAO1 genome. The lecA regions were found challenged by phage attacks and PAGI-2 (genomic island integrations. A prophage was linked to the loss of lecA. The lecB regions were found less impacted by such rearrangements but greater lecB than lecA genetic divergences were recorded. Sixteen combinations of LecA and LecB types were observed. Amino acid variations were mapped on PAO1 crystal structures. Most significant changes were observed on LecBPA7, and found close to the fucose binding site. Glycan array analyses were performed with purified LecBPA7. LecBPA7 was found less specific for fucosylated oligosaccharides than LecBPAO1, with a preference for H type 2 rather than type 1, and Lewisa rather than Lewisx. Comparison of the crystal structures of LecBPA7 and LecBPAO1 in complex with Lewisa showed these changes in specificity to have resulted from a modification of the water network between the lectin, galactose and GlcNAc residues. Incidence of these modifications on the interactions with calix[4]arene glycomimetics at the cell level was investigated. An aggregation test was used to establish the efficacy of these ligands

  7. Genomic Rearrangements and Functional Diversification of lecA and lecB Lectin-Coding Regions Impacting the Efficacy of Glycomimetics Directed against Pseudomonas aeruginosa

    Science.gov (United States)

    Boukerb, Amine M.; Decor, Aude; Ribun, Sébastien; Tabaroni, Rachel; Rousset, Audric; Commin, Loris; Buff, Samuel; Doléans-Jordheim, Anne; Vidal, Sébastien; Varrot, Annabelle; Imberty, Anne; Cournoyer, Benoit

    2016-01-01

    LecA and LecB tetrameric lectins take part in oligosaccharide-mediated adhesion-processes of Pseudomonas aeruginosa. Glycomimetics have been designed to block these interactions. The great versatility of P. aeruginosa suggests that the range of application of these glycomimetics could be restricted to genotypes with particular lectin types. The likelihood of having genomic and genetic changes impacting LecA and LecB interactions with glycomimetics such as galactosylated and fucosylated calix[4]arene was investigated over a collection of strains from the main clades of P. aeruginosa. Lectin types were defined, and their ligand specificities were inferred. These analyses showed a loss of lecA among the PA7 clade. Genomic changes impacting lec loci were thus assessed using strains of this clade, and by making comparisons with the PAO1 genome. The lecA regions were found challenged by phage attacks and PAGI-2 (genomic island) integrations. A prophage was linked to the loss of lecA. The lecB regions were found less impacted by such rearrangements but greater lecB than lecA genetic divergences were recorded. Sixteen combinations of LecA and LecB types were observed. Amino acid variations were mapped on PAO1 crystal structures. Most significant changes were observed on LecBPA7, and found close to the fucose binding site. Glycan array analyses were performed with purified LecBPA7. LecBPA7 was found less specific for fucosylated oligosaccharides than LecBPAO1, with a preference for H type 2 rather than type 1, and Lewisa rather than Lewisx. Comparison of the crystal structures of LecBPA7 and LecBPAO1 in complex with Lewisa showed these changes in specificity to have resulted from a modification of the water network between the lectin, galactose and GlcNAc residues. Incidence of these modifications on the interactions with calix[4]arene glycomimetics at the cell level was investigated. An aggregation test was used to establish the efficacy of these ligands. Great variations

  8. Arabidopsis Lectin Receptor Kinases LecRK-IX.1 and LecRK-IX.2 Are Functional Analogs in Regulating Phytophthora Resistance and Plant Cell Death.

    Science.gov (United States)

    Wang, Yan; Cordewener, Jan H G; America, Antoine H P; Shan, Weixing; Bouwmeester, Klaas; Govers, Francine

    2015-09-01

    L-type lectin receptor kinases (LecRK) are potential immune receptors. Here, we characterized two closely-related Arabidopsis LecRK, LecRK-IX.1 and LecRK-IX.2, of which T-DNA insertion mutants showed compromised resistance to Phytophthora brassicae and Phytophthora capsici, with double mutants showing additive susceptibility. Overexpression of LecRK-IX.1 or LecRK-IX.2 in Arabidopsis and transient expression in Nicotiana benthamiana increased Phytophthora resistance but also induced cell death. Phytophthora resistance required both the lectin domain and kinase activity, but for cell death, the lectin domain was not needed. Silencing of the two closely related mitogen-activated protein kinase genes NbSIPK and NbNTF4 in N. benthamiana completely abolished LecRK-IX.1-induced cell death but not Phytophthora resistance. Liquid chromatography-mass spectrometry analysis of protein complexes coimmunoprecipitated in planta with LecRK-IX.1 or LecRK-IX.2 as bait, resulted in the identification of the N. benthamiana ABC transporter NbPDR1 as a potential interactor of both LecRK. The closest homolog of NbPDR1 in Arabidopsis is ABCG40, and coimmunoprecipitation experiments showed that ABCG40 associates with LecRK-IX.1 and LecRK-IX.2 in planta. Similar to the LecRK mutants, ABCG40 mutants showed compromised Phytophthora resistance. This study shows that LecRK-IX.1 and LecRK-IX.2 are Phytophthora resistance components that function independent of each other and independent of the cell-death phenotype. They both interact with the same ABC transporter, suggesting that they exploit similar signal transduction pathways.

  9. New insights on the evolution of Leafy cotyledon1 (LEC1) type genes in vascular plants.

    Science.gov (United States)

    Cagliari, Alexandro; Turchetto-Zolet, Andreia Carina; Korbes, Ana Paula; Maraschin, Felipe Dos Santos; Margis, Rogerio; Margis-Pinheiro, Marcia

    2014-01-01

    NF-Y is a conserved oligomeric transcription factor found in all eukaryotes. In plants, this regulator evolved with a broad diversification of the genes coding for its three subunits (NF-YA, NF-YB and NF-YC). The NF-YB members can be divided into Leafy Cotyledon1 (LEC1) and non-LEC1 types. Here we presented a comparative genomic study using phylogenetic analyses to validate an evolutionary model for the origin of LEC-type genes in plants and their emergence from non-LEC1-type genes. We identified LEC1-type members in all vascular plant genomes, but not in amoebozoa, algae, fungi, metazoa and non-vascular plant representatives, which present exclusively non-LEC1-type genes as constituents of their NF-YB subunits. The non-synonymous to synonymous nucleotide substitution rates (Ka/Ks) between LEC1 and non-LEC1-type genes indicate the presence of positive selection acting on LEC1-type members to the fixation of LEC1-specific amino acid residues. The phylogenetic analyses demonstrated that plant LEC1-type genes are evolutionary divergent from the non-LEC1-type genes of plants, fungi, amoebozoa, algae and animals. Our results point to a scenario in which LEC1-type genes have originated in vascular plants after gene expansion in plants. We suggest that processes of neofunctionalization and/or subfunctionalization were responsible for the emergence of a versatile role for LEC1-type genes in vascular plants, especially in seed plants. LEC1-type genes besides being phylogenetic divergent also present different expression profile when compared with non-LEC1-type genes. Altogether, our data provide new insights about the LEC1 and non-LEC1 evolutionary relationship during the vascular plant evolution.

  10. LEC12 and LEC29 gain-of-function Chinese hamster ovary mutants reveal mechanisms for regulating VIM-2 antigen synthesis and E-selectin binding.

    Science.gov (United States)

    Patnaik, Santosh K; Potvin, Barry; Stanley, Pamela

    2004-11-26

    LEC12 and LEC29 are two gain-of-function Chinese hamster ovary glycosylation mutants that express the Fut9 gene encoding alpha(1,3)fucosyltransferase IX (alpha(1,3) Fuc-TIX). Both mutants express the Lewis X (Le(X)) determinant Galbeta(1,4)[Fucalpha(1,3)]GlcNAc, and LEC12, but not LEC29 cells, also express the VIM-2 antigen SAalpha(2,3)-Galbeta(1,4)GlcNAcbeta(1,3)Galbeta(1,4)[Fucalpha(1,3)]GlcNAc. Here we show that LEC29 cells transfected with a Fut9 cDNA express VIM-2, and thus LEC29 cells synthesize appropriate acceptors to generate the VIM-2 epitope. Semiquantitative reverse transcription-PCR showed that LEC12 has 10- to 20-fold less Fut9 gene transcripts than LEC29. However, Western analysis revealed that LEC12 has approximately 20 times more Fut9 protein than LEC29. The latter finding was consistent with our previous observation that LEC12 has approximately 40 times more in vitro alpha(1,3)Fuc-T activity than LEC29. The basis for the difference in Fut9 protein levels was found to lie in sequence differences in the 5'-untranslated regions (5'-UTR) of LEC12 and LEC29 Fut9 gene transcripts. Whereas reporter assays with the respective 5'-UTR regions linked to luciferase did not indicate a reduced translation efficiency caused by the LEC29 5'-UTR, transfected full-length LEC29 Fut9 cDNA or in vitro-synthesized full-length LEC29 Fut9 RNA gave less Fut9 protein than similar constructs with a LEC12 5'-UTR. This difference appears to be largely responsible for the reduced alpha(1,3)Fuc-TIX activity and lack of VIM-2 expression of LEC29 cells. This could be of physiological relevance, because LEC29 and parent Chinese hamster ovary cells transiently expressing a Fut9 cDNA were able to bind mouse E-selectin, although they did not express sialyl-Le(X).

  11. Stoichiometry-controlled compensation in liquid encapsulated Czochralski GaAs

    Science.gov (United States)

    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.

  12. Research on electrical pulse of 20-kV/30-Hz GaAs photoconductive switches

    Institute of Scientific and Technical Information of China (English)

    Jingli Wang; Lin Zhang; Binjie Xin; Xinmei Wang; Hong Liu

    2011-01-01

    Photoconductive semiconductor switches (PCSSs) are widely used in high power ultra-wideband source applications and precise synchronization control due to their high power low-jitter high-repetition-frequency. In this letter, a 14-mm gap semi-insulating GaAs PCSS biased under 20 kV is triggered by a 1064-nm laser with a repetition frequency of 30 Hz. Although the trigger condition is greater than the threshold of the lock-on effect, the high gain mode is not observed. The results indicate that the high gain mode of the PCSS is quenched by decreasing the remnant voltage of pulsed energy storage capacitor.%@@ Photoconductive semiconductor switches (PCSSs) are widely used in high power ultra- wideband source applications and precise synchronization control due to their high power low-jitter high-repetition-frequency.In this letter, a 14-mm gap semi-insulating GaAs PCSS biased under 20 kV is triggered by a 1064-nm laser with a repetition frequency of 30 Hz.Although the trigger condition is greater than the threshold of the lock-on effect, the high gain mode is not observed.The results indicate that the high gain mode of the PCSS is quenched by decreasing the remnant voltage of pulsed energy storage capacitor.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1991-12-31

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

  14. File list: Oth.Oth.50.AllAg.LEC [Chip-atlas[Archive

    Lifescience Database Archive (English)

    Full Text Available Oth.Oth.50.AllAg.LEC hg19 TFs and others Others LEC SRX503332,SRX503331,SRX503334,S...RX503333 http://dbarchive.biosciencedbc.jp/kyushu-u/hg19/assembled/Oth.Oth.50.AllAg.LEC.bed ...

  15. File list: Oth.Oth.05.AllAg.LEC [Chip-atlas[Archive

    Lifescience Database Archive (English)

    Full Text Available Oth.Oth.05.AllAg.LEC hg19 TFs and others Others LEC SRX503332,SRX503331,SRX503334,S...RX503333 http://dbarchive.biosciencedbc.jp/kyushu-u/hg19/assembled/Oth.Oth.05.AllAg.LEC.bed ...

  16. Autonomous Control System for Czochralski Growth of LEC GaAs

    Science.gov (United States)

    1987-12-29

    is an Intel Single Board Computer , including an 8085 microprocessor, 16 KBytes of read-only memory, 8 KBytes of random access memory, and an...Intel’s Multibus. The CPU consists of a Single Board Computer (iSBC 80-24) that holds the 8085 CPU, an 8-bit processor than can address up to 64 KBytes... Single Board Computer includes 2x8 KBytes of ROM and 8 KBytes of RAM. An additional 64 KBytes of RAM is provided by a Memory Expansion board (iSBC 064A

  17. Method of Automated Dynamic Assessment of reading literacy for Secondary Education (EdilLEC)/'Metodo de evaluacion dinamica automatizado' de competencias lectoras para educacion secundaria (EdiLEC)

    National Research Council Canada - National Science Library

    Perez, Ramiro Gilabert; Lloria, Amelia Mana; Pelluch, Laura Gil; Tatay, Ana C. Llorens; Clemente, Vicenta Avila; Gamez, Eduardo Vidal-Abarca

    2016-01-01

    .... Keywords reading literacy; PISA; dynamic assessment; Secondary Education Se presenta un nuevo metodo de evaluacion dinamica de la competencia lectora automatizado para educacion secundaria (EdiLEC...

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

    Science.gov (United States)

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

    2016-12-01

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

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

    Science.gov (United States)

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

    1998-05-01

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

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

    Science.gov (United States)

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-07-28

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

  2. Wavelength dependent laser-induced etching of Cr–O doped GaAs: Morphology studies by SEM and AFM

    Indian Academy of Sciences (India)

    B Joshi; S S Islam; H S Mavi; Vinita Kumari; T Islam; A K Shukla; Harsh

    2009-02-01

    The laser induced etching of semi-insulating GaAs $\\langle$100$\\rangle$ is carried out to create porous structure under super- and sub-bandgap photon illumination (ℎν). The etching mechanism is different for these separate illuminations where defect states play the key role in making distinction between these two processes. Separate models are proposed for both the cases to explain the etching efficiency. It is observed that under sub-bandgap photon illumination the etching process starts vigorously through the mediation of intermediate defect states. The defect states initiate the pits formation and subsequently pore propagation occurs due to asymmetric electric field in the pore. Formation of GaAs nanostructures is observed using scanning electron (SEM) and atomic force microscopy (AFM).

  3. Zinc supplementation decreases hepatic copper accumulation in LEC rat: a model of Wilson's disease.

    Science.gov (United States)

    Gonzalez, Blanca P Esparza; Niño Fong, Rodolfo; Gibson, Candace J; Fuentealba, I Carmen; Cherian, M George

    2005-01-01

    The effect of dietary zinc (Zn) supplementation on copper (Cu)-induced liver damage was investigated in Long-Evans Cinnamon rats (LEC), a model for Wilson's disease (WD). Four-week-old LEC (N=64) and control Long-Evans (LE) (N=32) female rats were divided into two groups; one group was fed with a Zn-supplemented diet (group I) and the other was given a normal rodent diet (group II). LEC rats were killed at 6, 8, 10, 12, 18, and 20 wk of age; the LE control rats were killed at 6, 12, 18, and 20 wk of age. Cu concentration in the liver was reduced in LEC rats fed the Zn-supplemented diet compared with LEC rats on the normal diet between 6 and 18 wk of age. Metallothionein (MT) concentration in the livers of LEC rats in group I increased between 12 and 20 wk of age, whereas hepatic MT concentration in LEC rats from group II decreased after 12 wk. Hepatocyte apoptosis, as determined by TUNEL, was reduced in Zn-supplemented LEC rats at all ages. Cholangiocellular carcinoma was observed only in LEC rats in group II at wk 20. These results suggest that Zn supplementation can reduce hepatic Cu concentration and delay the onset of clinical and pathological changes of Cu toxicity in LEC rats. Although the actual mechanism of protection is unknown, it could be explained by sequestration of dietary Cu by intestinal MT, induced by high dietary Zn content.

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

    Science.gov (United States)

    Ricco, Bruno

    1986-06-01

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

  5. A detailed model for defect concentration and dopant activation in GaAs

    Indian Academy of Sciences (India)

    Deepak; N Lakshminarayana

    2001-04-01

    Defects in semi-insulating (SI) GaAs are especially critical in determining the properties of devices in which dopants are introduced by ion-implantation. The defects in GaAs are native to the material and their concentrations are subsequently modified after ion-implantation and annealing. In this work, we have extended the existing models in the literature by incorporating a large set of defects and using the most recent values for formation energies of these defects. The model includes eight types of point defects, the vacancy of Ga and As, their antisites and interstitials of Ga and As on both sub-lattices, along with carbon related defects always present in SI–GaAs. We have also included Si and related defects when this element is implanted as an -type dopant. All these defects are considered in several charge states allowed by their stability conditions. The model assumes thermodynamic equilibrium between the point defects at an anneal temperature. Then the GaAs wafer is quenched so that the number of defects remain the same as those at the anneal temperature, but redistribution of charges occurs in various charge states. We find that the defect concentrations are extremely sensitive to the crystal stoichiometry, and good agreement with experimental data is shown. However, when we calculate the dopant activation in implanted GaAs, the quantitative agreement with experiments is not adequate. This discrepancy is explained on the basis of available formation energies for the defects.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-03-15

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

  7. Photovoltaic Response Characteristics of GaAs Photoconductive Switches Under High Gain Mode

    Institute of Scientific and Technical Information of China (English)

    DAI Hui-ying; SHI Wei

    2007-01-01

    Given is the experiment results in which the laser pulses of 1 046 nm and 532 nm are used to trigger the semi-insulation GaAs photoconductive semiconductor switch(PCSS) with an electrode distance of 4 mm. And made is an analysis of the switch's photovoltaic response characteristics under the high gain mode when the biased field is bigger than the Geng effect field. Also a theory is presented that the main reason for the photovoltaic pulse response delay is the transmission of charge domain, caused by the presence of EL2 energy level in the chip material. Finally, the transmission time of charge domain is calculated and a result that inosculates with the experiment is attained.

  8. MBE growth and properties of Cr-doped ZnTe on GaAs(001)

    Energy Technology Data Exchange (ETDEWEB)

    Hou, X.J. [Data Storage Institute, 5 Engineering Drive 1, Singapore 117608 (Singapore); Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Teo, K.L. [Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore)]. E-mail: eleteokl@nus.edu.sg; Sreenivasan, M.G. [Data Storage Institute, 5 Engineering Drive 1, Singapore 117608 (Singapore); Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Liew, T. [Data Storage Institute, 5 Engineering Drive 1, Singapore 117608 (Singapore); Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Chong, T.C. [Data Storage Institute, 5 Engineering Drive 1, Singapore 117608 (Singapore); Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore)

    2006-05-18

    Cr-doped ZnTe diluted magnetic semiconductor thin films were grown on semi-insulating GaAs [001] substrates at low temperature by solid-source molecular-beam epitaxy. Zn{sub 1-x}Cr {sub x}Te samples with Cr concentrations x 0.026 and x = 0.141 were prepared. The magnetization versus magnetic field (M-H) measurement showed a clear hysteresis loop at low temperature for these samples. For higher Cr doping with nominal Cr concentration of x > 0.18, we obtained a Curie temperature of 365 K; the highest reported so far for thin film sample. However, this strong ferromagnetic momentum could possibly be due to Cr{sub 1-{delta}}Te precipitate in the Cr-doped ZnTe system.

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

    Energy Technology Data Exchange (ETDEWEB)

    Gurevich, E L; Kittel, S; Hergenroeder, R [Leibniz-Institut fuer Analytische Wissenschaften-ISAS-e.V., 44139 Dortmund (Germany); Astrov, Yu A; Portsel, L M; Lodygin, A N; Tolmachev, V A; Ankudinov, A V, E-mail: evgeny.gurevich@isas.d, E-mail: yuri.astrov@mail.ioffe.r [Ioffe Physico-Technical Institute, RAS, 194021 St Petersburg (Russian Federation)

    2010-07-14

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

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

    Science.gov (United States)

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

    2010-07-01

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

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

    CERN Document Server

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

    1999-01-01

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

  12. Poole-Frenkel effect and phonon-assisted tunneling in GaAs nanowires.

    Science.gov (United States)

    Katzenmeyer, Aaron M; Léonard, François; Talin, A Alec; Wong, Ping-Show; Huffaker, Diana L

    2010-12-08

    We present electronic transport measurements of GaAs nanowires grown by catalyst-free metal-organic chemical vapor deposition. Despite the nanowires being doped with a relatively high concentration of substitutional impurities, we find them inordinately resistive. By measuring sufficiently high aspect ratio nanowires individually in situ, we decouple the role of the contacts and show that this semi-insulating electrical behavior is the result of trap-mediated carrier transport. We observe Poole-Frenkel transport that crosses over to phonon-assisted tunneling at higher fields, with a tunneling time found to depend predominantly on fundamental physical constants as predicted by theory. By using in situ electron beam irradiation of individual nanowires, we probe the nanowire electronic transport when free carriers are made available, thus revealing the nature of the contacts.

  13. Efficient LEC2 activation of OLEOSIN expression requires two neighboring RY elements on its promoter

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    As the main structural protein of oil body,OLEOSIN is highly expressed only during seed development. OLEOSIN promoter is a very useful tool for seed-specific gene engineering and seed bioreactor designing. The B3 domain transcription factor leafy cotyledon2 (LEC2) plays an important role in regulating seed development and seed-specific gene expression. Here,we first report how seed-specific B3 domain transcription factor leafy cotyledon2 (LEC2) efficiently activates OLEOSIN expression. The central promoter region of OLEOSIN,responsible for seed specificity and LEC2 activation,was determined by 5’-deletion analysis. Binding experiments in yeast cells and electrophoretic mobility shift assays showed that LEC2 specifically bound to two conserved RY elements in this region. In transient expression assays,mutation in either RY element dramatically reduced LEC2 activation of OLEOSIN promoter activity,while double mutation abolished it. Analysis of the distribution of RY elements in seed-specific genes activated by LEC2 also supported the idea that genes containing neighboring RY elements responded strongly to LEC2 activation. Therefore,we conclude that two neighboring RY elements are essential for efficient LEC2 activation of OLEOSIN expression. These findings will help us better utilize seed-specific promoter activity.

  14. Efficient LEC2 activation of OLEOSIN expression requires two neighboring RY elements on its promoter

    Institute of Scientific and Technical Information of China (English)

    CHE NanYing; YANG Yang; LI YanDong; WANG LiLi; HUANG Ping; GAO Yin; An ChengCai

    2009-01-01

    As the main structural protein of oil body, OLEOSIN is highly expressed only during seed development. OLEOSIN promoter is a very useful tool for seed-specific gene engineering and seed bioreactor designing. The B3 domain transcription factor leafy cotyledon2 (LEC2) plays an important role in regulating seed development and seed-specific gene expression. Here, we first report how seed-specific B3 domain transcription factor leafy cotyledon2 (LEC2) efficiently activates OLEOSIN expression. The central promoter region of OLEOSIN, responsible for seed specificity and LEC2 activation, was determined by 5'-deletion analysis. Binding experiments in yeast cells and electrophoretic mobility shift assays showed that LEC2 specifically bound to two conserved RY elements in this region, in transient expression assays, mutation in either RY element dramatically reduced LEC2 activation of OLEOSIN promoter activity, while double mutation abolished it. Analysis of the distribution of RY elements in seed-specific genes activated by LEC2 also supported the idea that genes containing neighboring RY elements responded strongly to LEC2 activation. Therefore, we conclude that two neighboring RY elements are essential for efficient LEC2 activation of OLEOSIN expression. These findings will help us better utilize seed-specific promoter activity.

  15. Abnormal hepatic copper accumulation of spheroid composed of liver cells from LEC rats in vitro.

    Science.gov (United States)

    Ueno, K; Yoshizawa, M; Satoh, T; Yoneda, S; Ohmichi, M; Yamazaki, M; Mori, Y; Suzuki, K T

    1995-11-01

    The LEC rat is a mutant strain displaying hereditary hepatitis, and shows abnormal accumulation of copper (Cu) similar to that occurring in Wilson's disease. We prepared a multicellular spheroid composed of LEC rat liver cells to investigate the mechanism for abnormal accumulation of Cu. These multicellular spheroids were prepared by detaching the monolayer on the collagen-conjugated thermo-responsive polymer coated culture dish at a temperature below the critical solution temperature and culturing on the non-adhesive substratum. Long-term cultured spheroids of LEC rat liver cells as well as SD rat liver cells were attempted. Non-parenchymal cells obtained by collagenase perfusion from the LEC liver were fewer than those from the SD liver. Cells from the LEC rat, over 11 weeks of age, did not form a cell sheet; however, a mixture of parenchymal cells from LEC rats over aged 11 weeks and non-parenchymal cells from SD rats of any age yielded intact spheroids. We examined the toxicity, the accumulation and distribution of Cu in spheroids. The accumulation of Cu in LEC spheroids was higher than that in SD spheroids. Results suggest that spheroids consisting of LEC liver cells are useful as an alternative model to in vivo tests to investigate the mechanism for abnormal accumulation of Cu in liver.

  16. Comparison of semi-insulating InAlAs and InP:Fe for InP-based buried-heterostructure QCLs

    Science.gov (United States)

    Flores, Y. V.; Aleksandrova, A.; Elagin, M.; Kischkat, J.; Kurlov, S. S.; Monastyrskyi, G.; Hellemann, J.; Golovynskyi, S. L.; Dacenko, O. I.; Kondratenko, S. V.; Tarasov, G. G.; Semtsiv, M. P.; Masselink, W. T.

    2015-09-01

    In a previous work [Flores et al., J. Cryst. Growth 398 (2014) 40] [3] we demonstrated the advantages of using a thin InAlAs spacer layer in the fabrication of buried-heterostructure quantum-cascade lasers (QCLs), as it improves the morphology of the interface between the laser core and the InP:Fe lateral cladding. In this paper we investigate aspects of InAlAs, which are relevant for its role as insulating lateral cladding of the laser sidewalls: carrier traps, electrical resistivity, and functionality as a sole lateral cladding. We find that a thin InAlAs spacer layer not only improves the regrowth interface morphology, but also eliminates interface-related shallow electronic states, thus improving the electrical resistivity of the interface. We further find that bulk InAlAs grown by gas-source molecular-beam epitaxy as well as InP:Fe are semi-insulating at room temperature, with specific resistivities of 3 ×107 Ω cm and 2 ×108 Ω cm, respectively. Both materials have also a high thermal activation energy for electrical conductivity (0.79 eV and 0.68 eV, respectively). In order to compare the performance of InP:Fe and InAlAs as a lateral cladding, lasers were fabricated from the same QCL wafer with differing stripe insulation materials. The resulting lasers differ mainly by the lateral insulation material: SiO2, InP:Fe (with InAlAs spacer), and pure InAlAs. All devices show a similar performance and similar temperature dependence, indicating insulating properties of InAlAs adequate for application in lateral regrowth of buried-heterostructure QCLs.

  17. Migration processes of the As interstitial in GaAs

    Science.gov (United States)

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

    2016-12-01

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

  18. Inactivation of wine spoilage yeasts Dekkera bruxellensis using low electric current treatment (LEC).

    Science.gov (United States)

    Lustrato, G; Vigentini, I; De Leonardis, A; Alfano, G; Tirelli, A; Foschino, R; Ranalli, G

    2010-08-01

    The objective of this study was to investigate the inactivation of a selected yeast Dekkera bruxellensis strain 4481 in red wine by application of low electric current treatment (LEC). LEC (200 mA) was applied for 60 days to a red wine, Montepulciano d'Abruzzo, in an alternative strategy to the SO(2) addition during wine storage. The LEC effect on both cell activity and microflora viability was assessed. LEC decreased significantly the survival viable cells and increased the death rate of D. bruxellensis strain 4481 yeast. A final comparison was made of the main physico-chemical parameters of the wine after the different treatments. The study suggests the importance of an appropriate LEC treatment which limits wine deterioration in terms of off-flavours synthesis. The results demonstrate that the growth of undesirable Dekkera can be inhibited by low voltage treatment; LEC was shown to be useful to prevent wine spoilage and has the potential of being a concrete alternative method for controlling wine spoilage. Wine spoilage can be avoided by preventing the growth of undesirable Dekkera yeasts, through the effective use of LEC in the winemaking process.

  19. THz conductivity of semi-insulating and magnetic CoFe2O4 nano-hollow structures through thermally activated polaron

    Science.gov (United States)

    Rakshit, Rupali; Serita, Kazunori; Tonouchi, Masayoshi; Mandal, Kalyan

    2016-11-01

    Herein, terahertz (THz) time domain spectroscopy is used to measure the complex conductivity of semi-insulating CoFe2O4 nanoparticles (NPs) and nano-hollow spheres (NHSs) with different diameters ranging from 100 to 350 nm having a nanocrystalline shell thickness of 19 to 90 nm, respectively. Interestingly, the magnitude of conductivity for CoFe2O4 NPs and NHSs of same average diameter (˜100 nm) for a given frequency of 0.3 THz is found to be 0.33 S/m and 9.08 S/m, respectively, indicating that the hollow structure exhibits greater THz conduction in comparison to its solid counterpart. Moreover, THz conductivity can be tailored by varying the nano-shell thickness of NHSs, and a maximum conductivity of 15.61 S/m is observed at 0.3 THz for NHSs of average diameter 250 nm. A detailed study reveals that thermally activated polaronic hopping plays the key role in determining the electrical transport property of CoFe2O4 nanostructures, which is found to solely depend on their magnitude of THz absorptivity. The non-Drude conductivity of all CoFe2O4 nanostructures is well described by the Polaron model instead of the Drude-Smith model, which is relevant for backscattering of free electrons in a nanostructured material. The Polaron model includes intra-particle and interparticle polaronic conductivities for closely spaced magnetic nanostructures and provides a mean free path of 29 nm for CoFe2O4 NPs of diameter 100 nm, which is comparable with its average crystallite size, indicating the applicability of the developed model for nanomaterials where charge transport is determined by polaronic hopping. Finally, we have demonstrated the morphology and size dependent magnetic measurements of ferrimagnetically aligned CoFe2O4 nanostructures through a vibrating sample magnetometer in the temperature range of 80-250 K, revealing that the disordered surface spin layer of nanostructures significantly controls their magnetism.

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

    Science.gov (United States)

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

    2016-12-01

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

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

    CERN Document Server

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

    2012-01-01

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

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

    CERN Document Server

    Boardman, D

    2002-01-01

    A new monolithic semi-insulating (SI) GaAs sensor design for X-ray imaging applications between 10-100keV has been proposed. Monolithic pixel detectors offer a number of advantages over hybrid bump-bonded detectors, such as high device yield, low costs and are easier to produce large scale arrays. In this thesis, an investigation is made of the use of a SI GaAs wafer as both a detector element and substrate for the epitaxially grown High Electron Mobility Transistors (HEMTs). The design of the HEMT transistors, optimised for this application, were produced with the aid of the Silvaco 'Virtual Wafer Fab' simulation package. It was determined that the device characteristics would consist of a small positive threshold voltage, a low off-state drain current and high transconductance. The final HEMT transistor design, that would be integrated to a pixel detector, had a threshold voltage of 0.17V, an off-state leakage current of approx 1nA and a transconductance of 7.4mS. A number of test detectors were characteris...

  3. Single CRD containing lectin from Macrobrachium rosenbergii (MrLec) participates in innate immunity against pathogen infections.

    Science.gov (United States)

    Huang, Xin; Li, Wen; Jin, Min; Ma, Fu-Tong; Huang, Ying; Shi, Yan-Ru; Zhao, Ling-Ling; Feng, Jin-Ling; Ren, Qian; Wang, Wen

    2016-04-01

    As a type of pattern-recognition proteins, lectins perform important functions in the innate immunity of crustaceans, including prawns. Although several reports showed that C-type lectin domain family (CLEC) importantly functions in host-pathogen interactions, limited research has focused on CLEC in Macrobrachium rosenbergii. In the present study, a new single CRD containing CLEC (designated as MrLec) was reported in freshwater prawns, M. rosenbergii. The full-length cDNA of MrLec consisted of 1027 bp with an open reading frame of 801 bp, which encoded a peptide of 266 amino acid residues. Genomic sequence for MrLec was also obtained from the M. rosenbergii, which contain 4 exons and 3 introns. MrLec was found to contain a single carbohydrate-recognition domain with an EPN motif. MrLec was ubiquitously distributed in various tissues of a normal prawn, particularly in the hepatopancreas and gills. MrLec expression in the gills was significantly upregulated after a challenge with Vibrio parahaemolyticus and downregulated at 24 h after MrLec RNA interference (MrLec-RNAi). The expression levels of some AMPs, including antilipopolysaccharide factor 1 (Alf1) and lysozyme 2 (Lyso2), also markedly decreased after MrLec-RNAi. Recombinant MrLec can agglutinate (Ca(2+)-dependent) and bind both Gram-negative and Gram-positive bacteria. Results suggested that MrLec participates in the recognition of invading pathogens and functions in the immune response of prawn against pathogen infections.

  4. Mechanism of enhanced lipid peroxidation in the liver of Long-Evans cinnamon (LEC) rats.

    Science.gov (United States)

    Yamamoto, H; Hirose, K; Hayasaki, Y; Masuda, M; Kazusaka, A; Fujita, S

    1999-11-01

    The Long-Evans Cinnamon (LEC) rat is a mutant strain of rats that accumulate copper (Cu) in the liver in much the same way as individuals who suffer from Wilson's disease (WD) and has been suggested as a model for this disease. Lipid peroxidation (LPO) is considered to be involved in the toxic action of Cu in the livers of LEC rats. We investigated the mechanism of LPO in the livers of LEC rats showing apparent signs of hepatitis. Several-fold higher LPO levels were observed in post-mitochondrial supernatant (S-9) fraction of livers from hepatitic LEC rats than in those from Wistar rats. To mimic living cells, we introduced NADPH-generating system (NADPH-gs) into the S-9 incubation system. Thus was ensured a constant supply of NADPH to vital enzymes that may be directly or indirectly involved in the generation and/or elimination of reactive oxygen species (ROSs), such as glutathione reductase (GSSG-R), which require NADPH for their reactions. The levels of LPO in liver S-9 from hepatitic LEC rats were further increased by incubating liver S-9 at 37 degrees C in the presence of NADPH-gs. This increase was inhibited by EDTA, butylated hydroxytoluene (BHT), and catalase (CAT), suggesting that some metal, most likely the accumulated Cu, and ROSs derived from hydrogen peroxide (H2O2) are involved in the increased levels of LPO in the livers of hepatitic LEC rats. The requirement of NADPH-gs for enhanced LPO in the livers of hepatitic LEC rats indicates the consumption of NADPH during reactions leading to LPO. It is known that H2O2, and consequently hydroxyl radical are generated during Cu-catalyzed glutathione (GSH) oxidation. The cyclic regeneration of GSH from GSSG by NADPH-dependent GSSG-R in the presence of NADPH-gs may cause sustained generation of hydroxyl radical in the presence of excess free Cu. The generation of H2O2 in S-9 fraction of livers from hepatitic LEC rats was observed to be significantly higher than that in S-9 fraction of livers from non

  5. Copper balance and ceruloplasmin in chronic hepatitis in a Wilson disease animal model, LEC rats

    Energy Technology Data Exchange (ETDEWEB)

    Komatsu, Yutaka; Ogra, Yasumitsu; Suzuki, Kazuo T. [Graduate School of Pharmaceutical Sciences, Chiba University, Inage, Chiba 263-8522 (Japan)

    2002-09-01

    In an animal model of Wilson disease, Long-Evans rats with cinnamon-colored coat (LEC rats), copper (Cu) accumulates in the liver with age up to the onset of acute hepatitis owing to a hereditary defective transporter for the efflux of Cu, ATP7B. The plasma Cu concentration is low in LEC rats because of the excretion of apo-ceruloplasmin (apo-Cp). However, toward and after the onset of chronic hepatitis, plasma Cu concentration increases in the form of holo-Cp, while the liver Cu concentration is maintained at a constant level without the occurrence of fulminant hepatitis. In the present study, the material balance of Cu was studied in LEC rats with chronic hepatitis in order to elucidate the mechanisms underlying the increase of holo-Cp in plasma and the maintenance of Cu at a constant level in the liver. The relationship between the Cu concentration and ferroxidase activity of Cp was analyzed in the plasma of LEC rats of different ages and of Wistar rats fed a Cu-deficient diet for different durations. Cu was suggested to be delivered to Cp in an all-or-nothing manner, resulting in the excretion of fully Cu-occupied holo-Cp (Cu{sub 6}-Cp) or totally Cu-unoccupied Cu{sub 0}-Cp (apo-Cp), but not partially Cu-occupied Cu{sub n}-Cp (where n=1-5). The increase of holo-Cp in acute and chronic hepatitis in LEC rats was explained by the delivery of Cu, accumulating in the non-metallothionein-bound form, to Cp outside the Golgi apparatus of the liver. The plasma Cu concentration and ferroxidase activity were proposed to be specific indicators of the appearance of non-metallothionein-bound Cu in the liver of LEC rats. (orig.)

  6. Structural Insight into Multivalent Galactoside Binding to Pseudomonas aeruginosa Lectin LecA

    NARCIS (Netherlands)

    Visini, Ricardo; Jin, Xian; Bergmann, Myriam; Michaud, Gaelle; Pertici, Francesca; Fu, Ou; Pukin, Aliaksei; Branson, Thomas R.; Thies-Weesie, Dominique M E; Kemmink, Johan; Gillon, Emilie; Imberty, Anne; Stocker, Achim; Darbre, Tamis; Pieters, Roland J.; Reymond, Jean Louis

    2015-01-01

    Multivalent galactosides inhibiting Pseudomonas aeruginosa biofilms may help control this problematic pathogen. To understand the binding mode of tetravalent glycopeptide dendrimer GalAG2 [(Gal-β-OC6H4CO-Lys-Pro-Leu)4(Lys-Phe-Lys-Ile)2Lys-His-Ile-NH2] to its target lectin LecA, crystal structures of

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

    Science.gov (United States)

    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.

  8. Multiple charge domains model for the lock-on effect in GaAs power photoconductive switches

    Energy Technology Data Exchange (ETDEWEB)

    Tian Liqiang; Shi Wei [Department of Applied Physics, Xi' an University of Technology, Xi' an 710048 (China)], E-mail: swshi@mail.xaut.edu.cn

    2008-06-07

    This paper reports that the lock-on field of semi-insulating (SI) GaAs photoconductive semiconductor switches (PCSSs) was measured under different bias voltages. Based on the experimental results and the transferred-electron effect, a model for the lock-on effect in GaAs PCSSs is proposed. It is shown that the charge domain with an ultrahigh electric field is due to a high photogenerated carrier density, which gives rise to intensive impact ionization accompanied by electron-hole recombination radiation within the domain. Since new domains can be nucleated uninterruptedly by the carriers generated by absorption of recombination radiation, the forefront domain crosses the switch at a speed alternating between the photon velocity and the carrier saturated drift velocity, which makes the observed velocity of carriers larger than the saturated drift velocity. The lock-on field results from the fixed number of a moving train of avalanching charge domains, the steady-state domains electric fields and the steadfast external electric field of the domains. The recovery of the lock-on effect is caused by domain quenching. The calculations agree with the experimental results. Moreover, the analytical results indicate that SI-GaAs PCSS is essentially a type of photo-activated charge domain device.

  9. The Theobroma cacao B3 domain transcription factor TcLEC2 plays a duel role in control of embryo development and maturation.

    Science.gov (United States)

    Zhang, Yufan; Clemens, Adam; Maximova, Siela N; Guiltinan, Mark J

    2014-04-24

    The Arabidopsis thaliana LEC2 gene encodes a B3 domain transcription factor, which plays critical roles during both zygotic and somatic embryogenesis. LEC2 exerts significant impacts on determining embryogenic potential and various metabolic processes through a complicated genetic regulatory network. An ortholog of the Arabidopsis Leafy Cotyledon 2 gene (AtLEC2) was characterized in Theobroma cacao (TcLEC2). TcLEC2 encodes a B3 domain transcription factor preferentially expressed during early and late zygotic embryo development. The expression of TcLEC2 was higher in dedifferentiated cells competent for somatic embryogenesis (embryogenic calli), compared to non-embryogenic calli. Transient overexpression of TcLEC2 in immature zygotic embryos resulted in changes in gene expression profiles and fatty acid composition. Ectopic expression of TcLEC2 in cacao leaves changed the expression levels of several seed related genes. The overexpression of TcLEC2 in cacao explants greatly increased the frequency of regeneration of stably transformed somatic embryos. TcLEC2 overexpressing cotyledon explants exhibited a very high level of embryogenic competency and when cultured on hormone free medium, exhibited an iterative embryogenic chain-reaction. Our study revealed essential roles of TcLEC2 during both zygotic and somatic embryo development. Collectively, our evidence supports the conclusion that TcLEC2 is a functional ortholog of AtLEC2 and that it is involved in similar genetic regulatory networks during cacao somatic embryogenesis. To our knowledge, this is the first detailed report of the functional analysis of a LEC2 ortholog in a species other then Arabidopsis. TcLEC2 could potentially be used as a biomarker for the improvement of the SE process and screen for elite varieties in cacao germplasm.

  10. Passive Q-Switching in a Flash-Lamp Pumped Nd∶YAG Laser with Ion-Implanted GaAs Wafer%用离子注入GaAs晶片实现闪光灯泵浦Nd∶YAG激光器中的被动调Q

    Institute of Scientific and Technical Information of China (English)

    王勇刚; 李朝阳; 马骁宇; 张志刚

    2004-01-01

    A passive Q-switched flash-lamp-pumped Nd∶YAG laser with the ion-implanted semi-insulating GaAs wafer is reported.The wafer is implanted with 400keV As+ ions in the concentration of 1016cm-2.Using GaAs wafer as an absorber and an output coupler,62ns pulse duration of single pulse is obtained.%对半绝缘GaAs晶片进行As+注入,注入能量为400keV,剂量为1016cm-2.用这种注入条件下的GaAs晶片作为吸收体和输出镜,在被动调Q闪光灯泵浦的Nd∶YAG激光器上获得了62ns的单脉冲宽度.这是迄今为止国内最好的报道结果.

  11. Specific association of lectin LecB with the surface of Pseudomonas aeruginosa: role of outer membrane protein OprF.

    Directory of Open Access Journals (Sweden)

    Horst Funken

    Full Text Available The fucose binding lectin LecB affects biofilm formation and is involved in pathogenicity of Pseudomonas aeruginosa. LecB resides in the outer membrane and can be released specifically by treatment of an outer membrane fraction with fucose suggesting that it binds to specific ligands. Here, we report that LecB binds to the outer membrane protein OprF. In an OprF-deficient P. aeruginosa mutant, LecB is no longer detectable in the membrane but instead in the culture supernatant indicating a specific interaction between LecB and OprF.

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

    Science.gov (United States)

    Tian, Liqiang; Shi, Wei; Feng, Qingqing

    2011-11-01

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

  13. The Arabidopsis lectin receptor kinase LecRK-I.9 enhances resistance to Phytophthora infestans in Solanaceous plants.

    Science.gov (United States)

    Bouwmeester, Klaas; Han, Miao; Blanco-Portales, Rosario; Song, Wei; Weide, Rob; Guo, Li-Yun; van der Vossen, Edwin A G; Govers, Francine

    2014-01-01

    Late blight caused by the plant pathogenic oomycete Phytophthora infestans is known as one of the most destructive potato diseases. Plant breeders tend to employ NB-LRR-based resistance for introducing genetically controlled late blight resistance in their breeding lines. However, P. infestans is able to rapidly escape this type of resistance, and hence, NB-LRR-based resistance in potato cultivars is often not durable. Previously, we identified a novel type of Phytophthora resistance in Arabidopsis. This resistance is mediated by the cell surface receptor LecRK-I.9, which belongs to the family of L-type lectin receptor kinases. In this study, we report that expression of the Arabidopsis LecRK-I.9 gene in potato and Nicotiana benthamiana results in significantly enhanced late blight resistance. Transcriptional profiling showed strong reduction in salicylic acid (SA)-mediated defence gene expression in LecRK-I.9 transgenic potato lines (TPLs). In contrast, transcripts of two protease inhibitor genes accumulated to extreme high levels, suggesting that LecRK-I.9-mediated late blight resistance is relying on a defence response that includes activation of protease inhibitors. These results demonstrate that the functionality of LecRK-I.9 in Phytophthora resistance is maintained after interfamily transfer to potato and N. benthamiana and suggest that this novel type of LecRK-based resistance can be exploited in breeding strategies to improve durable late blight resistance in Solanaceous crops.

  14. Structural basis of preferential binding of fucose-containing saccharide by the Caenorhabditis elegans galectin LEC-6.

    Science.gov (United States)

    Makyio, Hisayoshi; Takeuchi, Tomoharu; Tamura, Mayumi; Nishiyama, Kazusa; Takahashi, Hideyo; Natsugari, Hideaki; Arata, Yoichiro; Kasai, Ken-Ichi; Yamada, Yusuke; Wakatsuki, Soichi; Kato, Ryuichi

    2013-07-01

    Galectins are a group of lectins that can bind carbohydrate chains containing β-galactoside units. LEC-6, a member of galectins of Caenorhabditis elegans, binds fucose-containing saccharides. We solved the crystal structure of LEC-6 in complex with galactose-β1,4-fucose (Galβ1-4Fuc) at 1.5 Å resolution. The overall structure of the protein and the identities of the amino-acid residues binding to the disaccharide are similar to those of other galectins. However, further structural analysis and multiple sequence alignment between LEC-6 and other galectins indicate that a glutamic acid residue (Glu67) is important for the preferential binding between LEC-6 and the fucose moiety of the Galβ1-4Fuc unit. Frontal affinity chromatography analysis indicated that the affinities of E67D and E67A mutants for Galβ1-4Fuc are lower than that of wild-type LEC-6. Furthermore, the affinities of Glu67 mutants for an endogenous oligosaccharide, which contains a Galβ1-4Fuc unit, are drastically reduced relative to that of the wild-type protein. We conclude that the Glu67 in the oligosaccharide-binding site assists the recognition of the fucose moiety by LEC-6.

