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Sample records for semiinsulating gaas irradiated

  1. Noise behaviour of semi-insulating GaAs particle detectors before and after proton irradiation

    CERN Document Server

    Biggeri, U; Lanzieri, C; Leroy, C; Nava, F; Vanni, P

    1999-01-01

    Charge signal and noise were studied in non-irradiated and irradiated Schottky barrier, circular pad detectors of 100 mu m thick made on semi-insulating gallium arsenide at Alenia S.p.A., as a function of the reverse bias (V/sub a/), the shaping time ( tau ) and the fluence (f), for minimum ionising electrons yielded by a /sup 106/Ru source. The detectors have been irradiated with protons (energy 24 GeV) up to a fluence of about 2*10/sup 14/ p/cm/sup 2/. A charge signal degradation is observed for irradiated detectors. The charge signals for MIP's at 500 V are reduced from 12900 electrons before irradiation to 6600 electrons after about 2*10/sup 14/ p/cm/sup 2/ at a temperature of 7 degrees C and with a shaping time of 20 ns, typical of LHC inter-bunch crossing time (25 ns). The charge signal is found independent of tau for full depletion condition (V/sub a/>or =100 V). The measurement of the charge signal as a function of V/sub a/ shows that the full depletion voltage decreases from 100 V for non-irradiated ...

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

    Czech Academy of Sciences Publication Activity Database

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

    2017-01-01

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

  3. 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.

  4. 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.)

  5. 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...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-04-15

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-02-15

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

  8. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Castaldini, A.; Cavallini, A.; Polenta, L. [Univ. of Bologna (Italy); Canali, C.; Nava, F. [Univ. of Modena (Italy); Ferrini, R.; Galli, M. [Univ. of Pavia (Italy). Dipt. di Fisica

    1998-12-31

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

  10. Low temperature annealing effects on the performance of proton irradiated GaAs detectors

    Energy Technology Data Exchange (ETDEWEB)

    Vanni, P.; Nava, F.; Canali, C.; Castaldini, A.; Cavallini, A.; Polenta, L.; Lanzieri, C

    1999-08-01

    Semi-insulating, undoped, Liquid Encapsulated Czochralski (SI-U LEC) GaAs detectors have been irradiated with 24 GeV/c protons at the fluence of 5.6x10{sup 13} p/cm{sup 2}. The detector charge collection efficiency (CCE), for both electrons and holes is remarkably reduced after irradiation while the reverse current increases. The effect of annealing the detectors at temperatures ranging from 220 deg. C to 280 deg. C has been seen to reduce the reverse current and to increase the electron CCE, while the recovery of the hole CCE is negligible in irradiated detectors. Deep electron traps have been followed in their evolution with the heat treatment temperature by P-DLTS and C-V measurements. They recover by increasing the heat treatment temperature and this can explain the restoration observed in electron CCE.

  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. Wafer-scale processing technology for monolithically integrated GaSb thermophotovoltaic device array on semi-insulating GaAs substrate

    Science.gov (United States)

    Kim, Jung Min; Dutta, Partha S.; Brown, Eric; Borrego, Jose M.; Greiff, Paul

    2013-06-01

    This paper presents the entire fabrication and processing steps necessary for wafer scale monolithic integration of series interconnected GaSb devices grown on semi-insulating GaAs substrates. A device array has been fabricated on complete 50 mm (2 inch) diameter wafer using standard photolithography, wet chemical selective etching, dielectric deposition and single-sided metallization. For proof of concept of the wafer-scale feasibility of this process, six large-area series interconnected GaSb p-n junction thermophotovoltaic cells with each cell consisting of 24 small-area devices have been fabricated and characterized for its electrical connectivity. The fabrication process presented in this paper can be used for optoelectronic and electronic device technologies based on GaSb and related antimonide based compound semiconductors.

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

    Science.gov (United States)

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

    2017-02-01

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

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

    Directory of Open Access Journals (Sweden)

    Pranab Biswas

    2014-05-01

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

  15. 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}.

  16. Temperature and 8 MeV electron irradiation effects on GaAs solar cells

    Indian Academy of Sciences (India)

    2015-11-27

    Nov 27, 2015 ... 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 ...

  17. Temperature and 8 MeV electron irradiation effects on GaAs solar cells

    Indian Academy of Sciences (India)

    Abstract. 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 character- ization of cell properties like dark current under different ambient conditions and the stability of the cells against particle irradiation in space.

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

    Energy Technology Data Exchange (ETDEWEB)

    Castaldini, A.; Cavallini, A. E-mail: anna.cavallini@bo.infn.it; Polenta, L.; Canali, C.; Nava, F

    1999-04-21

    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.

  19. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1989-01-01

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

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

    Science.gov (United States)

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

    2017-03-01

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

  2. Identification of defects in GaAs induced by 1 MeV electron irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Lai, S.T.; Nener, B.D.; Faraone, L.; Nassibian, A.G. [Western Australia Univ., Nedlands, WA (Australia); Hotchkis, M.A.C. [Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW (Australia)

    1993-12-31

    This paper shows that 1 MeV electron irradiation on n-type vapor phase epitaxial (VPE) GaAs creates three electron traps E1, E2 and EL6, and results in the splitting of the EL2 center into two levels EL2-A and EL2-B. A 15 minutes isochronal anneal results in the annihilation of the E1 and E2 traps, a reduction in EL6 trap concentration, and the return of EL2 to a single level EL2-A. A defect model is outlined which correlates with the observed results. 4 refs., 2 tabs., 3 figs.

  3. Photo-irradiation effects on GaAs atomic layer epitaxial growth. GaAs no genshiso epitaxial seicho ni okeru hikari reiki koka

    Energy Technology Data Exchange (ETDEWEB)

    Mashita, M.; Kawakyu, Y.; Sasaki, M.; Ishikawa, H. (Toshiba Corp., Kawasaki (Japan). Research and Development Center)

    1990-08-10

    Single atomic layer epitaxy (ALE) aims at controlling a growing film at a precision of single molecular layer. In this article, it is reported that the growth temperature range of ALE was expanded by the vertical irradiation of KrF exima laser (248 nm) onto the substrate for the ALE growth of GaAs using the metalorganic chemical vapor deposition (MOCVD) method. Thanks for the results of the above experiment, it was demonstrated that the irradiation effect was not thermal, but photochemical. In addition, this article studies the possibility of adsorption layer irradiation and surface irradiation as the photo-irradiation mechanism, and points out that coexistence of both irradiation mechanisms can be considered and, in case of exima laser, strong possibility of direct irradiation of the adsorption layer because of its high power density. Hereinafter, by using both optical growth ALE and thermal growth ALE jointly, the degree of freedom of combination of hetero ALE increases and its application to various material systems becomes possible. 16 refs., 6 figs.

  4. Study of the Electron Distribution in GaN and GaAs after γ-Neutron Irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Tarasova, E. A.; Khananova, A. V.; Obolensky, S. V., E-mail: obolensk@rf.unn.ru [Lobachevsky State University of Nizhny Novgorod (Russian Federation); Zemlyakov, V. E. [Institute of Electronic Engineering “MIET” (Russian Federation); Sveshnikov, Yu. N.; Egorkin, V. I. [JSC Elma-Malachit (Russian Federation); Ivanov, V. A.; Medvedev, G. V. [JSC RPE “Salut” (Russian Federation); Smotrin, D. S. [Lobachevsky State University of Nizhny Novgorod (Russian Federation)

    2016-03-15

    The results of experimental studies of the parameters of GaN and GaAs structures before and after γ-neutron irradiation are reported. A special set of test diodes making it possible to reduce the error in the results of measuring the parameters of the structures, which is important in the design and optimization of the structure of semiconductor devices, is suggested.

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

    Energy Technology Data Exchange (ETDEWEB)

    Sato, Shin-ichiro, E-mail: sato.shinichiro@jaea.go.jp [Takasaki Advanced Radiation Research Institute, National Institutes for Quantum and Radiological Science and Technology, Takasaki 370-1292 (Japan); Optoelectronics and Radiation Effects Branch, U.S. Naval Research Laboratory, Washington, DC 20375 (United States); Schmieder, Kenneth J.; Warner, Jeffrey H.; Walters, Robert J. [Optoelectronics and Radiation Effects Branch, U.S. Naval Research Laboratory, Washington, DC 20375 (United States); Hubbard, Seth M.; Forbes, David V. [NanoPower Research Labs, Rochester Institute of Technology, Rochester, New York 14623 (United States); Ohshima, Takeshi [Takasaki Advanced Radiation Research Institute, National Institutes for Quantum and Radiological Science and Technology, Takasaki 370-1292 (Japan)

    2016-05-14

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

  6. GaAs preamplifier and LED driver for use in cryogenic and highly irradiated environments

    CERN Document Server

    Christoforou, Y

    1999-01-01

    A low-power dissipation, fast response and reasonable noise performance GaAs MESFETs preamplifier, able to work at low temperatures (89 K) and under high radiation doses, is presented. Attention is given to noise modeling for an application to particle detectors front-end electronics. Noise optimization can be achieved through careful layout design of the preamplifier's input transistor. This preamplifier is intended to be followed by a GaAs LED driver both working under the same physical conditions. A GaAs preamplifier and LED driver circuit has been designed and test results are presented and discussed in this paper.

  7. Establishment of equilibrium of electrostatic potential by photo-irradiation in a GaAs quantum well at low temperature

    Energy Technology Data Exchange (ETDEWEB)

    Yamaguchi, Masumi; Nomura, Shintaro; Delbecq, Matthieu; Tamura, Hiroyuki; Akazaki, Tatsushi, E-mail: m-yama@will.brl.ntt.co.j [NTT Basic Research Laboratories, NTT corp. 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198 (Japan)

    2010-02-01

    We measured photoluminescence (PL) spectra from a 20-nm GaAs/AlGaAs quantum well (QW) grown on an n-type substrate by selectively exciting the GaAs at 2 K. We observed a two-stage change of PL spectra as a function of the total amount of photo-irradiation (p x t) after cooling down. This corresponds to the process of establishing the equilibrium of electrostatic potential between the sample surface and QW and between the QW and n-doped substrate.

  8. 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.

  9. GaAs FET Device Fabrication and Ion Implantation Technology

    Science.gov (United States)

    1980-06-25

    NRL has centered on the growth of high purity undoped semi-insulating GaAs by 1 the pyrolytic boron nitride encapsulation technique. NRL ion...and Subtitle) ! 23A’.!WVRD .0 GR a .FEV GOCP.SSPONTNO.. PERFORING A IZ NAM AD1RIE.ATION AND ELEMENTNPROJET, TASImPLA A•ION,,ECHNOLOGY Qc Q epD ]&79

  10. 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.

  11. Laser Annealing of GaAs

    Science.gov (United States)

    1979-04-01

    100> direction of several semi-insulating GaAs samples. A 300 keV Kr+ implantation to a dose of 1015/cm2 is found to produce an amor- phous layer about...International Scince center SC5163 .6QTR 0 4-J z~ 43O fG== .- I.4.0 4- 00. 0 0<~4 4oo 4- = M 0 I44z . AW 0- -4 LQ 0 .4 o 4 vZ4 04 -n I-> . *C- -0 > - 0 r

  12. 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.

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

    OpenAIRE

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

    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...

  14. 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)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-02-15

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

  16. 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...

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

    Science.gov (United States)

    Troyon, M.; Smaali, K.

    2008-06-01

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

  18. Temperature dependence of the thermal diffusivity of GaAs in the 100-305 K range measured by the pulsed photothermal displacement technique

    Science.gov (United States)

    Soltanolkotabi, M.; Bennis, G. L.; Gupta, R.

    1999-01-01

    We have measured the variation of the value of the thermal diffusivity of semi-insulating GaAs in the 100-305 K range. The method used is the pulsed photothermal displacement technique. This is a noncontact technique, and the value of the thermal diffusivity is derived from the temporal evolution of the signal rather than its amplitude. This makes the technique less susceptible to uncertainties. We find that the temperature dependence of the thermal conductivity of semi-insulating GaAs follows a power law as T-1.62, in disagreement with results obtained previously. Possible reasons for the deviation within this very important intermediate temperature range are discussed.

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

    Directory of Open Access Journals (Sweden)

    Domenico Melisi

    2014-11-01

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

  20. 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.

  1. Formation of ordered arrays of Si and GaAs nanostructures by single-shot laser irradiation in near-field at the solid/liquid interface

    Science.gov (United States)

    Ulmeanu, M.; Petkov, P.; Hirshy, H.; Brousseau, E.

    2014-03-01

    We report a comprehensive study of a laser initiated liquid assisted technique to pattern Si and GaAs substrates. Silica colloidal particles masks, sizes 3 μ m and 700 nm, were formed on the substrates and three laser wavelengths: 355 nm/532 nm at 8 ps laser pulse duration and 800 nm at 70 fs laser pulse duration were used. The laser processing was assisted by liquid precursors, namely methanol and carbon tetrachloride. The regular structures develop from holes to bumps and nanorings, depending on the laser power and the size of the colloidal particle mask. Silica colloidal particles act both as a template mask and also based on the liquid-tuned optical field enhancement that shows near field enhancement effects. The patterns are defined by the liquid chemical composition and no influence of the pulse duration (ps or fs) was observed on their design.

  2. 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.

  3. Nonlinear Microwave Performance of an Optoelectronic CPW-to-Slot line Ring Resonator on GaAs Substrate

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Jong Chul [Kwangwoon University, Seoul (Korea, Republic of)

    1997-06-01

    A nonlinear optical-microwave interaction is carried out in an uniplanar CPW-to-Slot line ring resonator on the semi-insulating GaAs substrate, in which a Schottky photodetector is monolithic ally integrated as a coupling gap. When the capacitive reactance of the detector is modulated, the parametric amplification effect of the mixer occurs. In this device structure, the parametric amplification gain of 20 dB without the applied bias in RF signal is obtained. This microwave optoelectronic mixer can be used in the fiber-optic communication link. (author). 8 refs., 8 figs.

  4. 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.

  5. Electromagnetic modelling of GaAs membrane supported mm-wave receivers

    Energy Technology Data Exchange (ETDEWEB)

    Neculoiu, D [IMT Bucharest, 32B Erou Iancu Nicolae str., 72996, Bucharest (Romania); Electronics Department, POLITEHNICA University of Bucharest, 1-3 Iuliu Maniu Av., 061071 Bucharest (Romania); Muller, A [IMT Bucharest, 32B Erou Iancu Nicolae str., 72996, Bucharest (Romania); Konstantinidis, G [MRG-IESL-FORTH Heraklion, PO Box 1527, Crete (Greece)

    2006-04-01

    This paper presents a new electromagnetic modelling approach for the design of GaAs membrane supported monolithically integrated mm-wave receivers. The receivers structures are divided into membrane supported sections and bulk GaAs supported sections. Each block is modelled and designed using the full-wave electromagnetic simulation software Zeland IE3D. The Schottky diode is included in the model using the internal port feature. The design steps include the Schottky diode experimental characterization, design and measurements of membrane supported antenna demonstrators and linear/nonlinear simulations of the final receiver structures. The fabrication processes is based on GaAs micromachining. Two types of video detection receivers were designed, fabricated and tested: a 38 GHz double folded slot antenna receivers and a 45 GHz Yagi-Uda antenna receiver. Both circuits monolithically integrated the antenna with the Schottky diode on the same 2.2 {mu}m thin semiinsulating GaAs membrane. The experimental results demonstrate an isotropic voltage sensitivity of 3000 mV/mW at 38 GHz and 6000 mV/mW at 45 GHz, respectively. The measurements validate the modelling approach and open a window of opportunity for the development of innovative RF MEMS architectures operating at higher frequency, up to the sub-millimetre wave frequency range.

  6. Electromagnetic modelling of GaAs membrane supported mm-wave receivers

    Science.gov (United States)

    Neculoiu, D.; Muller, A.; Konstantinidis, G.

    2006-04-01

    This paper presents a new electromagnetic modelling approach for the design of GaAs membrane supported monolithically integrated mm-wave receivers. The receivers structures are divided into membrane supported sections and bulk GaAs supported sections. Each block is modelled and designed using the full-wave electromagnetic simulation software Zeland IE3D. The Schottky diode is included in the model using the internal port feature. The design steps include the Schottky diode experimental characterization, design and measurements of membrane supported antenna demonstrators and linear/nonlinear simulations of the final receiver structures. The fabrication processes is based on GaAs micromachining. Two types of video detection receivers were designed, fabricated and tested: a 38 GHz double folded slot antenna receivers and a 45 GHz Yagi-Uda antenna receiver. Both circuits monolithically integrated the antenna with the Schottky diode on the same 2.2 µm thin semiinsulating GaAs membrane. The experimental results demonstrate an isotropic voltage sensitivity of 3000 mV/mW at 38 GHz and 6000 mV/mW at 45 GHz, respectively. The measurements validate the modelling approach and open a window of opportunity for the development of innovative RF MEMS architectures operating at higher frequency, up to the sub-millimetre wave frequency range.

  7. 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)

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

    Energy Technology Data Exchange (ETDEWEB)

    Boardman, D.A. E-mail: d.boardman@surrey.ac.uk; Sellin, P.J

    2001-06-21

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

  9. Calculation of transport parameters of gamma-radiation detectors based on semi-insulating semiconductors

    Directory of Open Access Journals (Sweden)

    Zakharchenko A. A.

    2008-06-01

    Full Text Available A method of fast determination of the high resistivity detector charge collection parameters with the use of the detector dosimetric characteristics and by means of mathematical simulation is proposed. A problem of calculation of charge collection parameters is investigated for planar gamma-radiation dosimetric detectors made from semi-insulating compound semiconductor CdTe (CdZnTe. An applicability of the considered method is verified by computer simulation for HgI2 gamma-radiation detectors. The considered method can be used in the development of both dosimetry and spectrometry devices for radiation monitoring and for monitoring of characteristic devices operating in hard radiation fields. KEY WORDS: mobility, life time, semiconductor detectors, semi-insulating semiconductors, CdTe, CdZnTe, HgI2, Monte-Carlo method.

  10. Friedreich's ataxia GAA.TTC duplex and GAA.GAA.TTC triplex structures exclude nucleosome assembly.

    Science.gov (United States)

    Ruan, Haihe; Wang, Yuh-Hwa

    2008-11-07

    Both chromatin structure and formation of triplex DNA at expanded GAA TTC repeats have been shown to regulate the FXN gene silencing, which causes Friedreich's ataxia. Recent studies have suggested that the presence of heterochromatin at the long expanded GAA TTC repeats, which is enriched in hypoacetylated histones, deters the transcription of the FXN gene. However, neither direct histone binding nor the effect of histone acetylation on the GAA TTC duplex or the GAA GAA TTC triplex has been measured in vitro. In this study, GAA TTC repeating DNAs derived from the human FXN gene, and the GAA GAA TTC triplex, were examined for their ability to assemble single nucleosomes and nucleosome arrays. Competitive nucleosome reconstitution assays demonstrated that the GAA TTC duplex excludes nucleosomes (53% decrease compared to the pUC control DNA) and that the GAA GAA TTC triplex further lowers the nucleosome assembly efficiency (82% decrease compared to the duplex DNA). The difference in assembly efficiency is amplified more significantly when hypoacetylated histones are used, compared to assembly with hyperacetylated histones. By analyzing the formation of nucleosome arrays on GAA TTC-containing plasmids, the triplex structure was shown to destabilize the ability of adjacent sequences to assemble nucleosomes. These results provide the first direct binding measurements for the GAA TTC duplex and the GAA GAA TTC triplex, and on the effect of histone acetylation, towards dissecting the role of chromatin structure in silencing of the FXN gene. These findings suggest that these sequences could profoundly alter local chromatin structure, and the discrepancy between in vivo and in vitro results supports recent studies showing that, in addition to DNA sequences, other factors such as epigenetic marks could be involved in the mechanism for inhibition of FXN gene expression.

  11. 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.

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

    Science.gov (United States)

    Kurt, H. Hilal; Tanrıverdi, Evrim

    2017-07-01

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

  13. p- and n-type cubic GaN epilayers on GaAs

    Science.gov (United States)

    As, D. J.; Schikora, D.; Greiner, A.; Lübbers, M.; Mimkes, J.; Lischka, K.

    1996-10-01

    Temperature-dependent Hall-effect measurements are performed on cubic GaN layers grown by plasma-assisted molecular-beam epitaxy on (100) GaAs substrates. We find that under N-rich conditions, cubic GaN films are p-type with hole concentrations of ~=1013 cm-3 and mobilities of about 350 cm2/V s at room temperature. The acceptors have an activation energy of EA=0.445+/-0.015 eV. Ga-rich growth conditions result in n-type conductivity with electron concentrations of about 1014 cm-3 and room-temperature mobilities of μn~=100cm2/V s. Since for n-type samples a strong influence of the underlaying semi-insulating GaAs substrate is observed, a two-layer model is used to evaluate the Hall data, yielding a shallow donor with an activation energy of ED=0.16+/-0.07 eV and a deeper donor with EDD=0.60+/-0.10 eV.

  14. 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 (...

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

    CERN Document Server

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

    2012-01-01

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

  16. Development and characterization of a 3D GaAs X-ray detector for medical imaging

    Energy Technology Data Exchange (ETDEWEB)

    Gros d’Aillon, Eric, E-mail: eric.grosdaillon@cea.fr [CEA, LETI, MINATEC-Campus, 17 rue des Martyrs, F-38054 GRENOBLE (France); Avenel, Marie-Laure [CEA, LETI, MINATEC-Campus, 17 rue des Martyrs, F-38054 GRENOBLE (France); Farcage, Daniel [CEA, DEN-DPC, F-91191 GIF SUR YVETTE (France); Verger, Loïck [CEA, LETI, MINATEC-Campus, 17 rue des Martyrs, F-38054 GRENOBLE (France)

    2013-11-01

    Conventional semiconductor X-ray detectors for medical imaging have either a planar or a pixelated structure. The options available for detection materials are limited by the natural trade-off between the absorption of incident photons and the collection of free charge carriers with these two structures. This trade-off can be avoided by using az 3D structure, in which electrodes are drilled into the detector's volume. This article describes a prototype 3D semiconductor detector, using semi-insulating GaAs. A laser drilling technique was used to create electrodes in the volume of the material. The holes created were characterized by scanning electron microscopy. Electrode contacts were created using electroless Au deposition. The manufacturing process and the first gamma counting results obtained with {sup 241}Am and {sup 57}Co sources are presented. The system is capable of individual photon-counting without energy discrimination but requires further development to improve efficiency.

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

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, Yue; Lu, Wu-yue; Wang, Tao; Chen, Zhi-zhan, E-mail: zzchen@shnu.edu.cn [Department of Physics, Shanghai Normal University, 100 Guilin Road, Shanghai 200234 (China)

    2016-06-14

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Boardman, D

    2002-01-01

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

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

    Science.gov (United States)

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

    2011-03-01

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

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

    Directory of Open Access Journals (Sweden)

    Wei-Fu Wang

    2018-01-01

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

  1. 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.

  2. 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.

  3. High-speed photodiffractive effect in semi-insulating CdZnTe/ZnTe multiple quantum wells.

    Science.gov (United States)

    Partovi, A; Glass, A M; Olson, D H; Zydzik, G J; Short, K T; Feldman, R D; Austin, R F

    1992-05-01

    Single-pulse and cw measurements of the response of a semi-insulating CdZnTe/ZnTe multiple-quantum-well photorefractive device are presented. In single-pulse experiments, photodiffractive (absorption) gratings have been written with less than 1.8-microJ/cm(2) incident fluence, and a diffraction efficiency of 1.1% is obtained from the 1.56-microm active layer of the device. With an optimized structure, the ultimate response time of the device can be below 100 ps. In cw measurements a maximum diffraction efficiency of 1.35% is obtained.

  4. 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

  5. Next Generation Mid-Wave Infrared Cascaded Light Emitting Diodes: Growth of Broadband, Multispectral, and Single Color Devices on Gaas and Integrated Circuits

    Science.gov (United States)

    Provence, Sydney R.

    InAs/GaSb superlattices are an attractive material system for infrared light emitting diodes, due to the ability to tune the band gap throughout most of the infrared regime. A key consideration in the epitaxial growth of these heterostructures is crystalline material quality. In developing thick layers of epitaxially grown material, there are moderate amounts of elastic strain that can be incorporated into a heterostructure, beyond which deformations will form that will alleviate the lattice mismatch. This thesis investigates the optical and electronic properties of lattice-mismatched and strained materials through the study of thick dual-color light emitting diodes, broadband light emitting diodes, and InAs/GaSb superlattice devices developed on GaAs substrates and GaAs integrated circuits. A dual-color infrared light emitting diode is demonstrated emitting in the mid-wave infrared band at 3.81 mum and 4.72 mum. The design of the device stacks two independently operable InAs/GaSb superlattices structures on top of one another, so that 10 mum of material is grown with molecular beam epitaxy. Each layer is lattice-matched to a GaSb substrate. At quasi-continuous operation, radiances of 5.48 W/cm2-sr and 2.67 W/cm 2-sr are obtained. A broadband light emitting diode spanning the mid-wave infrared is demonstrated with eight stages of InAs/GaSb superlattices individually tuned to a different color. The performance of the device is compared with an identical eight stage device emitting in the middle of the mid-wave infrared. The emission of the fabricated broadband device spans from 3.2 ?m to 6 mum with peak radiance of 137.1 mW/cm2-sr. Growth of antimonide-based devices on GaAs is desirable to the relative transparency of semi-insulating substrates throughout the infrared, and as semi-insulating GaSb substrates are not available. The growth of bulk GaSb on GaAs is explored through different techniques in order to confine relaxation due to lattice mismatch strain to the

  6. Annealing effects on electrical and optical properties of ZnO films deposited on GaAs by metal organic chemical vapor deposition

    Science.gov (United States)

    Sun, Jingchang; Liang, Hongwei; Zhao, Jianze; Feng, Qiuju; Bian, Jiming; Zhao, Ziwen; Zhang, Heqiu; Luo, Yingmin; Hu, Lizhong; Du, Guotong

    2008-09-01

    ZnO thin film was deposited on semi-insulating GaAs by metal organic chemical vapor deposition (MOCVD). In situ annealing treatments were carried out under different temperature. Hall and photoluminescence (PL) measurements showed that the electrical and optical properties of ZnO film were sensitively dependent on annealing temperature. The as-deposited ZnO film showed n-type conductivity and intense near band edge (NBE) emission combined with rather weak deep level (DL) emission. After annealing in the temperature of 520 and 560 °C the films exhibit p-type conductivity, meanwhile secondary ion mass spectroscopy demonstrated arsenic ion was uniformly distributed in the ZnO films. Distinctly recombination of donor acceptor pair (DAP) was observed from the p-type ZnO film. The calculated arsenic related acceptor binding energy is nearly consistent with that of As Zn-2V Zn acceptor complex. When the annealing temperature up to 640 °C, Ga ion began to diffuse into ZnO film and the film returned to n-type as well as donor related emission reappeared in the spectrum. The influence of GaAs substrate on the electrical properties of ZnO films was also discussed.

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

    Science.gov (United States)

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

    2011-12-01

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

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

    Science.gov (United States)

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

    1990-01-01

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

  9. Two-photon photoluminescence and second-harmonic generation from unintentionally doped and semi-insulating GaN crystals

    Science.gov (United States)

    Godiksen, R. H.; Aunsborg, T. S.; Kristensen, P. K.; Pedersen, K.

    2017-11-01

    Unintentionally doped and semi-insulating Fe-doped GaN crystals grown by hydride vapor phase epitaxy have been investigated with two-photon photoluminescence and second-harmonic generation spectroscopy to reveal doping effects on the nonlinear optical properties and thus indirectly on crystal properties. Like for linear luminescence, it is found that Fe doping strongly reduces nonlinear luminescence. Recording of second-harmonic generation spectra in transmission probing bulk properties shows no significant difference between doped and un-doped crystals. Reflected second-harmonic generation probing 50-100 nm at the surface, on the other hand, shows significantly lower signal from the doped sample. Secondary ion mass spectroscopy shows that the Fe concentration is higher at the surface than in the bulk of the doped crystal. It is suggested that this causes higher defect density and degraded order in the surface region, thus reducing the second-harmonic signal.

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

    Science.gov (United States)

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

    2015-12-01

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

  11. Fabrication of 4H-SiC lateral double implanted MOSFET on an on-axis semi-insulating substrate without using epi-layer

    Science.gov (United States)

    Kim, Hyoung Woo; Seok, Ogyun; Moon, Jeong Hyun; Bahng, Wook; Jo, Jungyol

    2017-12-01

    4H-SiC lateral double implanted metal–oxide–semiconductor field effect transistors (LDIMOSFET) were fabricated on on-axis semi-insulating SiC substrates without using an epi-layer. The LDIMOSFET adopted a current path layer (CPL), which was formed by ion-implantation. The CPL works as a drift region between gate and drain. By using on-axis semi-insulating substrate and optimized CPL parameters, breakdown voltage (BV) of 1093 V and specific on-resistance (R on,sp) of 89.8 mΩ·cm2 were obtained in devices with 20 µm long CPL. Experimentally extracted field-effect channel mobility was 21.7 cm2·V‑1·s‑1 and the figure-of-merit (BV2/R on,sp) was 13.3 MW/cm2.

  12. Influence of implantation conditions of He{sup +} ions on the structure of a damaged layer in GaAs(001)

    Energy Technology Data Exchange (ETDEWEB)

    Shcherbachev, Kirill [National University of Science and Technology ' ' MISIS' ' , Leninskiy prosp. 4, 119049 Moscow (Russian Federation); Bailey, Melanie J. [Surrey Ion Beam Centre, Advanced Technology Institute, University of Surrey, Surrey (United Kingdom)

    2011-11-15

    An investigation into the influence of implantation conditions (dose, energy, and target temperature) of He{sup +} ions on the damage structure of GaAs (100) substrates was performed by HRXRD, scanning electron microscopy, and Nomarski microscopy. Blistering is shown to become apparent as characteristic features of isolines in RSMs. We propose that the formation of the defects yielding a characteristic XRDS is defined by the behavior of implanted atoms in the GaAs matrix, depending on two competing processes: (1) formation of the gas-filled bubbles; (2) diffusion of the He atoms from the bubbles toward the surface and deep into the GaAs substrate. We conclude that the gas-filled bubbles change the structure of the irradiated layer, resulting in the formation of strained crystalline areas of the GaAs matrix. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  13. Recent improvements in detection performances of radiation detectors based on bulk semi-insulating InP

    CERN Document Server

    Dubecky, F; Necas, V; Sekacova, M; Fornari, R; Gombia, E; Bohácek, P; Krempasky, M; Pelfer, P G

    2002-01-01

    In this work, bulk semi-insulating (SI) InP wafers of four various producers have been used for the fabrication of radiation detectors. The tested detectors were prepared starting from the different materials in just one run in order to be sure that their performances were not influenced by technological processes. On one type of material various electrode technologies were used with the aim to analyze their role on the detector performances. The fabricated detectors were tested for detection performance by the sup 2 sup 4 sup 1 Am and sup 5 sup 7 Co gamma-ray sources at below room temperature. The best detector was calibrated and tested also using sup 1 sup 3 sup 3 Ba and sup 1 sup 3 sup 7 Cs gamma sources. The best detector gives an energy resolution of 7 keV FWHM and a charge collection efficiency (CCE) of 82% (59.5 keV photopeak) at a temperature of 216 K. According to our knowledge, these results are the best which have been obtained with InP radiation detectors till now. The operation of SI InP detector...

  14. Si diffusion in GaAs

    Indian Academy of Sciences (India)

    Unknown

    Abstract. 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–.

  15. 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

  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. Simulation study of irradiated Si sensors equipped with metal- overhang for applications in LHC environment

    CERN Document Server

    Chatterji, Sudeep; Bhardwaj, Ashutosh; Srivastava-Ajay, K; Kumar, Ashish; Jha, Manoj Kumar; Shivpuri, R K; Khanna, S L

    2004-01-01

    The performance of metal-overhang (MO) equipped silicon micro-strip sensors, after irradiation for the preshower detector to be used in the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC), CERN, has been studied through simulations. Detailed calculations using Hamburg model have allowed the parameterization of these effects and helped to simulate the operation scenario of MO equipped sensors over ten years of LHC operation. The utility of overhanging metal extension as junction termination technique after space charge sign inversion (SCSI) has been explored in detail for the first time in this work. Several interesting results like a shift in the optimal oxide thickness in MO equipped structures after irradiation have been reported. The comparison of dielectric and semi-insulator passivated MO equipped structures after irradiation has been studied. Also, the impact of various crucial geometrical parameters like device depth (W//N), width of back N **+ layer used for ohmic contact (W/...

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

    Science.gov (United States)

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

    2017-05-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Auden, E.C., E-mail: eauden@sandia.gov; Vizkelethy, G.; Serkland, D.K.; Bossert, D.J.; Doyle, B.L.

    2017-05-15

    The Hecht equation can be used to model the nonlinear degradation of charge collection efficiency (CCE) in response to radiation-induced displacement damage in both fully and partially depleted GaAs photodiodes. CCE degradation is measured for laser-generated photocurrent as a function of fluence and bias in Al{sub 0.3}Ga{sub 0.7}As/GaAs/Al{sub 0.25}Ga{sub 0.75}As p-i-n photodiodes which have been irradiated with 12 MeV C and 7.5 MeV Si ions. CCE is observed to degrade more rapidly with fluence in partially depleted photodiodes than in fully depleted photodiodes. When the intrinsic GaAs layer is fully depleted, the 2-carrier Hecht equation describes CCE degradation as photogenerated electrons and holes recombine at defect sites created by radiation damage in the depletion region. If the GaAs layer is partially depleted, CCE degradation is more appropriately modeled as the sum of the 2-carrier Hecht equation applied to electrons and holes generated within the depletion region and the 1-carrier Hecht equation applied to minority carriers that diffuse from the field-free (non-depleted) region into the depletion region. Enhanced CCE degradation is attributed to holes that recombine within the field-free region of the partially depleted intrinsic GaAs layer before they can diffuse into the depletion region.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2003-06-16

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

  1. Ion-channeling studies of cubic GaN and In xGa 1 - xN on GaAs substrates

    Science.gov (United States)

    Portmann, J.; Haug, C.; Brenn, R.; Frey, T.; Schöttker, B.; As, D. J.

    1999-09-01

    Rutherford backscattering (RBS), dechanneling and angular scan measurements with 2 MeV 4He + ions have been performed to investigate molecular-beam epitaxially (MBE)-grown cubic GaN and In xGa 1 - xN layers on semi-insulating GaAs (0 0 1) substrates. The thickness of the epitaxial layers and the In concentration were determined by RBS, the crystalline quality by ion-channeling measurements. The predominant defect type was determined to be dislocations. Due to the lack of a perfect crystal we used an approximation for the minimum yield given by Lindhard and Barrett to normalize the measured minimum yields. The determined concentration of dislocations varies between 6×10 10 and 2.2×10 11 cm -2. Furthermore, a mosaic spread of crystallites was detected with angular scan measurements. Both the concentration of dislocations and the distribution of crystallite orientations do not show a significant dependence on the In concentration.

  2. Arsene GaAs solar array

    Science.gov (United States)

    Brambilla, L.; Caon, A.; Contini, R.; Daccolti, G.; Rossi, E.; Verzeni, G.; Bollani, B.; Flores, C.; Paletta, F.; Passoni, D.

    1993-01-01

    The GaAs solar array of ARSENE, a radioamateur spin stabilized spacecraft, is presented. The solar array uses typical Liquid Phase Epitaxy (LPE) solar cells and consists of six body mounted solar panels; each panel comprises an aluminum honeycomb substrate with aluminum skins insulated on the active area. For the qualification and acceptance of the ARSENE solar array, an engineering solar panel was submitted to the qualification tests including thermal vacuum, thermal shocks. The flight units are submitted to the thermal vacuum test. The final acceptance tests include rotational, acoustic and vibration tests performed at satellite level. Predicted power output, GaAs solar cell manufacturing, solar panel assembly and testing are discussed.

  3. 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.

  4. Airway smooth muscle dysfunction in Pompe (Gaa-/- ) mice.

    Science.gov (United States)

    Keeler, Allison M; Liu, Donghai; Zieger, Marina; Xiong, Lang; Salemi, Jeffrey; Bellvé, Karl; Byrne, Barry J; Fuller, David D; ZhuGe, Ronghua; ElMallah, Mai K

    2017-06-01

    Pompe disease is an autosomal recessive disorder caused by a deficiency of acid α-glucosidase (GAA), an enzyme responsible for hydrolyzing lysosomal glycogen. Deficiency of GAA leads to systemic glycogen accumulation in the lysosomes of skeletal muscle, motor neurons, and smooth muscle. Skeletal muscle and motor neuron pathology are known to contribute to respiratory insufficiency in Pompe disease, but the role of airway pathology has not been evaluated. Here we propose that GAA enzyme deficiency disrupts the function of the trachea and bronchi and this lower airway pathology contributes to respiratory insufficiency in Pompe disease. Using an established mouse model of Pompe disease, the Gaa-/- mouse, we compared histology, pulmonary mechanics, airway smooth muscle (ASM) function, and calcium signaling between Gaa-/- and age-matched wild-type (WT) mice. Lysosomal glycogen accumulation was observed in the smooth muscle of both the bronchi and the trachea in Gaa-/- but not WT mice. Furthermore, Gaa-/- mice had hyporesponsive airway resistance and bronchial ring contraction to the bronchoconstrictive agents methacholine (MCh) and potassium chloride (KCl) and to a bronchodilator (albuterol). Finally, calcium signaling during bronchiolar smooth muscle contraction was impaired in Gaa-/- mice indicating impaired extracellular calcium influx. We conclude that GAA enzyme deficiency leads to glycogen accumulation in the trachea and bronchi and impairs the ability of lower ASM to regulate calcium and respond appropriately to bronchodilator or constrictors. Accordingly, ASM dysfunction may contribute to respiratory impairments in Pompe disease. Copyright © 2017 the American Physiological Society.

  5. 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.

  6. 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.

  7. Panel fabrication utilizing GaAs solar cells

    Science.gov (United States)

    Mardesich, N.

    1984-01-01

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

  8. Optical pumping of hot phonons in GaAs

    Energy Technology Data Exchange (ETDEWEB)

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

    1982-06-30

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

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

    Science.gov (United States)

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

    1985-01-01

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

  10. Food irradiation

    Energy Technology Data Exchange (ETDEWEB)

    1987-02-28

    A brief article examines the controversy over food irradiation regarding the wholesomeness of irradiated food, its microbiological safety, loss of vitamins and changes in flavour. The benefits of food irradiation are also outlined including the destruction of certain food-borne pathogens and the prolongation of the shelf-life of food by killing pests and delaying the deterioration process.

  11. 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.

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

    Science.gov (United States)

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

    2009-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Lundeberg, T.; Zhou, J.

    1989-01-01

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

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

    Science.gov (United States)

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

    2007-06-01

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

  15. 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.

  16. 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

  17. 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.

  18. Long intronic GAA repeats causing Friedreich ataxia impede transcription elongation.

    Science.gov (United States)

    Punga, Tanel; Bühler, Marc

    2010-04-01

    Friedreich ataxia is a degenerative disease caused by deficiency of the protein frataxin (FXN). An intronic expansion of GAA triplets in the FXN-encoding gene, FXN, causes gene silencing and thus reduced FXN protein levels. Although it is widely assumed that GAA repeats block transcription via the assembly of an inaccessible chromatin structure marked by methylated H3K9, direct proof for this is lacking. In this study, we analysed different histone modification patterns along the human FXN gene in FRDA patient-derived lymphoblastoid cell lines. We show that FXN mRNA synthesis, but not turnover rates are affected by an expanded GAA repeat tract. Importantly, rather than preventing transcription initiation, long GAA repeat tracts affect transcription at the elongation step and this can occur independently of H3K9 methylation. Our data demonstrate that finding novel strategies to overcome the transcription elongation problem may develop into promising new treatments for FRDA.

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

    Science.gov (United States)

    Ebrahimi, Milad; Behnam, Mahdieh; Behranvand-Jazi, Nafiseh; Yari, Ladan; Sheikh-Kanlomilan, Sajad; Salehi, Mansoor; Tahmasebi, Pardis; Amini, Mohaddeseh; Behjati, Mohaddeseh; Hosseini, Nafisehsadat

    2017-01-01

    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. 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. 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. 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.

  20. 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.

  1. Atomic Layer Epitaxial Growth of Gaas on Porous Silicon Substrate

    OpenAIRE

    Mohamed Lajnef; Afrah Bardaoui; Isabelle Sagne; Radwan Chtouroua; Hatem Ezzaouia

    2008-01-01

    GaAs thin film has been grown on porous silicon by metal organic chemical vapour deposition (MOCVD) for different growth temperatures using atomic layer epitaxy (ALE) technique. The morphology of GaAs layer was investigated by atomic force microscopy (AFM). The effect of growth temperature is studied using photoluminescence measurements (PL).The photoluminescence spectra revealed a dissymmetry form toward high energies attributed to strain effect resulting from the lattice mismatch between Ga...

  2. 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. Copyright © 2015 Elsevier B.V. All rights reserved.

  3. Progressive GAA.TTC repeat expansion in human cell lines.

    Science.gov (United States)

    Ditch, Scott; Sammarco, Mimi C; Banerjee, Ayan; Grabczyk, Ed

    2009-10-01

    Trinucleotide repeat expansion is the genetic basis for a sizeable group of inherited neurological and neuromuscular disorders. Friedreich ataxia (FRDA) is a relentlessly progressive neurodegenerative disorder caused by GAA.TTC repeat expansion in the first intron of the FXN gene. The expanded repeat reduces FXN mRNA expression and the length of the repeat tract is proportional to disease severity. Somatic expansion of the GAA.TTC repeat sequence in disease-relevant tissues is thought to contribute to the progression of disease severity during patient aging. Previous models of GAA.TTC instability have not been able to produce substantial levels of expansion within an experimentally useful time frame, which has limited our understanding of the molecular basis for this expansion. Here, we present a novel model for studying GAA.TTC expansion in human cells. In our model system, uninterrupted GAA.TTC repeat sequences display high levels of genomic instability, with an overall tendency towards progressive expansion. Using this model, we characterize the relationship between repeat length and expansion. We identify the interval between 88 and 176 repeats as being an important length threshold where expansion rates dramatically increase. We show that expansion levels are affected by both the purity and orientation of the repeat tract within the genomic context. We further demonstrate that GAA.TTC expansion in our model is independent of cell division. Using unique reporter constructs, we identify transcription through the repeat tract as a major contributor to GAA.TTC expansion. Our findings provide novel insight into the mechanisms responsible for GAA.TTC expansion in human cells.

  4. Irradiation damage

    Energy Technology Data Exchange (ETDEWEB)

    Howe, L.M

    2000-07-01

    There is considerable interest in irradiation effects in intermetallic compounds from both the applied and fundamental aspects. Initially, this interest was associated mainly with nuclear reactor programs but it now extends to the fields of ion-beam modification of metals, behaviour of amorphous materials, ion-beam processing of electronic materials, and ion-beam simulations of various kinds. The field of irradiation damage in intermetallic compounds is rapidly expanding, and no attempt will be made in this chapter to cover all of the various aspects. Instead, attention will be focused on some specific areas and, hopefully, through these, some insight will be given into the physical processes involved, the present state of our knowledge, and the challenge of obtaining more comprehensive understanding in the future. The specific areas that will be covered are: point defects in intermetallic compounds; irradiation-enhanced ordering and irradiation-induced disordering of ordered alloys; irradiation-induced amorphization.

  5. Magnetic properties of 3d impurities in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Baykov, V.I. [Department of Materials Science, Royal Institute of Technology, SE-10044 Stockholm (Sweden)]. E-mail: vital@mse.kth.se; Korzhavyi, P.A. [Department of Materials Science, Royal Institute of Technology, SE-10044 Stockholm (Sweden); Smirnova, E.A. [Department of Theoretical Physics of Steel and Alloys, 119991 Moscow (Russian Federation); Abrikosov, I.A. [Department of Physics and Measurement Technology, Linkoeping University, SE-58183 Linkoeping (Sweden); Johansson, B. [Department of Materials Science, Royal Institute of Technology, SE-10044 Stockholm (Sweden)

    2007-03-15

    Electronic structure, thermodynamic, and magnetic properties of 3d-transition metal (TM) impurities in GaAs have been studied from first principles using Green's function approach. The studied TM impurities (V, Cr, Mn, and Fe) are found to form substitutional alloys on the Ga sublattice. The possibility of raising the Curie temperature T {sub C} in (GaMn)As by co-doping it with Cr impurities was examined on the basis of total energy difference between the disordered local moment (DLM) and the ferromagnetically ordered (FM) spin configurations. The calculated Curie temperature and magnetic moment have maxima for GaAs doped with Cr and Mn. The magnetic properties of Mn-doped GaAs are shown to be more sensitive to antisite As defects than those of Cr-doped GaAs. However, the Cr impurities are sensitive to the presence of acceptor defects, such as vacancies on the Ga sublattice. The investigation of the electronic structure of pseudo-ternary alloys (Ga{sub (1-x-y)}Mn{sub x}Cr{sub y})As has shown a mutual compensation of Mn and Cr impurities. Therefore, in order to reach the highest critical temperature, GaAs has to be separately doped with Cr or Mn impurities. The GaAs doped with Fe is found to be non-ferromagnetic.

