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Sample records for arsenides

  1. Gallium Arsenide

    Science.gov (United States)

    Brozel, Mike

    The history of gallium arsenide is complicated because the technology required to produce GaAs devices has been fraught with problems associated with the material itself and with difficulties in its fabrication. Thus, for many years, GaAs was labelled as "the semiconductor of the future, and it will always be that way." Recently, however, advances in compact-disc (CD) technology, fibre-optic communications and mobile telephony have boosted investment in GaAs research and development. Consequently, there have been advances in materials and fabrication technology and, as a result, GaAs devices now enjoy stable niche markets.

  2. Window structure for passivating solar cells based on gallium arsenide

    Science.gov (United States)

    Barnett, Allen M. (Inventor)

    1985-01-01

    Passivated gallium arsenide solar photovoltaic cells with high resistance to moisture and oxygen are provided by means of a gallium arsenide phosphide window graded through its thickness from arsenic rich to phosphorus rich.

  3. Spin Injection in Indium Arsenide

    Directory of Open Access Journals (Sweden)

    Mark eJohnson

    2015-08-01

    Full Text Available In a two dimensional electron system (2DES, coherent spin precession of a ballistic spin polarized current, controlled by the Rashba spin orbit interaction, is a remarkable phenomenon that’s been observed only recently. Datta and Das predicted this precession would manifest as an oscillation in the source-drain conductance of the channel in a spin-injected field effect transistor (Spin FET. The indium arsenide single quantum well materials system has proven to be ideal for experimental confirmation. The 2DES carriers have high mobility, low sheet resistance, and high spin orbit interaction. Techniques for electrical injection and detection of spin polarized carriers were developed over the last two decades. Adapting the proposed Spin FET to the Johnson-Silsbee nonlocal geometry was a key to the first experimental demonstration of gate voltage controlled coherent spin precession. More recently, a new technique measured the oscillation as a function of channel length. This article gives an overview of the experimental phenomenology of the spin injection technique. We then review details of the application of the technique to InAs single quantum well (SQW devices. The effective magnetic field associated with Rashba spin-orbit coupling is described, and a heuristic model of coherent spin precession is presented. The two successful empirical demonstrations of the Datta Das conductance oscillation are then described and discussed.

  4. A terminal molybdenum arsenide complex synthesized from yellow arsenic.

    Science.gov (United States)

    Curley, John J; Piro, Nicholas A; Cummins, Christopher C

    2009-10-19

    A terminal molybdenum arsenide complex is synthesized in one step from the reactive As(4) molecule. The properties of this complex with its arsenic atom ligand are discussed in relation to the analogous nitride and phosphide complexes. PMID:19764796

  5. Gallium arsenide solar array subsystem study

    Science.gov (United States)

    Miller, F. Q.

    1982-01-01

    The effects on life cycle costs of a number of technology areas are examined for a gallium arsenide space solar array. Four specific configurations were addressed: (1) a 250 KWe LEO mission - planer array; (2) a 250 KWe LEO mission - with concentration; (3) a 50 KWe GEO mission planer array; (4) a 50 KWe GEO mission - with concentration. For each configuration, a baseline system conceptual design was developed and the life cycle costs estimated in detail. The baseline system requirements and design technologies were then varied and their relationships to life cycle costs quantified. For example, the thermal characteristics of the baseline design are determined by the array materials and masses. The thermal characteristics in turn determine configuration, performance, and hence life cycle costs.

  6. Inhalation developmental toxicology studies: Gallium arsenide in mice and rats

    Energy Technology Data Exchange (ETDEWEB)

    Mast, T.J.; Greenspan, B.J.; Dill, J.A.; Stoney, K.H.; Evanoff, J.J.; Rommereim, R.L.

    1990-12-01

    Gallium arsenide is a crystalline compound used extensively in the semiconductor industry. Workers preparing solar cells and gallium arsenide ingots and wafers are potentially at risk from the inhalation of gallium arsenide dust. The potential for gallium arsenide to cause developmental toxicity was assessed in Sprague- Dawley rats and CD-1 (Swiss) mice exposed to 0, 10, 37, or 75 mg/m{sup 3} gallium arsenide, 6 h/day, 7 days/week. Each of the four treatment groups consisted of 10 virgin females (for comparison), and {approx}30 positively mated rats or {approx}24 positively mated mice. Mice were exposed on 4--17 days of gestation (dg), and rats on 4--19 dg. The day of plug or sperm detection was designated as 0 dg. Body weights were obtained throughout the study period, and uterine and fetal body weights were obtained at sacrifice (rats, 20 dg; mice, 18 dg). Implants were enumerated and their status recorded. Live fetuses were sexed and examined for gross, visceral, skeletal, and soft-tissue craniofacial defects. Gallium and arsenic concentrations were determined in the maternal blood and uterine contents of the rats (3/group) at 7, 14, and 20 dg. 37 refs., 11 figs., 30 tabs.