  15. Multivalency effects on Pseudomonas aeruginosa biofilm inhibition and dispersal by glycopeptide dendrimers targeting lectin LecA.

    Science.gov (United States)

    Bergmann, Myriam; Michaud, Gaëlle; Visini, Ricardo; Jin, Xian; Gillon, Emilie; Stocker, Achim; Imberty, Anne; Darbre, Tamis; Reymond, Jean-Louis

    2016-01-01

    The galactose specific lectin LecA partly mediates the formation of antibiotic resistant biofilms by Pseudomonas aeruginosa, an opportunistic pathogen causing lethal airways infections in immunocompromised and cystic fibrosis patients, suggesting that preventing LecA binding to natural saccharides might provide new opportunities for treatment. Here 8-fold (G3) and 16-fold (G4) galactosylated analogs of GalAG2, a tetravalent G2 glycopeptide dendrimer LecA ligand and P. aeruginosa biofilm inhibitor, were obtained by convergent chloroacetyl thioether (ClAc) ligation between 4-fold or 8-fold chloroacetylated dendrimer cores and digalactosylated dendritic arms. Hemagglutination inhibition, isothermal titration calorimetry and biofilm inhibition assays showed that G3 dendrimers bind LecA slightly better than their parent G2 dendrimers and induce complete biofilm inhibition and dispersal of P. aeruginosa biofilms, while G4 dendrimers show reduced binding and no biofilm inhibition. A binding model accounting for the observed saturation of glycopeptide dendrimer galactosyl groups and LecA binding sites is proposed based on the crystal structure of a G3 dendrimer LecA complex.

  16. Application of lectin microarray to crude samples: differential glycan profiling of lec mutants.

    Science.gov (United States)

    Ebe, Youji; Kuno, Atsushi; Uchiyama, Noboru; Koseki-Kuno, Shiori; Yamada, Masao; Sato, Takashi; Narimatsu, Hisashi; Hirabayashi, Jun

    2006-03-01

    We recently developed a novel system for lectin microarray based on the evanescent-field fluorescence-detection principle, by which even weak lectin-oligosaccharide interactions are detectable without a washing procedure. For its practical application, cell glycan analysis was performed for Chinese hamster ovary (CHO) cells and their glycan profile was compared with those of their glycosylation-defective Lec mutants. Each of the cell surface extracts gave a significantly different profile from that of the parental CHO cells in a manner reflecting denoted biosynthetic features. Hence, the developed lectin microarray system is considered to be fully applicable for differential glycan profiling of crude samples.

  17. El juicio cambiario en el borrador de anteproyecto de LEC de abril de 1997

    OpenAIRE

    Bonet Navarro, José

    1997-01-01

    Este trabajo es fruto de dos comunicaciones. En su primera parte, es síntesis de la comunicación titulada "Reflexiones sobre algunos aspectos generales del juicio cambiario", presentada y defendida oralmente en las "Jornadas Nacionales sobre el anteproyecto de Ley de Enjuiciamiento Civil " (Murcia, 7 a 10 de octubre de 1997). En su seginda parte se reproduce la comunicación titulada "Algunos aspectos particulares del juicio cambiario en el borrador de anteproyecto de LEC", presentada en el Co...

  18. CaLecRK-S.5, a pepper L-type lectin receptor kinase gene, confers broad-spectrum resistance by activating priming

    Science.gov (United States)

    Woo, Joo Yong; Jeong, Kwang Ju; Kim, Young Jin; Paek, Kyung-Hee

    2016-01-01

    In Arabidopsis, several L-type lectin receptor kinases (LecRKs) have been identified as putative immune receptors. However, to date, there have been few analyses of LecRKs in crop plants. Virus-induced gene silencing of CaLecRK-S.5 verified the role of CaLecRK-S.5 in broad-spectrum resistance. Compared with control plants, CaLecRK-S.5-silenced plants showed reduced hypersensitive response, reactive oxygen species burst, secondary metabolite production, mitogen-activated protein kinase activation, and defense-related gene expression in response to Tobacco mosaic virus pathotype P0 (TMV-P0) infection. Suppression of CaLecRK-S.5 expression significantly enhanced the susceptibility to Pepper mild mottle virus pathotype P1,2,3, Xanthomonas campestris pv. vesicatoria, Phytophthora capsici, as well as TMV-P0. Additionally, β-aminobutyric acid treatment and a systemic acquired resistance assay revealed that CaLecRK-S.5 is involved in priming of plant immunity. Pre-treatment with β-aminobutyric acid before viral infection restored the reduced disease resistance phenotypes shown in CaLecRK-S.5-silenced plants. Systemic acquired resistance was also abolished in CaLecRK-S.5-silenced plants. Finally, RNA sequencing analysis indicated that CaLecRK-S.5 positively regulates plant immunity at the transcriptional level. Altogether, these results suggest that CaLecRK-S.5-mediated broad-spectrum resistance is associated with the regulation of priming. PMID:27647723

  19. CaLecRK-S.5, a pepper L-type lectin receptor kinase gene, confers broad-spectrum resistance by activating priming.

    Science.gov (United States)

    Woo, Joo Yong; Jeong, Kwang Ju; Kim, Young Jin; Paek, Kyung-Hee

    2016-10-01

    In Arabidopsis, several L-type lectin receptor kinases (LecRKs) have been identified as putative immune receptors. However, to date, there have been few analyses of LecRKs in crop plants. Virus-induced gene silencing of CaLecRK-S.5 verified the role of CaLecRK-S.5 in broad-spectrum resistance. Compared with control plants, CaLecRK-S.5-silenced plants showed reduced hypersensitive response, reactive oxygen species burst, secondary metabolite production, mitogen-activated protein kinase activation, and defense-related gene expression in response to Tobacco mosaic virus pathotype P0 (TMV-P0) infection. Suppression of CaLecRK-S.5 expression significantly enhanced the susceptibility to Pepper mild mottle virus pathotype P1,2,3, Xanthomonas campestris pv. vesicatoria, Phytophthora capsici, as well as TMV-P0 Additionally, β-aminobutyric acid treatment and a systemic acquired resistance assay revealed that CaLecRK-S.5 is involved in priming of plant immunity. Pre-treatment with β-aminobutyric acid before viral infection restored the reduced disease resistance phenotypes shown in CaLecRK-S.5-silenced plants. Systemic acquired resistance was also abolished in CaLecRK-S.5-silenced plants. Finally, RNA sequencing analysis indicated that CaLecRK-S.5 positively regulates plant immunity at the transcriptional level. Altogether, these results suggest that CaLecRK-S.5-mediated broad-spectrum resistance is associated with the regulation of priming.

  20. Expression, purification, and evaluation of recombinant LecA as a candidate for an amebic colitis vaccine.

    Science.gov (United States)

    Barroso, L; Abhyankar, M; Noor, Z; Read, K; Pedersen, K; White, R; Fox, C; Petri, W A; Lyerly, D

    2014-02-26

    Entamoeba histolytica, which causes amebic colitis and liver abscess, is considered a major enteric pathogen in residents and travelers to developing countries where the disease is endemic. Interaction of this protozoan parasite with the intestine is mediated through the binding of the trophozoite stage to intestinal mucin and epithelium via a galactose and N-acetyl-d-galactosamine (Gal/GalNAc) lectin comprised of a disulfide linked heavy (ca. 180 kDa) and light chain (ca. 35 kDa) and a noncovalently bound intermediate subunit (ca. 150 kDa). Our efforts to develop a vaccine against this pathogen have focused on an internal 578 amino acid fragment, designated LecA, located within the cysteine-rich region of the heavy chain subunit because: (i) it is a major target of adherence-blocking antibodies of seropositive individuals and (ii) vaccination with his-tagged LecA provides protection in animal models. We developed a purification process for preparing highly purified non-tagged LecA using a codon-optimized gene expressed in Escherichia coli. The process consisted of: (i) cell lysis, collection and washing of inclusion bodies; (ii) solubilization and refolding of denatured LecA; and (iii) a polishing gel filtration step. The purified fragment existed primarily as a random coil with β-sheet structure, contained low endotoxin and nucleic acid, was highly immunoreactive, and elicited antibodies that recognized native lectin and that inhibited in vitro adherence of trophozoites to CHO cells. Immunization of CBA mice with LecA resulted in significant protection against cecal colitis. Our procedure yields sufficient amounts of highly purified LecA for future studies on stability, immunogenicity, and protection with protein-adjuvant formulations. Copyright © 2013 Elsevier Ltd. All rights reserved.

  1. Enhanced seed oil production in canola by conditional expression of Brassica napus LEAFY COTYLEDON1 and LEC1-LIKE in developing seeds.

    Science.gov (United States)

    Tan, Helin; Yang, Xiaohui; Zhang, Fengxia; Zheng, Xiu; Qu, Cunmin; Mu, Jinye; Fu, Fuyou; Li, Jiana; Guan, Rongzhan; Zhang, Hongsheng; Wang, Guodong; Zuo, Jianru

    2011-07-01

    The seed oil content in oilseed crops is a major selection trait to breeders. In Arabidopsis (Arabidopsis thaliana), LEAFY COTYLEDON1 (LEC1) and LEC1-LIKE (L1L) are key regulators of fatty acid biosynthesis. Overexpression of AtLEC1 and its orthologs in canola (Brassica napus), BnLEC1 and BnL1L, causes an increased fatty acid level in transgenic Arabidopsis plants, which, however, also show severe developmental abnormalities. Here, we use truncated napin A promoters, which retain the seed-specific expression pattern but with a reduced expression level, to drive the expression of BnLEC1 and BnL1L in transgenic canola. Conditional expression of BnLEC1 and BnL1L increases the seed oil content by 2% to 20% and has no detrimental effects on major agronomic traits. In the transgenic canola, expression of a subset of genes involved in fatty acid biosynthesis and glycolysis is up-regulated in developing seeds. Moreover, the BnLEC1 transgene enhances the expression of several genes involved in Suc synthesis and transport in developing seeds and the silique wall. Consistently, the accumulation of Suc and Fru is increased in developing seeds of the transgenic rapeseed, suggesting the increased carbon flux to fatty acid biosynthesis. These results demonstrate that BnLEC1 and BnL1L are reliable targets for genetic improvement of rapeseed in seed oil production.

  2. Applications of pixellated GaAs X-ray detectors in a synchrotron radiation beam

    CERN Document Server

    Watt, J; Campbell, M; Mathieson, K; Mikulec, B; O'Shea, V; Passmore, M S; Schwarz, C; Smith, K M; Whitehill, C

    2001-01-01

    Hybrid semiconductor pixel detectors are being investigated as imaging devices for radiography and synchrotron radiation beam applications. Based on previous work in the CERN RD19 and the UK IMPACT collaborations, a photon counting GaAs pixel detector (PCD) has been used in an X-ray powder diffraction experiment. The device consists of a 200 mu m thick SI-LEC GaAs detector patterned in a 64*64 array of 170 mu m pitch square pixels, bump-bonded to readout electronics operating in single photon counting mode. Intensity peaks in the powder diffraction pattern of KNbO/sub 3/ have been resolved and compared with results using the standard scintillator, and a PCD predecessor (the Omega 3). The PCD shows improved speed, dynamic range, 2-D information and comparable spatial resolution to the standard scintillator based systems. It also overcomes the severe dead time limitations of the Omega 3 by using a shutter based acquisition mode. A brief demonstration of the possibilities of the system for dental radiography and...

  3. Applications of pixellated GaAs X-ray detectors in a synchrotron radiation beam

    Energy Technology Data Exchange (ETDEWEB)

    Watt, J. E-mail: j.watt@physics.gla.ac.uk; Bates, R.; Campbell, M.; Mathieson, K.; Mikulec, B.; O' Shea, V.; Passmore, M-S.; Schwarz, C.; Smith, K.M.; Whitehill, C

    2001-03-11

    Hybrid semiconductor pixel detectors are being investigated as imaging devices for radiography and synchrotron radiation beam applications. Based on previous work in the CERN RD19 and the UK IMPACT collaborations, a photon counting GaAs pixel detector (PCD) has been used in an X-ray powder diffraction experiment. The device consists of a 200 {mu}m thick SI-LEC GaAs detector patterned in a 64x64 array of 170 {mu}m pitch square pixels, bump-bonded to readout electronics operating in single photon counting mode. Intensity peaks in the powder diffraction pattern of KNbO{sub 3} have been resolved and compared with results using the standard scintillator, and a PCD predecessor (the {omega}3). The PCD shows improved speed, dynamic range, 2-D information and comparable spatial resolution to the standard scintillator based systems. It also overcomes the severe dead time limitations of the {omega}3 by using a shutter based acquisition mode. A brief demonstration of the possibilities of the system for dental radiography and image processing are given, showing a marked reduction in patient dose and dead time compared with film.

  4. 47 CFR 52.23 - Deployment of long-term database methods for number portability by LECs.

    Science.gov (United States)

    2010-10-01

    ... switches that require software but not hardware changes to provide portability (“Hardware Capable Switches... number portability by LECs. 52.23 Section 52.23 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES (CONTINUED) NUMBERING Number Portability § 52.23 Deployment of...

  5. Expression of TGF-β2 in LECs of Age- Related Nuclear, Cortex Cataract and the Relationship among TGF-β2, Proliferation, Apoptosis and Transdifferentiation

    Institute of Scientific and Technical Information of China (English)

    YE Lin; CAI Xiaojun; ZHANG Baifang; LUO Hong; Deng Ping

    2006-01-01

    To detect the pathogenesis of age-related cataract, we analyzed the expression of TGF-β2mRNA, proliferation cell nuclear antigen (PCNA), Bcl-2/Bax, fibronection (FN), vimentin protein and the density of lens epithelial cells(LECs) of nuclear cataract, cortex cataract and normal LECs. Results showed that the expression level of TGFβ2 mRNA, FN and vimentin protein was higher in LECs of cortex cataract than that of nuclear cataract and normal lens. But the level of Bcl-2/Bax and PCNA was on the contrary. The density of LECs was (4250. 63± 275.05)/mm2 in cortex cataract. It was (5438. 40 ± 262.30)/mm2 in nuclear cataract, and (5368.63 ±211.07)/mm2 in normal LECs resepectively. There was significant difference between cortex and nuclear cataract (p<0.05). These suggested that TGF-β2 might take an important part in the process of age-related cataract. Age-related nuclear cataract was related to the proliferation LECs. While cortex cataract was related to the apoptosis and transdifferentiation of LECs.

  6. A biophysical study with carbohydrate derivatives explains the molecular basis of monosaccharide selectivity of the Pseudomonas aeruginosa lectin LecB.

    Directory of Open Access Journals (Sweden)

    Roman Sommer

    Full Text Available The rise of resistances against antibiotics in bacteria is a major threat for public health and demands the development of novel antibacterial therapies. Infections with Pseudomonas aeruginosa are a severe problem for hospitalized patients and for patients suffering from cystic fibrosis. These bacteria can form biofilms and thereby increase their resistance towards antibiotics. The bacterial lectin LecB was shown to be necessary for biofilm formation and the inhibition with its carbohydrate ligands resulted in reduced amounts of biofilm. The natural ligands for LecB are glycosides of D-mannose and L-fucose, the latter displaying an unusual strong affinity. Interestingly, although mannosides are much weaker ligands for LecB, they do form an additional hydrogen bond with the protein in the crystal structure. To analyze the individual contributions of the methyl group in fucosides and the hydroxymethyl group in mannosides to the binding, we designed and synthesized derivatives of these saccharides. We report glycomimetic inhibitors that dissect the individual interactions of their saccharide precursors with LecB and give insight into the biophysics of binding by LecB. Furthermore, theoretical calculations supported by experimental thermodynamic data suggest a perturbed hydrogen bonding network for mannose derivatives as molecular basis for the selectivity of LecB for fucosides. Knowledge gained on the mode of interaction of LecB with its ligands at ambient conditions will be useful for future drug design.

  7. MytiLec, a Mussel R-Type Lectin, Interacts with Surface Glycan Gb3 on Burkitt’s Lymphoma Cells to Trigger Apoptosis through Multiple Pathways

    Directory of Open Access Journals (Sweden)

    Imtiaj Hasan

    2015-12-01

    Full Text Available MytiLec; a novel lectin isolated from the Mediterranean mussel (Mytilus galloprovincialis; shows strong binding affinity to globotriose (Gb3: Galα1-4Galβ1-4Glc. MytiLec revealed β-trefoil folding as also found in the ricin B-subunit type (R-type lectin family, although the amino acid sequences were quite different. Classification of R-type lectin family members therefore needs to be based on conformation as well as on primary structure. MytiLec specifically killed Burkitt's lymphoma Ramos cells, which express Gb3. Fluorescein-labeling assay revealed that MytiLec was incorporated inside the cells. MytiLec treatment of Ramos cells resulted in activation of both classical MAPK/ extracellular signal-regulated kinase and extracellular signal-regulated kinase (MEK-ERK and stress-activated (p38 kinase and JNK Mitogen-activated protein kinases (MAPK pathways. In the cells, MytiLec treatment triggered expression of tumor necrosis factor (TNF-α (a ligand of death receptor-dependent apoptosis and activation of mitochondria-controlling caspase-9 (initiator caspase and caspase-3 (activator caspase. Experiments using the specific MEK inhibitor U0126 showed that MytiLec-induced phosphorylation of the MEK-ERK pathway up-regulated expression of the cyclin-dependent kinase inhibitor p21, leading to cell cycle arrest and TNF-α production. Activation of caspase-3 by MytiLec appeared to be regulated by multiple different pathways. Our findings, taken together, indicate that the novel R-type lectin MytiLec initiates programmed cell death of Burkitt’s lymphoma cells through multiple pathways (MAPK cascade, death receptor signaling; caspase activation based on interaction of the lectin with Gb3-containing glycosphingolipid-enriched microdomains on the cell surface.

  8. cDNA and Gene Structure of MytiLec-1, A Bacteriostatic R-Type Lectin from the Mediterranean Mussel (Mytilus galloprovincialis).

    Science.gov (United States)

    Hasan, Imtiaj; Gerdol, Marco; Fujii, Yuki; Rajia, Sultana; Koide, Yasuhiro; Yamamoto, Daiki; Kawsar, Sarkar M A; Ozeki, Yasuhiro

    2016-01-01

    MytiLec is an α-d-galactose-binding lectin with a unique primary structure isolated from the Mediterranean mussel (Mytilus galloprovincialis). The lectin adopts a β-trefoil fold that is also found in the B-sub-unit of ricin and other ricin-type (R-type) lectins. We are introducing MytiLec(-1) and its two variants (MytiLec-2 and -3), which both possess an additional pore-forming aerolysin-like domain, as members of a novel multi-genic "mytilectin family" in bivalve mollusks. Based on the full length mRNA sequence (911 bps), it was possible to elucidate the coding sequence of MytiLec-1, which displays an extended open reading frame (ORF) at the 5' end of the sequence, confirmed both at the mRNA and at the genomic DNA sequence level. While this extension could potentially produce a polypeptide significantly longer than previously reported, this has not been confirmed yet at the protein level. MytiLec-1 was revealed to be encoded by a gene consisting of two exons and a single intron. The first exon comprised the 5'UTR and the initial ATG codon and it was possible to detect a putative promoter region immediately ahead of the transcription start site in the MytiLec-1 genomic locus. The remaining part of the MytiLec-1 coding sequence (including the three sub-domains, the 3'UTR and the poly-A signal) was included in the second exon. The bacteriostatic activity of MytiLec-1 was determined by the agglutination of both Gram-positive and Gram-negative bacteria, which was reversed by the co-presence of α-galactoside. Altogether, these data support the classification of MytiLec-1 as a member of the novel mytilectin family and suggest that this lectin may play an important role as a pattern recognition receptor in the innate immunity of mussels.

  9. Toward the Rational Design of Galactosylated Glycoclusters That Target Pseudomonas aeruginosa Lectin A (LecA): Influence of Linker Arms That Lead to Low-Nanomolar Multivalent Ligands.

    Science.gov (United States)

    Wang, Shuai; Dupin, Lucie; Noël, Mathieu; Carroux, Cindy J; Renaud, Louis; Géhin, Thomas; Meyer, Albert; Souteyrand, Eliane; Vasseur, Jean-Jacques; Vergoten, Gérard; Chevolot, Yann; Morvan, François; Vidal, Sébastien

    2016-08-01

    Anti-infectious strategies against pathogen infections can be achieved through antiadhesive strategies by using multivalent ligands of bacterial virulence factors. LecA and LecB are lectins of Pseudomonas aeruginosa implicated in biofilm formation. A series of 27 LecA-targeting glycoclusters have been synthesized. Nine aromatic galactose aglycons were investigated with three different linker arms that connect the central mannopyranoside core. A low-nanomolar (Kd =19 nm, microarray) ligand with a tyrosine-based linker arm could be identified in a structure-activity relationship study. Molecular modeling of the glycoclusters bound to the lectin tetramer was also used to rationalize the binding properties observed.

  10. Pilot-scale Limestone Emission Control (LEC) process: A development project. Volume 1, Main report and appendices A, B, C, and D: Final report

    Energy Technology Data Exchange (ETDEWEB)

    Prudich, M.E. [Ohio Univ., Athens, OH (United States); Appell, K.W.; McKenna, J.D. [ETS, Inc., Roanoke, VA (United States)

    1994-03-01

    ETS, Inc., a pollution consulting firm with headquarters in Roanoke, Virginia, has developed a dry, limestone-based flue gas desulfurization (FGD) system. This SO{sub 2} removal system, called Limestone Emission Control (LEC), can be designed for installation on either new or existing coal-fired boilers. In the LEC process, the SO{sub 2} in the flue gas reacts with wetted granular limestone that is contained in a moving bed. A surface layer of principally calcium sulfate (CaSO{sub 4}) is formed on the limestone. Periodic removal of this surface layer by mechanical agitation allows high utilization of the limestone granules. A nominal 5,000 acfm LEC pilot plant has been designed, fabricated and installed on the slipstream of a 70,000 pph stoker boiler providing steam to Ohio University`s Athens, Ohio campus. A total of over 90 experimental trials have been performed using the pilot-scale moving-bed LEC dry scrubber as a part of this research project with run times ranging up to a high of 125 hours. SO{sub 2} removal efficiencies as high as 99.9% were achievable for all experimental conditions studied during which sufficient humidification was added to the LEC bed. The LEC process and conventional limestone scrubbing have been compared on an equatable basis using flue gas conditions that would be expected at the outlet of the electrostatic precipitator (ESP) of a 500 MW coal-fired power plant. The LEC was found to have a definite economic advantage in both direct capital costs and operating costs. Based on the success and findings of the present project, the next step in LEC process development will be a full-scale commercial demonstration unit.

  11. The Arabidopsis lectin receptor kinase LecRK-V.5 represses stomatal immunity induced by Pseudomonas syringae pv. tomato DC3000.

    Directory of Open Access Journals (Sweden)

    Marie Desclos-Theveniau

    2012-02-01

    Full Text Available Stomata play an important role in plant innate immunity by limiting pathogen entry into leaves but molecular mechanisms regulating stomatal closure upon pathogen perception are not well understood. Here we show that the Arabidopsis thaliana L-type lectin receptor kinase-V.5 (LecRK-V.5 negatively regulates stomatal immunity. Loss of LecRK-V.5 function increased resistance to surface inoculation with virulent bacteria Pseudomonas syringae pv tomato DC3000. Levels of resistance were not affected after infiltration-inoculation, suggesting that LecRK-V.5 functions at an early defense stage. By contrast, lines overexpressing LecRK-V.5 were more susceptible to Pst DC3000. Enhanced resistance in lecrk-V.5 mutants was correlated with constitutive stomatal closure, while increased susceptibility phenotypes in overexpression lines were associated with early stomatal reopening. Lines overexpressing LecRK-V.5 also demonstrated a defective stomatal closure after pathogen-associated molecular pattern (PAMP treatments. LecRK-V.5 is rapidly expressed in stomatal guard cells after bacterial inoculation or treatment with the bacterial PAMP flagellin. In addition, lecrk-V.5 mutants guard cells exhibited constitutive accumulation of reactive oxygen species (ROS and inhibition of ROS production opened stomata of lecrk-V.5. LecRK-V.5 is also shown to interfere with abscisic acid-mediated stomatal closure signaling upstream of ROS production. These results provide genetic evidences that LecRK-V.5 negatively regulates stomatal immunity upstream of ROS biosynthesis. Our data reveal that plants have evolved mechanisms to reverse bacteria-mediated stomatal closure to prevent long-term effect on CO(2 uptake and photosynthesis.

  12. Interactions between Zn and Cu in LEC rats, an animal model of Wilson's disease.

    Science.gov (United States)

    Santon, Alessandro; Giannetto, Sabrina; Sturniolo, Giacomo Carlo; Medici, Valentina; D'Incà, Renata; Irato, Paola; Albergoni, Vincenzo

    2002-03-01

    The effect of oral Zn treatment was studied in the liver and kidneys of 26 male Long-Evans Cinnamon (LEC) rats (mutant animals, 5 weeks old) in relation to both the interaction between Zn and Cu and the localisation and concentration of metallothionein (MT). Rats receiving 80 mg zinc acetate daily by gavage and control rats receiving no treatment were killed after 1 or 2 weeks. By immunohistochemical and analytical chemical techniques we revealed that treated rats had higher levels of MT in the hepatic and renal cells compared to untreated ones. Tissue Zn concentrations were significantly higher in treated rats compared to untreated whereas Cu concentrations decreased in the liver and kidneys as indicated by analytical chemical analyses. MT levels also decreased with treatment period. A histochemical procedure, obtained using autofluorescence of Cu-metallothioneins, confirms these findings: after 2 weeks, the signal decreased in both the liver and kidney sections. This gives a greater understanding of the mechanism of Cu metabolism in the two tissues considered. These results suggest that Zn acts both to compete for absorption on the luminal side of the intestinal epithelium and to induce the synthesis of MT.

  13. Role of p38 Mapk in development of acute hepatic injury in Long-Evans Cinnamon (LEC) rats, an animal model of human Wilson's disease.

    Science.gov (United States)

    Kadowaki, Shingo; Meguro, Saori; Imaizumi, Yoshitaka; Sakai, Hiroshi; Endoh, Daiji; Hayashi, Masanobu

    2013-12-30

    The Long-Evans Cinnamon (LEC) rat, an animal model of human Wilson's disease, spontaneously develops fulminant hepatitis associated with severe jaundice at about 4 months of age. In this study, we examined the changes in gene expression during progression of acute hepatic injury. When levels of gene expression in the liver of LEC rats at 13 weeks of age were compared to those in rats at 4 weeks of age using oligonucleotide arrays, 1,620 genes out of 7,700 genes analyzed showed more than 2-fold differences. Expression levels of 11 of 29 genes related to stress-activating protein kinase (SAPK) changed by more than 2-fold in the liver of LEC rats, but none of the SAPK-related genes showed changes in expression levels in the liver of control rats. Activity of p38 mapk in the liver of LEC rats at 13 weeks of age was about 8.1-fold higher than that in rats at 4 weeks of age. When LEC rats were administered SB203580, a p38 mapk-specific inhibitor, by s.c. injection twice a week from 10 to 13 weeks of age, activities of p38 mapk in the liver, activities of AST and ALT and concentrations of bilirubin in sera of rats administered SB203580 significantly decreased compared to those in rats not administered. These results showed that the increase in activities of p38 mapk was related to the occurrence of acute hepatic injury in LEC rats.

  14. Fabrication and Characterization of Planar Dipole Antenna Integrated with GaAs Based-Schottky Diode for On-chip Electronic Device Application

    Energy Technology Data Exchange (ETDEWEB)

    Mustafa, Farahiyah; Hashim, Abdul Manaf; Parimon, Norfarariyanti; Rahman, Shaharin Fadzli Abd; Rahman, Abdul Rahim Abdul [Material Innovations and Nanoelectronics Research Group, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor (Malaysia); Osman, Mohd Nizam [Telekom Research and Development, TM Innovation Centre, 63000 Cyberjaya (Malaysia); Aziz, Azlan Abdul; Hashim, Md Roslan, E-mail: manaf@fke.utm.my [Nano-Optoelectronics Research, Faculty of Physics, Universiti Sains Malaysia, 11800 Minden, Penang (Malaysia)

    2011-02-15

    The design and RF characteristics of planar dipole antennas facilitated with coplanar waveguide (CPW) structure on semi-insulated GaAs are performed and confirmed to work in super high frequency (SHF) range. As expected, the fundamental resonant frequency shifts to higher frequency when the length of antenna decreases. Interestingly, the resonant frequencies of antenna are almost unchanged with the variation of antenna width and metal thickness. It is shown experimentally that return loss down to -54 dB with a metal thickness of 50 nm is obtainable. Preliminary investigation on design, fabrication, and DC and RF characteristics of the integrated device (planar dipole antenna + Schottky diode) on AlGaAs/GaAs HEMT structure is presented. From the preliminary direct irradiation experiments using the integrated device, the Schottky diode is not turned on due to weak reception of RF signal by dipole antenna. Further extensive considerations on the polarization of irradiation etc. need to be carried out in order to improve the signal reception. These preliminary results provide a new breakthrough for on-chip electronic device application in nanosystems.

  15. Cucumis sativus L-type lectin receptor kinase (CsLecRK) gene family response to Phytophthora melonis, Phytophthora capsici and water immersion in disease resistant and susceptible cucumber cultivars.

    Science.gov (United States)

    Wu, Tingquan; Wang, Rui; Xu, Xiaomei; He, Xiaoming; Sun, Baojuan; Zhong, Yujuan; Liang, Zhaojuan; Luo, Shaobo; Lin, Yu'e

    2014-10-10

    L-type lectin receptor kinase (LecRK) proteins are an important family involved in diverse biological processes such as pollen development, senescence, wounding, salinity and especially in innate immunity in model plants such as Arabidopsis and tobacco. Till date, LecRK proteins or genes of cucumber have not been reported. In this study, a total of 25 LecRK genes were identified in the cucumber genome, unequally distributed across its seven chromosomes. According to similarity comparison of their encoded proteins, the Cucumis sativus LecRK (CsLecRK) genes were classified into six major clades (from Clade I to CladeVI). Expression of CsLecRK genes were tested using QRT-PCR method and the results showed that 25 CsLecRK genes exhibited different responses to abiotic (water immersion) and biotic (Phytophthora melonis and Phytophthora capsici inoculation) stresses, as well as that between disease resistant cultivar (JSH) and disease susceptible cultivar (B80). Among the 25 CsLecRK genes, we found CsLecRK6.1 was especially induced by P. melonis and P. capsici in JSH plants. All these results suggested that CsLecRK genes may play important roles in biotic and abiotic stresses.

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

    Energy Technology Data Exchange (ETDEWEB)

    Dreyhaupt, Andre

    2008-07-01

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

  17. Multiple Applications of GaAs semiconductors

    Science.gov (United States)

    Martel, Jenrené; Wonka, Willy

    2003-03-01

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

  18. OsLEC1lOsHAP3E Participates in the Determination of Meristem Identity in Both Vegetative and Reproductive Developments of Rice([F])

    Institute of Scientific and Technical Information of China (English)

    Jing-Jing Zhang; Hong-Wei Xue

    2013-01-01

    In the vegetative phase of plant development,the shoot apical meristem (SAM) produces leaf primordia in regular phyllotaxy,and transforms to the inflorescence meristem when the plant enters reproductive growth,which will undergo a series of identity differentiations and will finally form a complete and fertile panicle.Our previous studies indicated a tissue-specific expression pattern of the OsLEC1 (leafy cotyledon) gene,which is homologous to the Arabidopsis AtLEC1 gene and belongs to the CCAAT-binding protein HAP3 subfamily,during embryo development.Expression of additional OsLEC1 genomic sequences resulted in abnormalities in the development of leaves,panicles and spikelets.The spikelets in particular presented abnormities,including panicle and spikelet-like structures that occurred reiteratively inside prior spikelets,and the occasional spikelet structures that completely transformed into plantlets (a reproductive habit alteration from sexual to asexual called "pseudovivipary").Analysis showed that OsLEC1 interacts with several SEPALLATA-like MADS transcription factors,suggesting that increased levels of the OsLEC1 protein might interfere with the normal interaction network of these MADS proteins and lead to defective spikelet development.The expression of OsMADS1 was dramatically reduced,and the DNA methylation level of cytosine in certain regions of the OsMADS1 promoter was increased under OsLEC1 overexpression.These results indicate that OsLEC1 affects the development of leaves,panicles and spikelets,and is a key regulator of meristem identity determination in both rice (Oryza sativa) vegetative and reproductive development.

  19. The Arabidopsis thaliana lectin receptor kinase LecRK-I.9 is required for full resistance to Pseudomonas syringae and affects jasmonate signalling.

    Science.gov (United States)

    Balagué, Claudine; Gouget, Anne; Bouchez, Olivier; Souriac, Camille; Haget, Nathalie; Boutet-Mercey, Stéphanie; Govers, Francine; Roby, Dominique; Canut, Hervé

    2016-07-11

    On microbial attack, plants can detect invaders and activate plant innate immunity. For the detection of pathogen molecules or cell wall damage, plants employ receptors that trigger the activation of defence responses. Cell surface proteins that belong to large families of lectin receptor kinases are candidates to function as immune receptors. Here, the function of LecRK-I.9 (At5g60300), a legume-type lectin receptor kinase involved in cell wall-plasma membrane contacts and in extracellular ATP (eATP) perception, was studied through biochemical, gene expression and reverse genetics approaches. In Arabidopsis thaliana, LecRK-I.9 expression is rapidly, highly and locally induced on inoculation with avirulent strains of Pseudomonas syringae pv. tomato (Pst). Two allelic lecrk-I.9 knock-out mutants showed decreased resistance to Pst. Conversely, over-expression of LecRK-I.9 led to increased resistance to Pst. The analysis of defence gene expression suggests an alteration of both the salicylic acid (SA) and jasmonic acid (JA) signalling pathways. In particular, LecRK-I.9 expression during plant-pathogen interaction was dependent on COI1 (CORONATINE INSENSITIVE 1) and JAR1 (JASMONATE RESISTANT 1) components, and JA-responsive transcription factors (TFs) showed altered levels of expression in plants over-expressing LecRK-I.9. A similar misregulation of these TFs was obtained by JA treatment. This study identified LecRK-I.9 as necessary for full resistance to Pst and demonstrated its involvement in the control of defence against pathogens through a regulation of JA signalling components. The role of LecRK-I.9 is discussed with regard to the potential molecular mechanisms linking JA signalling to cell wall damage and/or eATP perception.

  20. cDNA and Gene Structure of MytiLec-1, A Bacteriostatic R-Type Lectin from the Mediterranean Mussel (Mytilus galloprovincialis

    Directory of Open Access Journals (Sweden)

    Imtiaj Hasan

    2016-05-01

    Full Text Available MytiLec is an α-d-galactose-binding lectin with a unique primary structure isolated from the Mediterranean mussel (Mytilus galloprovincialis. The lectin adopts a β-trefoil fold that is also found in the B-sub-unit of ricin and other ricin-type (R-type lectins. We are introducing MytiLec(-1 and its two variants (MytiLec-2 and -3, which both possess an additional pore-forming aerolysin-like domain, as members of a novel multi-genic “mytilectin family” in bivalve mollusks. Based on the full length mRNA sequence (911 bps, it was possible to elucidate the coding sequence of MytiLec-1, which displays an extended open reading frame (ORF at the 5′ end of the sequence, confirmed both at the mRNA and at the genomic DNA sequence level. While this extension could potentially produce a polypeptide significantly longer than previously reported, this has not been confirmed yet at the protein level. MytiLec-1 was revealed to be encoded by a gene consisting of two exons and a single intron. The first exon comprised the 5′UTR and the initial ATG codon and it was possible to detect a putative promoter region immediately ahead of the transcription start site in the MytiLec-1 genomic locus. The remaining part of the MytiLec-1 coding sequence (including the three sub-domains, the 3′UTR and the poly-A signal was included in the second exon. The bacteriostatic activity of MytiLec-1 was determined by the agglutination of both Gram-positive and Gram-negative bacteria, which was reversed by the co-presence of α-galactoside. Altogether, these data support the classification of MytiLec-1 as a member of the novel mytilectin family and suggest that this lectin may play an important role as a pattern recognition receptor in the innate immunity of mussels.

  1. Epitaxial lift-off GaAs solar cell from a reusable GaAs substrate

    Energy Technology Data Exchange (ETDEWEB)

    Geelen, A. van [Nijmegen Univ. (Netherlands). Res. Inst. for Mater.; Hageman, P.R. [Nijmegen Univ. (Netherlands). Res. Inst. for Mater.; Bauhuis, G.J. [Nijmegen Univ. (Netherlands). Res. Inst. for Mater.; Rijsingen, P.C. van [Nijmegen Univ. (Netherlands). Res. Inst. for Mater.; Schmidt, P. [Nijmegen Univ. (Netherlands). Res. Inst. for Mater.; Giling, L.J. [Nijmegen Univ. (Netherlands). Res. Inst. for Mater.

    1997-03-01

    Modifications to the existing epitaxial lift-off (ELO) method are described, which enable lift-off of large area devices (like solar cells). With the modified ELO method crack-free III-V films were obtained, up to 2 inch, in diameter and 1-6 {mu}m thick. For the first time epitaxial lift-off GaAs solar cells were made which contained an etch sensitive Al{sub 0.85}Ga{sub 0.15}As window layer. An energy conversion efficiency of 9.9% (AM1.5Gx1) was measured for the ELO GaAs cells. Compared to the thick GaAs reference cell, ELO cells still suffer from a low fill factor due to series and shunt resistances. Current GaAs ELO cells represent a power to weight ratio of 200 W kg{sup -1}. Because of the high selectivity of the ELO method, GaAs substrates remain unaffected after ELO. Reuse of a GaAs substrate after ELO was investigated in order to reduce the cost of III-V solar cell modules. With a simple cleaning procedure, GaAs substrates could be used at least four times without degradation of the minority carrier lifetime or carrier mobility of the grown epilayers. (orig.)

  2. Effect of GaAs native oxide upon the surface morphology during GaAs MBE growth

    Science.gov (United States)

    Ageev, O. A.; Solodovnik, M. S.; Balakirev, S. V.; Mikhaylin, I. A.; Eremenko, M. M.

    2016-08-01

    The GaAs native oxide effect upon the surface morphology of the GaAs epitaxial layer was studied with taking into account the main growth parameters of MBE technology: substrate temperature, effective As4/Ga flux ratio and growth rate. The MBE modes of atomically smooth and rough surfaces and surfaces with Ga droplet array formation were determined. The possibility of the obtaining of GaAs nanowires via GaAs native oxide layer was shown.

  3. EXAFS characterization of amorphous GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Ridgway, M.C.; Glover, C.J. [Australia National Univ., Canberra (Australia); Foran, G.J. [Australian Nuclear Science and Technology Organization, Menai (Australia); Yu, K.M. [Lawrence Berkeley National Lab., CA (United States). Materials Sciences Div.

    1998-12-31

    The structural parameters of stoichiometric, amorphous GaAs have been determined with extended x-ray absorption fine structure (EXAFS) measurements performed in transmission mode at 10 K. Amorphous GaAs samples were fabricated with a combination of epitaxial growth, ion implantation and selective chemical etching. Relative to a crystalline sample, the nearest-neighbor bond length and Debye-Waller factor both increased for amorphous material. In contrast, the coordination numbers about both Ga and As atoms in the amorphous phase decreased to {approximately} 3.85 atoms from the crystalline value of four. All structural parameters were independent of implantation conditions and as a consequence, were considered representative of intrinsic, amorphous GaAs as opposed to an implantation-induced extrinsic structure.

  4. Carbon doping of GaAs NWs

    Science.gov (United States)

    Salehzadeh Einabad, Omid

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

  5. The lectin receptor kinase LecRK-I.9 is a novel Phytophthora resistance component and a potential host target for a RXLR effector

    NARCIS (Netherlands)

    Bouwmeester, K.; Sain, de M.; Weide, R.; Gouget, A.; Klamer, S.; Canut, H.; Govers, F.

    2011-01-01

    In plants, an active defense against biotrophic pathogens is dependent on a functional continuum between the cell wall (CW) and the plasma membrane (PM). It is thus anticipated that proteins maintaining this continuum also function in defense. The legume-like lectin receptor kinase LecRK-I.9 is a pu

  6. Si diffusion in GaAs

    Indian Academy of Sciences (India)

    P Murugan; R Pothiraj; S D D Roy; K Ramachandran

    2002-08-01

    Theoretical studies are carried out to ascertain the dominant mechanism of Si diffusion in GaAs. Lattice dynamical model calculations have shown that the most probable diffusion mechanism is through a single vacancy even though several experiments cannot fix the mechanism as substitutional, substitutional–interstitial pair or neutral defect pair.

  7. GaAs optoelectronic neuron arrays

    Science.gov (United States)

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

    1993-01-01

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

  8. Gigant Eesti Gaas razdajot seti / Artur Tooman

    Index Scriptorium Estoniae

    Tooman, Artur, 1971-

    2004-01-01

    Eesti Gaas sõlmis firmadega, mis on aastate jooksul ehitanud kümneid kilomeetreid gaasitrasse, tähtajatud lepingud. Nüüd on viieteistkümnel firmal gaasijagamise litsents. Majandus- ja kommunikatsiooniministeeriumi kavandatavatest muutustest gaasi müümisel ja transportimisel. Kaart

  9. Characterization of semi-insulating materials by photoinduced current transient spectroscopy: Fe doped INP for micro-optoelectronics and CdZnTe for nuclear detection; Caracterisation de materiaux semi-isolants par spectroscopie de transitoirede courant photoinduit: materiaux INP dopes Fe pour la micro-optoelectronique et CDZNTE pour la detection nucleaire

    Energy Technology Data Exchange (ETDEWEB)

    Cherkaoui, K

    1998-07-01

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

  10. The lectin receptor kinase LecRK-I.9 is a novel Phytophthora resistance component and a potential host target for a RXLR effector.

    Directory of Open Access Journals (Sweden)

    Klaas Bouwmeester

    2011-03-01

    Full Text Available In plants, an active defense against biotrophic pathogens is dependent on a functional continuum between the cell wall (CW and the plasma membrane (PM. It is thus anticipated that proteins maintaining this continuum also function in defense. The legume-like lectin receptor kinase LecRK-I.9 is a putative mediator of CW-PM adhesions in Arabidopsis and is known to bind in vitro to the Phytophthora infestans RXLR-dEER effector IPI-O via a RGD cell attachment motif present in IPI-O. Here we show that LecRK-I.9 is associated with the plasma membrane, and that two T-DNA insertions lines deficient in LecRK-I.9 (lecrk-I.9 have a 'gain-of-susceptibility' phenotype specifically towards the oomycete Phytophthora brassicae. Accordingly, overexpression of LecRK-I.9 leads to enhanced resistance to P. brassicae. A similar 'gain-of-susceptibility' phenotype was observed in transgenic Arabidopsis lines expressing ipiO (35S-ipiO1. This phenocopy behavior was also observed with respect to other defense-related functions; lecrk-I.9 and 35S-ipiO1 were both disturbed in pathogen- and MAMP-triggered callose deposition. By site-directed mutagenesis, we demonstrated that the RGD cell attachment motif in IPI-O is not only essential for disrupting the CW-PM adhesions, but also for disease suppression. These results suggest that destabilizing the CW-PM continuum is one of the tactics used by Phytophthora to promote infection. As countermeasure the host may want to strengthen CW-PM adhesions and the novel Phytophthora resistance component LecRK-I.9 seems to function in this process.

  11. The lectin receptor kinase LecRK-I.9 is a novel Phytophthora resistance component and a potential host target for a RXLR effector.

    Science.gov (United States)

    Bouwmeester, Klaas; de Sain, Mara; Weide, Rob; Gouget, Anne; Klamer, Sofieke; Canut, Herve; Govers, Francine

    2011-03-01

    In plants, an active defense against biotrophic pathogens is dependent on a functional continuum between the cell wall (CW) and the plasma membrane (PM). It is thus anticipated that proteins maintaining this continuum also function in defense. The legume-like lectin receptor kinase LecRK-I.9 is a putative mediator of CW-PM adhesions in Arabidopsis and is known to bind in vitro to the Phytophthora infestans RXLR-dEER effector IPI-O via a RGD cell attachment motif present in IPI-O. Here we show that LecRK-I.9 is associated with the plasma membrane, and that two T-DNA insertions lines deficient in LecRK-I.9 (lecrk-I.9) have a 'gain-of-susceptibility' phenotype specifically towards the oomycete Phytophthora brassicae. Accordingly, overexpression of LecRK-I.9 leads to enhanced resistance to P. brassicae. A similar 'gain-of-susceptibility' phenotype was observed in transgenic Arabidopsis lines expressing ipiO (35S-ipiO1). This phenocopy behavior was also observed with respect to other defense-related functions; lecrk-I.9 and 35S-ipiO1 were both disturbed in pathogen- and MAMP-triggered callose deposition. By site-directed mutagenesis, we demonstrated that the RGD cell attachment motif in IPI-O is not only essential for disrupting the CW-PM adhesions, but also for disease suppression. These results suggest that destabilizing the CW-PM continuum is one of the tactics used by Phytophthora to promote infection. As countermeasure the host may want to strengthen CW-PM adhesions and the novel Phytophthora resistance component LecRK-I.9 seems to function in this process.