  6. GAA repeat polymorphism in Turkish Friedreich's ataxia patients.

    Science.gov (United States)

    Yilmaz, M Bertan; Koç, A Filiz; Kasap, Halil; Güzel, A Irfan; Sarica, Yakup; Süleymanova, Dilara

    2006-05-01

    Friedreich's ataxia (FRDA), the most common subtype of early onset hereditary spinocerebellar ataxia (SCA), is an autosomal recessive neurodegenerative disorder caused by unstable GAA tri-nucleotide expansions in the first intron of FRDA gene located at 9q13-q21.1 position. Results of GAA repeat polymorphism in 80 Turkish SCA patients and 38 family members of 11 typical FRDA patients were reported. GAA triplet repeat size ranged from approximately 7 to 34 in normal alleles and from approximately 66 to 1300 in mutant alleles. Twenty six patients were homozygous for GAA expansion and size of expanded alleles differed from approximately 425 to 1300 repeats. Children 2 and 6 years old (showing no ataxia symptoms) of one family had homozygous GAA expansions reaching approximately 925 repeats. All 11 families studied had at least 1 afflicted child and 9 parents and 2 siblings were carrier (heterozygous) with mutant alleles ranging from 66 to 850 repeats. Family studies confirmed the meiotic instability and stronger effect of expansion in the smaller alleles on phenotype and a negative correlation between GAA repeat expansion size and onset-age of the disease.

  7. AlGaInAs quantum-well lasers with semi-insulating buried-heterostructure for high-speed direct modulation up to 40 Gbps

    Science.gov (United States)

    Otsubo, K.; Matsuda, M.; Takada, K.; Okumura, S.; Uetake, A.; Ekawa, M.; Yamamoto, T.

    2009-11-01

    We introduce our recent works on directly-modulated AlGaInAs quantum-well lasers with semi-insulating buriedheterostructure for ultra-high-speed transmission. The short-cavity 1.3-μm-wavelength DFB lasers showed low-penalty transmission up to 13 km under direct modulation at 25 Gbps, as well as clearly-opened eye patterns by 40-Gbps direct modulation. For further reduction of driving current in the high-speed directly-modulated lasers, we developed the distributed reflector lasers with the active-region having the length of 100 μm or less, sandwiched by the passive reflectors. The fabricated distributed reflector lasers exhibited very high slope value of relaxation oscillation frequency of 4.0 GHz/mA1/2 and more. The distributed reflector lasers emitting in 1.3-μm wavelength region achieved 40-Gbps direct modulation with the driving current of 2/3 of that by the DFB lasers. By the distributed reflector lasers of 1.55- μm-wavelength, high temperature 40-Gbps operation was realized as well as reduction of driving current.

  8. Subsurface Fe-doped semi-insulating GaN templates for inhibition of regrowth interface pollution in AlGaN/GaN HEMT structures

    Science.gov (United States)

    Cordier, Y.; Azize, M.; Baron, N.; Bougrioua, Z.; Chenot, S.; Tottereau, O.; Massies, J.; Gibart, P.

    2008-03-01

    The regrowth of AlGaN/GaN high electron mobility transistor (HEMT) structures on semi-insulating (SI) GaN templates, after exposure to air, results in the presence of parasitic conducting channels at regrowth interface (RI). Air contamination of the SI GaN templates is responsible for n-type doping and explains this parallel conduction. The parasitic conducting channel results in poor pinch-off characteristics ( Ileakage˜1 mA/mm at bias gate-source voltage above pinch-off voltage) and poor inter-device isolation and makes necessary to equip reactors with acceptor sources to compensate the n-type doping at the RI. To overcome this, we developed a new method of local Fe doping used in GaN templates for inhibiting RI pollution and proved to be efficient. Using this annihilation method permits to reduce by several orders of magnitude buffer leakage current. Such HEMT structures regrown by metalorganic vapor phase epitaxy (MOVPE) or by molecular beam epitaxy (MBE) exhibit two-dimensional electron gas (2DEG) with 300 K mobilities above 2000 cm 2/V s at carrier densities 9-10×10 12 cm -2 with a perfect charge control.

  9. Inhibition of interface pollution in AlGaN/GaN HEMT structures regrown on semi-insulating GaN templates

    Science.gov (United States)

    Azize, M.; Bougrioua, Z.; Gibart, P.

    2007-02-01

    AlGaN/GaN high-electron mobility transistors (HEMTs) structures regrown by metalorganic vapour phase epitaxy (MOVPE) on semi-insulating (SI) GaN templates, after exposure to air, results in the presence of parasitic conducting channels at regrowth interface. Air contamination of the SI GaN templates generates this parallel conduction. The parasitic conducting channel involves poor pinch-off characteristics ( Ileakage˜0.1 mA at bias gate-source voltage above pinch off voltage) and poor inter-device isolation ( Ileakage˜0.001-0.1 mA). To overcome this, we developed a method of local Fe doping used in GaN templates for inhibiting regrowth interface pollution and proved to be efficient. Using this annihilation method permits to reduce 4-5 orders of magnitude buffer leakage current ( Ileakage˜ nA). Such HEMTs structures, with perfect charge control, have exhibited two-dimensional electron gas (2DEGs) with 300 K mobilities above 2000 cm 2 V -1 s -1 at carrier densities 9×10 12 cm -2.

  10. 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)

  11. 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.

  12. 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...

  13. Detection of interruptions in the GAA trinucleotide repeat expansion in the FXN gene of Friedreich ataxia.

    Science.gov (United States)

    Holloway, Timothy P; Rowley, Simone M; Delatycki, Martin B; Sarsero, Joseph P

    2011-03-01

    Friedreich ataxia is a neurodegenerative disorder caused by the expansion of a GAA trinucleotide repeat sequence within the first intron of the FXN gene. Interruptions in the GAA repeat may serve to alleviate the inhibitory effects of the GAA expansion on FXN gene expression and to decrease pathogenicity. We have developed a simple and rapid PCR- and restriction enzyme-based assay to assess the purity of GAA repeat sequences.

  14. 46 CFR Sec. 7 - Operation under current GAA/MSTS Southeast Asia Program.

    Science.gov (United States)

    2010-10-01

    ... 46 Shipping 8 2010-10-01 2010-10-01 false Operation under current GAA/MSTS Southeast Asia Program... AUTHORITY VOYAGE DATA Sec. 7 Operation under current GAA/MSTS Southeast Asia Program. In order to adapt the provisions of NSA Order 35 (OPR-2) to the particular circumstances of the present GAA/MSTS Southeast Asia...

  15. Effects of guanidinoacetic acid(gaa supplementation in rats with chronic renal failure(crf

    Directory of Open Access Journals (Sweden)

    Yoshiharu Tsubakihara

    2012-06-01

    *; p<0.05 vs Sham $; p<0.05 vs GAA 0In conclusion, we demonstrated a deficiency of GAA and CRT, and muscle weekness in CRF rats. However, oral GAA supplementation could recover muscle content of CRT and muscle capabilities in these rats.

  16. Intrinsic spin lifetimes in GaAs (110) quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Mueller, Georg; Roemer, Michael; Huebner, Jens; Oestreich, Michael [Institut fuer Festkoerperphysik, Gottfried Wilhelm Leibniz Universitaet Hannover, Hannover (Germany); Schuh, Dieter; Wegscheider, Werner [Institut fuer Experimentelle und Angewandte Physik, Universitaet Regensburg (Germany)

    2009-07-01

    GaAs(110) quantum wells attract great attention due to the long spin lifetime for electron spins along the growth axis and are, therefore, of interest for future spin based optoelectronic devices. At low temperatures, optical injection of a finite spin polarization yields strongly enhanced spin dephasing due to the Bir Aronov Pikus mechanism that arises from the exchange interaction between electrons and holes. Thus, the intrinsic spin lifetime in GaAs(110) quantum wells has been unknown. In this work, the non-demolition technique of spin noise spectroscopy, which only relies on statistical spin fluctuations, is applied to GaAs(110) quantum wells in order to measure the intrinsic spin lifetimes. Furthermore, the Brownian motion of the electrons modifies the linewidth of the measured spin noise spectra due to time of flight broadening. This effect uniquely allows to study electronic motion at thermal equilibrium.

  17. Irradiation subassembly

    Science.gov (United States)

    Seim, O.S.; Filewicz, E.C.; Hutter, E.

    1973-10-23

    An irradiation subassembly for use in a nuclear reactor is described which includes a bundle of slender elongated irradiation -capsules or fuel elements enclosed by a coolant tube and having yieldable retaining liner between the irradiation capsules and the coolant tube. For a hexagonal bundle surrounded by a hexagonal tube the yieldable retaining liner may consist either of six segments corresponding to the six sides of the tube or three angular segments each corresponding in two adjacent sides of the tube. The sides of adjacent segments abut and are so cut that metal-tometal contact is retained when the volume enclosed by the retaining liner is varied and Springs are provided for urging the segments toward the center of the tube to hold the capsules in a closely packed configuration. (Official Gazette)

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

    Science.gov (United States)

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

    2014-03-01

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

  19. 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

  20. Ion implanted GaAs nanowire pn junctions

    Energy Technology Data Exchange (ETDEWEB)

    Wegener, Katharina; Stichtenoth, Daniel; Ronning, Carsten [II. Institute of Physics, University of Goettingen (Germany); Gutsche, Christoph; Prost, Werner; Tegude, Franz Josef [Solid-State Electronics Department, University of Duisburg-Essen (Germany)

    2008-07-01

    Ion beam doping of materials offers advantages in comparison to doping during growth or by diffusion. First, the impurity concentration as well as the lateral and depth distributions of the dopants are precisely controllable, and secondly, almost all elements can be implanted isotope-selective even beyond any solubility limit. We present studies on ion implanted gallium arsenide (GaAs) nanowire pn junctions. Nominal intrinsic GaAs nanowires were grown by the vapour-liquid-solid mechanism using gold nanoparticles on top of GaAs(100) substrates. Sulphur, being a donor in GaAs, was implanted into the nanowires using different ion energies resulting in a uniform concentration profile. The now n-type doped nanowires were then reinserted into the metal organic vapour phase epitaxy system. After an annealing procedure, the growth of the nanowires was continued under the addition of an acceptor. Finally, the fabricated nanowire pn junctions were shaved from the growth substrate and processed with contacts on top of insulating carrier substrates. First results on the electrical characterization of these structures are shown.

  1. GaAs MESFET with lateral non-uniform doping

    Science.gov (United States)

    Wang, Y. C.; Bahrami, M.

    1983-01-01

    An analytical model of the GaAs MESFET with arbitrary non-uniform doping is presented. Numerical results for linear lateral doping profile are given as a special case. Theoretical considerations predict that better device linearity and improved F(T) can be obtained by using linear lateral doping when doping density increases from source to drain.

  2. High purity, low dislocation GaAs single crystals

    Science.gov (United States)

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

    1983-01-01

    Liquid encapsulated Czochralski crystal growth techniques for producing undoped, high resistivity, low dislocation material suitable for device applications is described. Technique development resulted in reduction of dislocation densities in 3 inch GaAs crystals. Control over the melt stoichiometry was determined to be of critical importance for the reduction of twinning and polycrystallinity during growth.

  3. High-Q optomechanical GaAs nanomembranes

    DEFF Research Database (Denmark)

    Liu, Jin; Usami, K.; Naesby, A.

    2011-01-01

    We demonstrate that suspended single-crystal GaAs nanomembranes exhibit mechanical Q-factors exceeding 2 × 106 at room temperature, which makes them a very promising platform for optomechanics. Because of the completely removed substrate and their millimeter-scale lateral size, the membranes can...

  4. Density-dependent electron scattering in photoexcited GaAs

    DEFF Research Database (Denmark)

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

    2013-01-01

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

  5. Venemaa gaas - kas lahendus Euroopa energiavajadusele? / Kaupo Pollisinski

    Index Scriptorium Estoniae

    Pollisinski, Kaupo, 1952-2014

    2007-01-01

    Euroopa energiavarustus ja energiapoliitika on viimastel aastatel pälvinud nii tipppoliitikute kui asjatundjate tähelepanu, riskide maandamiseks tuleb mitmekesistada nii kütuseliikide valikut kui energiatarnete geograafiat. Venemaa gaas Euroopas, Gazpromi ambitsioonikad plaanid. Naftajuhtmete uusprojektid, naftaekspordi ümbersuunamise kava. Lisatud graafikud, skeemid. Ilmunud ka: Kroon & Economy, nr. 4, 2007, lk. 28-41

  6. 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...

  7. Gallium Arsenide and Related Compounds, 1986.

    Science.gov (United States)

    1986-01-01

    Neida, S JPearton, MStavola and R Caruso 63-68 The use of selective pair luminescence to characterize semi-insulating GaAs E S Koteles, J Kafalas, S...changing the charge state iy t he neutron irradiation. 4. Summary The main acceptor in urdoped LEC SI-GaAs has been considered to be carbon. However, the...1986 Correlation between melt stoichiometry and activation efficiency in Si-implanted GaAs A. R. Von Neida, S. J. Pearton, M. Stavola, and R. Caruso AT&T

  8. 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

  9. The mismatch repair system protects against intergenerational GAA repeat instability in a Friedreich ataxia mouse model.

    Science.gov (United States)

    Ezzatizadeh, Vahid; Pinto, Ricardo Mouro; Sandi, Chiranjeevi; Sandi, Madhavi; Al-Mahdawi, Sahar; Te Riele, Hein; Pook, Mark A

    2012-04-01

    Friedreich ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by a dynamic GAA repeat expansion mutation within intron 1 of the FXN gene. Studies of mouse models for other trinucleotide repeat (TNR) disorders have revealed an important role of mismatch repair (MMR) proteins in TNR instability. To explore the potential role of MMR proteins on intergenerational GAA repeat instability in FRDA, we have analyzed the transmission of unstable GAA repeat expansions from FXN transgenic mice which have been crossed with mice that are deficient for Msh2, Msh3, Msh6 or Pms2. We find in all cases that absence of parental MMR protein not only maintains transmission of GAA expansions and contractions, but also increases GAA repeat mutability (expansions and/or contractions) in the offspring. This indicates that Msh2, Msh3, Msh6 and Pms2 proteins are not the cause of intergenerational GAA expansions or contractions, but act in their canonical MMR capacity to protect against GAA repeat instability. We further identified differential modes of action for the four MMR proteins. Thus, Msh2 and Msh3 protect against GAA repeat contractions, while Msh6 protects against both GAA repeat expansions and contractions, and Pms2 protects against GAA repeat expansions and also promotes contractions. Furthermore, we detected enhanced occupancy of Msh2 and Msh3 proteins downstream of the FXN expanded GAA repeat, suggesting a model in which Msh2/3 dimers are recruited to this region to repair mismatches that would otherwise produce intergenerational GAA contractions. These findings reveal substantial differences in the intergenerational dynamics of expanded GAA repeat sequences compared with expanded CAG/CTG repeats, where Msh2 and Msh3 are thought to actively promote repeat expansions. Copyright © 2012 Elsevier Inc. All rights reserved.

  10. 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.

  11. Irradiation of optically activated SI-GaAs high-voltage switches with low and high energy protons

    CERN Document Server

    Bertolucci, Ennio; Mettivier, G; Russo, P; Bisogni, M G; Bottigli, U; Fantacci, M E; Stefanini, A; Cola, A; Quaranta, F; Vasanelli, L; Stefanini, G

    1999-01-01

    Semi-Insulating Gallium Arsenide (SI-GaAs) devices have been tested for radiation hardness with 3-4 MeV or 24 GeV proton beams. These devices can be operated in dc mode as optically activated electrical switches up to 1 kV. Both single switches (vertical Schottky diodes) and multiple (8) switches (planar devices) have been studied, by analyzing their current-voltage (I-V) reverse characteristics in the dark and under red light illumination, both before and after irradiation. We propose to use them in the system of high-voltage (-600 V) switches for the microstrip gas chambers for the CMS experiment at CERN. Low energy protons (3-4 MeV) were used in order to produce a surface damage below the Schottky contact: their fluence (up to 2.6*10/sup 15/ p/cm/sup 2/) gives a high-dose irradiation. The high energy proton irradiation (energy: 24 GeV, fluence: 1.1*10/sup 14/ p/cm/sup 2/) reproduced a ten years long proton exposure of the devices in CMS experiment conditions. For low energy irradiation, limited changes of ...

  12. Paramagnetic Mn impurities on Ge and GaAs surfaces

    Science.gov (United States)

    Gambardella, P.; Brune, H.; Dhesi, S. S.; Bencok, P.; Krishnakumar, S. R.; Gardonio, S.; Veronese, M.; Grazioli, C.; Carbone, C.

    2005-07-01

    Individual Mn impurities deposited on Ge(100), Ge(111), and GaAs(110) substrates present magnetic moments significantly larger compared to the average Mn magnetization in bulklike Ga1-xMnxAs and MnxGe1-x dilute magnetic semiconductors. The Mn magnetic moment is shown to change considerably going from Ge(100), to GaAs(110), and Ge(111). Independently of the substrate, the Mn per atom moment decreases with increasing coverage owing to the formation of antiferromagnetic Mn clusters. We observe no evidence of magnetically ordered surface layers down to a temperature of 5K . The comparison of x-ray magnetic circular dichroism line shapes with that of a pure Mn d5 configuration reveals the partial delocalization of the Mn d states.

  13. Electrical Properties of Polytypic Mg Doped GaAs Nanowires

    Directory of Open Access Journals (Sweden)

    N. Cifuentes

    2016-01-01

    Full Text Available The electrical transport properties of individual Mg doped GaAs nanowires are investigated. It is shown that Mg can be successfully used as a nontoxic p-type dopant in GaAs nanowires. The doping levels, expanding over two orders of magnitude, and free holes mobility in the NW were obtained by the analysis of field effect transistors transfer curves. The temperature dependence of the electrical resistivity above room temperature shows that the polytypic structure of the NWs strongly modifies the NWs charge transport parameters, like the resistivity activation energy and holes mobility. At lower temperatures the NWs exhibit variable range hopping conduction. Both Mott and Efros-Shklovskii variable range hopping mechanisms were clearly identified in the nanowires.

  14. 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.

  15. Failure Mechanisms of GaAs Transistors - A Literature Survey

    Science.gov (United States)

    1990-03-01

    Orito et al, Large Size Dislocation-Free Gallium Arsenide Single Crystals for LSI Applications, GaAs IC Symposium, October 1986, Technical Digest 1986...the channel resistance is modulated by the channel dimensions and the transconductance is degraded by the parasitic resistance. gn = gmo /(l+Rs gmo ...gm is the terminal transconductance, gmo is the internal (Rs=0 ) transconductance and Rs is the parasitic source resistance. It’s obvious that it’s

  16. Solar heating of GaAs nanowire solar cells.

    Science.gov (United States)

    Wu, Shao-Hua; Povinelli, Michelle L

    2015-11-30

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

  17. Gaas Displacement Damage Dosimeter Based on Diode Dark Currents

    Directory of Open Access Journals (Sweden)

    Warner Jeffrey H.

    2017-01-01

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

  18. 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.

  19. 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. Copyright © 2015 Elsevier Inc. All rights reserved.

  20. 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.

  1. Hyperexpansion of GAA repeats affects post-initiation steps of FXN transcription in Friedreich's ataxia.

    Science.gov (United States)

    Kim, Eunah; Napierala, Marek; Dent, Sharon Y R

    2011-10-01

    Friedreich's ataxia (FRDA) is caused by biallelic expansion of GAA repeats leading to the transcriptional silencing of the frataxin (FXN) gene. The exact molecular mechanism of inhibition of FXN expression is unclear. Herein, we analyze the effects of hyperexpanded GAA repeats on transcription status and chromatin modifications proximal and distal to the GAA repeats. Using chromatin immunoprecipitation and quantitative PCR we detected significant changes in the chromatin landscape in FRDA cells relative to control cells downstream of the promoter, especially in the vicinity of the GAA tract. In this region, hyperexpanded GAAs induced a particular constellation of histone modifications typically associated with heterochromatin-like structures. Similar epigenetic changes were observed in GFP reporter construct containing 560 GAA repeats. Furthermore, we observed similar levels of FXN pre-mRNA at a region upstream of hyperexpanded GAA repeats in FRDA and control cells, indicating similar efficiency of transcription initiation. We also demonstrated that histone modifications associated with hyperexpanded GAA repeats are independent of initiation and progression of transcription. Our data provide strong evidence that FXN deficiency in FRDA patients results from a block of transition from initiation to a productive elongation of FXN transcription due to heterochromatin-like structures formed in the proximity of the hyperexpanded GAAs.

  2. Phytosanitary Irradiation

    Directory of Open Access Journals (Sweden)

    Guy J. Hallman

    2016-01-01

    Full Text Available Phytosanitary treatments disinfest traded commodities of potential quarantine pests. Phytosanitary irradiation (PI treatments use ionizing radiation to accomplish this, and, since their international commercial debut in 2004, the use of this technology has increased by ~10% annually. Generic PI treatments (one dose is used for a group of pests and/or commodities, although not all have been tested for efficacy are used in virtually all commercial PI treatments, and new generic PI doses are proposed, such as 300 Gy, for all insects except pupae and adult Lepidoptera (moths. Fresh fruits and vegetables tolerate PI better than any other broadly used treatment. Advances that would help facilitate the use of PI include streamlining the approval process, making the technology more accessible to potential users, lowering doses and broadening their coverage, and solving potential issues related to factors that might affect efficacy.

  3. GaAs radiovoltaic cell enhanced by Y{sub 2}SiO{sub 5} crystal for the development of new gamma microbatteries

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Zheng-Rong [Department of Nuclear Science and Engineering, Nanjing University of Aeronautics and Astronautics, 29 General Road, Jiangning District, Nanjing 211106 (China); Tang, Xiao-Bin, E-mail: tangxiaobin@nuaa.edu.cn [Department of Nuclear Science and Engineering, Nanjing University of Aeronautics and Astronautics, 29 General Road, Jiangning District, Nanjing 211106 (China); Jiangsu Key Laboratory of Material and Technology for Energy Conversion, Nanjing 211106 (China); Liu, Yun-Peng [Department of Nuclear Science and Engineering, Nanjing University of Aeronautics and Astronautics, 29 General Road, Jiangning District, Nanjing 211106 (China); Jiangsu Key Laboratory of Material and Technology for Energy Conversion, Nanjing 211106 (China); Xu, Zhi-Heng; Yuan, Zi-Cheng; Liu, Kai; Chen, Wang [Department of Nuclear Science and Engineering, Nanjing University of Aeronautics and Astronautics, 29 General Road, Jiangning District, Nanjing 211106 (China)

    2017-05-01

    Highlights: • A new gamma/GaAs multi-level structure radiovoltaic microbattery is proposed. • The properties of the new GaAs/YSO radiovoltaic cell was discussed. • The cell with Y{sub 2}SiO{sub 5} crystal can provide higher power and current output. • The irradiation resistance of Y{sub 2}SiO{sub 5} crystal under X-ray excitation was studied. - Abstract: The design of a new gamma/GaAs multi-level structure radiovoltaic microbattery enhanced by an Y{sub 2}SiO{sub 5} (YSO) crystal is proposed. By introducing the YSO crystal in the GaAs radiovoltaic cell, the output power from the cell was significantly improved. We focus on the enhancement mechanisms of performance output in one level of a multi-level structure. The radioluminescence spectra of the YSO crystal revealed its fluorescence in the wavelength range of approximately 300–700 nm. Light at the exact wavelength would normally be totally absorbed by the GaAs photovoltaic material. The radiovoltaic cells were tested using an X-ray tube to simulate the gamma rays emitted by a gamma-radioactive source. Experimental investigation showed that the YSO crystal can increase the cell output power. The output power of the new GaAs/YSO radiovoltaic cell was enhanced by more than four times compared to that of the conventional GaAs radiovoltaic cell. In addition, considering the importance of the YSO crystal in the new GaAs/YSO radiovoltaic cell, the irradiation resistance of the YSO crystal under X-ray excitation was also analysed.

  4. 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

  5. Laser biostimulation (Ne-He and Ga-As) effects as compared to the conventional therapy in several pelvic inflammatory diseases

    Science.gov (United States)

    Antipa, Ciprian; Dona, Dumitru; Podoleanu, Adrian Gh.; Crisan, Nicolae; Constantinescu, Camelia

    1993-05-01

    We studied the effects of the very low-power Gallium-Arsenic infrared semiconductor laser and low-power Helium-Neon laser irradiation, single or in combination, compared to the placebo and conventional therapy on the recovery of 118 female patients from our hospital with the diagnosis of chronic pelvic inflammatory disorders. Laser biostimulation therapy proved to be significantly more efficient as compared with placebo or conventional therapy. The most efficient of all kinds of irradiations was the combination between He-Ne and Ga-As (laserpuncture and scanning). After laser treatments we didn't find any significant local genital changes both at the bimanual examination (except provoked pain), and at the echographical examination. Soft and very low-power laser therapy can be a useful alternative to the conventional treatments for pelvic inflammatory diseases.

  6. Testing a GaAs cathode in SRF gun

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-03-28

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

  7. High-efficiency, thin-film- and concentrator solar cells from GaAs. Final report; High-efficiency, Duennschicht- und Konzentrator-Solarzellen aus Galliumarsenid. Abschlussbericht

    Energy Technology Data Exchange (ETDEWEB)

    Wettling, W. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Bett, A.W. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Pilkuhn, M. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Scholz, F. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Baldus, A. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Blieske, U. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Blug, A. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Duong, T. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Schetter, C. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Stollwerck, G. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Sulima, O. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Wegener, A. [Fraunhofer-Institut fuer Solare Energiesysteme (ISE), Freiburg im Breisgau (Germany); Doernen, A. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Frankowsky, G. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Haase, D. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Hahn, G. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Hangleiter, A. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Stauss, P. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Tsai, C.Y. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4; Zieger, K. [Stuttgart Univ. (Germany). Physikalisches Teilinstitut 4

    1996-10-01

    Main topic of the project was the manufacturing of highly efficient GaAs-solar cells and the fabrication of concentrator cells. During this process significant progress was made with the material preparation, the solar cell technology and the material and process characterisation. This succeeded in the following efficiencies: - GaAs solar cell made by MOVPE technology: 22.9% on 4 cm{sup 2} (AM1.5g) - GaAs solar cell made by LPE-ER process: 22.8% on 4 cm{sup 2} (AM1.5g) - GaAs concentrator solar cell made by LPE-ER process: 24.9% at C=100xAM1.5d - GaAs concentrator module with fresnel lenses: Module efficiency 20.1% (under irradiation of 793 W/m{sup 2}). Another main focus was the epitaxy of GaAs on Si substrate. Two different approaches were investigated. Together with the cooperation partner ASE, Heilbronn a selective growth technology was developed that led to a decreased crack formation. By a simultanous optimization of the other epitaxy and process parameters, the efficiency was increased up to 16.6% AM0 on 1 cm{sup 2} solar cells. Furthermore a hybrid epitaxy was investigated. A GaAs layer was deposited onto a Si substrate using MOVPE. The solar cell structure was grown with a low temperature LPE. Unexpected difficulties appeared with this process, so that fundamental experiments needed to be done with the LPE technology. So far, no solar cells could be manufactured with this method. In addition, work was performed on GaInP solar cells on GaAs substrate. An efficiency of 15.7% (AM0) was acchieved. (orig.) [Deutsch] Gegenstand des Projekts war die Herstellung hocheffizienter GaAs-Solarzellen und die Fertigung von Konzentratorsolarzellen. Dazu wurden wesentliche Fortschritte bei der Materialpraeparation, der Solarzellentechnologie und der Material- and Prozesscharakterisierung erzielt. Diese Erfolge druecken sich in den erzielten Wirkungsgraden aus: - GaAs-Solarzelle hergestellt mit MOVPE-Technologie: 22.9% auf 4 cm{sup 2} (AM1.5g) - GaAs-Solarzelle hergestellt

  8. The effect of incremental gamma-ray doses and incremental neutron fluences upon the performance of self-biased sup 1 sup 0 B-coated high-purity epitaxial GaAs thermal neutron detectors

    CERN Document Server

    Gersch, H K; Simpson, P A

    2002-01-01

    High-purity epitaxial GaAs sup 1 sup 0 B-coated thermal neutron detectors advantageously operate at room temperature without externally applied voltage. Sample detectors were systematically irradiated at fixed grid locations near the core of a 2 MW research reactor to determine their operational neutron dose threshold. Reactor pool locations were assigned so that fast and thermal neutron fluxes to the devices were similar. Neutron fluences ranged between 10 sup 1 sup 1 and 10 sup 1 sup 4 n/cm sup 2. GaAs detectors were exposed to exponential fluences of base ten. Ten detector designs were irradiated and studied, differentiated between p-i-n diodes and Schottky barrier diodes. The irradiated sup 1 sup 0 B-coated detectors were tested for neutron detection sensitivity in a thermalized neutron beam. Little damage was observed for detectors irradiated at neutron fluences of 10 sup 1 sup 2 n/cm sup 2 and below, but signals noticeably degraded at fluences of 10 sup 1 sup 3 n/cm sup 2. Catastrophic damage was appare...

  9. Effects of In-situ UV Irradiation on the Uniformity and Optical Properties of GaAsBi Epi-layers Grown by MBE

    Energy Technology Data Exchange (ETDEWEB)

    Beaton, Daniel A [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Steger, Mark [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Christian, Theresa [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Mascarenhas, Angelo J [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

    2017-12-14

    In-situ UV illumination influences the incorporation dynamics of bismuth adatom in GaAs. Here we use the inherent variation of the fluence across the sample to explore the role of the incident irradiation. With illumination it is found that steady state growth processes are achieved more quickly resulting in more abrupt interfaces, as well as uniform GaAs1-xGaAs1-xBixBix epi-layers. Comparisons of low temperature photoluminescence spectra show an increasing density of clusters of incorporated bismuth atoms with decreasing incident fluence.

  10. Effects of in-situ UV irradiation on the uniformity and optical properties of GaAsBi epi-layers grown by MBE

    Science.gov (United States)

    Beaton, Daniel A.; Steger, M.; Christian, T.; Mascarenhas, A.

    2018-02-01

    In-situ UV illumination influences the incorporation dynamics of bismuth adatom in GaAs. Here we use the inherent variation of the fluence across the sample to explore the role of the incident irradiation. With illumination it is found that steady state growth processes are achieved more quickly resulting in more abrupt interfaces, as well as uniform GaAs1-xBix epi-layers. Comparisons of low temperature photoluminescence spectra show an increasing density of clusters of incorporated bismuth atoms with decreasing incident fluence.

  11. Thin-film GaAs epitaxial life-off solar cells for space applications

    NARCIS (Netherlands)

    Schermer, J.J.; Mulder, P.; Bauhuis, G.J.; Larsen, P.K.; Oomen, G.; Bongers, E.

    2005-01-01

    In the present work the space compatibility of thin-film GaAs solar cells is studied. These cells are separated from their GaAs substrate by the epitaxial lift-off (ELO) technique and mounted behind a CMG cover glass which at the same time serves as a stable carrier for the thin film cells. In the

  12. 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...

  13. 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.

  14. Irradiation Facilities at CERN

    CERN Document Server

    Gkotse, Blerina; Carbonez, Pierre; Danzeca, Salvatore; Fabich, Adrian; Garcia, Alia, Ruben; Glaser, Maurice; Gorine, Georgi; Jaekel, Martin, Richard; Mateu,Suau, Isidre; Pezzullo, Giuseppe; Pozzi, Fabio; Ravotti, Federico; Silari, Marco; Tali, Maris

    2017-01-01

    CERN provides unique irradiation facilities for applications in many scientific fields. This paper summarizes the facilities currently operating for proton, gamma, mixed-field and electron irradiations, including their main usage, characteristics and information about their operation. The new CERN irradiation facilities database is also presented. This includes not only CERN facilities but also irradiation facilities available worldwide.

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

    Directory of Open Access Journals (Sweden)

    Ian Keeler

    2013-07-01

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

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

    Science.gov (United States)

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

    1992-01-01

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

  17. A GaAs MESFET Mixer with Very Low Intermodulation,

    Science.gov (United States)

    1986-09-30

    HESS, GM-15 IMOTE Project Officer Director, AFSTC West Coast Office SD/CWX AFSTC/WCO OL-AB ’ V .-’ -- a.. -a- -"- "."- ’ " -"- ."-2."r...SECURITY CLASSIFICATION OF THIS PAGE (Wheni Data Entered) ....... ’p V1111,11,illilillil PREFACE The author would like to thank R. Gowin f’or...FIGURES 1. I/ V characteristic of an Avantek AT1O650-5 GaAs MESFET in its linear region .................................................. 10 2

  18. Simple intrinsic defects in GaAs : numerical supplement.

    Energy Technology Data Exchange (ETDEWEB)

    Schultz, Peter Andrew

    2012-04-01

    This Report presents numerical tables summarizing properties of intrinsic defects in gallium arsenide, GaAs, as computed by density functional theory. This Report serves as a numerical supplement to the results published in: P.A. Schultz and O.A. von Lilienfeld, 'Simple intrinsic defects in GaAs', Modelling Simul. Mater. Sci Eng., Vol. 17, 084007 (2009), and intended for use as reference tables for a defect physics package in device models. The numerical results for density functional theory calculations of properties of simple intrinsic defects in gallium arsenide are presented.

  19. Konstruksjon av GaAs MMIC effektforsterker med integrert linearisering

    OpenAIRE

    Kippernes, Frank Åge

    2009-01-01

    Denne oppgaven tar for seg linearisering av GaAs MMIC effektforsterkere. Det er brukt en pHEMT-prosess og senterfrekvensen ligger på 2,45 GHz. Effektforsterkerne som er konstruert kan levere utgangseffekter i størrelsesorden 1 W. Agilent Advanced Design System (ADS) ble brukt til konstruksjon og simulering. Moderne modulasjonsteknikker med varierende envelope krever lineære forsterkere for å fungere. Ulinearitetene i forsterkeren vil forvrenge signalet og skape støy både i og utenfor båndet...

  20. Influence of Friedreich ataxia GAA noncoding repeat expansions on pre-mRNA processing.

    Science.gov (United States)

    Baralle, Marco; Pastor, Tibor; Bussani, Erica; Pagani, Franco

    2008-07-01

    The intronic GAA repeat expansion in the frataxin (FXN) gene causes the hereditary neurodegenerative disorder Friedreich ataxia. Although it is generally believed that GAA repeats block transcription elongation, direct proof in eukaryotic systems is lacking. We tested in hybrid minigenes the effect of GAA and TTC repeats on nascent transcription and pre-mRNA processing. Unexpectedly, disease-causing GAA(100) repeats did not affect transcriptional elongation in a nuclear HeLa Run On assay, nor did they affect pre-mRNA transcript abundance. However, they did result in a complex defect in pre-mRNA processing. The insertion of GAA but not TTC repeats downstream of reporter exons resulted in their partial or complete exclusion from the mature mRNAs and in the generation of a variety of aberrant splicing products. This effect of GAA repeats was observed to be position and context dependent; their insertion at different distances from the reporter exons had a variable effect on splice-site selection. In addition, GAA repeats bind to a multitude of different splicing factors and induced the accumulation of an upstream pre-mRNA splicing intermediate, which is not turned over into mature mRNA. When embedded in the homologous frataxin minigene system, the GAA repeats did not affect the pre-mRNA transcript abundance but did significantly reduce the splicing efficiency of the first intron. These data indicate an association between GAA noncoding repeats and aberrant pre-mRNA processing because binding of transcribed GAA repeats to a multitude of trans-acting splicing factors can interfere with normal turnover of intronic RNA and thus lead to its degradation and a lower abundance of mature mRNA.

  1. Disruption of the gaa Gene in Zebrafish Fails to Generate the Phenotype of Classical Pompe Disease.

    Science.gov (United States)

    Wu, Jing; Yang, Yi; Sun, Chengjun; Sun, Shaoyang; Li, Qiang; Yao, Yuxiao; Fei, Fei; Lu, Lingeng; Chang, Zhuo; Zhang, Wenting; Wang, Xu; Luo, Feihong

    2017-01-01

    The underlying pathogenic lesions of glycogen storage disease type II (GSD II) and the diversity of this disease among different species are still under exploration. Thus, we created an acid alpha-glucosidase (gaa) gene-mutated zebrafish model of GSD II and examined the sequential pathogenic changes. gaa mRNA and protein expression, enzymatic activity, and lysosomal glycogen accumulation were assessed, and the phenotypic changes were compared between wild-type (WT) and gaa-mutated zebrafish. The presence of a Δ13 frameshift mutation in the gaa gene was confirmed at both the DNA and transcribed mRNA levels by Sanger sequencing. The relative amount of gaa mRNA was decreased before 2 days postfertilization (dpf), after which it unexpectedly increased in the mutant compared with the WT zebrafish. Consistent with the mRNA expression, the Gaa enzymatic activity in the mutant was downregulated before 3 dpf, while the Gaa protein level was slightly decreased at 4 dpf and was maintained at a consistent level in the adult gaa mutant muscle tissue. However, more than half of the adult mutant zebrafish exhibited excessive glycogen accumulation in the liver and muscles, along with the presence of autophagosomes, as determined by transmission electron microscopy. Thus, we have successfully generated a frameshift mutation in the gaa gene in zebrafish. The unique gaa gene expression changes and mild GSD II features during the adult stage strongly indicate the existence of species-specific differences, as well as an underlying compensatory network, which may warrant further examination.

  2. 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.

  3. Thermal stress cycling of GaAs solar cells

    Science.gov (United States)

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

    1985-01-01

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

  4. Picosecond relaxation of X-ray excited GaAs

    Science.gov (United States)

    Tkachenko, Victor; Medvedev, Nikita; Lipp, Vladimir; Ziaja, Beata

    2017-09-01

    In this paper we present the current status of our theoretical studies on ultrafast relaxation of X-ray/XUV excited gallium arsenide. First, we discuss our previous approach, the unified model based on rate equations, two-temperature model and the extended Drude approach. By fitting the model to the available experimental data, we obtained realistic estimates on transient electronic temperature and electron-lattice thermalization timescale. Next, we make a step towards a rigorous description of the relaxation process with our hybrid code, XTANT. We extend the XTANT to include the band-specific effect of the suppression of collisional processes in GaAs, and perform dedicated simulations. We find that the extended model correctly describes the predicted transient non-isothermality of conduction and valence bands, however, currently, it cannot reproduce the experimentally observed reflectivity overshooting at 5 - 10 ps. The reason for this discrepancy is that the electron-phonon coupling rate implemented in XTANT, although successfully applied for diamond and silicon, clearly underestimates the strength of this coupling in GaAs. The outline for a respective model improvement is discussed.

  5. 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.

  6. SAC-B GaAs solar array

    Science.gov (United States)

    Brambilla, L.; Caon, A.; Contini, R.; D'Accolti, G.; Rossi, E.; Verzeni, G.; Flores, C.; Paletta, F.; Pedrazzoli, G.; Grattarola, M.

    1993-10-01

    This paper describes the electrical and mechanical design of the GaAs solar array of SAC-B, an Argentinian scientific satellite, planned for launch in 1995 into a 550-km circular orbit by Pegasus vehicle. The solar array is made up of four deployable wings, embodying approximately 1000 LPE GaAs solar cells, (30 x 41 sq mm), capable of providing about 215 W at 28 V at EOL. The mechanical structure of each panel comprises an aluminum honeycomb structure with carbon fiber skins; the active facesheet is covered with an insulating layer of kapton/fiberglass. Each panel is attached via a pair of hinges to the spacecraft body while a restraint/release mechanism holds the other panel edge to the spacecraft. Different considerations have been taken into account for the electrical and mechanical design of the solar array: geometrical constraints of the Pegasus static envelope and the satellite for the panel dimensioning, mission degradation factors, minimization of the magnetic moment, and realiability requirements. Several environmental tests (including thermal vacuum and vibration) are foreseen at panel and/or satellite level to verify performances during the mission.

  7. Friedreich's ataxia-associated GAA repeats induce replication-fork reversal and unusual molecular junctions.

    Science.gov (United States)

    Follonier, Cindy; Oehler, Judith; Herrador, Raquel; Lopes, Massimo

    2013-04-01

    Expansion of GAA/TTC repeats is the causative event in Friedreich's ataxia. GAA repeats have been shown to hinder replication in model systems, but the mechanisms of replication interference and expansion in human cells remained elusive. To study in vivo replication structures at GAA repeats, we designed a new plasmid-based system that permits the analysis of human replication intermediates by two-dimensional gel electrophoresis and EM. We found that replication forks transiently pause and reverse at long GAA/TTC tracts in both orientations. Furthermore, we identified replication-associated intramolecular junctions, located between GAA/TTC repeats and other homopurine-homopyrimidine tracts, that were associated with breakage of the plasmid fork not traversing the repeats. Finally, we detected postreplicative, sister-chromatid hemicatenanes on control plasmids, which were replaced by persistent homology-driven junctions at GAA/TTC repeats. These data prove that GAA/TTC tracts interfere with replication in humans and implicate postreplicative mechanisms in trinucleotide repeat expansion.

  8. GaAs LPE Growth Centrifuge - A Novel Facility to Produce High Purity GaAs Material

    Science.gov (United States)

    Katterloher, Reinhard; Jakob, Gerd; Konuma, Mitsuharu; Haegel, Nancy; Haller, Eugene E.

    GaAs photoconductive detectors could extend the spectral response cut-off up to 300 μm. A continuous progress in material research has led to the production of pure, lightly and heavily doped n-type GaAs layers using the liquid phase epitaxy technique (LPE). Sample detectors demonstrated the expected infrared characteristics of bulk type devices. Modeling of BIB detector types predicts an improved IR sensitivity due to the attainable higher doping of the infrared sensitive layer, but gives also an estimate of the severe material requirements for the n-type blocking layer. With a new centrifugal technique for the LPE material growth we intend to achieve this goal: Contamination from outside during the LPE growth process is reduced by a suspension of the crucible on active magnetic bearings in a completely closed environment. Technical details of this unique equipment, first results of the achieved material quality in the initial growth runs and future steps to optimize operational parameters will be reported.

  9. 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....

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

    Science.gov (United States)

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

    1987-05-01

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

  11. Structures of dislocations in GaAs and their modification by impurities

    OpenAIRE

    Stich, P.; Jones, R.; Öberg, Sven; Heggie, M I

    1994-01-01

    Local density functional theory is used to show that both α and β dislocations in GaAs are reconstructed. This is done by relaxing large 158-atom H-terminated clusters of GaAs containing 90° partial dislocations. The reconstruction is strongly influenced by impurities: acceptor pairs destroy the reconstruction of β partials but strengthen it for α dislocations. Donors have opposite effects. The implication of these results for the pinning of dislocations in GaAs is discussed. Local density...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-01-15

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

  13. Study of the electrical parameters degradation of GaAs sub-cells for triple junction space solar cells by computer simulation

    Science.gov (United States)

    Cappelletti, M. A.; Casas, G. A.; Morales, D. M.; Hasperue, W.; Blancá, E. L. Peltzer y.

    2016-11-01

    In this paper, a theoretical study of the electrical parameters degradation of different n-type GaAs sub-cells for InGaP/GaAs/Ge triple junction solar cells irradiated with 1 and 5 MeV electrons has been performed by means of computer simulation. Effects of base carrier concentration upon the maximum power point, short-circuit current, open circuit voltage, diffusion current, recombination current and series resistance of these devices have been researched using the displacement damage dose method, the one-dimensional PC1D device modeling program and a home-made numerical code based on genetic algorithms. The radiative recombination lifetime, damage constant for minority-carrier lifetime and carrier removal rate models for GaAs sub-cells have been used in the simulations. An analytical model has been proposed, which is useful to describe the radiation-induced degradation of diffusion current, recombination current and series resistance. Results obtained in this work can be used to predict the radiation resistance of solar cells over a wide range of energies.