  7. Framework structures of interconnected layers in calcium iron arsenides.

    Science.gov (United States)

    Stürzer, Tobias; Hieke, Christine; Löhnert, Catrin; Nitsche, Fabian; Stahl, Juliane; Maak, Christian; Pobel, Roman; Johrendt, Dirk

    2014-06-16

    The new calcium iron arsenide compounds Ca(n(n+1)/2)(Fe(1-x)M(x))(2+3n)M'(n(n-1)/2)As((n+1)(n+2)/2) (n = 1-3; M = Nb, Pd, Pt; M' = □, Pd, Pt) were synthesized and their crystal structures determined by single-crystal X-ray diffraction. The series demonstrates the structural flexibility of iron arsenide materials, which otherwise prefer layered structures, as is known from the family of iron-based superconductors. In the new compounds, iron arsenide tetrahedral layers are bridged by iron-centered pyramids, giving rise to so far unknown frameworks of interconnected FeAs layers. Channels within the structures are occupied with calcium and palladium or platinum, respectively. Common basic building blocks are identified that lead to a better understanding of the building principles of these structures and their relation to CaFe4As3.

  8. Laser and electron beam processing of silicon and gallium arsenide

    Energy Technology Data Exchange (ETDEWEB)

    Narayan, J.

    1979-10-01

    Laser (photon) and electron beams provide a controlled source of heat by which surface layers of silicon and gallium arsenide can be rapidly melted and cooled with rates exceeding 10/sup 80/C/sec. The melting process has been used to remove displacement damage in ion implanted Si and GaAs, to remove dislocations, loops and precipitates in silicon and to study impurity segregation and solubility limits. The mechanisms associated with various phenomena will be examined. The possible impact of laser and electron beam processing on device technology, particularly with respect to solar cells is discussed.

  9. Macroscopic diffusion models for precipitation in crystalline gallium arsenide

    Energy Technology Data Exchange (ETDEWEB)

    Kimmerle, Sven-Joachim Wolfgang

    2009-09-21

    Based on a thermodynamically consistent model for precipitation in gallium arsenide crystals including surface tension and bulk stresses by Dreyer and Duderstadt, we propose two different mathematical models to describe the size evolution of liquid droplets in a crystalline solid. The first model treats the diffusion-controlled regime of interface motion, while the second model is concerned with the interface-controlled regime of interface motion. Our models take care of conservation of mass and substance. These models generalise the well-known Mullins- Sekerka model for Ostwald ripening. We concentrate on arsenic-rich liquid spherical droplets in a gallium arsenide crystal. Droplets can shrink or grow with time but the centres of droplets remain fixed. The liquid is assumed to be homogeneous in space. Due to different scales for typical distances between droplets and typical radii of liquid droplets we can derive formally so-called mean field models. For a model in the diffusion-controlled regime we prove this limit by homogenisation techniques under plausible assumptions. These mean field models generalise the Lifshitz-Slyozov-Wagner model, which can be derived from the Mullins-Sekerka model rigorously, and is well understood. Mean field models capture the main properties of our system and are well adapted for numerics and further analysis. We determine possible equilibria and discuss their stability. Numerical evidence suggests in which case which one of the two regimes might be appropriate to the experimental situation. (orig.)

  10. Temperature dependence of carrier capture by defects in gallium arsenide

    Energy Technology Data Exchange (ETDEWEB)

    Wampler, William R. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Modine, Normand A. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-08-01

    This report examines the temperature dependence of the capture rate of carriers by defects in gallium arsenide and compares two previously published theoretical treatments of this based on multi phonon emission (MPE). The objective is to reduce uncertainty in atomistic simulations of gain degradation in III-V HBTs from neutron irradiation. A major source of uncertainty in those simulations is poor knowledge of carrier capture rates, whose values can differ by several orders of magnitude between various defect types. Most of this variation is due to different dependence on temperature, which is closely related to the relaxation of the defect structure that occurs as a result of the change in charge state of the defect. The uncertainty in capture rate can therefore be greatly reduced by better knowledge of the defect relaxation.

  11. Methods for forming group III-arsenide-nitride semiconductor materials

    Science.gov (United States)

    Major, Jo S. (Inventor); Welch, David F. (Inventor); Scifres, Donald R. (Inventor)

    2002-01-01

    Methods are disclosed for forming Group III-arsenide-nitride semiconductor materials. Group III elements are combined with group V elements, including at least nitrogen and arsenic, in concentrations chosen to lattice match commercially available crystalline substrates. Epitaxial growth of these III-V crystals results in direct bandgap materials, which can be used in applications such as light emitting diodes and lasers. Varying the concentrations of the elements in the III-V crystals varies the bandgaps, such that materials emitting light spanning the visible spectra, as well as mid-IR and near-UV emitters, can be created. Conversely, such material can be used to create devices that acquire light and convert the light to electricity, for applications such as full color photodetectors and solar energy collectors. The growth of the III-V crystals can be accomplished by growing thin layers of elements or compounds in sequences that result in the overall lattice match and bandgap desired.