  12. The antioxidant effect of DL-alpha-lipoic acid on copper-induced acute hepatitis in Long-Evans Cinnamon (LEC) rats.

    Science.gov (United States)

    Yamamoto, H; Watanabe, T; Mizuno, H; Endo, K; Fukushige, J; Hosokawa, T; Kazusaka, A; Fujita, S

    2001-01-01

    The Long-Evans Cinnamon (LEC) rats, due to a genetic defect, accumulate excess copper (Cu) in the liver in a manner similar to patients with Wilson's disease and spontaneously develop acute hepatitis with severe jaundice. In this study we examined the protective effect of DL-alpha-Lipoic acid (LA) against acute hepatitis in LEC rats. LA was administered to LEC rats by gavage in doses of 10, 30 and 100 mg/kg five times per week, starting at 8-weeks-old and continuing till 12-weeks-old. Although LA had little effect against the increases in serum transaminase activities, it suppressed the loss of body weight and prevented severe jaundice in a dose-dependent manner. Antioxidant system analyses in liver showed that LA treatment significantly suppressed the inactivations of catalase and glutathione peroxidase, and the induction of heme oxygenase-1, an enzyme which is inducible under oxidative stress. Furthermore, LA showed dose-dependent suppressive effect against increase in nonheme iron contents of both cytosolic and crude mitochondrial fractions in a dose-dependent manner. Although at the highest dose, LA slightly suppressed the accumulation of Cu in crude mitochondrial fraction, it had no effect on the accumulation of Cu in cytosolic fraction. While LA completely suppressed the increase in lipid peroxidation (LPO) in the microsomal fraction at the highest dose, the suppressive effect against LPO in crude mitochondrial fractions was slight. From these results, it is concluded that LA has antioxidant effects at the molecular level against the development of Cu-induced hepatitis in LEC rats. Moreover, mitochondrial oxidative damage might be involved in the development of acute hepatitis in LEC rats.

  13. Ectopic overexpression of castor bean LEAFY COTYLEDON2 (LEC2) in Arabidopsis triggers the expression of genes that encode regulators of seed maturation and oil body proteins in vegetative tissues.

    Science.gov (United States)

    Kim, Hyun Uk; Jung, Su-Jin; Lee, Kyeong-Ryeol; Kim, Eun Ha; Lee, Sang-Min; Roh, Kyung Hee; Kim, Jong-Bum

    2013-01-01

    The LEAFY COTYLEDON2 (LEC2) gene plays critically important regulatory roles during both early and late embryonic development. Here, we report the identification of the LEC2 gene from the castor bean plant (Ricinus communis), and characterize the effects of its overexpression on gene regulation and lipid metabolism in transgenic Arabidopsis plants. LEC2 exists as a single-copy gene in castor bean, is expressed predominantly in embryos, and encodes a protein with a conserved B3 domain, but different N- and C-terminal domains to those found in LEC2 from Arabidopsis. Ectopic overexpression of LEC2 from castor bean under the control of the cauliflower mosaic virus (CaMV) 35S promoter in Arabidopsis plants induces the accumulation of transcripts that encodes five major transcription factors (the LEAFY COTYLEDON1 (LEC1), LEAFY COTYLEDON1-LIKE (L1L), FUSCA3 (FUS3), and ABSCISIC ACID INSENSITIVE 3 (ABI3) transcripts for seed maturation, and WRINKELED1 (WRI1) transcripts for fatty acid biosynthesis), as well as OLEOSIN transcripts for the formation of oil bodies in vegetative tissues. Transgenic Arabidopsis plants that express the LEC2 gene from castor bean show a range of dose-dependent morphological phenotypes and effects on the expression of LEC2-regulated genes during seedling establishment and vegetative growth. Expression of castor bean LEC2 in Arabidopsis increased the expression of fatty acid elongase 1 (FAE1) and induced the accumulation of triacylglycerols, especially those containing the seed-specific fatty acid, eicosenoic acid (20:1(Δ11)), in vegetative tissues.

  14. Ectopic overexpression of castor bean LEAFY COTYLEDON2 (LEC2 in Arabidopsis triggers the expression of genes that encode regulators of seed maturation and oil body proteins in vegetative tissues

    Directory of Open Access Journals (Sweden)

    Hyun Uk Kim

    2014-01-01

    Full Text Available The LEAFY COTYLEDON2 (LEC2 gene plays critically important regulatory roles during both early and late embryonic development. Here, we report the identification of the LEC2 gene from the castor bean plant (Ricinus communis, and characterize the effects of its overexpression on gene regulation and lipid metabolism in transgenic Arabidopsis plants. LEC2 exists as a single-copy gene in castor bean, is expressed predominantly in embryos, and encodes a protein with a conserved B3 domain, but different N- and C-terminal domains to those found in LEC2 from Arabidopsis. Ectopic overexpression of LEC2 from castor bean under the control of the cauliflower mosaic virus (CaMV 35S promoter in Arabidopsis plants induces the accumulation of transcripts that encodes five major transcription factors (the LEAFY COTYLEDON1 (LEC1, LEAFY COTYLEDON1-LIKE (L1L, FUSCA3 (FUS3, and ABSCISIC ACID INSENSITIVE 3 (ABI3 transcripts for seed maturation, and WRINKELED1 (WRI1 transcripts for fatty acid biosynthesis, as well as OLEOSIN transcripts for the formation of oil bodies in vegetative tissues. Transgenic Arabidopsis plants that express the LEC2 gene from castor bean show a range of dose-dependent morphological phenotypes and effects on the expression of LEC2-regulated genes during seedling establishment and vegetative growth. Expression of castor bean LEC2 in Arabidopsis increased the expression of fatty acid elongase 1 (FAE1 and induced the accumulation of triacylglycerols, especially those containing the seed-specific fatty acid, eicosenoic acid (20:1Δ11, in vegetative tissues.

  15. Piezoelectric field in strained GaAs.

    Energy Technology Data Exchange (ETDEWEB)

    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.

  16. GaAs devices for new mobile communication systems application

    OpenAIRE

    Pettenpaul, E.; Schopf, K.J.

    1992-01-01

    A set of GaAs SMD devices has been developed for use in the new european mobile communication equipment, i.e. for DECT and PCN at 1900 and 1800 MHz, respectively. These devices cover the rf part of mobile communication terminals. The devices considered are a GaAs LNC chip for the receiver part, an upconversion mixer MMIC, a prescaler and GaAs power MESFETs as end-stages for the transmitter. The complete DECT, PCN block circuit including GaAs and Si devices will be described.

  17. Pilot-scale limestone emission control (LEC) process: A development project. Volume 1: Main report and appendices A, B, C, and D. Final report

    Energy Technology Data Exchange (ETDEWEB)

    1994-03-01

    ETS, Inc., a pollution consulting firm with headquarters in Roanoke, Virginia, has developed a dry, limestone-based flue gas desulfurization (FGD) system. This SO{sub 2} removal system, called Limestone Emission Control (LEC), can be designed for installation on either new or existing coal-fired boilers. In the LEC process, the SO{sub 2} in the flue gas reacts with wetted granular limestone that is contained in a moving bed. A surface layer of principally calcium sulfate (CaSO{sub 4}) is formed on the limestone. Periodic removal of this surface layer by mechanical agitation allows high utilization of the limestone granules. The primary goal of the current study is the demonstration of the techno/economic capability of the LEC system as a post-combustion FGD process capable of use in both existing and future coal-fired boiler facilities burning high-sulfur coal. A nominal 5,000 acfm LEC pilot plant has been designed, fabricated and installed on the slipstream of a 70,000 pph stoker boiler providing steam to Ohio University`s Athens, Ohio campus. The pilot plant was normally operated on the slipstream of the Ohio Univ. boiler plant flue gas, but also had the capability of operating at higher inlet SO{sub 2} concentrations (typically equivalent to 3-1/2% sulfur coal) than those normally available from the flue gas slipstream. This was accomplished by injecting SO{sub 2} gas into the slipstream inlet. The pilot plant was instrumented to provide around-the-clock operation and was fully outfitted with temperature, SO{sub 2}, gas flow and pressure drop monitors.

  18. Pilot-scale limestone emission control (LEC) process: A development project. Volume 1: Main report and appendices A, B, C, and D. Final report

    Energy Technology Data Exchange (ETDEWEB)

    1994-03-01

    ETS, Inc., a pollution consulting firm with headquarters in Roanoke, Virginia, has developed a dry, limestone-based flue gas desulfurization (FGD) system. This SO{sub 2} removal system, called Limestone Emission Control (LEC), can be designed for installation on either new or existing coal-fired boilers. In the LEC process, the SO{sub 2} in the flue gas reacts with wetted granular limestone that is contained in a moving bed. A surface layer of principally calcium sulfate (CaSO{sub 4}) is formed on the limestone. Periodic removal of this surface layer by mechanical agitation allows high utilization of the limestone granules. The primary goal of the current study is the demonstration of the techno/economic capability of the LEC system as a post-combustion FGD process capable of use in both existing and future coal-fired boiler facilities burning high-sulfur coal. A nominal 5,000 acfm LEC pilot plant has been designed, fabricated and installed on the slipstream of a 70,000 pph stoker boiler providing steam to Ohio University`s Athens, Ohio campus. The pilot plant was normally operated on the slipstream of the Ohio Univ. boiler plant flue gas, but also had the capability of operating at higher inlet SO{sub 2} concentrations (typically equivalent to 3-1/2% sulfur coal) than those normally available from the flue gas slipstream. This was accomplished by injecting SO{sub 2} gas into the slipstream inlet. The pilot plant was instrumented to provide around-the-clock operation and was fully outfitted with temperature, SO{sub 2}, gas flow and pressure drop monitors.

  19. Gallium Arsenide Field Effect Transistors with Semi-Insulated Gates.

    Science.gov (United States)

    1977-09-01

    lower carrier concentration . Use of epitaxially grown n+ l ayers was examined as an alternate approach . Dev ices fabricated from this materia l- were...was de- posi ted in preparation for annealing. Initial ly, the S1 3 N4 was deposited by a - - low-temperature, plasma —enhanced process. Unfortunately

  20. Linearity of photoconductive GaAs detectors to pulsed electrons

    Energy Technology Data Exchange (ETDEWEB)

    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.

  1. GaAs IMPATT diodes for microstrip circuit applications.

    Science.gov (United States)

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

    1972-01-01

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

  2. GaAs Medipix2 hybrid pixel detector

    CERN Document Server

    Kostamo, P; Vähänen, S; Tlustos, L; Fröjdh, C; Campbell, M; Zhilyaev, Y; Lipsanen, H

    2008-01-01

    A GaAs Medipix2 hybrid pixel detector based on high purity epitaxial GaAs material was successfully fabricated. The mesa type GaAs sensor with 256×256 pixels and total area of 1.4×1.4 cm2 was made of a 140-μm-thick epitaxial p–i–n structure utilizing reactive ion etching. A final thickness of approximately 110 μm for the all-epitaxial sensor element is achieved by back-thinning procedure. The sensor element is bump bonded to a Medipix2 read-out ASIC. The detector is capable of room temperature spectroscopic operation and it demonstrates the potential of GaAs for high resolution X-ray imaging systems operating at room temperature. This work describes the manufacturing process and electrical properties of the GaAs Medipix2 hybrid detector.

  3. D10.7.2: Results for GaAs photocathodes

    CERN Document Server

    Xiang, R

    2013-01-01

    HZDR plans to apply bulk GaAs photocathode in SRF gun for high current electron source. Supported by this project, a preparation system for GaAs photocathode has been developed. The cathode plugs special for GaAs wafer have been modified and proofed in SRF gun real running conditions. Virgin GaAs wafer was tested in the SRF gun cavity, and the first GaAs activation was performed.

  4. Diagnosis of abnormal biliary copper excretion by positron emission tomography with targeting of (64)Copper-asialofetuin complex in LEC rat model of Wilson's disease.

    Science.gov (United States)

    Bahde, Ralf; Kapoor, Sorabh; Bhargava, Kuldeep K; Palestro, Christopher J; Gupta, Sanjeev

    2014-01-01

    Identification by molecular imaging of key processes in handling of transition state metals, such as copper (Cu), will be of considerable clinical value. For instance, the ability to diagnose Wilson's disease with molecular imaging by identifying copper excretion in an ATP7B-dependent manner will be very significant. To develop highly effective diagnostic approaches, we hypothesized that targeting of radiocopper via the asialoglycoprotein receptor will be appropriate for positron emission tomography, and examined this approach in a rat model of Wilson's disease. After complexing (64)Cu to asialofetuin we studied handling of this complex compared with (64)Cu in healthy LEA rats and diseased homozygous LEC rats lacking ATP7B and exhibiting hepatic copper toxicosis. We analyzed radiotracer clearance from blood, organ uptake, and biliary excretion, including sixty minute dynamic positron emission tomography recordings. In LEA rats, (64)Cu-asialofetuin was better cleared from blood followed by liver uptake and greater biliary excretion than (64)Cu. In LEC rats, (64)Cu-asialofetuin activity cleared even more rapidly from blood followed by greater uptake in liver, but neither (64)Cu-asialofetuin nor (64)Cu appeared in bile. Image analysis demonstrated rapid visualization of liver after (64)Cu-asialofetuin administration followed by decreased liver activity in LEA rats while liver activity progressively increased in LEC rats. Image analysis resolved this difference in hepatic activity within one hour. We concluded that (64)Cu-asialofetuin complex was successfully targeted to the liver and radiocopper was then excreted into bile in an ATP7B-dependent manner. Therefore, hepatic targeting of radiocopper will be appropriate for improving molecular diagnosis and for developing drug/cell/gene therapies in Wilson's disease.

  5. Electrode pattern design for GaAs betavoltaic batteries

    Energy Technology Data Exchange (ETDEWEB)

    Chen Haiyang; Yin Jianhua; Li Darang, E-mail: haiyangchen@bit.edu.cn [School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China)

    2011-08-15

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

  6. Hydrogen molecules in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Lavrov, E.V.; Weber, J

    2003-12-31

    GaAs samples treated in a hydrogen plasma have been studied by Raman spectroscopy. In addition to the known Raman line at 3912 cm{sup -1} of H{sub 2} trapped at the interstitial T{sub Ga} site surrounded by Ga neighbors, two new Raman signals at 4043 and 4112 cm{sup -1} have been observed at room temperature. The 4043 cm{sup -1} line is assigned to H{sub 2} trapped at the interstitial T{sub As} site with As closest neighbors and the 4112 cm{sup -1} line is associated with H{sub 2} trapped in voids formed by the hydrogen plasma. Para-H{sub 2} trapped at the interstitial T{sub Ga} site is shown to be unstable against irradiation with the band-gap light at room temperature and can be observed only at temperatures below 120 K.

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

    CERN Multimedia

    2002-01-01

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

  8. Electrodeposition of Metal on GaAs Nanowires

    Science.gov (United States)

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

    2010-10-01

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

  9. GaAs Films Prepared by RF-Magnetron Sputtering

    Energy Technology Data Exchange (ETDEWEB)

    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.

  10. Simulation of silicon diffusion in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Saad, A.M., E-mail: daas005@yahoo.co.u [Al-Balga Applied University, P.O.Box 4545 - Amman - 11953 - Tela El Ali (Jordan); Velichko, O.I. [Department of Physics, Belarusian State University of Informatics and Radioelectronics, 6, P. Brovki Street, Minsk 220013 (Belarus)

    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 {sup o}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.

  11. Gaas tõstaks maakonna konkurentsivõimet / Marje Laugen

    Index Scriptorium Estoniae

    Laugen, Marje

    2005-01-01

    Tõrvas peeti Valgamaa gaasiprojekti arutelu, kus osalesid AS-i Eesti Gaas, AS-i Fortum Termest ning Tõrva linna-, Helme valla- ja Valga maavalitsuse esindajad. Kommenteerib Valga maavanem Georg Trashanov

  12. State of the art on epitaxial GaAs detectors

    Energy Technology Data Exchange (ETDEWEB)

    Sun, G.C. [Laboratoire des Milieux Desordonnes et Heterogenes, Universite Pierre et Marie Curie (Paris 6), 140 rue de Lourmel, 75015 Paris (France)]. E-mail: guocsun@ccr.jussieu.fr; Manez, N. [Laboratoire des Milieux Desordonnes et Heterogenes, Universite Pierre et Marie Curie (Paris 6), 140 rue de Lourmel, 75015 Paris (France); Zazoui, M. [Laboratoire des Milieux Desordonnes et Heterogenes, Universite Pierre et Marie Curie (Paris 6), 140 rue de Lourmel, 75015 Paris (France); Al-Ajili, A. [Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, Scotland (United Kingdom); Davidson, D.W. [Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, Scotland (United Kingdom); O' Shea, V. [Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, Scotland (United Kingdom); Quarati, F. [Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, Scotland (United Kingdom); Smith, K.M. [Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, Scotland (United Kingdom); Chambellan, D. [LIST/DIMRI, CEA Saclay, 91191 Gif sur Yvette (France); Gal, O. [LIST/DIMRI, CEA Saclay, 91191 Gif sur Yvette (France); Pillot, Ph. [LIST/DIMRI, CEA Saclay, 91191 Gif sur Yvette (France); Lenoir, M. [Hospital Armand Trousseau, 26 Avenue du Docteur Arnold Netter, 75571 Paris (France); Montagne, J.P. [Hospital Armand Trousseau, 26 Avenue du Docteur Arnold Netter, 75571 Paris (France); Bchetnia, A. [Laboratoire de Physique des Materiaux, Faculte des Sciences de Monastir, 5019 Monastir, Tunisie (Tunisia); Bourgoin, J.C. [GESEC R and D, 68 Avenue de la Foret, 77210 Avon (France)

    2005-07-01

    We first briefly review the performances for X-ray detection which are obtained using thin epitaxial GaAs layers. We then show that good detectors can be realized on thick and large area epitaxial GaAs layers which are now available, making them suitable for X-ray imaging. We finally discuss the main limitation imposed by the epitaxial nature of this new material and ways to overcome it.

  13. Novel GAA mutations in patients with Pompe disease.

    Science.gov (United States)

    Turaça, Lauro Thiago; de Faria, Douglas Oliveira Soares; Kyosen, Sandra Obikawa; Teixeira, Valber Dias; Motta, Fabiana Louise; Pessoa, Juliana Gilbert; Rodrigues E Silva, Marina; de Almeida, Sandro Soares; D'Almeida, Vânia; Munoz Rojas, Maria Verônica; Martins, Ana Maria; Pesquero, João Bosco

    2015-04-25

    Pompe disease is an autosomal recessive disorder linked to GAA gene that leads to a multi-system intralysosomal accumulation of glycogen. Mutation identification in the GAA gene can be very important for early diagnosis, correlation between genotype-phenotype and therapeutic intervention. For this purpose, peripheral blood from 57 individuals susceptible to Pompe disease was collected and all exons of GAA gene were amplified; the sequences and the mutations were analyzed in silico to predict possible impact on the structure and function of the human protein. In this study, 46 individuals presented 33 alterations in the GAA gene sequence, among which five (c.547-67C>G, c.547-39T>G, p.R437H, p.L641V and p.L705P) have not been previously described in the literature. The alterations in the coding region included 15 missense mutations, three nonsense mutations and one deletion. One insertion and other 13 single base changes were found in the non-coding region. The mutation p.G611D was found in homozygosis in a one-year-old child, who presented low levels of GAA activity, hypotonia and hypertrophic cardiomyopathy. Two patients presented the new mutation p.L705P in association with c.-32-13T>G. They had low levels of GAA activity and developed late onset Pompe disease. In our study, we observed alterations in the GAA gene originating from Asians, African-Americans and Caucasians, highlighting the high heterogeneity of the Brazilian population. Considering that Pompe disease studies are not very common in Brazil, this study will help to better understand the potential pathogenic role of each change in the GAA gene. Furthermore, a precise and early molecular analysis improves genetic counseling besides allowing for a more efficient treatment in potential candidates.

  14. Design optimization of GaAs betavoltaic batteries

    Energy Technology Data Exchange (ETDEWEB)

    Chen Haiyanag; Jiang Lan [Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Chen Xuyuan, E-mail: jianglan@bit.edu.cn, E-mail: jianglan@missouri.edu [Institute for Microsystems and Nano Technology, Vestfold University College, N-3103 (Norway)

    2011-06-01

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

  15. Crystal structure of MytiLec, a galactose-binding lectin from the mussel Mytilus galloprovincialis with cytotoxicity against certain cancer cell types

    Science.gov (United States)

    Terada, Daiki; Kawai, Fumihiro; Noguchi, Hiroki; Unzai, Satoru; Hasan, Imtiaj; Fujii, Yuki; Park, Sam-Yong; Ozeki, Yasuhiro; Tame, Jeremy R. H.

    2016-01-01

    MytiLec is a lectin, isolated from bivalves, with cytotoxic activity against cancer cell lines that express globotriaosyl ceramide, Galα(1,4)Galβ(1,4)Glcα1-Cer, on the cell surface. Functional analysis shows that the protein binds to the disaccharide melibiose, Galα(1,6)Glc, and the trisaccharide globotriose, Galα(1,4)Galβ(1,4)Glc. Recombinant MytiLec expressed in bacteria showed the same haemagglutinating and cytotoxic activity against Burkitt’s lymphoma (Raji) cells as the native form. The crystal structure has been determined to atomic resolution, in the presence and absence of ligands, showing the protein to be a member of the β-trefoil family, but with a mode of ligand binding unique to a small group of related trefoil lectins. Each of the three pseudo-equivalent binding sites within the monomer shows ligand binding, and the protein forms a tight dimer in solution. An engineered monomer mutant lost all cytotoxic activity against Raji cells, but retained some haemagglutination activity, showing that the quaternary structure of the protein is important for its cellular effects. PMID:27321048

  16. 3-D GaAs radiation detectors

    CERN Document Server

    Meikle, A R; Ledingham, Kenneth W D; Marsh, J H; Mathieson, K; O'Shea, V; Smith, K M

    2002-01-01

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

  17. Spectroscopy of GaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    West, L.C.

    1985-07-01

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

  18. Nondestructive tribochemistry-assisted nanofabrication on GaAs surface

    Science.gov (United States)

    Song, Chenfei; Li, Xiaoying; Dong, Hanshan; Yu, Bingjun; Wang, Zhiming; Qian, Linmao

    2015-03-01

    A tribochemistry-assisted method has been developed for nondestructive surface nanofabrication on GaAs. Without any applied electric field and post etching, hollow nanostructures can be directly fabricated on GaAs surfaces by sliding a SiO2 microsphere under an ultralow contact pressure in humid air. TEM observation on the cross-section of the fabricated area shows that there is no appreciable plastic deformation under a 4 nm groove, confirming that GaAs can be removed without destruction. Further analysis suggests that the fabrication relies on the tribochemistry with the participation of vapor in humid air. It is proposed that the formation and breakage of GaAs-O-Si bonding bridges are responsible for the removal of GaAs material during the sliding process. As a nondestructive and conductivity-independent method, it will open up new opportunities to fabricate defect-free and well-ordered nucleation positions for quantum dots on GaAs surfaces.

  19. Terahertz pulse detection by the GaAs Schottky diodes

    Science.gov (United States)

    Laperashvili, Tina; Kvitsiani, Orest; Imerlishvili, Ilia; Laperashvili, David

    2010-06-01

    We present the results of experimental studies of physical properties of the detection process of GaAs Schottky diodes for terahertz frequency radiation. The development of technology in the THz frequency band has a rapid progress recently. Considered as an extension of the microwave and millimeter wave bands, the THz frequency offers greater communication bandwidth than is available at microwave frequencies. The Schottky barrier contact has an important role in the operation of many GaAs devices. GaAs Schottky diodes have been the primary nonlinear device used in millimeter and sub millimeter wave detectors and receivers. GaAs Schottky diodes are especially interesting due to their high mobility transport characteristics, which allows for a large reduction of the resistance-capacitance (RC) time constant and thermal noise. In This work are investigated the electrical and photoelectric properties of GaAs Schottky diodes. Samples were obtained by deposition of different metals (Au, Ni, Pt, Pd, Fe, In, Ga, Al) on semiconductor. For fabrication metal-semiconductor (MS) structures is used original method of metal electrodepositing. In this method electrochemical etching of semiconductor surface occurs just before deposition of metal from the solution, which contains etching material and metal ions together. For that, semiconductor surface cleaning processes and metal deposition carries out in the same technological process. In the experiments as the electrolyte was used aqueous solution of chlorides. Metal deposition was carried out at room temperature.

  20. Raffinose, a plant galactoside, inhibits Pseudomonas aeruginosa biofilm formation via binding to LecA and decreasing cellular cyclic diguanylate levels

    Science.gov (United States)

    Kim, Han-Shin; Cha, Eunji; Kim, Yunhye; Jeon, Young Ho; Olson, Betty H.; Byun, Youngjoo; Park, Hee-Deung

    2016-05-01

    Biofilm formation on biotic or abiotic surfaces has unwanted consequences in medical, clinical, and industrial settings. Treatments with antibiotics or biocides are often ineffective in eradicating biofilms. Promising alternatives to conventional agents are biofilm-inhibiting compounds regulating biofilm development without toxicity to growth. Here, we screened a biofilm inhibitor, raffinose, derived from ginger. Raffinose, a galactotrisaccharide, showed efficient biofilm inhibition of Pseudomonas aeruginosa without impairing its growth. Raffinose also affected various phenotypes such as colony morphology, matrix formation, and swarming motility. Binding of raffinose to a carbohydrate-binding protein called LecA was the cause of biofilm inhibition and altered phenotypes. Furthermore, raffinose reduced the concentration of the second messenger, cyclic diguanylate (c-di-GMP), by increased activity of a c-di-GMP specific phosphodiesterase. The ability of raffinose to inhibit P. aeruginosa biofilm formation and its molecular mechanism opens new possibilities for pharmacological and industrial applications.

  1. Application study of improved LEC method in gas transmission station safety assessment%改进作业条件分析法在输气站场安全评价中的应用研究

    Institute of Scientific and Technical Information of China (English)

    曲莎; 樊建春; 张来斌

    2012-01-01

    输气站场是天然气输送的关键环节,站内设备繁多,管道密集,输送介质易燃易爆,且输送量大,作业活动存在很大风险.在调研分析输气站场主要危险活动的基础上,采用改进后的作业条件分析方法(LEC)分析了作业活动中发生事故的可能性、频率及后果,提出了改进措施.改进后的LEC法中的事故发生可能性(L)采用事故树(FTA)法进行定量分析,避免了取值的主观性.同时结合输气站场作业管理特点,在作业条件风险分析(LEC)基础上,增加了监控措施补偿系数M,包括危险事件监测措施补偿系数和危险事件控制措施两方面.分析结果表明,改进后的作业条件分析方法能够更加准确合理地评定作业危险等级,还可有效运用于输气站场的持续改进评价过程中.%The paper is aimed at presenting a renovated LEC method with the purpose of enhancing the safety of the natural gas transmission . As is known, it is the key link for the natural gas transmission stations to prevent all kinds of likely hazards, such as gas-fire and gas-explosion, which pushed us to work out the following renovated LEC method. In order to achieve our purpose, we have first of all improved the fault tree of gas fire and explosion through a quantitative analysis so as to overcome the subjectivity of evaluation. Secondly, combined with the characteristics of gas transmission station and based on the traditional LEC method) we have enhanced monitoring measures for compensation coefficient (M) to the LEC method, including the hazardous event monitoring measures compensation coefficient (M1) and hazardous events control measures (M2). Thirdly, we have worked out the chance probability of hazardous events by using the gas station hazards-identifying and fault-tree analysis in combination with the hazardous event monitoring measures (M1) and hazardous events control measures ( M2) by quantifying the probability and criticality. The analysis

  2. An iron-deficient diet stimulates the onset of the hepatitis due to hepatic copper deposition in the Long-Evans Cinnamon (LEC) rat

    Energy Technology Data Exchange (ETDEWEB)

    Sugawara, Naoki; Sugawara, Chieko [Sapporo Medical Univ. (Japan). Dept. of Public Health

    1999-09-01

    To study effects of dietary Cu and Fe levels on the onset of hepatitis in Long-Evans Cinnamon (LEC) rats, female rats (40 days old) were fed a semipurified diet containing 0.1 or 10 mg Cu/kg and 1.5 or 150 mg Fe/kg in a 2 x 2 factorial arrangement for 35 days. At 75 days after birth, LEC rats (+Cu-Fe) fed a Cu-sufficient but Fe-deficient diet (Cu, 10 mg/kg; Fe, 1.5 mg/kg) showed jaundice, with lethargy, anorexia, and malaise. The biochemical variables relating to liver function were significantly increased compared to three other groups, a Cu- and Fe-deficient (-Cu-Fe) group, a Cu-deficient but Fe-sufficient (-Cu+Fe) group, and a Cu and Fe sufficient (+Cu+Fe) group. Furthermore, the +Cu-Fe rat liver showed massive necrosis with huge nuclei. The other three groups presented no biochemical and histological findings of hepatitis. Hepatic Cu and metallothionein concentrations were 289 {+-} 87 (mean {+-} SD) {mu}g/g liver and 8.7 {+-} 1.8 mg/g liver, respectively, in the +Cu-Fe rats. However, in the +Cu+Fe group the values were 196 {+-} 28 {mu}g Cu/g liver and 10.8 {+-} 1.0 mg/g liver. Hepatic Fe deposition was not influenced significantly by the dietary Cu level. The +Cu-Fe group with jaundice showed the highest free Cu concentration in the liver among the four groups, but the hepatic free Fe concentration was similar to those in the -Cu+Fe and +Cu+Fe groups. Our results indicate that an Fe-deficient diet enhances the deposition of hepatic Cu due to increased absorption of Cu from the gastrointestinal tract. This deposition stimulated the onset of hepatitis. (orig.)

  3. Flow transitions in model Czochralski GaAs melt

    Institute of Scientific and Technical Information of China (English)

    CHEN Shu-xian; LI Ming-wei

    2006-01-01

    The flow and heat transfer of molten GaAs during Czochralski growth are studied with a time-dependent and three-dimensional turbulent flow model. A transition from axisymmetric flow to non-axisymmetric flow and then back to axisymmetric flow again with increasing the crucible rotation rate is predicted. In the non-axisymmetric regime, the thermal wave induced by the combination of coriolis force, buoyancy and viscous force in the GaAs melt is predicted for the first time. The thermal wave is confirmed to be baroclinic thermal wave. The origin of the transition to non-axisymmetric flow is baroclinic instability. The critical parameters for the transitions are presented, which are quantitatively in agreement with Fein and Preffer's experimental results. The calculated results can be taken as a reference for the growth of GaAs single-crystal of high quality.

  4. Electronic contribution to friction on GaAs

    Energy Technology Data Exchange (ETDEWEB)

    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.

  5. High resistivity and ultrafast carrier lifetime in argon implanted GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Walukiewicz, W.; Liliental-Weber, Z.; Jasinski, J. [Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Almonte, M.; Prasad, A.; Haller, E.E.; Weber, E.R. [Lawrence Berkeley National Laboratory and University of California, Berkeley, California 94720 (United States); Grenier, P.; Whitaker, J.F. [Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48109 (United States)

    1996-10-01

    We have investigated the optoelectronic and structural properties of GaAs that has been implanted with Ar ions and subsequently annealed. The material exhibits all the basic optical and electronic characteristics typically observed in nonstoichiometric, As implanted or low-temperature-grown GaAs. Annealing of Ar implanted GaAs at 600{degree}C produces a highly resistive material with a subpicosecond trapping lifetime for photoexcited carriers. Transmission electron microscopy shows that, instead of As precipitates, characteristic for the nonstoichiometeric GaAs, voids ranging in size from 3 to 5 nm are observed in Ar implanted and annealed GaAs. {copyright} {ital 1996 American Institute of Physics.}

  6. 14. 5% conversion efficiency GaAs solar cell fabricated on Si substrates

    Energy Technology Data Exchange (ETDEWEB)

    Itoh, Y.; Nishioka, T.; Yamamoto, A.; Yamaguchi, M.

    1986-12-08

    AlGaAs-GaAs heteroface p/sup +/-p-n solar cells have been fabricated directly on Si substrates using metalorganic chemical vapor deposition. GaAs on Si solar cell efficiency as high as exceeding 14.5% at AM1.5 was obtained by cleaning the substrate surface and repeating GaAs film growth interruption. This value is the highest ever reported for GaAs solar cells on Si substrates. Defects, which could not be observed in homoepitaxially grown GaAs film, were observed in the heteroepitaxial GaAs films through electron beam induced current image. Relatively low conversion efficiency of the GaAs cell on Si compared to the GaAs can be attributed to these defects.

  7. Terahertz radiation from delta-doped GaAs

    DEFF Research Database (Denmark)

    Birkedal, Dan; Hansen, Ole; Sørensen, Claus Birger;

    1994-01-01

    Terahertz pulse emission from four different delta-doped molecular beam epitaxially grown GaAs samples is studied. We observe a decrease of the emitted THz pulse amplitude as the distance of the delta-doped layer from the surface is increased, and a change in polarity of the THz pulses as compared...

  8. GaAs microwave SSPA`s: design and characteristics

    NARCIS (Netherlands)

    Hek, A.P. de; Vliet, F.E. van

    2002-01-01

    The performance of GaAs SSPA's is crucial to a rapidly increasing number of systems. This tutorial aims at clarifying the design choices and trade-offs, and at warning the new designer for pitfalls and unexpected problems. The tutorial starts, after a brief introduction, with a survey of the

  9. GaAs Photovoltaics on Polycrystalline Ge Substrates

    Science.gov (United States)

    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.

  10. Pilot experiment for muonium photo ionization in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Shimomura, K; Nishiyama, K; Nagamine, K [Muon Science Laboratory, IMSS, KEK, Tsukuba, Ibaraki, 305-0801 (Japan); Bakule, P; Pratt, F L [ISIS, Rutherford Appleton Laboratory, Chilton, Oxon OX11 0QX (United Kingdom); Ohishi, K; Ishida, K; Watanabe, I [Advanced Meson Science Laboratory, RIKEN, Wako, Saitama 351-0191 (Japan); Matsuda, Y [Graduate School of Arts and Science, University of Tokyo, 3-8-1 Komaba, Tokyo 153-8902 (Japan); Torikai, E, E-mail: koichiro.shimomura@kek.j [Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Kofu, Yamanashi, 400-8511 (Japan)

    2010-04-01

    Direct observation of muonium photo ionization in GaAs was tried for the first time, with wide range wave length from 1325nm to 800nm lasers in n-type GaAs at 15 K. Recently, Lichti et al. determined the energy levels in the band gap of T center muonium (as an acceptor) and BC muonium (as a donor) by reanalysis of the existing data obtained by various {mu}SR techniques for several semiconductors like Si, Ge, GaAs, GaP etc. In these semiconductors, GaAs is the best sample to apply the muonium photo ionization method for the first time, because the energy level of T center muonium is above 0.54 eV from the valence band, therefore the ionization energy for Mu{sub T}{sup -} {yields} Mu{sub T}{sup 0}+e{sup -} is 0.98eV (corresponding laser wave length is 1260nm), which is within the region of present OPO laser system produced, which was installed RIKEN-RAL

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

    Energy Technology Data Exchange (ETDEWEB)

    Oertel, Stefan

    2012-07-01

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

  12. Droplet-mediated formation of embedded GaAs nanowires in MBE GaAs1-x Bi x films

    Science.gov (United States)

    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.

  13. ON THE CONSTRUCTION OF WELL-CONDITIONED HIERARCHICAL BASES FOR TETRAHEDRAL H(curl)-CONFORMING N(E)D(E)LEC ELEMENT

    Institute of Scientific and Technical Information of China (English)

    Jianguo Xin; Nailong Guo; Wei Cai

    2011-01-01

    A partially orthonormal basis is constructed with better conditioning properties for tetrahedral H(curl)-conforming Nédélec elements.The shape functions are classified into several categories with respect to their topological entities on the reference 3-simplex.The basis functions in each category are constructed to achieve maximum orthogonality.The numerical study on the matrix conditioning shows that for the mass and quasi-stiffness matrices,and in a logarithmic scale the condition number grows linearly vs. order of approximation up to order three.For each order of approximation,the condition number of the quasi-stiffness matrix is about one order less than the corresponding one for the mass matrix.Also,up to order six of approximation the conditioning of the mass and quasistiffness matrices with the proposed basis is better than the corresponding one with the Ainsworth-Coyle basis Internat.J.Numer.Methods.Engrg.,58:2103-2130,2003.except for order four with the quasi-stiffness matrix.Moreover,with the new basis the composite matrix μM + S has better conditioning than the Ainsworth-Coyle basis for a wide range of the parameter μ.

  14. GaAs nanowires. Epitaxy, crystal structure-related properties and magnetic heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Hubmann, Joachim

    2016-07-01

    The intention of this work is twofold: On the one hand, we explore the controlability of GaAs nanowire growth concerning orientation, shape and crystal structure. These are necessary steps, since the growth of GaAs nanowires proceeds not necessarily uniformly, and in GaAs nanowires the in bulk unstable wurtzite phase, and the usual observed zinc-blende crystal phase may coexist in one and the same nanowire. On the other hand, we include ferromagnetic materials into GaAs nanowires. To do that, we produce either ''core/shell'' structures, where the GaAs nanowire is coated with a ferromagnetic ''shell'' material, or grow ferromagnetic nanoscale segments in GaAs nanowires.

  15. Experimental examination of gaas dissolution in in-p melt

    Science.gov (United States)

    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. Resistance Fluctuations in GaAs Nanowire Grids

    Directory of Open Access Journals (Sweden)

    Ivan Marasović

    2014-01-01

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

  17. Raman-scattering probe of anharmonic effects in GaAs

    Science.gov (United States)

    Verma, Prabhat; Abbi, S. C.; Jain, K. P.

    1995-06-01

    A comparative study of anharmonic effects in various structural forms of GaAs, namely crystalline, disordered and ion-implanted, and pulse laser annealed (PLA), using temperature-dependent Raman scattering, is reported for various phonon modes over the temperature range 10-300 K. The disordered and PLA samples are found to have greater anharmonicity than crystalline GaAs. The localized vibrational mode in PLA GaAs shows shorter relaxation time than the LO-phonon mode.

  18. Microstrip and suspended substrate GaAs bias-T

    Science.gov (United States)

    Gopalaswamy, A. D.; Das, Utpal

    2001-09-01

    For photodiode bias-Ts in optoelectronic ICs > 20dB isolation is essential at 2.5-10 GHz for the photodiode to work at both 2.5 and 10 Gbit/s. Designed micro strip and suspended substrate GaAs bias-Ts show 30-140 dB isolation and measured values are approximately 30 dB in the 2.5-10 Ghz range.

  19. Exciton-mediated photothermal cooling in GaAs membranes

    CERN Document Server

    Xuereb, André; Naesby, Andreas; Polzik, Eugene S; Hammerer, Klemens

    2012-01-01

    Cooling of the mechanical motion of a GaAs nano-membrane using the photothermal effect mediated by excitons was recently demonstrated by some of us [K. Usami, et al., Nature Phys. 8, 168 (2012)] and provides a clear example of the use of thermal forces to cool down mechanical motion. Here, we report on a single-free-parameter theoretical model to explain the results of this experiment which matches the experimental data remarkably well.

  20. Solar heating of GaAs nanowire solar cells.

    Science.gov (United States)

    Wu, Shao-Hua; Povinelli, Michelle L

    2015-11-30

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

  1. Processing and characterization of epitaxial GaAs radiation detectors

    CERN Document Server

    Wu, X; 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

    2015-01-01

    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 $\\mu\\textrm{m}$ - 130 $\\mu\\textrm{m}$ 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 $\\mu\\textrm{m}$/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 ($V_{\\textrm{fd}}$) of the detectors with 110 $\\mu\\textrm{m}$ epi-layer thickness is in the range of 8 V - 15 V and the leakage current density is about 10 nA/cm$^2$. 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 ve...

  2. Growth of High Quality GaAs by MBE

    Directory of Open Access Journals (Sweden)

    Naresh Chand

    1989-10-01

    Full Text Available This paper reviews the requirements and current practices in the molecular beam epitaxial (MBE growth af high-quality GaAs. High quality growth of GaAs means excellent control on the growth process andthe excellent surface, structural, electrical and optical properties of the deposited GaAs. Background material is presented about the MBE technique, the MBE system and its initial preparation for growth,molecular-beam source materials, substrate preparation and the growth conditions. The importance of meticulousness at every step is emphasized.Then, to illustrate that the MBE-GaAs has reached a level of perfection,experimental data is presented which shows an excellent control on the growth rate and its lateral uniformity (+- 0.75 per cent, the presence of verylow-level of background impurities (-low 1013 and high electronmobilities ( peak - 3 x 10to poer 5 cm2 v-1s-1 at 42 K for n - 3 x 10 to the power 13 (cm-3. In addition, we show that MBE-GaAs is intrinsically free from electron and hole deep traps. Chemical impurities in the impure arsenic source are shown to be the main limiting factors in determining the transport andoptical properties and formation of deep centers in MBE-GaAs. Such chemical impurities may, however, originate from other sources as well.

  3. Gallium Arsenide (GaAs) Quantum Photonic Waveguide Circuits

    CERN Document Server

    Wang, Jianwei; Jiang, Pisu; Bonneau, Damien; Engin, Erman; Silverstone, Joshua W; Lermer, Matthias; Beetz, Johannes; Kamp, Martin; Hofling, Sven; Tanner, Michael G; Natarajan, Chandra M; Hadfield, Robert H; Dorenbos, Sander N; Zwiller, Val; O'Brien, Jeremy L; Thompson, Mark G

    2014-01-01

    Integrated quantum photonics is a promising approach for future practical and large-scale quantum information processing technologies, with the prospect of on-chip generation, manipulation and measurement of complex quantum states of light. The gallium arsenide (GaAs) material system is a promising technology platform, and has already successfully demonstrated key components including waveguide integrated single-photon sources and integrated single-photon detectors. However, quantum circuits capable of manipulating quantum states of light have so far not been investigated in this material system. Here, we report GaAs photonic circuits for the manipulation of single-photon and two-photon states. Two-photon quantum interference with a visibility of 94.9 +/- 1.3% was observed in GaAs directional couplers. Classical and quantum interference fringes with visibilities of 98.6 +/- 1.3% and 84.4 +/- 1.5% respectively were demonstrated in Mach-Zehnder interferometers exploiting the electro-optic Pockels effect. This w...

  4. Thermal diffusion of Mn through GaAs overlayers on (Ga, Mn)As

    Energy Technology Data Exchange (ETDEWEB)

    Adell, J; Ulfat, I; Ilver, L; Kanski, J [Department of Applied Physics, Chalmers University of Technology, SE-412 96 Gothenburg (Sweden); Sadowski, J [Institute of Physics, Polish Academy of Sciences, PL-02-668 Warsaw (Poland); Karlsson, K [Department of Life Sciences, University of Skoevde, SE-541 28 Skoevde (Sweden)

    2011-03-02

    Thermally stimulated diffusion of Mn through thin layers of GaAs has been studied by x-ray photoemission. (Ga, Mn)As samples with 5 at% Mn were capped with 4, 6 and 8 monolayer (ML) GaAs, and Mn diffusing through the GaAs was trapped on the surface by means of amorphous As. It was found that the out-diffusion is completely suppressed for an 8 ML thick GaAs film. The short diffusion length is attributed to an electrostatic barrier formed at the (Ga, Mn)As/GaAs interface.

  5. Identification a novel mononucleotide deletion mutation in GAA in pompe disease patients

    Directory of Open Access Journals (Sweden)

    Milad Ebrahimi

    2017-01-01

    Full Text Available Background: Mutations in the acid alpha-glucosidase (GAA gene usually lead to reduced GAA activity. In this study, we analyzed the mutations of GAA and GAA enzyme activity from one sibling suspected Pompe disease and their first-degree relatives. Materials and Methods: In this cross-sectional study, GAA enzyme activity assay was assessed using tandem mass spectrometry. Polymerase chain reaction and Sanger sequencing were performed for GAA analysis. Results: GAA enzyme activity was significantly decreased in patients compared to the normal range (P = 0.02. Two individuals showed ten alterations in the GAA sequence, in which one of them (c. 1650del G has not been previously described in the literature. A single Guanine deletion (del-G was detected at codon 551 in exon 12. Conclusion: According to the literature, the detected change is a novel mutation. We hypothesized that the discovered deletion in the GAA might lead to a reduced activity of the gene product.