  14. Prismatic quantum heterostructures on MBE grown GaAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Fontcuberta i Morral, Anna [Walter Schottky Institut, TU Muenchen, Garching (Germany)

    2008-07-01

    Semiconductor nanowires are believed to play a decisive role in the electronic and optoelectronic devices of the XXI century. Their synthesis is a rapidly expanding field, due to the expectations that nanoscale objects and their associated phenomena have to offer to basic and applied science. Here we report on a new method for the growth of GaAs nanowires and related prismatic quantum heterostructures using Molecular Beam Epitaxy (MBE), by avoiding the use of gold as seed for the nanowires. The use of Molecular Beam Epitaxy presents an additional interest, as this technique allows us to produce ultra-pure nanowires and quantum heterostructures on the nanowire facets with very high crystalline quality and atomically sharp interfaces. This new versatility of MBE in the growth of nanostructures opens great possibilities for the generation of novel devices with additional optical and electronic functionalities, as it has been previously shown in planar structures.

  15. Towards quantum dots on GaAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

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

    2009-07-01

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

  16. GaAs Substrates for High-Power Diode Lasers

    Science.gov (United States)

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

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

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

    Science.gov (United States)

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

    2016-05-01

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

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Pulsed laser heating of silicon-nitride capped GaAs: Optical properties at high temperature

    Science.gov (United States)

    Bhat, A.; Yao, H. D.; Compaan, A.; Horak, A.; Rys, A.

    1988-09-01

    The optical properties of silicon nitride and gallium arsenide were studied at temperatures up to and beyond the melting point of GaAs by means of laser heating. XeCl excimer and pulsed dye laser pulses, ˜10 ns in duration, were used to heat the semiconductor under nitride capping layers of varying thickness. The transient reflectivity response at 514.5 nm was used together with a multilayer interference analysis to obtain the optical constants of solid and molten GaAs and of solid Si3N4 near the 1513-K melting point of GaAs. In addition, we report the melt duration as a function of laser pulse energy for GaAs with and without capping layers.

  3. 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...

  4. Friedreich's ataxia (GAA)n•(TTC)n repeats strongly stimulate mitotic crossovers in Saccharomyces cerevisae.

    Science.gov (United States)

    Tang, Wei; Dominska, Margaret; Greenwell, Patricia W; Harvanek, Zachary; Lobachev, Kirill S; Kim, Hyun-Min; Narayanan, Vidhya; Mirkin, Sergei M; Petes, Thomas D

    2011-01-13

    Expansions of trinucleotide GAA•TTC tracts are associated with the human disease Friedreich's ataxia, and long GAA•TTC tracts elevate genome instability in yeast. We show that tracts of (GAA)(230)•(TTC)(230) stimulate mitotic crossovers in yeast about 10,000-fold relative to a "normal" DNA sequence; (GAA)(n)•(TTC)(n) tracts, however, do not significantly elevate meiotic recombination. Most of the mitotic crossovers are associated with a region of non-reciprocal transfer of information (gene conversion). The major class of recombination events stimulated by (GAA)(n)•(TTC)(n) tracts is a tract-associated double-strand break (DSB) that occurs in unreplicated chromosomes, likely in G1 of the cell cycle. These findings indicate that (GAA)(n)•(TTC)(n) tracts can be a potent source of loss of heterozygosity in yeast.

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

    Science.gov (United States)

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

    2015-09-01

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

  6. A small molecule affecting the replication of trinucleotide repeat d(GAA)n.

    Science.gov (United States)

    He, Hanping; Hagihara, Masaki; Nakatani, Kazuhiko

    2009-10-12

    A newly designed ligand, methylcarbamoylnaphthyridine dimer (MCND), was synthesized and characterized. Ligand binding to d(GAA)(10) was investigated by UV thermal denaturation, circular dichroism spectroscopy, surface plasmon resonance, and cold-spray-ionization time-of-flight mass spectrometry. The results indicated that MCND bound to the d(GAA)(n) repeat to form a stable hairpin structure with a major binding stoichiometry of 3:1. The most likely binding site was identified as the G-G mismatch in the AGA/AGA triad. The polymerase stop assay showed that MCND binding to the d(GAA)(n) repeat effectively interfered with the extension of the primer at the first two GAA sites on the template with both prokaryotic Taq DNA polymerase and human DNA polymerase alpha.

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

    Science.gov (United States)

    Fonash, S. J.

    1978-01-01

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

  8. Computer simulation of GaAs and SOI devices using TCAD tools: an REU project

    OpenAIRE

    Goel, Ashok; Bergstrom, Sarah; Mojica-Campbell, Aleli

    1999-01-01

    An undergraduate research project is outlined whose goal was to use the TCAD tools to simulate the performances of GaAs- and SOI-based devices and to compare them with the corresponding silicon-based devices. Students used the Silvaco Corporation's "Virtual Wafer Fab" (VWF) package consisting of process simulation software called ATHENA, device layout software called DevEdit and device simulation software called ATLAS to simulate GaAs, SOI as well as conventional silicon devices. They explore...

  9. Local modification of GaAs nanowires induced by laser heating

    Energy Technology Data Exchange (ETDEWEB)

    Yazji, S; Zardo, I; Soini, M; Fontcuberta i Morral, A; Abstreiter, G [Walter Schottky Institut and Physik Department, Technische Universitaet Muenchen, Am Coulombwall 4, D-85748 Garching (Germany); Postorino, P, E-mail: ilaria.zardo@wsi.tum.de [Dipartimento di Fisica, Universita di Roma Sapienza, Piazzale Aldo Moro 5, I-00185 Roma (Italy)

    2011-08-12

    GaAs nanowires were heated locally under ambient air conditions by a focused laser beam which led to oxidation and formation of crystalline arsenic on the nanowire surface. Atomic force microscopy, photoluminescence and Raman spectroscopy experiments were performed on the same single GaAs nanowires in order to correlate their structural and optical properties. We show that the local changes of the nanowires act as a barrier for thermal transport which is of interest for thermoelectric applications.

  10. Suppression of Spontaneous Emission for Two-Dimentional GaAs photonic Crystal Microavities

    DEFF Research Database (Denmark)

    Søndergaard, Thomas; Broeng, Jes; Bjarklev, Anders Overgaard

    1999-01-01

    Spontaneous emission in two-dimentional photonic crystals in modelled through the concept of the position-dependent desity-of-state, and numerical results for a GaAs photoniccrystal microcavity are presented.......Spontaneous emission in two-dimentional photonic crystals in modelled through the concept of the position-dependent desity-of-state, and numerical results for a GaAs photoniccrystal microcavity are presented....

  11. Three-fold Symmetric Doping Mechanism in GaAs Nanowires

    DEFF Research Database (Denmark)

    Dastjerdi, M.H.T.; Fiordaliso, Elisabetta Maria; Leshchenko, E.D.

    2017-01-01

    A new dopant incorporation mechanism in Ga-assisted GaAs nanowires grown by molecular beam epitaxy is reported. Off-axis electron holography revealed that p-type Be dopants introduced in situ during molecular beam epitaxy growth of the nanowires were distributed inhomogeneously in the nanowire...... to explain the unique radial and azimuthal variation of the active dopants in the GaAs nanowires....

  12. Vapor phase epitaxial liftoff of GaAs and silicon single crystal films

    Energy Technology Data Exchange (ETDEWEB)

    Chang, W.; Kao, C.P.; Pike, G.A.; Slone, J.A.; Yablonovitch, E. [Electrical Engineering Department, University of California, Los Angeles, CA 90095-1594 (United States)

    1999-06-10

    Among the technologies for integrating GaAs devices with Si VLSI chips, epitaxial liftoff (ELO) is conspicuous for maintaining the quality of the single crystal epitaxial GaAs films. Traditionally, ELO is implemented in aqueous HF solution. It would be cleaner and simpler if ELO could be implemented in a vapor process. In this article, we will present the potential improvements in the ELO process by using a vapor phase etch to undercut thin films

  13. A novel GAA-repeat-expansion-based mouse model of Friedreich's ataxia.

    Science.gov (United States)

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

    2015-03-01

    Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by a GAA repeat expansion mutation within intron 1 of the FXN gene, resulting in reduced levels of frataxin protein. We have previously reported the generation of human FXN yeast artificial chromosome (YAC) transgenic FRDA mouse models containing 90-190 GAA repeats, but the presence of multiple GAA repeats within these mice is considered suboptimal. We now describe the cellular, molecular and behavioural characterisation of a newly developed YAC transgenic FRDA mouse model, designated YG8sR, which we have shown by DNA sequencing to contain a single pure GAA repeat expansion. The founder YG8sR mouse contained 120 GAA repeats but, due to intergenerational expansion, we have now established a colony of YG8sR mice that contain ~200 GAA repeats. We show that YG8sR mice have a single copy of the FXN transgene, which is integrated at a single site as confirmed by fluorescence in situ hybridisation (FISH) analysis of metaphase and interphase chromosomes. We have identified significant behavioural deficits, together with a degree of glucose intolerance and insulin hypersensitivity, in YG8sR FRDA mice compared with control Y47R and wild-type (WT) mice. We have also detected increased somatic GAA repeat instability in the brain and cerebellum of YG8sR mice, together with significantly reduced expression of FXN, FAST-1 and frataxin, and reduced aconitase activity, compared with Y47R mice. Furthermore, we have confirmed the presence of pathological vacuoles within neurons of the dorsal root ganglia (DRG) of YG8sR mice. These novel GAA-repeat-expansion-based YAC transgenic FRDA mice, which exhibit progressive FRDA-like pathology, represent an excellent model for the investigation of FRDA disease mechanisms and therapy. © 2015. Published by The Company of Biologists Ltd.

  14. Epitaxial growth of Bi ultra-thin films on GaAs by electrodeposition

    Energy Technology Data Exchange (ETDEWEB)

    Plaza, M. [Dpto. Fisica de Materiales, Universidad Complutense de Madrid, 28040 Madrid (Spain); Abuin, M. [Dpto. Fisica de Materiales, Universidad Complutense de Madrid, 28040 Madrid (Spain); Unidad Asociada IQFR(CSIC)-UCM, Madrid 28040 (Spain); Mascaraque, A., E-mail: arantzazu.mascaraque@fis.ucm.es [Dpto. Fisica de Materiales, Universidad Complutense de Madrid, 28040 Madrid (Spain); Unidad Asociada IQFR(CSIC)-UCM, Madrid 28040 (Spain); Gonzalez-Barrio, M.A. [Dpto. Fisica de Materiales, Universidad Complutense de Madrid, 28040 Madrid (Spain); Unidad Asociada IQFR(CSIC)-UCM, Madrid 28040 (Spain); Perez, L. [Dpto. Fisica de Materiales, Universidad Complutense de Madrid, 28040 Madrid (Spain); Instituto de Sistemas Optoelectronicos y Microtecnologia, Universidad Politecnica de Madrid, 28040 Madrid (Spain)

    2012-05-15

    Highlights: Black-Right-Pointing-Pointer Electrodeposition of Bi films on GaAs substrates with different orientations. Black-Right-Pointing-Pointer Ultra thin films - 50 nm - are continuous and smooth. Black-Right-Pointing-Pointer Bi always grows with (0 1 L) orientations. Black-Right-Pointing-Pointer Epitaxial growth onto As terminated surfaces. Black-Right-Pointing-Pointer Proposed model based on structural and chemical considerations. - Abstract: We report on the growth of thin bismuth films on GaAs substrates with different orientations by means of electrochemical deposition. Atomic force microscopy reveals that the films are continuous and exhibit low roughness when they are grown under the appropriate overpotential. {omega}-2{theta} X-ray diffraction scans only show reflections that can be indexed as (0 1 L), meaning that Bi grows onto GaAs only in combinations of the (0 0 1) and (0 1 0) orientations. The matching between the GaAs substrate and the Bi layer has been studied by asymmetric X-ray scans, finding that Bi grows epitaxially on GaAs(1 1 0) and GaAs(1 1 1)B, both As-terminated surfaces. We explain these results by structural and chemical considerations.

  15. InAs quantum dots nucleation on (100) and anisotropic (631)-oriented GaAs substrates

    Science.gov (United States)

    Eugenio-López, E.; Lopez-Lopez, M.; Gorbatchev, A. Yu.; Espinosa-Vega, L. I.; Cortes-Mestizo, I. E.; Mercado-Ornelas, C. A.; Del Rı´o-De Santiago, A.; Méndez-García, Victor H.

    2018-01-01

    Different mechanisms of adatoms nucleation are studied for the self-assembling of InAs quantum dots (QDs) on smooth and nanoscale faceted GaAs surface morphologies. The experiments were performed on GaAs(100) and GaAs(631), and prior to the arrival of InAs the GaAs surface morphology was intentionally altered by changing the growth temperature of the buffer layer, TBL. For the reflection high-energy electron diffraction (RHEED) analysis, an equilibrium interlayer mass transport model is proposed through which, the critical thickness (Hc) and the InAs diffusion length can be estimated. For InAs growth on (100) substrates the Hc did not show significant dependence on TBL, but the adatoms diffusion length slightly reduced as TBL increases, which is in agreement with the changes on QDs density as observed by atomic force microscopy (AFM). For samples grown on GaAs (631)-oriented substrates it was found that both the nucleation mode of InAs and the Hc depends on TBL. The changes are associated to the growth of InAs on GaAs surface faceted corrugation that allows the self-organizing InAs QDs along [-113].

  16. Effects of Friedreich's ataxia (GAA)n*(TTC)n repeats on RNA synthesis and stability.

    Science.gov (United States)

    Krasilnikova, Maria M; Kireeva, Maria L; Petrovic, Vladimir; Knijnikova, Nelli; Kashlev, Mikhail; Mirkin, Sergei M

    2007-01-01

    Expansions of (GAA)n repeats within the first intron of the frataxin gene reduce its expression, resulting in a hereditary neurodegenerative disorder, Friedreich's ataxia. While it is generally believed that expanded (GAA)n repeats block transcription elongation, fine mechanisms responsible for gene repression are not fully understood. To follow the effects of (GAA)n*(TTC)n repeats on gene expression, we have chosen E. coli as a convenient model system. (GAA)n*(TTC)n repeats were cloned into bacterial plasmids in both orientations relative to a promoter, and their effects on transcription and RNA stability were evaluated both in vitro and in vivo. Expanded (GAA)n repeats in the sense strand for transcription caused a significant decrease in the mRNA levels in vitro and in vivo. This decrease was likely due to the tardiness of the RNA polymerase within expanded (GAA)n runs but was not accompanied by the enzyme's dissociation and premature transcription termination. Unexpectedly, positioning of normal- and carrier-size (TTC)n repeats into the sense strand for transcription led to the appearance of RNA transcripts that were truncated within those repetitive runs in vivo. We have determined that these RNA truncations are consistent with cleavage of the full-sized mRNAs at (UUC)n runs by the E. coli degradosome.

  17. Creatine prevents the inhibition of energy metabolism and lipid peroxidation in rats subjected to GAA administration.

    Science.gov (United States)

    Kolling, Janaína; Wyse, Angela T S

    2010-09-01

    Guanidinoacetate methyltransferase (GAMT) deficiency is an inherited neurometabolic disorder, biochemically characterized by the tissue accumulation of guanidinoacetate (GAA). Affected patients present epilepsy and mental retardation whose etiopathogeny is unclear. Previous reports have shown that GAA alters brain energy metabolism and that creatine, which is depleted in patients with GAMT deficiency, can act as a neuroprotector; as such, in the present study we investigated the effect of creatine administration on some of the altered parameters of energy metabolism (complex II, Na(+),K(+)-ATPase and creatine kinase) and lipid peroxidation caused by intrastriatal administration of GAA in adult rats. Animals were pretreated for 7 days with daily intraperitonial administrations of creatine. Subsequently, these animals were divided into two groups: Group 1 (sham group), rats that suffered surgery and received saline; and group 2 (GAA-treated). Thirty min after GAA or saline, the animals were sacrificed and the striatum dissected out. Results showed that the administration of creatine was able to reverse the activities of complex II, Na(+),K(+)-ATPase and creatine kinase, as well as, the levels of thiobarbituric acid reactive substances (TBARS), an index of lipid peroxidation. These findings indicate that the energy metabolism deficit caused by GAA may be prevented by creatine, which probably acts as an antioxidant since it was able to prevent lipid peroxidation. These data may contribute, at least in part, to a better understanding of the mechanisms related to the energy deficit and oxidative stress observed in GAMT deficiency.

  18. Development of a feasible assay for the detection of GAA mutations in patients with Pompe disease.

    Science.gov (United States)

    Er, Tze-Kiong; Chen, Chih-Chieh; Chien, Yin-Hsiu; Liang, Wen-Chen; Kan, Tzu-Min; Jong, Yuh-Jyh

    2014-02-15

    Pompe disease is an inherited autosomal recessive deficiency of acid α-glucosidase (GAA) and is due to pathogenic sequence variants in the corresponding GAA gene. While the analysis of enzyme activity remains the diagnostic test of choice for individuals with Pompe disease, mutation analysis remains for establishing a definitive diagnosis. High resolution melting (HRM) analysis was performed to screen GAA mutations. Genomic DNA was extracted from peripheral blood samples of the two patients with Pompe disease and 250 normal controls. Exons 2 through 20 of the GAA gene were screened by the HRM analysis. The results were subsequently confirmed by direct sequencing. This assay proved to be feasible in detecting seven known (c.2T>C, c.1726G>A, c.1845G>A, c.1935C>A, c.1958C>A, c.2238G>C, and c.2815_2816del) GAA mutations. Each mutation could be readily and accurately identified in the difference plot curves. We estimated the carrier frequency of the most common mutation, c.1935G>A (p.D645E), in the Taiwanese population to be 0.2%. In clinical practice, we suggest that HRM analysis is assumed as a fast and reliable method for screening GAA gene mutations especially the most common mutations which are responsible for Pompe disease among the Taiwanese populations. © 2013.

  19. 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.

  20. 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.

  1. Deficiency of RecA-dependent RecFOR and RecBCD pathways causes increased instability of the (GAA*TTC)n sequence when GAA is the lagging strand template.

    Science.gov (United States)

    Pollard, Laura M; Chutake, Yogesh K; Rindler, Paul M; Bidichandani, Sanjay I

    2007-01-01

    The most common mutation in Friedreich ataxia is an expanded (GAA*TTC)n sequence, which is highly unstable in human somatic cells and in the germline. The mechanisms responsible for this genetic instability are poorly understood. We previously showed that cloned (GAA*TTC)n sequences replicated in Escherichia coli are more unstable when GAA is the lagging strand template, suggesting erroneous lagging strand synthesis as the likely mechanism for the genetic instability. Here we show that the increase in genetic instability when GAA serves as the lagging strand template is seen in RecA-deficient but not RecA-proficient strains. We also found the same orientation-dependent increase in instability in a RecA+ temperature-sensitive E. coli SSB mutant strain (ssb-1). Since stalling of replication is known to occur within the (GAA*TTC)n sequence when GAA is the lagging strand template, we hypothesized that genetic stability of the (GAA*TTC)n sequence may require efficient RecA-dependent recombinational restart of stalled replication forks. Consistent with this hypothesis, we noted significantly increased instability when GAA was the lagging strand template in strains that were deficient in components of the RecFOR and RecBCD pathways. Our data implicate defective processing of stalled replication forks as a mechanism for genetic instability of the (GAA*TTC)n sequence.

  2. Estudio de la naturaleza y distribucion de defectos en obleas de GaAs mediante tecnicas de inyeccion de haces

    OpenAIRE

    Mendez Martín, Bianchi

    1991-01-01

    Los estudios realizados sobre el gaas presentados en esta memoria aportan información acerca de la naturaleza de defectos (dislocaciones y defectos puntuales) en obleas de gaas semiconductor y gaas semiaislante. El empleo de la catodoluminiscencia (cl) y la microscopia electroacustica de barrido (meab) de forma combinada nos ha permitido obtener resultados nuevos tanto acerca de las posibilidades de aplicación de estas tecnicas a semiconductores III-v como sobre la caracterización de las oble...

  3. Impurity effects on both the creation and the migration of Ga vacancies in GaAs

    Science.gov (United States)

    Lee, Jong-Lam; Wei, Long; Tanigawa, Shoichiro; Kawabe, Mitsuo

    1991-07-01

    The effects of impurities, such as Si and Be, on both the creation and the migration of Ga vacancies in annealing of GaAs were investigated by a slow positron beam technique. The results show that vacancies diffuse from the surface during the annealing and one of the dominant types is a monovacancy of Ga, VGa, in Be-doped GaAs and/or Si-doped GaAs, while the other is a divacancy of VGa-VAs in undoped GaAs. In annealing the bilayer structures composed of the Si-doped layer grown on the Be-doped layer, it was found that VGa is a major type of defect rather than VGa-VAs if the Si concentration is higher or lower than the Be one in GaAs, but VGa-VAs is dominant if the concentrations of the impurities are similar. This proposes that the interaction between Si and Be is stronger than that of VAs-BeGa and/or VGa-SiGa. The Ga interstitial IGa is created in the Be-doped layer where IGa interacts with VGa created from the surface and suppresses the migration of VGa. This supports the validity of the kick-out mechanism involving a column-III interstitial rather than the Longini mechanism for Be diffusion in GaAs. In Si-doped GaAs, VGa is created from the surface and the diffusion constant of VGa decreases with the increase of Si doping concentration. This implies that VGa forms a complex of SiGa-VGa and the interaction time of VGa at the Si donor by making a complex of SiGa-VGa is a rate-limiting step in the diffusion of VGa in GaAs. The present results propose the creation of IGa and VGa in the Be-diffused GaAs and in Si-diffused GaAs, respectively. This is consistent with the Fermi-level effect of the impurities on the creation of those defects.

  4. 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...

  5. 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

    2015-01-01

    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.

  6. Hyperexpansion of GAA repeats affects post-initiation steps of FXN transcription in Friedreich’s ataxia

    Science.gov (United States)

    Kim, Eunah; Napierala, Marek; Dent, Sharon Y. R.

    2011-01-01

    Friedreich’s ataxia (FRDA) is caused by biallelic expansion of GAA repeats leading to the transcriptional silencing of the frataxin (FXN) gene. The exact molecular mechanism of inhibition of FXN expression is unclear. Herein, we analyze the effects of hyperexpanded GAA repeats on transcription status and chromatin modifications proximal and distal to the GAA repeats. Using chromatin immunoprecipitation and quantitative PCR we detected significant changes in the chromatin landscape in FRDA cells relative to control cells downstream of the promoter, especially in the vicinity of the GAA tract. In this region, hyperexpanded GAAs induced a particular constellation of histone modifications typically associated with heterochromatin-like structures. Similar epigenetic changes were observed in GFP reporter construct containing 560 GAA repeats. Furthermore, we observed similar levels of FXN pre-mRNA at a region upstream of hyperexpanded GAA repeats in FRDA and control cells, indicating similar efficiency of transcription initiation. We also demonstrated that histone modifications associated with hyperexpanded GAA repeats are independent of initiation and progression of transcription. Our data provide strong evidence that FXN deficiency in FRDA patients results from a block of transition from initiation to a productive elongation of FXN transcription due to heterochromatin-like structures formed in the proximity of the hyperexpanded GAAs. PMID:21745819

  7. Fully deleted adenovirus persistently expressing GAA accomplishes long-term skeletal muscle glycogen correction in tolerant and nontolerant GSD-II mice.

    Science.gov (United States)

    Kiang, Anne; Hartman, Zachary C; Liao, Shaoxi; Xu, Fang; Serra, Delila; Palmer, Donna J; Ng, Philip; Amalfitano, Andrea

    2006-01-01

    Glycogen storage disease type II (GSD-II) patients manifest symptoms of muscular dystrophy secondary to abnormal glycogen storage in cardiac and skeletal muscles. For GSD-II, we hypothesized that a fully deleted adenovirus (FDAd) vector expressing hGAA via nonviral regulatory elements (PEPCK promoter/ApoE enhancer) would facilitate long-term efficacy and decrease propensity to generate anti-hGAA antibody responses against hepatically secreted hGAA. Intravenous delivery of FDAdhGAA into GAA-tolerant or nontolerant GAA-KO mice resulted in long-term hepatic secretion of hGAA. Specifically, nontolerant mice achieved complete reversal of cardiac glycogen storage and near-complete skeletal glycogen correction for at least 180 days and tolerant mice for minimally 300 days coupled with the preservation of muscle strength. Anti-hGAA antibody levels in both mouse strains were significantly less relative to those previously generated by CMV-driven hGAA expression in nontolerant GAA-KO mice. However, plasma GAA levels decreased in nontolerant GAA-KO mice despite long-term intrahepatic GAA expression from the persistent vector. This intriguing result is discussed in light of other examples of "tolerance" induction by gene-transfer-based approaches.

  8. Transcriptome assessment of the Pompe (Gaa-/-) mouse spinal cord indicates widespread neuropathology.

    Science.gov (United States)

    Turner, S M F; Falk, D J; Byrne, B J; Fuller, D D

    2016-11-01

    Pompe disease, caused by deficiency of acid alpha-glucosidase (GAA), leads to widespread glycogen accumulation and profound neuromuscular impairments. There has been controversy, however, regarding the role of central nervous system pathology in Pompe motor dysfunction. We hypothesized that absence of GAA protein causes progressive activation of neuropathological signaling, including pathways associated with cell death. To test this hypothesis, genomic data (Affymetrix Mouse Gene Array 2.0ST) from the midcervical spinal cord in 6 and 16 mo old Pompe (Gaa(-/-)) mice were evaluated (Broad Institute Molecular Signature Database), along with spinal cord histology. The midcervical cord was selected because it contains phrenic motoneurons, and phrenic-diaphragm dysfunction is prominent in Pompe disease. Several clinically important themes for the neurologic etiology of Pompe disease emerged from this unbiased genomic assessment. First, pathways associated with cell death were strongly upregulated as Gaa(-/-) mice aged, and motoneuron apoptosis was histologically verified. Second, proinflammatory signaling was dramatically upregulated in the Gaa(-/-) spinal cord. Third, many signal transduction pathways in the Gaa(-/-) cervical cord were altered in a manner suggestive of impaired synaptic function. Notably, glutamatergic signaling pathways were downregulated, as were "synaptic plasticity pathways" including genes related to neuroplasticity. Fourth, many genes and pathways related to cellular metabolism are dysregulated. Collectively, the data unequivocally confirm that systemic absence of GAA induces a complex neuropathological cascade in the spinal cord. Most importantly, the results indicate that Pompe is a neurodegenerative condition, and this underscores the need for early therapeutic intervention capable of targeting the central nervous system. Copyright © 2016 the American Physiological Society.

  9. Friedreich ataxia: Detection of GAA repeat expansions and frataxin point mutations.

    Science.gov (United States)

    Pandolfo, Massimo

    2006-01-01

    Friedreich ataxia (FA) is an autosomal-recessive disease primarily characterized by progressive neurological disability. A significant proportion of patients also present with a hypertrophic cardiomyopathy, which may, in some cases, cause premature death. FA is caused by insufficient levels of the protein, frataxin, which is involved in mitochondrial iron metabolism. All patients carry at least one copy of an intronic GAA triplet-repeat expansion that interferes with frataxin transcription. Normal chromosomes contain up to 35 to 40 GAA triplets in an Alu sequence localized in the first intron of the frataxin gene; FA chromosomes carry from approx 70 to more than 1000 GAA triplets. The molecular diagnosis of FA is, therefore, based on the detection of this expansion, which is present in homozygosity in more than 95% of the cases. The remaining patients are heterozygous for the GAA expansion and carry a frataxin point mutation as the other pathogenic allele. The expanded GAA triplet repeat may be detected by polymerase chain reaction (PCR) amplification followed by agarose gel electrophoresis analysis. In our hands, carefully performed PCR testing, in particular, if fragment detection is enhanced by hybridization with a GAA oligonucleotide probe, is as effective in identifying patients and carriers as is Southern blot analysis of genomic DNA, and allows a more accurate sizing of the repeat. Furthermore, in the case of smaller expansions, the amplified fragment may be directly sequenced to identify very rare nonpathogenic variant repeats, such as GAAGGA. Sequence analysis of the five coding exons of the frataxin gene should be performed in clinically affected individuals who are heterozygous for an expanded GAA repeat to identify point mutations.

  10. Modelling property changes in graphite irradiated at changing irradiation temperature

    CSIR Research Space (South Africa)

    Kok, S

    2011-01-01

    Full Text Available A new method is proposed to predict the irradiation induced property changes in nuclear; graphite, including the effect of a change in irradiation temperature. The currently used method; to account for changes in irradiation temperature, the scaled...

  11. High temperature GaAs X-ray detectors

    Science.gov (United States)

    Lioliou, G.; Whitaker, M. D. C.; Barnett, A. M.

    2017-12-01

    Two GaAs p+-i-n+ mesa X-ray photodiodes were characterized for their electrical and photon counting X-ray spectroscopic performance over the temperature range of 100 °C to -20 °C. The devices had 10 μm thick i layers with different diameters: 200 μm (D1) and 400 μm (D2). The electrical characterization included dark current and capacitance measurements at internal electric field strengths of up to 50 kV/cm. The determined properties of the two devices were compared with previously reported results that were made with a view to informing the future development of photon counting X-ray spectrometers for harsh environments, e.g., X-ray fluorescence spectroscopy of planetary surfaces in high temperature environments. The best energy resolution obtained (Full Width at Half Maximum at 5.9 keV) decreased from 2.00 keV at 100 °C to 0.66 keV at -20 °C for the spectrometer with D1, and from 2.71 keV at 100 °C to 0.71 keV at -20 °C for the spectrometer with D2. Dielectric noise was found to be the dominant source of noise in the spectra, apart from at high temperatures and long shaping times, where the main source of photopeak broadening was found to be the white parallel noise.

  12. Optical parametric oscillation in orientation patterned GaAs waveguides

    Science.gov (United States)

    Oron, M. B.; Blau, P.; Pearl, S.; Katz, M.

    2012-02-01

    Orientation patterned GaAs waveguides for parametric conversion from near to mid-infrared have been fabricated by MOCVD growth on OPGaAs templates. A monolithic OPO cavity was formed by dielectric facet coating. Parametric oscillation characteristics were investigated using a pulsed source tunable in the range of 1.98-2.05μm. Type I and II parametric interactions have been observed, differing in QPM wavelength. OPO threshold power of 7W, using a pulsed pump, and 5.7W using a CW laser was obtained in a 13mm long waveguide of 39μm period. Overall Parametric peak power of 0.6W at pulsed pump peak power of 11.6W was generated at signal & idler wavelengths of 3.6μm & 4.5μm respectively and pump wavelength of 2.015μm. Tuning curves for Type I and type II parametric operation in OPGaAs WGs have been calculated and verified by the measured signal and idler wavelengths.

  13. 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.

  14. Optically pumped room-temperature GaAs nanowire lasers

    Science.gov (United States)

    Saxena, Dhruv; Mokkapati, Sudha; Parkinson, Patrick; Jiang, Nian; Gao, Qiang; Tan, Hark Hoe; Jagadish, Chennupati

    2013-12-01

    Near-infrared lasers are important for optical data communication, spectroscopy and medical diagnosis. Semiconductor nanowires offer the possibility of reducing the footprint of devices for three-dimensional device integration and hence are being extensively studied in the context of optoelectronic devices. Although visible and ultraviolet nanowire lasers have been demonstrated widely, progress towards room-temperature infrared nanowire lasers has been limited because of material quality issues and Auger recombination. (Al)GaAs is an important material system for infrared lasers that is extensively used for conventional lasers. GaAs has a very large surface recombination velocity, which is a serious issue for nanowire devices because of their large surface-to-volume ratio. Here, we demonstrate room-temperature lasing in core-shell-cap GaAs/AlGaAs/GaAs nanowires by properly designing the Fabry-Pérot cavity, optimizing the material quality and minimizing surface recombination. Our demonstration is a major step towards incorporating (Al)GaAs nanowire lasers into the design of nanoscale optoelectronic devices operating at near-infrared wavelengths.

  15. Analysis of the active layer in SI GaAs Schottky diodes

    Energy Technology Data Exchange (ETDEWEB)

    Castaldini, A.; Cavallini, A.; Polenta, L. [Bologna Univ. (Italy). Dipt. di Fisica]|[INFM, Bologna (Italy); Canali, C. [INFM and Dipartimento di Scienze dell`Ingegneria, Universita` di Modena, Via Campi 213/B, Modena (Italy); Nava, F. [INFN and Dipartimento di Fisica, Universita` di Modena, Via Campi 213/A, Modena (Italy)

    1998-06-01

    The behavior of the active region width W of semi-insulating gallium arsenide Schottky diodes versus reverse biasing has been investigated by optical beam induced current and surface potential techniques. It has been found that at low applied voltages, W follows the square root law peculiar to a Schottky barrier while, for a bias higher than 20 V, the active layer increases linearly with the voltage applied. To go deeper into this matter, the spatial distribution of the electric field has been analyzed in a wide range of bias voltages and it has been observed that at high voltages a plateau occurs, followed by a linear decrease down to a quasi-zero value. In terms of space charge distribution this means that there is a box-shaped space charge region moving towards the ohmic contact at increasing bias. (orig.) 21 refs.

  16. Irradiation Creep in Graphite

    Energy Technology Data Exchange (ETDEWEB)

    Ubic, Rick; Butt, Darryl; Windes, William

    2014-03-13

    An understanding of the underlying mechanisms of irradiation creep in graphite material is required to correctly interpret experimental data, explain micromechanical modeling results, and predict whole-core behavior. This project will focus on experimental microscopic data to demonstrate the mechanism of irradiation creep. High-resolution transmission electron microscopy should be able to image both the dislocations in graphite and the irradiation-induced interstitial clusters that pin those dislocations. The team will first prepare and characterize nanoscale samples of virgin nuclear graphite in a transmission electron microscope. Additional samples will be irradiated to varying degrees at the Advanced Test Reactor (ATR) facility and similarly characterized. Researchers will record microstructures and crystal defects and suggest a mechanism for irradiation creep based on the results. In addition, the purchase of a tensile holder for a transmission electron microscope will allow, for the first time, in situ observation of creep behavior on the microstructure and crystallographic defects.

  17. Large Lateral Photovoltaic Effect in MoS2/GaAs Heterojunction

    Science.gov (United States)

    Hao, Lanzhong; Liu, Yunjie; Han, Zhide; Xu, Zhijie; Zhu, Jun

    2017-10-01

    Molybdenum disulfide (MoS2) nanoscaled films are deposited on GaAs substrates via magnetron sputtering technique, and MoS2/GaAs heterojunctions are fabricated. The lateral photovoltaic effect (LPE) of the fabricated MoS2/GaAs heterojunctions is investigated. The results show that a large LPE can be obtained in the MoS2/ n-GaAs heterojunction. The LPE exhibits a linear dependence on the position of the laser illumination and the considerably high sensitivity of 416.4 mV mm- 1. This sensitivity is much larger than the values in other reported MoS2-based devices. Comparatively, the LPE in the MoS2/ p-GaAs heterojunction is much weaker. The mechanisms to the LPE are unveiled by constructing the energy-band alignment of the MoS2/GaAs heterojunctions. The excellent LPE characteristics make MoS2 films combined with GaAs semiconductors promising candidates for the application of high-performance position-sensitive detectors.

  18. 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.

  19. Mosaic GaAs crystals for hard x-ray astronomy

    Science.gov (United States)

    Ferrari, C.; Zanotti, L.; Zappettini, A.; Arumainathan, S.

    2008-08-01

    Recently the design of a Laue lens with field of view of 30 arcseconds and for x-rays in the energy range from 100 keV to 1 MeV has been proposed in which mosaic crystals are used as focussing elements. The proper mosaic angular spread is chosen as a compromise between intensity and energy resolution of the Laue lens. In the present work we consider the use of GaAs crystals as optical elements for hard x-ray astronomy. GaAs crystals have essentially the same electron density and lattice spacing as germanium, and are characterized by spontaneous formation of "cellular structures" with dislocations distribution at the boundaries between perfect zones of the crystal. Because of the presence of cellular structures Czochralsky grown GaAs show a natural degree of mosaicity. Several GaAs ingots grown by liquid encapsulating Czochralsky technique have been characterized by high resolution x-ray diffraction. Bragg diffraction profiles have been measured along ingot axes and diameters of doped, undoped or stoichiometry deviated GaAs crystals. Full width at half maximum values ranging from 15 to 40 arcseconds depending on the position were measured close to the proposed 30 arcsecond mosaicity required for the Laue lens. Appropriate growth conditions allow the control of the dislocation density and the modification of cellular structure responsible of the crystal mosaicity so that the possibility of obtaining crystals with a given degree of mosaicity by tuning the LEC growth conditions is proposed.

  20. 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.

  1. 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...

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

    Science.gov (United States)

    Yeh, Y. C. M.

    1981-01-01

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

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

    Science.gov (United States)

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

    2016-08-02

    Friedreich's ataxia (FRDA) is caused by the expansion of GAA repeats located in the Frataxin (FXN) gene. The GAA repeats continue to expand in FRDA patients, aggravating symptoms and contributing to disease progression. The mechanism leading to repeat expansion and decreased FXN transcription remains unclear. Using single-molecule analysis of replicated DNA, we detected that expanded GAA repeats present a substantial obstacle for the replication machinery at the FXN locus in FRDA cells. Furthermore, aberrant origin activation and lack of a proper stress response to rescue the stalled forks in FRDA cells cause an increase in 3'-5' progressing forks, which could enhance repeat expansion and hinder FXN transcription by head-on collision with RNA polymerases. Treatment of FRDA cells with GAA-specific polyamides rescues DNA replication fork stalling and alleviates expansion of the GAA repeats, implicating DNA triplexes as a replication impediment and suggesting that fork stalling might be a therapeutic target for FRDA. Copyright © 2016 The Author(s). Published by Elsevier Inc. All rights reserved.

  4. Structure-specific recognition of Friedreich's ataxia (GAA)n repeats by benzoquinoquinoxaline derivatives.

    Science.gov (United States)

    Bergquist, Helen; Nikravesh, Abbas; Fernández, Raquel Domingo; Larsson, Veronica; Nguyen, Chi-Hung; Good, Liam; Zain, Rula

    2009-11-02

    Expansion of GAA triplet repeats in intron 1 of the FXN gene reduces frataxin expression and causes Friedreich's ataxia. (GAA)n repeats form non-B-DNA structures, including triple helix H-DNA and higher-order structures (sticky DNA). In the proposed mechanisms of frataxin gene silencing, central unanswered questions involve the characterization of non-B-DNA structure(s) that are strongly suggested to play a role in frataxin expression. Here we examined (GAA)n binding by triplex-stabilizing benzoquinoquinoxaline (BQQ) and the corresponding triplex-DNA-cleaving BQQ-1,10-phenanthroline (BQQ-OP) compounds. We also examined the ability of these compounds to act as structural probes for H-DNA formation within higher-order structures at pathological frataxin sequences in plasmids. DNA-complex-formation analyses with a gel-mobility-shift assay and sequence-specific probing of H-DNA-forming (GAA)n sequences by single-strand oligonucleotides and triplex-directed cleavage demonstrated that a parallel pyrimidine (rather than purine) triplex is the more stable motif formed at (GAA)n repeats under physiologically relevant conditions.

  5. Homozygotic intronic GAA mutation in three siblings with late-onset Pompe's disease.

    Science.gov (United States)

    Grzesiuk, Anderson Kuntz; Shinjo, Sueli Mieko Oba; da Silva, Roseli; Machado, Marcela; Galera, Marcial Francis; Marie, Suely Kazue Nagahashi

    2010-04-01

    Pompe's disease (PD) is a metabolic myopathy caused by the accumulation of lysosomal glycogen, secondary to acid alpha-glucosidase (GAA) enzyme deficiency. Childhood and late-onset forms are described, differing by the age of onset and symptoms. In this study were analyzed affected siblings with Pompe's disease (PD) and their distinct clinical and pathological presentations. Diagnosis was performed by the clinical presentation of limb-girdle dystrophies and respiratory compromise. Confirmatory diagnoses were conducted by muscle biopsy, GAA activity measurement and by GAA gene genotyping. The findings suggested muscular involvement due to GAA deficiency. GAA genotyping showed they are homozygous for the c.-32-3C>A mutation. Herein we reported a family where three out of five siblings were diagnosed with late-onset PD, although it is a rare metabolic disease inherited in an autossomal recessive manner. We emphasize the importance of including this presentation within the differential diagnoses of the limb-girdle dystrophies once enzyme replacement therapy is available.

  6. Origin of the suppression in low frequency terahertz conductivity in dilute GaAs nitride and bismide alloys

    DEFF Research Database (Denmark)

    Cocker, Tylor; Lu, Xianfeng; Cooke, David

    We have performed time-resolved terahertz spectroscopy on GaAs1-xBix (x=7%) and observed a low-frequency suppression of the real conductivity previously seen only in dilute GaAs nitrides. We have developed a modified Drude model with a frequency-dependent scattering time that provides excellent a...

  7. 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.

  8. Spectrally resolved localized states in GaAs1- x Bi x

    Science.gov (United States)

    Christian, Theresa M.; Alberi, Kirstin; Beaton, Daniel A.; Fluegel, Brian; Mascarenhas, Angelo

    2017-03-01

    The role of localized states and their influence on the broader band structure remains a crucial question in understanding the band structure evolution in GaAs1- x Bi x . In this work, we present clear spectroscopic observations of recombination at several localized states in GaAs1- x Bi x . Sharp and recognizable photoluminescence features appear in multiple samples and redshift as a function of GaBi fraction between x = 0.16% and 0.4% at a linearized rate of 34 meV per % Bi, weaker than the redshift associated with band-to-band recombination. Interpreting these results in terms of radiative recombination between localized holes and free electrons sheds light on the relative movement of the conduction band minimum and the characteristics of localized bismuth-related trap states in GaAs1- x Bi x alloys.

  9. Tensile GaAs(111) quantum dashes with tunable luminescence below the bulk bandgap

    Energy Technology Data Exchange (ETDEWEB)

    Yerino, Christopher D., E-mail: christopher.yerino@yale.edu; Jung, Daehwan; Lee, Minjoo Larry [Department of Electrical Engineering, Yale University, New Haven, Connecticut 06520 (United States); Simmonds, Paul J.; Liang, Baolai [California NanoSystems Institute, University of California, Los Angeles, California 90095 (United States); Dorogan, Vitaliy G.; Ware, Morgan E.; Mazur, Yuriy I.; Salamo, Gregory J. [Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, Arkansas 72701 (United States); Huffaker, Diana L. [California NanoSystems Institute, University of California, Los Angeles, California 90095 (United States); Department of Electrical Engineering, University of California, Los Angeles, California 90095 (United States)

    2014-08-18

    Strain-based band engineering in quantum dots and dashes has been predominantly limited to compressively strained systems. However, tensile strain strongly reduces the bandgaps of nanostructures, enabling nanostructures to emit light at lower energies than they could under compressive strain. We demonstrate the self-assembled growth of dislocation-free GaAs quantum dashes on an InP(111)B substrate, using a 3.8% tensile lattice-mismatch. Due to the high tensile strain, the GaAs quantum dashes luminesce at 110–240 meV below the bandgap of bulk GaAs. The emission energy is readily tuned by adjusting the size of the quantum dashes via deposition thickness. Tensile self-assembly creates new opportunities for engineering the band alignment, band structure, and optical properties of epitaxial nanostructures.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-11-15

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

  11. Nanoscale Footprints of Self-Running Gallium Droplets on GaAs Surface

    Science.gov (United States)

    Wu, Jiang; Wang, Zhiming M.; Li, Alvason Z.; Benamara, Mourad; Li, Shibin; Salamo, Gregory J.

    2011-01-01

    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. PMID:21673965

  12. 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.

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

    Science.gov (United States)

    Lajnef, M.; Chtourou, R.; Ezzaouia, H.

    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 Shottky junctions. The electric analysis allowed us to determine the n factor and the barrier height Фb0 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.

  14. 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.

  15. XPS study of chemically etched GaAs and InP

    Science.gov (United States)

    Bertrand, P. A.

    1982-03-01

    The surface composition of p-type GaAs etched in HCl or Br2 in methanol, and n-type InP etched in HCl, H2SO4, HNO3 or Br2 in methanol were studied by means of X-ray photoelectron spectroscopy (XPS). The surface compositions of GaAs and the binding energy of the surface As atoms vary with the etching solution and with the extent of oxidation of the surface. The full width at half-maximum of the Ga(3p) photoelectron peak increases upon exposure of etched GaAs to air. The XPS results are compared with Schottky barrier heights previously measured for similarly prepared surfaces with Pb contacts. The amount of oxidized P on InP surfaces is higher after an HNO3 etch than after HCl, H2SO4, of Br2/methanol treatments. An HCl etch leaves an unoxidized slightly In-rich surface.