  12. First principles predictions of intrinsic defects in aluminum arsenide, AlAs : numerical supplement.

    Energy Technology Data Exchange (ETDEWEB)

    Schultz, Peter Andrew

    2012-04-01

    This Report presents numerical tables summarizing properties of intrinsic defects in aluminum arsenide, AlAs, as computed by density functional theory. This Report serves as a numerical supplement to the results published in: P.A. Schultz, 'First principles predictions of intrinsic defects in Aluminum Arsenide, AlAs', Materials Research Society Symposia Proceedings 1370 (2011; SAND2011-2436C), and intended for use as reference tables for a defect physics package in device models.

  13. Gallium Arsenide (GaAs) Quantum Photonic Waveguide Circuits

    CERN Document Server

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

    2014-01-01

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

  14. Noble Metal Arsenides and Gold Inclusions in Northwest Africa 8186

    Science.gov (United States)

    Srinivasan, P.; Agee, C. B.; McCubbin, F. M.; Rahman, Z.; Keller, L. P.

    2016-01-01

    CK carbonaceous chondrites are a highly thermally altered group of carbonaceous chondrites, experiencing temperatures ranging between approx.576-867 C. Additionally, the mineralogy of the CK chondrites record the highest overall oxygen fugacity of all chondrites, above the fayalite-magnetite-quartz (FMQ) buffer. Metallic Fe-Ni is extremely rare in CK chondrites, but magnetite and Fe,Ni sulfides are commonly observed. Noble metal-rich inclusions have previously been found in some magnetite and sulfide grains. These arsenides, tellurides, and sulfides, which contain varying amounts of Pt, Ru, Os, Te, As, Ir, and S, are thought to form either by condensation from a solar gas, or by exsolution during metamorphism on the chondritic parent body. Northwest Africa (NWA) 8186 is a highly metamorphosed CK chondrite. This meteorite is predominately composed of NiO-rich forsteritic olivine (Fo65), with lesser amounts of plagioclase (An52), augite (Fs11Wo49), magnetite (with exsolved titanomagnetite, hercynite, and titanohematite), monosulfide solid solution (with exsolved pentlandite), and the phosphate minerals Cl-apatite and merrillite. This meteorite contains coarse-grained, homogeneous silicates, and has 120deg triple junctions between mineral phases, which indicates a high degree of thermal metamorphism. The presence of NiO-rich olivine, oxides phases all bearing Fe3+, and the absence of metal, are consistent with an oxygen fugacity above the FMQ buffer. We also observed noble metal-rich phases within sulfide grains in NWA 8186, which are the primary focus of the present study.

  15. The comparison between gallium arsenide and indium gallium arsenide as materials for solar cell performance using Silvaco application

    Energy Technology Data Exchange (ETDEWEB)

    Zahari, Suhaila Mohd; Norizan, Mohd Natashah; Mohamad, Ili Salwani; Osman, Rozana Aina Maulat; Taking, Sanna [School of Microelectronic Engineering, Universiti Malaysia Perlis, Kampus Pauh Putra, 02600 Arau, Perlis (Malaysia)

    2015-05-15

    The work presented in this paper is about the development of single and multilayer solar cells using GaAs and InGaAs in AM1.5 condition. The study includes the modeling structure and simulation of the device using Silvaco applications. The performance in term of efficiency of Indium Gallium Arsenide (InGaAs) and GaAs material was studied by modification of the doping concentration and thickness of material in solar cells. The efficiency of the GaAs solar cell was higher than InGaAs solar cell for single layer solar cell. Single layer GaAs achieved an efficiency about 25% compared to InGaAs which is only 2.65% of efficiency. For multilayer which includes both GaAs and InGaAs, the output power, P{sub max} was 8.91nW/cm² with the efficiency only 8.51%. GaAs is one of the best materials to be used in solar cell as a based compared to InGaAs.

  16. A study of the applicability of gallium arsenide and silicon carbide as aerospace sensor materials

    Science.gov (United States)

    Hurley, John S.

    1990-01-01

    Most of the piezoresistive sensors, to date, are made of silicon and germanium. Unfortunately, such materials are severly restricted in high temperature environments. By comparing the effects of temperature on the impurity concentrations and piezoresistive coefficients of silicon, gallium arsenide, and silicon carbide, it is being determined if gallium arsenide and silicon carbide are better suited materials for piezoresistive sensors in high temperature environments. The results show that the melting point for gallium arsenide prevents it from solely being used in high temperature situations, however, when used in the alloy Al(x)Ga(1-x)As, not only the advantage of the wider energy band gas is obtained, but also the higher desire melting temperature. Silicon carbide, with its wide energy band gap and higher melting temperature suggests promise as a high temperature piezoresistive sensor.