  6. GAA triplet-repeats cause nucleosome depletion in the human genome.

    Science.gov (United States)

    Zhao, Hongyu; Xing, Yongqiang; Liu, Guoqing; Chen, Ping; Zhao, Xiujuan; Li, Guohong; Cai, Lu

    2015-08-01

    Although there have been many investigations into how trinucleotide repeats affect nucleosome formation and local chromatin structure, the nucleosome positioning of GAA triplet-repeats in the human genome has remained elusive. In this work, the nucleosome occupancy around GAA triplet-repeats across the human genome was computed statistically. The results showed a nucleosome-depleted region in the vicinity of GAA triplet-repeats in activated and resting CD4(+) T cells. Furthermore, the A-tract was frequently adjacent to the upstream region of GAA triplet-repeats and could enhance the depletion surrounding GAA triplet-repeats. In vitro chromatin reconstitution assays with GAA-containing plasmids also demonstrated that the inserted GAA triplet-repeats destabilized the ability of recombinant plasmids to assemble nucleosomes. Our results suggested that GAA triplet-repeats have lower affinity to histones and can change local nucleosome positioning. These findings may be helpful for understanding the mechanism of Friedreich's ataxia, which is associated with GAA triplet-repeats at the chromatin level.

  7. Gate Drain Underlapped-PNIN-GAA-TFET for Comprehensively Upgraded Analog/RF Performance

    Science.gov (United States)

    Madan, Jaya; Chaujar, Rishu

    2017-02-01

    This work integrates the merits of gate-drain underlapping (GDU) and N+ source pocket on cylindrical gate all around tunnel FET (GAA-TFET) to form GDU-PNIN-GAA-TFET. It is analysed that the source pocket located at the source-channel junction narrows the tunneling barrier width at the tunneling junction and thereby enhances the ON-state current of GAA-TFET. Further, it is obtained that the GDU resists the extension of carrier density (built-up under the gated region) towards the drain side (under the underlapped length), thereby suppressing the ambipolar current and reducing the parasitic capacitances of GAA-TFET. Consequently, the amalgamated merits of both engineering schemes are obtained in GDU-PNIN-GAA-TFET that thus conquers the greatest challenges faced by TFET. Thus, GDU-PNIN-GAA-TFET results in an up-gradation in the overall performance of GAA-TFET. Moreover, it is realised that the RF figure of merits FOMs such as cut-off frequency (fT) and maximum oscillation frequency (fMAX) are also considerably improved with integration of source pocket on GAA-TFET. Thus, the improved analog and RF performance of GDU-PNIN-GAA-TFET makes it ideal for low power and high-speed applications.

  8. Thermal diffusion of Mn through GaAs overlayers on (Ga, Mn)As.

    Science.gov (United States)

    Adell, J; Ulfat, I; Ilver, L; Sadowski, J; Karlsson, K; Kanski, J

    2011-03-02

    Thermally stimulated diffusion of Mn through thin layers of GaAs has been studied by x-ray photoemission. (Ga, Mn)As samples with 5 at% Mn were capped with 4, 6 and 8 monolayer (ML) GaAs, and Mn diffusing through the GaAs was trapped on the surface by means of amorphous As. It was found that the out-diffusion is completely suppressed for an 8 ML thick GaAs film. The short diffusion length is attributed to an electrostatic barrier formed at the (Ga, Mn)As/GaAs interface.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  10. Electrical and structural characterization of GaAs on InP grown by OMCVD; application to GaAs MESFETs

    Science.gov (United States)

    Azoulay, R.; Clei, A.; Dugrand, L.; Draïdia, auN.; Leroux, G.; Biblemont, S.

    1991-01-01

    The growth of GaAs on InP has attracted considerable interest recently because of the possibility of integration of GaAs electronic devices and 1.3 μm optical devices on the same wafer. In this work, we have investigated the growth of GaAs MESFETs and doped channel MIS-like FETs on InP by atmospheric pressure OMCVD. Because of the difference between the thermal expansion coefficient of GaAs and InP, the layers are under biaxial strain. The lowest FWHM of the (004) reflection curve of the double crystal X-ray diffraction spectra is 110 arc sec for a 12 μm thick layer. We have investigated the influence of the substrate temperature and of the arsine molar fraction on the residual carrier concentration of layers grown side by side on GaAs and on InP. The GaAs layers grown on InP are much more compensated than the layers grown on GaAs, indicating a higher incorporation of impurities. On MESFETs grown on InP, gm = 200mS/mm with Fmax higher than 30 GHz. On doped-channel MIS-like FETs on InP, we have measured gm = 145mS/mm.

  11. X-ray diffraction from single GaAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Biermanns, Andreas

    2012-11-12

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

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

    Science.gov (United States)

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

    2004-09-01

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

  13. Influence of cooling on the working parameters of GaAs detectors

    CERN Document Server

    Golovnia, S N; Tsyupa, Yu P; Vorobev, A P; Koretskaja, O B; Okaevich, L P; Tolbanov, O P

    2002-01-01

    The results of the measurements working parameters of GaAs detector samples as the basis for the design of the X-ray sensitive detectors are presented. To select the optimal operating conditions for GaAs detectors the study of the temperature dependence of their working parameters has been done.

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

    Energy Technology Data Exchange (ETDEWEB)

    Mendez-Garcia, V.H. [Optical Communications Research Institute (IICO), Universidad Autonoma de San Luis Potosi Av. Karakorum 1470, Lomas 4a Seccion, 78210 San Luis Potosi (Mexico)]. E-mail: vmendez@cactus.iico.uaslp.mx; Ramirez-Arenas, F.J. [Optical Communications Research Institute (IICO), Universidad Autonoma de San Luis Potosi Av. Karakorum 1470, Lomas 4a Seccion, 78210 San Luis Potosi (Mexico); Lastras-Martinez, A. [Optical Communications Research Institute (IICO), Universidad Autonoma de San Luis Potosi Av. Karakorum 1470, Lomas 4a Seccion, 78210 San Luis Potosi (Mexico); Cruz-Hernandez, E. [Physics Department, Centro de Investigacion y de Estudios Avanzados del IPN, Apartado Postal 14470, D.F. Mexico (Mexico); Pulzara-Mora, A. [Physics Department, Centro de Investigacion y de Estudios Avanzados del IPN, Apartado Postal 14470, D.F. Mexico (Mexico); Rojas-Ramirez, J.S. [Physics Department, Centro de Investigacion y de Estudios Avanzados del IPN, Apartado Postal 14470, D.F. Mexico (Mexico); Lopez-Lopez, M. [Physics Department, Centro de Investigacion y de Estudios Avanzados del IPN, Apartado Postal 14470, D.F. Mexico (Mexico)

    2006-05-30

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

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

    Science.gov (United States)

    Gheen, Gregory; Cheng, Li-Jen

    1987-01-01

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

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

    DEFF Research Database (Denmark)

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

    2002-01-01

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

  17. Implementation and Performance of GaAs Digital Signal Processing ASICs

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  19. Modulation Spectroscopy of GaAs Covered by InAs Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    金鹏; 孟宪权; 张子旸; 李成明; 曲胜春; 徐波; 刘峰奇; 王占国; 李乙钢; 张存洲; 潘士宏

    2002-01-01

    Contactless electroreflectance has been employed at room temperature to study the Fermi level pinning atundoped-n+ GaAs surfaces covered by 1.6 and 1.8 monolayer (ML) InAs quantum dots (QDs). It is shownthat the 1.8 ML InAs QD moves the Fermi level at GaAs surface to the valence band maximum by about 70 meVcompared to bare GaAs, whereas 1.6 ML InAs on GaAs does not modify the Fermi level. It is corzfirmed thatthe modiffication of the 1.8 ML InAs deposition on the Fermi level at GaAs surface is due to the QDs, which aresurrounded by some oxidized InAs facets, rather than the wetting layer.

  20. Controlling crystal phases in GaAs nanowires grown by Au-assisted molecular beam epitaxy.

    Science.gov (United States)

    Dheeraj, D L; Munshi, A M; Scheffler, M; van Helvoort, A T J; Weman, H; Fimland, B O

    2013-01-11

    Control of the crystal phases of GaAs nanowires (NWs) is essential to eliminate the formation of stacking faults which deteriorate the optical and electronic properties of the NWs. In addition, the ability to control the crystal phase of NWs provides an opportunity to engineer the band gap without changing the crystal material. We show that the crystal phase of GaAs NWs grown on GaAs(111)B substrates by molecular beam epitaxy using the Au-assisted vapor-liquid-solid growth mechanism can be tuned between wurtzite (WZ) and zinc blende (ZB) by changing the V/III flux ratio. As an example we demonstrate the realization of WZ GaAs NWs with a ZB GaAs insert that has been grown without changing the substrate temperature.

  1. Electric field and space-charge distribution in SI GaAs: effect of high-energy proton irradiation

    CERN Document Server

    Castaldini, A; Polenta, L; Canali, C; Nava, F

    1999-01-01

    The effect of irradiation on semi-insulating gallium arsenide Schottky diodes has been investigated by means of surface potential measurements and spectroscopic techniques. Before and after irradiation the electric field exhibits a Mott barrier-like distribution, and the box-shaped space charge modifies its distribution with irradiation. The increase in density or the generation of some traps changes the compensation ratio producing a deeper active region and a more homogeneous distribution of the electric field. The latter phenomenon is also observed by EBIC images of edge-mounted diodes.

  2. Modeling frequency dependence of GaAs MESFET characteristics

    Science.gov (United States)

    Conger, Jeff; Peczalski, Andrzej; Shur, Michael S.

    1994-01-01

    We present a new method of modeling the output conductance dispersion of GaAs MESFET's. High frequency model parameters are extracted and then used to model high frequency output conductance over a wide range of bias conditions. The model is then used to simulate and analyze the effect of output conductance dispersion on the performance of DCFL and SCFL logic gates. Whereas the DCFL performance is not significantly affected by the high frequency effects, the noise margin of SCFL decreases by almost a factor of 30% above 100 kHz, with an associated decrease in the voltage swing and gate delay.

  3. Laser Liftoff of GaAs Thin Films

    OpenAIRE

    Hayes, Garrett J.; Clemens, Bruce M.

    2014-01-01

    The high cost of single crystal III-V substrates limits the use of GaAs and related sphalerite III-V materials in many applications, especially photovoltaics. Separating epitaxially-grown layers from a growth substrate can reduce costs, however the current approach, which uses an acid to laterally etch an epitaxial sacrificial layer, is slow and can damage other device layers. Here, we demonstrate a new approach that is orders of magnitude faster, and that enables more freedom in the selectio...

  4. Investigation of Optically Induced Avalanching in GaAs

    Science.gov (United States)

    1989-06-01

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

  5. Electrode pattern design for GaAs betavoltaic batteries

    Institute of Scientific and Technical Information of China (English)

    Chen Haiyang; Yin Jianhua; Li Darang

    2011-01-01

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

  6. GaAs MMIC building blocks for TV applications

    OpenAIRE

    Philippe, Pascal; Pertus, Marcel

    1990-01-01

    GaAs MMICs mixers and oscillators have been fabricated for application to VHF-UHF and satellite TV tuners using a 0.7 mm gate length MESFET process available in the Philips Microwave Limeil Foundry, in France. Various mixer configurations have been evaluated which show improved intermodulation/noise figure performance as compared to silicon bipolar circuits. Best circuits have input IP3 over 10 dBm with associated noise figure lower than 10 dB at 2 GHz. The oscillators tested are the multivib...

  7. Electronic properties of delta -doped GaAs

    Science.gov (United States)

    Gold, A.; Ghazali, A.; Serre, J.

    1992-07-01

    For temperature zero the authors study the effects of disorder on the electronic properties of the two-dimensional electron gas which exists in planar-doped ( delta -doped) GaAs. The density of states, the Fermi level, the single-particle relaxation time and the electron mobility are calculated as functions of the dopant concentration. The transition from a band tail to an impurity band and the nature of the metal-insulator transition are discussed. The authors compare the theoretical results on the mobility with some available experimental data.

  8. Observation of As-Grown Defects in Zn-Doped GaAs by Positron Lifetime Spectra

    Institute of Scientific and Technical Information of China (English)

    WANG Zhu; WANG Shao-Jie; CHEN Zhi-Quan

    2000-01-01

    Positron lifetime spectra were measured for the Zn-doped p-type GaAs. In comparing the horizontal-Bridgman-method-grown and the floating-zone-method grown p-type GaAs with the liquid-encapsulation-Czochvalski-grown p-type GaAs samples, positron trapping into vacancy type defects was observed in the former two grown p-type GaAs. Shallow positron traps were detected, and the dominant ones were attributed to acceptor the in p-type GaAs.

  9. GaAs clean up studied with synchrotron radiation photoemission

    Science.gov (United States)

    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.

  10. Sn nanothreads in GaAs: experiment and simulation

    Science.gov (United States)

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

    2016-12-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Galiana, B.; Benedicto, M.; Tejedor, P. [Instituto de Ciencia de Materiales de Madrid, C.S.I.C., Sor Juana Ines de la Cruz 3, 28049 Madrid (Spain)

    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.

  12. Design and Fabrication of Planar GaAs Gunn Diodes

    Science.gov (United States)

    Kim, Mi-Ra; Lee, Seong-Dae; Chae, Yeon-Sik; Rhee, Jin-Koo

    We studied planar graded-gap injector GaAs Gunn diodes designed for operation at 94GHz. Two types of planar Gunn diodes were designed and fabricated. In the first diode, a cathode was situated inside a circular anode with a diameter of 190μm. The distance between the anode and cathode varied from 60μm to 68μm depending on the cathode size. Also, we designed a structure with a constant distance between the anode and cathode of 10μm. In the second diode, the anode was situated inside the cathode for the flip-chip mounting on the oscillator circuits. The fabrication of the Gunn diode was based on ohmic contact metallization, mesa etching, and air-bridge and overlay metallization. DC measurements were carried out, and the nature of the negative differential resistance, the operating voltage, and the peak current in the graded-gap injector GaAs Gunn diodes are discussed for different device structures. It is shown that the structure with the shorter distance between the cathode and anode has a higher peak current, higher breakdown voltage, and lower threshold voltage than those of the structure with the larger distance between the cathode and anode.

  13. Bismuth alloying properties in GaAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-09-15

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

  14. High-efficiency nanostructured window GaAs solar cells.

    Science.gov (United States)

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

    2013-10-09

    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.

  15. New photocathode using ZnSe substrates with GaAs active layer

    Science.gov (United States)

    Jin, Xiuguang; Takeda, Yoshikazu; Fuchi, Shingo

    2017-03-01

    GaAs active layers were successfully fabricated on ZnSe substrates using a metalorganic vapor phase epitaxy system. As a photocathode, a GaAs active layer shows a high quantum efficiency (QE) of 9% at 532 nm laser light illumination, which is comparable to a QE of 11% from GaAs bulk. In addition, a photoemission current of 10 µA was obtained from this photocathode. One more important point is that this photocathode could realize back-side illumination of 532 nm laser light, and thus its widespread applications are expected in microscopy and accelerator fields.

  16. X-ray photoelectron spectroscopy study of the effects of ultrapure water on GaAs

    Science.gov (United States)

    Massies, J.; Contour, J. P.

    1985-06-01

    X-ray photoelectron spectroscopy has been used to investigate the effects of de-ionized water on chemical etched GaAs surfaces. When the treatment with water is performed in static conditions (stagnant water) a Ga-rich oxide layer is formed on GaAs at the rate of 10-20 Å h-1. In contrast, when the GaAs surface is treated in dynamic conditions (running water), no oxide buildup is observed. Moreover, running water can remove the oxide film formed in static conditions, as well as oxidized layers due to air exposure. These results are discussed in the framework of cleaning prior to molecular beam epitaxy.

  17. Proposal to develop GaAs detectors for physics at the LHC

    CERN Document Server

    Beaumont, S P; Booth, C N; Buttar, C M; Carraresi, L; Colocci, M; Combley, F; D'Auria, S D; del Papa, C; Dogru, M; Edwards, M; Fiori, F; Francescato, A; Hou, Y; Lynch, J G; Lisowski, B; Matheson, J; Newett, S; Nuti, M; O'Shea, V; Pelfer, P G; Raine, P H; Sharp, P H; Skillicorn, Ian O; Smith, K M; Tartoni, N; ten Have, I; Turnbull, R M; Vanni, U; Vinattieri, A; Zichichi, Antonino; CERN. Geneva. Detector Research and Development Committee

    1990-01-01

    The present proposal first describes the results obtained using GaAs Schottky diode detectors which we have constructed, and the initial steps which we have taken towards the design of a GaAs preamplifier to match the detectors. We then propose a continuation of the programme of work towards a demonstration detector module for an LHC pre-shower tracker detector based on GaAs, within a time-scale of two years. The module will be compatible with the design of the proposed pre-shower tracker using silicon detectors (DRDC/P3), and should allow direct substitution for comparison purposes.

  18. Growth and Photoluminescence of GaAs Quantum Dots on Si(1O0)

    Institute of Scientific and Technical Information of China (English)

    张建国; 李广海; 张勇; 晋云霞; 张立德

    2001-01-01

    GaAs quantum dots (QDs) with high density and remarkable uniformity in dot size and distribution grown on Si(100) surface with artificial topography by radio-frequency sputtering have been demonstrated. The photoluminescence spectrum has been recorded. The growth of GaAs QDs is initiated with the preferential nucleation of small dots along ripples controlled by the Stranski-Krastanow growth mode. This method may be useful in combining high-speed and optoelectronic GaAs devices with Si integrated-circuit technology.

  19. An Improved Nonlinear Circuit Model for GaAs Gunn Diode in W-Band Oscillator

    Science.gov (United States)

    Zhang, Bo; Fan, Yong; Zhang, Yonghong

    An improved nonlinear circuit model for a GaAs Gunn diode in an oscillator is proposed based on the physical mechanism of the diode. This model interprets the nonlinear harmonic character on the Gunn diode. Its equivalent nonlinear circuit of which can assist in the design of the Gunn oscillator and help in the analysis of the fundamental and harmonic characteristics of the GaAs Gunn diode. The simulation prediction and the experiment of the Gunn oscillator show the feasibility of the nonlinear circuit model for the GaAs Gunn oscillator.

  20. Growth Interruption Effect on the Fabrication of GaAs Concentric Multiple Rings by Droplet Epitaxy

    Directory of Open Access Journals (Sweden)

    Fedorov A

    2010-01-01

    Full Text Available Abstract We present the molecular beam epitaxy fabrication and optical properties of complex GaAs nanostructures by droplet epitaxy: concentric triple quantum rings. A significant difference was found between the volumes of the original droplets and the final GaAs structures. By means of atomic force microscopy and photoluminescence spectroscopy, we found that a thin GaAs quantum well-like layer is developed all over the substrate during the growth interruption times, caused by the migration of Ga in a low As background.

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

    DEFF Research Database (Denmark)

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

    2016-01-01

    A single-junction core-shell GaAs nanowire (NW) solar cell on Si (1 1 1) substrates is presented. A Ga-assisted vapor–liquid–solid growth mechanism was used for the formation of a patterned array of radial p-i-n GaAs NWs encapsulated in AlInP passivation. Novel device fabrication utilizing facet......-dependent properties to minimize passivation layer removal for electrical contacting is demonstrated. Thorough electrical characterization and analysis of the cell is reported. The electrostatic potential distribution across the radial p-i-n junction GaAs NW is investigated by off-axis electron holography....

  2. Preflight study of San Marco D/L GaAs solar cell panels

    Science.gov (United States)

    Day, J. H., Jr.

    1984-01-01

    The solar array for the San Marco D/L spacecraft is described and the performance of 4 GaAs solar cell panels are examined. In comparison to the typical Si solar cell panel for San Marco D/L, it is shown that each GaAs solar cell panel provides at least 23 percent more specific power at maximum output and 28 deg C. Also described here, are several measurements that will be made to evaluate the relative performance of Si and GaAs solar cell panels during the San Marco D/L flight.

  3. Transient Velocity Assessment in Gallium Arsenide, and of Other GaAs Characteristics Related to Device Functions

    Science.gov (United States)

    2012-03-29

    RW-809 ^ C^> Scientific Program Officer: Mr . Sven A. Roosild, DARPA/DSO 1400 Wilson Blvd. Arlington, VA 22209 Contractor: Oregon Graduate...of acoustic phonons, non-parabolicity of the conduction band minimum and intervaliey scattering through the admixture of p-type states. He concluded...llarrlta 1985 LEC (HP) 50 5 Goutereaux et_ al. lUrrltt 1985 LEC (HP) 50 5 Ilakemore et_ al. MOCSEMHAD 1985 IXC (HP) 50 0.5 Dobrllla et al. MRS /5F0 1985

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

    Science.gov (United States)

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

    2014-01-01

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

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

    Science.gov (United States)

    Galiev, G. B.; Klimov, E. A.; Vasiliev, A. L.; Imamov, R. M.; Pushkarev, S. S.; Trunkin, I. N.; Maltsev, P. P.

    2017-01-01

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

  6. Antireflection coatings for GaAs solar cell applications

    Energy Technology Data Exchange (ETDEWEB)

    Alexieva, Z I; Nenova, Z S; Bakardjieva, V S; Dikov, Hr M; Milanova, M M, E-mail: alexieva@phys.bas.b [Central Laboratory of Applied Physics, Bulgarian Academy of Sciences, 59 St Petersrburg Blvd, 4000 Plovdiv (Bulgaria)

    2010-04-01

    A double-layer structure of Al{sub 2}O{sub 3} over ZrO{sub 2} film is studied. Minimization of the average weighted reflectance is carried out to optimize the thickness of the two layers in the antireflection coating. An optimal value of 2.17% for the weighted average reflection is estimated. The optimal thicknesses of the layers are 49 nm for the bottom and 45 nm for the top layer. Low temperature spin coating technique is used to deposit ZrO{sub 2} and Al{sub 2}O{sub 3} films from sol gel solutions on polished silicon wafers, GaAs multilayer heterostructures and AlGaAs/GaAs solar cells. The density of the short-circuit photocurrent increases from 25 mA.cm{sup -2} for solar cells without an antireflection coating to 36 mA.cm{sup -2} for those with a double layer coating.

  7. Antireflection coatings for GaAs solar cell applications

    Science.gov (United States)

    Alexieva, Z. I.; Nenova, Z. S.; Bakardjieva, V. S.; Milanova, M. M.; Dikov, Hr M.

    2010-04-01

    A double-layer structure of Al2O3 over ZrO2 film is studied. Minimization of the average weighted reflectance is carried out to optimize the thickness of the two layers in the antireflection coating. An optimal value of 2.17% for the weighted average reflection is estimated. The optimal thicknesses of the layers are 49 nm for the bottom and 45 nm for the top layer. Low temperature spin coating technique is used to deposit ZrO2 and Al2O3 films from sol gel solutions on polished silicon wafers, GaAs multilayer heterostructures and AlGaAs/GaAs solar cells. The density of the short-circuit photocurrent increases from 25 mA.cm-2 for solar cells without an antireflection coating to 36 mA.cm-2 for those with a double layer coating.

  8. Analysis of LED degradation; proton-bombarded GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Hooft, G.W. ' t; Opdorp, C. van (Philips Gloeilampenfabrieken N.V., Eindhoven (Netherlands). Forschungslaboratorium)

    1984-03-01

    An analysis is given of the degradation of light-emitting, Zn-diffused GaAs diodes after proton bombardment. Use is made of a generally applicable method by which the external bulk quantum efficiency and the injection efficiency of an LED can be determined separately. Owing to the increase of non-radiative recombination being larger in the bulk than in the space-charge region, the injection efficiency at constant current first starts to increase and then decreases as a function of irradiation fluence. Furthermore, it is shown that the apparent bulk quantum efficiency decreases superlinearly with the irradiation fluence. This is consistent with the theory for a linear-graded pn junction and the assumption that the concentration of additional killer centres is directly proportional to the irradiation fluence.

  9. Indirect excitons in (111) GaAs double quantum wells

    Science.gov (United States)

    Hubert, C.; Biermann, K.; Hernández-Mínguez, A.; Santos, P. V.

    2017-08-01

    We study the dynamics of indirect (or dipolar) excitons (interwell IXs) in GaAs (111) double quantum wells (DQWs) subjected to a transverse electric field. In comparison with single (111) QWs, these DQWs can store, for a comparable applied fields and optical excitation density, a density of interwell IXs much larger than in SQWs, thus leading to stronger interwell IX- IX repulsive interactions. We show by means of spatially-resolved optical spectroscopy that interwell IXs in (111) DWQs can be transported over distances exceeding 60 μm. From the spectral dependence of the interwell IX spatial distribution profiles, we show that the long transport distances are due to drift forces arising from the strong interwell IX- IX interactions.

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

    Science.gov (United States)

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

    1987-01-01

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

  11. Development of GaAs Detectors for Physics at the LHC

    CERN Multimedia

    Chu, Zhonghua; Krais, R; Rente, C; Syben, O; Tenbusch, F; Toporowsky, M; Xiao, Wenjiang; Cavallini, A; Fiori, F; Edwards, M; Geppert, R; Goppert, R; Haberla, C; Hornung, M F; Irsigler, R; Rogalla, M; Beaumont, S; Raine, C; Skillicorn, I; Margelevicius, J; Meshkinis, S; Smetana, S; Jones, B; Santana, J; Sloan, T; Zdansky, K; Alexiev, D; Donnelly, I J; Canali, C; Chiossi, C; Nava, F; Pavan, P; Kubasta, J; Tomiak, Z; Tchmil, V; Tchountonov, A; Tsioupa, I; Dogru, M; Gray, R; Hou, Yuqian; Manolopoulos, S; Walsh, S; Aizenshtadt, G; Budnitsky, D L; Gossen, A; Khludkov, S; Koretskaya, O B; Okaevitch, L; Potapov, A; Stepanov, V E; Tolbanov, O; Tyagev, A; Matulionis, A; Pozela, J; Kavaliauskiene, G; Kazukauskas, V; Kiliulis, R; Rinkevicius, V; Slenys, S; Storasta, J V

    2002-01-01

    % RD-8 Development of GaAs Detectors for Physics at the LHC \\\\ \\\\The aims of the collaboration are to investigate the available material options, performance and limitations of simple pad, pixel and microstrip GaAs detectors for minimum ionising particles with radiation hardness and speed which are competitive with silicon detectors. This new technology was originally developed within our university laboratories but now benefits from increasing industrial interest and collaboration in detector fabrication. Initial steps have also been taken towards the fabrication of GaAs preamplifiers to match the detectors in radiation hardness. The programme of work aims to construct a demonstration detector module for an LHC forward tracker based on GaAs.

  12. CMOS compatible route for GaAs based large scale flexible and transparent electronics

    KAUST Repository

    Nour, Maha A.

    2014-08-01

    Flexible electronics using gallium arsenide (GaAs) for nano-electronics with high electron mobility and optoelectronics with direct band gap are attractive for many applications. Here we describe a state-of-the-art CMOS compatible batch fabrication process of transforming traditional electronic circuitry into large-area flexible, semitransparent platform. We show a simple release process for peeling off 200 nm of GaAs from 200 nm GaAs/300 nm AlAs stack on GaAs substrate using diluted hydrofluoric acid (HF). This process enables releasing a single top layer compared to peeling off all layers with small sizes at the same time. This is done utilizing a network of release holes which contributes to the better transparency (45 % at 724 nm wavelength) observed.

  13. High Purity GaAs Far IR Photoconductor With Enhanced Quantum Efficieny Project

    Data.gov (United States)

    National Aeronautics and Space Administration — This proposal introduces an innovative concept aimed to significantly enhance the quantum efficiency of a far-infrared GaAs photoconductor and achieve sensitivity...

  14. Electromagnetically induced transparency due to intervalence band coherence in a GaAs quantum well.

    Science.gov (United States)

    Phillips, Mark; Wang, Hailin

    2003-05-15

    We demonstrate electromagnetically induced transparency in the transient optical response in a GaAs quantum well by using the nonradiative coherence between the heavy-hole and the light-hole valence bands.

  15. Experimental study on the activation process of GaAs spin—polarized electron source

    Institute of Scientific and Technical Information of China (English)

    RuanCun-Jun

    2003-01-01

    GaAs spin-polarized electron source is a new kind of electron source, where the GaAs semiconductor crystal is used as a photocathode under the irradiation of helicity light. In this paper the activation process of the GaAs spin-polarized electron source is unvestigated experimentally in detail, during which the negative electron affinity of the photo cathode should be achieved more carefully by absorbing the caesium and oxygen on the surface of the GaAs crystal under ultrahigh vacuum conditions. Besides the different activation processes, the important physical parameters are studied to achieve the optimum activation results. At the same time the stability and lifetime of the polarized electron beam are explored for future experiments. Some important experimental data have been acquired.

  16. Experimental study on the activation process of GaAs spin-polarized electron source

    Institute of Scientific and Technical Information of China (English)

    阮存军

    2003-01-01

    GaAs spin-polarized electron source is a new kind of electron source, where the GaAs semiconductor crystal is used as a photocathode under the irradiation of helicity light. In this paper the activation process of the GaAs spin-polarized electron source is investigated experimentally in detail, during which the negative electron affinity of the photo cathode should be achieved more carefully by absorbing the caesium and oxygen on the surface of the GaAs crystal under ultrahigh vacuum conditions. Besides the different activation processes, the important physical parameters are studied to achieve the optimum activation results. At the same time the stability and lifetime of the polarized electron beam are explored for future experiments. Some important experimental data have been acquired.

  17. Activation processes on GaAs photocathode by different currents of oxygen source

    Science.gov (United States)

    Miao, Zhuang; Shi, Feng; Cheng, Hongchang; Wang, Shufei; Zhang, Xiaohui; Yuan, Yuan; Chen, Chang

    2015-04-01

    In order to know the influence of activation processes on GaAs photocathodes, three GaAs samples were activated by a fixed current of cesium source and different currents of oxygen source. The current of caesium source is same during activation to ensure initial adsorption of caesium quantum is similar, which is the base to show the difference during alternation activation of caesium and oxygen. Analysed with the activation data, it is indicated that Cs-to-O current ratio of 1.07 is the optimum ratio to obtain higher sensitivity and better stability. According to double dipole model, stable and uniform double dipole layers of GaAs-O-Cs:Cs-O-Cs are formed and negative electron affinity is achieved on GaAs surface by activation with cesium and oxygen. The analytical result is just coincident with the model. Thus there is an efficient technological method to improve sensitivity and stability of GaAs photocathode.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

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

    Science.gov (United States)

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

    2002-01-01

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

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

    Science.gov (United States)

    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.

  1. Terrace width distribution during unstable homoepitaxial growth of GaAs(110): An experimental study

    Energy Technology Data Exchange (ETDEWEB)

    Crespillo, M.L. [Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), Sor Juana Ines de la Cruz s/n, Cantoblanco, 28049 Madrid (Spain)]. E-mail: mcrespillo@icmm.csic.es; Sacedon, J.L. [Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), Sor Juana Ines de la Cruz s/n, Cantoblanco, 28049 Madrid (Spain); Tejedor, P. [Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), Sor Juana Ines de la Cruz s/n, Cantoblanco, 28049 Madrid (Spain)

    2006-07-15

    The temporal evolution of the step bunching instability formed during GaAs homoepitaxial growth on the GaAs(110) vicinal to (111)A has been studied by atomic force microscopy (AFM) and the step-step distribution has been quantified as a function of deposition time. Analysis of the AFM data has shown that neither the terrace width distribution (TWD) nor the terrace height distribution (THD) fit to a Gaussian function in the initial stages of growth, but both evolve with time as the bunching instability develops. After deposition of 500 ML of GaAs the TWD exhibits a clear Gaussian behavior while the THD is very well fitted to a Lorentzian distribution. The GaAs surface morphology initially shows a great dispersion in terrace height and width values with a clear anisotropy along the <001> tilt direction, but evidence of self-controlled growth is observed irrespective of layer thickness.

  2. Anharmonicity in Light Scattering by Optical Phonons in GaAs1-xBix

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-05-28

    We present a Raman spectroscopic study of GaAs 1-xBix epilayers grown by molecular beam epitaxy. We have investigated the anharmonic effect on the GaAs-like longitudinal optical phonon mode (LO'GaAs) of GaAs 1-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 GaAs 1-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 GaAs 1-xBix.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  5. Sidewall GaAs tunnel junctions fabricated using molecular layer epitaxy

    Directory of Open Access Journals (Sweden)

    Takeo Ohno and Yutaka Oyama

    2012-01-01

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

  6. The apparent effect of sample surface damage on the dielectric parameters of GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Engelbrecht, J.A.A. [Physics Department, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031 (South Africa)], E-mail: Japie.Engelbrecht@nmmu.ac.za; Hashe, N.G. [Physics Department, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031 (South Africa); Hillie, K.T. [CSIR-NML Laboratory, P.O. Box 395, Pretoria 0001 (South Africa); Claassens, C.H. [Physics Department, University of the Free State, Bloemfontein 9300 (South Africa)

    2007-12-15

    The dielectric and optical parameters determined by infrared reflectance spectroscopy and computer simulation of a set of GaAs substrates of various surface topologies are reported. The influence of surface damage on the parameters is noted.

  7. Ferromagnetic GaAs structures with single Mn delta-layer fabricated using laser deposition.

    Science.gov (United States)

    Danilov, Yuri A; Vikhrova, Olga V; Kudrin, Alexey V; Zvonkov, Boris N

    2012-06-01

    The new technique combining metal-organic chemical vapor epitaxy with laser ablation of solid targets was used for fabrication of ferromagnetic GaAs structures with single Mn delta-doped layer. The structures demonstrated anomalous Hall effect, planar Hall effect, negative and anisotropic magnetoresistance in temperature range of 10-35 K. In GaAs structures with only single Mn delta-layer (without additional 2D hole gas channel or quantum well) ferromagnetism was observed for the first time.

  8. Evolution of Wurtzite Structured GaAs Shells Around InAs Nanowire Cores

    Directory of Open Access Journals (Sweden)

    Kim Y

    2009-01-01

    Full Text Available Abstract GaAs was radially deposited on InAs nanowires by metal–organic chemical vapor deposition and resultant nanowire heterostructures were characterized by detailed electron microscopy investigations. The GaAs shells have been grown in wurtzite structure, epitaxially on the wurtzite structured InAs nanowire cores. The fundamental reason of structural evolution in terms of material nucleation and interfacial structure is given.

  9. Molecular beam epitaxial growth and structural characterization of ZnS on (001) GaAs

    Science.gov (United States)

    Benz, R. G., II; Huang, P. C.; Stock, S. R.; Summers, C. J.

    1988-01-01

    The effect of surface nucleation processes on the quality of ZnS layers grown on (001) GaAs substrates by molecular beam epitaxy is reported. Reflection high energy electron diffraction indicated that nucleation at high temperatures produced more planar surfaces than nucleation at low temperatures, but the crystalline quality as assessed by X-ray double crystal diffractometry is relatively independent of nucleation temperature. A critical factor in layer quality was the initial roughness of the GaAs surfaces.

  10. Effect of nitride chemical passivation of the surface of GaAs photodiodes on their characteristics

    Science.gov (United States)

    Kontrosh, E. V.; Lebedeva, N. M.; Kalinovskiy, V. S.; Soldatenkov, F. Yu; Ulin, V. P.

    2016-11-01

    Characteristics of GaAs photodiodes have been studied before and after the chemical nitridation of their surface in hydrazine sulfide solutions, which leads to substitution of surface As atoms with N atoms to give a GaN monolayer. The resulting nitride coatings hinder the oxidation of GaAs in air and provide a decrease in the density of surface states involved in recombination processes. The device characteristics improved by nitridation are preserved during a long time.

  11. Development of a GaAs Monolithic Surface Acoustic Wave Integrated Circuit

    Energy Technology Data Exchange (ETDEWEB)

    Baca, A.G.; Casalnuovo, S.C.; Drummond, T.J.; Frye, G.C.; Heller, E.J.; Hietala, V.M.; Klem, J.F.

    1999-03-08

    An oscillator technology using surface acoustic wave delay lines integrated with GaAs MESFET electronics has been developed for GaAs-based integrated microsensor applications. The oscillator consists of a two-port SAW delay line in a feedback loop with a four-stage GaAs MESFET amplifier. Oscillators with frequencies of 470, 350, and 200 MHz have been designed and fabricated. These oscillators are also promising for other RF applications.

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

    Directory of Open Access Journals (Sweden)

    Sara Anjomani Virmouni

    2015-03-01

    Full Text Available 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.

  13. Development of a GaAs Monolithic Surface Acoustic Wave Integrated Circuit

    Energy Technology Data Exchange (ETDEWEB)

    Baca, A.G.; Casalnuovo, S.C.; Drummond, T.J.; Frye, G.C.; Heller, E.J.; Hietala, V.M.; Klem, J.F.

    1999-03-08

    An oscillator technology using surface acoustic wave delay lines integrated with GaAs MESFET electronics has been developed for GaAs-based integrated microsensor applications. The oscillator consists of a two-port SAW delay line in a feedback loop with a four-stage GaAs MESFET amplifier. Oscillators with frequencies of 470, 350, and 200 MHz have been designed and fabricated. These oscillators are also promising for other RF applications.

  14. High quality superconducting NbN thin films on GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Marsili, Francesco; Fiore, Andrea [COBRA Research Institute, Eindhoven University of Technology, PO Box 513, NL-5600MB Eindhoven (Netherlands); Gaggero, Alessandro; Leoni, Roberto [Istituto di Fotonica e Nanotecnologie (IFN), CNR, via Cineto Romano 42, I-00156 Roma (Italy); Li, Lianhe H; Surrente, Alessandro [Institute of Photonics and Quantum Electronics (IPEQ), Ecole Polytechnique Federale de Lausanne (EPFL), Station 3, CH-1015 Lausanne (Switzerland); Levy, Francis, E-mail: francesco.marsili@epfl.c [Institute of Condensed Matter Physics (IPMC), Ecole Polytechnique Federale de Lausanne (EPFL), Station 3, CH-1015 Lausanne (Switzerland)

    2009-09-15

    A very promising way to increase the detection efficiency of nanowire superconducting single-photon detectors (SSPDs) consists in integrating them with advanced optical structures such as distributed Bragg reflectors (DBRs) and optical waveguides. This requires transferring the challenging SSPD technology from the usual substrates, i.e. sapphire and MgO, to an optical substrate like GaAs, on which DBRs and waveguides can be easily obtained. Therefore, we optimized the deposition process of few-nm thick superconducting NbN films on GaAs and AlAs/GaAs-based DBRs at low temperatures (substrate temperature T{sub S} = 400 {sup 0}C), in order to prevent As evaporation. NbN films ranging from 150 to 3 nm in thickness were then deposited on single-crystal MgO, GaAs, MgO-buffered GaAs and DBRs by current-controlled DC magnetron sputtering (planar, circular, balanced configuration) of Nb in an Ar+N{sub 2} plasma. 5.5 nm thick NbN films on GaAs exhibit T{sub C} = 10.7 K, {Delta}T{sub C} = 1.1 K and RRR = 0.7. The growth of such high quality thin NbN films on GaAs and DBRs has never been reported before.

  15. Development of GaAs Gunn Diodes and Their Applications to Frequency Modulated Continuous Wave Radar

    Science.gov (United States)

    Choi, Seok-Gyu; Han, Min; Baek, Yong-Hyun; Ko, Dong-Sik; Baek, Tae-Jong; Lee, Sang-Jin; Kim, Jin-Ho; Lee, Seong-Dae; Kim, Mi-Ra; Chae, Yeon-Sik; Kathalingam, Adaikalam; Rhee, Jin-Koo

    2010-11-01

    In this work, we have designed and fabricated the GaAs Gunn diodes for a 94 GHz waveguide voltage controlled oscillator (VCO) which is one of the important parts in a frequency modulated continuous wave (FMCW) radar application. For fabrication of the high power GaAs Gunn diodes, we adopted a graded gap injector which enhances the output power and conversion efficiency by effectively removing the dead-zone. We have measured RF characteristics of the fabricated GaAs Gunn diodes. The operating current, oscillation frequency, and output power of the fabricated GaAs Gunn diodes are presented as a function of the anode diameters. The operating current increases with anode diameters, whereas the oscillation frequency decreases. The higher oscillation frequency was obtained from 60 µm anode diameters of the fabricated Gunn GaAs diodes and higher power was obtained from 68 µm. Also, for application of the 94 GHz FMCW radar system, we have fabricated the 94 GHz waveguide VCO. From the fabricated GaAs Gunn diodes of anode diameter of 60 µm, we have obtained the improved VCO performance.

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

    Directory of Open Access Journals (Sweden)

    Bouravleuv AD

    2009-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Zhou Lin

    2008-01-01

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

  18. Metalorganic vapor phase epitaxy of GaAs on Si using II a-flouride buffer layers

    Science.gov (United States)

    Tiwari, A. N.; Freundlich, A.; Beaumont, B.; Blunier, S.; Zogg, H.; Teodoropol, S.; Vèrié, C.

    1992-11-01

    Metalorganic vapor phase epitaxy has been used for the first time to grow epitaxial GaAs layers on (111) and (100) oriented Si either using CaF 2 or stacked (Ca,Sr)F 2/CaF 2 as a buffer. The GaAs layers show sharp and well resolved electron channeling patterns. The Rutherford backscattering (RBS) ion channeling minimum yield is 5% for (111) orientation and 6% for (100) orientation. The GaAs(111) layers are untwinned. The strain in the GaAs layer has been measured with RBS and X-ray diffraction and it is found that the thermal mismatch-induced strain in the GaAs layer is considerably lower than in similar GaAs films grown without flouride buffer.

  19. Ammonia plasma passivation of GaAs in downstream microwave and radio-frequency parallel plate plasma reactors

    OpenAIRE

    Aydil, Eray S.; Giapis, Konstantinos P.; Gottscho, Richard A.; Donnelly, Vincent M.; Yoon, Euijoon

    1993-01-01

    The poor electronic properties of the GaAs surface and GaAs–insulator interfaces, generally resulting from large density of surface/interface states, have limited GaAs device technology. Room-temperature ammonia plasma (dry) passivation of GaAs surfaces, which reduces the surface state density, is investigated as an alternative to wet passivation techniques. Plasma passivation is more compatible with clustered-dry processing which provides better control of the processing environment, and thu...

  20. Influence of substrate orientation on the structural quality of GaAs nanowires in molecular beam epitaxy.

    Science.gov (United States)

    Zhang, Zhi; Shi, Sui-Xing; Chen, Ping-Ping; Lu, Wei; Zou, Jin

    2015-01-26

    In this study, the effect of substrate orientation on the structural quality of Au-catalyzed epitaxial GaAs nanowires grown by a molecular beam epitaxy reactor has been investigated. It was found that the substrate orientations can be used to manipulate the nanowire catalyst composition and the catalyst surface energy and, therefore, to alter the structural quality of GaAs nanowires grown on different substrates. Defect-free wurtzite-structured GaAs nanowires grown on the GaAs (110) substrate have been achieved under our growth conditions.

  1. Passive Q-switching of diode-pumped Yb:YAG microchip laser with ion-implanted GaAs

    Institute of Scientific and Technical Information of China (English)

    Yonggang Wang(王勇刚); Xiaoyu Ma(马骁宇); Bin Zhong(钟斌); Desong Wang(王德松); Qiulin Zhang(张秋琳); Baohua Feng(冯宝华)

    2004-01-01

    We reported a passive Q-switched diode laser pumped Yb:YAG microchip laser with an ion-implanted semiinsulating GaAs wafer. The wafer was implanted with 400-kev As+ in the concentration of 1016 ions/cm2.To decrease the non-saturable loss, we annealed the ion-implanted GaAs at 500 ℃ for 5 minutes and coated both sides of the ion-implanted GaAs with antireflection (AR) and high reflection (HR) films,respectively. Using GaAs wafer as an absorber and an output coupler, we obtained 52-ns pulse duration of single pulse.

  2. Disruption of Higher Order DNA Structures in Friedreich's Ataxia (GAA)(n) Repeats by PNA or LNA Targeting

    DEFF Research Database (Denmark)

    Bergquist, Helen; Rocha, Cristina S. J.; Alvarez-Asencio, Ruben;

    2016-01-01

    Expansion of (GAA)n repeats in the first intron of the Frataxin gene is associated with reduced mRNA and protein levels and the development of Friedreich’s ataxia. (GAA)n expansions form non-canonical structures, including intramolecular triplex (H-DNA), and R-loops and are associated with epigen......Expansion of (GAA)n repeats in the first intron of the Frataxin gene is associated with reduced mRNA and protein levels and the development of Friedreich’s ataxia. (GAA)n expansions form non-canonical structures, including intramolecular triplex (H-DNA), and R-loops and are associated...