  16. 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%.

  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. Spin lifetimes of electrons injected into GaAs and GaN

    Science.gov (United States)

    Krishnamurthy, Srinivasan; van Schilfgaarde, Mark; Newman, Nathan

    2003-09-01

    The spin relaxation times of electrons in GaAs and GaN are determined with a model that includes momentum scattering by phonons and ionized impurities, and spin scattering by the Elliot-Yafet, D'yakonov-Perel, and Bir-Aronov-Pikus mechanisms. Accurate bands generated using a long-range tight-binding Hamiltonian obtained from empirical pseudopotentials are used. The inferred temperature dependence of the spin relaxation lifetime agrees well with measured values in GaAs. We further show that the spin lifetimes decrease rapidly with injected electron energy and reach a local maximum at the longitudinal optical phonon energy. Our calculation predicts that electron spin lifetime in pure GaN is about three orders of magnitude longer than in GaAs at all temperatures, primarily as a result of the lower spin-orbit interaction and higher conduction band density of states.

  19. Excision of Expanded GAA Repeats Alleviates the Molecular Phenotype of Friedreich's Ataxia.

    Science.gov (United States)

    Li, Yanjie; Polak, Urszula; Bhalla, Angela D; Rozwadowska, Natalia; Butler, Jill Sergesketter; Lynch, David R; Dent, Sharon Y R; Napierala, Marek

    2015-06-01

    Friedreich's ataxia (FRDA) is an autosomal recessive neurological disease caused by expansions of guanine-adenine-adenine (GAA) repeats in intron 1 of the frataxin (FXN) gene. The expansion results in significantly decreased frataxin expression. We report that human FRDA cells can be corrected by zinc finger nuclease-mediated excision of the expanded GAA repeats. Editing of a single expanded GAA allele created heterozygous, FRDA carrier-like cells and significantly increased frataxin expression. This correction persisted during reprogramming of zinc finger nuclease-edited fibroblasts to induced pluripotent stem cells and subsequent differentiation into neurons. The expression of FRDA biomarkers was normalized in corrected patient cells and disease-associated phenotypes, such as decreases in aconitase activity and intracellular ATP levels, were reversed in zinc finger nuclease corrected neuronal cells. Genetically and phenotypically corrected patient cells represent not only a preferred disease-relevant model system to study pathogenic mechanisms, but also a critical step towards development of cell replacement therapy.

  20. 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.

  1. Production of nanometer-size GaAs nanocristals by nanosecond laser ablation in liquid.

    Science.gov (United States)

    Abderrafi, Kamal; Jiménez, Ernesto; Ben, Teresa; Molina, Sergio I; Ibáñez, Rafael; Chirvony, Vladimir; Martínez-Pastor, Juan P

    2012-08-01

    This paper reports the formation and characterization of spherical GaAs quantum dots obtained by nanosecond pulsed laser ablation in a liquid (ethanol or methanol). The produced bare GaAs nanoparticles demonstrate rather narrow size distribution which depends on the applied laser power density (from 4.25 to 13.9 J/cm2 in our experiments) and is as low as 2.5 nm for the highest power used. The absolute value of the average diameter also decreases significantly, from 13.7 to 8.7 nm, as the laser power increases in this interval. Due to the narrow nanoparticle size dispersion achieved at the highest laser powers two absorption band edges are clearly distinguishable at about 1.72 and 3.15 eV which are ascribed to E0 and E1 effective optical transitions, respectively. A comparison of the energies with those known for bulk GaAs allows one to conclude that an average diameter of the investigated GaAs nanoparticles is close to 10 nm, i.e., they are quantum dots. High resolution transmission electron microscopy (HRTEM) images show that the bare GaAs nanoparticles are nanocrystalline, but many of them exhibit single/multiple twin boundary defects or even polycrystallinity. The formation of the GaAs crystalline core capped with a SiO2 shell was demonstrated by HRTEM and energy dispersive X-ray (EDX) spectroscopy. Effective band edges can be better distinguished in SiO2 capped nanoparticles than in bare ones, In both cases the band edges are correlated with size quantum confinement effect.

  2. 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.

  3. Involvement of Agrobacterium tumefaciens Galacturonate Tripartite ATP-Independent Periplasmic (TRAP) Transporter GaaPQM in Virulence Gene Expression.

    Science.gov (United States)

    Zhao, Jinlei; Binns, Andrew N

    2015-12-04

    Monosaccharides capable of serving as nutrients for the soil bacterium Agrobacterium tumefaciens are also inducers of the vir regulon present in the tumor-inducing (Ti) plasmid of this plant pathogen. One such monosaccharide is galacturonate, the predominant monomer of pectin found in plant cell walls. This ligand is recognized by the periplasmic sugar binding protein ChvE, which interacts with the VirA histidine kinase that controls vir gene expression. Although ChvE is also a member of the ChvE-MmsAB ABC transporter involved in the utilization of many neutral sugars, it is not involved in galacturonate utilization. In this study, a putative tripartite ATP-independent periplasmic (TRAP) transporter, GaaPQM, is shown to be essential for the utilization of galacturonic acid; we show that residue R169 in the predicted sugar binding site of the GaaP is required for activity. The gene upstream of gaaPQM (gaaR) encodes a member of the GntR family of regulators. GaaR is shown to repress the expression of gaaPQM, and the repression is relieved in the presence of the substrate for GaaPQM. Moreover, GaaR is shown to bind putative promoter regions in the sequences required for galacturonic acid utilization. Finally, A. tumefaciens strains carrying a deletion of gaaPQM are more sensitive to galacturonate as an inducer of vir gene expression, while the overexpression of gaaPQM results in strains being less sensitive to this vir inducer. This supports a model in which transporter activity is crucial in ensuring that vir gene expression occurs only at sites of high ligand concentration, such as those at a plant wound site. Copyright © 2016, American Society for Microbiology. All Rights Reserved.

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

    Science.gov (United States)

    Bergquist, Helen; Rocha, Cristina S J; Álvarez-Asencio, Rubén; Nguyen, Chi-Hung; Rutland, Mark W; Smith, C I Edvard; Good, Liam; Nielsen, Peter E; Zain, Rula

    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 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)4-PNA binding of the repeat abolished all detectable triplex DNA structures, whereas (CTT)5-PNA did not. We present evidence that (GAA)4-PNA can invade the DNA at the repeat region by binding the DNA CTT strand, thereby preventing non-canonical-DNA formation, and that triplex invasion complexes by (CTT)5-PNA form at the GAA repeats. Locked nucleic acid (LNA) oligonucleotides also inhibited triplex formation at GAA repeat expansions, and atomic force microscopy analysis showed significant relaxation of plasmid morphology in the presence of GAA-LNA. Thus, by inhibiting disease related higher order DNA structures in the Frataxin gene, such PNA and LNA oligomers may have potential for discovery of drugs aiming at recovering Frataxin expression.

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

    Science.gov (United States)

    Bergquist, Helen; Rocha, Cristina S. J.; Álvarez-Asencio, Rubén; Nguyen, Chi-Hung; Rutland, Mark. W.; Smith, C. I. Edvard; Good, Liam; Nielsen, Peter E.; Zain, Rula

    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 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)4-PNA binding of the repeat abolished all detectable triplex DNA structures, whereas (CTT)5-PNA did not. We present evidence that (GAA)4-PNA can invade the DNA at the repeat region by binding the DNA CTT strand, thereby preventing non-canonical-DNA formation, and that triplex invasion complexes by (CTT)5-PNA form at the GAA repeats. Locked nucleic acid (LNA) oligonucleotides also inhibited triplex formation at GAA repeat expansions, and atomic force microscopy analysis showed significant relaxation of plasmid morphology in the presence of GAA-LNA. Thus, by inhibiting disease related higher order DNA structures in the Frataxin gene, such PNA and LNA oligomers may have potential for discovery of drugs aiming at recovering Frataxin expression. PMID:27846236

  6. NANOSTRUCTURE PATTERNING UNDER ENERGETIC PARTICLE BEAM IRRADIATION

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Lumin [Regents of the University of Michigan; Lu, Wei [Regents of the University of Michigan

    2013-01-31

    Energetic ion bombardment can lead to the development of complex and diverse nanostructures on or beneath the material surface through induced self-organization processes. These self-organized structures have received particular interest recently as promising candidates as simple, inexpensive, and large area patterns, whose optical, electronic and magnetic properties are different from those in the bulk materials [1-5]. Compared to the low mass efficiency production rate of lithographic methods, these self-organized approaches display new routes for the fabrication of nanostructures over large areas in a short processing time at the nanoscale, beyond the limits of lithography [1,4]. Although it is believed that surface nanostructure formation is based on the morphological instability of the sputtered surface, driven by a kinetic balance between roughening and smoothing actions [6,7], the fundamental mechanisms and experimental conditions for the formation of these nanostructures has still not been well established, the formation of the 3-D naopatterns beneath the irradiated surface especially needs more exploration. During the last funding period, we have focused our efforts on irradiation-induced nanostructures in a broad range of materials. These structures have been studied primarily through in situ electron microscopy during electron or ion irradiation. In particular, we have performed studies on 3-D void/bubble lattices (in metals and CaF2), embedded sponge-like porous structure with uniform nanofibers in irradiated semiconductors (Ge, GaSb, and InSb), 2-D highly ordered pattern of nanodroplets (on the surface of GaAs), hexagonally ordered nanoholes (on the surface of Ge), and 1-D highly ordered ripple and periodic arrays (of Cu nanoparticles) [3,8-11]. The amazing common feature in those nanopatterns is the uniformity of the size of nanoelements (nanoripples, nanodots, nanovoids or nanofibers) and the distance separating them. Our research focuses on the

  7. A 600-MHz median-type digital filter on GaAs

    Science.gov (United States)

    Vainjo, Olli; Sundaram, Mani; Long, Stephen I.; Neuvo, Yrjo

    1992-01-01

    A single-chip GaAs implementation of an FIR-median hybrid filter is presented. The very high-speed digital filter combines linear averaging structures to a median selector. The filter operates on 5-b samples with ECL-compatible I/O interfaces. The 1500-transistor LSI device with 3.6-sq mm chip size was processed with a 1.0-micron GaAs depletion-mode (D-mode) MESFET process. The filter demonstrates 600-MHz sample rate when operated in test mode utilizing special built-in feedback.

  8. Measurement of the Thermal Diffusivity of GaAs by Pulsed Photothermal Spectroscopy

    Science.gov (United States)

    Bennis, G. L.; Vyas, Reeta; Gupta, R.; Ang, S.; Brown, W. D.

    1997-03-01

    Pulsed photothermal spectroscopy has been used to measure thermal diffusivity of GaAs. In this technique, a short pulse of radiation from a Ti-Sapphire laser is used to produce local heating on a sample of GaAs wafer. The heating of the sample is monitored by deflection of a weak cw laser beam (probe beam). The thermal diffusivity of the sample is deduced from the time evolution of the deflection of the probe beam. Results of the latest measurements will be presented.

  9. Hopping conduction in GaAs layers grown by molecular-beam epitaxy at low temperatures

    OpenAIRE

    Shimogishi, F.; Mukai, K; Fukushima, S; Otsuka, N.

    2002-01-01

    The electrical conductivity of GaAs layers grown by molecular-beam epitaxy at low temperatures was studied by using the van der Pauw method. The electrical conductivity of thick GaAs layers grown at temperatures above 200 °C changes with the concentration of antisite As atoms following the nearest-neighbor hopping model. From the dependence of the conductivity on the average spacing of antisite As atoms, the Bohr radius of the donor wave function in the hydrogen like model was estimated to be...

  10. Periodically oriented GaAs templates and waveguide structures for frequency conversion

    Science.gov (United States)

    Oron, M. B.; Shusterman, S.; Blau, P.

    2008-02-01

    Material preparation methods and device fabrication technologies for realization of low loss periodically oriented GaAs waveguides are reported. Planar waveguide structures were grown by MOCVD on periodically patterned templates prepared by wafer bonding and selective layer removal. Ridge waveguides were designed and fabricated from the planar structures with emphasis on waveguide loss minimization. Record low losses of 2.0db/cm in periodically oriented waveguides and 0.95db/cm in single domain waveguides were measured. Routes for further loss reduction in patterned GaAs waveguides are discussed and initial results from further work to reduce waveguide corrugation are presented.

  11. 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.

  12. Anomalous Coulomb drag between bilayer graphene and a GaAs electron gas

    Science.gov (United States)

    Simonet, Pauline; Hennel, Szymon; Overweg, Hiske; Steinacher, Richard; Eich, Marius; Pisoni, Riccardo; Lee, Yongjin; Märki, Peter; Ihn, Thomas; Ensslin, Klaus; Beck, Mattias; Faist, Jérôme

    2017-10-01

    We report on Coulomb drag experiments between a bilayer graphene flake and a GaAs two-dimensional electron gas, where the charge-carrier densities of both systems can be tuned independently. For both p- and n-type graphene charge carriers, we observe that the Coulomb drag unexpectedly changes direction when the temperature is lowered. We find this phenomenon to be dominant when the Fermi wave vector in graphene is larger than in GaAs. At temperatures above ≈ 70 {{K}}, the drag signal is consistent with momentum exchange. In all discussed regimes, the Onsager relation is respected.

  13. Photoconductive optically driven deformable membrane for spatial light modulator applications utilizing GaAs substrates

    Science.gov (United States)

    Haji-Saeed, Bahareh; Kolluru, Rathna; Pyburn, Dana; Leon, Roberto; Sengupta, Sandip K.; Testorf, Markus; Goodhue, William; Khoury, Jed; Drehman, Alvin; Woods, Charles L.; Kierstead, John

    2006-04-01

    The fabrication and characterization of an optically addressable deformable mirror for a spatial light modulator is described. Device operation utilizes an electrostatically driven pixellated aluminized polymeric membrane mirror supported above an optically controlled photoconductive GaAs substrate. A 5 μm thick grid of patterned photoresist supports the 2 μm thick aluminized Mylar membrane. A conductive ZnO layer is placed on the back side of the GaAs wafer. A standard Michelson interferometer is used to measure mirror deformation data as a function of illumination, applied voltage, and frequency. A simplified analysis of device operation is also presented.

  14. Super-Lattice Light Emitting Diodes (SLEDS) on GaAs

    Science.gov (United States)

    2016-03-31

    epitaxial growth to expose the underlying GaAs crystal . This process must be done carefully when growing on an integrated circuit (IC) susceptible to...relaxed, GaSb layers must first be grown on GaAs. When a relaxed layer forms, stress should ideally be relieved with 90° or Lomar dislocations which...characterization,” J. Crystal Growth 111, 683 (1991). [6] I. Vurgaftman, J. R. Meyer, C.A. Hoffman, D. Redfern, J. Antoszewski, L. Faraone, and J. R

  15. 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.

  16. 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....

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-12-04

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

  18. Complexes between two GAA Repeats within DNA introduced into Cos-1 cells.

    Science.gov (United States)

    Krasilnikova, Maria M

    2012-11-01

    We have recently shown that GAA repeats severely impede replication elongation during the first replication cycle of transfected DNA wherein the chromatin is still at the formation stage.(1) Here we extend this study by showing that two GAA repeats located within the same plasmid in the direct orientation can form complexes upon transient transfection of mammalian Cos-1 cells. However, these complexes do not form in DNA that went through several replication rounds in mammalian cells. We suggest that formation of such complexes in mammalian genomes can contribute to genomic instability.

  19. AGC-2 Irradiation Report

    Energy Technology Data Exchange (ETDEWEB)

    Rohrbaugh, David Thomas [Idaho National Lab. (INL), Idaho Falls, ID (United States); Windes, William [Idaho National Lab. (INL), Idaho Falls, ID (United States); Swank, W. David [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2016-06-01

    The Next Generation Nuclear Plant (NGNP) will be a helium-cooled, very high temperature reactor (VHTR) with a large graphite core. In past applications, graphite has been used effectively as a structural and moderator material in both research and commercial high temperature gas cooled reactor (HTGR) designs.[ , ] Nuclear graphite H 451, used previously in the United States for nuclear reactor graphite components, is no longer available. New nuclear graphites have been developed and are considered suitable candidates for the new NGNP reactor design. To support the design and licensing of NGNP core components within a commercial reactor, a complete properties database must be developed for these current grades of graphite. Quantitative data on in service material performance are required for the physical, mechanical, and thermal properties of each graphite grade with a specific emphasis on data related to the life limiting effects of irradiation creep on key physical properties of the NGNP candidate graphites. Based on experience with previous graphite core components, the phenomenon of irradiation induced creep within the graphite has been shown to be critical to the total useful lifetime of graphite components. Irradiation induced creep occurs under the simultaneous application of high temperatures, neutron irradiation, and applied stresses within the graphite components. Significant internal stresses within the graphite components can result from a second phenomenon—irradiation induced dimensional change. In this case, the graphite physically changes i.e., first shrinking and then expanding with increasing neutron dose. This disparity in material volume change can induce significant internal stresses within graphite components. Irradiation induced creep relaxes these large internal stresses, thus reducing the risk of crack formation and component failure. Obviously, higher irradiation creep levels tend to relieve more internal stress, thus allowing the

  20. Production of a functional human acid maltase in tobacco seeds: biochemical analysis, uptake by human GSDII cells, and in vivo studies in GAA knockout mice.

    Science.gov (United States)

    Martiniuk, Frank; Reggi, Serena; Tchou-Wong, Kam-Meng; Rom, William N; Busconi, Matteo; Fogher, Corrado

    2013-10-01

    Genetic deficiency of acid alpha glucosidase (GAA) results in glycogen storage disease type II (GSDII) or Pompe's disease. To investigate whether we could generate a functional recombinant human GAA enzyme (tobrhGAA) in tobacco seeds for future enzyme replacement therapy, we subcloned the human GAA cDNA into the plant expression plasmid-pBI101 under the control of the soybean β-conglycinin seed-specific promoter and biochemically analyzed the tobrhGAA. Tobacco seeds contain the metabolic machinery that is more compatible with mammalian glycosylation-phosphorylation and processing. We found the tobrhGAA to be enzymatically active was readily taken up by GSDII fibroblasts and in white blood cells from whole blood to reverse the defect. The tobrhGAA corrected the enzyme defect in tissues at 7 days after a single dose following intraperitoneal (IP) administration in GAA knockout (GAA(-/-)) mice. Additionally, we could purify the tobrhGAA since it bound tightly to the matrix of Sephadex G100 and can be eluted by competition with maltose. These data demonstrate indirectly that the tobrhGAA is fully functional, predominantly proteolytically cleaved and contains the minimal phosphorylation and mannose-6-phosphate residues essential for biological activity.

  1. 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.)

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

    Science.gov (United States)

    van der Wal, Erik; Bergsma, Atze J; van Gestel, Tom J M; In 't Groen, Stijn L M; Zaehres, Holm; Araúzo-Bravo, Marcos J; Schöler, Hans R; van der Ploeg, Ans T; Pijnappel, W W M Pim

    2017-06-16

    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. Copyright © 2017 The Author(s). Published by Elsevier Inc. All rights reserved.

  3. Replication in mammalian cells recapitulates the locus-specific differences in somatic instability of genomic GAA triplet-repeats.

    Science.gov (United States)

    M Rindler, Paul; Clark, Rhonda M; Pollard, Laura M; De Biase, Irene; Bidichandani, Sanjay I

    2006-01-01

    Friedreich ataxia is caused by an expanded (GAA.TTC)n sequence in intron 1 of the FXN gene. Small pool PCR analysis showed that pure (GAA.TTC)44+ sequences at the FXN locus are unstable in somatic cells in vivo, displaying both expansions and contractions. On searching the entire human and mouse genomes we identified three other genomic loci with pure (GAA.TTC)44+ sequences. Alleles at these loci showed mutation loads of GAA.TTC)n sequences. Repeat instability was evaluated following replication of a (GAA.TTC)115 sequence in transfected COS1 cells under the control of the SV40 origin of replication located at one of five different distances from the repeat. Indeed, depending on the location of the SV40 origin relative to the (GAA.TTC)n sequence, we noted either no instability, predominant expansion or both expansion and contraction. These data suggest that mammalian DNA replication is a possible mechanism underlying locus-specific differences in instability of GAA triplet-repeat sequences.

  4. 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.

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

    Science.gov (United States)

    Desalvo, Gregory C.; Barnett, Allen M.

    1989-01-01

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

  6. The Creation of Multimedia Resources to Support the Gaelic Athletic Association (GAA) Coach Education Programme (CEP)

    Science.gov (United States)

    Crotty, Yvonne; D'Arcy, Jimmy; Sweeney, David

    2016-01-01

    The Gaelic Athletic Association (GAA) is an Irish amateur sporting and cultural organisation. It represents in excess of 20,000 teams nationwide and is committed to supporting the development of players and coaches through its Coach Education Programme (CEP). A strategic goal of the CEP is to supplement the traditional field based coach education…

  7. Transition from ballistic to drift motion in high-field transport in GaAs

    Directory of Open Access Journals (Sweden)

    Hey R.

    2013-03-01

    Full Text Available With strong THz pulses, we measure ultrafast transport of electrons, holes, and an electron-hole plasma in GaAs. The transition from ballistic to drift-like transport is strongly influenced by electron-hole scattering.

  8. 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...

  9. 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

  10. Optically controlled current filamentation in GaAs photoconductive semiconductor switches

    Energy Technology Data Exchange (ETDEWEB)

    Zutavern, F.J.; Baca, A.; Helgeson, W.D.; Hjalmarson, H.P.; Loubriel, G.M.; McLaughlin, D.L.; O`Malley, M.W.

    1993-08-01

    The use of focused laser beams and fiber optics to control the location and density of current filaments in GaAs photoconductive semiconductor switches (PCSS) is described in this paper. An intensified CCD camera is used to monitor the infrared photoluminescence of the filaments during fast initiation of high gain switching for several sizes of lateral GaAs PCSS (e. g. 0.5{times}5, 1{times}5, 2.5{times}5, 2{times}30, and 15{times}20 mm{sup 2}). The switches are triggered with either a focused, mode-locked, Nd:YAG laser (532 and 1064 nm) or fiber-optically coupled semiconductor laser diodes ({approximately}900 nm). The dependencies of the size, location, and density of the current filaments on the optical trigger, switch voltage, and switch current will be discussed. The impact of optically controlled current filaments on device design and lifetime is emphasized. Electro-optical switching amplification is demonstrated using the high gain switching mode of GaAs (lock-on). A single semiconductor laser diode is used to trigger a small GaAs PCSS. This PCSS is used to drive a 15-element laser diode array. Both electrical and optical pulse compression, sharpening, and amplification are achieved. Estimates for electrical and optical power gains are 8000 and 750 respectively.

  11. 1 GHz GaAs Buck Converter for High Power Amplifier Modulation Applications

    NARCIS (Netherlands)

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

    2012-01-01

    A fully integrated 1 GHz buck converter output stage, including on-chip inductor and DC output filtering has been realized, in a standard high-voltage breakdown GaAs MMIC technology. This is a significant step forward in designing highspeed power control of supply-modulated HPAs (high power

  12. simulation of a nonlinear gaas mesfet model for use in the design of ...

    African Journals Online (AJOL)

    A computer program has been developed that performs a large-signal simulation of a GaAs. Metal-Semiconductor-Field-Effect-Transistor. (MESFET) using the Curtice-Ettenberg model fl]. The model is then used to desig11 11011-linear microwave circuits such as frequency multipliers a11d power amplifiers. The simulation ...

  13. Simulation of a Nonlinear GaAs MESFET Model for use in the ...

    African Journals Online (AJOL)

    A computer program has been developed that performs a large-signal simulation of a GaAs Metal-Semiconductor-Field-Effect-Transistor (MESFET) using the Curtice-Ettenberg model [1]. The model is then used to design non-linear microwave circuits such as frequency multipliers and power amplifiers. The simulation ...

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

    DEFF Research Database (Denmark)

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

    1996-01-01

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

  15. 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...

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

    Science.gov (United States)

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

    2007-06-01

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

  17. Twins and strain relaxation in zinc-blende GaAs nanowires grown on silicon

    Energy Technology Data Exchange (ETDEWEB)

    Piñero, J.C., E-mail: josecarlos.pinero@uca.es [Dpto. Ciencias de los Materiales, Universidad de Cádiz, 11510, Puerto Real, Cádiz (Spain); Araújo, D.; Pastore, C.E.; Gutierrez, M. [Dpto. Ciencias de los Materiales, Universidad de Cádiz, 11510, Puerto Real, Cádiz (Spain); Frigeri, C. [Istituto CNR-IMEM Parco Area delle Scienze 37/A, Fontanini, 43010, Parma (Italy); Benali, A.; Lelièvre, J.F.; Gendry, M. [INL-Institut des Nanotechnologies de Lyon, UMR 5270 Ecole Centrale de Lyon 36, Avenue Guy de Collongue, 69134, Ecully Cedex (France)

    2017-02-15

    Highlights: • A TEM-HREM study of GaAs nanowires, growth over Si, is presented. • Misfit dislocations are detected in the Si/GaAs magma interface. • The study demonstrates strain relaxation through twin formation in some nanowires. - Abstract: To integrate materials with large lattice mismatch as GaAs on silicon (Si) substrate, one possible approach, to improve the GaAs crystalline quality, is to use nanowires (NWs) technology. In the present contribution, NWs are grown on <111> oriented Si substrates by molecular beam epitaxy (MBE) using vapor-liquid-solid (VLS) method. Transmission electron microscopy (TEM) analyses show that NWs are mainly grown alternating wurtzite and zinc blend (ZB) phases, and only few are purely ZB. On the latter, High Resolution Electron Microscopy (HREM) evidences the presence of twins near the surface of the NW showing limited concordance with the calculations of Yuan (2013) [1], where {111} twin planes in a <111>-oriented GaAs NW attain attractive interactions mediated by surface strain. In addition, such twins allow slight strain relaxation and are probably induced by the local huge elastic strain observed by HREM in the lattice between the twin and the surface. The latter is attributed to some slight bending of the NW as shown by the inversion of the strain from one side to the other side of the NW.

  18. 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...

  19. Free Carrier Induced Spectral Shift for GaAs Filled Metallic Hole Arrays

    Science.gov (United States)

    2012-03-13

    Bahae, G. I. Stegeman, K. Al-hemyari, J. S. Aitchison , and C. N. Ironside, “Limitation due to three-photon absorption on the useful spectral range...absorption coefficient, is expressed as Eq. (3), where P indicates the principal value of the integral [20]. For intrinsic GaAs bulk, the absorption

  20. Ultralow-power GaAs MESFET MSI circuits using two-phase dynamic FET logic

    DEFF Research Database (Denmark)

    Lassen, Peter Stuhr; Long, S. I.; Nary, K. R.

    1993-01-01

    Two-phase dynamic FET logic (TDFL) gates are used in GaAs MESFET MSI circuits to implement very low power 4-b ripple carry adders and a variable modulus (2 to 31) prescaler. Operation of the adders is demonstrated at 500 MHz with an associated power dissipation of less than 1.0 mW and at 750 MHz...

  1. 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.

  2. Computer-Aided Design of Microstrip GaAs Mesfet Amplifiers

    DEFF Research Database (Denmark)

    Nielsen, Niels Ole

    1976-01-01

    Results on computer-aided design of broadband GaAs MESFET amplifiers in microstrip is presented. The analysis of an amplifier is based on measured scattering parameters and a model of the microstrip structure, which includes parasitics and junction effects. The optimized performance of one stage...

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

    DEFF Research Database (Denmark)

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

    2003-01-01

    We present scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) measurements of CdSe nanocrystals covalently attached to doped GaAs substrates using monolayers of 1,6-hexanedithiol. STM measurements showed the formation of stable, densely packed, homogeneous monolayers...

  4. Energy Band Structure Studies Of Zinc-Blende GaAs and InAs ...

    African Journals Online (AJOL)

    A self-consistent calculation of the structural and electronic properties of zinc blende GaAs and InAs has been carried out. The calculations were done using the full potential-linearized augmented plane wave (FPLAPW) method within the density functional theory (DFT). The exchange-correlation energy used is the ...

  5. A 2.5 gb/s GaAs ATM Mux Demux ASIC

    DEFF Research Database (Denmark)

    Madsen, Jens Kargaard; Lassen, Peter Stuhr

    1995-01-01

    This paper describes the design and implementation of a high speed GaAs ATM Mux Demur ASIC (AMDA) which is the key element in a high speed ATM Add-Drop unit. This unit is used in a new distributed ATM multiplexing-demultiplexing architecture for broadband switching systems. The Add-Drop unit...

  6. Wideband Monolithic Microwave Integrated Circuit Frequency Converters with GaAs mHEMT Technology

    DEFF Research Database (Denmark)

    Krozer, Viktor; Johansen, Tom Keinicke; Djurhuus, Torsten

    2005-01-01

    We present monolithic microwave integrated circuit (MMIC) frequency converter, which can be used for up and down conversion, due to the large RF and IF port bandwidth. The MMIC converters are based on commercially available GaAs mHEMT technology and are comprised of a Gilbert mixer cell core...

  7. GaAs detectors with an ultra-thin Schottky contact for spectrometry of charged particles

    Energy Technology Data Exchange (ETDEWEB)

    Chernykh, S.V., E-mail: chsv_84@mail.ru [National University of Science and Technology “MISIS”, Moscow (Russian Federation); Research Institute of Experimental and Theoretical Physics, Almaty (Kazakhstan); Chernykh, A.V. [National University of Science and Technology “MISIS”, Moscow (Russian Federation); Didenko, S.I.; Baryshnikov, F.M. [National University of Science and Technology “MISIS”, Moscow (Russian Federation); Research Institute of Experimental and Theoretical Physics, Almaty (Kazakhstan); Burtebayev, N. [Research Institute of Experimental and Theoretical Physics, Almaty (Kazakhstan); Institute of Nuclear Physics, Almaty (Kazakhstan); Britvich, G.I. [Institute of High Energy Physics, Protvino, Moscow region (Russian Federation); Chubenko, A.P. [Research Institute of Experimental and Theoretical Physics, Almaty (Kazakhstan); P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow (Russian Federation); Guly, V.G.; Glybin, Yu.N. [LLC “SNIIP Plus”, Moscow (Russian Federation); Zholdybayev, T.K.; Burtebayeva, J.T.; Nassurlla, M. [Research Institute of Experimental and Theoretical Physics, Almaty (Kazakhstan); Institute of Nuclear Physics, Almaty (Kazakhstan)

    2017-02-11

    For the first time, samples of particle detectors based on high-purity GaAs epilayers with an active area of 25 and 80 mm{sup 2} and an ultra-thin Pt Schottky barrier were fabricated for use in the spectrometry of charged particles and their operating characteristics were studied. The obtained FWHM of 14.2 (for 25 mm{sup 2} detector) and 15.5 keV (for 80 mm{sup 2} detector) on the 5.499 MeV line of {sup 238}Pu is at the level of silicon spectrometric detectors. It was found that the main component that determines the energy resolution of the detector is a fluctuation in the number of collected electron–hole pairs. This allows us to state that the obtained energy resolution is close to the limit for VPE GaAs. - Highlights: • VPE GaAs particle detectors with an active area of 25 and 80 mm{sup 2} were fabricated. • 120 Å ultra-thin Pt Schottky barrier was used as a rectifying contact. • The obtained FWHM of 14.2 keV ({sup 238}Pu) is at the level of Si spectrometric detectors. • Various components of the total energy resolution were analyzed. • It was shown that obtained energy resolution is close to its limit for VPE GaAs.

  8. Cavity Optomechnics with 150nm-thick GaAs Membrane

    DEFF Research Database (Denmark)

    Usami, K.; Melholt Nielsen, B.; Naesby, A.

    2010-01-01

    semiconductor integrated devices further. To investigate the optomechanical properties of a fabricated 150nm-thick intrinsic GaAs membrane (1.3mm1.9mm) a 975nm-laser (below band gap) is used to probe the mechanical resonances via beam deflection method. An 810nmlaser (above band gap), which is mode...

  9. Etching of GaAs substrates to create As-rich surface

    Indian Academy of Sciences (India)

    Several different cleaning procedures for GaAs (100) substrates are compared using X-ray photoelectron spectroscopy and optical microscopy. This work emphasizes the effect of the last etching step: using either HCl, HF–ethanol (5%) or static deionized water after HCl cleaning. All the procedures except HCl solution (1 ...

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

    Indian Academy of Sciences (India)

    Abstract. 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 calcula-.

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

    Indian Academy of Sciences (India)

    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 ...

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

    Indian Academy of Sciences (India)

    Administrator

    formation of qualitatively superior nanostructure under sub-bandgap photon illumination. 2. Experimental. Two pieces of samples were prepared from Cr–O doped. GaAs 〈100〉 wafer with a resistivity of 10. 7 ohm-cm in HF solution. Prior to etching the samples were degreased with acetone, propane and methanol. The Cr ...

  13. Direct determination of sizes of excitations from optical measurements on ion-implanted GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Aspnes, D.E.; Kelso, S.M.; Olson, C.G.; Lynch, D.W.

    1982-06-28

    Using a simple model that describes the decrease of the amplitudes of optical structures in ion-implanted crystals, projected areas of several valence and core excitons in GaAs are determined. The last remnant of crystal-related optical structure vanishes for crystallite areas less than (16 A)/sup 2/.

  14. 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.

  15. Very Heavily Doped N-Type GaAs Obtained With Pulsed Laser Annealing

    Science.gov (United States)

    Rys, Andrzej; Chin, Tim; Compaan, Alvin; Bhat, Ajit

    1988-08-01

    A study of carrier activation and mobility was performed in pulsed laser annealed samples of GaAs implanted with doses of Si and Se from 2.2x1012 to 6.0x1014 cm-2. The samples were annealed using a pulsed XeCl excimer laser ( λ=308 nm) and a pulsed dye laser ( λ=728 nm) with energy densities from 0.1 to 0.9 J/cm2 and a 10 nsec pulse. Very high carrier concentrations of 3x1019 and 1.5x1019 cm-3 were obtained for best n-type GaAs samples annealed with the dye laser and excimer laser, respectively. Dye laser consistently produced higher activation than excimer laser annealing. A transient reflectivity experiment was performed to identify the GaAs melt threshold and the melt phase dynamics of the GaAs,under the nitride cap. The threshold energies for cap damage were 0.34 and 0.12 J/cm2 for excimer and dye lasers, respectively. High carrier activation, as measured by Van der Pauw method, was achieved even for lightly doped samples although the room temperature Hall mobility was low. Raman spectroscopy was used to identify the threshold energies for the GaAs implant layer recrystallization and for optimum carrier activation.

  16. 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...

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

    Science.gov (United States)

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

    1992-01-01

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

  18. Conversion Matrix Analysis of GaAs HEMT Active Gilbert Cell Mixers

    OpenAIRE

    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 simulation with Angelov HEMT model in Agilent Advanced Design System (ADS) and by chip measurement results.

  19. Role of wave functions in electromagnetism : RAS from GaAs (110)

    NARCIS (Netherlands)

    Wijers, C.M.J.; de Boeij, P.L.

    2001-01-01

    We have calculated the reflectance anisotropy for the GaAs (110) surface using the discrete cellular method. This method extends the range of application of standard discrete dipole calculations by incorporating nonlocal polarizabilitites. The method adds a second quantum mechanical channel of

  20. Chromosome fragility at GAA tracts in yeast depends on repeat orientation and requires mismatch repair.

    Science.gov (United States)

    Kim, Hyun-Min; Narayanan, Vidhya; Mieczkowski, Piotr A; Petes, Thomas D; Krasilnikova, Maria M; Mirkin, Sergei M; Lobachev, Kirill S

    2008-11-05

    Expansion of triplex-forming GAA/TTC repeats in the first intron of FXN gene results in Friedreich's ataxia. Besides FXN, there are a number of other polymorphic GAA/TTC loci in the human genome where the size variations thus far have been considered to be a neutral event. Using yeast as a model system, we demonstrate that expanded GAA/TTC repeats represent a threat to eukaryotic genome integrity by triggering double-strand breaks and gross chromosomal rearrangements. The fragility potential strongly depends on the length of the tracts and orientation of the repeats relative to the replication origin, which correlates with their propensity to adopt triplex structure and to block replication progression. We show that fragility is mediated by mismatch repair machinery and requires the MutSbeta and endonuclease activity of MutLalpha. We suggest that the mechanism of GAA/TTC-induced chromosomal aberrations defined in yeast can also operate in human carriers with expanded tracts.

  1. Effects of Friedreich's ataxia GAA repeats on DNA replication in mammalian cells.

    Science.gov (United States)

    Chandok, Gurangad S; Patel, Mayank P; Mirkin, Sergei M; Krasilnikova, Maria M

    2012-05-01

    Friedreich's ataxia (FRDA) is a common hereditary degenerative neuro-muscular disorder caused by expansions of the (GAA)n repeat in the first intron of the frataxin gene. The expanded repeats from parents frequently undergo further significant length changes as they are passed on to progeny. Expanded repeats also show an age-dependent instability in somatic cells, albeit on a smaller scale than during intergenerational transmissions. Here we studied the effects of (GAA)n repeats of varying lengths and orientations on the episomal DNA replication in mammalian cells. We have recently shown that the very first round of the transfected DNA replication occurs in the lack of the mature chromatin, does not depend on the episomal replication origin and initiates at multiple single-stranded regions of plasmid DNA. We now found that expanded GAA repeats severely block this first replication round post plasmid transfection, while the subsequent replication cycles are only mildly affected. The fact that GAA repeats affect various replication modes in a different way might shed light on their differential expansions characteristic for FRDA.

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

    Science.gov (United States)

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

    2016-06-15

    Respiratory and/or lingual dysfunction are among the first motor symptoms in Pompe disease, a disorder resulting from absence or dysfunction of the lysosomal enzyme acid α-glucosidase (GAA). Here, we histologically evaluated the medulla, cervical and thoracic spinal cords in 6 weeks old asymptomatic Pompe (Gaa(-/-)) mice to determine if neuropathology in respiratory motor regions has an early onset. Periodic acid-Schiff (PAS) staining indicated glycogen accumulation was exclusively occurring in Gaa(-/-) hypoglossal, mid-cervical and upper thoracic motoneurons. Markers of DNA damage (Tunel) and ongoing apoptosis (Cleaved Caspase 3) did not co-localize with PAS staining, but were prominent in a medullary region which included the nucleus tractus solitarius, and also in the thoracic spinal dorsal horn. We conclude that respiratory-related motoneurons are particularly susceptible to GAA deficiency and that neuronal glycogen accumulation and neurodegeneration may occur independently in early stage disease. The data support early therapeutic intervention in Pompe disease. Copyright © 2016. Published by Elsevier B.V.

  3. Carbon, oxygen, boron, hydrogen and nitrogen in the LEC growth of SI GaAs: a thermochemical approach

    Science.gov (United States)

    Korb, J.; Flade, T.; Jurisch, M.; Köhler, A.; Reinhold, Th; Weinert, B.

    1999-03-01

    The ChemSage code [Eriksson and Hack, Metall. Trans. B 12 (1990) 1013] to minimize the total Gibbs free energy was used to calculate phase equilibria in the complex thermochemical system representing LEC GaAs crystal growth which comprises the growth atmosphere, the liquid boron oxide, the GaAs melt and solid phases including the GaAs crystal. The behaviour of C, B, O, N and H in the crystal growth melt at 1509.42 K is investigated in dependence on relevant technological parameters.

  4. Solvent-mediated self-assembly of hexadecanethiol on GaAs (0 0 1)

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Xiaohuan; Dubowski, Jan J., E-mail: jan.j.dubowski@usherbrooke.ca

    2014-04-01

    Graphical abstract: - Highlights: • Outstanding quality hexadecanethiol self-assembled monolayers (HDT SAM) produced on GaAs (0 0 1) due to the mediated role of water in an alcoholic environment. • HDT SAM formed in chloroform exhibit excellent electronic passivation properties in contrast to their structural characteristics. • Low dielectric constant solvents do not necessary provide conditions advantageous for the formation of high quality alkanethiol SAM. • Photoluminescence emitting materials allow to investigate the mechanisms of both electronic and chemical passivation and, thus, they are an excellent platform for studying the mechanisms of SAM formation on solid substrates. - Abstract: We have investigated the influence of solvents on the quality of hexadecanethiol (HDT) self-assembled monolayers (SAM) formed on GaAs (0 0 1) in chloroform, ethanol and ethanol/water 1:1 characterized by their increasing dielectric constants from 4.8 (chloroform) to 24.5 (ethanol) and water (80.1). Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) data show that the incubation in ethanol/water 1:1 solution creates conditions favouring inter-molecular interaction leading to the formation of an outstanding quality HDT SAM on GaAs (0 0 1). Incubation in low-dielectric constant solvents is not offering advantageous conditions for growing HDT SAM on GaAs. The chloroform environment, while weakening the thiol–thiol interaction, induces the oxidation of the GaAs surface and, in particular, formation of Ga{sub 2}O{sub 3}. This reduces the concentration of surface defects responsible for non-radiative recombination and leads to an enhanced photoluminescence emission, despite the fact that HDT SAM formed in chloroform are highly disordered, exhibiting the worst chemical passivation among the investigated samples.

  5. 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.

  6. Alleviating GAA Repeat Induced Transcriptional Silencing of the Friedreich's Ataxia Gene During Somatic Cell Reprogramming.

    Science.gov (United States)

    Polak, Urszula; Li, Yanjie; Butler, Jill Sergesketter; Napierala, Marek

    2016-12-01

    Friedreich's ataxia (FRDA) is the most common autosomal recessive ataxia. This severe neurodegenerative disease is caused by an expansion of guanine-adenine-adenine (GAA) repeats located in the first intron of the frataxin (FXN) gene, which represses its transcription. Although transcriptional silencing is associated with heterochromatin-like changes in the vicinity of the expanded GAAs, the exact mechanism and pathways involved in transcriptional inhibition are largely unknown. As major remodeling of the epigenome is associated with somatic cell reprogramming, modulating chromatin modification pathways during the cellular transition from a somatic to a pluripotent state is likely to generate permanent changes to the epigenetic landscape. We hypothesize that the epigenetic modifications in the vicinity of the GAA repeats can be reversed by pharmacological modulation during somatic cell reprogramming. We reprogrammed FRDA fibroblasts into induced pluripotent stem cells (iPSCs) in the presence of various small molecules that target DNA methylation and histone acetylation and methylation. Treatment of FRDA iPSCs with two compounds, sodium butyrate (NaB) and Parnate, led to an increase in FXN expression and correction of repressive marks at the FXN locus, which persisted for several passages. However, prolonged culture of the epigenetically modified FRDA iPSCs led to progressive expansions of the GAA repeats and a corresponding decrease in FXN expression. Furthermore, we uncovered that differentiation of these iPSCs into neurons also results in resilencing of the FXN gene. Taken together, these results demonstrate that transcriptional repression caused by long GAA repeat tracts can be partially or transiently reversed by altering particular epigenetic modifications, thus revealing possibilities for detailed analyses of silencing mechanism and development of new therapeutic approaches for FRDA.

  7. 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.

  8. The Birmingham Irradiation Facility

    CERN Document Server

    Dervan, P; Hodgson, P; Marin-Reyes, H; Wilson, J

    2013-01-01

    At the end of 2012 the proton irradiation facility at the CERN PS [1] will shut down for two years. With this in mind, we have been developing a new ATLAS scanning facility at the University of Birmingham Medical Physics cyclotron. With proton beams of energy approximately 30 MeV, fluences corresponding to those of the upgraded Large Hadron Collider (HL-LHC) can be reached conveniently. The facility can be used to irradiate silicon sensors, optical components and mechanical structures (e.g. carbon fibre sandwiches) for the LHC upgrade programme. Irradiations of silicon sensors can be carried out in a temperature controlled cold box that can be scanned through the beam. The facility is described in detail along with the first tests carried out with mini (1 x 1 cm^2 ) silicon sensors.

  9. 8-9 and 14-15 meu Two-Color 640x486 GaAs/AlGaAs Quantum Well Infrared Photodetector (QWIP) Focal Plane Array Camera

    Science.gov (United States)

    Guanapala, S.; Bandara, S.; Singh, A.; Liu, J.; Rafol, S.; Luong, E.; Mumolo, J.; Tran, N.; Vincent, J.; Shott, C.; hide

    1999-01-01

    An optimized long-wavelength two-color Quantum Well Infrared Phototdetector (QWIP) device structure has been designed. This device structure was grown on a three-inch semi-insulating GaAs substrate by molecular beam epitaxy (MBE).

  10. The study of 1 MeV electron irradiation induced defects in N-type and P-type monocrystalline silicon

    Science.gov (United States)

    Babaee, S.; Ghozati, S. B.