  17. Surface-enhanced gallium arsenide photonic resonator with a quality factor of six million

    CERN Document Server

    Guha, Biswarup; Cadiz, Fabian; Morgenroth, Laurence; Ulin, Vladimir; Berkovitz, Vladimir; Lemaître, Aristide; Gomez, Carmen; Amo, Alberto; Combrié, Sylvian; Gérard, Bruno; Leo, Giuseppe; Favero, Ivan

    2016-01-01

    Gallium Arsenide and related compound semiconductors lie at the heart of optoelectronics and integrated laser technologies. Shaped at the micro and nano-scale, they allow strong interaction with quantum dots and quantum wells, and promise to result in stunning devices. However gallium arsenide optical structures presently exhibit lower performances than their silicon-based counterparts, notably in nanophotonics where the surface plays a chief role. Here we report on advanced surface control of miniature gallium arsenide optical resonators, using two distinct techniques that produce permanent results. One leads to extend the lifetime of free-carriers and enhance luminescence, while the other strongly reduces surface absorption originating from mid-gap states and enables ultra-low optical dissipation devices. With such surface control, the quality factor of wavelength-sized optical disk resonators is observed to rise up to six million at telecom wavelength, greatly surpassing previous realizations and opening n...

  18. Progress to a Gallium-Arsenide Deep-Center Laser

    Directory of Open Access Journals (Sweden)

    Janet L. Pan

    2009-10-01

    Full Text Available Although photoluminescence from gallium-arsenide (GaAs deep-centers was first observed in the 1960s, semiconductor lasers have always utilized conduction-to-valence-band transitions. Here we review recent materials studies leading to the first GaAs deep-center laser. First, we summarize well-known properties: nature of deep-center complexes, Franck-Condon effect, hotoluminescence. Second, we describe our recent work: insensitivity of photoluminescence with heating, striking differences between electroluminescence and photoluminescence, correlation between transitions to deep-states and absence of bandgap-emission. Room-temperature stimulated-emission from GaAs deep-centers was observed at low electrical injection, and could be tuned from the bandgap to half-the-bandgap (900–1,600 nm by changing the electrical injection. The first GaAs deep-center laser was demonstrated with electrical injection, and exhibited a threshold of less than 27 mA/cm2 in continuous-wave mode at room temperature at the important 1.54 μm fiber-optic wavelength. This small injection for laser action was explained by fast depopulation of the lower state of the optical transition (fast capture of free holes onto deep-centers, which maintains the population inversion. The evidence for laser action included: superlinear L-I curve, quasi-Fermi level separations satisfying Bernard-Duraffourg’s criterion, optical gains larger than known significant losses, clamping of the optical-emission from lossy modes unable to reach laser action, pinning of the population distribution during laser action.

  19. High-field phase-diagram of Fe arsenide superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Jo, Y.J.; Jaroszynski, J.; Yamamoto, A.; Gurevich, A.; Riggs, S.C.; Boebinger, G.S.; Larbalestier, D. [National High Magnetic Field Laboratory, Florida State University, Tallahassee-FL 32310 (United States); Wen, H.H. [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Zhigadlo, N.D.; Katrych, S.; Bukowski, Z.; Karpinski, J. [Laboratory for Solid State Physics, ETH Zuerich, CH-8093 Zuerich (Switzerland); Liu, R.H.; Chen, H.; Chen, X.H. [Hefei National Laboratory for Physical Science a Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Balicas, L., E-mail: balicas@magnet.fsu.ed [National High Magnetic Field Laboratory, Florida State University, Tallahassee-FL 32310 (United States)

    2009-05-01

    Here, we report an overview of the phase-diagram of single-layered and double-layered Fe arsenide superconductors at high magnetic fields. Our systematic magneto-transport measurements of polycrystalline SmFeAsO{sub 1-x}F{sub x} at different doping levels confirm the upward curvature of the upper critical magnetic field H{sub c2}(T) as a function of temperature T defining the phase boundary between the superconducting and metallic states for crystallites with the ab planes oriented nearly perpendicular to the magnetic field. We further show from measurements on single-crystals that this feature, which was interpreted in terms of the existence of two superconducting gaps, is ubiquitous among both series of single- and double-layered compounds. In all compounds explored by us the zero temperature upper critical field H{sub c2}(0), estimated either through the Ginzburg-Landau or the Werthamer-Helfand-Hohenberg single gap theories, strongly surpasses the weak-coupling Pauli paramagnetic limiting field. This clearly indicates the strong-coupling nature of the superconducting state and the importance of magnetic correlations for these materials. Our measurements indicate that the superconducting anisotropy, as estimated through the ratio of the effective masses gamma = (m{sub c}/m{sub ab}){sup 1/2} for carriers moving along the c-axis and the ab-planes, respectively, is relatively modest as compared to the high-T{sub c} cuprates, but it is temperature, field and even doping dependent. Finally, our preliminary estimations of the irreversibility field H{sub m}(T), separating the vortex-solid from the vortex-liquid phase in the single-layered compounds, indicates that it is well described by the melting of a vortex lattice in a moderately anisotropic uniaxial superconductor.