  3. Magnetic Resonance of Defects in Heteroepitaxial Semiconductor Structures

    Science.gov (United States)

    1992-05-11

    Resistivity of Low-Temperature MBE GaAs," in: Semi-Insulating II/V Materials 1990, Eds. A.G. Milnes and C.J. Miner ( Adam Hilger, Bristol 1990), p. 111. 6...Resistivity of Low-Temperature MBE GaAs," in: Semi-Insulating III/V Materials 1990, Eds. A.G. Milnes and C.J. Miner ( Adam Hilger, Bristol 1990), p...and Temperature on the Structure of Low-Temperature GaAs, Z Liliental- Weber, A. Claverie, P. Werner, W. Schaff , and E. R. Weber, in: Defects in

  4. Defect studies in low-temperature-grown GaAs

    Energy Technology Data Exchange (ETDEWEB)

    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. Defect studies in low-temperature-grown GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Bliss, David Emory [Univ. of California, Berkeley, CA (United States)

    1992-11-01

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

  6. Amplification of GAA/TTC triplet repeat in vitro: preferential expansion of (TTC)n strand.

    Science.gov (United States)

    Wu, M J; Chow, L W; Hsieh, M

    1998-08-14

    Several human hereditary neuromuscular and neurodegenerative diseases are caused by abnormal expansion of triplet repeat sequences (TRSs) CAG/CTG, CGG/CCG, or GAA/TTC on certain chromosomes. It is generally accepted that multiple slippage synthesis accounts for the instabilities of TRS. Earlier in vitro experiments by Behn-Krappa and Doerfler showed that TRS with high GC content can be expanded. In contrast, here we demonstrated that certain AT-rich TRSs, (TTC)17, (GAA)10/(TTC)10 and (GAA)17/(TTC)17, were also expansion-prone in PCR. With respect to the sequence of TRS, surprisingly, we found that the AT-rich (GAA)17/(TTC)17 extended more efficiently than the GC-rich (CAG)17/(CTG)17. This strongly suggested that the AT content of the repeat may influence TRS expansion. Furthermore, to examine the expansion of single-stranded TRS, we showed that only (TTC)17, but not the complementary (GAA)17, can be expanded. This suggested that a T-T mismatch may stabilize compatible secondary structures, most likely hairpins, for slippage synthesis. However, another poly-pyrimidine TRS, (CCT)17, is not amplification-prone in PCR. Due to the high C-content, this TRS is unlikely to adopt hairpin structures at the high pH used for PCR. Thus, the single-stranded PCR experiment may serve as an indirect assay for the ability of a sequence to adopt a hairpin conformation. When amplification was performed in reactions using Klenow DNA polymerase, only the double-stranded TRSs can be expanded. The reaction rate for (GAA)10/(TTC)10 was slower than for (GAA)17/(TTC)17, suggesting that the length of the repeat may be important for the amplification of TRS. The findings of these in vitro experiments may aid in understanding TRS expansion in vivo.

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

    Institute of Scientific and Technical Information of China (English)

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

    2012-01-01

    Early research has shown that the varied doping structures of the active layer of GaAs photocathodes have beenproven 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.

  8. GaAs surface wet cleaning by a novel treatment in revolving ultrasonic atomization solution

    Energy Technology Data Exchange (ETDEWEB)

    Li Zaijin; Hu Liming; Wang Ye; Yang Ye; Peng Hangyu; Zhang Jinlong; Qin Li; Liu Yun; Wang Lijun, E-mail: lizaijin@126.co [Key Laboratory of Excited State Processes, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China)

    2010-03-15

    A novel process for the wet cleaning of GaAs surface is presented. It is designed for technological simplicity and minimum damage generated within the GaAs surface. It combines GaAs cleaning with three conditions consisting of (1) removal of thermodynamically unstable species and (2) surface oxide layers must be completely removed after thermal cleaning, and (3) a smooth surface must be provided. Revolving ultrasonic atomization technology is adopted in the cleaning process. At first impurity removal is achieved by organic solvents; second NH{sub 4}OH:H{sub 2}O{sub 2}:H{sub 2}O = 1:1:10 solution and HCl: H{sub 2}O{sub 2}:H{sub 2}O = 1:1:20 solution in succession to etch a very thin GaAs layer, the goal of the step is removing metallic contaminants and forming a very thin oxidation layer on the GaAs wafer surface; NH{sub 4}OH:H{sub 2}O = 1:5 solution is used as the removed oxide layers in the end. The effectiveness of the process is demonstrated by the operation of the GaAs wafer. Characterization of the oxide composition was carried out by X-ray photoelectron spectroscopy. Metal-contamination and surface morphology was observed by a total reflection X-ray fluorescence spectroscopy and atomic force microscope. The research results show that the cleaned surface is without contamination or metal contamination. Also, the GaAs substrates surface is very smooth for epitaxial growth using the rotary ultrasonic atomization technology. (semiconductor technology)

  9. GaAs integrated circuits and heterojunction devices

    Science.gov (United States)

    Fowlis, Colin

    1986-06-01

    The state of the art of GaAs technology in the U.S. as it applies to digital and analog integrated circuits is examined. In a market projection, it is noted that whereas analog ICs now largely dominate the market, in 1994 they will amount to only 39 percent vs. 57 percent for digital ICs. The military segment of the market will remain the largest (42 percent in 1994 vs. 70 percent today). ICs using depletion-mode-only FETs can be constructed in various forms, the closest to production being BFL or buffered FET logic. Schottky diode FET logic - a lower power approach - can reach higher complexities and strong efforts are being made in this direction. Enhancement type devices appear essential to reach LSI and VLSI complexity, but process control is still very difficult; strong efforts are under way, both in the U.S. and in Japan. Heterojunction devices appear very promising, although structures are fairly complex, and special fabrication techniques, such as molecular beam epitaxy and MOCVD, are necessary. High-electron-mobility-transistor (HEMT) devices show significant performance advantages over MESFETs at low temperatures. Initial results of heterojunction bipolar transistor devices show promise for high speed A/D converter applications.

  10. Ultrafast terahertz emission properties in GaAs semiconductor

    Science.gov (United States)

    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.

  11. Planar GaAs diodes for THz frequency mixing applications

    Science.gov (United States)

    Bishop, William L.; Crowe, Thomas W.; Mattauch, Robert J.; Dossal, Hasan

    1992-01-01

    Schottky barrier diodes for terahertz applications are typically fabricated as a micron to sub-micron circular anode metallization on GaAs which is contacted with a sharp wire (whisker). This structure has the benefits of the simplicity of the fabrication of the diode chip, the minimal shunt capacitance of the whisker contact and the ability of the whisker wire to couple energy to the diode. However, whisker-contacted diodes are costly to assembly and difficult to qualify for space applications. Also, complex receiver systems which require many diodes are difficult to assemble. The objective of this paper is to discuss the advantages of planar Schottky diodes for high frequency receiver applications and to summarize the problems of advancing the planar technology to the terahertz frequency range. Section 2 will discuss the structure, fabrication and performance of state-of-the-art planar Schottky diodes. In Section 3 the problems of designing and fabricating planar diodes for terahertz frequency operation are discussed along with a number of viable solutions. Section 4 summarizes the need for further research and cooperation between diode designers and RF engineers.

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

    Science.gov (United States)

    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.

  13. Tidal and subtidal flow patterns o a tropical continental shelf semi-insulated by coral reefs

    NARCIS (Netherlands)

    Tarya, A.; Hoitink, A.J.F.; Vegt, van der M.

    2010-01-01

    The present study sets out to describe the tidal and subtidal water motion at the Berau coastal shelf, which represents a tropical continental shelf area of variable width hosting a complex of barrier reefs along its oceanic edge. Moored and shipboard measurements on currents and turbulence were mad

  14. Growth and Characterization of Semi-Insulating GaN Films Grown by MOCVD

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    High resistivity unintentionally doped GaN films were grown on (0001) sapphire substrates by metalorganic chemical vapor deposition. The surface morphology of the layer was measured by both atomic force microscopy and scanning electron microscopy. The results show that the films have mirror-like surface morphology with root mean square of 0.3 nm. The full width at half maximum of double crystal X-ray diffraction rocking curve for (0002) GaN is about 5.22 arcmin, indicative of high crystal quality. The resistivity of the GaN epilayers at room temperature and at 250 ℃ was measured to be approximate 109 and 106 Ω·cm respectively, by variable temperature Hall measurement. Deep level traps in the GaN epilayers were investigated by thermally stimulated current and resistivity measurements.

  15. Surface-plasma interactions in GaAs subjected to capacitively coupled RF plasmas

    CERN Document Server

    Surdu-Bob, C C

    2002-01-01

    Surface compositional changes in GaAs due to RF plasmas of different gases have been investigated by XPS and etch rates were measured using AFM. Angular Resolved XPS (ARXPS) was also employed for depth analysis of the composition of the surface layers. An important role in this study was determination of oxide thickness using XPS data. The study of surface - plasma interaction was undertaken by correlating results of surface analysis with plasma diagnosis. Different experiments were designed to accurately measure the BEs associated with the Ga 3d, Ga 2p sub 3 sub / sub 2 and LMM peaks using XPS analysis and propose identification in terms of the oxides of GaAs. Along with GaAs wafers, some reference compounds such as metallic Ga and Ga sub 2 O sub 3 powder were used. A separate study aiming the identification of the GaAs surface oxides formed on the GaAs surface during and after plasma processing was undertaken. Surface compositional changes after plasma treatment, prior to surface analysis are considered, wi...

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Abdulsattar, Mudar Ahmed, E-mail: mudarahmed3@yahoo.com [Ministry of Science and Technology, Baghdad (Iraq); Hussein, Mohammed T.; Hameed, Hadeel Ali [Department of Physics, College of Science, University of Baghdad, Baghdad (Iraq)

    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.

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

    Directory of Open Access Journals (Sweden)

    Mudar Ahmed Abdulsattar

    2014-12-01

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

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

    Science.gov (United States)

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

    2014-12-01

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

  20. Measurement of GaAs start duration in different solution concentration using infrared images

    Institute of Scientific and Technical Information of China (English)

    LIU Lin; YE YuTang; WU YunFeng; FANG Liang; LU JiaJia

    2008-01-01

    This paper proposes a new infrared method to measure the start duration of GaAs substrate in chemi-cal etching. When etching starts, the temperature of liquid-film will change because of heat release in the chemical reaction. As a result, the start duration of GaAs can be tested by collecting real-time in-frared thermal images in the course of temperature variation. Both theoretical analysis and experi-mental results show that the line shape liquid film of a 2-mm width is a good monitoring subject. By making use of the grey distribution change of a certain cross section of the line shape liquid film, the start duration of reaction between GaAs and H2SO4-H2O2-H2O is obtained. The start durations of reac-tion between GaAs substrate and H2SO4: H2O2:H2O (=5:1:50 and 15:3:50) solution are about 0.2 s and 0.3-0.4 s, respectively. This result and relative method will impulse the research of wet chemical etching technology of GaAs and so on.

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

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  3. n-Type Doping of Vapor–Liquid–Solid Grown GaAs Nanowires

    Directory of Open Access Journals (Sweden)

    Gutsche Christoph

    2011-01-01

    Full Text Available Abstract In this letter, n-type doping of GaAs nanowires grown by metal–organic vapor phase epitaxy in the vapor–liquid–solid growth mode on (111B GaAs substrates is reported. A low growth temperature of 400°C is adjusted in order to exclude shell growth. The impact of doping precursors on the morphology of GaAs nanowires was investigated. Tetraethyl tin as doping precursor enables heavily n-type doped GaAs nanowires in a relatively small process window while no doping effect could be found for ditertiarybutylsilane. Electrical measurements carried out on single nanowires reveal an axially non-uniform doping profile. Within a number of wires from the same run, the donor concentrations ND of GaAs nanowires are found to vary from 7 × 1017 cm-3 to 2 × 1018 cm-3. The n-type conductivity is proven by the transfer characteristics of fabricated nanowire metal–insulator-semiconductor field-effect transistor devices.

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

    Energy Technology Data Exchange (ETDEWEB)

    Cardozo, Benjamin Lewin [Univ. of California, Berkeley, CA (United States)

    2004-01-01

    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 1013 cm-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.

  5. GaAs Based InAs/GaSb Superlattice Short Wavelength Infrared Detectors Grown by Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    TANG Bao; XU Ying-Qiang; ZHOU Zhi-Qiang; HAO Rui-Ting; WANG Guo-Wei; REN Zheng-Wei; NIU Zhi-Chuan

    2009-01-01

    InAs/GaSb superlattice (SL) short wavelength infrared photoconduction detectors are grown by molecular beam epitaxy on GaAs(O01) semi-insulating substrates. An interracial misfit mode A1Sb quantum dot layer and a thick GaSb layer are grown as buffer layers. The detectors containing a 200-period 2 ML/8 ML InAs/GaSb SL active layer are fabricated with a pixel area of 800×800 μm2 without using passivation or antireflection coatings. Corresponding to the 50% cutoff wavelengths of 2.05 μm at 77K and 2.25 μ m at 300 K, the peak detectivities of the detectors are 4 × 109 cm·Hz1/2/W at 77K and 2 × 108 cm.Hz1/2/W at 30OK, respectively.

  6. In situ transmission electron microscopy analyses of thermally annealed self catalyzed GaAs nanowires grown by molecular beam epitaxy

    DEFF Research Database (Denmark)

    Ambrosini, S.; Wagner, Jakob Birkedal; Booth, Tim;

    2011-01-01

    Self catalyzed GaAs nanowires grown on Si-treated GaAs substrates were studied with a transmission electron microscope before and after annealing at 600◦C. At room temperature the nanowires have a zincblende structure and are locally characterized by a high density of rotational twins and stackin...

  7. Immune responses and hypercoagulation in ERT for Pompe disease are mutation and rhGAA dose dependent.

    Directory of Open Access Journals (Sweden)

    Sushrusha Nayak

    Full Text Available Enzyme replacement therapy (ERT with recombinant human acid-α-glucosidase (rhGAA is the only FDA approved therapy for Pompe disease. Without ERT, severely affected individuals (early onset succumb to the disease within 2 years of life. A spectrum of disease severity and progression exists depending upon the type of mutation in the GAA gene (GAA, which in turn determines the amount of defective protein produced and its enzymatic activity. A large percent of the early onset patients are also cross reactive immunological material negative (CRIM- and develop high titer immune responses to ERT with rhGAA. New insights from our studies in pre-clinical murine models reveal that the type of Gaa mutation has a profound effect on the immune responses mounted against ERT and the associated toxicities, including activation of clotting factors and disseminated intravascular coagulation (DIC. Additionally, the mouse strain affects outcomes, suggesting the influence of additional genetic components or modifiers. High doses of rhGAA (20 mg/kg are currently required to achieve therapeutic benefit. Our studies indicate that lower enzyme doses reduce the antibody responses to rhGAA, reduce the incidence of immune toxicity and avoid ERT-associated anaphylaxis. Therefore, development of rhGAA with increased efficacy is warranted to limit immunotoxicities.

  8. Disruption of Higher Order DNA Structures in Friedreich's Ataxia (GAA)(n) Repeats by PNA or LNA Targeting

    DEFF Research Database (Denmark)

    Bergquist, Helen; Rocha, Cristina S. J.; Alvarez-Asencio, Ruben

    2016-01-01

    Expansion of (GAA)n repeats in the first intron of the Frataxin gene is associated with reduced mRNA and protein levels and the development of Friedreich’s ataxia. (GAA)n expansions form non-canonical structures, including intramolecular triplex (H-DNA), and R-loops and are associated with epigen......Expansion of (GAA)n repeats in the first intron of the Frataxin gene is associated with reduced mRNA and protein levels and the development of Friedreich’s ataxia. (GAA)n expansions form non-canonical structures, including intramolecular triplex (H-DNA), and R-loops and are associated...... with epigenetic modifications. With the aim of interfering with higher order H-DNA (like) DNA structures within pathological (GAA)n expansions, we examined sequence-specific interaction of peptide nucleic acid (PNA) with (GAA)n repeats of different lengths (short: n=9, medium: n=75 or long: n=115) by chemical...... probing of triple helical and single stranded regions. We found that a triplex structure (H-DNA) forms at GAA repeats of different lengths; however, single stranded regions were not detected within the medium size pathological repeat, suggesting the presence of a more complex structure. Furthermore, (GAA...

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

    Energy Technology Data Exchange (ETDEWEB)

    Boulanger, J. P.; Chia, A. C. E.; LaPierre, R. R., E-mail: lapierr@mcmaster.ca [Department of Engineering Physics, McMaster University, Hamilton, Ontario L8S 4L7 (Canada)

    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%.

  10. Ultrathin MgO diffusion barriers for ferromagnetic electrodes on GaAs(001).

    Science.gov (United States)

    Sarkar, Anirban; Wang, Shibo; Grafeneder, Wolfgang; Arndt, Martin; Koch, Reinhold

    2015-04-24

    Ultrathin MgO(100) films serving as a diffusion barrier between ferromagnetic electrodes and GaAs(001) semiconductor templates have been investigated. Using Fe as an exemplary ferromagnetic material, heterostructures of Fe/MgO/GaAs(001) were prepared at 200 °C with the MgO thickness ranging from 1.5 to 3 nm. Structural characterization reveals very good crystalline ordering in all layers of the heterostructure. Auger electron spectroscopy depth-profiling and cross-sectional high-resolution transmission electron microscopy evidence diffusion of Fe into MgO and-for too thin MgO barriers-further into GaAs(001). Our results recommend a MgO barrier thickness larger than or equal to 2.6 nm for its application as a reliable diffusion barrier on GaAs(001) in spintronics devices.

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

    Directory of Open Access Journals (Sweden)

    Tchernycheva M

    2010-01-01

    Full Text Available Abstract 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(211A and GaAs(111B 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.

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

    Science.gov (United States)

    Zhang, X; Dubrovskii, V G; Sibirev, N V; Cirlin, G E; Sartel, C; Tchernycheva, M; Harmand, J C; Glas, F

    2010-07-24

    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.

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

    Science.gov (United States)

    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.

  14. Improvement of Porous GaAs (100 Structure through Electrochemical Etching Based on DMF Solution

    Directory of Open Access Journals (Sweden)

    Muhamad Ikram Md Taib

    2014-01-01

    Full Text Available We report on the fabrication of porous GaAs (100 using three different acids, H2SO4, HF, and HCl, diluted in DMF based solutions. The mixture of H2SO4 with DMF showed the best porous structures in comparison to other acids. The concentration of the DMF solution was then varied for a fixed concentration of H2SO4. It was apparent that the different concentration of the DMF solvent gave different types of morphology of the porous GaAs. Furthermore, a higher current density improved the uniformity of the pores distribution. The best porous GaAs exhibited well-defined circular shaped pores with high uniformity. To the best of our knowledge, such structure produced in such manner has never been reported so far. Finally, the optimum etching conditions of the pores were proposed.

  15. Determination of Doping Density in GaAs Semiconductor by Wavelength-Dependent Photoacoustic Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Lim, Jongtae; Choi, Oklim; Boo, Doo Wan; Choi, Joonggill [Yonsei Univ., Seoul (Korea, Republic of)

    2014-03-15

    The wavelength dependence of the photoacoustic signal for n-type GaAs semiconductors in the region of the band-gap energies was investigated. The significant changes in the phase and amplitude of the photoacoustic signal near the band-gap absorption wavelengths were observed to occur when the Si-doping densities in GaAs were varied. Particularly, the first derivatives of the photoacoustic phase vs. wavelength graphs were evaluated and fitted with single Gaussian functions. The peak centers and the widths of the Gaussian curves clearly showed linear relationships with the log values of the Si-doping densities in n-type GaAs semiconductors. It is proposed that the wavelength-dependent PA spectroscopy can be used as a simple and nondestructive method for measuring the doping densities in bulk semiconductors.

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

    Science.gov (United States)

    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.

  17. Nanoscale footprints of self-running gallium droplets on GaAs surface.

    Directory of Open Access Journals (Sweden)

    Jiang Wu

    Full Text Available In this work, the nanoscale footprints of self-driven liquid gallium droplet movement on a GaAs (001 surface will be presented and analyzed. The nanoscale footprints of a primary droplet trail and ordered secondary droplets along primary droplet trails are observed on the GaAs surface. A well ordered nanoterrace from the trail is left behind by a running droplet. In addition, collision events between two running droplets are investigated. The exposed fresh surface after a collision demonstrates a superior evaporation property. Based on the observation of droplet evolution at different stages as well as nanoscale footprints, a schematic diagram of droplet evolution is outlined in an attempt to understand the phenomenon of stick-slip droplet motion on the GaAs surface. The present study adds another piece of work to obtain the physical picture of a stick-slip self-driven mechanism in nanoscale, bridging nano and micro systems.

  18. Damped oscillations in reflection high energy electron diffraction during GaAs MBE

    Energy Technology Data Exchange (ETDEWEB)

    Van Hove, J.M.; Lent, C.S.; Pukite, P.R.; Cohen, P.I.

    1983-07-01

    Oscillations in the time evolution of electron diffraction during MBE growth of GaAs are shown to be related to periodic variations in the step distributions on GaAs surfaces during epitaxial growth. Unintentionally doped GaAs surfaces were first prepared by MBE. Then the Ga flux is interrupted until an instrument limited diffraction pattern was obtained. During this process the angular width of the specular beam was measured versus time. When the Ga flux there are intensity oscillations that are weak near the Bragg angle. At the Bragg angle, where the diffraction is insensitive to surface steps, the length of the specular RHEED streak does not change. At angles between the Bragg angles, where steps lengthen the streaks, there are periodic variations in the streak length. We interpret the results in terms of a model in which a partially completed surface has a step distribution with smaller average terrace lengths than a completed surface.

  19. Recombination dynamics in aerotaxy-grown Zn-doped GaAs nanowires

    Science.gov (United States)

    Zhang, Wei; Yang, Fangfang; Messing, Maria E.; Mergenthaler, Kilian; Pistol, Mats-Erik; Deppert, Knut; Samuelson, Lars; Magnusson, Martin H.; Yartsev, Arkady

    2016-11-01

    In this paper we have investigated the dynamics of photo-generated charge carriers in a series of aerotaxy-grown GaAs nanowires (NWs) with different levels of Zn doping. Time-resolved photo-induced luminescence and transient absorption have been employed to investigate radiative (band edge transition) and non-radiative charge recombination processes, respectively. We find that the photo-luminescence (PL) lifetime of intrinsic GaAs NWs is significantly increased after growing an AlGaAs shell over them, indicating that an AlGaAs shell can effectively passivate the surface of aerotaxy-grown GaAs NWs. We observe that PL decay time as well as PL intensity decrease with increasing Zn doping, which can be attributed to thermally activated electron trapping with the trap density increased due to the Zn doping level.

  20. Electric characterization of GaAs deposited on porous silicon by electrodeposition technique

    Energy Technology Data Exchange (ETDEWEB)

    Lajnef, M., E-mail: Mohamed.lajnef@yahoo.fr [Laboratoire de Photovoltaique et de Semi-conducteurs, Centre de Recherche et des Technologies de l' Energie, BP. 95, Hammam-Lif 2050 (Tunisia); Chtourou, R.; Ezzaouia, H. [Laboratoire de Photovoltaique et de Semi-conducteurs, Centre de Recherche et des Technologies de l' Energie, BP. 95, Hammam-Lif 2050 (Tunisia)

    2010-03-01

    GaAs thin films were synthesized on porous Si substrate by the electrodeposition technique. The X-ray diffraction studies showed that the as-grown films were crystallised in mixed phase nature orthorhombic and cubic of GaAs. The GaAs film was then electrically characterized using current-voltage (I-V) and capacitance-voltage (C-V) techniques by the way of Al/GaAs Schottky junctions. The electric analysis allowed us to determine the n factor and the barrier height {phi}{sub b0} parameters of Al/GaAs Schottky junctions. The (C-V) characteristics were recorded at frequency signal 1 MHz in order to identify the effect of the surface states on the behaviour of the capacitance of the device.

  1. Efficiency enhancement in GaAs solar cells using self-assembled microspheres.

    Science.gov (United States)

    Chang, Te-Hung; Wu, Pei-Hsuan; Chen, Sheng-Hui; Chan, Chia-Hua; Lee, Cheng-Chung; Chen, Chii-Chang; Su, Yan-Kuin

    2009-04-13

    In this study we develop an efficient light harvesting scheme that can enhance the efficiency of GaAs solar cells using self-assembled microspheres. Based on the scattering of the microspheres and the theory of photonic crystals, the path length can be increased. In addition, the self-assembly of microspheres is one of the simplest and the fastest methods with which to build a 2D periodic structure. The experimental results are confirmed by the use of a simulation in which a finite-difference time-domain (FDTD) method is used to analyze the absorption and electric field of the 2D periodic structure. Both the results of the numerical simulations and the experimental results show an increase in the conversion power efficiency of GaAs solar cell of about 25% when 1 microm microspheres were assembled on the surface of GaAs solar cells.

  2. Performance of Series Connected GaAs Photovoltaic Converters under Multimode Optical Fiber Illumination

    Directory of Open Access Journals (Sweden)

    Tiqiang Shan

    2014-01-01

    Full Text Available In many military and industrial applications, GaAs photovoltaic (PV converters are connected in series in order to generate the required voltage compatible with most common electronics. Multimode optical fibers are usually used to carry high-intensity laser and illuminate the series connected GaAs PV converters in real time. However, multimode optical fiber illumination has a speckled intensity pattern. The series connected PV array is extremely sensitive to nonuniform illumination; its performance is limited severely by the converter that is illuminated the least. This paper quantifies the effects of multimode optical fiber illumination on the performance of series connected GaAs PV converters, analyzes the loss mechanisms due to speckles, and discusses the maximum illumination efficiency. In order to describe the illumination dependent behavior detailedly, modeling of the series connected PV array is accomplished based on the equivalent circuit for PV cells. Finally, a series of experiments are carried out to demonstrate the theory analysis.

  3. Use of anodic oxide films to control the diffusion of zinc in GaAs

    Science.gov (United States)

    Cutlerywala, H.; Roedel, R. J.

    1994-06-01

    Experiments were performed to diffuse zinc into GaAs through anodic oxide layers of varying thickness and density. Using electrochemical profiling to determine both the electrically active zinc concentration and the diffusion depth with high resolution, the following results were found. The depth of the junction varies inversely with the thickness and the density of the oxide. However, the surface concentration appears to be independent of oxide thickness or density, attaining a value identical to that found for diffusion into a bare GaAs sample. These results demonstrate that the most significant impact of the oxide is to delay the introduction of the zinc into the GaAs lattice. In short, the anodic oxide cannot be used as either a mask or as a zinc concentration attenuator.

  4. Variations in first principles calculated defect energies in GaAs and their effect on practical predictions

    Indian Academy of Sciences (India)

    Deepak; D Balamurugan; K Nandi

    2003-01-01

    There is an abundant literature on calculations of formation and ionization energies of point defects in GaAs. Since most of these energies, especially the formation energies, are difficult to measure, the calculations are primary means of obtaining their values. However, based on the assumptions of the calculations, the reported values differ greatly among the various calculations. In this paper we discuss the sources of errors and their impact on practical predictions valuable in GaAs device fabrication. In particular, we have compared a large set of computed energies and selected the most appropriate values. Then, in the context of GaAs material quality, we investigated the impact of errors in calculation of formation energies on the performance of the GaAs substrate for device fabrication. We find that in spite of the errors inherent in ab initio calculations, it is possible to correctly predict the behaviour of GaAs substrate.

  5. Solid phase epitaxial regrowth of (100)GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Almonte, Marlene Isabel [California Univ., Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering

    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.

  6. Identification and Functional Characterization of GAA Mutations in Colombian Patients Affected by Pompe Disease.

    Science.gov (United States)

    Niño, Mónica Yasmín; Mateus, Heidi Eliana; Fonseca, Dora Janeth; Kroos, Marian A; Ospina, Sandra Yaneth; Mejía, Juan Fernando; Uribe, Jesús Alfredo; Reuser, Arnold J J; Laissue, Paul

    2013-01-01

    Pompe disease (PD) is a recessive metabolic disorder characterized by acid α-glucosidase (GAA) deficiency, which results in lysosomal accumulation of glycogen in all tissues, especially in skeletal muscles. PD clinical course is mainly determined by the nature of the GAA mutations. Although ~400 distinct GAA sequence variations have been described, the genotype-phenotype correlation is not always evident.In this study, we describe the first clinical and genetic analysis of Colombian PD patients performed in 11 affected individuals. GAA open reading frame sequencing revealed eight distinct mutations related to PD etiology including two novel missense mutations, c.1106 T > C (p.Leu369Pro) and c.2236 T > C (p.Trp746Arg). In vitro functional studies showed that the structural changes conferred by both mutations did not inhibit the synthesis of the 110 kD GAA precursor form but affected the processing and intracellular transport of GAA. In addition, analysis of previously described variants located at this position (p.Trp746Gly, p.Trp746Cys, p.Trp746Ser, p.Trp746X) revealed new insights in the molecular basis of PD. Notably, we found that p.Trp746Cys mutation, which was previously described as a polymorphism as well as a causal mutation, displayed a mild deleterious effect. Interestingly and by chance, our study argues in favor of a remarkable Afro-American and European ancestry of the Colombian population. Taken together, our report provides valuable information on the PD genotype-phenotype correlation, which is expected to facilitate and improve genetic counseling of affected individuals and their families.

  7. A method for adjusting the performances of epitaxial GaAs X-ray detectors

    CERN Document Server

    Sun, G C

    2002-01-01

    To detect high-energy photons using compound semiconductor detectors such as GaAs requires enlargement of the depleted zone, which is limited by the residual doping of the semiconductor. We discuss a technique by which the extension of the space charge region of a diode can be increased. It consists in compensating the residual doping impurities with defects introduced by electron irradiation. Results are presented to illustrate and evaluate the limits of this technique in the case of GaAs p/i/n structures.

  8. Low temperature growth and electrical characterization of insulators for GaAs MISFETS

    Science.gov (United States)

    Borrego, J. M.; Ghandhi, S. K.

    1981-01-01

    Progress in the low temperature growth of oxides and layers on GaAs and the detailed electrical characterization of these oxides is reported. A plasma anodization system was designed, assembled, and put into operation. A measurement system was assembled for determining capacitance and conductance as a function of gate voltage for frequencies in the range from 1 Hz to 1 MHz. Initial measurements were carried out in Si-SiO2 capacitors in order to test the system and in GaAs MIS capacitors abricated using liquid anodization.

  9. Molecular dynamics simulation of ion-beam-amorphization of Si, Ge and GaAs

    CERN Document Server

    Nord, J D; Keinonen, J

    2002-01-01

    We use molecular dynamics simulations to study ion-irradiation-induced amorphization in Si, Ge and GaAs using several different interatomic force models. We find that the coordination number is higher, and the average bond length longer, for the irradiated amorphous structures than for the molten ones in Si and Ge. For amorphous GaAs, we suggest that longer Ga-Ga bonds, also present in pure Ga, are produced during the irradiation. In Si the amorphization is found to proceed via growth of amorphous regions, and low energy recoils are found to induce athermal recrystallization during irradiation.

  10. Multilayers of InGaAs Nanostructures Grown on GaAs(210 Substrates

    Directory of Open Access Journals (Sweden)

    Wang Zhiming

    2010-01-01

    Full Text Available Abstract 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.

  11. The Mn site in Mn-doped Ga-As nanowires: an EXAFS study

    OpenAIRE

    d'Acapito, F.; Rovezzi, M.; Boscherini, F; Jabeen, F; Bais, G.; Piccin, M.; Rubini, S.; Martelli, F.

    2012-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Kang, M.; Al-Heji, A. A.; Shende, O.; Huang, S.; Jeon, S.; Goldman, R. S., E-mail: rsgold@umich.edu [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Beskin, I. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-1040 (United States)

    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.

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

    Science.gov (United States)

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

    2014-05-01

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

  14. Surface compositional changes in GaAs subjected to argon plasma treatment

    Energy Technology Data Exchange (ETDEWEB)

    Surdu-Bob, C.C.; Sullivan, J.L.; Saied, S.O.; Layberry, R.; Aflori, M

    2002-12-30

    X-ray photoelectron spectroscopy (XPS) has been employed to study surface compositional changes in GaAs (1 0 0) subjected to argon plasma treatment. The experimental results have been explained in terms of predicted argon ion energies, measured ion densities and etch rates. A model is proposed for the processes taking place at the surface of GaAs in terms of segregation, sputtering and surface relaxation. Stopping and range of ions in matter (SRIM) code has also been employedan aid to identification of the mechanisms responsible for the compositional changes. Argon plasma treatment induced surface oxidation at very low energies and sputtering and surface damage with increasing energy.

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

    DEFF Research Database (Denmark)

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

    1974-01-01

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

  16. Resonant behaviour of GaAs LO phonons in a GaAs-AlAs superlattice

    Science.gov (United States)

    Zhang, Shulin; T, A. Gant; M, Delaney; M, V. Klein; J, Klem; H, Morkoc

    1988-03-01

    Resonant Raman scattering from GaAs LO phonons in a 59Å GaAs/20Å AlAs superlattice was studied. The relevant intersubband energies were determined. The results suggest that all of the exciton transitions from the hole subbands HH1, LH1, HH2, HH3, LH2 and HH4 to the electron subbands CB1 and CB2 in the energy region covered by our incident dye laser were observed and a justificative analysis may involve effects due to valence band mixing and to 3D electronic miniband structure.

  17. Modeling and Design of Graphene GaAs Junction Solar Cell

    Directory of Open Access Journals (Sweden)

    Yawei Kuang

    2015-01-01

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

  18. Binding Energy of Biexcitons in GaAs Quantum-Well Wires

    Institute of Scientific and Technical Information of China (English)

    LIU Jian-Jun; CHEN Xiao-Fang; LI Shu-Shen

    2004-01-01

    @@ The binding energy of a biexciton in GaAs quantum-well wires is calculated variationally by use ofa two-parameter trial wavefunction and a one-dimensional equivalent potential model. There is no artificial parameter added in our calculation. Our results agree fairly well with the previous results. It is found that the binding energies are closely correlative to the size of wire. The binding energy of biexcitons is smaller than that of neutral bound excitons in GaAs quantum-well wires when the dopant is located at the centre of the wires.

  19. Cathodoluminescence studies of GaAs nano-wires grown on shallow-trench-patterned Si

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Ling; Fan, Wen-Chung; Ku, Jui-Tai; Chang, Wen-Hao; Chen, Wei-Kuo; Chou, Wu-Ching [Department of Electrophysics, National Chiao Tung University, Hsinchu 300, Taiwan (China); Ko, Chih-Hsin; Wu, Cheng-Hsien; Lin, You-Ru; Wann, Clement H [Taiwan Semiconductor Manufacturing Co., Ltd, Hsinchu 300, Taiwan (China); Hsu, Chao-Wei; Chen, Yung-Feng; Su, Yan-Kuin, E-mail: acceptor.ep89g@nctu.edu.tw, E-mail: wuchingchou@mail.nctu.edu.tw [Institute of Microelectronics and Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 701, Taiwan (China)

    2010-11-19

    The optical properties of GaAs nano-wires grown on shallow-trench-patterned Si(001) substrates were investigated by cathodoluminescence. The results showed that when the trench width ranges from 80 to 100 nm, the emission efficiency of GaAs can be enhanced and is stronger than that of a homogeneously grown epilayer. The suppression of non-radiative centers is attributed to the trapping of both threading dislocations and planar defects at the trench sidewalls. This approach demonstrates the feasibility of growing nano-scaled GaAs-based optoelectronic devices on Si substrates.

  20. Investigation of the radiation hardness of GaAs sensors in an electron beam

    CERN Document Server

    K. Afanaciev, K; P. Bernitt, P; G. Chelkov, G; J. Gajewski, J; M. Gostkin, M; Ch Grah, Ch; R. Heller, R; H. Henschel, H; A. Ignatenko, A; Z. Krumshteyn, Z; S. Kulis, S; W. Lange, W; W. Lohmann, W; D. Mokeev, D; V. Novikov, V; M. Ohlerich, M; A. Rosca, A; A. Sapronov, A; R.S. Schmidt, R S; S. Schuwalow, S; O. Tolbanov, O; A. Tyazhev, A

    2012-01-01

    A compact and finely grained sandwich calorimeter is designed to instrument the very forward region of a detector at a future e+e− collider. The calorimeter will be exposed to low energy e+e− pairs originating from beamstrahlung, resulting in absorbed doses of about one MGy per year. GaAs pad sensors interleaved with tungsten absorber plates are considered as an option for this calorimeter. Several Cr-doped GaAs sensor prototypes were produced and irradiated with 8.5–10 MeV electrons up to a dose of 1.5 MGy. The sensor performance was measured as a function of the absorbed dose.

  1. Selective growth of GaAs by organometallic vapor phase epitaxy at atmospheric pressure

    Science.gov (United States)

    Azoulay, R.; Dugrand, L.

    1991-01-01

    Complete selective epitaxy of GaAs by organometallic vapor phase epitaxy at atmospheric pressure was achieved by using TMG, AsH3, and AsCl3 as starting gases. Selectivity was observed at growth temperatures ranging from 650 to 750 °C. The blocking of polycrystal deposition on the mask, Si3N4, or W, is attributed to the adsorption of HCl on the mask, thus preventing the nucleation of GaAs. On the openings, the growth rate may be adjusted by controlling the TMG/AsCl3 ratio. When TMG/AsCl3<1, no growth occurs, but etching is observed.

  2. The LDA+U calculation of electronic band structure of GaAs

    Science.gov (United States)

    Bahuguna, B. P.; Sharma, R. O.; Saini, L. K.

    2016-05-01

    We present the electronic band structure of bulk gallium arsenide (GaAs) using first principle approach. A series of calculations has been performed by applying norm-conserving pseudopotentials and ultrasoft non-norm-conserving pseudopotentials within the density functional theory. These calculations yield too small band gap as compare to experiment. Thus, we use semiemperical approach called local density approximation plus the multi-orbital mean-field Hubbard model (LDA+U), which is quite effective in order to describe the band gap of GaAs.

  3. Recent Development of GaAs MMIC's for Wireless Communication Systems

    OpenAIRE

    1998-01-01

    This paper describes the recent development of GaAs MMICs for wireless communication systems such as the digital cellular phone, the satellite communication system, the local area network and the automatic radar system. The InGaP-emitter heterojunction bipolar transistor (HBT) for the 1.5-GHz digital cellular phones exhibited the output power of 31dBm at 1.5 GHz with the power-added efficiency of 68.8% and the adjacent channel power (ACP) of - 48 dBc at 50 kHz offset. The GaAs microwave signa...

  4. Chromium compensated gallium arsenide detectors for X-ray and γ-ray spectroscopic imaging

    Energy Technology Data Exchange (ETDEWEB)

    Veale, M.C., E-mail: matthew.veale@stfc.ac.uk [Rutherford Appleton Laboratory, Science and Technology Facilities Council, OX11 0QX (United Kingdom); Bell, S.J.; Duarte, D.D. [Rutherford Appleton Laboratory, Science and Technology Facilities Council, OX11 0QX (United Kingdom); Faculty of Engineering and Physical Sciences, University of Surrey, GU2 7XH (United Kingdom); French, M.J.; Schneider, A.; Seller, P.; Wilson, M.D. [Rutherford Appleton Laboratory, Science and Technology Facilities Council, OX11 0QX (United Kingdom); Lozinskaya, A.D.; Novikov, V.A.; Tolbanov, O.P.; Tyazhev, A.; Zarubin, A.N. [Siberian Physical–Technical Institute of Tomsk State University, Tomsk (Russian Federation)

    2014-07-01

    Semi-insulating GaAs material of 500 μm thickness grown using the Liquid Encapsulated Czochralski (LEC) method has been compensated with chromium to produce high resistivity single crystals suitable for spectroscopic imaging applications. Results are presented for the performance of three small pixel detectors each with 80×80 pixels on a 250 μm pitch, fabricated with metal contacts and bonded to a spectroscopic imaging ASIC. Current–voltage measurements demonstrated a material resistivity of 2.5×10{sup 9} Ω cm at room temperature. At an optimised bias voltage, the average energy resolution at 60 keV (FWHM) was in the range 2.8–3.3 keV per pixel. An analysis of the voltage dependent X-ray spectroscopy suggests that the electron mobility lifetime (μτ{sub e}) for each detector is in the range 2.1–4.5×10{sup −5} cm{sup 2} V{sup −1}. The spectroscopic imaging capability of the detectors is also demonstrated in X-ray absorption spectroscopy measurements.

  5. Growth, Antimony Incorporation Behaviour and Beryllium Doping of GaAs1-ySby Grown on GaAs by Molecular Beam Epitaxy

    Institute of Scientific and Technical Information of China (English)

    GAO Han-Chao; WANG Wen-Xin; JIANG Zhong-Wei; LIU Jian; YANG Cheng-Liang; WU Dian-Zhong; ZHOU Jun-Ming; CHEN Hong

    2008-01-01

    @@ A series of GaAs1-ySby epilayers are grown on GaAs substrates under different growth conditions, Different antimony compositions of samples with beryllium doping are obtained.A non-equilibrium thermodynamics model is used to calibrate and fit the Sb composition.Activation energy of 0.37eV for the dissociation process of Sb4 molecules is obtained.Carrier mobility and concentration of samples are influenced by the Sb composition.Quasi-qualitative analysis of mobility is used to explain the relations among Sb composition, carrier mobility and concentration.High resolution x-ray diffraction (HRXRD) rocking curves and Hall effects measurements are used to determine the crystal quality, carrier mobility and concentration.

  6. Reflectance-anisotropy study of the dynamics of molecular beam epitaxy growth of GaAs and InGaAs on GaAs(001)

    Energy Technology Data Exchange (ETDEWEB)

    Ortega-Gallegos, J.; Lastras-Martinez, A.; Lastras-Martinez, L.F. [Instituto de Investigacion en Comunicacion Optica, Universidad Autonoma de San Luis Potosi. Alvaro Obregon 64, San Luis Potosi (Mexico); Balderas-Navarro, R.E. [Instituto de Investigacion en Comunicacion Optica, Universidad Autonoma de San Luis Potosi. Alvaro Obregon 64, San Luis Potosi (Mexico); Facultad de Ciencias, Universidad Autonoma de San Luis Potosi. Alvaro Obregon 64, San Luis Potosi (Mexico)

    2008-07-01

    Reflectance-Anisotropy (RA) observations during the Molecular Beam Epitaxy (MBE) growth of zincblende semiconductors films were carried out using the E{sub 1} optical transition as a probe. We follow the kinetics of the deposition of GaAs and In{sub 0.3}Ga{sub 0.7}As on GaAs(001) at growth rates of 0.2 and 0.25 ML/s, respectively. During growth we used a constant As{sub 4} or As{sub 2} flux pressure of 5 x 10{sup -6} Torr. Clear RA-oscillations were observed during growth with a period that nearly coincides with the growth period for a Ga-As bilayer. RHEED was used as an auxiliary technique in order to obtain a correlation between RHEED and RA oscillations. On the basis of our results, we argue that RAS oscillations are mainly associated to periodic changes in surface atomic structure. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Surface kinetics study of metal-organic vapor phase epitaxy of GaAs1-yBiy on offcut and mesa-patterned GaAs substrates

    Science.gov (United States)

    Guan, Yingxin; Forghani, Kamran; Kim, Honghyuk; Babcock, Susan E.; Mawst, Luke J.; Kuech, Thomas F.

    2017-04-01

    The influence of the surface step termination on the metal-organic vapor phase epitaxy of GaAs1-yBiy was explored by examining the epitaxial layer growth rate, composition, and morphology characteristics on the offcut and mesa-patterned (001) GaAs substrates. Vicinal surfaces offcut to (111)B with a high density of As-terminated steps ('B-steps') increased the GaAs1-yBiy layer growth rate as well as possessed the fastest lateral growth rate on mesa-patterned substrates at a growth temperature of 420 °C, indicating that B-steps enhanced the Ga incorporation. With Bi accumulation on the surface, the Ga incorporation rate was reduced by the Bi preferential presence at B-steps blocking the Ga incorporation. Vicinal surfaces offcut to (111)A, which generated Ga-terminated steps ('A-steps') enhanced the Bi incorporation rate during growth at 380 °C. This work reveals that the surface step termination plays an important role in the growth of the metastable alloy. Appropriate choices of both the substrate surface-step structure and other growth parameters could lead to an enhanced Bi incorporation.

  8. MOCVD growth of GaAs on Si using (Al,In) GaAs/GaAs buffer layer

    Energy Technology Data Exchange (ETDEWEB)

    Fujita, K.; Shiba, Y.; Asai, K. (Advanced Tech. Research Labs., Sumitomo Metal Industries, Ltd., Hyogo (Japan))

    1991-01-01

    GaAs was grown on Si using an (Al,In)GaAs/GaAs buffer layer. The etch pit density (EPD) revealed by molten KOH could be reduced by adding Al{sub x}Ga{sub 1-x}As or In{sub x}Ga{sub 1-x}As to the GaAs buffer layer, depending on the composition (x); the lowest EPD, 4x10{sup 6} cm{sup -2} was obtained when x was 0.3 in Al{sub x}Ga{sub 1-x}As. To understand the results, the initial growth stage of GaAs on Si was investigated by scanning electron microscopy. GaAs growth using an Al{sub 0.3}Ga{sub 0.7}As layer produced small islands at a sufficiently high density that the islands coalesced, unlike those without the layer. The dependence of EPD and island density on the composition (x) were almost the same. This result indicates that improvement of the quality of the GaAs layer is related to the coalescence of the GaAs island at an early stage of the growth of GaAs on Si. (orig.).