    2017-12-01

    Despite extensive use of GaAs cells in space, silicon cells are still being used. The reason is that not only they provide a good compromise between efficiency and cost, but also some countries do not have the required technology for manufacturing GaAs. Behavior of a silicon cell under any levels of charged particle irradiation could be deducted from the results of a damage equivalent 1 MeV electron irradiation using the NASA EQflux open source software package. In this paper for the first time, we have studied the behavior of a silicon cell before and after 1 MeV electron irradiation with 1014, 1015 and 1016 electrons-cm-2 fluences, using SILVACO TCAD simulation software package. Simulation was carried out at room temperature under AM0 condition. Results reveal that open circuit voltage and efficiency decrease after irradiation while short circuit current shows a slight increase in the trend around 5 × 1016 electrons-cm-2, and short circuit current loss plays an important role on efficiency changes rather than open circuit voltage.

  11. Fuel or irradiation subassembly

    Science.gov (United States)

    Seim, O.S.; Hutter, E.

    1975-12-23

    A subassembly for use in a nuclear reactor is described which incorporates a loose bundle of fuel or irradiation pins enclosed within an inner tube which in turn is enclosed within an outer coolant tube and includes a locking comb consisting of a head extending through one side of the inner sleeve and a plurality of teeth which extend through the other side of the inner sleeve while engaging annular undercut portions in the bottom portion of the fuel or irradiation pins to prevent movement of the pins.

  12. Direct observation of the E- resonant state in GaA s1 -xB ix

    Science.gov (United States)

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

    2015-12-01

    Bismuth-derived resonant states with T2 symmetry are detected in the valence band of GaA s1 -xB ix 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 GaA s1 -xB ix . Our results provide key insight for clarifying the mechanisms by which isovalent impurities alter the band structure of the host semiconductor.

  13. Growth and Photovoltaic Properties of High-Quality GaAs Nanowires Prepared by the Two-Source CVD Method

    National Research Council Canada - National Science Library

    Ying Wang; Zaixing Yang; Xiaofeng Wu; Ning Han; Hanyu Liu; Shuobo Wang; Jun Li; WaiMan Tse; SenPo Yip; Yunfa Chen; Johnny C Ho

    2016-01-01

    .... In this work, highly crystalline, dense, and long GaAs NWs are successfully synthesized using a two-source method on non-crystalline SiO2 substrates by a simple solid-source chemical vapor deposition method...

  14. 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.

  15. Detection of a novel mutation in the GAA gene in an Iranian child with glycogen storage disease type II.

    Science.gov (United States)

    Galehdari, Hamid; Emami, Mozhgan; Mohammadian, Gholamreza; Khodadadi, Ali; Azmoon, Somayeh; Baradaran, Masumeh

    2013-02-01

    Glycogen storage disease II (GSDII or Pompe disease, OMIM # 232300) is an autosomal recessive hereditary lysosomal disorder. Mutations in the GAA gene usually lead to reduced acid α-glucosidase (acid maltase, GAA, OMIM *606800, EC 3.1.26.2) activity, which results in impaired degradation and subsequent accumulation of glycogen within lysosomes. We present an Iranian boy, who was diagnosed with GSDII based upon clinical and biochemical findings. A single adenine insertion (insA) was detected at codon 693 that leads to a predicted premature stop codon at codon 736 in the GAA gene. The parents were heterozygous for the same change. According to the human genome mutation database (www.hgmd.org) and lecture reviews, the detected change is a novel mutation. We suppose that the discovered insertion in the GAA gene might lead to a reduced activity of the gene product. This assumption is in agreement with biochemical and clinical signs in the patient.

  16. NSUF Irradiated Materials Library

    Energy Technology Data Exchange (ETDEWEB)

    Cole, James Irvin [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2015-09-01

    The Nuclear Science User Facilities has been in the process of establishing an innovative Irradiated Materials Library concept for maximizing the value of previous and on-going materials and nuclear fuels irradiation test campaigns, including utilization of real-world components retrieved from current and decommissioned reactors. When the ATR national scientific user facility was established in 2007 one of the goals of the program was to establish a library of irradiated samples for users to access and conduct research through competitively reviewed proposal process. As part of the initial effort, staff at the user facility identified legacy materials from previous programs that are still being stored in laboratories and hot-cell facilities at the INL. In addition other materials of interest were identified that are being stored outside the INL that the current owners have volunteered to enter into the library. Finally, over the course of the last several years, the ATR NSUF has irradiated more than 3500 specimens as part of NSUF competitively awarded research projects. The Logistics of managing this large inventory of highly radioactive poses unique challenges. This document will describe materials in the library, outline the policy for accessing these materials and put forth a strategy for making new additions to the library as well as establishing guidelines for minimum pedigree needed to be included in the library to limit the amount of material stored indefinitely without identified value.

  17. Childhood Head and Neck Irradiation

    Science.gov (United States)

    ... Thyroid Association ® www.thyroid.org Childhood Head & Neck Irradiation What is the thyroid gland? The thyroid gland ... Thyroid Association ® www.thyroid.org Childhood Head & Neck Irradiation Thyroid nodules (see Thyroid Nodule brochure) • Thyroid nodules ...

  18. Above 8GHz Static T-Flip-Flop Operation using FT=22.9GHz GaAs MESFETs

    DEFF Research Database (Denmark)

    Riishøj, J; Danielsen, Per Lander

    1992-01-01

    A static SCFL Toggle Flip-Flop GaAs IC having maximum operating frequency of Fdiv=8.25GHz has been designed using a commercially available GaAs MESFET foundry service. The average Ft for the present wafer is Ft=22.9GHz giving a very high Fdiv/Ft-ratio of Fdiv/Ft=0.36. In addition output voltage...

  19. Effects of capacitance at crossover wirings in power GaAs M.E.S.F.E.T.s

    Science.gov (United States)

    Aono, Y.; Higashisaka, A.; Hasegawa, F.

    1980-05-01

    Power GaAs FETs with an air-bridge crossover were compared with those of SiO2 crossover to find the effect of the capacitance at the crossover points. The capacitance of SiO2 crossover points is much smaller than that of the gate pad or the gate busbar in power GaAs FETs, and deterioration of the microwave performance due to that capacitance is negligible.

  20. 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.

  1. 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.

  2. A GAA repeat expansion reporter model of Friedreich's ataxia recapitulates the genomic context and allows rapid screening of therapeutic compounds.

    Science.gov (United States)

    Lufino, Michele M P; Silva, Ana M; Németh, Andrea H; Alegre-Abarrategui, Javier; Russell, Angela J; Wade-Martins, Richard

    2013-12-20

    Friedreich's ataxia (FRDA) is caused by large GAA expansions in intron 1 of the frataxin gene (FXN), which lead to reduced FXN expression through a mechanism not fully understood. Understanding such mechanism is essential for the identification of novel therapies for FRDA and this can be accelerated by the development of cell models which recapitulate the genomic context of the FXN locus and allow direct comparison of normal and expanded FXN loci with rapid detection of frataxin levels. Here we describe the development of the first GAA-expanded FXN genomic DNA reporter model of FRDA. We modified BAC vectors carrying the whole FXN genomic DNA locus by inserting the luciferase gene in exon 5a of the FXN gene (pBAC-FXN-Luc) and replacing the six GAA repeats present in the vector with an ∼310 GAA repeat expansion (pBAC-FXN-GAA-Luc). We generated human clonal cell lines carrying the two vectors using site-specific integration to allow direct comparison of normal and expanded FXN loci. We demonstrate that the presence of expanded GAA repeats recapitulates the epigenetic modifications and repression of gene expression seen in FRDA. We applied the GAA-expanded reporter model to the screening of a library of novel small molecules and identified one molecule which up-regulates FXN expression in FRDA patient primary cells and restores normal histone acetylation around the GAA repeats. These results suggest the potential use of genomic reporter cell models for the study of FRDA and the identification of novel therapies, combining physiologically relevant expression with the advantages of quantitative reporter gene expression.

  3. Anti-phase boundaries-Free GaAs epilayers on "quasi-nominal" Ge-buffered silicon substrates

    Science.gov (United States)

    Bogumilowicz, Y.; Hartmann, J. M.; Cipro, R.; Alcotte, R.; Martin, M.; Bassani, F.; Moeyaert, J.; Baron, T.; Pin, J. B.; Bao, X.; Ye, Z.; Sanchez, E.

    2015-11-01

    We have obtained Anti-Phase Boundary (APB) free GaAs epilayers on "quasi-nominal" (001) silicon substrates, while using a thick germanium strain relaxed buffer between the GaAs layer and the silicon substrate in order to accommodate the 4% lattice mismatch between the two. As silicon (001) substrates always have a small random offcut angle from their nominal surface plane, we call them "quasi-nominal." We have focused on the influence that this small (≤0.5°) offcut angle has on the GaAs epilayer properties, showing that it greatly influences the density of APBs. On 0.5° offcut substrates, we obtained smooth, slightly tensile strained (R = 106%) GaAs epilayers that were single domain (e.g., without any APB), showing that it is not necessary to use large offcut substrates, typically 4° to 6°, for GaAs epitaxy on silicon. These make the GaAs layers more compatible with the existing silicon manufacturing technology that uses "quasi-nominal" substrates.

  4. 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.

  5. Novel anti-reflection technology for GaAs single-junction solar cells using surface patterning and Au nanoparticles.

    Science.gov (United States)

    Kim, Youngjo; Lam, Nguyen Dinh; Kim, Kangho; Kim, Sangin; Rotermund, Fabian; Lim, Hanjo; Lee, Jaejin

    2012-07-01

    Single-junction GaAs solar cell structures were grown by low-pressure MOCVD on GaAs (100) substrates. Micro-rod arrays with diameters of 2 microm, 5 microm, and 10 microm were fabricated on the surfaces of the GaAs solar cells via photolithography and wet chemical etching. The patterned surfaces were coated with Au nanoparticles using an Au colloidal solution. Characteristics of the GaAs solar cells with and without the micro-rod arrays and Au nanoparticles were investigated. The short-circuit current density of the GaAs solar cell with 2 microm rod arrays and Au nanoparticles increased up to 34.9% compared to that of the reference cell without micro-rod arrays and Au nanoparticles. The conversion efficiency of the GaAs solar cell that was coated with Au nanoparticles on the patterned surface with micro-rod arrays can be improved from 14.1% to 19.9% under 1 sun AM 1.5G illumination. These results show that micro-rod arrays and Au nanoparticle coating can be applied together in surface patterning to achieve a novel cost-effective anti-reflection technology.

  6. 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

  7. Studies in the growth of ZnSe on GaAs(001)

    Energy Technology Data Exchange (ETDEWEB)

    Riley, J. [La Trobe University, Bundoora, VIC (Australia). School of Physics; Wolfframm, D.; Evans, A. [North East Wales Institute, Plas Coch, Wrexham, (United Kingdom). Department of Physics; Westwood, D. [University of Wales Cardiff, Cardiff (United Kingdom). Department of Physics and Astronomy

    1996-12-31

    Full text: This paper reports a study of the Molecular Beam Epitaxial (MBE) growth of ZnSe on GaAs substrates using elemental sources. Growth rates of ZnSe as a function of Zn:Se flux ratio for constant Zn flux were determined over a wider range of values than previously reported. Careful measurements of atomic fluxes and sample thickness lead to a determination of the sticking coefficients of Zn and Se which are at variance with many previously reported values. The temperature dependence of the sticking coefficients of Zn and Se have been measured carefully and provide evidence for a greater desorption of As from the growing surface that previously thought, an effect which persists at low growth temperatures. Measurements at high flux ratio supports the use of a precursor model to describe MBE growth of ZnSe on GaAs substrates

  8. Coherent control and charge echo in a GaAs charge qubit

    Science.gov (United States)

    Wang, Bao-Chuan; Chen, Bao-Bao; Cao, Gang; Li, Hai-Ou; Xiao, Ming; Guo, Guo-Ping

    2017-03-01

    In fulfilling the non-adiabatic requirement of pulse sequences, it is challenging to perform multi-pulse quantum control of a charge qubit. By optimizing our charge qubit and pulse parameters, we experimentally demonstrate the coherent control and echo process of a GaAs charge qubit. We firstly employed a single non-adiabatic voltage pulse to perform the Larmor oscillation experiment and determine the optimal σx operation pulses. Then, we produced Ramsey fringes using two σx=π/2 pulses and extracted the decoherence time T2\\ast∼ 112 \\text{ps} from the Ramsey fringes. More importantly, we successfully applied a charge echo pulse sequence to increase the extracted inhomogeneous dephasing time to ∼1360 ps. Our results show that the low-frequency noise is the important dephasing limiter of the coherence time of the charge qubit in the GaAs system.

  9. 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...... different due to the lateral strain induced by the lattice mismatch. This structural difference explains why the ladder-type pattern observed previously by scanning tunneling microscopy only appears for the In/GaAs(001) and InAs/GaAs(001) surfaces, but not for the InAs clean surface. The structural model we...... propose for the In-stabilized GaAs(001)-c(8x2) surface, which fully agrees with the scanning tunneling microscopy results, should therefore generally apply to strained InAs(001) surfaces....

  10. Fabrication and electrical properties of axial and radial GaAs nanowire pn junction diode arrays

    Science.gov (United States)

    Li, Jun-Shuai; Zhang, Xia; Yan, Xin; Chen, Xiong; Li, Liang; Cui, Jian-Gong; Huang, Yong-Qing; Ren, Xiao-Min

    2014-12-01

    We report on the fabrications and characterizations of axial and radial GaAs nanowire pn junction diode arrays. The nanowires are grown on n-doped GaAs (111)B substrates using the Au-catalyzed vapor—liquid—solid mechanism by metal—organic chemical vapor deposition (MOCVD). Diethyl—zinc and silane are used as p- and n-type dopant precursors, respectively. Both the axial and radial diodes exhibit diode-like J—V characteristics and have similar performances under forward bias. Under backward bias, the axial diode has a large leakage current, which is attributed to the bending of the pn junction interface induced by two doping mechanisms in Au-catalyzed nanowires. The low leakage current and high rectification ratio make the radial diode more promising in electrical and optoelectronic devices.

  11. Electrons, holes, and excitons in GaAs polytype quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Climente, Juan I.; Segarra, Carlos; Rajadell, Fernando; Planelles, Josep, E-mail: josep.planelles@uji.es [Departament de Química Física i Analítica, Universitat Jaume I, E-12080 Castelló (Spain)

    2016-03-28

    Single and multi-band k⋅p Hamiltonians for GaAs crystal phase quantum dots are used to assess ongoing experimental activity on the role of such factors as quantum confinement, spontaneous polarization, valence band mixing, and exciton Coulomb interaction. Spontaneous polarization is found to be a dominating term. Together with the control of dot thickness [Vainorius et al., Nano Lett. 15, 2652 (2015)], it enables wide exciton wavelength and lifetime tunability. Several new phenomena are predicted for small diameter dots [Loitsch et al., Adv. Mater. 27, 2195 (2015)], including non-heavy hole ground state, strong hole spin admixture, and a type-II to type-I exciton transition, which can be used to improve the absorption strength and reduce the radiative lifetime of GaAs polytypes.

  12. 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.

  13. Position control of self-catalyzed MBE-grown GaAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Bauer, Benedikt; Rudolph, Andreas; Weiss, Dieter; Schuh, Dieter; Soda, Marcello; Zweck, Josef; Reiger, Elisabeth [Institut fuer Experimentelle und Angewandte Physik, Universitaet Regensburg (Germany); Fontcuberta i Morral, Anna [Institut des Materiaux, EPFL Lausanne (Switzerland)

    2010-07-01

    Nanowires grown in bottom-up processes are regarded as possible building blocks of future electronic devices. For integrating them into conventional electronic circuits controlling the position and diameter of the nanowires is inevitable. We report on position controlled GaAs nanowires grown via self-catalyzed growth using MBE. Starting with a GaAs (111)B substrate covered by a thin SiO{sub 2} layer we use E-beam lithography in combination with wet chemical etching to define arrays of holes with diameters of 100 nm and varying interhole distances between 200 and 2000 nm. These holes in the SiO{sub 2} layer act as nucleation sites for nanowire growth. The nanowires are oriented in the [111] direction and are restricted to the patterned areas. SEM/TEM characterizations show that the nanowires have a hexagonal shape with {l_brace}110{r_brace} side facets and zinc blende as dominant crystal structure.

  14. 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

  15. 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)

  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. 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.

  18. The role of titanium at the SrTiO3/GaAs epitaxial interface

    Science.gov (United States)

    Meunier, B.; Bachelet, R.; Grenet, G.; Botella, C.; Regreny, P.; Largeau, L.; Penuelas, J.; Saint-Girons, G.

    2016-01-01

    We study the role of a Ti surface treatment applied to the As-terminated GaAs (001) substrate surface prior to SrTiO3 (STO) epitaxial growth by comparing STO/GaAs samples prepared with and without Ti interlayers. Reflection high energy electron diffraction, transmission electron microscopy and x-ray photoelectron spectroscopy are used to assess the structural and chemical properties of the layers and interfaces. Without Ti interlayer, a polycrystalline TiGa compound is formed near the interface. It significantly degrades STO structural properties. A Ti interlayer efficiently prevents the formation of this unwanted compound by limiting As desorption from the GaAs substrate during STO growth. It improves significantly the structural quality of the oxide layer.

  19. 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.)

  20. 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.

  1. 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.

  2. 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.

  3. Residual Carbon and Oxygen Surface Contamination of Chemically Etched GaAs (001) Substrates

    Science.gov (United States)

    Saliètes, A.; Massies, J.; Contour, J. P.

    1986-01-01

    Several different cleaning procedures for GaAs (001) substrates are compared using X-ray photoelectron spectroscopy. This work emphasizes the effect of the last etching step: HCl-, HF-ethanol (10%), bromine-methanol (1%), performed on a spinner (3000 rpm) operated in a nitrogen dry box, and running deionized water (RDIW). These four etchants lead to deoxidized surfaces, although RDIW leaves a fractional coverage of sligthly bounded oxygen species (≃0.15 monolayer). The residual carbon contamination is around 0.2 monolayer whatever the etchant used and is removable by flash heating at 400°C under ultrahigh vacuum. RDIW, HCl- and HF-ethanol do not produce any significant etching of the GaAs matrix whereas bromine-methanol (1%) removes ≃0.2 μm per cm3 of solution.

  4. Photoassisted MOVPE grown (n)ZnSe/(p +)GaAs heterojunction solar cells

    Science.gov (United States)

    Parent, D. W.; Rodriguez, A.; Ayers, J. E.; Jain, F. C.

    2003-04-01

    We report the electrical characteristics of (n)ZnSe/(p +)GaAs heterostructure solar cells grown by depositing an n-type ZnSe epilayer using photoassisted metal organic vapor phase epitaxy on p + type GaAs (1 0 0) substrates. A study of the solar cell efficiency as a function of ZnSe epilayer thickness is also presented. Our preliminary results show that an epilayer thickness of 1.5 μm produced the highest efficiency for the cells tested, (4.27% under AM1.5 conditions, no anti-reflective coating). We also demonstrate a method to pattern ZnSe/GaAs structures with an inexpensive methanol/bromine etch process.

  5. The design and fabrication of anisotropically-etched GaAs solar cells

    Science.gov (United States)

    Holm, P. M.; Roedel, R. J.

    Anisotropically-etched GaAs solar cells have been designed and fabricated in the laboratory. The cells, which have a regular array of surface serrations, V-shaped or U-shaped in cross-section, show dramatic improvement in performance over conventional planar devices. These devices were fabricated using bromine-methanol etching to form the grooves and shallow Zn diffusion to form the junction in GaAs substrate material. The efficiency and short circuit current in the best serrated device were 6.7 percent and 16.5 mA/sq cm; planar devices were approximately 50 percent lower in both cases. A ray-tracing and metallization pattern model shows good qualitative agreement with these results.

  6. 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.

  7. A GaAs phase digitizing and summing system for microwave signal storage

    Science.gov (United States)

    Vu, Tho T.; Hattis, James M.

    1989-02-01

    The analysis, design, and development of a microwave signal storage prototype system using phase-quantization sampling are described. A GaAs 4-bit D/A converter has been demonstrated in a 3-bit DRFM prototype system with digital Si emitter-coupled logic (ECL) and RF microwave components at a sample rate of 200 MHz and exhibiting typically a -17-dBc harmonic suppression. A monolithic GaAs A/D and D/A converter has been demonstrated within an RF signal acquisition system. Performance data on the monolithic sampler reveal that the 3-bit quantization system exhibits signal reconstruction with harmonic supression exceeding 25 dB across an IF bandwidth of greater than 900 MHz.

  8. Deep Level Defects In Ion Implanted Laser Annealed Bulk GaAs

    Science.gov (United States)

    Dlodlo, Mqhele E.; Rys, Andrzej; Ahmed, Akhter U.; Edgar, James H.

    1990-02-01

    In this paper, we report on the carrier activation and deep level crystal defects in pulsed excimer laser (A = 308 nm) anealed samples of GaAs implanted with Si and Se to a dose ranging from 2.2 x 1012 to 6.0 x 10" cm'. The residual defects in the pulsed-laser annealed GaAs have been investigated by means of photo-induced current transient spectroscopy (PITS). The electron concentration and carrier mobility were studied by Hall effect and Van der Pauw measurements. Although the implanted layer recrystallization was good and the sheet carrier concentration was high, the electron mobility was low. The correlation between deep traps, the carrier concentration, the electron mobility, and laser light intensity is presented.

  9. Anisotropy of mosaic structure of GaAsP layers grown on GaAs substrates

    Energy Technology Data Exchange (ETDEWEB)

    Saka, T. [Daido Institute of Technology, 10-3, Takiharu-cho, Minami-ku, Nagoya 457-8530 (Japan); Kato, T. [Daido Steel Co. Ltd., 2-30, Daido-cho, Minami-ku, Nagoya 457-8545 (Japan); Jin, X.G.; Tanioku, M.; Ujihara, T.; Takeda, Y. [Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Yamamoto, N.; Nakagawa, Y.; Mano, A.; Okumi, S.; Yamamoto, M.; Nakanishi, T. [Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602 (Japan); Horinaka, H.; Matsuyama, T. [Faculty of Engineering, Osaka Prefecture University, 1-1, Gakuen-cho, Sakai 599-8531 (Japan); Yasue, T.; Koshikawa, T. [Fundamental Electronics Research Institute, Osaka Electro-Communication University, 18-8, Hatsu-cho, Neyagawa 572-8530 (Japan)

    2009-08-15

    The crystalline structure of GaAsP layers grown on GaAs and GaP(001) substrates, used for spin polarized photocathodes, has been investigated by X-ray diffraction. The layers on the GaAs substrate possess a mosaic structure observable by X-ray topography and consist of many large blocks. The mosaicity is anisotropic and the distribution of the mosaic is restricted within the (110) plane, and the blocks zigzag around the [110] direction. The layer grown on the GaP substrate was uniform and no mosaic was observed in the topographs. The results indicate that different mechanisms of strain release occur in GaAsP layers for tensile and compressive strains. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

  10. Ab initio study of (Fe, Ni) doped GaAs: Magnetic, electronic properties and Faraday rotation

    Science.gov (United States)

    Sbai, Y.; Ait Raiss, A.; Bahmad, L.; Benyoussef, A.

    2017-06-01

    The interesting diluted magnetic semiconductor (DMS), Gallium Arsenide (GaAs), was doped with the transition metals magnetic impurities: iron (Fe) and Nickel (Ni), in one hand to study the magnetic and magneto-optical properties of the material Ga(Fe, Ni) As, in the other hand to investigate the effect of the doping on the properties of this material, the calculations were performed within the spin polarized density functional theory (DFT) and generalized gradient approximation (GGA) with AKAI KKR-CPA method, the density of states (DOS) for different doping concentrations were calculated, giving the electronical properties, as well as the magnetic state and magnetic states energy, also the effect of these magnetic impurities on the Faraday rotation as magneto-optical property. Furthermore, we found the stable magnetic state for our doped material GaAs.

  11. Absorption from Neutral Acceptors in GaAs and GaP

    DEFF Research Database (Denmark)

    Christensen, Ove

    1973-01-01

    We present a new calculation of the absorption due to transitions of holes between neutral acceptors and the various valence-band sublevels in GaAs and GaP. The acceptor wave function was approximated by a previously suggested expression for ground-state wave functions appropriate to complicated ...... band extrema. Numerical calculations of the absorption from intervalence-band transitions of free holes and neutral acceptors have been performed. Good agreement with experimental results is obtained....

  12. Propagation of surface acoustic waves in n-type GaAs films

    Science.gov (United States)

    Wu, Chhi-Chong; Tsai, Jensan

    1983-05-01

    The effect of nonparabolicity on the amplification of surface acoustic waves in n-type GaAs films is investigated quantum mechanically in the GHz frequency region. Numerical results show that the amplification coefficient for the nonparabolic band structure is enhanced due to the nonlinear nature of the energy band in semiconductors. Moreover, the amplification coefficients in semiconductors depend on the temperature, the electronic screening effect, the frequency of sound waves, the applied electric field, and the thickness of the semiconductor film.

  13. Growth of ZnO thin films on GaAs by pulsed laser deposition

    NARCIS (Netherlands)

    Craciun, V.; Elders, J.; Gardeniers, Johannes G.E.; Geretovsky, J.; Boyd, Ian W.

    1995-01-01

    ZnO thin films have been grown on GaAs substrates using the pulsed laser deposition technique with or without a photodeposited SiO2 buffer layer. The presence of the SiO2 layer has a beneficial effect on the crystalline quality of the grown ZnO films. Highly c-axis oriented ZnO films having a full

  14. Spin-orbit splitting of the cyclotron resonance in GaAs

    Science.gov (United States)

    Tonello, P.; Lipparini, E.

    2004-08-01

    We have studied the relevance of spin-orbit coupling to the splitting of the cyclotron resonance of electron space-charge layers in GaAs recently observed by Manger [Phys. Rev. B 63, 121203R (2001)]. We show that the spin-orbit interaction couples density and spin-density excitations in the long-wavelength limit and is able to explain all the features observed in the experiment.

  15. 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.

  16. The characterisation of selective proton damage on GaAs solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Aliyu, Y.H. (School of Electrical, Electronic and Systems Engineering, Wales Univ., Cardiff (United Kingdom)); Morgan, D.V. (School of Electrical, Electronic and Systems Engineering, Wales Univ., Cardiff (United Kingdom)); Bunce, R.W. (School of Electrical, Electronic and Systems Engineering, Wales Univ., Cardiff (United Kingdom))

    1993-01-16

    Selective ion bombardment damage was induced on n/n[sup +] GaAs Schottky barrier solar cell structure using several proton energies and doses. The damage in the surface, interface, and the bulk regions were characterised by I-V, C-V, and thermally stimulated current technique (TSC). A correlation between the selective damages and the nature of the defects and their location was obtained. (orig.)

  17. Modeling of chemical vapor deposition. II. Gas phase epitaxy of (100) GaAs

    Science.gov (United States)

    Korec, J.; Heyen, M.

    1982-12-01

    The approach described in part I of this paper is applied here to model the CVD of GaAs in a halide transport system. A quantitative description of the effect of growth temperature on the growth rate is obtained. Also the effect of GaCl and arsenic vapor pressure on the growth rate is described. The theoretical estimate of the transition point between etching and growth is close to the experimental value.

  18. Perubahan Sel Imun Pulpitis Akibat Biomodulasi Laser GaA1As

    OpenAIRE

    Nugrohowati Nugrohowati

    2015-01-01

    The objective of this study was to disclose the effect of GaA1As laser biomodulation on pulpitis immune response. The use of laser is still disputable, because of the biomodulation effect of laser remains unclear, particularly on immune response of pulpitis. Laser is  astressor because it produces stress wave that may cause stress on pulp. Modulation of immune system occurred in each variable of immune system component was considred to be GAS (General Adaptation Syndrome). The applied design ...

  19. Self-pumped and double phase conjugation in GaAs with applied dc electric field

    Science.gov (United States)

    Chua, P. L.; Liu, D. T. H.; Cheng, L. J.

    1990-01-01

    Self-pumped and double phase conjugation are first demonstrated in undoped GaAs with applied dc electric field at 1.06 micron wavelength. Phase-conjugate reflectivities of up to 3 percent and 0.5 percent, respectively, are obtained and other dependences are reported. Reported values of the self-pumped phase-conjugate reflectivity are compared with those of InP.

  20. Surface passivation of GaAs nanowires by the atomic layer deposition of AlN

    Energy Technology Data Exchange (ETDEWEB)

    Shtrom, I. V., E-mail: igorstrohm@mail.ru; Bouravleuv, A. D. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Samsonenko, Yu. B.; Khrebtov, A. I. [Russian Academy of Sciences, St. Petersburg National Research Academic University—Nanotechnology Research and Education Center (Russian Federation); Soshnikov, I. P. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Reznik, R. R.; Cirlin, G. E., E-mail: cirlin@beam.ioffe.ru [Russian Academy of Sciences, St. Petersburg National Research Academic University—Nanotechnology Research and Education Center (Russian Federation); Dhaka, V.; Perros, A.; Lipsanen, H. [Aalto University (Finland)

    2016-12-15

    It is shown that the atomic layer deposition of thin AlN layers can be used to passivate the surface states of GaAs nanowires synthesized by molecular-beam epitaxy. Studies of the optical properties of samples by low-temperature photoluminescence measurements shows that the photoluminescence-signal intensity can be increased by a factor of up to five by passivating the nanowires with a 25-Å-thick AlN layer.

  1. Smart Power Devices and ICs Using GaAs and Wide and Extreme Bandgap Semiconductors

    OpenAIRE

    Chow, T. Paul; Omura, Ichiro; Higashiwaki, Masataka; Kawarada, Hiroshi; Pala, Vipindas

    2017-01-01

    We evaluate and compare the performance and potential of GaAs and of wide and extreme bandgap semiconductors (SiC, GaN, Ga2O3, diamond), relative to silicon, for power electronics applications. We examine their device structures and associated materials/process technologies and selectively review the recent experimental demonstrations of high voltage power devices and IC structures of these semiconductors. We discuss the technical obstacles that still need to be addressed and overcome before ...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2016-07-15

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

  3. Formation of arsenic sulfide on GaAs surface under illumination in acidified thiourea electrolytes

    Energy Technology Data Exchange (ETDEWEB)

    Khader, Mahmoud M., E-mail: mmkhader@qu.edu.qa [Department of Chemistry and Earth Sciences, College of Arts and Sciences, Qatar University, P.O. 2713, Doha (Qatar); AlJaber, Amina S. [Department of Chemistry and Earth Sciences, College of Arts and Sciences, Qatar University, P.O. 2713, Doha (Qatar)

    2011-10-15

    The present article reports the formation of arsenic sulfide films on GaAs by the potentiodynamic polarization in acidified thiourea (TU) electrolytes under photo-illumination. Oxidation of TU competes with the oxidation of GaAs itself and leads to the formation of surface arsenic-sulfide films. Surface chemical composition is investigated by X-ray photoelectron spectroscopy (XPS), demonstrating the formation of As-sulfide as the XPS peaks at binding energies of 42.6 and 162.5 eV for As 3d and S 2p, respectively, are observed. XPS results also show diminishing of Ga species from the surface while As-sulfide is forming. Though, As-sulfide is predominantly formed on the surface, but the inductive coupling plasma-mass spectroscopy (ICP-MS) analysis still shows a preferential dissolution of As ions into electrolytes. These results indicate that Ga ions diffuse into the bulk of the electrode material. The formation of As-sulfide, initially, enhances the photocurrent generation; presumably, due to suppressing electron-hole recombination processes. Further deposition of As-sulfide deteriorates GaAs photoactivity due to retarding light absorptivity because of depositing a thick As-sulfide film. The morphology of the As-sulfide film is characterized by scanning electron microscopy (SEM) that shows the formation of smooth and nonporous films in TU electrolytes acidified by H{sub 2}SO{sub 4} of concentration {>=}0.2 M. Electrochemical impedance measurements show that GaAs corrosion is limited by the growth and oxidation of the sulfide layer.

  4. Technique for producing 'good' GaAs solar cells using poor-quality substrates

    Science.gov (United States)

    Hovel, H. J.; Wooddall, J. M.

    1975-01-01

    Relatively good GaAs solar cells can be made from poor-quality substrates by making the junction deep (greater than 1 micron) instead of shallow and by 'leaching' both the pGaAs and nGaAs regions during the growth process. AM0 efficiencies of 14.7% (19% AM1) have been obtained from substrates with starting substrate diffusion lengths of 0.6 micron.

  5. Safety of irradiated foods

    Energy Technology Data Exchange (ETDEWEB)

    Iwahara, Shigeo (Foods Medicines Safety Center (Japan)); Kobayashi, Kazuo

    1983-01-01

    The safety of 7 irradiated foods (potato, onion, rice, wheat, vienna sausage, fish paste and mandarine orange), in terms of 2-year long-term toxic effect, reproductive physiology and possible teratogenesis, was studied using 3 generations of rats, mice and monkeys. The genetic toxicity was studied by means of various mutagenicity tests. The details of the studies conducted by the authors to date and some overseas data were reported. The available data showed no toxic effect.

  6. 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.

  7. 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%.

  8. Optical properties of heavily doped GaAs nanowires and electroluminescent nanowire structures

    Energy Technology Data Exchange (ETDEWEB)

    Lysov, A; Offer, M; Gutsche, C; Regolin, I; Geller, M; Prost, W; Tegude, F-J [Center for Nanointegration Duisburg-Essen, University of Duisburg-Essen, D-47048 Duisburg (Germany); Topaloglu, S, E-mail: andrey.lysov@uni-due.de [Department of Electronics Engineering, Maltepe University, Marmara Egitim Koeyue, 34857, Maltepe, Istanbul (Turkey)

    2011-02-25

    We present GaAs electroluminescent nanowire structures fabricated by metal organic vapor phase epitaxy. Electroluminescent structures were realized in both axial pn-junctions in single GaAs nanowires and free-standing nanowire arrays with a pn-junction formed between nanowires and substrate, respectively. The electroluminescence emission peak from single nanowire pn-junctions at 10 K was registered at an energy of around 1.32 eV and shifted to 1.4 eV with an increasing current. The line is attributed to the recombination in the compensated region present in the nanowire due to the memory effect of the vapor-liquid-solid growth mechanism. Arrayed nanowire electroluminescent structures with a pn-junction formed between nanowires and substrate demonstrated at 5 K a strong electroluminescence peak at 1.488 eV and two shoulder peaks at 1.455 and 1.519 eV. The main emission line was attributed to the recombination in the p-doped GaAs. The other two lines correspond to the tunneling-assisted photon emission and band-edge recombination in the abrupt junction, respectively. Electroluminescence spectra are compared with the micro-photoluminescence spectra taken along the single p-, n- and single nanowire pn-junctions to find the origin of the electroluminescence peaks, the distribution of doping species and the sharpness of the junctions.

  9. Optical properties of heavily doped GaAs nanowires and electroluminescent nanowire structures

    Science.gov (United States)

    Lysov, A.; Offer, M.; Gutsche, C.; Regolin, I.; Topaloglu, S.; Geller, M.; Prost, W.; Tegude, F.-J.

    2011-02-01

    We present GaAs electroluminescent nanowire structures fabricated by metal organic vapor phase epitaxy. Electroluminescent structures were realized in both axial pn-junctions in single GaAs nanowires and free-standing nanowire arrays with a pn-junction formed between nanowires and substrate, respectively. The electroluminescence emission peak from single nanowire pn-junctions at 10 K was registered at an energy of around 1.32 eV and shifted to 1.4 eV with an increasing current. The line is attributed to the recombination in the compensated region present in the nanowire due to the memory effect of the vapor-liquid-solid growth mechanism. Arrayed nanowire electroluminescent structures with a pn-junction formed between nanowires and substrate demonstrated at 5 K a strong electroluminescence peak at 1.488 eV and two shoulder peaks at 1.455 and 1.519 eV. The main emission line was attributed to the recombination in the p-doped GaAs. The other two lines correspond to the tunneling-assisted photon emission and band-edge recombination in the abrupt junction, respectively. Electroluminescence spectra are compared with the micro-photoluminescence spectra taken along the single p-, n- and single nanowire pn-junctions to find the origin of the electroluminescence peaks, the distribution of doping species and the sharpness of the junctions.

  10. Ga-assisted MBE grown GaAs nanowires and related quantum heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Fontcuberta i Morral, Anna [Ecole Polytechnique Federale de Lausanne (Switzerland); Walter Schottky Institut, Technische Universitaet Muenchen (Germany)

    2010-07-01

    Nanowires represent model systems for studying a variety of low dimensional phenomena as well as building blocks for the future generation of nanoscale devices. The most exploited nanowire growth technique is the vapor-liquid-solid (VLS) method, which employs gold as a seed for the growth. Synthesis of nanowires by molecular beam epitaxy (MBE) and without using gold as a catalyst gives the opportunity to study nanowires produced in extremely clean conditions and correlate it with optical and electronic properties. We present the method for growing GaAs nanowires by MBE without using gold as a catalyst. By changing the growth conditions we have managed to obtain high quality radial and axial heterostructures. For the latter, nanowires with atomically sharp zinc-blende/wurtzite heterostructures have been obtained. These structures exhibit novel optical properties for a pure GaAs material. In particular, we show how the emission of the nanowire can be tuned from 1.51 eV down to 1.43 eV. Theoretical calculations of the band alignment between wurtzite and zinc-blende GaAs are presented to explain the results. Finally, novel applications enabled by these types of quantum heterostructures are also briefly discussed.

  11. Degradation mechanism(s) of GaAs solar cells with Cu contacts.

    Science.gov (United States)

    van Leest, R H; de Kleijne, K; Bauhuis, G J; Mulder, P; Cheun, H; Lee, H; Yoon, W; van der Heijden, R; Bongers, E; Vlieg, E; Schermer, J J

    2016-04-21

    Substrate-based GaAs solar cells having a dense Au/Cu front contact grid with 45% surface coverage were exposed to accelerated life testing at temperatures between 200 and 300 °C. TEM analysis of the front contacts was used to gain a better understanding of the degradation process. During accelerated life testing at 200 °C only intermixing of the Au and Cu in the front contact occurs, without any significant influence on the J-V curve of the cells, even after 1320 h (55 days) of accelerated life testing. At temperatures ≥250 °C a recrystallization process occurs in which the metals of the contact and the GaAs front contact layer interact. Once the grainy recrystallized layer starts to approach the window, diffusion via grain boundaries to the window and into the active region of the solar cells occurs, causing a decrease in Voc due to enhanced non-radiative recombination via Cu trap levels introduced in the active region of the solar cell. To be a valid simulation of space conditions the accelerated life testing temperature should be future experiments, in order to avoid recrystallization of the metals with the GaAs contact layer.

  12. Properties of a Light-Modified-Breakdown Detector in GaAs.

    Science.gov (United States)

    Ballantyne, J M; Baukus, J P; Lavin, J M

    1973-10-01

    The properties of a bulk-effect millimeter-wave detector made from high-purity epitaxial GaAs are discussed. The devices are operated at 4.2 K in a new light-modified-breakdown (LMB) mode with dc bias above avalanche breakdown. When operated in the LMB mode as a direct video detector, circuit-limited response time (10-90% pulse) less than 20 nsec is observed, which is an order of magnitude faster than the response of bulk GaAs and InSb mixers. NEP values of less than 10(-10) W (D* on the order of 10(10)) in the video detector mode have been measured over the 10-70 GHz frequency range. The dependence of detector performance on operating parameters and frequency is given and compared with the predictions of hot-electron theory developed for InSb detectors. Its performance is also compared with that of microwave-biased InSb, thermal, pyroelectric, and photoionized-impurity GaAs detectors and with point contact, Schottky barrier, and MOM (tunneling) diodes and is shown to provide significant advantages of either burnout resistance, risetime, or noise over competitors in the millimeter spectral region.

  13. ECR plasma synthesis of silicon nitride films on GaAs and InSb

    Energy Technology Data Exchange (ETDEWEB)

    Barbour, J.C.; Lovejoy, M.L.; Ashby, C.I.H.; Howard, A.J.; Custer, J.S.; Shul, R.J.

    1993-12-31

    Growth of high-quality dielectric films from Electron Cyclotron Resonance (ECR) plasmas provides for low-temperature surface passivation of compound semiconductors. Silicon nitride (SiN{sub x}) films were grown at temperatures from 30 to 250 C on GaAs substrates. Stress in films was measured as a function of bias applied during growth (varied from 0 to 200 V), and of sample annealing treatments. Composition profiles of the samples were measured using ion beam analysis. The GaAs photoluminescence (PL) signal after SiN{sub x} growth without an applied bias (ion energy {congruent}30 eV) was twice as large as the PL signal from the cleaned GaAs substrate. The PL signal from samples biased at -50 and -100 V indicated that damage degraded the passivation quality, while atomic force microscopy of these samples showed a three fold increase in rms surface roughness relative to unbiased samples. The sample grown with a bias of -200 V showed the largest reduction in film stress but also the smallest PL signal.

  14. Characterization of photon recycling in thin crystalline GaAs light emitting diodes

    Science.gov (United States)

    Patkar, M. P.; Lundstrom, M. S.; Melloch, M. R.

    1995-08-01

    Gallium arsenide light emitting diodes (LEDs) were fabricated using molecular beam epitaxial films on GaAs substrates and removed by epitaxial lift-off (ELO). Lifted off devices were then mounted on a Si wafer using a Pd/Au/Cr contact layer, which also served as a back surface reflector. Devices were characterized by electrical and optical measurements, and the results for devices on the GaAs substrate were compared to those for ELO devices. ELO LEDs coated with a ZnS/MgF2 antireflection coating exhibited an optical output that was up to six times that of LEDs on GaAs substrates. At the same time, the measured current-voltage characteristics of the ELO devices displayed a lower n=1 current component. ELO LEDs with efficiencies up to 12.5% were realized. We attribute these results to photon recycling enhanced by the back-surface reflector in the ELO LEDs. The luminescence versus current and current versus voltage characteristics of the LEDs were analyzed to obtain the nonradiative minority carrier lifetimes and the photon recycling factors. The results demonstrate that the measured characteristics are well described by photon recycling theory. ELO LEDs may prove useful for characterizing recombination processes in LEDs, and thin-crystalline structures could provide substantial efficiency enhancements for LEDs and solar cells.

  15. Synthesis and characterization of GaAs thin films grown on ITO substrates

    Science.gov (United States)

    Chamekh, M.; Lajnef, M.; Zerroual, L.; Chtourou, R.

    2010-11-01

    Gallium arsenide (GaAs) thin films have been deposited on ITO-coated glass substrates from acid aqueous solution by electrodeposition technique. The structure and the morphology of the samples were analyzed by X-ray diffraction (XRD) and atomic force microscope (AFM). The optical characteristics were investigated at room temperature using a UV-Vis spectrometer. At lower deposition time, the XRD patterns exhibit a mixture of both cubic and orthorhombic GaAs phases. With further increase of the film thickness, only orthorhombic structure was observed with a preferred (100) orientation. By applying the Debye-Scherrer method, the estimated crystallite size for the (200) orientation ranged from 30 to 50 nm, whereas for the (022) orientation was found to be 13-22 nm. From the AFM measurements, the rms surface roughness ranged between 11.4 and 18.4 nm. The analysis of the optical absorption data of the annealed GaAs film deposited at different times revealed direct band gap energy in the range of 1.60-1.85 eV. The large blueshifts observed in this study can be fully explained by the Burstein-Moss effect.

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

    Directory of Open Access Journals (Sweden)

    Santiago Silvestre

    2015-04-01

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

  17. 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.)

  18. Study of thermally activated reaction between Mn and GaAs(111) surface

    Energy Technology Data Exchange (ETDEWEB)

    Soares, M.V.; Jurca, H.F.; Zarpellon, J.; Varalda, J.; Schreiner, W.H.; Mosca, D.H.

    2014-11-03

    We investigate the chemical reactivity of ultra-thin films of Mn on As-terminated (111) GaAs surface kept at ultra-high vacuum conditions in the temperature interval ranging from room temperature to 400 °C. The experiments were performed using a customized molecular beam epitaxy system equipped with reflection high energy electron diffraction and X-ray photoelectron spectroscopy techniques. These analyses were complemented with X-ray diffraction measurements to put in evidence the formation of intermediate compounds. Only Ga{sub 1−x}Mn{sub x}As and sub-arsenised MnAs{sub x} compounds are possibly formed below 200 °C. The onset of the reactivity occurs around 200 °C when ordered compounds such as MnAs and MnGa are observed. The formation of compounds more rich in Mn like Mn{sub 3}Ga and Mn{sub 2}As is found for deposition temperatures of 300 and 400 °C. - Highlights: • Surface chemistry of Mn in contact with GaAs surface • Formation of Mn-based compounds • Solid state reactions of Mn on GaAs.