  20. Noble Metal Arsenides and Gold Inclusions in Northwest Africa 8186

    Science.gov (United States)

    Srinivasan, P.; McCubbin, F. M.; Rahman, Z.; Keller, L. P.; Agee, C. B.

    2016-01-01

    CK carbonaceous chondrites are a highly thermally altered group of carbonaceous chondrites, experiencing temperatures ranging between approximately 576-867 degrees Centigrade. Additionally, the mineralogy of the CK chondrites record the highest overall oxygen fugacity of all chondrites, above the fayalite-magnetite-quartz (FMQ) buffer. Me-tallic Fe-Ni is extremely rare in CK chondrites, but magnetite and Fe,Ni sulfides are commonly observed. Noble metal-rich inclusions have previously been found in some magnetite and sulfide grains. These arsenides, tellurides, and sulfides, which contain varying amounts of Pt, Ru, Os, Te, As, Ir, and S, are thought to form either by condensation from a solar gas, or by exsolution during metamorphism on the chondritic parent body. Northwest Africa (NWA) 8186 is a highly metamorphosed CK chondrite. This meteorite is predominately composed of NiO-rich forsteritic olivine (Fo65), with lesser amounts of plagioclase (An52), augite (Fs11Wo49), magnetite (with exsolved titanomagnetite, hercynite, and titanohematite), monosulfide solid solution (with exsolved pentlandite), and the phosphate minerals Cl-apatite and merrillite. This meteorite contains coarse-grained, homogeneous silicates, and has 120-degree triple junctions between mineral phases, which indicates a high degree of thermal metamorphism. The presence of NiO-rich olivine, oxides phases all bearing Fe3 plus, and the absence of metal, are consistent with an oxygen fugacity above the FMQ buffer. We also observed noble metal-rich phases within sulfide grains in NWA 8186, which are the primary focus of the present study.

  1. Indium Phosphide Window Layers for Indium Gallium Arsenide Solar Cells

    Science.gov (United States)

    Jain, Raj K.

    2005-01-01

    Window layers help in reducing the surface recombination at the emitter surface of the solar cells resulting in significant improvement in energy conversion efficiency. Indium gallium arsenide (In(x)Ga(1-x)As) and related materials based solar cells are quite promising for photovoltaic and thermophotovoltaic applications. The flexibility of the change in the bandgap energy and the growth of InGaAs on different substrates make this material very attractive for multi-bandgap energy, multi-junction solar cell approaches. The high efficiency and better radiation performance of the solar cell structures based on InGaAs make them suitable for space power applications. This work investigates the suitability of indium phosphide (InP) window layers for lattice-matched In(0.53)Ga(0.47)As (bandgap energy 0.74 eV) solar cells. We present the first data on the effects of the p-type InP window layer on p-on-n lattice-matched InGaAs solar cells. The modeled quantum efficiency results show a significant improvement in the blue region with the InP window. The bare InGaAs solar cell performance suffers due to high surface recombination velocity (10(exp 7) cm/s). The large band discontinuity at the InP/InGaAs heterojunction offers a great potential barrier to minority carriers. The calculated results demonstrate that the InP window layer effectively passivates the solar cell front surface, hence resulting in reduced surface recombination and therefore, significantly improving the performance of the InGaAs solar cell.

  2. Light transport through disordered layers of dense gallium arsenide submicron particles

    NARCIS (Netherlands)

    Van der Beek, T.; Barthelemy, P.J.C.; Johnson, P.M.; Wiersma, D.S.; Lagendijk, A.

    2012-01-01

    We present a study of optical transport properties of powder layers with submicrometer, strongly scattering gallium arsenide (GaAs) particles. Uniform, thin samples with well controlled thicknesses were created through the use of varying grinding times, sedimentation fractionation, annealing, and a

  3. Gallium interstitial contributions to diffusion in gallium arsenide

    Directory of Open Access Journals (Sweden)

    Joseph T. Schick

    2011-09-01

    have been encountered in fitting experimental results for heavily p-type, Ga-rich gallium arsenide by simply extending a model for gallium interstitial diffusion which has been used for less p-doped material.

  4. Spontaneous atomic ordering in MOVPE grown gallium arsenide antimonide

    Science.gov (United States)

    Jiang, Weiyang

    process. It is unlikely that the ordering mechanism is similar to the dimer-induced strain models that have been successfully used to explain CuPt ordering in InGaP. We propose a simple model based on alternating incorporation of group V adatoms at step edges. Keywords. GaAsSb; MOVPE; Bi surfactant; TEM; CuAu ordering. Subject. Gallium Arsenide Antimonide; Metalorganic Vapor-phase Epitaxy; Bismuth Surfactant; Transmission Electron Microscopy; CuAu Ordering.