  9. GAA Deficiency in Pompe Disease Is Alleviated by Exon Inclusion in iPSC-Derived Skeletal Muscle Cells

    Directory of Open Access Journals (Sweden)

    Erik van der Wal

    2017-06-01

    Full Text Available Pompe disease is a metabolic myopathy caused by deficiency of the acid α-glucosidase (GAA enzyme and results in progressive wasting of skeletal muscle cells. The c.-32-13T>G (IVS1 GAA variant promotes exon 2 skipping during pre-mRNA splicing and is the most common variant for the childhood/adult disease form. We previously identified antisense oligonucleotides (AONs that promoted GAA exon 2 inclusion in patient-derived fibroblasts. It was unknown how these AONs would affect GAA splicing in skeletal muscle cells. To test this, we expanded induced pluripotent stem cell (iPSC-derived myogenic progenitors and differentiated these to multinucleated myotubes. AONs restored splicing in myotubes to a similar extent as in fibroblasts, suggesting that they act by modulating the action of shared splicing regulators. AONs targeted the putative polypyrimidine tract of a cryptic splice acceptor site that was part of a pseudo exon in GAA intron 1. Blocking of the cryptic splice donor of the pseudo exon with AONs likewise promoted GAA exon 2 inclusion. The simultaneous blocking of the cryptic acceptor and cryptic donor sites restored the majority of canonical splicing and alleviated GAA enzyme deficiency. These results highlight the relevance of cryptic splicing in human disease and its potential as therapeutic target for splicing modulation using AONs.

  10. SEMICONDUCTOR TECHNOLOGY: GaAs surface wet cleaning by a novel treatment in revolving ultrasonic atomization solution

    Science.gov (United States)

    Zaijin, Li; Liming, Hu; Ye, Wang; Ye, Yang; Hangyu, Peng; Jinlong, Zhang; Li, Qin; Yun, Liu; Lijun, Wang

    2010-03-01

    A novel process for the wet cleaning of GaAs surface is presented. It is designed for technological simplicity and minimum damage generated within the GaAs surface. It combines GaAs cleaning with three conditions consisting of (1) removal of thermodynamically unstable species and (2) surface oxide layers must be completely removed after thermal cleaning, and (3) a smooth surface must be provided. Revolving ultrasonic atomization technology is adopted in the cleaning process. At first impurity removal is achieved by organic solvents; second NH4OH:H2O2:H2O = 1:1:10 solution and HCl: H2O2:H2O = 1:1:20 solution in succession to etch a very thin GaAs layer, the goal of the step is removing metallic contaminants and forming a very thin oxidation layer on the GaAs wafer surface; NH4OH:H2O = 1:5 solution is used as the removed oxide layers in the end. The effectiveness of the process is demonstrated by the operation of the GaAs wafer. Characterization of the oxide composition was carried out by X-ray photoelectron spectroscopy. Metal-contamination and surface morphology was observed by a total reflection X-ray fluorescence spectroscopy and atomic force microscope. The research results show that the cleaned surface is without contamination or metal contamination. Also, the GaAs substrates surface is very smooth for epitaxial growth using the rotary ultrasonic atomization technology.

  11. Control over the number density and diameter of GaAs nanowires on Si(111) mediated by droplet epitaxy.

    Science.gov (United States)

    Somaschini, Claudio; Bietti, Sergio; Trampert, Achim; Jahn, Uwe; Hauswald, Christian; Riechert, Henning; Sanguinetti, Stefano; Geelhaar, Lutz

    2013-08-14

    We present a novel approach for the growth of GaAs nanowires (NWs) with controllable number density and diameter, which consists of the combination between droplet epitaxy (DE) and self-assisted NW growth. In our method, GaAs islands are initially formed on Si(111) by DE and, subsequently, GaAs NWs are selectively grown on their top facet, which acts as a nucleation site. By DE, we can successfully tailor the number density and diameter of the template of initial GaAs islands and the same degree of control is transferred to the final GaAs NWs. We show how, by a suitable choice of V/III flux ratio, a single NW can be accommodated on top of each GaAs base island. By transmission electron microscopy, as well as cathodo- and photoluminescence spectroscopy, we confirmed the high structural and optical quality of GaAs NWs grown by our method. We believe that this combined approach can be more generally applied to the fabrication of different homo- or heteroepitaxial NWs, nucleated on the top of predefined islands obtained by DE.

  12. An 8 channel GaAs IC front-end discriminator for RPC detectors

    CERN Document Server

    Giannini, F; Orengo, G; Cardarelli, R

    1999-01-01

    Although not traditionally considered for particle detector readout, circuit solutions based upon GaAs IC technologies can offer considerable performance advantages in high speed detector signal processing: high f sub T devices, such as the GaAs MESFET, allow the realization of front-end tuned amplifiers and comparators with the same detector time resolution. Such a feature is well-suited for RPC particle detectors, characterized by short pulse duration and constant shaping responses. A new design procedure shows the suitability of high speed narrow band GaAs amplifiers as voltage-sensitive input stages of front-end discriminators to perform the required voltage amplification for the following comparator, ensuring, at the same time, SNR optimisation, high gain and low power consumption. As an application of the proposed approach, a full-custom analog chip has been designed and realized using 0.6 mu m GaAs MESFET technology from Triquint foundry. Eight channels of a front-end discriminator composed of a tuned ...

  13. Capacitance-voltage characteristics of GaAs ion-implanted structures

    Directory of Open Access Journals (Sweden)

    Privalov E. N.

    2008-08-01

    Full Text Available A noniterative numerical method is proposed to calculate the barrier capacitance of GaAs ion-implanted structures as a function of the Schottky barrier bias. The features of the low- and high-frequency capacitance-voltage characteristics of these structures which are due to the presence of deep traps are elucidated.

  14. Depth-dependent Detection Mechanisms of Coherent Phonons in n-type GaAs

    Directory of Open Access Journals (Sweden)

    Petek Hrvoje

    2013-03-01

    Full Text Available Transient reflectivity measurements at different probing wavelengths reveal detection mechanisms of coherent phonon and phonon-plasmon coupled modes of n-doped GaAs to be strongly depth-dependent due to the carrier depletion at the surface.

  15. Linear scaling calculation of an n-type GaAs quantum dot.

    Science.gov (United States)

    Nomura, Shintaro; Iitaka, Toshiaki

    2007-09-01

    A linear scale method for calculating electronic properties of large and complex systems is introduced within a local density approximation. The method is based on the Chebyshev polynomial expansion and the time-dependent method, which is tested on the calculation of the electronic structure of a model n-type GaAs quantum dot.

  16. Density-dependent electron scattering in photoexcited GaAs in strongly diffusive regime

    DEFF Research Database (Denmark)

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

    2013-01-01

    In a series of systematic optical pump–terahertz probe experiments, we study the density-dependent electron scattering rate in photoexcited GaAs in the regime of strong carrier diffusion. The terahertz frequency-resolved transient sheet conductivity spectra are perfectly described by the Drude...

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

    NARCIS (Netherlands)

    Kulik, M; Komarov, FF; Maczka, D

    1999-01-01

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

  18. Heat flow model for pulsed laser melting and rapid solidification of ion implanted GaAs

    Science.gov (United States)

    Kim, Taeseok; Pillai, Manoj R.; Aziz, Michael J.; Scarpulla, Michael A.; Dubon, Oscar D.; Yu, Kin M.; Beeman, Jeffrey W.; Ridgway, Mark C.

    2010-07-01

    In order to further understand the pulsed-laser melting (PLM) of Mn and N implanted GaAs, which we have used to synthesize thin films of the ferromagnetic semiconductor Ga1-xMnxAs and the highly mismatched alloy GaNxAs1-x, we have simulated PLM of amorphous (a-) and crystalline (c-) GaAs. We present a numerical solution to the one-dimensional heat equation, accounting for phase-dependent reflectivity, optical skin depth, and latent heat, and a temperature-dependent thermal conductivity and specific heat. By comparing the simulations with experimental time-resolved reflectivity and melt depth versus laser fluence, we identify a set of thermophysical and optical properties for the crystalline, amorphous, and liquid phases of GaAs that give reasonable agreement between experiment and simulation. This work resulted in the estimation of thermal conductivity, melting temperature and latent heat of fusion of a-GaAs of 0.008 W/cm K at 300 K, 1350 K, and 2650 J/cm3, respectively. These materials properties also allow the prediction of the solidification velocity of crystalline and ion-amorphized GaAs.

  19. Method of Making Self-Aligned GAAS/ALGAAS FET’s.

    Science.gov (United States)

    having a predetermined crystalline structure is obtained having a heavily doped top GaAs layer, having a heavily doped AlGaAs layer under the top layer...recess is wider at the base of the recess than at the top of the recess because of the predetermined crystalline structure and the orientation-dependent

  20. X-ray diffraction study on pressure-induced phase transformation in nanocrystalline GaAs

    DEFF Research Database (Denmark)

    Jiang, Jianzhong; Olsen, J. S.; Gerward, Leif

    2002-01-01

    We have shown that the onset and transition pressures of the GaAs I --> II transition are 17 GPa and 20 GPa, respectively, for both bulk and nanophase material. The observed gradual change in resistivity of nanophase GaAs,at the semiconductor-to-metal transition is explained by the two...

  1. Reduction of fast surface states on p-type GaAs

    Science.gov (United States)

    Ahrenkiel, R. K.; Wagner, R. S.; Pattillo, S.; Dunlavy, D.; Jervis, T.; Kazmerski, L. L.; Ireland, P. J.

    1982-04-01

    Native oxides and oxyfluorides were grown on GaAs by a glow discharge plasma process. Analysis of metal-insulator-semiconductor structures based on oxyfluoride dielectrics indicated vastly different interface properties compared to pure oxide dielectrics. Whereas oxide structures showed high densities of fast surface states, oxyfluorides showed no evidence of such effects.

  2. Divacancy complexes induced by Cu diffusion in Zn-doped GaAs

    Science.gov (United States)

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

    2013-08-01

    Positron annihilation spectroscopy was applied to investigate the nature and thermal behavior of defects induced by Cu diffusion in Zn-doped p-type GaAs crystals. Cu atoms were intentionally introduced in the GaAs lattice through thermally activated diffusion from a thin Cu capping layer at 1100 °C under defined arsenic vapor pressure. During isochronal annealing of the obtained Cu-diffused GaAs in the temperature range of 450-850 K, vacancy clusters were found to form, grow and finally disappear. We found that annealing at 650 K triggers the formation of divacancies, whereas further increasing in the annealing temperature up to 750 K leads to the formation of divacancy-copper complexes. The observations suggest that the formation of these vacancy-like defects in GaAs is related to the out-diffusion of Cu. Two kinds of acceptors are detected with a concentration of about 1016 - 1017 cm-3, negative ions and arsenic vacancy copper complexes. Transmission electron microscopy showed the presence of voids and Cu precipitates which are not observed by positron measurements. The positron binding energy to shallow traps is estimated using the positron trapping model. Coincidence Doppler broadening spectroscopy showed the presence of Cu in the immediate vicinity of the detected vacancies. Theoretical calculations suggested that the detected defect is VGaVAs-2CuGa.

  3. Modeling of compound semiconductors: Analytical bond-order potential for Ga, As, and GaAs

    Science.gov (United States)

    Albe, Karsten; Nordlund, Kai; Nord, Janne; Kuronen, Antti

    2002-07-01

    An analytical bond-order potential for GaAs is presented, that allows one to model a wide range of properties of GaAs compound structures, as well as the pure phases of gallium and arsenide, including nonequilibrium configurations. The functional form is based on the bond-order scheme as devised by Abell-Tersoff and Brenner, while a systematic fitting scheme starting from the Pauling relation is used for determining all adjustable parameters. Reference data were taken from experiments if available, or computed by self-consistent total-energy calculations within the local density-functional theory otherwise. For fitting the parameters, only structural data of the metallic phases of gallium and arsenide as well as those of different GaAs phases were used. A number of tests on point defect properties, surface properties, and melting behavior have been performed afterward in order to validate the accuracy and transferability of the potential model, but were not part of the fitting procedure. While point defect properties and surfaces with low As content are found to be in good agreement with literature data, the description of As-rich surface reconstructions is not satisfactory. In the case of molten GaAs we find support for a structural model based on experiment that indicates a polymerized arsenic phase in the melt.

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

    Science.gov (United States)

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

    2015-09-16

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Galiana, B. [Instituto de Ciencia de Materiales de Madrid, CSIC, Sor Juana Inés de la Cruz 3, 28049 Madrid (Spain); Departamento de Física, Universidad Carlos III de Madrid, Avenida de la Universidad 30, 28911 Madrid (Spain); Benedicto, M.; Díez-Merino, L.; Tejedor, P. [Instituto de Ciencia de Materiales de Madrid, CSIC, Sor Juana Inés de la Cruz 3, 28049 Madrid (Spain); Lorbek, S.; Hlawacek, G.; Teichert, C. [Institut für Physik, Montanuniversität Leoben, Franz Josef St., 18A-8700 Leoben (Austria)

    2013-10-28

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

  6. Modification of the Absorption Edge of GaAs Arising from Hot-Electron Effects

    DEFF Research Database (Denmark)

    McGroddy, J. C.; Christensen, Ove

    1973-01-01

    We have observed a large enhancement of the electric-field-induced optical absorption arising from hot-electron effects in n-type GaAs at 77 K. The magnitude and field dependence of the enhancement can be approximately accounted for by a theory attributing the effect to broadening of the final st...

  7. Transient four-wave mixing in T-shaped GaAs quantum wires

    DEFF Research Database (Denmark)

    Langbein, Wolfgang Werner; Gislason, Hannes; Hvam, Jørn Märcher

    1999-01-01

    The binding energy of excitons and biexcitons and the exciton dephasing in T-shaped GaAs quantum wires is investigated by transient four-wave mixing. The T-shaped structure is fabricated by cleaved-edge overgrowth, and its geometry is engineered to optimize the one-dimensional confinement...

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

    Energy Technology Data Exchange (ETDEWEB)

    Aleshkin, V. Ya., E-mail: aleshkin@ipmras.ru [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

    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.

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

    Science.gov (United States)

    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.

  10. Many-Body Effect in Spin Dephasing in n-Type GaAs Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    WENG Ming-Qi; WU Ming-Wei

    2005-01-01

    @@ By constructing and numerically solving the kinetic Bloch equations we perform a many-body study of the spin dephasing due to the D'yakonov-Perel' effect in n-type GaAs (100) quantum wells for high temperatures.

  11. Growth mode transitions induced by hydrogen-assisted MBE on vicinal GaAs(110)

    Energy Technology Data Exchange (ETDEWEB)

    Tejedor, P. [Instituto de Ciencia de Materiales de Madrid (C.S.I.C)., Sor Juana Ines de la Cruz s/n, Cantoblanco, 28049 Madrid (Spain)]. E-mail: ptejedor@icmm.csic.es; Crespillo, M.L. [Instituto de Ciencia de Materiales de Madrid (C.S.I.C)., Sor Juana Ines de la Cruz s/n, Cantoblanco, 28049 Madrid (Spain); Joyce, B.A. [Imperial College of Science, Technology and Medicine, The Blackett Laboratory, London SW7 2BZ (United Kingdom)

    2006-07-15

    The homoepitaxial growth of GaAs by hydrogen-assisted molecular beam epitaxy (H-MBE) on (110) substrates vicinal to (111)A has been studied by reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM) for different kinetic regimes. When the GaAs growth rate is limited by the kinetics of adatom incorporation to steps, the presence of chemisorbed H on the surface after oxide removal promotes the incorporation of adatoms to steps from the lower terraces, leading to the formation of multiatomic step arrays or ridge patterns by a combination of step propagation and two-dimensional layer-by-layer growth. Supply of atomic H during epitaxy favours three-dimensional growth, leading to Ga-induced surface roughening or mound formation. At high temperatures, the Ga-As interactions at step edges are faster and stable growth of GaAs occurs by step propagation, leading to a faceted surface when H is used both during oxide removal and/or MBE growth.

  12. 2.5 Gb/s laser-driver GaAS IC

    DEFF Research Database (Denmark)

    Riishøj, Jesper

    1993-01-01

    A laser-diode driver GaAs IC incorporating an optional NRZ/RZ (non-return-to-zero/return-to-zero) conversion facility, having ECL (emitter-coupled logic) and SCFL (source-coupled FET logic)-compatible inputs and providing a 0-60-mA adjustable output current into a 50-Ω/5-V termination at bit rates...

  13. Heat load of a GaAs photocathode in an SRF electron gun

    Institute of Scientific and Technical Information of China (English)

    WANG Er-Dong; ZHAO Kui; J(o)rg Kewisch; Ilan Ben-Zvi; Andrew Burrill; Trivini Rao; WU Qiong; Animesh Jain; Ramesh Gupta; Doug Holmes

    2011-01-01

    A great deal of effort has been made over the last decades to develop a better polarized electron source for high energy physics. Several laboratories operate DC guns with a gallium arsenide photocathode, which yield a highly polarized electron beam. However, the beam's emittance might well be improved by using a superconducting radio frequency (SRF) electron gun, which delivers beams of a higher brightness than that from DC guns because the field gradient at the cathode is higher. SRF guns with metal and CsTe cathodes have been tested successfully. To produce polarized electrons, a Gallium-Arsenide photo-cathode must be used: an experiment to do so in a superconducting RF gun is under way at BNL. Since a bulk gallium arsenide (GaAs) photocathode is normal conducting, a problem arises from the heat load stemming from the cathode. We present our measurements of the electrical resistance of GaAs at cryogenic temperatures, a prediction of the heat load and verification by measuring the quality factor of the gun with and without the cathode at 2 K. We simulate heat generation and flow from the GaAs cathode using the ANSYS program. By following the findings with the heat load model, we designed and fabricated a new cathode holder (plug) to decrease the heat load from GaAs.

  14. GaAs Wideband Low Noise Amplifier Design for Breast Cancer Detection System

    DEFF Research Database (Denmark)

    Yan, Lei; Krozer, Viktor; Delcourt, Sebastien

    2009-01-01

    Modern wideband systems require low-noise receivers with bandwidth approaching 10 GHz. This paper presents ultra-wideband stable low-noise amplifier MMIC with cascode and source follower buffer configuration using GaAs technology. Source degeneration, gate and shunt peaking inductors are used to ...

  15. Purcell effect of GaAs quantum dots by photonic crystal microcavities

    Institute of Scientific and Technical Information of China (English)

    Kazuaki Sakoda; Takashi Kuroda; Naoki Ikeda; Takaaki Mano; Yoshimasa Sugimoto; Tetsuyuki Ochiai; Keiji Kuroda; Shunsuke Ohkouchi; Nobuyuki Koguchi; Kiyoshi Asakawa

    2009-01-01

    We fabricate photonic crystal slab microcavities embedded with GaAs quantum dots by electron beam lithography and droplet epitaxy.The Purcell effect of exciton emission of the quantum dots is confirmed by the micro photoluminescence measurement.The resonance wavelengths,widths,and polarization are consistent with numerical simulation results.

  16. Direct, etching of GaAs Crystal Excited by a Vacuum Ultraviolet Lamp

    Institute of Scientific and Technical Information of China (English)

    韩正甫; 廖艳林; 周红军; 蒋作宏; 张国斌; 曹卓良

    2003-01-01

    A successful direct, etching system excited by a vacuum ultraviolet hollow-cathode lamp is reported. The result shows that the facility can transfer a mesh pattern exactly and directly to n-type GaAs wafer, which is the same as that direct, etched by synchrotron radiation.

  17. Resonant Raman Study Of ZnSe Epitaxial Layers Grown On GaAs Substrates

    Science.gov (United States)

    Djibladze, Merab I.; Dorosh, I. I.; Zlenko, A. A.; Kekelidze, George N.; Pashinin, Vladimir P.; Prokhorov, Kirill A.

    1989-05-01

    Quantitative difference between Raman and resonant Raman scattering spectra of thin ZnSe layers on GaAs substrates is presented. The dynamics of changing of Raman scattering properties while shortenning the exciting light wavelength for ZnSe/GaAs heterojunction is given. The difference in polarization spectra is demonstrated.

  18. Passively Q-switched Self-frequency Doubling NYAB laser with GaAs Saturable Absorber

    Institute of Scientific and Technical Information of China (English)

    ZHAO Shengzhi(赵圣之); ZHENG Jiaan(郑加安); CHEN Lei(陈磊); CHENG Zhenxiang(程振祥); CHEN Huanchu(陈焕矗)

    2002-01-01

    By using a passive Q-switch with GaAs saturable absorber, the Q-switched self-frequency doubling NYAB laser at 0.531μm has been successfully realized. The pulse width and the single pulse energy are measured. The numerical solutions of the coupling wave rate equations are in agreement with the experimental results.

  19. Structural analysis of the indium-stabilized GaAs(001)-c(8×2) surface

    DEFF Research Database (Denmark)

    Lee, T.-L.; Kumpf, C.; Kazimirov, A.

    2002-01-01

    The indium-stabilized GaAs(001)-c(8x2) surface was investigated by surface x-ray diffraction and x-ray standing waves. We find that the reconstruction closely resembles the c(8x2) structure described by the recently proposed unified model for clean III-V semiconductor surfaces [Kumpf , Phys. Rev....

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

    Energy Technology Data Exchange (ETDEWEB)

    Brown, Evan; Sheng, Chunyang; Nakano, Aiichiro [Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Shimamura, Kohei; Shimojo, Fuyuki [Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Department of Physics, Kumamoto University, Kumamoto 860-8555 (Japan)

    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.

  1. Properties of Excitons Bound to Neutral Donors in GaAs Quantum-Well Wires

    Institute of Scientific and Technical Information of China (English)

    LIU Jian-Jun; WANG Xue-Feng

    2005-01-01

    @@ In the effective mass approximation, the binding energy of an exciton bound to a neutral donor (D0, X) is calcu-lated variationally for rectangular GaAs quantum-well wires (QWWs) by using a three-parameter wavefunction.

  2. Control of the lateral growth morphology in GaAs Droplet Epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Somaschini, C; Bietti, S; Sanguinetti, S; Koguchi, N [LNESS and Dipartimento di Scienza dei Materiali dell' Universita di Milano-Bicocca, via Cozzi 53, 20125 Milano (Italy); Fedorov, A, E-mail: stefano.sanguinetti@mater.unimib.i [CNISM, LNESS and Dipartimento di Fisica del Politecnico di Milano, via Anzani 42, 22100 Como (Italy)

    2010-09-01

    We present the detailed fabrication method of two different GaAs nanostructures with cylindrical symmetry by the Droplet Epitaxy technique. Concentric Multiple Rings or Coupled Rings/Disks are successfully obtained, exploiting the lateral growth around the Ga droplets, through a fine control of the crystallization dynamics.

  3. Conversion Matrix Analysis of GaAs HEMT Active Gilbert Cell Mixers

    DEFF Research Database (Denmark)

    Jiang, Chenhui; Johansen, Tom Keinicke; Krozer, Viktor

    2006-01-01

    In this paper, the nonlinear model of the GaAs HEMT active Gilbert cell mixer is investigated. Based on the model, the conversion gain expression of active Gilbert cell mixers is derived theoretically by using conversion matrix analysis method. The expression is verified by harmonic balance simul...... simulation with Angelov HEMT model in Agilent Advanced Design System (ADS) and by chip measurement results....

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

    Energy Technology Data Exchange (ETDEWEB)

    Bruhn, Thomas [Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstr.36, D-10623 Berlin (Germany); Leibniz-Institut für Analytische Wissenschaften - ISAS - e.V., Albert-Einstein-Str.9, 12489 Berlin (Germany); Fimland, Bjørn-Ove [Department of Electronics and Telecommunications, Norwegian University of Science and Technology, NO-7491 Trondheim (Norway); Vogt, Patrick, E-mail: patrick.vogt@tu-berlin.de [Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstr.36, D-10623 Berlin (Germany)

    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.

  5. Tuning single GaAs quantum dots in resonance with a rubidium vapor

    NARCIS (Netherlands)

    Akopian, N.; Perinetti, U.; Wang, L.; Rastelli, A.; Schmidt, O.G.; Zwiller, V.

    2010-01-01

    We study single GaAs quantum dots with optical transitions that can be brought into resonance with the widely used D2 transitions of rubidium atoms. We achieve resonance by Zeeman or Stark shifting the quantum dot levels. We discuss an energy stabilization scheme based on the absorption of quantum d

  6. X-ray diffraction study on pressure-induced phase transformation in nanocrystalline GaAs

    DEFF Research Database (Denmark)

    Jiang, Jianzhong; Olsen, J. S.; Gerward, Leif;

    2002-01-01

    We have shown that the onset and transition pressures of the GaAs I --> II transition are 17 GPa and 20 GPa, respectively, for both bulk and nanophase material. The observed gradual change in resistivity of nanophase GaAs,at the semiconductor-to-metal transition is explained by the two-component ...

  7. Laplace DLTS of molecular beam epitaxy GaAs grown on (100) and (211)B substrates

    Energy Technology Data Exchange (ETDEWEB)

    Mari, R.H.; Shafi, M.; Henini, M. [School of Physics and Astronomy, Nottingham Nanotechnology and Nanoscience Centre University of Nottingham, Nottingham NG7 2RD (United Kingdom)

    2009-12-15

    Deep Level Transient Spectroscopy (DLTS) and Laplace DLTS (LDLTS) techniques have been employed to study defects in n-type GaAs grown by MBE on (100) and (211)B GaAs planes. The DLTS spectra were different for the two GaAs substrate orientations. Five and four defect states are found in samples grown on (100) and (211)B GaAs planes, respectively with activation energies ranging from 0.054 eV to 0.570 eV. For all of the traps observed in our samples we obtained small activation energies as compared to the previous data published in literature on n-GaAs samples grown by MBE. This can be explained by the fact that the emission of the carriers depends on the applied electric field and temperature dependence of the carrier concentration. These two phenomena seem to explain the small trap energies seen in our samples. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. A comparison of GaAs and Si hybrid solar power systems

    Science.gov (United States)

    Heinbockel, J. H.; Roberts, A. S., Jr.

    1977-01-01

    Five different hybrid solar power systems using silicon solar cells to produce thermal and electric power are modeled and compared with a hybrid system using a GaAs cell. Among the indices determined are capital cost per unit electric power plus mechanical power, annual cost per unit electric energy, and annual cost per unit electric plus mechanical work. Current costs are taken to be $35,000/sq m for GaAs cells with an efficiency of 15% and $1000/sq m for Si cells with an efficiency of 10%. It is shown that hybrid systems can be competitive with existing methods of practical energy conversion. Limiting values for annual costs of Si and GaAs cells are calculated to be 10.3 cents/kWh and 6.8 cents/kWh, respectively. Results for both systems indicate that for a given flow rate there is an optimal operating condition for minimum cost photovoltaic output. For Si cell costs of $50/sq m optimal performance can be achieved at concentrations of about 10; for GaAs cells costing 1000/sq m, optimal performance can be obtained at concentrations of around 100. High concentration hybrid systems offer a distinct cost advantage over flat systems.

  9. Monolithic integration of optical grade GaAs on Si (001) substrates deeply patterned at a micron scale

    Energy Technology Data Exchange (ETDEWEB)

    Bietti, Sergio; Scaccabarozzi, Andrea; Bonera, Emiliano; Miglio, Leo; Sanguinetti, Stefano [L-NESS and Dip. di Scienza dei Materiali, Universitá di Milano Bicocca, Via Cozzi 53, I–20125 Milano (Italy); Frigeri, Cesare [CNR-IMEM Institute, Parco Area delle Scienze 37/A, I–43100 Parma (Italy); Bollani, Monica [CNR–IFN, L–NESS, via Anzani 42, I–22100 Como (Italy); Falub, Claudiu V.; Känel, Hans von [Laboratory for Solid State Physics, ETH Zurich, Schafmattstrasse 16, CH-8093 Zurich (Switzerland)

    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.

  10. Formation of a pn junction on an anisotropically etched GaAs surface using metalorganic chemical vapor deposition

    Science.gov (United States)

    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.

  11. Surface science analysis of GaAs photocathodes following sustained electron beam delivery

    Energy Technology Data Exchange (ETDEWEB)

    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.

  12. Comparison of Two Different PCR-based Methods for Detection of GAA Expansions in Frataxin Gene.

    Science.gov (United States)

    Entezam, Mona; Amirfiroozi, Akbar; Togha, Mansoureh; Keramatipour, Mohammad

    2017-02-01

    Expansion of GAA trinucleotide repeats is the molecular basis of Friedreich's ataxia (FRDA). Precise detection of the GAA expansion repeat in frataxin gene has always been a challenge. Different molecular methods have been suggested for detection of GAA expansion, including; short-PCR, long-PCR, Triplet repeat primed-PCR (TP-PCR) and southern blotting. The aim of study was to evaluate two PCR-based methods, TP-PCR and long-PCR, and to explore the use of TP-PCR accompanying with long-PCR for accurate genotyping of FRDA patients. Blood samples were collected from six Iranian patients suspected to FRDA, who referred to the Department of Medical Genetics at Tehran University of Medical Sciences during the year 2014. For one of these patients' four asymptomatic members of the family were also recruited for the analysis. DNA extraction was performed by two different methods. TP-PCR and long-PCR were carried out in all samples. The type of this study is assessment / investigation of methods. Using a combination of the above methods, the genotypes of all samples were confirmed as five homozygous mutants (expanded GAA repeats), two heterozygous and three homozygous normal (normal repeat size). The results obtained by TP-PCR are consistent with long-PCR results. The presence or absence of expanded alleles can be identified correctly by TP-PCR. Performing long-PCR and Fluorescent-long-PCR enables accurate genotyping in all samples. This approach is highly reliable. It could be successfully used for detection of GAA expansion repeats.

  13. Surface science analysis of GaAs photocathodes following sustained electron beam delivery

    Directory of Open Access Journals (Sweden)

    V. Shutthanandan

    2012-06-01

    Full Text Available Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power free electron lasers (FEL. Photocathode quantum efficiency degradation is due to residual gases in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes, which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include helium ion microscopy, Rutherford backscattering spectrometry (RBS, atomic force microscopy, and secondary ion mass spectrometry (SIMS. In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the continuous electron beam accelerator facility (CEBAF photoinjector and one unused, were also analyzed using transmission electron microscopy (TEM and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but show evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements, the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.

  14. Surface science analysis of GaAs photocathodes following sustained electron beam delivery

    Energy Technology Data Exchange (ETDEWEB)

    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. Influence of GaAs Substrate Orientation on InAs Quantum Dots: Surface Morphology, Critical Thickness, and Optical Properties

    Directory of Open Access Journals (Sweden)

    Liang BL

    2007-01-01

    Full Text Available AbstractInAs/GaAs heterostructures have been simultaneously grown by molecular beam epitaxy on GaAs (100, GaAs (100 with a 2° misorientation angle towards [01−1], and GaAs (n11B (n = 9, 7, 5 substrates. While the substrate misorientation angle increased from 0° to 15.8°, a clear evolution from quantum dots to quantum well was evident by the surface morphology, the photoluminescence, and the time-resolved photoluminescence, respectively. This evolution revealed an increased critical thickness and a delayed formation of InAs quantum dots as the surface orientation departed from GaAs (100, which was explained by the thermal-equilibrium model due to the less efficient of strain relaxation on misoriented substrate surfaces.

  16. Optical and Surface Characteristics of Mg-Doped GaAs Nanocrystalline Thin Film Deposited by Thermionic Vacuum Arc Technique

    Science.gov (United States)

    Pat, Suat; Özen, Soner; Şenay, Volkan; Korkmaz, Şadan

    2017-01-01

    Magnesium (Mg) is the most promising p-type dopant for gallium arsenide (GaAs) semiconductor technology. Mg-doped GaAs nanocrystalline thin film has been deposited at room temperature by the thermionic vacuum arc technique, a rapid deposition method for production of doped GaAs material. The microstructure and surface and optical properties of the deposited sample were investigated by x-ray diffraction analysis, scanning electron microscopy, energy-dispersive x-ray spectroscopy, atomic force microscopy, ultraviolet-visible spectrophotometry, and interferometry. The crystalline direction of the deposited sample was determined to be (220) plane and (331) plane at 44.53° and 72.30°, respectively. The Mg-doped GaAs nanocrystalline sample showed high transmittance.

  17. Characteristics of THz Emission from GaAs Crystal Excited by 400 nm and 800 nm Optical Pulses

    Institute of Scientific and Technical Information of China (English)

    YANG Yu-Ping; XU Xin-Long; YAN Wei; WANG Li

    2005-01-01

    @@ THz emission spectroscopy is used to study the generation mechanism dependent behaviour of terahertz (THz) electromagnetic waves from the GaAs crystal under excitation by 400 nm and 800 nm femtosecond (fs) pulses,respectively. The wavelength dependence of the emission spectrum under two types of THz generation mechanisms is analysed. Under the optical rectification mechanism, a slight enhancement of the spectral amplitude in the high-frequency regime is observed in a GaAs(110) crystal by the excitation of a 400-nm optical pulse compared with that of 800nm. Whereas an obvious red shift of the amplitude spectrum occurs in the GaAs(100) sample under the transient photoconduction mechanism. These phenomena are explained in detail by the duration of the optical pump pulse and the band structure of GaAs, respectively.

  18. Photoluminescence and transmission spectra of nanocrystalline GaAs1-xSbx embedded in silica films

    Institute of Scientific and Technical Information of China (English)

    Liu Fa-Min; Zhang Li-De; Li Guo-Hua

    2005-01-01

    The composite films of the nanocrystalline GaAs1-xSbx-SiO2 have been successfully deposited on glass and GaSb substrates by radio frequency magnetron co-sputtering. The 10K photoluminescence (PL) properties of the nanocrys-talline GaAs1-xSbx indicated that the PL peaks of the GaAs1-xSbx nanocrystals follow the quantum confinement model very closely. Optical transmittance spectra showed that there is a large blue shift of optical absorption edge in nanocrystalline GaAs1-xSbx-SiO2 composite films, as compared with that of the corresponding bulk semiconductor,which is due to the quantum confinement effect.

  19. Structural and morphological characterizations of ZnO films grown on GaAs substrates by MOCVD

    Energy Technology Data Exchange (ETDEWEB)

    Agouram, S.; Zuniga Perez, J.; Munoz-Sanjose, V. [Universitat de Valencia, Departamento de Fisica Aplicada y Electromagnetismo, Burjassot (Spain)

    2007-07-15

    ZnO films were grown on GaAs(100), GaAs(111)A and GaAs(111)B substrates by metal organic chemical vapour deposition (MOCVD). Diethylzinc (DEZn) and tertiarybutanol (t-butanol) were used as Zn and O precursors, respectively. The influence of the growth temperature and GaAs substrate orientation on the crystalline orientation and morphology of the ZnO grown films has been analysed. Crystallinity of grown films was studied by X-ray diffraction (XRD); thickness and morphology of ZnO films were investigated by scanning electron microscopy (SEM). SEM results reveal significant differences between morphologies depending on growth temperature but not significant differences were detected on the texture of grown films. (orig.)

  20. Distinct disease phenotypes linked to different combinations of GAA mutations in a large late-onset GSDII sibship

    National Research Council Canada - National Science Library

    Sampaolo, Simone; Esposito, Teresa; Farina, Olimpia; Formicola, Daniela; Diodato, Daria; Gianfrancesco, Fernando; Cipullo, Federica; Cremone, Gaetana; Cirillo, Mario; Del Viscovo, Luca; Toscano, Antonio; Angelini, Corrado; Di Iorio, Giuseppe

    2013-01-01

    Glycogenosis type II (GSDII or Pompe disease) is an autosomal recessive disease, often characterized by a progressive accumulation of glycogen within lysosomes caused by a deficiency of α-1,4-glucosidase (GAA; acid maltase...

  1. Threading dislocations in GaAs epitaxial layers on various thickness Ge buffers on 300 mm Si substrates

    Science.gov (United States)

    Bogumilowicz, Y.; Hartmann, J. M.; Rochat, N.; Salaun, A.; Martin, M.; Bassani, F.; Baron, T.; David, S.; Bao, X.-Y.; Sanchez, E.

    2016-11-01

    We have grown GaAs epitaxial layers on Ge buffers, themselves on Si (001) substrates, using an Applied Materials 300 mm metal organic chemical vapor deposition tool. We varied the Ge buffer thickness between 0.36 and 1.38 μm and studied the properties of a 0.27 μm thick GaAs layer on top. We found that increasing the Ge buffer thickness yielded smoother GaAs films with an rms surface roughness as low as 0.5 nm obtained on a 5×5 μm2 area. The bow of the substrate increased following a linear law with the epitaxial stack thickness up to 240 μm for a 1.65 μm stack. We have also characterized the threading dislocations present in the GaAs layers using X-ray diffraction and cathodoluminescence. Increasing the Ge buffer thickness resulted in lower threading dislocation densities, enabling us to obtain anti-phase boundary - free GaAs films with a threading dislocation density as low as 3×107 cm-2. In addition, atomic force microscopy surface topology measurements showed the presence of pits in the GaAs layers whose density agreed well with other threading dislocation density assessments. It thus seems that threading dislocations can in certain cases induce some growth rate variations, making them visible in as-grown GaAs films. Using thicker Ge buffers results in smoother films with less threading dislocations, with the side effect of increasing the bow on the wafer. If bow is not an issue, this is a practical approach to improve the GaAs (on Ge buffer) on silicon quality.

  2. Efficient THZ Source Based on Cascaded Optical Down-Conversion in Orientation-Patterned GaAs Structures

    Science.gov (United States)

    2008-11-20

    structured nonlinear optical materials , GaAs, optical THz generation, cavity-enhanced, nonlinear-optical frequency down-conversion, quasi-phasematched...Many nonlinear optical materials are relatively transparent at THz frequencies below lowest phonon resonance (e.g. at 8 THz for GaAs and 5 THz for... optical materials : both collinear (forward and backward) and noncollinear phase matching was used to generate broadly tunable, 20-190cm-1 (0.6-5.7 THz

  3. Direct Growth of High-Quality InP Layers on GaAs Substrates by MOCVD

    Directory of Open Access Journals (Sweden)

    K. F. Yarn

    2003-01-01

    group V partial pressure, growth rate and V/III ratios. A mirror-like, uniform surface and high crystal quality of the metamorphic buffer layer directly grown on a GaAs substrate can be achieved. Finally, to investigate the performance of the metamorphic microwave devices, we also fabricate the InAlAs/InGaAs metamorphic HEMT on GaAs substrates.

  4. Scaling behavior of GaAs and GaMnAs quantum rings grown by droplet epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Placidi, E. [Istituto di Struttura della Materia, CNR, Via del Fosso del Cavaliere 100, 00133 Roma (Italy); Dipartimento di Fisica, Universita di Roma ' Tor Vergata,' via della Ricerca Scientifica 1, 00133 Roma Italy (Italy); Arciprete, F.; Balzarotti, A.; Patella, F. [Dipartimento di Fisica, Universita di Roma ' Tor Vergata,' via della Ricerca Scientifica 1, 00133 Roma Italy (Italy)

    2012-10-01

    The transition from the liquid phase of Ga droplets to the formation of GaAs and GaMnAs quantum rings has been studied as a function of temperature. We show that different aggregation processes involve the GaAs (GaMnAs) island and the droplet formation. Furthermore, the aspect ratio of the islands exhibits an anomalous scaling law related to a tendency to aggregate in the vertical direction.

  5. Investigation of pre-structured GaAs surfaces for subsequent site-selective InAs quantum dot growth

    Directory of Open Access Journals (Sweden)

    Gröger Roland

    2011-01-01

    Full Text Available Abstract In this study, we investigated pre-structured (100 GaAs sample surfaces with respect to subsequent site-selective quantum dot growth. Defects occurring in the GaAs buffer layer grown after pre-structuring are attributed to insufficient cleaning of the samples prior to regrowth. Successive cleaning steps were analyzed and optimized. A UV-ozone cleaning is performed at the end of sample preparation in order to get rid of remaining organic contamination.

  6. Spin-Resolved Electronic Structure of Ultrathin Epitaxial Fe Films on Vicinal and Singular GaAs(100) Substrates

    Energy Technology Data Exchange (ETDEWEB)

    Morton, S A; Waddill, G D; Spangenberg, M; Seddon, E A; Neal, J; Shen, T; Tobin, J G

    2003-03-10

    Recently there has been considerable interest in the study of spin injection at ferromagnetic semiconductor heterojunctions and ferromagnetic metal--semiconductor contacts. Studies of ntype semiconductors have demonstrated spin-coherent transport over large distances5 and the persistence of spin coherence over a sizeable time scale. Clearly such investigations have been stimulated by the potential of the development of ''spintronics'', electronic devices utilizing the information of the electron spin states. To understand and improve the magnetic properties of ultrathin Fe films on GaAs has been the aim of many research groups over recent years. The interest in this system has both technological and fundamental scientific motivations. Technologically, Fe on GaAs may serve to realize spin electronic devices. From a fundamental science point of view, Fe on GaAs serves as a prototype for studies of the interplay between the crystalline structure and morphology of an ultrathin film, its electronic structure and the long range magnetic order it exhibits. Furthermore, it is well known that an oxidized Cs layer on GaAs substantially alters the work-function of the GaAs surface, which plays a very important role in the application of GaAs as a spin polarized electron source.

  7. Radiation damage effects on double-junction GaInP{sub 2}/GaAs solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yueyuan [Key Laboratory for Photonic and Electronic Bandgap Materials, Ministry of Education, School of Physics and Electronic Engineering, Harbin Normal University, Harbin 150025 (China); Hu, Jianmin, E-mail: hujianmin@foxmail.com [Key Laboratory for Photonic and Electronic Bandgap Materials, Ministry of Education, School of Physics and Electronic Engineering, Harbin Normal University, Harbin 150025 (China); Wu, Yiyong [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Xu, Jianwen; Lu, Jianfeng [Shanghai Institute of Space Power Sources, Shanghai 200233 (China); Zhao, Huijie [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Qian, Bin [Shanghai Institute of Space Power Sources, Shanghai 200233 (China)

    2014-07-01

    The radiation effects on a double-junction GaInP{sub 2}/GaAs solar cell were studied under exposures of 100 keV protons, 10 MeV protons and 1 MeV electrons, in terms of changes on electrical properties and spectral response. The results indicate that the electrical property degradation of the double-junction GaInP{sub 2}/GaAs solar cell under irradiation occurs mainly due to the damage in the GaAs sub-cell. The GaAs sub-cell damage is primarily attributed to the decrease in collection efficiency of the minority carriers coming from its base bottom. It is revealed from the cell behavior under exposure to 100 keV protons irradiation that under the AM0 illumination, there is no obvious damage defected in the tunnel junction between the GaInP{sub 2} and the GaAs sub cells. In addition, the tunnel junction between the GaInP{sub 2} and the GaAs sub-cells is stable and no boundary traps are formed.

  8. Superconducting NbN single-photon detectors on GaAs with an AlN buffer layer

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, Ekkehart; Merker, Michael; Ilin, Konstantin; Siegel, Michael [Institut fuer Mikro- und Nanoelektronische Systeme (IMS), Karlsruher Institut fuer Technologie, Hertzstrasse 16, 76187 Karlsruhe (Germany)

    2015-07-01

    GaAs is the material of choice for photonic integrated circuits. It allows the monolithic integration of single-photon sources like quantum dots, waveguide based optical circuits and detectors like superconducting nanowire single-photon detectors (SNSPDs) onto one chip. The growth of high quality NbN films on GaAs is challenging, due to natural occurring surface oxides and the large lattice mismatch of about 27%. In this work, we try to overcome these problems by the introduction of a 10 nm AlN buffer layer. Due to the buffer layer, the critical temperature of 6 nm thick NbN films was increased by about 1.5 K. Furthermore, the critical current density at 4.2 K of NbN flim deposited onto GaAs with AlN buffer is 50% higher than of NbN film deposited directly onto GaAs substrate. We successfully fabricated NbN SNSPDs on GaAs with a AlN buffer layer. SNSPDs were patterned using electron-beam lithography and reactive-ion etching techniques. Results on the study of detection efficiency and jitter of a NbN SNSPD on GaAs, with and without AlN buffer layer will be presented and discussed.

  9. Tight-binding calculation of the electronic states of bulk-terminated GaAs(311)A and B surfaces

    Institute of Scientific and Technical Information of China (English)

    贾瑜; 马丙现; 姚乾凯; 唐明生

    2002-01-01

    We have carried out theoretical investigations on the electronic structure of GaAs(311)A and GaAs(311)B sur-faces. The bulk electronic structure of GaAs has been described by the second-neighbour tight-binding formalism andthe surface electronic structure was evaluated via an analytic Green function method. First, we present the surfaceband structure together with the projected bulk band of both Ga-terminated and As-terminated for GaAs(311)A andGaAs(311)B surfaces, respectively. In each case, the number of surface states is determined, and the localized surfacefeatures and orbitproperties of these surface states along -Y-S-X- high symmetry lines of the surface Brillouinzone are discussed. For the Ga-terminated GaAs(311)A (1×1) surface, we have tested two possible structure models,i.e. "the bridge site" and "the hollow site" models. In comparison with the angle-resolved photoelectron spectroscopystudied recently, the results have shown that the surface electronic states of the hollow site model are in good agreementwith the experiments, whereas those of the bridge site model are not. So we have concluded that the hollow site modelis favourable for the Ga-terminated GaAs(311) (1× 1) surface and the bridge site model should be excluded.