  19. Optical properties of heavily doped GaAs nanowires and electroluminescent nanowire structures.

    Science.gov (United States)

    Lysov, A; Offer, M; Gutsche, C; Regolin, I; Topaloglu, S; Geller, M; Prost, W; Tegude, F-J

    2011-02-25

    We present GaAs electroluminescent nanowire structures fabricated by metal organic vapor phase epitaxy. Electroluminescent structures were realized in both axial pn-junctions in single GaAs nanowires and free-standing nanowire arrays with a pn-junction formed between nanowires and substrate, respectively. The electroluminescence emission peak from single nanowire pn-junctions at 10 K was registered at an energy of around 1.32 eV and shifted to 1.4 eV with an increasing current. The line is attributed to the recombination in the compensated region present in the nanowire due to the memory effect of the vapor-liquid-solid growth mechanism. Arrayed nanowire electroluminescent structures with a pn-junction formed between nanowires and substrate demonstrated at 5 K a strong electroluminescence peak at 1.488 eV and two shoulder peaks at 1.455 and 1.519 eV. The main emission line was attributed to the recombination in the p-doped GaAs. The other two lines correspond to the tunneling-assisted photon emission and band-edge recombination in the abrupt junction, respectively. Electroluminescence spectra are compared with the micro-photoluminescence spectra taken along the single p-, n- and single nanowire pn-junctions to find the origin of the electroluminescence peaks, the distribution of doping species and the sharpness of the junctions.

  20. Characterization of Ge-on-Si virtual substrates and single junction GaAs solar cells

    Science.gov (United States)

    Ginige, R.; Corbett, B.; Modreanu, M.; Barrett, C.; Hilgarth, J.; Isella, G.; Chrastina, D.; von Känel, H.

    2006-06-01

    A virtual substrate consisting of a Ge layer grown directly on Si without an intervening SiGe graded layer is characterized. The nominally 100% Ge overlayer is fully relaxed and contains a small amount (3%) of unintentional Si. A dislocation density of 108 cm-2 is estimated for the virtual substrate prior to GaAs epitaxial growth, which is reduced by a factor of 100 after the growth of GaAs. On this novel virtual substrate 1 cm2 single-junction GaAs photovoltaic cells were realized with an efficiency of 11.7% under AM0 compared with 20.2% for cells grown on a crystalline Ge substrate. Due to the high dislocation density a 50-fold higher dark current is measured in the virtual substrate cells compared to the crystalline Ge cells, leading to a lower short circuit current and open-circuit voltage of the cells fabricated on the virtual substrates. The post-GaAs growth dislocation density is estimated as 1 × 107 cm-2 in the base region and 4 × 105 cm-2 in the emitter region based on modelling and measurements.

  1. Anisotropic Pauli Spin Blockade of Holes in a GaAs Double Quantum Dot

    Science.gov (United States)

    Wang, Qingwen; Klochan, Oleh; Hung, Jo-Tzu; Culcer, Dimitrie; Farrer, Ian; Ritchie, David; Hamilton, Alex

    Electrically defined semiconductor quantum dots are appealing systems for spin manipulation and quantum information processing. Thanks to the weak hyperfine interaction and the strong spin-orbit interaction, heavy-holes in GaAs are promising candidates for all-electrical spin manipulation. However, making stable quantum dots in GaAs has only become possible recently, mainly because of difficulties in device fabrication and device stability. Here we present electrical transport measurements of heavy-holes in a lateral double quantum dot based on a GaAs /AlxGa1 - x As heterostructure. We observe clear Pauli spin blockade and show that the lifting of the spin blockade by an external magnetic field is extremely anisotropic. Numerical calculations of heavy-hole transport through a double quantum dot in the presence of strong spin-orbit interaction demonstrate quantitative agreement with experimental results, which indicates that the observed anisotropy can be explained by the anisotropic hole g-factor and the surface Dresselhaus spin-orbit coupling.

  2. Uniaxial strain effects on the band structure and effective masses of wurtzite GaAs

    Science.gov (United States)

    Cheiwchanchamnangij, Tawinan; Lambrecht, Walter

    2010-03-01

    While GaAs in bulk form has the zincblende structure, recent interest in the wurtzite form of GaAs arises in the context of nanowires. The band structure of wurtzite GaAs is calculated using the full-potential (FP) linearized muffin-tin orbital (LMTO) method within the local density approximation. The relativistic and spin-orbit coupling effects are included when obtaining the conduction and valence band effective mass tensors and related Rashba-Sheka-Pikus Hamiltonian parameters. The effects of c-axis uniaxial strain on the band structure is investigated and used to determine the relevant strain deformation potentials. It is found that under increasing uniaxial strain, a crossing of the γ5 and γ1 valence band levels occurs first, followed at higher strain by an additional crossing of the γ3 and γ1 conduction bands.. The latter is related to a corresponding direct to indirect (γ-L) crossing under uniaxial strain in zinblende.

  3. Friedreich ataxia is not only a GAA repeats expansion disorder: implications for molecular testing and counselling.

    Science.gov (United States)

    Hoffman-Zacharska, Dorota; Mazurczak, Tomasz; Zajkowski, Tomasz; Tataj, Renata; Górka-Skoczylas, Paulina; Połatyńska, Katarzyna; Kępczyński, Łukasz; Stasiołek, Mariusz; Bal, Jerzy

    2016-08-01

    Friedreich ataxia (FRDA) is the most common hereditary ataxia. It is an autosomal recessive disorder caused by mutations of the FXN gene, mainly the biallelic expansion of the (GAA)n repeats in its first intron. Heterozygous expansion/point mutations or deletions are rare; no patients with two point mutations or a point mutation/deletion have been described, suggesting that loss of the FXN gene product, frataxin, is lethal. This is why routine FRDA molecular diagnostics is focused on (GAA)n expansion analysis. Additional tests are considered only in cases of heterozygous expansion carriers and an atypical clinical picture. Analyses of the parent's carrier status, together with diagnostic tests, are performed in rare cases, and, because of that, we may underestimate the frequency of deletions. Even though FXN deletions are characterised as 'exquisitely rare,' we were able to identify one case (2.4 %) of a (GAA)n expansion/exonic deletion in a group of 41 probands. This was a patient with very early onset of disease with rapid progression of gait instability and hypertrophic cardiomyopathy. We compared the patient's clinical data to expansion/deletion carriers available in the literature and suggest that, in clinical practice, the FXN deletion test should be taken into account in patients with early-onset, rapid progressive ataxia and severe scoliosis.

  4. Friedreich ataxia: executive control is related to disease onset and GAA repeat length.

    Science.gov (United States)

    Nachbauer, Wolfgang; Bodner, Thomas; Boesch, Sylvia; Karner, Elfriede; Eigentler, Andreas; Neier, Lisa; Benke, Thomas; Delazer, Margarete

    2014-02-01

    Friedreich ataxia (FRDA) is the most frequent inherited ataxia. Neuropsychological studies suggest that FRDA may be associated with specific cognitive impairment. Very little is known about the relation between cognitive performance, demographics and disease-related parameters, such as GAA repeat size, age of onset and disease duration. The present investigation aimed at assessing cognitive functions in a representative sample of FRDA patients and at identifying the most relevant disease-related parameters. Twenty-nine adult FRDA patients underwent neuropsychological tests assessing executive functions, attention, memory and visual perception. Performance was compared with 28 age- and education-matched controls as well as with standardized norms. The relation between neuropsychological outcome, demographical variables and disease-related parameters was assessed. Cognitive impairment affected only a subgroup of patients and mostly concerned attentional and executive functions. Good cognitive performance was associated with a later disease onset, shorter GAA repeat length and lower burden of disease. Age at disease onset has been found to be a good predictor when a cut-off of 14 years was chosen. No correlation was found between cognitive performance and education, age or disease duration. The present study extends earlier findings in FRDA showing that performance in attentional and executive function tasks is best predicted by the age at disease onset. Moreover, executive functions show a clear relationship to disease severity and repeat size of the shorter GAA allele. These findings therefore have important implications for patient counselling regarding education and career choices.

  5. 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.

  6. Use of nitrogen as a carrier gas in LP-MOCVD for growth of GaAs AlGaAs and quantum well infrared photodetectors heterostructures

    Science.gov (United States)

    Zalevsky, Igor D.; Chelny, Alexander A.; Gorbylev, Vladimir A.; Avetisyan, Grachik H.; Kulikov, Vladimir B.

    1995-04-01

    In this paper the growth of GaAs and AlGaAs metal organic chemical vapor deposition (MOCVD) when nitrogen is used as carrier gas instead of hydrogen have been investigated. Properties of epilayers were studied in dependence from such parameters of epitaxy process as V/III ratio in gas phase, susceptor temperature and pressure in reactor. We fixed a conductivity types conversion from n- to p-type when mole fraction of Al in AlGaAs was increased from 19% to 67%. The abroad of conversion is near 40%. The increasing of methyl-radicals from trimethylaluminum concentration is a possible reason of this fact. To demonstrate the possibility of device structure growth by using in MOCVD nitrogen as carrier gas in first time the Quantum Well Infrared Photodetectors heterostructures have been fabricated. Some features of devices parameters are discussed. A device with mesa-structure has a dark current density of 1(DOT)10-6 A at U equals 2 V and T equals 77 K; the responsivity at U equals 2 V and 45 degree(s) angle incidence of IR-radiation was S equals 0.1 A/W ((lambda) max equals 10.7 mkm).

  7. Liquid phase epitaxial growth of GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Wynne, Danielle Ivy [Univ. of California, Berkeley, CA (United States). Materials Science and Mineral Engineering

    1997-10-01

    Research into new semiconductor materials for measurement of electromagnetic radiation over a wide range of energies has been an active field for several decades. There is a strong desire to identify and develop new materials which can lead to improved detectors. Such devices are expected to solve problems that cannot be solved using the semiconductor materials and device structures which have been traditionally used for radiation detection. In order for a detector which is subjected to some type of irradiation to respond, the radiation must undergo an interaction with the detector. The net result of the radiation interaction in a broad category of detectors is the generation of mobile electric charge carriers (electrons and/or holes) within the detector active volume. This charge is collected at the detector contacts and it forms the basic electrical signal. Typically, the collection of the charge is accomplished through the imposition of an electric field within the detector which causes the positive and/or negative charges created by the radiation to flow in opposite directions to the contacts. For the material to serve as a good radiation detector, a large fraction (preferably 100%) of all carriers created by the interacting incident radiation must be collected. Charge trapping by deep level impurities and structural defects can seriously degrade detector performance. The focus of this thesis is on far infrared and X-ray detection. In X-ray detector applications of p-I-n diodes, the object is to measure accurately the energy distribution of the incident radiation quanta. One important property of such detectors is their ability to measure the energy of individual incident photons with high energy resolution.

  8. 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

  9. ATF Neutron Irradiation Program Irradiation Vehicle Design Concepts

    Energy Technology Data Exchange (ETDEWEB)

    Geringer, J. W. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division; Katoh, Yutai [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division; Howard, Richard H. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division; Cetiner, N. O. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division; Petrie, Christian M. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division; Smith, Kurt R. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division; McDuffee, J. M. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division

    2016-03-01

    The Japan Atomic Energy Agency (JAEA) under the Civil Nuclear Energy Working Group (CNWG) is engaged in a cooperative research effort with the U.S. Department of Energy (DOE) to explore issues related to nuclear energy, including research on accident-tolerant fuels and materials for use in light water reactors. This work develops a draft technical plan for a neutron irradiation program on the candidate accident-tolerant fuel cladding materials and elements using the High Flux Isotope Reactor (HFIR). The research program requires the design of a detailed experiment, development of test vehicles, irradiation of test specimens, possible post irradiation examination and characterization of irradiated materials and the shipment of irradiated materials to Japan. This report discusses the conceptual design, the development and irradiation of the test vehicles.

  10. (GAA)n microsatellite as an indicator of the A genome reorganization during wheat evolution and domestication.

    Science.gov (United States)

    Adonina, Irina G; Goncharov, Nikolay P; Badaeva, Ekaterina D; Sergeeva, Ekaterina M; Petrash, Nadezhda V; Salina, Elena A

    2015-01-01

    Although the wheat A genomes have been intensively studied over past decades, many questions concerning the mechanisms of their divergence and evolution still remain unsolved. In the present study we performed comparative analysis of the A genome chromosomes in diploid (Triticum urartu Tumanian ex Gandilyan, 1972, Triticum boeoticum Boissier, 1874 and Triticum monococcum Linnaeus, 1753) and polyploid wheat species representing two evolutionary lineages, Timopheevi (Triticum timopheevii (Zhukovsky) Zhukovsky, 1934 and Triticum zhukovskyi Menabde & Ericzjan, 1960) and Emmer (Triticum dicoccoides (Körnicke ex Ascherson & Graebner) Schweinfurth, 1908, Triticum durum Desfontaines, 1798, and Triticum aestivum Linnaeus, 1753) using a new cytogenetic marker - the pTm30 probe cloned from Triticum monococcum genome and containing (GAA)56 microsatellite sequence. Up to four pTm30 sites located on 1AS, 5AS, 2AS, and 4AL chromosomes have been revealed in the wild diploid species, although most accessions contained one-two (GAA)n sites. The domesticated diploid species Triticum monococcum differs from the wild diploid species by almost complete lack of polymorphism in the distribution of (GAA)n site. Only one (GAA)n site in the 4AL chromosome has been found in Triticum monococcum. Among three wild emmer (Triticum dicoccoides) accessions we detected 4 conserved and 9 polymorphic (GAA)n sites in the A genome. The (GAA)n loci on chromosomes 2AS, 4AL, and 5AL found in of Triticum dicoccoides were retained in Triticum durum and Triticum aestivum. In species of the Timopheevi lineage, the only one, large (GAA)n site has been detected in the short arm of 6A(t) chromosome. (GAA)n site observed in Triticum monococcum are undetectable in the A(b) genome of Triticum zhukovskyi, this site could be eliminated over the course of amphiploidization, while the species was established. We also demonstrated that changes in the distribution of (GAA)n sequence on the A-genome chromosomes of diploid

  11. Craniospinal irradiation techniques

    Energy Technology Data Exchange (ETDEWEB)

    Scarlatescu, Ioana, E-mail: scarlatescuioana@gmail.com; Avram, Calin N. [Faculty of Physics, West University of Timisoara, Bd. V. Parvan 4, 300223 Timisoara (Romania); Virag, Vasile [County Hospital “Gavril Curteanu” - Oradea (Romania)

    2015-12-07

    In this paper we present one treatment plan for irradiation cases which involve a complex technique with multiple beams, using the 3D conformational technique. As the main purpose of radiotherapy is to administrate a precise dose into the tumor volume and protect as much as possible all the healthy tissues around it, for a case diagnosed with a primitive neuro ectoderm tumor, we have developed a new treatment plan, by controlling one of the two adjacent fields used at spinal field, in a way that avoids the fields superposition. Therefore, the risk of overdose is reduced by eliminating the field divergence.

  12. Manipulation of morphology and structure of the top of GaAs nanowires grown by molecular-beam epitaxy

    Science.gov (United States)

    Li, Lixia; Pan, Dong; Yu, Xuezhe; So, Hyok; Zhao, Jianhua

    2017-10-01

    Self-catalyzed GaAs nanowires (NWs) are grown on Si (111) substrates by molecular-beam epitaxy. The effect of different closing sequences of the Ga and As cell shutters on the morphology and structural phase of GaAs NWs is investigated. For the sequences of closing the Ga and As cell shutters simultaneously or closing the As cell shutter 1 min after closing the Ga cell shutter, the NWs grow vertically to the substrate surface. In contrast, when the As cell shutter is closed first, maintaining the Ga flux is found to be critical for the following growth of GaAs NWs, which can change the growth direction from [111] to . The evolution of the morphology and structural phase transition at the tips of these GaAs NWs confirm that the triple-phase-line shift mode is at work even for the growth with different cell shutter closing sequences. Our work will provide new insights for better understanding of the growth mechanism and realizing of the morphology and structure control of the GaAs NWs. Project supported partly by the MOST of China (No. 2015CB921503), the National Natural Science Foundation of China (Nos. 61504133, 61334006, 61404127), and Youth Innovation Promotion Association, CAS (No. 2017156).

  13. Photodetector fabrication by dielectrophoretic assembly of GaAs nanowires grown by a two-steps method

    Science.gov (United States)

    García Núñez, Carlos; Braña, Alejandro F.; López, Nair; Pau, José L.; García, Basilio J.

    2017-08-01

    GaAs nanowires (NWs) are promising advanced materials for the development of high performance photodetectors in the visible and infrared range. In this work, we optimize the epitaxial growth of GaAs NWs compared to conventional procedures, by introducing a novel two-steps growth method that exhibits an improvement of the resulting NW aspectratio and an enhancement of the NW growth rate. Moreover, we investigate the contactless manipulation of NWs using non-uniform electric fields to assemble a single GaAs NW on conductive electrodes, resulting in assembly yields above 90%/site and an alignment yields of around 95%. The electrical characteristics of the dielectrophoretic contact formed between the NW and the electrode have been measured, observing that the use of n-type Al-doped ZnO (AZO) as electrode material for NW alignment produces Schottky barrier contacts with the GaAs NW body. Moreover, our results show the fast fabrication of diodes with rectifying characteristics due to the formation of a low-resistance contact between the Ga catalytic droplet at the tip of the NW and the AZO electrode. The current-voltage measurements of a single GaAs NW diode under different illumination conditions show a strong light responsivity of the forward bias characteristic mainly produced by a change on the series resistance.

  14. Expanded GAA repeats impair FXN gene expression and reposition the FXN locus to the nuclear lamina in single cells.

    Science.gov (United States)

    Silva, Ana M; Brown, Jill M; Buckle, Veronica J; Wade-Martins, Richard; Lufino, Michele M P

    2015-06-15

    Abnormally expanded DNA repeats are associated with several neurodegenerative diseases. In Friedreich's ataxia (FRDA), expanded GAA repeats in intron 1 of the frataxin gene (FXN) reduce FXN mRNA levels in averaged cell samples through a poorly understood mechanism. By visualizing FXN expression and nuclear localization in single cells, we show that GAA-expanded repeats decrease the number of FXN mRNA molecules, slow transcription, and increase FXN localization at the nuclear lamina (NL). Restoring histone acetylation reverses NL positioning. Expanded GAA-FXN loci in FRDA patient cells show increased NL localization with increased silencing of alleles and reduced transcription from alleles positioned peripherally. We also demonstrate inefficiencies in transcription initiation and elongation from the expanded GAA-FXN locus at single-cell resolution. We suggest that repressive epigenetic modifications at the expanded GAA-FXN locus may lead to NL relocation, where further repression may occur. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  15. The Friedreich ataxia GAA repeat expansion mutation induces comparable epigenetic changes in human and transgenic mouse brain and heart tissues.

    Science.gov (United States)

    Al-Mahdawi, Sahar; Pinto, Ricardo Mouro; Ismail, Ozama; Varshney, Dhaval; Lymperi, Stefania; Sandi, Chiranjeevi; Trabzuni, Daniah; Pook, Mark

    2008-03-01

    Friedreich ataxia (FRDA) is caused by a homozygous GAA repeat expansion mutation within intron 1 of the FXN gene, leading to reduced expression of frataxin protein. Evidence suggests that the mutation may induce epigenetic changes and heterochromatin formation, thereby impeding gene transcription. In particular, studies using FRDA patient blood and lymphoblastoid cell lines have detected increased DNA methylation of specific CpG sites upstream of the GAA repeat and histone modifications in regions flanking the GAA repeat. In this report we show that such epigenetic changes are also present in FRDA patient brain, cerebellum and heart tissues, the primary affected systems of the disorder. Bisulfite sequence analysis of the FXN flanking GAA regions reveals a shift in the FRDA DNA methylation profile, with upstream CpG sites becoming consistently hypermethylated and downstream CpG sites becoming consistently hypomethylated. We also identify differential DNA methylation at three specific CpG sites within the FXN promoter and one CpG site within exon 1. Furthermore, we show by chromatin immunoprecipitation analysis that there is overall decreased histone H3K9 acetylation together with increased H3K9 methylation of FRDA brain tissue. Further studies of brain, cerebellum and heart tissues from our GAA repeat expansion-containing FRDA YAC transgenic mice reveal comparable epigenetic changes to those detected in FRDA patient tissue. We have thus developed a mouse model that will be a valuable resource for future therapeutic studies targeting epigenetic modifications of the FXN gene to increase frataxin expression.

  16. Long intronic GAA*TTC repeats induce epigenetic changes and reporter gene silencing in a molecular model of Friedreich ataxia.

    Science.gov (United States)

    Soragni, E; Herman, D; Dent, S Y R; Gottesfeld, J M; Wells, R D; Napierala, M

    2008-11-01

    Friedreich ataxia (FRDA) is caused by hyperexpansion of GAA*TTC repeats located in the first intron of the FXN gene, which inhibits transcription leading to the deficiency of frataxin. The FXN gene is an excellent target for therapeutic intervention since (i) 98% of patients carry the same type of mutation, (ii) the mutation is intronic, thus leaving the FXN coding sequence unaffected and (iii) heterozygous GAA*TTC expansion carriers with approximately 50% decrease of the frataxin are asymptomatic. The discovery of therapeutic strategies for FRDA is hampered by a lack of appropriate molecular models of the disease. Herein, we present the development of a new cell line as a molecular model of FRDA by inserting 560 GAA*TTC repeats into an intron of a GFP reporter minigene. The GFP_(GAA*TTC)(560) minigene recapitulates the molecular hallmarks of the mutated FXN gene, i.e. inhibition of transcription of the reporter gene, decreased levels of the reporter protein and hypoacetylation and hypermethylation of histones in the vicinity of the repeats. Additionally, selected histone deacetylase inhibitors, known to stimulate the FXN gene expression, increase the expression of the GFP_(GAA*TTC)(560) reporter. This FRDA model can be adapted to high-throughput analyses in a search for new therapeutics for the disease.

  17. Spectral properties of proton irradiated gallium nitride blue diodes

    Science.gov (United States)

    Gaudreau, F.; Carlone, C.; Houdayer, A.; Khanna, S. M.

    2001-12-01

    The permanent damage induced by 2 MeV proton irradiation at room temperature is reported for gallium nitride based blue emitting diodes (CREE model C430-DH85). Both optical and electrical device characteristics were measured. The I-V dependence was obtained as a function of temperature. At low voltages, the current is proportional to the exponential of the voltage at a constant temperature and the slope of the I-V curve is independent of temperature for the range 75-350 K, confirming the tunneling mechanism of the carrier injection. The room-temperature curve was studied as a function of 2-MeV proton irradiation in the fluence range 10/sup 11/ to 10/sup 15/ cm/sup -2/. It is hardly affected up to a fluence of 3/spl times/10/sup 12/ cm/sup -2/. Higher fluences do not affect the tunneling mechanism, but proton irradiation affects the saturation value of the current. The integrated electroluminescence versus voltage curves were obtained as a function of fluence, but the results were not amenable to a degradation constant interpretation. To gain insight into the degradation mechanism, the electroluminescence was analyzed spectrally and found to be the sum of the band-to-band transition in blue color at /spl ap/430 nm and a parasitic yellow band. The contribution of each transition was determined. The ratio of the contributions depends on driving current, temperature, and fluence. Treated individually, both the band-to-band and the yellow transition are related to fluence. The 2-MeV proton radiation damage constant is (7/spl plusmn/1)/spl times/10/sup -14/ cm/sup -2/ for the band-to-band and (2.0/spl plusmn/0.4)/spl times/10/sup -14/ cm/sup -2/ for the yellow transitions. The degradation of space charge recombination and diffusion of minority carriers cause the degradation of the electroluminescence. GaN light-emitting diodes (LEDs) are about two orders of magnitude more resistant to 2-MeV proton irradiation than GaAs LEDs.

  18. International Developments of Food Irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Loaharanu, P. [Head, Food Preservation Section, Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, Wagramerstr. 5, A-1400, Vienna (Austria)

    1997-12-31

    Food irradiation is increasingly accepted and applied in many countries in the past decade. Through its use, food losses and food-borne diseases can be reduced significantly, and wider trade in many food items can be facilitated. The past five decades have witnessed a positive evolution on food irradiation according to the following: 1940`s: discovery of principles of food irradiation; 1950`s: initiation of research in advanced countries; 1960`s: research and development were intensified in some advanced and developing countries; 1970`s: proof of wholesomeness of irradiated foods; 1980`s: establishment of national regulations; 1990`s: commercialization and international trade. (Author)

  19. Food irradiation and the consumer

    Science.gov (United States)

    A Thomas, P.

    The poster presents a review of research work undertaken on the perception and understanding that consumers have of food irradiation. Food irradiation is not a revolutionary new food processing technique, in fact it is probably one of the most investigated methods presently available. Many countries such as Belgium, France, Denmark, Italy, Spain, the Netherlands and the United States of America permit food irradiation. In Britain it is presently banned although this is currently under review. Awareness of food irradiation by the general public in Britain, although not extensively researched would appear to be increasing, especially in the light of recent media coverage. New quantitative and qualitative work indicates that the general public are concerned about the safety and effectiveness of food irradiation. Research has shown that a large proportion of consumers in Britain, if given the opportunity to purchase irradiated food, would not do so. Further exploration into this response revealed the fact that consumers are confused over what food irradiation is. In addition, there is concern over the detection of irradiated food. The views presented in this paper, of the consumer reaction to irradiated food are of great importance to those involved in the food industry and industries allied to it, which are ultimately dependent on the consumer for their commercial survival.

  20. Food irradiation and sterilization

    Science.gov (United States)

    Josephson, Edward S.

    Radiation sterilization of food (radappertization) requires exposing food in sealed containers to ionizing radiation at absorbed doses high enough (25-70 kGy) to kill all organisms of food spoilage and public health significance. Radappertization is analogous to thermal canning is achieving shelf stability (long term storage without refrigeration). Except for dry products in which autolysis is negligible, the radappertization process also requires that the food be heated to an internal temperature of 70-80°C (bacon to 53°C) to inactivate autolytic enzymes which catalyze spoilage during storage without refrigeration. To minimize the occurence of irradiation induced off-flavors and odors, undesirable color changes, and textural and nutritional losses from exposure to the high doses required for radappertization, the foods are vacuum sealed and irradiated frozen (-40°C to -20°C). Radappertozed foods have the characteristic of fresh foods prepared for eating. Radappertization can substitute in whole or in part for some chemical food additives such as ethylene oxide and nitrites which are either toxic, carcinogenic, mutagenic, or teratogenic. After 27 years of testing for "wholesomeness" (safety for consumption) of radappertized foods, no confirmed evidence has been obtained of any adverse effecys of radappertization on the "wholesomeness" characteristics of these foods.

  1. Nano-structure fabrication of GaAs using AFM tip-induced local oxidation method: different doping types and plane orientations

    Directory of Open Access Journals (Sweden)

    Moon Kyoung-Sook

    2011-01-01

    Full Text Available Abstract In this study, we have fabricated nano-scaled oxide structures on GaAs substrates that are doped in different conductivity types of p- and n-types and plane orientations of GaAs(100 and GaAs(711, respectively, using an atomic force microscopy (AFM tip-induced local oxidation method. The AFM-induced GaAs oxide patterns were obtained by varying applied bias from approximately 5 V to approximately 15 V and the tip loading forces from 60 to 180 nN. During the local oxidation, the humidity and the tip scan speed are fixed to approximately 45% and approximately 6.3 μm/s, respectively. The local oxidation rate is further improved in p-type GaAs compared to n-type GaAs substrates whereas the rate is enhanced in GaAs(100 compared to and GaAs(711, respectively, under the identical conditions. In addition, the oxide formation mechanisms in different doping types and plane orientations were investigated and compared with two-dimensional simulation results.

  2. Antisense Oligonucleotides Promote Exon Inclusion and Correct the Common c.-32-13T>G GAA Splicing Variant in Pompe Disease

    NARCIS (Netherlands)

    E. van der Wal (Erik); A.J. Bergsma (Atze); J. Pijnenburg (Joon); A.T. van der Ploeg (Ans); W.W.M.P. Pijnappel (Pim)

    2017-01-01

    textabstractThe most common variant causing Pompe disease is c.-32-13T>G (IVS1) in the acid α-glucosidase (GAA) gene, which weakens the splice acceptor of GAA exon 2 and induces partial and complete exon 2 skipping. It also allows a low level of leaky wild-type splicing, leading to a childhood/adult

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-04-15

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

  4. Development of a clinical assay for detection of GAA mutations and characterization of the GAA mutation spectrum in a Canadian cohort of individuals with glycogen storage disease, type II.

    Science.gov (United States)

    McCready, M E; Carson, N L; Chakraborty, P; Clarke, J T R; Callahan, J W; Skomorowski, M A; Chan, A K J; Bamforth, F; Casey, R; Rupar, C A; Geraghty, M T

    2007-12-01

    Glycogen storage disease, type II (GSDII; Pompe disease; acid maltase deficiency) is an autosomal recessive disease caused by mutations of the GAA gene that lead to deficient acid alpha-glucosidase enzyme activity and accumulation of lysosomal glycogen. Although measurement of acid alpha-glucosidase enzyme activity in fibroblasts remains the gold standard for the diagnosis of GSDII, analysis of the GAA gene allows confirmation of clinical or biochemical diagnoses and permits predictive and prenatal testing of individuals at risk of developing GSDII. We have developed a clinical molecular test for the detection of GAA mutations based on cycle sequencing of the complete coding region. GAA exons 2-20 are amplified in six independent PCR using intronic primers. The resulting products were purified and sequenced. Preliminary studies using this protocol were conducted with DNA from 21 GSDII-affected individuals from five centers across Canada. In total, 41 of 42 mutations were detected (96.7% detection rate). Mutations spanned intron 1 through exon 19 and included nine novel mutations. Haplotype analysis of recurrent mutations further suggested that three of these mutations are likely to have occurred independently at least twice. Additionally, we report the identification of the c.-32-13T>G GAA mutation in an individual with infantile variant GSDII, despite reports of this mutation being associated almost exclusively with late-onset forms of the disease. The development of a clinical molecular test provides an important tool for the management and counseling of families and individuals with GSDII, and has provided useful information about the GAA mutation spectrum in Canada.

  5. Development of polycrystal GaAs solar cells. Quarterly technical progress report No. 1, January 15-April 30, 1979

    Energy Technology Data Exchange (ETDEWEB)

    Miller, D.L.; Cohen, M.J.; Harris, J.S. Jr.; Ballantyne, J.; Hoyte, A.; Stefanakos, E.

    1979-05-01

    The objective of this program is to develop a thin film GaAs solar cell technology with the potential of yielding cells with 12 to 15% efficiency and to develop thin film growth techniques which are compatible with the low cost production goal of $500/kW-peak. Progress is reported on a study of junction formation in large grain polycrystal GaAs; characterization of the electronic properties of polycrystal GaAs grown by MBE on low cost foreign substrates; optimizing the structure of AlGaAs-GaAs heterojunction Schottky barrier solar cells; and a variety of grain boundary measurements, including Scanning Light Microscopy (SLM), Deep Level Transient Spectroscopy (DLTS), SIMS, and temperature dependent resistivity.

  6. Corrugated surfaces formed on GaAs(331)A substrates: the template for laterally ordered InGaAs nanowires.

    Science.gov (United States)

    Gong, Zheng; Niu, Zhichuan; Fang, Zhidan

    2006-02-28

    Morphology evolution of high-index GaAs(331)A surfaces during molecular beam epitaxy (MBE) growth has been investigated in order to achieve regularly distributed step-array templates and fabricate spatially ordered low-dimensional nano-structures. Atomic force microscope (AFM) measurements have shown that the step height and terrace width of GaAs layers increase monotonically with increasing substrate temperature. By using the step arrays formed on GaAs(331)A surfaces as the templates, we have fabricated highly ordered InGaAs nanowires. The improved homogeneity and the increased density of the InGaAs nanowires are attributed to the modulated strain field caused by vertical multi-stacking, as well as the effect of corrugated surface of the template. Photoluminescence (PL) tests confirmed remarkable polarization anisotropy.

  7. Local monitoring of atomic steps on GaAs(001) surface under oxidation, wet removal of oxides and thermal smoothing

    Energy Technology Data Exchange (ETDEWEB)

    Akhundov, I.O.; Kazantsev, D.M. [Rzhanov Institute of Semiconductor Physics, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, 630090 Novosibirsk (Russian Federation); Alperovich, V.L., E-mail: alper@isp.nsc.ru [Rzhanov Institute of Semiconductor Physics, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, 630090 Novosibirsk (Russian Federation); Sheglov, D.V. [Rzhanov Institute of Semiconductor Physics, 630090 Novosibirsk (Russian Federation); Kozhukhov, A.S.; Latyshev, A.V. [Rzhanov Institute of Semiconductor Physics, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, 630090 Novosibirsk (Russian Federation)

    2017-06-01

    Highlights: • Specific atomic steps are monitored on the structured GaAs surface by ex situ AFM. • Oxidation and wet oxide removal keep the position and shape of atomic steps intact. • Thermal surface smoothing is studied on the structured GaAs surface. • The deviation from equilibrium towards growth during smoothing is revealed. • The step length smoothing kinetics is described by Monte Carlo simulation. - Abstract: The GaAs(001) step-terraced surface relief is studied under oxidation, wet oxide removal and thermal smoothing by ex situ atomic force microscopy with local monitoring of specific atomic steps using lithographic marks for surface area localization. Oxidation in the air and wet oxide removal lead to the formation of monatomic dips on terraces, while atomic steps keep their position and shape. Monitoring step mean position under thermal smoothing allows us to determine the deviation from equilibrium. The experimental smoothing kinetics is well described by Monte Carlo simulation.

  8. Catalytic Mechanism of Pd Adsorption on S-Terminated GaAs(001-(2 × 6 Surface

    Directory of Open Access Journals (Sweden)

    Deng-feng Li

    2013-01-01

    Full Text Available Structural and electronic properties of Pd adsorption on clean and S-terminated GaAs(001-(2 × 6 surfaces are studied using first-principle simulations. Our calculations show that the Pd atom prefers to occupy the HH3 site. The Pd atom is lower than the S atom with 0.15 Å. The density of states analysis confirms that S–Ga bond plays an important role in Heck reaction. We also find that the Pd catalysis activity for Pd adsorption on clean GaAs(001-(2 × 6 surface is weak while it is enhanced when the Pd atom is adsorbed on the S-terminated GaAs(001-(2 × 6 surface, which is in good agreement with the experiments.

  9. 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.

  10. Intersublevel infrared photodetector with strain-free GaAs quantum dot pairs grown by high-temperature droplet epitaxy.

    Science.gov (United States)

    Wu, Jiang; Shao, Dali; Dorogan, Vitaliy G; Li, Alvason Z; Li, Shibin; DeCuir, Eric A; Manasreh, M Omar; Wang, Zhiming M; Mazur, Yuriy I; Salamo, Gregory J

    2010-04-14

    Normal incident photodetection at mid infrared spectral region is achieved using the intersublevel transitions from strain-free GaAs quantum dot pairs in Al(0.3)Ga(0.7)As matrix. The GaAs quantum dot pairs are fabricated by high temperature droplet epitaxy, through which zero strain quantum dot pairs are obtained from lattice matched materials. Photoluminescence, photoluminescence excitation optical spectroscopy, and visible-near-infrared photoconductivity measurement are carried out to study the electronic structure of the photodetector. Due to the intersublevel transitions from GaAs quantum dot pairs, a broadband photoresponse spectrum is observed from 3 to 8 microm with a full width at half-maximum of approximately 2.0 microm.

  11. An explicit continuous analytical model for Gate All Around (GAA) MOSFETs including the hot-carrier degradation effects.

    Science.gov (United States)

    Abdi, M A; Djeffal, F; Bentrcia, T; Arar, D

    2011-10-01

    In this paper, an explicit and continuous analytical model including interfacial hot-carrier effects is developed for a deep submicron Gate All Around (GAA) MOSFETs. Explicit analytical expressions of the surface potential, drain current and transconductance are given for all operating modes. Exploiting this new device model, we have found that the incorporation of a high-k layer, Gate Stack (GS), between oxide region and gate metal leads to drain current enhancement, improved transconductance parameter and enhanced interfacial hot-carrier immunity. The developed approaches are verified and validated by the good agreement found with the 2D numerical simulations for wide range of device parameters and bias conditions. GS GAA MOSFET design can alleviate the critical problem and further improve the immunity of hot-carrier effects of GAA MOSFET-based circuits in the deep submicron working domain.

  12. Novel, complex interruptions of the GAA repeat in small, expanded alleles of two affected siblings with late-onset Friedreich ataxia.

    Science.gov (United States)

    Stolle, Catherine A; Frackelton, Edward C; McCallum, Jennifer; Farmer, Jennifer M; Tsou, Amy; Wilson, Robert B; Lynch, David R

    2008-07-15

    Friedreich ataxia (FA) is an autosomal recessive disorder associated with expanded GAA repeats in intron 1 of the FRDA gene. Two siblings presented with a mild form of FA at >60 years of age. Both had a large expansion (>600 repeats) and a small expansion (120 repeats) by long-range PCR. Sequence analysis of the small allele revealed multiple, complex interruptions in the GAA repeat. These 2 patients presented later than predicted from their allele size alone, when compared with a large cohort of FA patients. Accounting for the interruptions in the GAA repeat, though, did not make the age of onset consistent with that noted in other patients. Three additional patients with late onset FA and small expanded alleles also exhibited interrupted GAA repeats that were not associated with inappropriately late onset. Our observations suggest that interrupted GAA repeats do not clearly impact the age of onset in FA. (c) 2008 Movement Disorder Society.

  13. The effects of radiation on gallium arsenide radiation detectors

    CERN Document Server

    Bates, R L; D'Auria, S D; O'Shea, V; Raine, C; Smith, K M

    1997-01-01

    Semi-insulating, undoped, Liquid Encapsulated Czochralski (SI-U LEC) GaAs detectors have been irradiated with 1MeV neutrons, 24GeV/c protons, and 300MeV/c pions. The maximum fluences used were 6, 3, and 1.8~10$^{14}$ particles/cm$^{2}$ respectively. For all three types of irradiation the charge collection efficiencies (cce) of the detector are reduced due to the reduction in the electron and hole mean free paths. Pion and proton irradiations produce a greater reduction in cce than neutron irradiation with the pions having the greatest effect. The effect of annealing the detectors at room temperature, at 200$^{o}$C and at 450$^{o}$C with a flash lamp have been shown to reduce the leakage current and increase the cce of the irradiated detectors. The flash-lamp anneal produced the greatest increase in the cce from 26% to 70% by increasing the mean free path of the electrons. Two indium-doped samples were irradiated with 24GeV/c protons and demonstrated no improvement over SI U GaAs with respect to post-irradiati...

  14. Time-resolved photoluminescence characterization of GaAs nanowire arrays on native substrate

    Science.gov (United States)

    Dagytė, Vilgailė; Barrigón, Enrique; Zhang, Wei; Zeng, Xulu; Heurlin, Magnus; Otnes, Gaute; Anttu, Nicklas; Borgström, Magnus T.

    2017-12-01

    Time-resolved photoluminescence (TRPL) measurements of nanowires (NWs) are often carried out on broken-off NWs in order to avoid the ensemble effects as well as substrate contribution. However, the development of NW-array solar cells could benefit from non-destructive optical characterization to allow faster feedback and further device processing. With this work, we show that different NW array and substrate spectral behaviors with delay time and excitation power can be used to determine which part of the sample dominates the detected spectrum. Here, we evaluate TRPL characterization of dense periodic as-grown GaAs NW arrays on a p-type GaAs substrate, including a sample with uncapped GaAs NWs and several samples passivated with AlGaAs radial shell of varied composition and thickness. We observe a strong spectral overlap of substrate and NW signals and find that the NWs can absorb part of the substrate luminescence signal, thus resulting in a modified substrate signal. The level of absorption depends on the NW-array geometry, making a deconvolution of the NW signal very difficult. By studying TRPL of substrate-only and as-grown NWs at 770 and 400 nm excitation wavelengths, we find a difference in spectral behavior with delay time and excitation power that can be used to assess whether the signal is dominated by the NWs. We find that the NW signal dominates with 400 nm excitation wavelength, where we observe two different types of excitation power dependence for the NWs capped with high and low Al composition shells. Finally, from the excitation power dependence of the peak TRPL signal, we extract an estimate of background carrier concentration in the NWs.

  15. Growth and electronic properties of two-dimensional systems on (110) oriented GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Fischer, F.

    2005-07-01

    As the only non-polar plane the (110) surface has a unique role in GaAs. Together with Silicon as a dopant it is an important substrate orientation for the growth of n-type or p-type heterostructures. As a consequence, this thesis will concentrate on growth and research on that surface. In the course of this work we were able to realize two-dimensional electron systems with the highest mobilities reported so far on this orientation. Therefore, we review the necessary growth conditions and the accompanying molecular process. The two-dimensional electron systems allowed the study of a new, intriguing transport anisotropy not explained by current theory. Moreover, we were the first growing a two-dimensional hole gas on (110) GaAs with Si as dopant. For this purpose we invented a new growth modulation technique necessary to retrieve high mobility systems. In addition, we discovered and studied the metal-insulator transition in thin bulk p-type layers on (110) GaAs. Besides we investigated the activation process related to the conduction in the valence band and a parallelly conducting hopping band. The new two-dimensional hole gases revealed interesting physics. We studied the zero B-field spin splitting in these systems and compared it with the known theory. Furthermore, we investigated the anisotropy of the mobility. As opposed to the expectations we observed a strong persistent photoconductivity in our samples. Landau levels for two dimensional hole systems are non-linear and can show anticrossings. For the first time we were able to resolve anticrossings in a transport experiment and study the corresponding activation process. Finally, we compared these striking results with theoretical calculations. (orig.)

  16. Polarization and charge limit studies of strained GaAs photocathodes

    Energy Technology Data Exchange (ETDEWEB)

    Saez, P.J.

    1997-03-01

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

  17. GaSb on GaAs solar cells Grown using interfacial misfit arrays (Conference Presentation)

    Science.gov (United States)

    Nelson, George T.; Juang, Bor-Chau; Slocum, Michael A.; Bittner, Zachary S.; Laghumavarapu, Ramesh Babu B.; Huffaker, Diana L.; Hubbard, Seth M.

    2017-04-01

    State of the art InGaP2/GaAs/In0.28Ga0.72As inverted metamorphic (IMM) solar cells have achieved impressive results, however, the thick metamorphic buffer needed between the lattice matched GaAs and lattice mismatched InGaAs requires significant effort and time to grow and retains a fairly high defect density. One approach to this problem is to replace the bottom InGaAs junction with an Sb-based material such as 0.73 eV GaSb or 1.0 eV Al0.2Ga0.8Sb. By using interfacial misfit (IMF) arrays, the high degree of strain (7.8%) between GaAs and GaSb can be relaxed solely by laterally propagating 90° misfit dislocations that are confined to the GaAs-GaSb interface layer. We have used molecular beam epitaxy to grow GaSb single junction solar cells homoepitaxially on GaSb and heteroepitaxially on GaAs using IMF. Under 15-sun AM1.5 illumination, the control cell achieved 5% efficiency with a WOC of 366 mV, while the IMF cell was able to reach 2.1% with WOC of 546 mV. Shunting and high non-radiative dark current were main cause of FF and efficiency loss in the IMF devices. Threading dislocations or point defects were the expected source behind the losses, leading to minority carrier lifetimes less than 1ns. Deep level transient spectroscopy (DLTS) was used to search for defects electrically and two traps were found in IMF material that were not detected in the homoepitaxial GaSb device. One of these traps had a trap density of 7 × 1015 cm-3, about one order of magnitude higher than the control cell defect at 4 × 1016 cm-3.