  5. Biological availability of nickel arsenides: toxic effects of particulate Ni/sub 5/As/sub 2/

    Energy Technology Data Exchange (ETDEWEB)

    Gurley, L.R.; Tobey, R.A.; Valdez, J.G.; Halleck, M.S.; Barham, S.S.

    1981-01-01

    Considerations of (1) oil shale retort operating conditions, (2) oil shale elemental composition, (3) nickel and arsenic physico-chemical properties, and (4) oil shale matrix structure lead to the suggestion that nickel arsenides may be formed during the oil shale retorting process. The biological effects of nickel arsenides have not been previously studied. However, similarities between nickel subarsenide and nickel subsulfide and nickel subselenimide, both of which are known potent carcinogens, have caused concern that nickel arsenides may have adverse effects on biological systems. To determine if fugitive nickel arsenides from an oil shale retort could pose a threat to personnel in the workplace or to other living organisms in the environment, a program to study the toxicity of nickel arsenides has been initiated. Five stable nickel arsenides (Ni/sub 5/As/sub 2/, Ni/sub 2/As, Ni/sub 11/As/sub 8/, NiAs, and NiAs/sub 2/) and nickel arsenic sulfide (NiAsS) are considered possible species for study.

  6. First-Principles Determination of Ultrahigh Thermal Conductivity of Boron Arsenide: A Competitor for Diamond?

    Science.gov (United States)

    Lindsay, L.; Broido, D. A.; Reinecke, T. L.

    2013-07-01

    We have calculated the thermal conductivities (κ) of cubic III-V boron compounds using a predictive first principles approach. Boron arsenide is found to have a remarkable room temperature κ over 2000Wm-1K-1; this is comparable to those in diamond and graphite, which are the highest bulk values known. We trace this behavior in boron arsenide to an interplay of certain basic vibrational properties that lie outside of the conventional guidelines in searching for high κ materials, and to relatively weak phonon-isotope scattering. We also find that cubic boron nitride and boron antimonide will have high κ with isotopic purification. This work provides new insight into the nature of thermal transport at a quantitative level and predicts a new ultrahigh κ material of potential interest for passive cooling applications.

  7. Suppression of decoherence in gallium arsenide multiple quantum wells by means of bang-bang control

    Energy Technology Data Exchange (ETDEWEB)

    Takasago, K. [Department of Physics, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551 (Japan)], E-mail: takasago.k.aa@m.titech.ac.jp; Ogawa, Y.; Minami, F. [Department of Physics, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551 (Japan)

    2008-05-15

    We performed a three-pulse six-wave mixing (SWM) measurement on a gallium arsenide (GaAs) multiple quantum well and observed the time-resolved SWM signal using the heterodyne detection technique. The second pulse acts as a {pi} pulse that reverses the time evolution of the non-Markovian dynamics. By changing the pulse interval conditions, we confirmed the suppression of exciton decoherence by {pi} pulse irradiation (bang-bang control)

  8. Indium arsenide nanowire field-effect transistors for pH and biological sensing

    Energy Technology Data Exchange (ETDEWEB)

    Upadhyay, S.; Krogstrup, P.; Nygård, J., E-mail: nygard@nbi.dk [Center for Quantum Devices and Nanoscience Center, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen (Denmark); Frederiksen, R.; Lloret, N.; Martinez, K. L. [Bio-Nanotechnology and Nanomedicine Laboratory, Department of Chemistry and Nanoscience Center, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen (Denmark); De Vico, L.; Jensen, J. H. [Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen (Denmark)

    2014-05-19

    Indium Arsenide is a high mobility semiconductor with a surface electron accumulation layer that allows ohmic electrical contact to metals. Here, we present nanowire devices based on this material as a platform for chemical and biological sensing. The sensing principle involves the binding of a charged species at the sensor surface transduced via field effect into a change in current flowing through the sensor. We show the sensitivity of the platform to the H{sup +} ion concentration in solution as proof of principle and demonstrate the sensitivity to larger charged protein species. The sensors are highly reproducible and reach a detection limit of 10 pM for Avidin.

  9. Growth of Gold-assisted Gallium Arsenide Nanowires on Silicon Substrates via Molecular Beam Epitaxy

    Directory of Open Access Journals (Sweden)

    Ramon M. delos Santos

    2008-06-01

    Full Text Available Gallium arsenide nanowires were grown on silicon (100 substrates by what is called the vapor-liquid-solid (VLS growth mechanism using a molecular beam epitaxy (MBE system. Good quality nanowires with surface density of approximately 108 nanowires per square centimeter were produced by utilizing gold nanoparticles, with density of 1011 nanoparticles per square centimeter, as catalysts for nanowire growth. X-ray diffraction measurements, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy revealed that the nanowires are epitaxially grown on the silicon substrates, are oriented along the [111] direction and have cubic zincblende structure.