  10. Impact of growth parameters on the morphology and microstructure of epitaxial GaAs nanowires grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Z.Y. [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500 Yu Tian Road, Shanghai 200083 (China); Chen, P.P., E-mail: ppchen@mail.sitp.ac.cn [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500 Yu Tian Road, Shanghai 200083 (China); Liao, Z.M. [Materials Engineering, University of Queensland, St. Lucia, QLD 4072 (Australia); Shi, S.X.; Sun, Y.; Li, T.X.; Zhang, Y.H. [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500 Yu Tian Road, Shanghai 200083 (China); Zou, J. [Materials Engineering, University of Queensland, St. Lucia, QLD 4072 (Australia); Center for Microscopy and Microanalysis, University of Queensland, St. Lucia, QLD 4072 (Australia); Lu, W. [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500 Yu Tian Road, Shanghai 200083 (China)

    2013-12-15

    Highlights: •Defect-free wurtzite GaAs nanowires were obtained by MBE at low growth temperature. •Some GaAs nanowires grown at low temperature show the morphology of two shoulders. •High growth temperature favors the formation of nanowires with uniform diameter. •Low V/III flux ratio causes many kinked GaAs nanowires. •A phase separation of the catalyst is observed under very Ga-rich condition. -- Abstract: The effect of the growth temperature and V/III flux ratio on the morphology and microstructure of GaAs nanowires grown on GaAs (1 1 1){sub B} substrates by Au-assisted molecular beam epitaxy with solid As{sub 4} source was investigated. It has been found that a low growth temperature of 400 °C can result in defect-free wurtzite structured nanowire with syringe-like morphology, while nanowires with more homogeneous diameter can be obtained at high temperatures (500 °C and 550 °C) with many stacking faults. It was also found that, at a low V/III flux ratio, GaAs nanowires had a shrinking neck section, while a high V/III flux ratio may result in disappearance of the shrinking necking section. For the Ga very rich condition, a phase separation of the catalysts can be observed, leaving a small Au–Ga droplet covered by the outer pure Ga droplet.

  11. MOVPE of n-doped GaAs and modulation doped GaAs/AlGaAs nanowires

    Science.gov (United States)

    Sladek, K.; Klinger, V.; Wensorra, J.; Akabori, M.; Hardtdegen, H.; Grützmacher, D.

    2010-02-01

    Two different fabrication approaches were compared to obtain conductive GaAs nanowires: on one hand by modulation doping of GaAs/AlGaAs core/shell nanowires, on the other hand by Si-doping of GaAs nanowires. Modulation doped GaAs/AlGaAs core-shell nanowires were grown by selective area metal organic vapor phase epitaxy (MOVPE) on GaAs (1 1 1) substrates. The influences of growth parameters and mask design on aspect ratio of the core structures were investigated. The specialty of this study was that the growth mode was switched from vertical GaAs wire growth to the AlGaAs conformal shell overgrowth by intentionally changing the growth chemistry from the use of a more stable group III source - trimethylgallium (TMGa) to more easily decomposed sources - the alternative sources triethylgallium (TEGa) and dimethylethylaminealane (DMEAAl). It was found that the diameter and length of the core structures strongly depend on the arsenic partial pressure and growth temperature as well as mask design. The uniformity of shell growth is also influenced by the mask design. Additionally an alternative approach for the production of conductive GaAs nanowires was under study. To this end, the influence of Si-doping on GaAs core growth was investigated. It was found that doping has a detrimental impact on growth morphology leading to an undesirable enhanced growth rate on the nanowire side facets.

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

    Directory of Open Access Journals (Sweden)

    O. G. Ibarra-Manzano

    2012-02-01

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

  13. Charge collection efficiency of GaAs detectors studied with low-energy heavy charged particles

    CERN Document Server

    Bates, R; Linhart, V; O'Shea, V; Pospísil, S; Raine, C; Smith, K; Sinor, M; Wilhelm, I

    1999-01-01

    Epitaxially grown GaAs layers have recently been produced with sufficient thickness and low enough free carrier concentration to permit their use as radiation detectors. Initial tests have shown that the epi-material behaves as a classical semiconductor as the depletion behaviour follows the square root dependency on the applied bias. This article presents the results of measurements of the growth of the active depletion depth with increasing bias using low-energy protons and alpha particles as probes for various depths and their comparison to values extrapolated from capacitance measurements. From the proton and alpha particle spectroscopic measurements, an active depth of detector material that collects 100% of the charge generated inside it was determined. The consistency of these results with independent capacitance measurements supports the idea that the GaAs epi-material behaves as a classical semiconductor. (author)

  14. A portable X-ray apparatus with GaAs linear array

    Energy Technology Data Exchange (ETDEWEB)

    Ardashev, E.N.; Gorokhov, S.A. [Institute of High Energy Physics, 142281 Protvino (Russian Federation); Polkovnikov, M.K., E-mail: pmk@ihep.ru [Institute of High Energy Physics, 142281 Protvino (Russian Federation); Lobanov, I.S.; Vorobiev, A.P. [Institute of High Energy Physics, 142281 Protvino (Russian Federation)

    2011-08-21

    The widely growing interest to the digital diagnostics and analysis systems, that have many advantages in comparison with the traditional (film) systems, in data taking, data storing, and data transmitting, requires a new detection technology. One of the most promising system for medical radiography today is a scanning type apparatus with some linear array detectors. The constructed apparatus is a device with some semiconductor GaAs detectors as sensitive elements to form the image while scanning an object. GaAs detectors are the detectors of the direct transformation of X-ray radiation into the electrical. The present paper describes the results of the construction and testing of the portable X-ray unit for traumatic examination and orthopedic manipulation in stationer clinics and at the first aid in medicine of catastrophe.

  15. A portable X-ray apparatus with GaAs linear array

    Science.gov (United States)

    Ardashev, E. N.; Gorokhov, S. A.; Polkovnikov, M. K.; Lobanov, I. S.; Vorobiev, A. P.

    2011-08-01

    The widely growing interest to the digital diagnostics and analysis systems, that have many advantages in comparison with the traditional (film) systems, in data taking, data storing, and data transmitting, requires a new detection technology. One of the most promising system for medical radiography today is a scanning type apparatus with some linear array detectors. The constructed apparatus is a device with some semiconductor GaAs detectors as sensitive elements to form the image while scanning an object. GaAs detectors are the detectors of the direct transformation of X-ray radiation into the electrical. The present paper describes the results of the construction and testing of the portable X-ray unit for traumatic examination and orthopedic manipulation in stationer clinics and at the first aid in medicine of catastrophe.

  16. Diffusion of $^{56}$Co in GaAs and SiGe alloys

    CERN Multimedia

    Koskelo, O K

    2007-01-01

    Following our previous diffusion studies performed with the modified radiotracer technique, we propose to determine the diffusion of cobalt in GaAs and SiGe alloys under intrinsic conditions. In the literature only three previous studies for Co diffusion in GaAs may be found and the results differ by over four orders of magnitude from each other. For Co diffusion in SiGe alloys no previous data is available in the literature. For Co diffusion in Ge one study may be found but the results have been obtained with material having increased dislocation density. For dislocation-free material no previous measurements are available. For such experiments we ask for two runs of 3 shifts (total of 6 shifts) with $^{56}$Co$^{+}$ ion beam.

  17. Mechanism analysis of Gen Ⅲ LLL image intensifier GaAs cathode photoelectric emission disability

    Science.gov (United States)

    Xu, Jiangtao; Yan, Lei; Cheng, Yaojin; Han, Kunye; Liu, Beibei; Zhang, Taimin

    2013-08-01

    The focus of the third generation image intensifier photocathode sensitivity decreases in the GaAs are analyzed, and proposed solutions,experimental results show that the tube microchannel plate(mcp), screen GaAs cathode discharge gas is caused by decreased sensitivity of the main reasons. Paper used two-layer model, and even negative electron affinity(NET) interface barrier theory of the photoelectric cathode drop mechanism was discussed , when the photocathode emission levels of CO adsorption and other harmful gas, chemical adsorption layer of ionic bond formation will lead to production of cathode surface barrier interfaces. Cathode surface adsorption of the pollutants more ,the interface barrier becomes thicker, the smaller the electron surface escape probability, when the cathode interface thicker barrier to the electron surface escape is zero, the cathode photoemission end of life.

  18. Experimental study and chemical application of GaAs semiconductor laser treating trigeminal neuralgia

    Science.gov (United States)

    Qiu, Ke-Qum; Cao, Shu-Chen; Wang, Hu-Zhong; Wang, Ke-Ning; Xiao, Ton-Ha; Shen, Ke-Wei

    1993-03-01

    GaAs semiconductor laser was used to treat trigeminal neuralgia with an effective rate of 91.1%, and no side effects were found in 67 cases. Changes in and the recovery of the trigeminal nerve cell were studied with light and electromicroscope. Discussed in this article are the time length and quantity of laser treatment with low power. Experimental study and clinical application of the GaAs semiconductor laser have been carried out in our department since 1987. One-hundred-fifteen patients with various diseases in the maxillofacial region (including 67 cases of trigeminal neuralgia) have been treated with satisfactory effects and without any side-effects. The wavelength of the laser is 904 mu, the largest pulse length is 200 mu, and the average power is 2000 HZ.

  19. Spectral dependence of the refractive index of single-crystalline GaAs for optical applications

    Energy Technology Data Exchange (ETDEWEB)

    Plotnichenko, V G; Nazaryants, V O; Kryukova, E B; Dianov, E M, E-mail: victor@fo.gpi.ac.r [Fibre Optics Research Center of the Russian Academy of Sciences, 38 Vavilov Street, Moscow 119333 (Russian Federation)

    2010-03-17

    The refractive index of crystalline GaAs is measured by the method of interference refractometry in the wavenumber range from 10 500 to 540 cm{sup -1} (or the wavelength range from 0.9 to 18.6 {mu}m) with a resolution of 0.1 cm{sup -1}. The measurement results are approximated by the generalized Cauchy dispersion formula of the 8th power. Spectral wavelength dependences of the first- and second-order derivatives of the refractive index are calculated, and the zero material dispersion wavelength is found to be {lambda}{sub 0} = 6.61 {mu}m. Using three GaAs plates of different thicknesses we managed to raise the refractive index measurement accuracy up to 4 x 10{sup -4} or 0.02%, being nearly by an order of magnitude better than the data available.

  20. Evidence for grain boundary passivation by oxidation in polycrystalline GaAs solar cells

    Science.gov (United States)

    Kazmerski, L. L.; Ireland, P. J.

    1980-02-01

    The chemistry and composition of grain boundaries in polycrystalline GaAs grown by liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE) are examined using complementary Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS) and X-ray photoelectron spectroscopy (XPS). The effects of an unintentional residual-oxygen partial pressure during LPE growth are investigated in terms of grain boundary passivation. Depth-compositional data verify the grain boundary localization of oxides using an in situ, UHV fracturing technique. Indications of distributions of these oxides over the grain boundary are presented. The performances of Au Schottky barrier solar cells fabricated from the polycrystalline LPE and MBE GaAs are compared and differences are explained in terms of grain boundary activity.

  1. High gain GaAs photoconductive semiconductor switches for ground penetrating radar

    Energy Technology Data Exchange (ETDEWEB)

    Loubriel, G.M.; Aurand, J.F.; Buttram, M.T.; Zutavern, F.J.; Helgeson, W.D.; O`Malley, M.W. [Sandia National Labs., Albuquerque, NM (United States); Brown, D.J. [Ktech Corp., Albuquerque, NM (United States)

    1996-07-01

    The ability of high gain GaAs Photoconductive Semiconductor switches (PCSS) to deliver high peak power, fast risetime pulses when triggered with small laser diode arrays makes them suitable for their use in radars that rely on fast impulses. This type of direct time domain radar is uniquely suited for observation of large structures under ground because it can operate at low frequencies and at high average power. This paper will summarize the state-of-the-art in high gain GaAs switches and discuss their use in a radar transmitter. We will also present a summary of an analysis of the effectiveness of different pulser geometries that result in transmitted pulses with varying frequency content. To this end we developed a simple model that includes transmit and receive antenna response, attenuation and dispersion of the electromagnetic impulses by the soil, and target cross sections.

  2. Strain-driven growth of GaAs(111) quantum dots with low fine structure splitting

    Energy Technology Data Exchange (ETDEWEB)

    Yerino, Christopher D.; Jung, Daehwan; Lee, Minjoo Larry, E-mail: minjoo.lee@yale.edu [Department of Electrical Engineering, Yale University, New Haven, Connecticut 06520 (United States); Simmonds, Paul J. [Departments of Physics and Materials Science and Engineering, Boise State University, Boise, Idaho 83725 (United States); Liang, Baolai; Huffaker, Diana L. [California NanoSystems Institute and Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States); Schneider, Christian; Unsleber, Sebastian; Vo, Minh; Kamp, Martin [Technische Physik, Physikalisches Institut and Wilhelm Conrad Röntgen-Research Center for Complex Material Systems, Universität Würzburg, Am Hubland, D-97074 Würzburg (Germany); Höfling, Sven [Technische Physik, Physikalisches Institut and Wilhelm Conrad Röntgen-Research Center for Complex Material Systems, Universität Würzburg, Am Hubland, D-97074 Würzburg (Germany); SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews, KY16 9SS (United Kingdom)

    2014-12-22

    Symmetric quantum dots (QDs) on (111)-oriented surfaces are promising candidates for generating polarization-entangled photons due to their low excitonic fine structure splitting (FSS). However, (111) QDs are difficult to grow. The conventional use of compressive strain to drive QD self-assembly fails to form 3D nanostructures on (111) surfaces. Instead, we demonstrate that (111) QDs self-assemble under tensile strain by growing GaAs QDs on an InP(111)A substrate. Tensile GaAs self-assembly produces a low density of QDs with a symmetric triangular morphology. Coherent, tensile QDs are observed without dislocations, and the QDs luminescence at room temperature. Single QD measurements reveal low FSS with a median value of 7.6 μeV, due to the high symmetry of the (111) QDs. Tensile self-assembly thus offers a simple route to symmetric (111) QDs for entangled photon emitters.

  3. Impulse-coupling coefficients from a pulsed-laser ablation of semiconductor GaAs

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Impulse-coupling coefficients from 1.06 - μm, 10-ns Nd:YAG pulsed-laser radiation to GaAs targets with different areas were measured using the ballistic pendulum method in the laser power density ranging from 4.0 × 108 to 5.0 × 109 W·cm-2.A detonation wave model of the plasma was established theoretically. The expansion process of plasma after the laser pulse ends is described in detail, and the impulse-coupling coefficients from pulsed laser with different energies to GaAs with different areas were calculated using the given model. It is found that the theoretical results agree well with the experimental data.

  4. Effects of atomic hydrogen and deuterium exposure on high polarization GaAs photocathodes

    Energy Technology Data Exchange (ETDEWEB)

    M. Baylac; P. Adderley; J. Brittian; J. Clark; T. Day; J. Grames; J. Hansknecht; M. Poelker; M. Stutzman; A. T. Wu; A. S. Terekhov

    2005-12-01

    Strained-layer GaAs and strained-superlattice GaAs photocathodes are used at Jefferson Laboratory to create high average current beams of highly spin-polarized electrons. High electron yield, or quantum efficiency (QE), is obtained only when the photocathode surface is atomically clean. For years, exposure to atomic hydrogen or deuterium has been the photocathode cleaning technique employed at Jefferson Laboratory. This work demonstrates that atomic hydrogen cleaning is not necessary when precautions are taken to ensure that clean photocathode material from the vendor is not inadvertently dirtied while samples are prepared for installation inside photoemission guns. Moreover, this work demonstrates that QE and beam polarization can be significantly reduced when clean high-polarization photocathode material is exposed to atomic hydrogen from an rf dissociator-style atomic hydrogen source. Surface analysis provides some insight into the mechanisms that degrade QE and polarization due to atomic hydrogen cleaning.

  5. Optical anisotropy induced by mechanical strain around the fundamental gap of GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Ortega-Gallegos, J.; Lastras-Martinez, A.; Lastras-Martinez, L.F. [Instituto de Investigacion en Comunicacion Optica, Universidad Autonoma de San Luis Potosi, Alvaro Obregon 64, San Luis Potosi (Mexico); Balderas-Navarro, R.E. [Instituto de Investigacion en Comunicacion Optica, Universidad Autonoma de San Luis Potosi, Alvaro Obregon 64, San Luis Potosi (Mexico); Facultad de Ciencias, Universidad Autonoma de San Luis Potosi, Alvaro Obregon 64, San Luis Potosi (Mexico)

    2008-07-01

    We report on a theoretical-experimental study of reflectance anisotropy spectroscopy (RAS) of GaAs (001) crystals under uniaxial stress. The study was carried out in the energy region around the fundamental transition. RAS spectra in the energy range from 1.2-1.7 eV were measured with a photoelastic-modulator-based spectrometer. To induce an optical anisotropy, the GaAs crystals were thinned down to 400 {mu}m and an calibrated uniaxial stress was applied by deflection. RAS showed a line shape consisting of an oscillation at around E{sub 0}. On the basis of a perturbative approach employing the Pikus-Bir Hamiltonian, we calculated the RAS line shape and found a close agreement with the experimental spectra. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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

    Science.gov (United States)

    Lebib, A.; Hannanchi, R.; Beji, L.; EL Jani, B.

    2016-12-01

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

  7. Implantation and diffusion of $^{73}$As in GaAs and GaP

    CERN Document Server

    Bösker, G; Stolwijk, N A; Mehrer, H; Burchard, A

    2000-01-01

    Self-diffusion on the As sublattice in intrinsic GaAs and foreign- atom diffusion on the P sublattice in intrinsic GaP were investigated in a direct way by As tracer diffusion measurements using the radioisotope /sup 73/As. For this purpose /sup 73/As was implanted in both materials at the ISOLDE facility of CERN. Then diffusion annealings were performed followed by serial sectioning and counting of the radioactivity in each section. The resulting profiles were simulated within a computer model which accounts for the observed loss of tracer to the diffusion ambient. The so-obtained diffusion coefficients for As in GaAs and GaP are compared with existing diffusivities in these compounds. (25 refs).

  8. Electron gas quality at various (110)-GaAs interfaces as benchmark for cleaved edge overgrowth

    Science.gov (United States)

    Riedi, S.; Reichl, C.; Berl, M.; Alt, L.; Maier, A.; Wegscheider, W.

    2016-12-01

    We study molecular beam epitaxial growth on the unusual (110) surface of GaAs substrates as prerequisite for cleaved edge overgrown structures. We present the first systematic comparison of the quality of two dimensional electron systems on simultaneously overgrown (110) GaAs monitor wafers with ex situ as well as in situ cleaved (110) facets. Our study confirms that characterization of the monitor wafer is a valid benchmark for the magnetotransport characteristics of structures grown on cleaved facets. We show that deviating results can be traced back to (110) substrates of lower quality. We also demonstrate that the roughness of the in situ cleaved facets is decisive for the quality of the induced electron gas.

  9. GaAs Solar Cells on V-Grooved Silicon via Selective Area Growth: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Warren, Emily L [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Jain, Nikhil [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Tamboli, Adele C [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Vaisman, Michelle [Yale University; Li, Qiang [Hong Kong University of Science and Technology; Lau, Kei May [Hong Kong University of Science and Technology

    2017-08-31

    Interest in integrating III-Vs onto Si has recently resurged as a promising pathway towards high-efficiency, low-cost tandem photovoltaics. Here, we present a single junction GaAs solar cell grown monolithically on polished Si (001) substrates using V-grooves, selective area growth, and aspect ratio trapping to mitigate defect formation without the use of expensive, thick graded buffers. The GaAs is free of antiphase domains and maintains a relatively low TDD of 4x107 cm-2, despite the lack of a graded buffer. This 6.25 percent-efficient demonstration solar cell shows promise for further improvements to III-V/Si tandems to enable cost-competitive photovoltaics.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-12-01

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

  11. GaAs epitaxy on Si substrates: modern status of research and engineering

    Energy Technology Data Exchange (ETDEWEB)

    Bolkhovityanov, Yu B; Pchelyakov, O P [Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation)

    2008-05-31

    While silicon and gallium arsenide are dominant materials in modern micro- and nanoelectronics, devices fabricated from them still use Si and GaAs substrates only separately. Integrating these materials on the (highest effeciency) substrate of Si has been the subject of much research effort for more than twenty years. This review systematizes and generalizes the current understanding of the fundamental physical mechanisms governing the epitaxial growth of GaAs and its related III-V compounds on Si substrates. Basic techniques avilable for improving the quality of such heterostructures are described, and recent advances in fabricating device-quality A{sup III}B{sup V}/Si heterostructures and devices on their bases are also presented. (reviews of topical problems)

  12. Flow Instability of Molten GaAs in the Czochralski Configuration

    Institute of Scientific and Technical Information of China (English)

    Shuxian CHEN; Mingwei LI

    2007-01-01

    The flow and heat transfer of molten GaAs under the interaction of buoyancy, Marangoni and crystal rotation in the Czochralski configuration are numerically studied by using a time-dependent and three-dimensional turbulent flow model for the first time. The transition from axisymmetric flow to non-axisymmetric flow and then returning to axisymmetric flow again with increasing centrifugal and coriolis forces by increasing the crystal rotation rate was numerically observed. The origin of the transition to non-axisymmetric flow has been proved to be baroclinic instability. Several important characteristics of baroclinic instability in the CZ GaAs melt have been predicted. These characteristics are found to be in agreement with experimental observations.

  13. Chemical Composition of Nanoporous Layer Formed by Electrochemical Etching of p-Type GaAs

    Science.gov (United States)

    Bioud, Youcef A.; Boucherif, Abderraouf; Belarouci, Ali; Paradis, Etienne; Drouin, Dominique; Arès, Richard

    2016-10-01

    We have performed a detailed characterization study of electrochemically etched p-type GaAs in a hydrofluoric acid-based electrolyte. The samples were investigated and characterized through cathodoluminescence (CL), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). It was found that after electrochemical etching, the porous layer showed a major decrease in the CL intensity and a change in chemical composition and in the crystalline phase. Contrary to previous reports on p-GaAs porosification, which stated that the formed layer is composed of porous GaAs, we report evidence that the porous layer is in fact mainly constituted of porous As2O3. Finally, a qualitative model is proposed to explain the porous As2O3 layer formation on p-GaAs substrate.

  14. Electrical conduction properties of Si delta-doped GaAs grown by MBE

    Energy Technology Data Exchange (ETDEWEB)

    Yildiz, A., E-mail: yildizab@gmail.co [Department of Physics, Faculty of Science and Arts, Gazi University, Teknikokular, 06500 Ankara (Turkey); Department of Physics, Faculty of Science and Arts, Ahi Evran University, 40040 Kirsehir (Turkey); Lisesivdin, S.B. [Nanotechnology Research Center, Bilkent University, Bilkent, 06800 Ankara (Turkey); Altuntas, H.; Kasap, M.; Ozcelik, S. [Department of Physics, Faculty of Science and Arts, Gazi University, Teknikokular, 06500 Ankara (Turkey)

    2009-11-15

    The temperature dependent Hall effect and resistivity measurements of Si delta-doped GaAs are performed in a temperature range of 25-300 K. The temperature dependence of carrier concentration shows a characteristic minimum at about 200 K, which indicates a transition from the conduction band conduction to the impurity band conduction. The temperature dependence of the conductivity results are in agreement with terms due to conduction band conduction and localized state hopping conduction in the impurity band. It is found that the transport properties of Si delta-doped GaAs are mainly governed by the dislocation scattering mechanism at high temperatures. On the other hand, the conductivity follows the Mott variable range hopping conduction (VRH) at low temperatures in the studied structures.

  15. Gallium surface diffusion on GaAs (001) surfaces measured by crystallization dynamics of Ga droplets

    Energy Technology Data Exchange (ETDEWEB)

    Bietti, Sergio, E-mail: sergio.bietti@mater.unimib.it; Somaschini, Claudio; Esposito, Luca; Sanguinetti, Stefano [L–NESS and Dipartimento di Scienza dei Materiali, Università di Milano Bicocca, Via Cozzi 55, I–20125 Milano (Italy); Fedorov, Alexey [L–NESS and CNR–IFN, via Anzani 42, I-22100 Como (Italy)

    2014-09-21

    We present accurate measurements of Ga cation surface diffusion on GaAs surfaces. The measurement method relies on atomic force microscopy measurement of the morphology of nano–disks that evolve, under group V supply, from nanoscale group III droplets, earlier deposited on the substrate surface. The dependence of the radius of such nano-droplets on crystallization conditions gives direct access to Ga diffusion length. We found an activation energy for Ga on GaAs(001) diffusion E{sub A}=1.31±0.15 eV, a diffusivity prefactor of D₀=0.53(×2.1±1) cm² s⁻¹ that we compare with the values present in literature. The obtained results permit to better understand the fundamental physics governing the motion of group III ad–atoms on III–V crystal surfaces and the fabrication of designable nanostructures.

  16. The miniband spectrum in (AlAs) sub M (GaAs) sub N (111)

    CERN Document Server

    Karavaev, G F; Egunov, R M

    2002-01-01

    The electron states for energies in the conduction band of (AlAs) sub M (GaAs) sub N (111) superlattices with M >= N (N < 10) are considered. The properties of such superlattices are mainly determined by electrons of X-valley in AlAs and L-valley in GaAs. The calculations are carried out on the basis of the envelope-function model of interface band mixing. Miniband spectra, symmetry and localization of wave functions, and also probabilities of the interminiband infrared absorption are defined and analyzed. It is shown that the latter have a significant magnitude not only at light polarization along the superlattice growth axis, but also at normal incidence of a light wave to the surface. The analysis has been normal incidence of a light wave to the surface. The analysis has shown the importance of consideration of X sub 5 -states belonging to the valence band for infrared absorption

  17. Monte Carlo study of GaN versus GaAs terahertz quantum cascade structures

    Science.gov (United States)

    Bellotti, Enrico; Driscoll, Kristina; Moustakas, Theodore D.; Paiella, Roberto

    2008-03-01

    Due to their large optical phonon energies, nitride semiconductors are promising for the development of terahertz quantum cascade lasers with dramatically improved high-temperature performance relative to existing GaAs devices. Here, we present a rigorous Monte Carlo study of carrier dynamics in two structures based on the same design scheme for emission at 2THz, consisting of GaN /AlGaN or GaAs /AlGaAs quantum wells. The population inversion and hence the gain coefficient of the nitride device are found to exhibit a much weaker (by a factor of over 3) temperature dependence and to remain large enough for laser action even without cryogenic cooling.

  18. LEED and AES characterization of the GaAs(110)-ZnSe interface

    Science.gov (United States)

    Tu, D.-W.; Kahn, A.

    1984-01-01

    In this paper, a study is conducted of the composition and structure of epitaxial ZnSe films grown by congruent evaporation on GaAs(110) at a rate of 2 A/min. It is found that the films grown on 300 C GaAs are nearly stoichiometric and form an abrupt interface with the substrate. Films grown at higher temperature (T greater than 350-400 C) are Se rich. The crystallinity of films grown at 300 C is good and their surface atomic geometry is identical to that of a ZnSe crystal. The GaAs-ZnSe interface geometry seems to be dominated by the Se-substrate bonds. The adsorption of Se, during the formation of very thin ZnSe films (2-3 A), produces a (1 x 2) LEED pattern and modifications of the LEED I-V profiles, which probably indicate a change in the substrate atomic relaxation.

  19. Epitaxial two-dimensional nitrogen atomic sheet in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Harada, Yukihiro, E-mail: y.harada@eedept.kobe-u.ac.jp; Yamamoto, Masuki; Baba, Takeshi; Kita, Takashi [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501 (Japan)

    2014-01-27

    We have grown an epitaxial two-dimensional nitrogen (N) atomic sheet in GaAs by using the site-controlled N δ-doping technique. We observed a change of the electronic states in N δ-doped GaAs from the isolated impurity centers to the delocalized impurity band at 1.49 eV with increasing N-doping density. According to the excitation-power- and temperature-dependent photoluminescence (PL) spectra, the emission related to localized levels below the impurity band edge was dominant at low excitation power and temperature, whereas the effects of the localized levels can be neglected by increasing the excitation power and temperature. Furthermore, a clear Landau shift of the PL-peak energy was observed at several Tesla in the Faraday configuration, in contrast to the case in the impurity limit.

  20. Weak interaction between germanene and GaAs(0001) by H intercalation: A route to exfoliation

    KAUST Repository

    Kaloni, Thaneshwor P.

    2013-11-13

    Epitaxial germanene on a semiconducting GaAs(0001) substrate is studied by ab initio calculations. The germanene-substrate interaction is found to be strong for direct contact but can be substantially reduced by H intercalation at the interface. Our results indicate that it is energetically possible to take the germanene off the GaAs(0001) substrate. While mounted on the substrate, the electronic structure shows a distinct Dirac cone shift above the Fermi energy with a splitting of 175 meV. On the other hand, we find for a free standing sheet a band gap of 24 meV, which is due to the intrinsic spin orbit coupling.

  1. Effect of temperature on (TV) statics characteristics of GaAs Mesfet

    Science.gov (United States)

    Fares, Z.; Saidi, Y.; Aliouat, W.

    2016-10-01

    The GaAs metal semiconductor field effect transistors called mesfets are the most active components used in microwave applications. To better exploit the performance of these components circuits, it is necessary to develop techniques for sophisticated numerical computation based on physical mechanisms that govern the operation of these devices. The static properties of GaAs MESFET could be determined from an original analytical study based on the resolution of the semiconductor fundamental equations. Then we will study the equation of thermal resistance as a function of the physical parameters of MESFETs by analogy electric thermal resistance RTH will be determined as the ratio of the difference of temperature on the thermal dissipation. The model took into account the difference between the temperature of the component and the ambient temperature and the effect of temperature on the parameters of the component.

  2. Characterization of thick epitaxial GaAs layers for X-ray detection

    CERN Document Server

    Samic, H; Donchev, V; Nghia, N X; Gandouzi, M; Zazoui, M; Bourgoin, J C; El-Abbassi, H; Rath, S; Sellin, P J

    2002-01-01

    We have studied the current-voltage and capacitance-voltage characteristics of p/i/n structures made on non-intentionally doped epitaxial GaAs layers grown by the chemical reaction method. Deep level transient spectroscopy demonstrates that these layers contain a low defect concentration. X-ray photoconductivity shows that the diffusion length is large. The homogeneity of the properties of these layers, which has been evaluated over large area (cm sup 2), is confirmed by photoluminescence mapping.

  3. Position-controlled uniform GaAs nanowires on silicon using nanoimprint lithography.

    Science.gov (United States)

    Munshi, A M; Dheeraj, D L; Fauske, V T; Kim, D C; Huh, J; Reinertsen, J F; Ahtapodov, L; Lee, K D; Heidari, B; van Helvoort, A T J; Fimland, B O; Weman, H

    2014-02-12

    We report on the epitaxial growth of large-area position-controlled self-catalyzed GaAs nanowires (NWs) directly on Si by molecular beam epitaxy (MBE). Nanohole patterns are defined in a SiO2 mask on 2 in. Si wafers using nanoimprint lithography (NIL) for the growth of positioned GaAs NWs. To optimize the yield of vertical NWs the MBE growth parameter space is tuned, including Ga predeposition time, Ga and As fluxes, growth temperature, and annealing treatment prior to NW growth. In addition, a non-negligible radial growth is observed with increasing growth time and is found to be independent of the As species (i.e., As2 or As4) and the growth temperatures studied. Cross-sectional transmission electron microscopy analysis of the GaAs NW/Si substrate heterointerface reveals an epitaxial growth where NW base fills the oxide hole opening and eventually extends over the oxide mask. These findings have important implications for NW-based device designs with axial and radial p-n junctions. Finally, NIL positioned GaAs/AlGaAs core-shell heterostructured NWs are grown on Si to study the optical properties of the NWs. Room-temperature photoluminescence spectroscopy of ensembles of as-grown core-shell NWs reveals uniform and high optical quality, as required for the subsequent device applications. The combination of NIL and MBE thereby demonstrates the successful heterogeneous integration of highly uniform GaAs NWs on Si, important for fabricating high throughput, large-area position-controlled NW arrays for various optoelectronic device applications.

  4. Photovoltaic characteristics of diffused P/+N bulk GaAs solar cells

    Science.gov (United States)

    Borrego, J. M.; Keeney, R. P.; Bhat, I. B.; Bhat, K. N.; Sundaram, L. G.; Ghandhi, S. K.

    1982-01-01

    The photovoltaic characteristics of P(+)N junction solar cells fabricated on bulk GaAs by an open tube diffusion technique are described in this paper.Spectral response measurements were analyzed in detail and compared to a computer simulation in order to determine important material parameters. It is projected that proper optimization of the cell parameters can increase the efficiency of the cells from 12.2 percent to close to 20 percent.

  5. Characterization of Femtosecond Low-Temperature-Grown GaAs Photoconductive Switch

    Institute of Scientific and Technical Information of China (English)

    林位株; 刘智刚; 廖睿; 张海潮; 郭冰; 文锦辉; 赖天树

    2002-01-01

    A photoconductive response time, as short as 350 fs, of a low-temperature-grown GaAs (LT-GaAs) micro-coplanar photoconductive switch has been measured and modelled to the ultrafast trapping of the photoexcited carriers in LT-GaAs. The coherent interference of the pump and probe pulses results in a narrow spike photocurrent autocorrelation signal which maps the femtosecond optical pulses.

  6. Characterization of device isolation in GaAs MESFET circuits by boron implantation

    Energy Technology Data Exchange (ETDEWEB)

    Clauwaert, F.; Van Daele, P.; Lagasse, P.

    1987-03-01

    The use of boron implantation for the electrical isolation of MESFET's and other electronic components in GaAs high speed digital IC's has been investigated. The sheet isolation resistance was measured as a function of the implantation energy and dose and of the anneal temperature and time. Topics considered include fabrication, integrated circuits, electric conductivity, annealing, transistors, ion implantation, and digital systems.

  7. Femtosecond differential transmission measurements on low temperature GaAs metal-semiconductor-metal structures

    DEFF Research Database (Denmark)

    Keil, Ulrich Dieter Felix; Hvam, Jørn Märcher; Tautz, S.

    1997-01-01

    We report on differential transmission measurements on low temperature grown (LT)-GaAs with and without applied electrical fields at different wavelengths. Electrical fields up to 100 kV/cm can be applied via an interdigitated contact structure to our LT GaAs samples which have been removed from....... The response time of a biased metal-semiconductor-metal detector, therefore, exceeds the carrier life time of the substrate material. (C) 1997 American Institute of Physics....

  8. Interface dynamics and crystal phase switching in GaAs nanowires

    OpenAIRE

    Jacobsson, Daniel; Panciera, Federico; Tersoff, Jerry; Reuter, Mark C.; Lehmann, Sebastian; Hofmann, Stephan; Dick, Kimberly A.; Ross, Frances M

    2016-01-01

    This is the author accepted manuscript. The final version is available from Nature Publishing Group via http://dx.doi.org/10.1038/nature17148 Controlled formation of non-equilibrium crystal structures is one of the most important challenges in crystal growth. Catalytically grown nanowires are ideal systems for studying the fundamental physics of phase selection, and could lead to new electronic applications based on the engineering of crystal phases. Here we image gallium arsenide (GaAs) n...

  9. Terahertz-Induced Changes of Optical Spectra in GaAs Quantum Wells

    Institute of Scientific and Technical Information of China (English)

    MI Xian-Wu; CAO Jun-Cheng

    2004-01-01

    @@ We have theoretically investigated optical absorption spectra in GaAs quantum well (QW) driven by both a strong terahertz (THz) field and a near-infrared field within the theory of density matrix. In presence of a strong THz field, the optical transitions in the QW subbands are altered by the THz field. The alteration has a direct impact on the optical absorption and results in the Autler-Townes splitting and the sidebands generation, which is in agreement with the experiments.

  10. A robust physics-oriented statistical GaAs MESFET model

    OpenAIRE

    Bandler, J.W.; Biernacki, R.M.; Cai, Q; Chen, S. H.

    1994-01-01

    In this paper we present a robust physics-oriented statistical GaAs MESFET model. Our model integrates the DC Khatibzadeh and Trew model for DC simulation with the Ladbrooke formulas for small-signal analysis (KTL). Accuracy of the statistical KTL model is verified by Monte Carlo simulations using device measurements. Statistical extraction and postprocessing of device physical parameters are carried out by HarPE.

  11. EFFECTS OF OPERATING CONDITIONS ON THE DEPOSITION OF GaAs IN A VERTICAL CVD REACTOR

    OpenAIRE

    JAE-SANG BAEK; JIN-HYO BOO; YOUN-JEA KIM

    2008-01-01

    A numerical study is needed to gain insight into the growth mechanism and improve the reactor design or optimize the deposition condition in chemical vapor deposition (CVD). In this study, we have performed a numerical analysis of the deposition of gallium arsenide (GaAs) from trimethyl gallium (TMG) and arsine in a vertical CVD reactor. The effects of operating parameters, such as the rotation velocity of susceptor, inlet velocity, and inlet TMG fraction, are investigated and presented. The ...

  12. High quality GaAs single photon emitters on Si substrate

    Energy Technology Data Exchange (ETDEWEB)

    Bietti, S.; Sanguinetti, S. [Dipartimento di Scienza dei Materiali and L-NESS, Università, di Milano Bicocca, Via Cozzi 53,I-20125 Milano (Italy); Cavigli, L.; Accanto, N.; Vinattieri, A. [Dipartimento di Fisica e Astronomia, LENS and CNISM, Università, di Firenze, Via Sansone 1, I-50019 Firenze (Italy); Minari, S.; Abbarchi, M. [Dipartimento di Fisica e Astronomia, LENS and CNISM, Universita di Firenze, Via Sansone 1, I-50019 Firenze (Italy); Isella, G. [Dipartimento di Fisica and L-NESS, Politecnico di Milano, Via Anzani 42, 22100 Como (Italy); Frigeri, C. [CNR-IMEM Institute, Parco Area delle Scienze 31/A, 43100 Parma (Italy); Gurioli, M. [Dipartimento di Fisica e Astronomia, LENS and CNISM, Universita, di Firenze, Via Sansone 1, I-50019 Firenze (Italy)

    2013-12-04

    We describe a method for the direct epitaxial growth of a single photon emitter, based on GaAs quantum dots fabricated by droplet epitaxy, working at liquid nitrogen temperatures on Si substrates. The achievement of quantum photon statistics up to T=80 K is directly proved by antibunching in the second order correlation function as measured with a H anbury Brown and Twiss interferometer.

  13. Super-Lattice Light Emitting Diodes (SLEDS) on GaAs

    Science.gov (United States)

    2016-03-31

    done using multiple techniques . Some of these techniques are thermocompression bonding , glass frit bonding , and adhesive bonding . It was decided to...method on predesigned GaAs RIIC that would drive the SLEDS. New developments showed that wafer bonding can be another succesful aproch to GSLEDS...infrared light emitting diodes (LEDs). Typically, the LED arrays are mated with CMOS read-in integrated circuit (RIIC) chips using flip-chip bonding . In

  14. Impurity and Defect Behavior in High-Purity Epitaxial GaAs.

    Science.gov (United States)

    1979-09-26

    Japanese Journal of Applied Physics 9, 156 (1970). -113- 11. T...Saito and F. Hasegawa, "Cause of the High Resis- tance Region at Vapour Epitaxial GaAs Layer-Sub- strate Interface", Japanese Journal of Applied Physics 10...Ryuzan, "Electrical Prop- erties of n-Type Gallium Arsenide at High Tempera- tures", Japanese Journal of Applied Physics 10, 392 (1971). 35. P.

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

    Science.gov (United States)

    Ullah, A. R.; Gluschke, J. G.; Krogstrup, P.; Sørensen, C. B.; Nygård, J.; Micolich, A. P.

    2017-03-01

    GaAs was central to the development of quantum devices but is rarely used for nanowire-based quantum devices with InAs, InSb and SiGe instead taking the leading role. p-type GaAs nanowires offer a path to studying strongly confined 0D and 1D hole systems with strong spin-orbit effects, motivating our development of nanowire transistors featuring Be-doped p-type GaAs nanowires, AuBe alloy contacts and patterned local gate electrodes towards making nanowire-based quantum hole devices. We report on nanowire transistors with traditional substrate back-gates and EBL-defined metal/oxide top-gates produced using GaAs nanowires with three different Be-doping densities and various AuBe contact processing recipes. We show that contact annealing only brings small improvements for the moderately doped devices under conditions of lower anneal temperature and short anneal time. We only obtain good transistor performance for moderate doping, with conduction freezing out at low temperature for lowly doped nanowires and inability to reach a clear off-state under gating for the highly doped nanowires. Our best devices give on-state conductivity 95 nS, off-state conductivity 2 pS, on-off ratio ˜ {10}4, and sub-threshold slope 50 mV/dec at T=4 K. Lastly, we made a device featuring a moderately doped nanowire with annealed contacts and multiple top-gates. Top-gate sweeps show a plateau in the sub-threshold region that is reproducible in separate cool-downs and indicative of possible conductance quantisation highlighting the potential for future quantum device studies in this material system.

  16. First-principles study of fully relaxed vacancies in GaAs

    OpenAIRE

    Laasonen, K; Nieminen, Risto M.; Puska, Martti J.

    1992-01-01

    The structural and electronic properties of vacancies in GaAs have been studied using ab initio molecular dynamics. The atomic structures of vacancies in different charge states have been optimized by using a simulated-annealing procedure. The neighbor-atom relaxations are modest for neutral, singly negative, and doubly negative Ga vacancies as well as for the neutral As vacancy. In the case of singly and doubly negative As vacancies, very strong inward relaxations are found. These inward rel...

  17. Magnetic anisotropy of single Mn acceptors in GaAs in an external magnetic field

    OpenAIRE

    Bozkurt, M Murat; Mahani, MR; Studer, P; Tang, J-M; Schofield, SR; Curson, NJ; Flatté, ME Michael; Silov, AY Andrei; Hirjibehedin, CF; Canali, CM; Koenraad, PM Paul

    2013-01-01

    We investigate the effect of an external magnetic field on the physical properties of the acceptor hole states associated with single Mn acceptors placed near the (110) surface of GaAs. Crosssectional scanning tunneling microscopy images of the acceptor local density of states (LDOS) show that the strongly anisotropic hole wavefunction is not significantly affected by a magnetic field up to 6 T. These experimental results are supported by theoretical calculations based on a tightbinding model...

  18. Raman scattering probe of ion-implanted and pulse laser annealed GaAs

    Science.gov (United States)

    Verma, Prabhat; Jain, K. P.; Abbi, S. C.

    1996-04-01

    We report Raman scattering studies of phosphorus-ion-implanted and subsequently pulse laser annealed (PLA) GaAs. The threshold value of implantation fluence for the disappearance of one-phonon modes in the Raman spectrum of ion-implanted GaAs sample is found to be greater than that for the two-phonon modes by an order of magnitude. The phonon correlation length decreases with increasing disorder. The lattice reconstruction process during PLA creates microcrystallites for incomplete annealing, whose sizes can be given by the phonon correlation lengths, and are found to increase with the annealing power density. The intensity ratio of the Raman spectra corresponding to the allowed longitudinal-optical (LO)-phonon mode to the forbidden transverse-optical (TO)-phonon mode, ILO/ITO, is used as a quantitative measure of crystallinity in the implantation and PLA processes. The threshold annealing power density is estimated to be 20 MW/cm2 for 70 keV phosphorus-ion-implanted GaAs at a fluence of 5×1015 ions/cm2. The localized vibrational mode of phosphorus is observed in PLA samples for fluences above 1×1015 ions/cm2.

  19. Photoluminescence of pulsed ruby laser annealed crystalline and ion implanted GaAs

    Science.gov (United States)

    Lowndes, D. H.; Feldman, B. J.

    1981-11-01

    In an effort to understand the origin of effects earlier found to be present in p-n junctions formed by pulsed laser annealing (PLA) of ion implanted semiconducting GaAs, photoluminescence (PL) studies were carried out. PL spectra have been obtained at 4K, 77K and 300K, for both n- and p-type GaAs, for laser energy densities 0 equal to or less than E/sub 1/ equal to or less than 0.6 J/sq cm. It is found that PLA of c-GaAs alters the PL spectrum and decreases the PL intensity, corresponding to an increase in density of non-radiative recombination centers with increasing E/sub 1/. The variation of PL intensity with E/sub 1/ is found to be different for n- and p-type material. No PL is observed from high dose (1 or 5 x 10 to the 15th power ions/sq cm) Si- or Zn- implanted GaAs, either before or after laser annealing. The results suggest that the ion implantation step is primarily responsible for formation of defects associated with the loss of radiative recombination, with pulsed annealing contributing only secondarily.