  18. Removal of ion-implanted photoresists on GaAs using two organic solvents in sequence

    Energy Technology Data Exchange (ETDEWEB)

    Oh, Eunseok; Na, Jihoon; Lee, Seunghyo; Lim, Sangwoo, E-mail: swlim@yonsei.ac.kr

    2016-07-15

    Highlights: • Two-step photoresist removal process using two organic solvents was developed. • Photoresist on trench patterned GaAs was removed by two-step sequence. • Acetonitrile with dimethyl sulfoxide removed implanted photoresists at 30 °C. • Affinity and permeability of solvent through photoresist determine photoresist removal. - Abstract: Organic solvents can effectively remove photoresists on III–V channels without damage or etching of the channel material during the process. In this study, a two-step sequential photoresist removal process using two different organic solvents was developed to remove implanted ArF and KrF photoresists at room temperature. The effects of organic solvents with either low molar volumes or high affinities for photoresists were evaluated to find a proper combination that can effectively remove high-dose implanted photoresists without damaging GaAs surfaces. The performance of formamide, acetonitrile, nitromethane, and monoethanolamine for the removal of ion-implanted ArF and KrF photoresists were compared using a two-step sequential photoresist removal process followed by treatment in dimethyl sulfoxide (DMSO). Among the various combinations, the acetonitrile + DMSO two-step sequence exhibited the best removal of photoresists that underwent ion implantation at doses of 5 × 10{sup 13}–5 × 10{sup 15} atoms/cm{sup 2} on both flat and trench-structured GaAs surfaces. The ability of the two-step process using organic solvents to remove the photoresists can be explained by considering the affinities of solvents for a polymer and its permeability through the photoresist.

  19. Materials characterization for process integration of multi-channel gate all around (GAA) devices

    Science.gov (United States)

    Muthinti, Gangadhara Raja; Loubet, Nicolas; Chao, Robin; de la Peña, Abraham A.; Li, Juntao; Guillorn, Michael A.; Yamashita, Tenko; Kanakasabapathy, Sivananda; Gaudiello, John; Cepler, Aron J.; Sendelbach, Matthew; Emans, Susan; Wolfling, Shay; Ger, Avron; Kandel, Daniel; Koret, Roy; Lee, Wei Ti; Gin, Peter; Matney, Kevin; Wormington, Matthew

    2017-03-01

    Multi-channel gate all around (GAA) semiconductor devices march closer to becoming a reality in production as their maturity in development continues. From this development, an understanding of what physical parameters affecting the device has emerged. The importance of material property characterization relative to that of other physical parameters has continued to increase for GAA architecture when compared to its relative importance in earlier architectures. Among these materials properties are the concentration of Ge in SiGe channels and the strain in these channels and related films. But because these properties can be altered by many different process steps, each one adding its own variation to these parameters, their characterization and control at multiple steps in the process flow is crucial. This paper investigates the characterization of strain and Ge concentration, and the relationships between these properties, in the PFET SiGe channel material at the earliest stages of processing for GAA devices. Grown on a bulk Si substrate, multiple pairs of thin SiGe/Si layers that eventually form the basis of the PFET channel are measured and characterized in this study. Multiple measurement techniques are used to measure the material properties. In-line X-Ray Photoelectron Spectroscopy (XPS) and Low Energy X-Ray Fluorescence (LE-XRF) are used to characterize Ge content, while in-line High Resolution X-Ray Diffraction (HRXRD) is used to characterize strain. Because both patterned and un-patterned structures were investigated, scatterometry (also called optical critical dimension, or OCD) is used to provide valuable geometrical metrology.

  20. Sensorial evaluation of irradiated mangoes

    Energy Technology Data Exchange (ETDEWEB)

    Broisler, Paula Olhe; Cruz, Juliana Nunes da; Sabato, Susy Frey [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)]. E-mails: paulabroisler@hotmail.com; juliananc@ig.com.br; sfsabato@ipen.br

    2007-07-01

    Mango (Mangifera indica L.) is a tropical fruit of great economical relevance in the world, mainly for tropical countries like Brazil. It consists in the second tropical fruit more important grown in the world. On the other hand it is a very perishable fruit and its delivery to distant points is restricted due to short shelf life at environmental temperature. Food irradiation process is applied to fruits for their preservation, once it promotes disinfestation and even maturation retard, among other mechanisms. The Brazilian legislation permits the food irradiation and does not restrict the doses to be delivered. In order to verify eventual changes, sensorial evaluation is very important to study how irradiation affects the quality of the fruit and its acceptability. Mangoes were irradiated in a Cobalto-60 source, from the Radiation Technology Center, CTR, of IPEN/CNEN-SP at doses 0,5 kGy e 0,75 kGy. The sensorial evaluation was measured through Acceptance Test where irradiated samples were offered together with control sample to the tasters who answered their perception through hedonic scale. The parameters Color, Odor, Flavor and Texture were analyzed. Statistical analysis showed that only Odor parameter was different from control (sample irradiated at 0.5 kGy). Few tasters indicated that irradiated mangoes had fewer odors in relation to non-irradiated samples. (author)

  1. E. coli mismatch repair acts downstream of replication fork stalling to stabilize the expanded (GAA.TTC)(n) sequence.

    Science.gov (United States)

    Bourn, Rebecka L; Rindler, Paul M; Pollard, Laura M; Bidichandani, Sanjay I

    2009-02-10

    Expanded triplet repeat sequences are known to cause at least 16 inherited neuromuscular diseases. In addition to short-length changes, expanded triplet repeat tracts frequently undergo large changes, often amounting to hundreds of base-pairs. Such changes might occur when template or primer slipping creates insertion/deletion loops (IDLs), which are normally repaired by the mismatch repair system (MMR). However, in prokaryotes and eukaryotes, MMR promotes large changes in the length of (CTG.CAG)(n) sequences, the motif most commonly associated with human disease. We tested the effect of MMR on instability of the expanded (GAA.TTC)(n) sequence, which causes Friedreich ataxia, by comparing repeat instability in wild-type and MMR-deficient strains of Escherichia coli. As expected, the prevalence of small mutations increased in the MMR-deficient strains. However, the prevalence of large contractions increased in the MMR mutants specifically when GAA was the lagging strand template, the orientation in which replication fork stalling is known to occur. After hydroxyurea-induced stalling, both orientations of replication showed significantly more large contractions in MMR mutants than in the wild-type, suggesting that fork stalling may be responsible for the large contractions. Deficiency of MMR promoted large contractions independently of RecA status, a known determinant of (GAA.TTC)(n) instability. These data suggest that two independent mechanisms act in response to replication stalling to prevent instability of the (GAA.TTC)(n) sequence in E. coli, when GAA serves as the lagging strand template: one that is dependent on RecA-mediated restart of stalled forks, and another that is dependent on MMR-mediated repair of IDLs. While MMR destabilizes the (CTG.CAG)(n) sequence, it is involved in stabilization of the (GAA.TTC)(n) sequence. The role of MMR in triplet repeat instability therefore depends on the repeat sequence and the orientation of replication.

  2. GAA repeat expansion mutation mouse models of Friedreich ataxia exhibit oxidative stress leading to progressive neuronal and cardiac pathology.

    Science.gov (United States)

    Al-Mahdawi, Sahar; Pinto, Ricardo Mouro; Varshney, Dhaval; Lawrence, Lorraine; Lowrie, Margaret B; Hughes, Sian; Webster, Zoe; Blake, Julian; Cooper, J Mark; King, Rosalind; Pook, Mark A

    2006-11-01

    Friedreich ataxia (FRDA) is a neurodegenerative disorder caused by an unstable GAA repeat expansion mutation within intron 1 of the FXN gene. However, the origins of the GAA repeat expansion, its unstable dynamics within different cells and tissues, and its effects on frataxin expression are not yet completely understood. Therefore, we have chosen to generate representative FRDA mouse models by using the human FXN GAA repeat expansion itself as the genetically modified mutation. We have previously reported the establishment of two lines of human FXN YAC transgenic mice that contain unstable GAA repeat expansions within the appropriate genomic context. We now describe the generation of FRDA mouse models by crossbreeding of both lines of human FXN YAC transgenic mice with heterozygous Fxn knockout mice. The resultant FRDA mice that express only human-derived frataxin show comparatively reduced levels of frataxin mRNA and protein expression, decreased aconitase activity, and oxidative stress, leading to progressive neurodegenerative and cardiac pathological phenotypes. Coordination deficits are present, as measured by accelerating rotarod analysis, together with a progressive decrease in locomotor activity and increase in weight. Large vacuoles are detected within neurons of the dorsal root ganglia (DRG), predominantly within the lumbar regions in 6-month-old mice, but spreading to the cervical regions after 1 year of age. Secondary demyelination of large axons is also detected within the lumbar roots of older mice. Lipofuscin deposition is increased in both DRG neurons and cardiomyocytes, and iron deposition is detected in cardiomyocytes after 1 year of age. These mice represent the first GAA repeat expansion-based FRDA mouse models that exhibit progressive FRDA-like pathology and thus will be of use in testing potential therapeutic strategies, particularly GAA repeat-based strategies.

  3. Spin Splitting in GaAs (100) Two-Dimensional Holes

    OpenAIRE

    Habib, B.; Tutuc, E.; Melinte, S.; Shayegan, M.; Wasserman, D.; Lyon, S. A.; Winkler, R.

    2004-01-01

    We measured Shubnikov-de Haas (SdH) oscillations in GaAs (100) two-dimensional holes to determine the inversion asymmetry-induced spin splitting. The Fourier spectrum of the SdH oscillations contains two peaks, at frequencies $f_-$ and $f_+$, that correspond to the hole densities of the two spin subbands and a peak, at frequency $f_\\mathrm{tot}$, corresponding to the total hole density. In addition, the spectrum exhibits an anomalous peak at $f_\\mathrm{tot}/2$. We also determined the effectiv...

  4. Structural properties of perfect ZnTe epilayers on (001) GaAs substrates

    Energy Technology Data Exchange (ETDEWEB)

    Lang, M. (ForschungsInst. fuer Optoelektronik, Univ. Linz (Austria)); Schikora, D.; Widmer, T. (and others)

    1994-04-14

    We report on molecular beam epitaxy and hot-wall beam epitaxy growth of ZnTe epilayers on (001) GaAs substrates. The surface reconstruction of (001) ZnTe is measured by reflection high-energy electron diffraction (RHEED). The RHEED pattern as a function of the beam equivalent pressure ratio p[sub Te]/p[sub Zn] and substrate temperature is studied. Mosaic structures of the ZnTe epilayers grown under optimized conditions are investigated quantitatively by high resolution X-ray diffraction and photoluminescence. These data, which are related to the three-dimensional perfection of epilayers, are contrasted to RHEED measurements of the surface morphology

  5. Antisites and anisotropic diffusion in GaAs and GaSb

    KAUST Repository

    Tahini, H. A.

    2013-10-02

    The significant diffusion of Ga under Ga-rich conditions in GaAs and GaSb is counter intuitive as the concentration of Ga vacancies should be depressed although Ga vacancies are necessary to interpret the experimental evidence for Ga transport. To reconcile the existence of Ga vacancies under Ga-rich conditions, transformation reactions have been proposed. Here, density functional theory is employed to calculate the formation energies of vacancies on both sublattices and the migration energy barriers to overcome the formation of the vacancy-antisite defect. Transformation reactions enhance the vacancy concentration in both materials and migration energy barriers indicate that Ga vacancies will dominate.

  6. Ultrafast properties of femtosecond-laser-ablated GaAs and its application to terahertz optoelectronics.

    Science.gov (United States)

    Madéo, Julien; Margiolakis, Athanasios; Zhao, Zhen-Yu; Hale, Peter J; Man, Michael K L; Zhao, Quan-Zhong; Peng, Wei; Shi, Wang-Zhou; Dani, Keshav M

    2015-07-15

    We report on the first terahertz (THz) emitter based on femtosecond-laser-ablated gallium arsenide (GaAs), demonstrating a 65% enhancement in THz emission at high optical power compared to the nonablated device. Counter-intuitively, the ablated device shows significantly lower photocurrent and carrier mobility. We understand this behavior in terms of n-doping, shorter carrier lifetime, and enhanced photoabsorption arising from the ablation process. Our results show that laser ablation allows for efficient and cost-effective optoelectronic THz devices via the manipulation of fundamental properties of materials.

  7. Photoluminescence Investigations of InGaAsN Alloys Lattice-Matched to GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Jones, E.D.; Modine, N.R.; Allerman, A.A.; Fritz, I.J.; Kurtz, S.R.; Wright, A.F.; Tozer, S.T.; Wei, Xing

    1999-06-01

    InGaAsN is a semiconductor alloy system with the property that the inclusion of only 2% nitrogen reduces the bandgap by more than 30%. In this paper, we have measured the conduction-band mass measurements by three different techniques for 2% nitrogen in InGaAsN lattice matched to GaAs. Additionally, we also report pressure dependent measurements of the conduction-band mass between ambient and 40 kbar. Based on our results, we suggest that the observed changes in masses are a result of {Lambda}-X mixing.

  8. 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 substrate by epitaxial lift off. In the presence of an electric field, both, the absorption bleaching due to phase space filling and field induced absorption changes due to the Franz-Keldysh effect contribute to the transmission changes. We observe an extended carrier lifetime with applied field...

  9. Doping incorporation paths in catalyst-free Be-doped GaAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Casadei, Alberto; Heiss, Martin; Colombo, Carlo; Ruelle, Thibaud; Fontcuberta i Morral, Anna [Laboratoire des Materiaux Semiconducteurs, Institut des Materiaux, Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne (Switzerland); Krogstrup, Peter; Roehr, Jason A.; Upadhyay, Shivendra; Sorensen, Claus B.; Nygard, Jesper [Nano-Science Center and Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen, Copenhagen (Denmark)

    2013-01-07

    The incorporation paths of Be in GaAs nanowires grown by the Ga-assisted method in molecular beam epitaxy have been investigated by electrical measurements of nanowires with different doping profiles. We find that Be atoms incorporate preferentially via the nanowire side facets, while the incorporation path through the Ga droplet is negligible. We also show that Be can diffuse into the volume of the nanowire giving an alternative incorporation path. This work is an important step towards controlled doping of nanowires and will serve as a help for designing future devices based on nanowires.

  10. Advanced digital modulation: Communication techniques and monolithic GaAs technology

    Science.gov (United States)

    Wilson, S. G.; Oliver, J. D., Jr.; Kot, R. C.; Richards, C. R.

    1983-01-01

    Communications theory and practice are merged with state-of-the-art technology in IC fabrication, especially monolithic GaAs technology, to examine the general feasibility of a number of advanced technology digital transmission systems. Satellite-channel models with (1) superior throughput, perhaps 2 Gbps; (2) attractive weight and cost; and (3) high RF power and spectrum efficiency are discussed. Transmission techniques possessing reasonably simple architectures capable of monolithic fabrication at high speeds were surveyed. This included a review of amplitude/phase shift keying (APSK) techniques and the continuous-phase-modulation (CPM) methods, of which MSK represents the simplest case.

  11. GaAs Wideband Low Noise Amplifier Design for Breast Cancer Detection System

    DEFF Research Database (Denmark)

    Yan, Lei; Krozer, Viktor; Delcourt, Sebastien

    2009-01-01

    to explore simultaneous wideband noise optimization and input power matching requirement. The low-noise amplifier circuit operates across a band of 0.3 to 10 GHz with a gain of around 14 dB and the measured noise figure NF below 1.5 dB up to 8 GHz. Measured small-signal results show good stability and very......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...

  12. 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...... model, directly yielding the electron scattering rates. A diffusion model is applied to determine the spatial extent of the photoexcited electron-hole gas at each moment after photoexcitation, yielding the time-dependent electron density, and hence the density-dependent electron scattering time. We find...

  13. Breakdown of the Korringa law of nuclear spin relaxation in metallic GaAs.

    Science.gov (United States)

    Kölbl, Dominikus; Zumbühl, Dominik M; Fuhrer, Andreas; Salis, Gian; Alvarado, Santos F

    2012-08-24

    We present nuclear spin relaxation measurements in GaAs epilayers using a new pump-probe technique in all-electrical, lateral spin-valve devices. The measured T(1) times agree very well with NMR data available for T>1 K. However, the nuclear spin relaxation rate clearly deviates from the well-established Korringa law expected in metallic samples and follows a sublinear temperature dependence T(1)(-1) is proportional to T(0.6) for 0.1 K≤T≤10 K. Further, we investigate nuclear spin inhomogeneities.

  14. Methods of Ga droplet consumption for improved GaAs nanowire solar cell efficiency

    Science.gov (United States)

    Dastjerdi, M. H. T.; Boulanger, J. P.; Kuyanov, P.; Aagesen, M.; LaPierre, R. R.

    2016-11-01

    We describe methods of Ga droplet consumption in Ga-assisted GaAs nanowires, and their impact on the crystal structure at the tip of nanowires. Droplets are consumed under different group V flux conditions and the resulting tip crystal structure is examined by transmission electron microscopy. The use of GaAsP marker layers provides insight into the behavior of the Ga droplet during different droplet consumption conditions. Lower group V droplet supersaturations lead to a pure zincblende stacking-fault-free tip crystal structure, which improved the performance of a nanowire-based photovoltaic device.

  15. Formation of local ferromagnetic areas on GaAs by focused Mn ion beam implantation

    Energy Technology Data Exchange (ETDEWEB)

    Kasai, M. [Department of Systems Innovation, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560 8531 (Japan); Yanagisawa, J. [Department of Systems Innovation, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560 8531 (Japan) and Research Center for Materials Science at Extreme Conditions, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560 8531 (Japan)]. E-mail: yanagisawa@ee.es.osaka-u.ac.jp; Tanaka, H. [Institute of Science and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567 0047 (Japan); Hasegawa, S. [Institute of Science and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567 0047 (Japan); Asahi, H. [Institute of Science and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567 0047 (Japan); Gamo, K. [Kansai Advanced Research Center, National Institute of Information and Communications Technology, 588 2 Iwaoka, Nishi-ku, Kobe, Hyogo 651 2492 (Japan); Akasaka, Y. [Department of Systems Innovation, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560 8531 (Japan); Research Center for Materials Science at Extreme Conditions, Osaka University, 1-3 Machikaneyama-cho, Toyonaka, Osaka 560 8531 (Japan)

    2006-01-15

    Magnetic and chemical properties of Mn-implanted surfaces of a GaAs substrate were investigated using a magnetic force microscope (MFM) and X-ray photoemission spectroscopy (XPS). The Mn implanted region was changed to a grain structure after annealing at 840 deg. C for 10 s, and ferromagnetic characteristics were observed in each grain. From the XPS spectra, it was found that implanted Mn was chemically bonded with other elements, indicating the formation of ferromagnetic materials such as GaMn and MnAs.

  16. Optical coupling of GaAs photodetectors integrated with lithium niobate waveguides

    Energy Technology Data Exchange (ETDEWEB)

    Chan, W.K.; Yan, A.Y.Y.; Gmitter, T.J.; Florez, L.T.; Jackel, J.L.; Hwang, D.M.; Yablonovitch, E.; Bhat, R.; Harbison, J.P. (Bellcore, Red Bank, NJ (US))

    1990-03-01

    The optical coupling of GaAs photodetectors integrated with LiNbO{sub 3} waveguides using epitaxial liftoff is measured and compared to calculations based on a complex index model. The measured coupling is found to be comparable to that obtained in epitaxial semi-conductor waveguide detectors, but lower than expected. Low coupling efficiency is attributed to the presence of a low index barrier layer, not present in semiconductor-based structures, at the GaAs-LiNbO{sub 3} interface. The authors propose a simple method to restore the coupling to its original value without the need to eliminate the barrier layer.

  17. Current flow mechanism in GaAs solar cells with GaInAs quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Mintairov, Mikhail, E-mail: mamint@scell.ioffe.ru; Evstropov, Valery; Shvarts, Maxim; Mintairov, Sergey; Salii, Roman; Kalyuzhnyy, Nikolay [Ioffe Institute, 26 Polytechnicheskaya str., St.-Petersburg, 194021 (Russian Federation)

    2016-06-17

    Resistance-less dark IV-curves of GaAs solar cells with and without quantum-dimensional objects allied to both quantum dot and quantum well have been obtained and analyzed. Anomalous large increase of the pre-exponential factors was observed in tested (with quantum objects) p-n junctions. According to proposed interpretation embedding of quantum objects in p-n junction created new current flow mechanisms. As a result current flows through recombination transitions inside quantum objects in space charge region of p-n junction.

  18. Strain-induced fermi contour anisotropy of GaAs 2D holes.

    Science.gov (United States)

    Shabani, J; Shayegan, M; Winkler, R

    2008-03-07

    We report measurements of magnetoresistance commensurability peaks, induced by a square array of antidots, in GaAs (311)A two-dimensional holes as a function of applied in-plane strain. The data directly probe the shapes of the Fermi contours of the two spin subbands that are split thanks to the spin-orbit interaction and strain. The experimental results are in quantitative agreement with the predictions of accurate energy band calculations, and reveal that the majority spin subband has a severely distorted Fermi contour whose anisotropy can be tuned with strain.

  19. Semiconductor topography in aqueous environments: Tunneling microscopy of chemomechanically polished (001) GaAs

    Science.gov (United States)

    Sonnenfeld, Richard; Schneir, J.; Drake, B.; Hansma, P. K.; Aspnes, D. E.

    1987-06-01

    Scanning tunneling microscopy (STM) of (001) GaAs samples immersed in aqueous solutions has been used to assess the effectiveness of a standard bromine-methanol chemomechanical polish to produce flat surfaces over length scales from 5 to 1000 nm. The STM images reveal irregular 100-nm features coexisting with large areas of average roughness of the order of a few nanometers. The precision, stability, and reproducibility of these images suggest that immersion STM could be used to study surface chemical processes in real time.

  20. Circuit demonstrations in a GaAs BiFET technology

    Science.gov (United States)

    Zampardi, P. J.; Beccue, S. M.; Yu, J.; Pedrotti, K.; Pierson, R. L.; Ho, W. J.; Chang, M. F.; Wang, K. C.

    1995-09-01

    In this paper, wer present several circuits demonstrating the versatility of our GaAs BiFET technology. Among the circuits presented here are a 360 ps access time SRAM, a 2 GHz 2-bit single-chip DRFM, a reduced power laser driver at 1.5 GHz, and an OEIC suitable for 4 Gb/s systems. This technology will have a significant impact on many areas of circuit research such as delta-sigma analog to digital convertors and mixed-mode applications.

  1. Circularly polarized lasing in chiral modulated semiconductor microcavity with GaAs quantum wells

    CERN Document Server

    Demenev, A A; Schneider, C; Brodbeck, S; Kamp, M; Höfling, S; Lobanov, S V; Weiss, T; Gippius, N A; Tikhodeev, S G

    2016-01-01

    We report the elliptically, close to circularly polarized lasing at $\\hbar\\omega = 1.473$ and 1.522 eV from an AlAs/AlGaAs Bragg microcavity with 12 GaAs quantum wells in the active region and chiral-etched upper distributed Bragg refractor under optical pump at room temperature. The advantage of using the chiral photonic crystal with a large contrast of dielectric permittivities is its giant optical activity, allowing to fabricate a very thin half-wave plate, with a thickness of the order of the emitted light wavelength, and to realize the monolithic control of circular polarization.

  2. Technology computer aided design for Si, SiGe and GaAs integrated circuits

    CERN Document Server

    Armstrong, GA

    2007-01-01

    The first book to deal with a broad spectrum of process and device design, and modelling issues related to semiconductor devices, bridging the gap between device modelling and process design using TCAD. Examples for types of Si-, SiGe-, GaAs- and InP-based heterostructure MOS and bipolar transistors are compared with experimental data from state-of-the-art devices. With various aspects of silicon heterostructures, this book presents a comprehensive perspective of emerging fields and covers topics ranging from materials to fabrication, devices, modelling and applications. Aimed at research-and-

  3. Consumer acceptance of irradiated food

    Energy Technology Data Exchange (ETDEWEB)

    Loaharanu, P. [Head, Food Preservation Section, Joint FAO/ IAEA Division of Nuclear Techniques in Food and Agriculture, Wagramerstr. 5, A-1400, Vienna (Austria)

    1997-12-31

    There was a widely held opinion during the 1970`s and 1980`s that consumers would be reluctant to purchase irradiated food, as it was perceived that consumers would confuse irradiated food with food contaminated by radionuclides. Indeed, a number of consumer attitude surveys conducted in several western countries during these two decades demonstrated that the concerns of consumers on irradiated food varied from very concerned to seriously concerned.This paper attempts to review parameters conducting in measuring consumer acceptance of irradiated food during the past three decades and to project the trends on this subject. It is believed that important lessons learned from past studies will guide further efforts to market irradiated food with wide consumer acceptance in the future. (Author)

  4. Irradiation of fresh fish

    Science.gov (United States)

    Yueh-jen, Yen; Jin-lai, Zhou; Shao-chun, Lai

    Occasionally, in China, marine products can not be provided for the markets in good quality, for during the time when they are being transported from the sea port to inland towns or even at the time when they are unloaded from the ship, they are beginning to spoil. Obviously, it is very important that appropiate measures should be taken to prevent them from decay. Our study has proved that the shelf life of fresh Flatfish (Cynoglossue robustus) and Silvery pomfret (stromateoides argenteus), which, packed in sealed containers, are irradiated by 1.5 kGy, 2.2 kGy and 3.0 kGy, can be stored for about 13-26 days at 3° - 5° C.

  5. 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...... faults. Selected area diffraction patterns and high-resolution transmission electron microscopy images show that nanowires undergo structural modifications upon annealing, suggesting a decrease of defect density following the thermal treatment....

  6. Irradiation for xenogeneic transplantation

    Energy Technology Data Exchange (ETDEWEB)

    Halperin, E.C.; Knechtle, S.J.; Harland, R.C.; Yamaguchi, Yasua; Sontag, M.; Bollinger, R.R. (Duke Univ., Durham, NC (USA). Dept. of Radiology Duke Univ., Durham, NC (USA). Dept. of Microbiology and Immunology)

    1990-05-01

    Xenogeneic transplantation (XT) is the transplantation of organs or tissues from a member of one species to a member of another. Mammalian species frequently have circulating antibody which is directed against the foreign organ irrespective of known prior antigen exposure. This antibody may lead to hyperacute rejection once it ensues so efforts must be directed towards eliminating the pre-existing antibody. In those species in which hyperacute rejection of xenografts does not occur, cell-mediated refection, similar to allograft rejection, may occur. It is in the prevention of this latter form of refection that radiation is most likely to be beneficial in XT. Both total lymphoid irradiation (TLI) and selective lyphoid irradiation (LSI) have been investigated for use in conjunction with XT. TLI has contributed to the prolongation of pancreatic islet-cell xenografts from hamsters to rats. TLI has also markedly prolonged the survival of cardiac transplants from hamsters to rats. A more modest prolongation of graft survival has been seen with the use of TLI in rabbit-to-rat exchanges. Therapy with TLI, cyclosporine, and splenectomy has markedly prolonged the survival of liver transplants from hamsters to rats, and preliminary data suggest that TLI may contribute to the prolongation of graft survival in the transplantation of hearts from monkeys to baboons. SLI appears to have prolonged graft survival, when used in conjunction with anti-lymphocyte globulin, in hamster-to-rat cardiac graft exchanges. The current state of knowledge of the use of irradiaiton in experimental XT is reviewed. (author). 38 refs.; 1 fig.; 5 tabs.

  7. Modification of structural and optical properties of polyvinyl alcohol/polyethylene glycol thin film by laser irradiation

    Science.gov (United States)

    Nouh, S. A.; Benthami, K.; Abutalib, M. M.

    2016-02-01

    The effect of infrared laser irradiation on the structural and the optical properties of polyvinyl alcohol/polyethylene glycol (PVA/PEG) co-polymer has been investigated. Thin films of PVA/PEG (nearly 50 µm thickness) were irradiated up to 15 J/cm2 of Ga-As laser pulses of 904 nm, 5 W power, and 200-ns pulse duration. The resultant effect of laser irradiation on the structural properties of PVA/PEG has been investigated using X-ray diffraction and Fourier transform infrared spectroscopy (FTIR). Further, the refractive index and the color difference between the exposed samples and the pristine have been studied. FTIR spectroscopy showed that the PVA/PEG samples exhibited degradation under the effect of laser irradiation up to 9 J/cm2, where crosslinking started and continued until 15 J/cm2. The refractive index had a minimum value of 1.5020 at 9 J/cm2, accompanied by a high degree of ordering and maximum value of 1.5640 at 15 J/cm2, with an increase in disordering character due to the degradation and crosslinking formation inside the sample, respectively. Moreover, the color intensity ΔE was greatly increased with increasing the laser fluence, accompanied by a significant increase in the yellow color component.

  8. Improvement in GAAS device yield and performance through substrate defect gettering

    Science.gov (United States)

    Magee, T. J.; Peng, J.; Ormond, R.; Armistead, R. A.; Malbon, M.; Evans, C. A., Jr.

    1980-06-01

    The use of mechanically produced, back surface damage as a means of gettering impurities and defects in GaAs wafers has been investigated. Comparative analyses have been done on both ion implantation and mechanical back surface damage gettering techniques. The increased thermal stability of mechanically produced damage has shown ion implantation techniques to be less effective for gettering over long anneal periods at elevated temperatures. Stress gradients produced by graded dislocation distributions produce reductions in front surface defect concentrations and effective gettering of Au and Cr at the back surfaces. Thermal stability times of back surface damage at anneal temperatures of 700-800 C is typically on the order of 2 - 3 hours, corresponding to the point at which major back surface microstructural damage is largely annealed. Increases in the thermal stability period were attained by encapsulating the back surface with an As-doped SiO2 layer. Gettering of Cr by back surface damage was also investigated at low temperatures (300 C - 400 C) for anneal periods of 10 - 300 hrs. Measurable concentrations of Cr were detected with the process characterized by an activation energy of approximately 0.88 eV and a time dependent term, exp (theta square root of t). Using the developed gettering procedures, FET structures were fabricated on VPE layers on pregettered GaAs wafers. Dramatic improvements in yield per wafer, noise figures at higher frequencies and input capacitance values were obtained on "inscreened" wafers processed through a normal fabrication line.

  9. Oxide heterostructures for high density 2D electron gases on GaAs

    Science.gov (United States)

    Kornblum, Lior; Faucher, Joseph; Morales-Acosta, Mayra D.; Lee, Minjoo L.; Ahn, Charles H.; Walker, Frederick J.

    2018-01-01

    2D electron gases (2DEGs) that form at oxide interfaces provide a rich testbed of phenomena for condensed matter research, with emerging implementations in devices. Integrating such oxide systems with semiconductors advances these interesting phenomena toward technological applications. This approach further opens prospects of new functionalities arising from the potential to couple the 2DEG carriers with the semiconductor. In this work, we demonstrate the first integration of oxide 2DEGs with a direct bandgap III-V semiconductor. The growth and structural characteristics of (001) GdTiO3-SrTiO3 (GTO-STO) heterostructures on (001) GaAs are described. Analysis of the magnetotransport data yields a high electron density of ˜2 × 1014 cm-2 per GTO-STO interface, and points to the oxide interface as the source of the carriers. The effect of structure and defects on the transport properties is discussed within the context of the growth conditions and their limitations. These results provide a route for integrating oxide 2DEGs and other functional oxides with GaAs toward future device prospects and integration schemes.

  10. Picosecond spin relaxation in low-temperature-grown GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Uemura, M.; Honda, K.; Yasue, Y.; Tackeuchi, A., E-mail: atacke@waseda.jp [Department of Applied Physics, Waseda University, Tokyo 169-8555 (Japan); Lu, S. L.; Dai, P. [Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Science, Suzhou (China)

    2014-03-24

    The spin relaxation process of low-temperature-grown GaAs is investigated by spin-dependent pump and probe reflectance measurements with a sub-picosecond time resolution. Two very short carrier lifetimes of 2.0 ps and 28 ps, which can be attributed to nonradiative recombinations related to defects, are observed at 10 K. The observed spin polarization shows double exponential decay with spin relaxation times of 46.2 ps (8.0 ps) and 509 ps (60 ps) at 10 K (200 K). The observed picosecond spin relaxation, which is considerably shorter than that of conventional GaAs, indicates the strong relevance of the Elliott-Yafet process as the spin relaxation mechanism. For the first (second) spin relaxation component, the temperature and carrier density dependences of the spin relaxation time indicate that the Bir-Aronov-Pikus process is also effective at temperatures between 10 K and 77 K, and that the D'yakonov-Perel’ process is effective between 125 K (77 K) and 200 K.

  11. Growth process of GaAs ripples as a function of incident Ar-ion dose

    Energy Technology Data Exchange (ETDEWEB)

    Datta, D.; Mondal, Shyamal [Surface Physics Division, Saha Institute of Nuclear Physics, 1/AF Bidhan Nagar, Kolkata 700064 (India); Bhattacharyya, S.R., E-mail: satyar.bhattacharyya@saha.ac.in [Surface Physics Division, Saha Institute of Nuclear Physics, 1/AF Bidhan Nagar, Kolkata 700064 (India)

    2012-02-15

    We report periodic ripple formation on GaAs sputtered by 60 keV Ar ions at an angle of 60 Degree-Sign over a large range of ion doses from 1 Multiplication-Sign 10{sup 17} to 1 Multiplication-Sign 10{sup 19} ions/cm{sup 2} under Atomic Force Microscopy (AFM) study. Initially in the dose range between 1 Multiplication-Sign 10{sup 17} and 4 Multiplication-Sign 10{sup 17} ions/cm{sup 2}, only very small roughness is formed on the surface and from the dose of 5 Multiplication-Sign 10{sup 17} ions/cm{sup 2}, the ripples start to form and attain a well-defined structure at a dose around 9 Multiplication-Sign 10{sup 17} ions/cm{sup 2}, remain stable and then from a dose of 4 Multiplication-Sign 10{sup 18} ions/cm{sup 2}, the ripple structures become very rough, periodicity breaks down and step-like features become prominent all over the surface. Parameters like rms roughness, ripple wavelength, amplitude etc. are measured from the AFM image analysis. The results are discussed with the help existing formalism with the understanding of preferential sputtering of one of the components of GaAs.

  12. Self-assembly of Silver Nanoparticles and Multiwall Carbon Nanotubes on Decomposed GaAs Surfaces

    Science.gov (United States)

    Al-Harthi, S. H.; Revathy, K. P.; Gard, F.; Mesli, A.; George, A. K.; Bartringer, J.; Mamor, M.; Unnikrishnan, N. V.

    2010-11-01

    Atomic Force Microscopy complemented by Photoluminescence and Reflection High Energy Electron Diffraction has been used to study self-assembly of silver nanoparticles and multiwall carbon nanotubes on thermally decomposed GaAs (100) surfaces. It has been shown that the decomposition leads to the formation of arsenic plate-like structures. Multiwall carbon nanotubes spin coated on the decomposed surfaces were mostly found to occupy the depressions between the plates and formed boundaries. While direct casting of silver nanoparticles is found to induce microdroplets. Annealing at 300°C was observed to contract the microdroplets into combined structures consisting of silver spots surrounded by silver rings. Moreover, casting of colloidal suspension consists of multiwall carbon nanotubes and silver nanoparticles is observed to cause the formation of 2D compact islands. Depending on the multiwall carbon nanotubes diameter, GaAs/multiwall carbon nanotubes/silver system exhibited photoluminescence with varying strength. Such assembly provides a possible bottom up facile way of roughness controlled fabrication of plasmonic systems on GaAs surfaces.

  13. Thermostimulated THz Radiation Emission of GaAs at Surface Plasmon-Phonon Polariton Frequencies

    Directory of Open Access Journals (Sweden)

    Edmundas ŠIRMULIS

    2014-06-01

    Full Text Available The THz radiation reflection, absorption and emission spectra of conductive n-GaAs/air surface are considered. The influence of thermostimulated surface plasmon-phonon (SPP polariton oscillations on THz radiation reflection, absorption and emission of high conductivity GaAs polished plates with electron density n = 7∙1017 cm–3 and 4∙1018 cm–3 and thickness of 350 mm is studied experimentally. The frequencies of thermostimulated transverse and longitudinal optical phonons and SPP oscillations, which characterize a heated lattice state, were determined. It is found that the heated highly doped interface layer (GaAs/air emits the THz radiation at selected frequencies of SPP oscillations in the (7 – 8 THz and (10 – 15 THz ranges. It is shown that thermal heating of the GaAs/air interface enhances the absorption of the incident THz radiation. The huge decrease of the incident radiation reflectivity at the SPP frequencies with an increase of GaAs temperature is observed experimentally. DOI: http://dx.doi.org/10.5755/j01.ms.20.2.6318

  14. Fabrication and characterization of the noble metal nanostructures on the GaAs surface

    Science.gov (United States)

    Gladskikh, Polina V.; Gladskikh, Igor A.; Toropov, Nikita A.; Vartanyan, Tigran A.

    2016-04-01

    Self-assembled silver, gold, and copper nanostructures on the monocrystalline GaAs (100) wafer surface were obtained via physical vapor deposition and characterized by optical reflection spectroscopy, scanning electron microscopy, and current-voltage curve measurements. Reflection spectra of the samples with Ag equivalent thicknesses of 2, 5, 7.5, and 10 nm demonstrated wide plasmonic bands in the visible range of spectra. Thermal annealing of the nanostructures led to narrowing of the plasmonic bands of Au and Ag nanostructures caused by major transformations of the film morphology. While the as prepared films predominantly had a small scale labyrinth structure, after annealing well-separated nanoislands are formed on the gallium arsenide surface. A clear correlation between films morphology and their optical and electrical properties is elucidated. Annealing of the GaAs substrate with Ag nanostructures at 100 °C under control of the resistivity allowed us to obtain and fix the structure at the percolation threshold. It is established that the samples at the percolation threshold possess the properties of resistance switching and hysteresis.

  15. Defect study of MOVPE-grown InGaP layers on GaAs

    Science.gov (United States)

    Knauer, A.; Krispin, P.; Balakrishnan, V. R.; Weyers, M.

    2004-12-01

    MOVPE-grown n-type GaAs/InGaP/GaAs structures with different GaAs cap layer thicknesses were studied by deep-level transient spectroscopy. An electron trap E1 with a thermal activation energy of 0.75 eV is formed in lattice matched InGaP after the MOVPE growth, if is not capped by sufficiently thick GaAs. The lattice mismatch of the InGaP layer influences the thermal activation energy of the deep defect, but not its occurrence or concentration. The starting surface concentration of the deep level defect as well as its diffusion at room temperature into the InGaP are apparently promoted by intrinsic defects in the InGaP layer determined by its growth condition. The shape of the depth profiles suggests that an extrinsic defect moves via interstitial sites into empty substitutional sites of the InGaP lattice. Oxygen atoms on phosphorus sites are probable candidates for the E1-related defects.

  16. Conductance deep-level transient spectroscopic study of anomalous hole trap in GaAs MESFETs

    Science.gov (United States)

    Balakrishnan, V. R.; Kumar, Vikram; Ghosh, Subhasis

    1998-10-01

    The anomalous `hole' trap like peaks observed in conductance DLTS spectra of GaAs MESFETs have been previously studied and have been associated with surface states present in the ungated regions at the GaAs-passivant interface. Besides these peaks, the conductance DLTS study of thermal emission and capture by these interface traps also indicates the presence of an associated surface conducting layer. These results show that electrons from this thin conducting layer interact with the interface states giving rise to a temperature-dependent surface leakage current when the Schottky gate is reverse biased with respect to the source and/or drain. This surface current affects both the capture and the emission processes of the interface traps. From the conductance DLTS measurements on GaAs MESFETs passivated with 0268-1242/13/10/007/img6 films, we have extracted a characteristic thermal activation energy of 0.43 eV for the interface electron traps, in both of these modes. A two-dimensional interface state band model has been used to explain our experimental results reported in this work.

  17. Structural and Electrical Characterization of Oxidated, Nitridated and Oxi-nitridated (100) GaAs Surfaces

    Science.gov (United States)

    Paul, Narayan Chandra; Nakamura, Kazuki; Takebe, Masahide; Takemoto, Akira; Inokuma, Takao; Iiyama, Koichi; Takamiya, Saburo; Higashimine, Koichi; Ohtsuka, Nobuo; Yonezawa, Yasuto

    2003-07-01

    Oxidation by the UV & ozone process, nitridation by the nitrogen helicon-wave-excited plasma process, and the combination of these processes are applied to (100) GaAs wafers. An atomic force microscope, X-ray photoelectron spectroscopy, a transmission electron microscope, photoluminescence and electrical characteristics (current-voltage and capacitance-voltage) were used to analyze the influences of these processes on the structure and composition of the surfaces and the interfaces. Metal-insulator-semiconductor (MIS) diodes and Schottky diodes were fabricated in order to investigate the electrical influences of these processes. The oxidation slightly disorders GaAs surfaces. Nitridation of a bare surface creates about a 2-nm-thick strongly disordered layer, which strongly deteriorates the electrical and photoluminescence characteristics. Nitridation of oxidated wafers (oxi-nitridation) forms firm amorphous GaON layers, which contain GaN, with very flat and sharp GaON/GaAs interfaces, where crystal disorder is hardly observed. It improves the current-voltage (I-V) and capacitance-voltage (C-V) characteristics and the photoluminescence intensity. Results of the structural and the electrical characterizations qualitatively coincide well with each other.

  18. A 1.2 THz Planar Tripler Using GaAs Membrane Based Chips

    Science.gov (United States)

    Bruston, J.; Maestrini, A.; Pukala, D.; Martin, S.; Nakamura, B.; Mehdi, I.

    2001-01-01

    Fabrication technology for submillimeter-wave monolithic circuits has made tremendous progress in recent years and it is now possible to fabricate sub-micron GaAs Schottky devices on a number of substrate types, such as membranes, frame-less membranes or substrateless circuits. These new technologies allow designers to implement very high frequency circuits, either Schottky mixers or multipliers, in a radically new manner. This paper will address the design, fabrication, and preliminary results of a 1.2 THz planar tripler fabricated on a GaAs frame-less membrane, the concept of which was described previously. The tripler uses a diode pair in an antiparallel configuration similar to designs used at lower frequency. To date, this tripler has produced a peak output power of 80 microW with 0.9% efficiency at room temperature (at 1126 GHz). The measured fix-tuned 3 dB bandwidth is about 3.5%. When cooled, the output power reached a peak of 195 microW at 120 K and 250 microW at 50 K. The ease with which this circuit was implemented along with the superb achieved performance indicates that properly designed planar devices such as this tripler can now usher in a new era of practical very high frequency multipliers.

  19. 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...

  20. Integration of a curved hybrid waveguide lens and photodetector array in a GaAs waveguide.

    Science.gov (United States)

    Vu, T Q; Tsai, C S; Kao, Y C

    1992-09-01

    For the first time, we believe, the integration of a waveguide lens and a photodetector array in GaAs for operation at a 1.3-microm wavelength is reported. The waveguide lens is a newly devised curved hybrid Fresnel/Bragg chirp grating lens fabricated by the ion-million technique. Desirable performance characteristics, including high throughput efficiency, freedom from coma (up to +/-4 deg off axis), and a near-diffraction-limited focal-spot size, have been demonstrated with this curved hybrid lens. The 10-element photodetector array of the InGaAs photoconducting type shows a measured gain-bandwidth product that is higher than 1 GHz at high frequency, while at a lower frequency the gain is in the range of several thousands. The curved-hybrid-lens-photodetector array combination realized in the GaAs 5 x 13 mm(2) in size has produced a well-resolved element spacing of 10 microm with cross talk that is lower than -14 dB. This lens-photodetector array combination constitutes a basc structure for the realization of monolit ic acousto-optic and electro-optic circuits such as integrated-optic rf spectrum analyzers and multiport switches.

  1. Nanostructured GaAs solar cells via metal-assisted chemical etching of emitter layers.

    Science.gov (United States)

    Song, Yunwon; Choi, Keorock; Jun, Dong-Hwan; Oh, Jungwoo

    2017-10-02

    GaAs solar cells with nanostructured emitter layers were fabricated via metal-assisted chemical etching. Au nanoparticles produced via thermal treatment of Au thin films were used as etch catalysts to texture an emitter surface with nanohole structures. Epi-wafers with emitter layers 0.5, 1.0, and 1.5 um in thickness were directly textured and a window layer removal process was performed before metal catalyst deposition. A nanohole-textured emitter layer provides effective light trapping capabilities, reducing the surface reflection of a textured solar cell by 11.0%. However, because the nanostructures have high surface area to volume ratios and large numbers of defects, various photovoltaic properties were diminished by high recombination losses. Thus, we have studied the application of nanohole structures to GaAs emitter solar cells and investigated the cells' antireflection and photovoltaic properties as a function of the nanohole structure and emitter thickness. Due to decreased surface reflection and improved shunt resistance, the solar cell efficiency increased from 4.25% for non-textured solar cells to 7.15% for solar cells textured for 5 min.