  10. Ab initio study of the unusual thermal transport properties of boron arsenide and related materials

    Science.gov (United States)

    Broido, D. A.; Lindsay, L.; Reinecke, T. L.

    2013-12-01

    Recently, using a first principles approach, we predicted that zinc blende boron arsenide (BAs) will have an ultrahigh lattice thermal conductivity, κ, of over 2000 Wm-1K-1 at room temperature (RT), comparable to that of diamond. Here, we provide a detailed ab initio examination of phonon thermal transport in boron arsenide, contrasting its unconventional behavior with that of other related materials, including the zinc blende crystals boron nitride (BN), boron phosphide, boron antimonide, and gallium nitride (GaN). The unusual vibrational properties of BAs contribute to its weak phonon-phonon scattering and phonon-isotope scattering, which are responsible for its exceptionally high κ. The thermal conductivity of BAs has contributions from phonons with anomalously large mean free paths (˜2 μm), two to three times those of diamond and BN. This makes κ in BAs sensitive to phonon scattering from crystal boundaries. An order of magnitude smaller RT thermal conductivity in a similar material, zinc blende GaN, is connected to more separated acoustic phonon branches, larger anharmonic force constants, and a large isotope mixture on the heavy rather than the light constituent atom. The striking difference in κ for BAs and GaN demonstrates the importance of using a microscopic first principles thermal transport approach for calculating κ. BAs also has an advantageous RT coefficient of thermal expansion, which, combined with the high κ value, suggests that it is a promising material for use in thermal management applications.

  11. THE QUANTUM-WELL STRUCTURES OF SELF ELECTROOPTIC-EFFECT DEVICES AND GALLIUM-ARSENIDE

    Directory of Open Access Journals (Sweden)

    Mustafa TEMİZ

    1996-02-01

    Full Text Available Multiple quantum-well (MQW electroabsorptive self electro optic-effect devices (SEEDs are being extensively studied for use in optical switching and computing. The self electro-optic-effect devices which has quantum-well structures is a new optoelectronic technology with capability to obtain both optical inputs and outputs for Gallium-Arsenide/Aluminum Gallium-Arsenide (GaAs/AlGaAs electronic circuits. The optical inputs and outputs are based on quantum-well absorptive properties. These quantum-well structures consist of many thin layers of semiconductors materials of GaAs/AlGaAs which have emerged some important directions recently. The most important advance in the physics of these materials since the early days has been invention of the heterojunction structures which is based at present on GaAs technology. GaAs/AlGaAs structures present some important advantages to relevant band gap and index of refraction which allow to form the quantum-well structures and also to make semiconductor lasers, dedectors and waveguide optical switches.

  12. Outdoor Performance of a Thin-Film Gallium-Arsenide Photovoltaic Module

    Energy Technology Data Exchange (ETDEWEB)

    Silverman, T. J.; Deceglie, M. G.; Marion, B.; Cowley, S.; Kayes, B.; Kurtz, S.

    2013-06-01

    We deployed a 855 cm2 thin-film, single-junction gallium arsenide (GaAs) photovoltaic (PV) module outdoors. Due to its fundamentally different cell technology compared to silicon (Si), the module responds differently to outdoor conditions. On average during the test, the GaAs module produced more power when its temperature was higher. We show that its maximum-power temperature coefficient, while actually negative, is several times smaller in magnitude than that of a Si module used for comparison. The positive correlation of power with temperature in GaAs is due to temperature-correlated changes in the incident spectrum. We show that a simple correction based on precipitable water vapor (PWV) brings the photocurrent temperature coefficient into agreement with that measured by other methods and predicted by theory. The low operating temperature and small temperature coefficient of GaAs give it an energy production advantage in warm weather.

  13. Electronic structure, magnetic and superconducting properties of co-doped iron-arsenide superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Rosner, Helge; Schnelle, Walter; Nicklas, Michael; Leithe-Jasper, Andreas [MPI CPfS Dresden (Germany); Weikert, Franziska [Los Alamos National Laboratory, New Mexico (United States); HLD Dresden Rossendorf (Germany); Wosnitza, Joachim [HLD Dresden Rossendorf (Germany)

    2013-07-01

    We present a joint experimental and theoretical study of co-doped iron-arsenide superconductors of the 122 family A{sub 1-x}K{sub x}Fe{sub 2-y}T{sub y}As{sub 2} (A = Ba,Sr,Eu; T = Co,Ru,Rh). In these systems, the co-doping enables the separation of different parameters - like electron count, disorder or the specific geometry of the FeAs layer - with respect to the position of the respective compounds in the general 122 phase diagram. For a series of compounds, we investigate the relevance of the different parameters for the magnetic, thermodynamic and superconducting properties. Our experimental investigations are supported by density functional electronic structure calculations applying different approximations for doping and disorder.