  20. Surface photovoltage spectroscopy of pulsed laser deposited undoped ZnSe/n{sup +}GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Ganguli, Tapas; Kumar, Shailendra; Kukreja, L.M.; Rustagi, K.C. [Laser Physics Division, Centre for Advanced Technology, Indore (India)

    2002-03-04

    We report surface photovoltage (SPV) spectra of ZnSe thin films deposited on n{sup +}GaAs substrates in the wavelength range of 400-800 nm. In the above bandgap region of ZnSe (below 450 nm), we find that the major contribution to SPV comes from trapping and re-emission from the slow states at the ZnSe surface and ZnSe/GaAs interface. The effect of interference of light on the SPV spectra, has been analysed for subbandgap wavelength excitation of ZnSe (470-800 nm). In spite of the presence of a large number of subbandgap states in ZnSe, the major contribution to SPV in this wavelength range comes from the substrate. The difference in the magnitudes of the SPV between the bare n{sup +}GaAs and the ZnSe/n+GaAs is due to the reduction of surface recombination velocity (SRV) of the minority carriers in n{sup +}GaAs. (author)

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

    Science.gov (United States)

    Meulenberg, Andrew

    1996-01-01

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

  2. Magnetic properties of ultra thin epitaxial Fe films on GaAs(001)

    Energy Technology Data Exchange (ETDEWEB)

    Morton, S A; Tobin, J G; Spangenberg, M; Neal, J R; Shen, T H; Waddill, G D; Matthew, J D; Greig, D; Malins, A R; Seddon, E A; Hopkinson, M

    2003-10-02

    The magnetic properties of epitaxial Fe films on GaAs in the range of the first few monolayers have been the subject of a considerable number of investigations in recent years. The absence of magnetic signatures at room temperature has been attributed to the existence of a magnetic ''dead'' layer as well as superparamagnetism. By examining the temperature dependence of the magnetic linear dichroism of the Fe core level photoelectrons, we found that these ''non-ferromagnetic'' layers had in fact a Curie temperature, T{sub c}, substantially lower than room temperature, e.g., a T{sub c} of about 240K for thin films of a nominal thickness of 0.9 nm. The values of Curie temperature were sensitive to the initial GaAs substrate conditions and the thickness of the Fe over-layer with a layer of thickness of 1.25 nm showing a T{sub c} above room temperature. The data suggest that the ultrathin Fe films on GaAs(001) are ferromagnetic, although a weaker exchange interaction in the films lead to a substantial reduction in Curie temperature.

  3. Temperature and 8 MeV electron irradiation effects on GaAs solar cells

    Indian Academy of Sciences (India)

    Asha Rao; Sheeja Krishnan; Ganesh Sajeev; K Siddappa

    2010-06-01

    GaAs solar cells hold the record for the highest single band-gap cell efficiency. Successful application of these cells in advanced space-borne systems demand characterization of cell properties like dark current under different ambient conditions and the stability of the cells against particle irradiation in space. In this paper, the results of the studies carried out on the effect of 8 MeV electron irradiation on the electrical properties of GaAs solar cells are presented. The – (current–voltage) characteristics of the cells under dark and AM1.5 illumination condition are studied and 8 MeV electron irradiation was carried out on the cells where they were exposed to graded doses of electrons from 1 to 100 kGy. The devices were also characterized using capacitance measurements at various frequencies before and after irradiation. The effect of electron irradiation on the solar cell parameters was studied. It is found that only small changes were observed in the GaAs solar cell parameters up to an electron dose of 100 kGy, exhibiting good tolerance for electrons of 8 MeV energy.

  4. Epitaxial lift-off technology of GaAs multijunction solar cells

    Science.gov (United States)

    Knyps, P.; Dumiszewska, E.; Kaszub, W.; Przewłoka, A.; Strupinski, W.

    2016-12-01

    Epitaxial lift-off (ELO) is a process which enables the removal of solar cell structures (one junction GaAs, two junction GaAs/InGaP or three junction GaAs/InGaAs/InGaP) from the substrate on which they are grown and their transfer onto lightweight carriers such as metal or polymeric insulator films. The said solar cells exhibit superior power conversion efficiency compared with alternative single-junction photovoltaic cell designs such as those based on crystalline Si, copper indium gallium sulfide (CIGS) or CdTe. The major advantage of ELO solar cells is the potential for wafer reuse, which can enable significant manufacturing cost reduction by minimizing the consumption of expensive wafers. Here in this work we have grown one junction GaAs solar cells on GaAs (100) substrates. A 10 nm thick AlAs layer has been used as a release layer, which has been selectively etched in HF solution. We have investigated different methods of transferring thin films onto polymer and copper foils, including the usage of temporary mounting adhesives and electro-conductive pastes. Lift-off has been demonstrated to be a very promising technique for producing affordable solar cells with a very high efficiency of up to 30%.

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

    Directory of Open Access Journals (Sweden)

    Santiago Silvestre

    2015-04-01

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

  6. Accurate characterization and modeling of transmission lines for GaAs MMIC's

    Science.gov (United States)

    Finlay, Hugh J.; Jansen, Rolf H.; Jenkins, John A.; Eddison, Ian G.

    1988-06-01

    The authors discuss computer-aided design (CAD) tools together with high-accuracy microwave measurements to realize improved design data for GaAs monolithic microwave integrated circuits (MMICs). In particular, a combined theoretical and experimental approach to the generation of an accurate design database for transmission lines on GaAs MMICs is presented. The theoretical approach is based on an improved transmission-line theory which is part of the spectral-domain hybrid-mode computer program MCLINE. The benefit of this approach in the design of multidielectric-media transmission lines is described. The program was designed to include loss mechanisms in all dielectric layers and to include conductor and surface roughness loss contributions. As an example, using GaAs ring resonator techniques covering 2 to 24 GHz, accuracies in effective dielectric constant and loss of 1 percent and 15 percent respectively, are presented. By combining theoretical and experimental techniques, a generalized MMIC microstrip design database is outlined.

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

    DEFF Research Database (Denmark)

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

    2017-01-01

    GaAs was central to the development of quantum devices but is rarely used for nanowire-based quantum devices with InAs, InSb and SiGe instead taking the leading role. p-type GaAs nanowires offer a path to studying strongly confined 0D and 1D hole systems with strong spin–orbit effects, motivating...... our development of nanowire transistors featuring Be-doped p-type GaAs nanowires, AuBe alloy contacts and patterned local gate electrodes towards making nanowire-based quantum hole devices. We report on nanowire transistors with traditional substrate back-gates and EBL-defined metal/oxide top......}^{4}$, and sub-threshold slope 50 mV/dec at $T=4$ K. Lastly, we made a device featuring a moderately doped nanowire with annealed contacts and multiple top-gates. Top-gate sweeps show a plateau in the sub-threshold region that is reproducible in separate cool-downs and indicative of possible conductance...

  8. On magnetism and the insulator-to-metal transition in p-doped GaAs

    Science.gov (United States)

    Chapler, Brian; Myers, R. C.; Mack, S.; Frenzel, A.; Pursley, B. C.; Burch, K. S.; Singley, E. J.; Dattelbaum, A. M.; Samarth, N.; Awschalom, D. D.; Basov, D. N.

    2011-03-01

    Although Ga 1-x Mn x As is often described as the prototypical ferromagnetic semiconductor, many aspects of the electronic structure and nature of mediating carriers remain open. A central question in this regard is whether the insulator-to-metal transition (IMT) in p -doped GaAs is significantly modified when dopants are magnetic. We address this through an infrared spectroscopic study of GaAs doped with either non-magnetic Be or magnetic Mn acceptors. Through our comparison, we are able to isolate effects of magnetic dopants in GaAs from those associated with disorder and proximity to the IMT. Here we show Mn-doped samples exhibit an unusual electronic transport regime, combining elements of both metallic and insulating behavior, at doping concentrations far beyond the onset of the IMT. Be-doped films however, reveal genuine metallicity just above the IMT boundary. These results underscore the pivotal role of magnetism in transport and optical phenomena of Ga 1-x Mn x As.

  9. Interface dynamics and crystal phase switching in GaAs nanowires

    Science.gov (United States)

    Jacobsson, Daniel; Panciera, Federico; Tersoff, Jerry; Reuter, Mark C.; Lehmann, Sebastian; Hofmann, Stephan; Dick, Kimberly A.; Ross, Frances M.

    2016-03-01

    Controlled formation of non-equilibrium crystal structures is one of the most important challenges in crystal growth. Catalytically grown nanowires are ideal systems for studying the fundamental physics of phase selection, and could lead to new electronic applications based on the engineering of crystal phases. Here we image gallium arsenide (GaAs) nanowires during growth as they switch between phases as a result of varying growth conditions. We find clear differences between the growth dynamics of the phases, including differences in interface morphology, step flow and catalyst geometry. We explain these differences, and the phase selection, using a model that relates the catalyst volume, the contact angle at the trijunction (the point at which solid, liquid and vapour meet) and the nucleation site of each new layer of GaAs. This model allows us to predict the conditions under which each phase should be observed, and use these predictions to design GaAs heterostructures. These results could apply to phase selection in other nanowire systems.

  10. Temperature dependence of the optical properties of high-density GaAs quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Ryan P.; Kim, Jongsu [Yeungnam University, Gyeongsan (Korea, Republic of); Lee, Sangjun; Noh, Samkyu [Korea Research Institute of Standards and Science, Daejeon (Korea, Republic of); Kim, Jinsoo [Chonbuk National University, Jeonju (Korea, Republic of); Leem, Jaeyoung [Inje University, Gimhae (Korea, Republic of); Song, Jindong [Korea Institute of Science and Technology, Seoul (Korea, Republic of)

    2012-05-15

    We investigate the effect of the quantum dot (QD) density on the thermal escape and the retrapping processes of carriers for unstrained GaAs/AlGaAs QDs through temperature-dependent photoluminescence measurements. We fabricated high-density GaAs QDs (8.4 x 10{sup 10}/cm{sup 2}, dot-dot distance ∼34 nm) on an Al{sub 0.3}Ga{sub 0.7}As/GaAs (111)A surface by using droplet epitaxy. The average lateral size and height of the GaAs QDs are 24 and 6 nm, respectively. Temperature-dependent photoluminescence (PL) studies show that high-density GaAs QDs undergo a sigmoidal-shape energy shift. The sigmoidal dependence of the PL peak energy can be explained by thermal escaping of carriers followed by re-trapping by QDs. Our analysis indicates that the re-trapping probability of thermally-escaped carriers increases with decreasing dot-to-dot distance (corresponding to an increase in the QD density).

  11. Intense electron beams from GaAs photocathodes as a tool for molecular and atomic physics

    Energy Technology Data Exchange (ETDEWEB)

    Krantz, Claude

    2009-10-28

    We present cesium-coated GaAs photocathodes as reliable sources of intense, quasi-monoenergetic electron beams in atomic and molecular physics experiments. In long-time operation of the Electron Target of the ion storage ring TSR in Heidelberg, cold electron beams could be realised at steadily improving intensity and reliability. Minimisation of processes degrading the quantum efficiency allowed to increase the extractable current to more than 1mA at usable cathode lifetimes of 24 h or more. The benefits of the cold electron beam with respect to its application to electron cooling and electron-ion recombination experiments are discussed. Benchmark experiments demonstrate the superior cooling force and energy resolution of the photoelectron beam compared to its thermionic counterparts. The long period of operation allowed to study the long-time behaviour of the GaAs samples during multiple usage cycles at the Electron Target and repeated in-vacuum surface cleaning by atomic hydrogen exposure. An electron emission spectroscopy setup has been implemented at the photocathode preparation chamber of the Electron Target. Among others, this new facility opened the way to a novel application of GaAs (Cs) photocathodes as robust, ultraviolet-driven electron emitters. Based on this principle, a prototype of an electron gun, designed for implementation at the HITRAP setup at GSI, has been built and taken into operation successfully. (orig.)

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

    Science.gov (United States)

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

    2014-06-11

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

  13. Periodic Two-Dimensional GaAs and InGaAs Quantum Rings Grown on GaAs (001) by Droplet Epitaxy.

    Science.gov (United States)

    Tung, Kar Hoo Patrick; Huang, Jian; Danner, Aaron

    2016-06-01

    Growth of ordered GaAs and InGaAs quantum rings (QRs) in a patterned SiO2 nanohole template by molecular beam epitaxy (MBE) using droplet epitaxy (DE) process is demonstrated. DE is an MBE growth technique used to fabricate quantum nanostructures of high crystal quality by supplying group III and group V elements in separate phases. In this work, ordered QRs grown on an ordered nanohole template are compared to self-assembled QRs grown with the same DE technique without the nanohole template. This study allows us to understand and compare the surface kinetics of Ga and InGa droplets when a template is present. It is found that template-grown GaAs QRs form clustered rings which can be attributed to low mobility of Ga droplets resulting in multiple nucleation sites for QR formation when As is supplied. However, the case of template-grown InGaAs QRs only one ring is formed per nanohole; no clustering is observed. The outer QR diameter is a close match to the nanohole template diameter. This can be attributed to more mobile InGa droplets, which coalesce from an Ostwald ripening to form a single large droplet before As is supplied. Thus, well-patterned InGaAs QRs are demonstrated and the kinetics of their growth are better understood which could potentially lead to improvements in the future devices that require the unique properties of patterned QRs.

  14. Radiation damage by high-energy electrons in GaAs: DLTS investigation; Strahlenschaedigung durch Hochenergieelektronen in GaAs: Eine DLTS-Untersuchung

    Energy Technology Data Exchange (ETDEWEB)

    Lehmann, B.

    1991-10-01

    An isothermal variation of the DLTS technique is developed and applied to the study of displacement damage in GaAs, through the determination of threshold energies and displacement cross sections. Its results correspond to those of an LED based method. A pronounced anisotropy is found for the threshold energy. A linearly increasing displacement probability function is shown to properly model the displacement cross section in <100> direction, as compared with the <111> direction which requires only a single step function. Differences in the damage between these two directions are as large as a factor of two. (orig.). [Deutsch] Die Schwellenergie und der Wirkungsquerschnitt, als zentrale Groessen in der Beschreibung von Versetzungsschaeden, konnten fuer GaAs ermittelt werden. Als Messmethode wurde dazu eine isothermische Variante der DLTS entwickelt. Deren Ergebnisse befinden sich im Einklang mit solchen eines lebensdauerempfindlichen Messverfahrens. Fuer die Schwellenergie resultiert eine ausgepraegte Anisotropie; der Wirkungsquerschnitt wird fuer die <100> Orientierung mit einer linear ansteigenden und dann saettigenden Wahrscheinlichkeitsfunktion beschrieben, welche die Versetzungsschaedigung, gegenueber der stufenfoermigen Schwelle in <111> Richtung, um gut die Haelfte reduziert. (orig.).

  15. High-resolution X-ray diffraction characterisation of piezoelectric InGaAs / GaAs multiquantum wells and superlattices on (111)B GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Sanz-Hervas, A.; Aguilar, M. [Madrid, Univ. (Spain). Dept. Tecnologia Electronica. E.T.S.I. Telecomunicacion; Lopez, M.; Llorente, C.; Lorenzo, R.; Abril, E. J. [Valladolid, Real de Burgos Univ. (Spain). Dept. Teoria de la Senal u Comunicaciones e Ingegneria Telematica. E.T.S.I. Telecomunicacion; Sacedon, A.; Sanchez, J. L.; Calleja, E.; Munoz, E. [Madrid, Univ. (Spain). Dept. Ingegnieria Electronica. E.T.S.I. Telecomunicacion

    1997-02-01

    In this paper the authors show some examples of strained InGaAs / GaAs multilayers on (111)B GaAs substrates studied by high-resolution X-ray diffractometry. The samples consisted of a multiquantum well or superlattice embedded in the intrinsic region of a p-i-n photodiode. They have analysed piezoelectric (111)B structures with 3, 7, 10, and 40 periods and different indium contents and compared the results with identical structures simultaneously grown on (001) substrates. The interpretation of the diffraction profiles has been carried out with a computer simulation model developed in our labs, which allows the calculation of symmetric and asymmetric reflections regardless of the substrate orientation or miscut angle. The agreement between the experimental scans and the theory was very satisfactory in all the samples, which has enabled us to determine the main structural parameters of the diodes, Asymmetric 224{+-} reflections on (111)B structures have been simulated for the first time. They have also compared the structural parameters obtained by high-resolution X-ray diffractometry with the results deduced from photoluminescence and photocurrent spectroscopies.

  16. New Gate Dielectric Oxides for GaAs and Other Semiconductors*

    Science.gov (United States)

    Hong, M.

    2000-03-01

    It is well known that electrons move much faster in GaAs than in Si, and this attribute makes the GaAs-based metal oxide semiconductor field effect transistors (MOSFETs) very attractive for high-frequency, high-speed circuits applications. However, identifying a proper insulating oxide for GaAs has been a problem puzzling researchers over 35 years. Recently we discovered that the use of a mixed oxide dielectric Ga_2O_3(Gd_2O_3)^1 formed inversion and accumulation channels on GaAs surfaces, with a low interfacial density of states (D_it) of mid-10^10 cm-2eV-1. Subsequently, we have demonstrated the p- and n- inversion channel MOSFETs^2 and CMOS circuits^3. All oxides in this work were prepared by ultrahigh vacuum deposition from e-beam sources. The initial growth ( 10 Åof Ga_2O_3(Gd_2O_3) film on GaAs takes place from nucleating a thin epitaxial layer of pure Gd_2O_3. In fact, mono-domain, single crystalline Gd_2O3 films (ɛ =12) can be grown on GaAs (100) surface in the (110) Mn_2O3 structure, and that show leakage currents as low as 10-4 A/cm^2 at 10 MV/cm for a film only 25 Åthick^4. We have extended our studies to other rare earth oxides and other semiconductors. For example, low-D_it GaN MOS diodes and GaN MOSFETs operated at 400^circC were obtained. The GaN MOSFET has potential applications in high power switching and high temperature device operation. More remarkably, we have found recently that another rare earth oxide, Y_2O3 (ɛ = 18) showed excellent electrical properties as a gate dielectric for Si, to replace the current SiO_2, where the thickness is now approaching the quantum limit^5. *In collaboration with J. Kwo, A. R. Kortan, J. N. Baillargeon, J. P. Mannaerts, F. Ren, Y. C. Wang, T. S. Lay, H. Ng, R. Opila, K. L. Queeney, Y. J. Chabal, T. Boone, J. J. Krajewski, A. M. Sergent, J. M. Rosamilia, M. Passlack, D. W. Murphy, and A. Y. Cho. 1. M. Hong, et al, J. Vac. Sci. Technol. B14, 2297, (1996). 2. F. Ren et al, IEDM Technical Digest, p.943, (1996

  17. Structural and morphological TEM characterization of GaAs based nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Soda, Marcello

    2012-02-03

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

  18. Chemical beam epitaxy of GaAs1-xNx using MMHy and DMHy precursors, modeled by ab initio study of GaAs(100) surfaces stability over As2, H2 and N2

    Science.gov (United States)

    Valencia, Hubert; Kangawa, Yoshihiro; Kakimoto, Koichi

    2017-06-01

    Using ab initio calculations, a simple model for GaAs1-xNx vapor-phase epitaxy on (100) surface of GaAs was created. By studying As2 and H2 molecules adsorptions and As/N atom substitutions on (100) GaAs surfaces, we obtain a relative stability diagram of all stable surfaces under varying As2, H2, and N2 conditions. We previously proved that this model could describe the vapor-phase epitaxy of GaAs1-x Nx with simple, fully decomposed, precursors. In this paper, we show that in more complex reaction conditions using monomethylhydrazine (MMHy), and dimethylhydrazine (DMHy), it is still possible to use our model to obtain an accurate description of the temperature and pressure stability domains for each surfaces, linked to chemical beam epitaxy (CBE) growth conditions. Moreover, the different N-incorporation regimes observed experimentally at different temperature can be explain and predict by our model. The use of MMHy and DMHy precursors can also be rationalized. Our model should then help to better understand the conditions needed to obtain an high quality GaAs1-xNx using vapor-phase epitaxy.

  19. High Quality GaAs Growth by MBE on Si Using GeSi Buffers and Prospects for Space Photovoltaics

    Science.gov (United States)

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

    2005-01-01

    III-V solar cells on Si substrates are of interest for space photovoltaics since this would combine high performance space cells with a strong, lightweight and inexpensive substrate. However, the primary obstacles blocking III-V/Si cells from achieving high performance to date have been fundamental materials incompatabilities, namely the 4% lattice mismatch between GaAs and Si, and the large mismatch in thermal expansion coefficient. In this paper, we report on the molecular beam epitaxial (MBE) growth and properties of GaAs layers and single junction GaAs cells on Si wafers which utilize compositionally graded GeSi Intermediate buffers grown by ultra-high vacuum chemical vapor deposition (UHVCVD) to mitigate the large lattice mismatch between GaAs and Si. Ga As cell structures were found to incorporate a threading dislocation density of 0.9-1.5 x 10 (exp 6) per square centimeter, identical to the underlying relaxed Ge cap of the graded buffer, via a combination of transmission electron microscopy, electron beam induced current, and etch pit density measurements. AlGaAs/GaAs double heterostructures wre grown on the GeSi/Si substrates for time-resolved photoluminescence measurements, which revealed a bulk GaAs minority carrier lifetime in excess of 10 ns, the highest lifetime ever reported for GaAs on Si. A series of growth were performed to ass3ss the impact of a GaAs buffer to a thickness of only 0.1 micrometer. Secondary ion mass spectroscopy studies revealed that there is negligible cross diffusion of Ga, As and Ge at he III-V/Ge interface, identical to our earlier findings for GaAs grown on Ge wafers using MBE. This indicates that there is no need for a buffer to "bury" regions of high autodopjing,a nd that either pn or np configuration cells are easily accomodated by these substrates. Preliminary diodes and single junction Al Ga As heteroface cells were grown and fabricated on the Ge/GeSi/Si substrates for the first time. Diodes fabricated on GaAs, Ge and Ge

  20. Single-Crystal Y2O3 Epitaxially on GaAs(001 and (111 Using Atomic Layer Deposition

    Directory of Open Access Journals (Sweden)

    Y. H. Lin

    2015-10-01

    Full Text Available Single-crystal atomic-layer-deposited (ALD Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\ films 2 nm thick were epitaxially grown on molecular beam epitaxy (MBE GaAs(001-4 \\(\\times\\ 6 and GaAs(111A-2 \\(\\times\\ 2 reconstructed surfaces. The in-plane epitaxy between the ALD-oxide films and GaAs was observed using \\textit{in-situ} reflection high-energy electron diffraction in our uniquely designed MBE/ALD multi-chamber system. More detailed studies on the crystallography of the hetero-structures were carried out using high-resolution synchrotron radiation X-ray diffraction. When deposited on GaAs(001, the Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\ films are of a cubic phase and have (110 as the film normal, with the orientation relationship being determined: Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\(\\(110\\[\\(001\\][\\(\\overline{1}10\\]//GaAs(\\(001\\[\\(110\\][\\(1\\overline{1}0\\]. On GaAs(\\(111\\A, the Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\ films are also of a cubic phase with (\\(111\\ as the film normal, having the orientation relationship of Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\(\\(111\\[\\(2\\overline{1}\\overline{1}\\] [\\(01\\overline{1}\\]//GaAs (\\(111\\ [\\(\\overline{2}11\\][\\(0\\overline{1}1\\]. The relevant orientation for the present/future integrated circuit platform is (\\(001\\. The ALD-Y\\(_{\\mathrm{2}}\\O\\(_{\\mathrm{3}}\\/GaAs(\\(001\\-4 \\(\\times\\ 6 has shown excellent electrical properties. These include small frequency dispersion in the capacitance-voltage CV curves at accumulation of ~7% and ~14% for the respective p- and n-type samples with the measured frequencies of 1 MHz to 100 Hz. The interfacial trap density (Dit is low of ~10\\(^{12}\\ cm\\(^{−2}\\eV\\(^{−1}\\ as extracted from measured quasi-static CVs. The frequency dispersion at accumulation and the D\\(_{it}\\ are the lowest ever achieved among all the ALD-oxides on GaAs(\\(001\\.

  1. 基于格雷厄姆风险评价方法的外来植物风险评价体系研究%Study on the risk assessment system in introducing exotic plants based on LEC method

    Institute of Scientific and Technical Information of China (English)

    申敬民; 邓伦秀; 杨成华

    2015-01-01

    the building of the exotic plants assessment system and employment of this system to con-duct the risk assessment is very important in avoidance of invasion of exotic plants before their intro-duction. In this paper,we used the LEC method to evaluate the exotic plants in 3 aspects such as in-vasion risk possibility,frequency and consequence,and also we defined the criteria to score the per-formance of the exotic plants and calculate the risk value,which were then divided into different risk level . According to the evaluation results of 34 species of exotic Asteraceae ,the risk assessment sys-tem was found reasonable in selecting indicators,easy for practice and reliable in result,and could be used as a basis of managing the introduction of exotic plants.%通过建立外来植物评价体系,在有意引入外来植物前进行风险评估,对控制外来植物入侵风险有着重大意义.本文以格雷厄姆风险评价方法(LEC法)为研究方法,从发生风险的可能性、频率及后果三方面对外来植物进行评价,并制定相应的评分标准,根据外来植物的实际表现得出相应分值,以乘积方式计算出植物的风险值,并按照评估结果将外来入侵植物划分为不同风险等级,提出相应的管理策略.通过对34种菊科外来植物的评价结果,说明外来植物风险评价体系指标合理,操作简练,结论正确,可以作为管理部门引进外来植物的重要依据.

  2. Theoretical and experimental study of highly textured GaAs on silicon using a graphene buffer layer

    Science.gov (United States)

    Alaskar, Yazeed; Arafin, Shamsul; Lin, Qiyin; Wickramaratne, Darshana; McKay, Jeff; Norman, Andrew G.; Zhang, Zhi; Yao, Luchi; Ding, Feng; Zou, Jin; Goorsky, Mark S.; Lake, Roger K.; Zurbuchen, Mark A.; Wang, Kang L.

    2015-09-01

    A novel heteroepitaxial growth technique, quasi-van der Waals epitaxy, promises the ability to deposit three-dimensional GaAs materials on silicon using two-dimensional graphene as a buffer layer by overcoming the lattice and thermal expansion mismatch. In this study, density functional theory (DFT) simulations were performed to understand the interactions at the GaAs/graphene hetero-interface as well as the growth orientations of GaAs on graphene. To develop a better understanding of the molecular beam epitaxy-grown GaAs films on graphene, samples were characterized by x-ray diffraction (θ-2θ scan, ω-scan, grazing incidence XRD and pole figure measurement) and transmission electron microscopy. The realizations of smooth GaAs films with a strong (111) oriented fiber-texture on graphene/silicon using this deposition technique are a milestone towards an eventual demonstration of the epitaxial growth of GaAs on silicon, which is necessary for integrated photonics application.

  3. ZnSe Window Layers for GaAs and GaInP2 Solar Cells

    Science.gov (United States)

    Olsen, Larry C.

    1997-01-01

    This report concerns studies of the use of n-type ZnSe as a window layer for n/p GaAs and GaInP2 solar cells. Emphasis was placed in this phase of the project on characterizing the interface between n-type ZnSe films grown on epi-GaAs films grown onto single crystal GaAs. Epi-GaAs and heteroepitaxial ZnSe films were grown by MOCVD with a Spire 50OXT Reactor. After growing epitaxial GaAs films on single crystal GaAs wafers, well-oriented crystalline ZnSe films were grown by MOCVD. ZnSe films were grown with substrate temperatures ranging from 250 C to 450 C. Photoluminescence studies carried out by researchers at NASA Lewis determined that the surface recombination velocity at a GaAs surface was significantly reduced after the deposition of a heteroepitaxial layer of ZnSe. The optimum temperature for ZnSe deposition appears to be on the order of 350 C.

  4. Optical anisotropy in self-assembled InAs nanostructures grown on GaAs high index substrate.

    Science.gov (United States)

    Bennour, M; Saidi, F; Bouzaïene, L; Sfaxi, L; Maaref, H

    2012-01-15

    We present a study of the optical properties of InAs self-assembled nanostructures grown by molecular beam epitaxy on GaAs(11N)A substrates (N = 3-5). Photoluminescence (PL) measurements revealed good optical properties of InAs quantum dots (QDs) grown on GaAs(115)A compared to those grown on GaAs(113)A and (114)A orientations substrate. An additional peak localized at 1.39 eV has been shown on PL spectra of both GaAs(114)A and (113)A samples. This peak persists even at lower power density. Supporting on the polarized photoluminescence characterization, we have attributed this additional peak to the quantum strings (QSTs) emission. A theoretical study based on the resolution of the three dimensional Schrödinger equation, using the finite element method, including strain and piezoelectric-field effect was adopted to distinguish the observed photoluminescence emission peaks. The mechanism of QDs and QSTs formation on such a high index GaAs substrates was explained in terms of piezoelectric driven atoms and the equilibrium surfaces at edges.

  5. GaAs microcrystals selectively grown on silicon: Intrinsic carbon doping during chemical beam epitaxy with trimethylgallium

    Science.gov (United States)

    Molière, T.; Jaffré, A.; Alvarez, J.; Mencaraglia, D.; Connolly, J. P.; Vincent, L.; Hallais, G.; Mangelinck, D.; Descoins, M.; Bouchier, D.; Renard, C.

    2017-01-01

    The monolithic integration of III-V semiconductors on silicon and particularly of GaAs has aroused great interest since the 1980s. Potential applications are legion, ranging from photovoltaics to high mobility channel transistors. By using a novel integration method, we have shown that it is possible to achieve heteroepitaxial integration of GaAs crystals (typical size 1 μ m) on silicon without any structural defect such as antiphase domains, dislocations, or stress, usually reported for direct GaAs heteroepitaxy on silicon. However, concerning their electronic properties, conventional free carrier characterization methods are impractical due to the micrometric size of GaAs crystals. In order to evaluate the GaAs material quality for optoelectronic applications, a series of indirect analyses such as atom probe tomography, Raman spectroscopy, and micro-photoluminescence as a function of temperature were performed. These revealed a high content of partially electrically active carbon originating from the trimethylgallium used as the Ga precursor. Nevertheless, the very good homogeneity observed by this doping mechanism and the attractive properties of carbon as a dopant once controlled to a sufficient degree are a promising route to device doping.

  6. 1.3 m m InGaAsN/ GaAs Lasers Grown by MOCVD Using TBAs and DMHy Sources

    Institute of Scientific and Technical Information of China (English)

    Gray Lin; C. M. Lu; C. H. Chiou; I. F. Chen; T. D. Lee; J. Y. Chi; D.A. Livshits

    2003-01-01

    We have demonstrated InGaAsN/ GaAs single quantum well (SQW) lasers grown by MOCVD using TBAs and DMHy sources. For un-buffer-strained InGaAsN/ GaAs system, our SQW lasers of 1.3 m m range is among the best in terms of transparency and threshold current density.

  7. GaAs PIN二极管的新等效电路模型%A Novel Equivalent Circuit Model of GaAs PIN Diodes

    Institute of Scientific and Technical Information of China (English)

    吴茹菲; 张海英; 尹军舰; 李潇; 刘会东; 刘训春

    2008-01-01

    A novel equivalent circuit model for a GaAs PIN diode is presented based on physical analysis. The diode is divided into three parts., the p+ n- junction, the I-layer, and the n- n+ junction, which are modeled separately. The entire model is then formed by combining the three sub-models. In this way, the model's accuracy is greatly enhanced. Furthermore, the corresponding parameter extraction method is easy, requiring no rigorous experiment or measurement. To validate this newly proposed model, fifteen groups of diodes are fabricated. Measurement shows that the model exactly represents behavior of GaAs PIN diodes under both forward and reversely biased conditions.%基于物理原理的分析,提出了GaAs PIN二极管的一种新等效电路模型.GaAs PIN二极管被分成P+n-结、基区和n-n+结三部分分别建模,总的模型由三个子模型组成,从而极大地提高了模型的准确性.相应的模型参数提取过程不要求苛刻的实验或测试条件,简便易操作.研制了15组GaAs PIN二极管来验证模型,测试结果表明模型准确地反映了GaAs PIN二极管的正向和反向特性.

  8. Impact of thermal annealing on nonequilibrium carrier dynamics in single-crystal, freestanding GaAs mesostructures

    Science.gov (United States)

    Mikulics, M.; Hardtdegen, H.; Adam, R.; Grützmacher, D.; Gregušová, D.; Novák, J.; Kordoš, P.; Sofer, Z.; Serafini, J.; Zhang, J.; Sobolewski, Roman; Marso, M.

    2014-04-01

    We report on the impact of thermal annealing to carrier transport and transient, subpicosecond photoresponse of freestanding GaAs mesostructures. Our measurements included micro-photoluminescence and dark current and responsivity studies as well as optical femtosecond characterization. The fabricated GaAs mesostructures consisted of both mesowires and platelets that were integrated into coplanar striplines to form a photoconductive switch. We demonstrate that an optimized annealing process of our mesostructures, performed at 600 °C for 20 min, led to restoring bulklike properties of our freestanding devices. They exhibited dark currents below 600 pA at 10 V bias, responsivity of 0.2 A W-1 at 30 V, and mobility as high as 7300 cm2 V s-1. The annealed freestanding GaAs photodetectors were characterized by subpicosecond carrier relaxation dynamics with negligible trapping and a cutoff frequency of 1.3 THz. The latter characteristics make them excellent candidates for THz-bandwidth optoelectronics.

  9. High-performance GaAs metal-insulator-semiconductor field-effect transistors enabled by self-assembled nanodielectrics

    Science.gov (United States)

    Lin, H. C.; Ye, P. D.; Xuan, Y.; Lu, G.; Facchetti, A.; Marks, T. J.

    2006-10-01

    High-performance GaAs metal-insulator-semiconductor field-effect-transistors (MISFETs) fabricated with very thin self-assembled organic nanodielectrics (SANDs), deposited from solution at room temperature, are demonstrated. A submicron gate-length depletion-mode n-channel GaAs MISFET with SAND thicknesses ranging from 5.5to16.5nm exhibit a gate leakage current density <10-5A/cm2 at a gate bias smaller than 3V, a maximum drain current of 370mA/mm at a forward gate bias of 2V, and a maximum intrinsic transconductance of 170mS/mm. The importance of appropriate GaAs surface chemistry treatments on SAND/GaAs interface properties is also presented. Application of SANDs to III-V compound semiconductors affords more opportunities to manipulate the complex III-V surface chemistry with broad materials options.

  10. Energetics of island formation of AlAs, GaAs, and InAs on Si(100)

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Geunjung; Efimov, Oleg; Yoon, Younggui [Chung-Ang University, Seoul (Korea, Republic of)

    2012-03-15

    We study the energetics of island formation of AlAs, GaAs, and InAs on Si(100)2x1 substrates from first-principles. Si(100)2x1:As is stable under As-rich conditions in all cases. Si(100)2x1:(AlAs) and Si(100)2x1:(GaAs) are stable under Al-rich and Ga-rich conditions, respectively. However, the surface energy of Si(100)2x1:InAs is higher than that of Si(100)2x1:As under In-rich conditions. The energies of thicker epitaxial overlayer films of AlAs, GaAs, and InAs are predicted to be higher than the corresponding energies of these monolayer films.

  11. Fabrication of GaAs symmetric pyramidal mesas prepared by wet-chemical etching using AlAs interlayer

    Science.gov (United States)

    Kicin, S.; Cambel, V.; Kuliffayová, M.; Gregušová, D.; Kováčová, E.; Novák, J.; Kostič, I.; Förster, A.

    2002-01-01

    We present a wet-chemical-etching method developed for the preparation of GaAs four-sided pyramid-shaped mesas. The method uses a fast lateral etching of AlAs interlayer that influences the cross-sectional profiles of etched structures. We have tested the method using H3PO4:H2O2:H2O etchant for the (100) GaAs patterning. The sidewalls of the prepared pyramidal structures together with the (100) bottom facet formed the cross-sectional angles 25° and 42° for mask edges parallel, resp. perpendicular to {011} cleavage planes. For mask edges turned in 45° according to the cleavage planes, 42° cross-sectional angles were obtained. Using the method, symmetric and more than 10-μm-high GaAs "Egyptian" pyramids with smooth tilted facets were prepared.

  12. Strain-induced high ferromagnetic transition temperature of MnAs epilayer grown on GaAs (110

    Directory of Open Access Journals (Sweden)

    Pan Guoqiang

    2011-01-01

    Full Text Available Abstract MnAs films are grown on GaAs surfaces by molecular beam epitaxy. Specular and grazing incidence X-ray diffractions are used to study the influence of different strain states of MnAs/GaAs (110 and MnAs/GaAs (001 on the first-order magnetostructural phase transition. It comes out that the first-order magnetostructural phase transition temperature T t, at which the remnant magnetization becomes zero, is strongly affected by the strain constraint from different oriented GaAs substrates. Our results show an elevated T t of 350 K for MnAs films grown on GaAs (110 surface, which is attributed to the effect of strain constraint from different directions. PACS: 68.35.Rh, 61.50.Ks, 81.15.Hi, 07.85.Qe

  13. High-performance K-band GaAs power field-effect transistors prepared by molecular beam epitaxy

    Science.gov (United States)

    Saunier, P.; Shih, H. D.

    1983-01-01

    The maturity of the molecular beam epitaxy (MBE) technique for preparing device quality GaAs material for microwave applications is demonstrated by the excellent performance characteristics of K-band GaAs power field-effect transistors (FETs) fabricated on the MBE wafers. An output power of 710 mW with 4.5-dB gain and 17.7 percent power-added efficiency was achieved at 21 GHz with a 1.26-mm gate width pi-gate device. A similar device with a 0.56-mm gate width produced an output power of 320 mW with 5.0-dB gain and 26.6 percent power-added efficiency at 21 GHz. These are the best results yet reported to date for GaAs power FETs operated in the K-band frequency range.

  14. Focusing effect of bent GaAs crystals for gamma-ray Laue lenses: Monte Carlo and experimental results

    CERN Document Server

    Virgilli, E; Rosati, P; Bonnini, E; Buffagni, E; Ferrari, C; Stephen, J B; Caroli, E; Auricchio, N; Basili, A; Silvestri, S

    2015-01-01

    We report on results of observation of the focusing effect from the planes (220) of Gallium Arsenide (GaAs) crystals. We have compared the experimental results with the simulations of the focusing capability of GaAs tiles through a developed Monte Carlo. The GaAs tiles were bent using a lapping process developed at the cnr/imem - Parma (Italy) in the framework of the laue project, funded by ASI, dedicated to build a broad band Laue lens prototype for astrophysical applications in the hard X-/soft gamma-ray energy range (80-600 keV). We present and discuss the results obtained from their characterization, mainly in terms of focusing capability. Bent crystals will significantly increase the signal to noise ratio of a telescope based on a Laue lens, consequently leading to an unprecedented enhancement of sensitivity with respect to the present non focusing instrumentation.

  15. Collinear phase-matching study of terahertz-wave generation via difference frequency mixed in GaAs and Inp

    Institute of Scientific and Technical Information of China (English)

    HUANG Lei; SUN Bo; YAO Jian-quan; WANG Peng

    2008-01-01

    The collinearly phase-matching condition of terahertz-wave generation via difference frequency mixed in GaAs and InP is theoretically studied.In collinear phase-matching,the optimum phase-matching wave bands of these two crystals are calculated.The optimum phase-matching wave bands in GaAs and InP are 0.95~1.38 μm and 0.7~0.96 μm respectively.The influence of the wavelength choice of the pump wave on the coherent length in THz-wave tuning is also discussed.The influence of the temperature alteration on the phase-matching and the temperature tuning properties in GaAs crystal are calculated and analyzed.It can serve for the following experiments as a theoretical evidence and a reference aswell.

  16. Persistent photoconductivity in uniforndy and selectively silicon doped AlAs / GaAs short period superlattices

    Science.gov (United States)

    Jeanjean, P.; Sicart, J.; Robert, J. L.; Mollot, F.; Planel, R.

    1991-04-01

    Hall and photo-Hall measurements have been carried out between 4 K et 400 K on MBE deposited AlAs / GaAs superiattices (SPS) with short period (25 Å dopage uniforme, alors que les SPS dopées sélectivement dans GaAs ne présentent qu'une seule barrière (un seul plateau). Ainsi la microstructure GaAs / AlAs apparaît être un outil particulièrement intéressant pour confirmer la validité du modèle multibarrière proposé récemment pour le centre DX dans AlxGal{1-x} As: Si.

  17. Growth of GaAs from a free surface melt under controlled arsenic pressure in a partially confined configuration

    Science.gov (United States)

    Gatos, H. C.; Lagowski, J.; Wu, Y.

    1988-01-01

    A partially confined configuration for the growth of GaAs from melt in space was developed, consisting of a triangular prism containing the seed crystal and source material in the form of a rod. It is suggested that the configuration overcomes two obstacles in the growth of GaAs in space: total confinement in a quartz crucible and lack of arsenic pressure control. Ground tests of the configuration show that it is capable of crystal growth in space and is useful for studying the growth of GaAs from a free-surface melt on earth. The resulting chemical composition, electrical property variations, and phenomenological models to account for the results are presented.

  18. Increased Photoconductivity Lifetime in GaAs Nanowires by Controlled n-Type and p-Type Doping.

    Science.gov (United States)

    Boland, Jessica L; Casadei, Alberto; Tütüncüoglu, Gözde; Matteini, Federico; Davies, Christopher L; Jabeen, Fauzia; Joyce, Hannah J; Herz, Laura M; Fontcuberta I Morral, Anna; Johnston, Michael B

    2016-04-26

    Controlled doping of GaAs nanowires is crucial for the development of nanowire-based electronic and optoelectronic devices. Here, we present a noncontact method based on time-resolved terahertz photoconductivity for assessing n- and p-type doping efficiency in nanowires. Using this technique, we measure extrinsic electron and hole concentrations in excess of 10(18) cm(-3) for GaAs nanowires with n-type and p-type doped shells. Furthermore, we show that controlled doping can significantly increase the photoconductivity lifetime of GaAs nanowires by over an order of magnitude: from 0.13 ns in undoped nanowires to 3.8 and 2.5 ns in n-doped and p-doped nanowires, respectively. Thus, controlled doping can be used to reduce the effects of parasitic surface recombination in optoelectronic nanowire devices, which is promising for nanowire devices, such as solar cells and nanowire lasers.

  19. High quality GaAs quantum nanostructures grown by droplet epitaxy on Ge and Ge-on-Si substrates

    Energy Technology Data Exchange (ETDEWEB)

    Bietti, Sergio; Sanguinetti, Stefano [Dipartimento di Scienza dei Materiali, Milano (Italy); L-NESS, Universitaedi Milano Bicocca, Milano (Italy); Cavigli, Lucia; Abbarchi, Marco; Vinattieri, Anna; Gurioli, Massimo [Dipartimento di Fisica, LENS, Firenze (Italy); CNISM, Universitaedi Firenze, Firenze (Italy); Fedorov, Alexey; Cecchi, Stefano; Isa, Fabio; Isella, Giovanni [CNISM, L-NESS, Como (Italy); Dipartimento di Fisica del Politecnico di Milano, Como (Italy)

    2012-02-15

    We report on the growth and optical characterization by macro and micro photoluminescence measurements of high optical quality GaAs quantum nanostructures grown by droplet epitaxy on Ge and Si substrates. The quantum nanostructures show optical performances comparable to those achievable with the most advanced realized on GaAs substrates. The adopted growth procedures show also the possibility to fabricate the active layer maintaining a low thermal budget compatible with back-end integration of the fabricated materials on integrated circuits. We demonstrate the possibility to embed GaAs nanostructured devices such as intersubband detectors and single quantum emitters on Si substrates. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Broadband control of emission wavelength of InAs/GaAs quantum dots by GaAs capping temperature

    Energy Technology Data Exchange (ETDEWEB)

    Kaizu, Toshiyuki, E-mail: kaizu@crystal.kobe-u.ac.jp [Center for Supports to Research and Education Activities, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501 (Japan); Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501 (Japan); Matsumura, Takuya; Kita, Takashi [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501 (Japan)

    2015-10-21

    We investigated the effects of the GaAs capping temperature on the morphological and photoluminescence (PL) properties of InAs quantum dots (QDs) on GaAs(001). The broadband tuning of the emission wavelength from 1.1 to 1.3 μm was achieved at room temperature by only adjusting the GaAs capping temperature. As the capping temperature was decreased, the QD shrinkage due to In desorption and In-Ga intermixing during the capping process was suppressed. This led to QDs with a high aspect ratio, and resultantly, the emission wavelength shifted toward the longer-wavelength side. In addition, the linearly polarized PL intensity elucidated anisotropic characteristics reflecting the shape anisotropy of the embedded QDs, in which a marked change in polarization anisotropy occurred at capping temperatures lower than 460 °C.