  2. Highly indistinguishable and strongly entangled photons from symmetric GaAs quantum dots.

    Science.gov (United States)

    Huber, Daniel; Reindl, Marcus; Huo, Yongheng; Huang, Huiying; Wildmann, Johannes S; Schmidt, Oliver G; Rastelli, Armando; Trotta, Rinaldo

    2017-05-26

    The development of scalable sources of non-classical light is fundamental to unlocking the technological potential of quantum photonics. Semiconductor quantum dots are emerging as near-optimal sources of indistinguishable single photons. However, their performance as sources of entangled-photon pairs are still modest compared to parametric down converters. Photons emitted from conventional Stranski-Krastanov InGaAs quantum dots have shown non-optimal levels of entanglement and indistinguishability. For quantum networks, both criteria must be met simultaneously. Here, we show that this is possible with a system that has received limited attention so far: GaAs quantum dots. They can emit triggered polarization-entangled photons with high purity (g(2)(0) = 0.002±0.002), high indistinguishability (0.93±0.07 for 2 ns pulse separation) and high entanglement fidelity (0.94±0.01). Our results show that GaAs might be the material of choice for quantum-dot entanglement sources in future quantum technologies.

  3. Crystal bending by surface damaging in mosaic GaAs crystals for the LAUE project

    Science.gov (United States)

    Buffagni, E.; Bonnini, E.; Zappettini, A.; Guadalupi, G. M.; Rossi, F.; Ferrari, C.

    2013-09-01

    Curved crystals used as optical elements of a Laue lens for hard x- and gamma-ray astronomy have a larger diffraction efficiency with respect to perfect flat crystals. In this work we show how to achieve the bending of the crystals by a controlled surface damaging which introduces defects in a superficial layer of few tens micrometers in thickness undergoing a highly compressive strain. Several silicon, gallium arsenide and germanium wafer crystals have been treated. The local and mean curvature radii of each sample have been determined by means of high resolution x-ray diffraction measurements in Bragg condition at low energy (8 keV). (100) oriented silicon and (111) oriented germanium samples showed spherical curvatures, whereas (100) oriented GaAs treated samples evidenced an elliptical curvature with major axes corresponding to the x1x0.2 cm3 GaAs crystals (100) oriented with a radius of curvature of 40 m were prepared for the Laue Lens. Using a x-ray tube set at a distance of 20 m from the crystal for the first time the focusing of the (022) diffracted beam at a distance of 20 m was observed.

  4. Growth initiation processes for GaAs and AlGaAs in CBE

    CERN Document Server

    Hill, D

    2002-01-01

    'in-growth' reconstruction to stabilise. However unlike for TMGa, GaAs growth with TEGa proceeds by a non-self limiting growth mode and TEGa rapidly dissociates. The result of this is that TEGa decomposes on top of other TEGa molecules, or their fragments and due to the high flux rate this leads to a 'stacking-up' of Ga on the surface. The presence of excess Ga provides a rapid increase of surface reflectance and then its subsequent decay as the excess Ga is incorporated by the increasing As content of the surface. The average growth rate during the transient period is equal to that of subsequent 'post-transient' period. However it is not certain as to whether the growth rate is constant throughout the transient period. The aim of this work was to investigate the nature of the transient period found in reflectance anisotropy (RA) measurements of high III:V BEP ratio growth of gallium arsenide (GaAs) and aluminium gallium arsenide (AIGaAs) by chemical beam epitaxy (CBE). Growth at substrate temperatures betwee...

  5. Highly indistinguishable and strongly entangled photons from symmetric GaAs quantum dots

    Science.gov (United States)

    Huber, Daniel; Reindl, Marcus; Huo, Yongheng; Huang, Huiying; Wildmann, Johannes S.; Schmidt, Oliver G.; Rastelli, Armando; Trotta, Rinaldo

    2017-01-01

    The development of scalable sources of non-classical light is fundamental to unlocking the technological potential of quantum photonics. Semiconductor quantum dots are emerging as near-optimal sources of indistinguishable single photons. However, their performance as sources of entangled-photon pairs are still modest compared to parametric down converters. Photons emitted from conventional Stranski–Krastanov InGaAs quantum dots have shown non-optimal levels of entanglement and indistinguishability. For quantum networks, both criteria must be met simultaneously. Here, we show that this is possible with a system that has received limited attention so far: GaAs quantum dots. They can emit triggered polarization-entangled photons with high purity (g(2)(0) = 0.002±0.002), high indistinguishability (0.93±0.07 for 2 ns pulse separation) and high entanglement fidelity (0.94±0.01). Our results show that GaAs might be the material of choice for quantum-dot entanglement sources in future quantum technologies. PMID:28548081

  6. GaAs Coupled Micro Resonators with Enhanced Sensitive Mass Detection

    Directory of Open Access Journals (Sweden)

    Tony Chopard

    2014-12-01

    Full Text Available This work demonstrates the improvement of mass detection sensitivity and time response using a simple sensor structure. Indeed, complicated technological processes leading to very brittle sensing structures are often required to reach high sensitivity when we want to detect specific molecules in biological fields. These developments constitute an obstacle to the early diagnosis of diseases. An alternative is the design of coupled structures. In this study, the device is based on the piezoelectric excitation and detection of two GaAs microstructures vibrating in antisymmetric modes. GaAs is a crystal which has the advantage to be micromachined easily using typical clean room processes. Moreover, we showed its high potential in direct biofunctionalisation for use in the biological field. A specific design of the device was performed to improve the detection at low mass and an original detection method has been developed. The principle is to exploit the variation in amplitude at the initial resonance frequency which has in the vicinity of weak added mass the greatest slope. Therefore, we get a very good resolution for an infinitely weak mass: relative voltage variation of 8%/1 fg. The analysis is based on results obtained by finite element simulation.

  7. Electron Tunneling Counting Statistics of a GaAs Quantum Dot at Thermal Equilibrium

    Science.gov (United States)

    Zhang, Xinchang; Xiao, Ming; Yablonovitch, Eli; Jiang, Hongwen

    2008-03-01

    Full counting statistics (FCS) is an innovative way to investigate current fluctuations of mesoscopic conductors which can provide additional information beyond the conventional average current measurement [1]. Suppression of the 2nd moment and the 3rd moment were observed in a many-electron quantum dot(QD)under nonequilibrium conditions [1]. Here we studied the FCS of single electron tunneling of a GaAs QD in the few electron regime at thermal equilibrium in the in-plane magnetic fields. The device consists of a multiple-surface-gates defined GaAs QD integrated with a very sensitive, high bandwidth field effect transitor (FET) channel for the QD charge state read-out. Monitoring the FET current revealed two sequences of random telegraph signals which represent the electron tunneling onto and off the QD in real time. When the QD level is aligned with Fermi level of the reservoir, the statistics shows a maximum value of both mean () and standard deviation (sigma), but a minimum skewness in its distribution function. It was also found that an in-plane magnetic field suppresses both and sigma, but enhances the skewness. [1], S. Gustavsson et. al, PRL 96, 76695(2006). .

  8. Ion Back-Bombardment of GaAs Photocathodes Inside DC High Voltage Electron Guns

    CERN Document Server

    Grames, Joseph M; Brittian, Joshua; Charles, Daniel; Clark, Jim; Hansknecht, John; Lynn Stutzman, Marcy; Poelker, Matthew; Surles-Law, Kenneth E

    2005-01-01

    The primary limitation for sustained high quantum efficiency operation of GaAs photocathodes inside DC high voltage electron guns is ion back-bombardment of the photocathode. This process results from ionization of residual gas within the cathode/anode gap by the extracted electron beam, which is subsequently accelerated backwards to the photocathode. The damage mechanism is believed to be either destruction of the negative electron affinity condition at the surface of the photocathode or damage to the crystal structure by implantation of the bombarding ions. This work characterizes ion formation within the anode/cathode gap for gas species typical of UHV vacuum chambers (i.e., hydrogen, carbon monoxide and methane). Calculations and simulations are performed to determine the ion trajectories and stopping distance within the photocathode material. The results of the simulations are compared with test results obtained using a 100 keV DC high voltage GaAs photoemission gun and beamline at currents up to 10 mA D...

  9. Sub-Poissonian Narrowing of Length Distributions Realized in Ga-Catalyzed GaAs Nanowires.

    Science.gov (United States)

    Koivusalo, Eero S; Hakkarainen, Teemu V; Guina, Mircea D; Dubrovskii, Vladimir G

    2017-09-13

    Herein, we present experimental data on the record length uniformity within the ensembles of semiconductor nanowires. The length distributions of Ga-catalyzed GaAs nanowires obtained by cost-effective lithography-free technique on silicon substrates systematically feature a pronounced sub-Poissonian character. For example, nanowires with the mean length ⟨L⟩ of 2480 nm show a length distribution variance of only 367 nm(2), which is more than twice smaller than the Poisson variance h⟨L⟩ of 808 nm(2) for this mean length (with h = 0.326 nm as the height of GaAs monolayer). For 5125 nm mean length, the measured variance is 1200 nm(2) against 1671 nm(2) for Poisson distribution. A supporting model to explain the experimental findings is proposed. We speculate that the fluctuation-induced broadening of the length distribution is suppressed by nucleation antibunching, the effect which is commonly observed in individual vapor-liquid-solid nanowires but has never been seen for their ensembles. Without kinetic fluctuations, the two remaining effects contributing to the length distribution width are the nucleation randomness for nanowires emerging from the substrate and the shadowing effect on long enough nanowires. This explains an interesting time evolution of the variance that saturates after a short incubation stage but then starts increasing again due to shadowing, remaining, however, smaller than the Poisson value for a sufficiently long time.

  10. Multilayers of GaAs/Mn deposited on a substrate of GaAs (001)

    Energy Technology Data Exchange (ETDEWEB)

    Bernal-Salamanca, M; Pulzara-Mora, A; Rosales-Rivera, A [Laboratorio de Magnetismo y Materiales Avanzados, Universidad Nacional de Colombia, Sede Manizales, A.A. 127 (Colombia); Molina-Valdovinos, S; Melendez-Lira, M [Physics Department, Centro de Investigacion y Estudios Avanzados del IPN, Av. IPN No. 2508, Apartado Postal 14-740, 07000 Mexico D.F (Mexico); Lopez-Lopez, M, E-mail: aopulzaram@unal.edu.c [Centro de Fisica Aplicada y Tecnologia Avanzada, Universidad Nacional Autonoma de Mexico, Apartado Postal 1-1010, Queretaro 76000 (Mexico)

    2009-05-01

    In this work GaAs/Mn multilayers were deposited on GaAs (001) substrates by R.F magnetron sputtering technique, varying the deposition time (tg). Scanning electron and atomic force Microscopy studies were realized on the surface of the samples in order to determine the morphology and average roughness. X-ray diffraction spectra show that our samples tend to do amorphous. Raman spectroscopy at room temperature was employed to analyze the structural properties of the samples. We found that for a GaAs film taken as reference, the Raman spectra is dominated by the transverse (TO) and longitudinal (LO) modes located at 266 cm{sup -1} and 291 cm{sup -1}, respectively. However, for the GaAs/Mn multilayers the TO and LO modes decrease dramatically, and the Mn Raman modes in the range of 100 cm{sup -1} and 250 cm{sup -1} are evidenced. Additional new peaks located around 650 and 690 cm {sup -1} are only observed for the samples with high Mn content. By using the mass reduced model we estimate that the Mn related peaks are located at 650.2 cm{sup -1} and 695.2 cm{sup -1}, in good agreement with the experimental data, these peaks are correlated with excitations due to (Mn){sub m}As{sub n} localized structures.

  11. Thermodynamic analysis of the deposition of GaAs epitaxial layers prepared by the MOCVD method

    Energy Technology Data Exchange (ETDEWEB)

    Leitner, J.; Mikulec, J. (Dept. of Materials for Electronics, Prague Inst. of Chemical Tech. (Czechoslovakia)); Vonka, P. (Dept. of Physical Chemistry, Prague Inst. of Chemical Tech. (Czechoslovakia)); Stejskal, J.; Hladina, R.; Klima, P. (TESLA Research Inst. of Radiocommunication, Prague (Czechoslovakia))

    1991-06-01

    On the basis of a detailed thermodynamic analysis of the Ga-As-C-H system, the initial conditions have been determined, under which the reaction of trimethylgallium (TMGa) and arsine in a hydrogen atmosphere produces a single condensed phase - solid GaAs. Liquid gallium with a small amount of dissolved arsenic is formed simultaneously when the initial ratio of the elements is B{sup V}/A{sup III}<1, whereas solid graphite is simultaneously deposited at a high initial concentration of TMGa, especially at an elevated temperature and a decreased pressure. The equilibrium concentrations of the gaseous substances are strongly influenced by the initial B{sup V}/A{sup III} ratio. As{sub 2}, As{sub 4}, and CH{sub 4} are the dominant species if B{sup V}/A{sup III}>1, while CH{sub 4}, GaCH{sub 3}, GaH and GaH{sub 2} are the most abundant if B{sup V}/A{sup III} < 1. The calculated deposition diagrams are in good qualitative agreement with experimental results published in the literature. A comparison of the calculated composition of the gaseous phase and the results of experiments under the conditions used for the deposition of GaAs epitaxial layers leads to the conclusion that the course and results of the deposition process are significantly affected by transport and kinetic phenomena. (orig.).

  12. Early stages of Cs adsorption mechanism for GaAs nanowire surface

    Science.gov (United States)

    Diao, Yu; Liu, Lei; Xia, Sihao; Feng, Shu

    2018-03-01

    In this study, the adsorption mechanism of Cs adatoms on the (100) surface of GaAs nanowire with [0001] growth direction is investigated utilizing first principles method based on density function theory. The adsorption energy, work function, atomic structure and electronic property of clean surface and Cs-covered surfaces with different coverage are discussed. Results show that when only one Cs is adsorbed on the surface, the most favorable adsorption site is BGa-As. With increasing Cs coverage, work function gradually decreases and gets its minimum at 0.75 ML, then rises slightly when Cs coverage comes to 1 ML, indicating the existence of 'Cs-kill' phenomenon. According to further analysis, Cs activation process can effectively reduce the work function due to the formation of a downward band bending region and surface dipole moment directing from Cs adatom to the surface. As Cs coverage increases, the conduction band minimum and valence band maximum both shift towards lower energy side, contributed by the orbital hybridization between Cs-5s, Cs-5p states and Ga-4p, As-4s, As-4p states near Fermi level. The theoretical calculations and analysis in this study can improve the Cs activation technology for negative electron affinity optoelectronic devices based on GaAs nanowires, and also provide a reference for the further Cs/O or Cs/NF3 activation process.

  13. Effect of catalyst diameter on vapour-liquid-solid growth of GaAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

    O' Dowd, B. J., E-mail: odowdbj@tcd.ie; Shvets, I. V. [CRANN, School of Physics, Trinity College, the University of Dublin, Dublin D2 (Ireland); Wojtowicz, T.; Kolkovsky, V.; Wojciechowski, T.; Zgirski, M. [Institute of Physics, Polish Academy of Sciences, Warsaw 02-668 (Poland); Rouvimov, S. [Notre Dame Integrated Imaging Facility (NDIIF), University of Notre Dame, Notre Dame, Indiana 46556 (United States); Liu, X.; Pimpinella, R.; Dobrowolska, M.; Furdyna, J. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States)

    2014-08-14

    GaAs nanowires were grown on (111)B GaAs substrates using the vapour-liquid-solid mechanism. The Au/Pt nanodots used to catalyse wire growth were defined lithographically and had varying diameter and separation. An in-depth statistical analysis of the resulting nanowires, which had a cone-like shape, was carried out. This revealed that there were two categories of nanowire present, with differing height and tapering angle. The bimodal nature of wire shape was found to depend critically on the diameter of the Au-Ga droplet atop the nanowire. Transmission electron microscopy analysis also revealed that the density of stacking faults in the wires varied considerably between the two categories of wire. It is believed that the cause of the distinction in terms of shape and crystal structure is related to the contact angle between the droplet and the solid-liquid interface. The dependency of droplet diameter on contact angle is likely related to line-tension, which is a correction to Young's equation for the contact angle of a droplet upon a surface. The fact that contact angle may influence resulting wire structure and shape has important implications for the planning of growth conditions and the preparation of wires for use in proposed devices.

  14. Effect of GaAs (100) substrate surface reconstruction on magnetic properties of Ni thin films

    Energy Technology Data Exchange (ETDEWEB)

    Akbulut, Salih, E-mail: sakbulut@gyte.edu.tr [Gebze Institute of Technology, Physics Department, Istanbul Caddesi PK 41400, Gebze (Turkey); Akbulut, Ayşenur [Gebze Institute of Technology, Physics Department, Istanbul Caddesi PK 41400, Gebze (Turkey); Özdemir, Mustafa [Marmara University, Physics Department, Göztepe, Istanbul (Turkey); Yildiz, Fikret, E-mail: fyildiz@gyte.edu.tr [Gebze Institute of Technology, Physics Department, Istanbul Caddesi PK 41400, Gebze (Turkey)

    2015-01-01

    Effects of (4×6) and (2×4) reconstructed surfaces of GaAs (100) substrate on magnetic properties have been investigated for nickel thin films by using ferromagnetic resonance technique. The films were grown by molecular beam epitaxy in ultrahigh vacuum condition, with 20–40 nm thickness range. X-ray diffraction measurements showed that all films have a single crystalline structure. In the film plane the nickel films exhibited a combination of two fold and four fold anisotropy induced by unsatisfied tetrahedral bonds of Ga and As rows oriented along [110] and [11{sup ¯}0] directions. Effects of different reconstructions on magnetic anisotropies were discovered to be more dominant in the film normal. The physical mechanisms responsible for the observed surface reconstruction and thickness dependence of magnetic anisotropy are discussed in detail. - Highlights: • Epitaxial Ni films were grown on (4×6) and (2×4) reconstructed GaAs (100) surfaces. • There are 2 fold uniaxial and 4 fold cubic magnetic anisotropies in the film plane. • Effect of reconstruction on magnetic anisotropy is in the film normal direction.

  15. Preparation of clean GaAs(100) studied by synchrotron radiation photoemission

    Science.gov (United States)

    Liu, Zhi; Sun, Yun; Machuca, Francisco; Pianetta, Piero; Spicer, William E.; Pease, R. F. W.

    2003-01-01

    Chemical cleaning of the GaAs(100) surface has been studied with high-resolution photoemission spectroscopy using synchrotron radiation (in the range of 30-1300 eV) at the Stanford Synchrotron Radiation Laboratory. The high surface sensitivity of the technique has allowed us to identify the chemical state of the surface species after both the chemical cleaning and final vacuum processing steps. In order to eliminate contamination from the surroundings, all chemical cleaning steps were performed in an Ar purged glovebox attached to the load lock allowing samples to be transferred into the system without being exposed to air. Samples were etched in H2SO4:H2O2:H2O solution and then heat cleaned in vacuum at 500 °C. After chemical etching in the solution, elemental As (~2 ML), arsenic oxides (<0.2 ML), gallium oxides (<0.2 ML), and C (0.5~1 ML) are found on the surface. Subsequent annealing at <500 °C in ultrahigh vacuum produces a stoichiometric, oxide-free surface as determined by valence-band and core-level photoemission. In addition, C has been reduced to less than 0.1 ML. We believe that the C can be removed by heating because the elemental As from the earlier cleaning step tends to protect the GaAs surface. The chemical reactions and species at different cleaning stages are discussed.

  16. Electronic dynamics due to exchange interaction with holes in GaAs

    Science.gov (United States)

    Schneider, Hans Christian; Krauß, Michael

    2010-02-01

    We present an investigation of electron-spin dynamics in p-doped bulk GaAs due to the electron-hole exchange interaction, aka the Bir-Aronov-Pikus mechanism. We discuss under which conditions a spin relaxation times for this mechanism is, in principle, accessible to experimental techniques, in particular to 2-photon photoemission, but also Faraday/Kerr effect measurements. We give numerical results for the spin relaxation time for a range of p-doping densities and temperatures. We then go beyond the relaxation time approximation and calculate numerically the spin-dependent electron dynamics by including the spin-flip electron-hole exchange scattering and spin-conserving carrier Coulomb scattering at the level of Boltzmann scattering integrals. We show that the electronic dynamics deviates from the simple spin-relaxation dynamics for electrons excited at high energies where the thermalization does not take place faster than the spin relaxation time. We also present a derivation of the influence of screening on the electron-hole exchange scattering and conclude that it can be neglected for the case of GaAs, but may become important for narrow-gap semiconductors.

  17. Picosecond spin relaxation in low-temperature-grown GaAs

    Science.gov (United States)

    Uemura, M.; Honda, K.; Yasue, Y.; Lu, S. L.; Dai, P.; Tackeuchi, A.

    2014-03-01

    The spin relaxation process of low-temperature-grown GaAs is investigated by spin-dependent pump and probe reflectance measurements with a sub-picosecond time resolution. Two very short carrier lifetimes of 2.0 ps and 28 ps, which can be attributed to nonradiative recombinations related to defects, are observed at 10 K. The observed spin polarization shows double exponential decay with spin relaxation times of 46.2 ps (8.0 ps) and 509 ps (60 ps) at 10 K (200 K). The observed picosecond spin relaxation, which is considerably shorter than that of conventional GaAs, indicates the strong relevance of the Elliott-Yafet process as the spin relaxation mechanism. For the first (second) spin relaxation component, the temperature and carrier density dependences of the spin relaxation time indicate that the Bir-Aronov-Pikus process is also effective at temperatures between 10 K and 77 K, and that the D'yakonov-Perel' process is effective between 125 K (77 K) and 200 K.

  18. A novel homozygous mutation at the GAA gene in Mexicans with early-onset Pompe disease.

    Science.gov (United States)

    Esmer, Carmen; Becerra-Becerra, Rosario; Peña-Zepeda, Claudia; Bravo-Oro, Antonio

    2013-10-01

    Glycogen-storage disease type II, also named Pompe disease, is caused by the deficiency of the enzyme acid alpha-glucosidase, which originates lysosomal glycogen accumulation leading to progressive neuromuscular damage. Early-onset Pompe disease shows a debilitating and frequently fulminating course. To date, more than 300 mutations have been described; the majority of them are unique to each affected individual. Most early-onset phenotypes are associated with frameshift mutations leading to a truncated alpha-glucosidase protein with loss of function. Founder effects are responsible from many cases from few highprevalence world regions. Herein we described two apparently unrelated cases affected with classical early-onset Pompe disease, both pertaining to a small region from Central Mexico (the State of San Luis Potosí), the same novel homozygous frameshift mutation at gene GAA (c.1987delC) was demonstrated in both cases. This GAA gene deletion implies a change of glutamine to serine at codon 663, and a new reading frame that ends after 33 base pairs, which leads to the translation of a truncated protein. This report contributes to widen the knowledge on the effect of pathogenic mutations in Pompe disease. Here we postulate the existence of a founder effect.

  19. 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

    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......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...... 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 $\\sim {10...

  20. AFIP-4 Irradiation Summary Report

    Energy Technology Data Exchange (ETDEWEB)

    Danielle M Perez; Misti A Lillo; Gray S. Chang; Glenn A Roth; Nicolas Woolstenhulme; Daniel M Wachs

    2011-09-01

    The Advanced Test Reactor (ATR) Full size plate In center flux trap Position (AFIP) experiment AFIP-4 was designed to evaluate the performance of monolithic uranium-molybdenum (U-Mo) fuels at a scale prototypic of research reactor fuel plates. The AFIP-4 test further examine the fuel/clad interface and its behavior under extreme conditions. After irradiation, fission gas retention measurements will be performed during post irradiation (PIE). The following report summarizes the life of the AFIP-4 experiment through end of irradiation, including a brief description of the safety analysis, as-run neutronic analysis results, hydraulic testing results, and thermal analysis results.

  1. AFIP-4 Irradiation Summary Report

    Energy Technology Data Exchange (ETDEWEB)

    Danielle M Perez; Misti A Lillo; Gray S. Chang; Glenn A Roth; Nicolas Woolstenhulme; Daniel M Wachs

    2012-01-01

    The Advanced Test Reactor (ATR) Full size plate In center flux trap Position (AFIP) experiment AFIP-4 was designed to evaluate the performance of monolithic uranium-molybdenum (U-Mo) fuels at a scale prototypic of research reactor fuel plates. The AFIP-4 test further examine the fuel/clad interface and its behavior under extreme conditions. After irradiation, fission gas retention measurements will be performed during post irradiation (PIE)1,2. The following report summarizes the life of the AFIP-4 experiment through end of irradiation, including a brief description of the safety analysis, as-run neutronic analysis results, hydraulic testing results, and thermal analysis results.

  2. Craniospinal Irradiation for Trilateral Retinoblastoma Following Ocular Irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Marks, Lawrence B.; Bentel, Gunilla; Sherouse, George W.; Spencer, David P.; Light, Kim

    2015-01-15

    A case study is presented. Craniospinal radiotherapy and a three-field pineal boost for trilateral retinoblastoma were delivered to a patient previously irradiated for ocular retinoblastoma. The availability of CT-based three-dimensional treatment planning provided the capability of identifying the previously irradiated volume as a three-dimensional anatomic structure and of designing a highly customized set of treatment beams that minimized reirradiation of that volume.

  3. Catalyst-free selective-area epitaxy of GaAs nanowires by metal-organic chemical vapor deposition using triethylgallium

    Science.gov (United States)

    Kim, Hyunseok; Ren, Dingkun; Farrell, Alan C.; Huffaker, Diana L.

    2018-02-01

    We demonstrate catalyst-free growth of GaAs nanowires by selective-area metal-organic chemical vapor deposition (MOCVD) on GaAs and silicon substrates using a triethylgallium (TEGa) precursor. Two-temperature growth of GaAs nanowires—nucleation at low temperature followed by nanowire elongation at high temperature—almost completely suppresses the radial overgrowth of nanowires on GaAs substrates while exhibiting a vertical growth yield of almost 100%. A 100% growth yield is also achieved on silicon substrates by terminating Si(111) surfaces by arsenic prior to the nanowire growth and optimizing the growth temperature. Compared with trimethylgallium (TMGa) which has been exclusively employed in the vapor–solid phase growth of GaAs nanowires by MOCVD, the proposed growth technique using TEGa is advantageous because of lower growth temperature and fully suppressed radial overgrowth. It is also known that GaAs grown by TEGa induce less impurity incorporation compared with TMGa, and therefore the proposed method could be a building block for GaAs nanowire-based high-performance optoelectronic and nanoelectronic devices on both III–V and silicon platforms.

  4. Antisense Oligonucleotides Promote Exon Inclusion and Correct the Common c.-32-13T>G GAA Splicing Variant in Pompe Disease

    Directory of Open Access Journals (Sweden)

    Erik van der Wal

    2017-06-01

    Full Text Available The most common variant causing Pompe disease is c.-32-13T>G (IVS1 in the acid α-glucosidase (GAA gene, which weakens the splice acceptor of GAA exon 2 and induces partial and complete exon 2 skipping. It also allows a low level of leaky wild-type splicing, leading to a childhood/adult phenotype. We hypothesized that cis-acting splicing motifs may exist that could be blocked using antisense oligonucleotides (AONs to promote exon inclusion. To test this, a screen was performed in patient-derived primary fibroblasts using a tiling array of U7 small nuclear RNA (snRNA-based AONs. This resulted in the identification of a splicing regulatory element in GAA intron 1. We designed phosphorodiamidate morpholino oligomer-based AONs to this element, and these promoted exon 2 inclusion and enhanced GAA enzyme activity to levels above the disease threshold. These results indicate that the common IVS1 GAA splicing variant in Pompe disease is subject to negative regulation, and inhibition of a splicing regulatory element using AONs is able to restore canonical GAA splicing and endogenous GAA enzyme activity.

  5. Antisense Oligonucleotides Promote Exon Inclusion and Correct the Common c.-32-13T>G GAA Splicing Variant in Pompe Disease.

    Science.gov (United States)

    van der Wal, Erik; Bergsma, Atze J; Pijnenburg, Joon M; van der Ploeg, Ans T; Pijnappel, W W M Pim

    2017-06-16

    The most common variant causing Pompe disease is c.-32-13T>G (IVS1) in the acid α-glucosidase (GAA) gene, which weakens the splice acceptor of GAA exon 2 and induces partial and complete exon 2 skipping. It also allows a low level of leaky wild-type splicing, leading to a childhood/adult phenotype. We hypothesized that cis-acting splicing motifs may exist that could be blocked using antisense oligonucleotides (AONs) to promote exon inclusion. To test this, a screen was performed in patient-derived primary fibroblasts using a tiling array of U7 small nuclear RNA (snRNA)-based AONs. This resulted in the identification of a splicing regulatory element in GAA intron 1. We designed phosphorodiamidate morpholino oligomer-based AONs to this element, and these promoted exon 2 inclusion and enhanced GAA enzyme activity to levels above the disease threshold. These results indicate that the common IVS1 GAA splicing variant in Pompe disease is subject to negative regulation, and inhibition of a splicing regulatory element using AONs is able to restore canonical GAA splicing and endogenous GAA enzyme activity. Copyright © 2017 The Author(s). Published by Elsevier Inc. All rights reserved.

  6. (Irradiation creep of graphite)

    Energy Technology Data Exchange (ETDEWEB)

    Kennedy, C.R.

    1990-12-21

    The traveler attended the Conference, International Symposium on Carbon, to present an invited paper, Irradiation Creep of Graphite,'' and chair one of the technical sessions. There were many papers of particular interest to ORNL and HTGR technology presented by the Japanese since they do not have a particular technology embargo and are quite open in describing their work and results. In particular, a paper describing the failure of Minor's law to predict the fatigue life of graphite was presented. Although the conference had an international flavor, it was dominated by the Japanese. This was primarily a result of geography; however, the work presented by the Japanese illustrated an internal program that is very comprehensive. This conference, a result of this program, was better than all other carbon conferences attended by the traveler. This conference emphasizes the need for US participation in international conferences in order to stay abreast of the rapidly expanding HTGR and graphite technology throughout the world. The United States is no longer a leader in some emerging technologies. The traveler was surprised by the Japanese position in their HTGR development. Their reactor is licensed and the major problem in their graphite program is how to eliminate it with the least perturbation now that most of the work has been done.

  7. Stillbirths and male irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Boice, John D. Jr. [International Epidemiology Institute, Rockville, MD (United States)]. E-mail: boicej@compuserve.com; Robison, Leslie L. [University of Minnesota, Minneapolis, MN (United States); Mertens, Ann [University of Texas M D Anderson Cancer Center, Houston, TX (United States); Stovall, Marilyn; Green, Daniel M.; Mulvihill, John J.; ); Roswell Park Cancer Institute, Buffalo, NY (United States); University of Oklahoma, Oklahoma City, OK (US))

    2000-09-01

    Little (1999) recently reviewed the evidence that paternal preconception irradiation in the Sellafield workforce (Parker et al 1999) and among Japanese atomic bomb survivors (Otake et al 1990) might be associated with an increased risk of stillbirth. He concluded that the association reported for radiation workers was statistically incompatible with the absence of an association seen among the exposed Japanese parents. These studies and analyses illustrate the considerable difficulty in assessing stillbirths conceived by men exposed to ionising radiation at work. For example, occupational doses may not be sufficiently large to result in a detectable effect and maternal factors that are associated with stillbirths and important to adjust for may not be available. These papers also bring to focus a relevant but not well-studied public health issue, namely, what are the reproductive risks for men and women exposed to potential mutagens? We wish to emphasise here the theoretical and practical advantages of addressing this issue in persons not with low dose occupational or acute atomic bomb exposures, but with higher dose medical experiences; in particular, in survivors of cancers of childhood, adolescents, and young adulthood (Blatt 1999, Bryne et al 1998, Sankila et al 1998, Green et al 1997, Hawkins and Stevens 1996). Letter-to-the-editor.

  8. A 2-10 GHz GaAs MMIC opto-electronic phase detector for optical microwave signal generators

    DEFF Research Database (Denmark)

    Bruun, Marlene; Gliese, Ulrik Bo; Petersen, Anders Kongstad

    1994-01-01

    Optical transmission of microwave signals becomes increasingly important. Techniques using beat between optical carriers of semiconductor lasers are promising if efficient optical phase locked loops are realized. A highly efficient GaAs MMIC optoelectronic phase detector for a 2-10 GHz OPLL...

  9. The equilibrium shape of InAs quantum dots grown on a GaAs(001) substrate

    CERN Document Server

    Pehlke, E; Scheffler, M; Pehlke, Eckhard; Moll, Nikolaj; Scheffler, Matthias

    1996-01-01

    The equilibrium shape of strained InAs quantum dots grown epitaxially on a GaAs(001) substrate is derived as a function of volume. InAs surface energies are calculated within density-functional theory, and a continuum approach is applied for the elastic relaxation energies.

  10. Ohmic contact formation process on low n-type gallium arsenide (GaAs) using indium gallium zinc oxide (IGZO)

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Seong-Uk [Samsung-SKKU Graphene Center and School of Electronics and Electrical Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Product and Test Engineering Team, System LSI Division, Samsung Electronics Co., Ltd, Yongin 446-711 (Korea, Republic of); Jung, Woo-Shik [Department of Electrical Engineering, Stanford University, Stanford, CA 94305 (United States); Lee, In-Yeal; Jung, Hyun-Wook; Kim, Gil-Ho [Samsung-SKKU Graphene Center and School of Electronics and Electrical Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Park, Jin-Hong, E-mail: jhpark9@skku.edu [Samsung-SKKU Graphene Center and School of Electronics and Electrical Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

    2014-02-01

    Highlights: • We propose a method to fabricate non-gold Ohmic contact on low n-type GaAs with IGZO. • 0.15 A/cm{sup 2} on-current and 1.5 on/off-current ratio are achieved in the junction. • InAs and InGaAs formed by this process decrease an electron barrier height. • Traps generated by diffused O atoms also induce a trap-assisted tunneling phenomenon. - Abstract: Here, an excellent non-gold Ohmic contact on low n-type GaAs is demonstrated by using indium gallium zinc oxide and investigating through time of flight-secondary ion mass spectrometry, X-ray photoelectron spectroscopy, transmission electron microscopy, J–V measurement, and H [enthalpy], S [entropy], Cp [heat capacity] chemistry simulation. In is diffused through GaAs during annealing and reacts with As, forming InAs and InGaAs phases with lower energy bandgap. As a result, it decreases the electron barrier height, eventually increasing the reverse current. In addition, traps generated by diffused O atoms induce a trap-assisted tunneling phenomenon, increasing generation current and subsequently the reverse current. Therefore, an excellent Ohmic contact with 0.15 A/cm{sup 2} on-current density and 1.5 on/off-current ratio is achieved on n-type GaAs.

  11. Growth of GaAs “nano ice cream cones” by dual wavelength pulsed laser ablation

    Science.gov (United States)

    Schamp, C. T.; Jesser, W. A.; Shivaram, B. S.

    2007-05-01

    Harmonic generation crystals inherently offer the possibility of using multiple wavelengths of light in a single laser pulse. In the present experiment, the fundamental (1064 nm) and second harmonic (532 nm) wavelengths from an Nd:YAG laser are focused together on GaAs and GaSb targets for ablation. Incident energy densities up to about 45 J/cm 2 at 10 Hz with substrate temperatures between 25 and 600 °C for durations of about 60 s have been used in an ambient gas pressure of about 10 -6 Torr. The ablated material was collected on electron-transparent amorphous carbon films for TEM analysis. Apart from a high density of isolated nanocrystals, the most common morphology observed consists of a crystalline GaAs cone-like structure in contact with a sphere of liquid Ga, resembling an "ice cream cone", typically 50-100 nm in length. For all of the heterostuctures of this type, the liquid/solid/vacuum triple junction is found to correspond to the widest point on the cone. These heterostructures likely form by preferential evaporation of As from molten GaAs drops ablated from the target. The resulting morphology minimizes the interfacial and surface energies of the liquid Ga and solid GaAs.

  12. First principles calculations of La2O3/GaAs interface properties under biaxial strain and hydrostatic pressure

    Science.gov (United States)

    Shi, Li-Bin; Li, Ming-Biao; Xiu, Xiao-Ming; Liu, Xu-Yang; Zhang, Kai-Cheng; Li, Chun-Ran; Dong, Hai-Kuan

    2017-04-01

    La2O3 is a potential dielectric material with high permittivity (high-κ) for metal-oxide-semiconductor (MOS) devices. However, band offsets and oxide defects should still be concerned. Smaller band offsets and carrier traps increase leakage current, and degenerate performance of the devices. In this paper, the interface behaviors of La2O3/GaAs under biaxial strain and hydrostatic pressure are investigated, which is performed by first principles calculations based on density functional theory (DFT). Strain engineering is attempted to improve performance of the metal/La2O3/GaAs devices. First of all, we creatively realize band alignment of La2O3/GaAs interface under biaxial strain and hydrostatic pressure. The proper biaxial tensile strain can effectively increase valence band offsets (VBO) and conduction band offsets (CBO), which can be used to suppress leakage current. However, the VBO will decrease with the increase of hydrostatic pressure, indicating that performance of the devices is degenerated. Then, a direct tunneling leakage current model is used to investigate current and voltage characteristics of the metal/La2O3/GaAs. The impact of biaxial strain and hydrostatic pressure on leakage current is discussed. At last, formation energies and transition levels of oxygen interstitial (Oi) and oxygen vacancy (VO) in La2O3 are assessed. We investigate how they will affect performance of the devices.

  13. High Quality GaAs Epilayers Grown on Si Substrate Using 100 nm Ge Buffer Layer

    Directory of Open Access Journals (Sweden)

    Wei-Cheng Kuo

    2016-01-01

    Full Text Available We present high quality GaAs epilayers that grow on virtual substrate with 100 nm Ge buffer layers. The thin Ge buffer layers were modulated by hydrogen flow rate from 60 to 90 sccm to improve crystal quality by electron cyclotron resonance chemical vapor deposition (ECR-CVD at low growth temperature (180°C. The GaAs and Ge epilayers quality was verified by X-ray diffraction (XRD and spectroscopy ellipsometry (SE. The full width at half maximum (FWHM of the Ge and GaAs epilayers in XRD is 406 arcsec and 220 arcsec, respectively. In addition, the GaAs/Ge/Si interface is observed by transmission electron microscopy (TEM to demonstrate the epitaxial growth. The defects at GaAs/Ge interface are localized within a few nanometers. It is clearly showed that the dislocation is well suppressed. The quality of the Ge buffer layer is the key of III–V/Si tandem cell. Therefore, the high quality GaAs epilayers that grow on virtual substrate with 100 nm Ge buffer layers is suitable to develop the low cost and high efficiency III–V/Si tandem solar cells.

  14. Vertically aligned GaAs nanowires on graphite and few-layer graphene: generic model and epitaxial growth.

    Science.gov (United States)

    Munshi, A Mazid; Dheeraj, Dasa L; Fauske, Vidar T; Kim, Dong-Chul; van Helvoort, Antonius T J; Fimland, Bjørn-Ove; Weman, Helge

    2012-09-12

    By utilizing the reduced contact area of nanowires, we show that epitaxial growth of a broad range of semiconductors on graphene can in principle be achieved. A generic atomic model is presented which describes the epitaxial growth configurations applicable to all conventional semiconductor materials. The model is experimentally verified by demonstrating the growth of vertically aligned GaAs nanowires on graphite and few-layer graphene by the self-catalyzed vapor-liquid-solid technique using molecular beam epitaxy. A two-temperature growth strategy was used to increase the nanowire density. Due to the self-catalyzed growth technique used, the nanowires were found to have a regular hexagonal cross-sectional shape, and are uniform in length and diameter. Electron microscopy studies reveal an epitaxial relationship of the grown nanowires with the underlying graphitic substrates. Two relative orientations of the nanowire side-facets were observed, which is well explained by the proposed atomic model. A prototype of a single GaAs nanowire photodetector demonstrates a high-quality material. With GaAs being a model system, as well as a very useful material for various optoelectronic applications, we anticipate this particular GaAs nanowire/graphene hybrid to be promising for flexible and low-cost solar cells.

  15. Progress in GaAs Metamorphic HEMT Technology for Microwave Applications. High Efficiency Ka-Band MHEMT Power MMICs

    Science.gov (United States)

    Smith, P. M.; Dugas, D.; Chu, K.; Nichols, K.; Duh, K. H.; Fisher, J.; MtPleasant, L.; Xu, D.; Gunter, L.; Vera, A.

    2003-01-01

    This paper reviews recent progress in the development of GaAs metamorphic HEMT (MHEMT) technology for microwave applications. Commercialization has begun, while efforts to further improve performance, manufacturability and reliability continue. We also report the first multi-watt MHEMT MMIC power amplifiers, demonstrating up to 3.2W output power and record power-added efficiency (PAE) at Ka-band.

  16. Polarization dependence of the electroabsorption in low-temperature grown GaAs for above band-gap energies

    DEFF Research Database (Denmark)

    Ruff, M.; Streb, D.; Dankowski, S. U.

    1996-01-01

    We have measured the electroabsorption in low-temperature grown GaAs by performing room-temperature transmission experiments in the spectral range from 1.3 to 1.9 eV for different electric fields induced by a voltage applied to a metal-semiconductor-metal structure. The devices were separated fro...

  17. GaAs on Si epitaxy by aspect ratio trapping: Analysis and reduction of defects propagating along the trench direction

    Energy Technology Data Exchange (ETDEWEB)

    Orzali, Tommaso, E-mail: tommaso.orzali@sematech.org; Vert, Alexey; O' Brien, Brendan; Papa Rao, Satyavolu S. [SEMATECH, 257 Fuller Rd Suite 2200, Albany, New York 12203 (United States); Herman, Joshua L.; Vivekanand, Saikumar [College of Nanoscale Science and Engineering, SUNY Polytechnic Institute, 251 Fuller Road, Albany, New York 12203 (United States); Hill, Richard J. W. [Now at Micron Technologies, 8000 S Federal Way, Boise, Idaho 83716 (United States); Karim, Zia [AIXTRON, Inc., 1139 Karlstad Dr., Sunnyvale, California 94089 (United States)

    2015-09-14

    The Aspect Ratio Trapping technique has been extensively evaluated for improving the quality of III-V heteroepitaxial films grown on Si, due to the potential for terminating defects at the sidewalls of SiO{sub 2} patterned trenches that enclose the growth region. However, defects propagating along the trench direction cannot be effectively confined with this technique. We studied the effect of the trench bottom geometry on the density of defects of GaAs fins, grown by metal-organic chemical vapor deposition on 300 mm Si (001) wafers inside narrow (<90 nm wide) trenches. Plan view and cross sectional Scanning Electron Microscopy and Transmission Electron Microscopy, together with High Resolution X-Ray Diffraction, were used to evaluate the crystal quality of GaAs. The prevalent defects that reach the top surface of GaAs fins are (111) twin planes propagating along the trench direction. The lowest density of twin planes, ∼8 × 10{sup 8 }cm{sup −2}, was achieved on “V” shaped bottom trenches, where GaAs nucleation occurs only on (111) Si planes, minimizing the interfacial energy and preventing the formation of antiphase boundaries.

  18. Electron spin relaxation in GaAs1-xBix: Effects of spin-orbit tuning by Bi incorporation

    Science.gov (United States)

    Tong, H.; Marie, X.; Wu, M. W.

    2012-09-01

    The electron spin relaxation in n-type and intrinsic GaAs1-xBix with Bi composition 0≤x≤0.1 is investigated from the microscopic kinetic spin Bloch equation approach. The incorporation of Bi is shown to markedly decrease the spin relaxation time as a consequence of the modification of the spin-orbit interaction, which shows the feasibility of GaAs1-xBix in the applications of spintronic devices. We demonstrate that the density and temperature dependences of spin relaxation time in GaAs1-xBix resemble the ones in GaAs. Meanwhile, the Bir-Aronov-Pikus mechanism is found to be negligible compared to the D'yakonov-Perel' mechanism in intrinsic sample. Due to the absence of direct measurement of the electron effective mass in the whole compositional range under investigation, we further explore the effect of a possible variation of electron effective mass on the electron spin relaxation.

  19. COMMENT: Comment on 'Density dependence of electron-spin polarization and relaxation in intrinsic GaAs at room temperature'

    Science.gov (United States)

    Jiang, J. H.; Wu, M. W.

    2009-12-01

    We comment on the conclusion by Teng et al (2009 J. Phys. D: Appl. Phys. 42 135111) that the Bir-Aronov-Pikus mechanism is more important than the D'yakonov-Perel' mechanism at a high carrier density in intrinsic bulk GaAs. We point out that the spin relaxation is solely from the D'yakonov-Perel' mechanism.

  20. Spin Qubits in GaAs Heterostructures and Gating of InAs Nanowires for Lowtemperature Measurements

    DEFF Research Database (Denmark)

    Nissen, Peter Dahl

    voltages for barrier induction (Vg 􀀀1 to 􀀀2V), but low temperature gate sweeps suggest that device stability could be affected by the differences in device processing for the two gate geometries. For the GaAs heterostructure we investigate two new ideas for realizing spin qubits...