  14. Ultraviolet Beam Focusing in Gallium Arsenide by Direct Excitation of Surface Plasmon Polaritons

    Directory of Open Access Journals (Sweden)

    Senfeng Lai

    2015-01-01

    Full Text Available This paper proposed that ultraviolet beam could be focused by gallium arsenide (GaAs through direct excitation of surface plasmon polaritons. Both theoretical analysis and computer simulation showed that GaAs could be a reasonably good plasmonic material in the air in the deep ultraviolet waveband. With a properly designed bull’s eye structure etched in GaAs, the ultraviolet electric field could be enhanced to as high as 20 times the incident value, and the full-width-half-maximum (FWHM of the light beam could be shrunk from ~48° to ~6°. As a plasmonic material, GaAs was compared to Ag and Al. Within the studied ultraviolet waveband, the field enhancement in GaAs was much stronger than Ag but not as high as Al.

  15. Ultrafast Relaxation Dynamics of Photo-excited Dirac Fermion in Three Dimensional Dirac Semimetal Cadmium Arsenide

    CERN Document Server

    Lu, Wei; Liu, Xuefeng; Lu, Hong; Li, Caizhen; Lai, Jiawei; Zhao, Chuan; Tian, Ye; Liao, Zhimin; Jia, Shuang; Sun, Dong

    2016-01-01

    Three dimensional (3D) Dirac semimetal exhibiting ultrahigh mobility has recently attracted enormous research interests as 3D analogues of graphene. From the prospects of future application toward electronic/optoelectronic devices with extreme performance, it is crucial to understand the relaxation dynamics of photo-excited carriers and their coupling with lattice. In this work, we report ultrafast transient reflection measurements of photo-excited carrier dynamics in cadmium arsenide (Cd3As2), which is among the most stable Dirac semimetals that have been confirmed experimentally. With low energy probe photon of 0.3 eV, photo-excited Dirac Fermions dynamics closing to Dirac point are probed. Through transient reflection measurements on bulk and nanoplate samples that have different doping intensities, and systematic probe wavelength, pump power and lattice temperature dependent measurements, the dynamical evolution of carrier distributions can be retrieved qualitatively using a two-temperature model. The pho...

  16. Methods for forming group III-V arsenide-nitride semiconductor materials

    Science.gov (United States)

    Major, Jo S. (Inventor); Welch, David F. (Inventor); Scifres, Donald R. (Inventor)

    2000-01-01

    Methods are disclosed for forming Group III--arsenide-nitride semiconductor materials. Group III elements are combined with group V elements, including at least nitrogen and arsenic, in concentrations chosen to lattice match commercially available crystalline substrates. Epitaxial growth of these III-V crystals results in direct bandgap materials, which can be used in applications such as light emitting diodes and lasers. Varying the concentrations of the elements in the III-V crystals varies the bandgaps, such that materials emitting light spanning the visible spectra, as well as mid-IR and near-UV emitters, can be created. Conversely, such material can be used to create devices that acquire light and convert the light to electricity, for applications such as full color photodetectors and solar energy collectors. The growth of the III-V crystals can be accomplished by growing thin layers of elements or compounds in sequences that result in the overall lattice match and bandgap desired.

  17. Ultrafast photocurrents and terahertz radiation in gallium arsenide and carbon based nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Prechtel, Hans Leonhard

    2011-08-15

    In this thesis we developed a measurement technique based on a common pump-probe scheme and coplanar stripline circuits that enables time-resolved photocurrent measurements of contacted nanosystems with a micrometer spatial and a picosecond time resolution. The measurement technique was applied to lowtemperature grown gallium arsenide (LT-GaAs), carbon nanotubes (CNTs), graphene, and p-doped gallium arsenide (GaAs) nanowires. The various mechanisms responsible for the generation of current pulses by pulsed laser excitation were reviewed. Furthermore the propagation of the resulting electromagnetic radiation along a coplanar stripline circuit was theoretically and numerically treated. The ultrafast photocurrent response of low-temperature grown GaAs was investigated. We found two photocurrent pulses in the time-resolved response. We showed that the first pulse is consistent with a displacement current pulse. We interpreted the second pulse to result from a transport current process. We further determined the velocity of the photo-generated charge carriers to exceed the drift, thermal and quantum velocities of single charge carriers. Hereby, we interpreted the transport current pulse to stem from an electron-hole plasma excitation. We demonstrated that the photocurrent response of CNTs comprises an ultrafast displacement current and a transport current. The data suggested that the photocurrent is finally terminated by the recombination lifetime of the charge carriers. To the best of our knowledge, we presented in this thesis the first recombination lifetime measurements of contacted, suspended, CVD grown CNT networks. In addition, we studied the ultrafast photocurrent dynamics of freely suspended graphene contacted by metal electrodes. At the graphene-metal interface, we demonstrated that built-in electric fields give rise to a photocurrent with a full-width-half-maximum of a few picoseconds and that a photo-thermoelectric effect generates a current with a decay time

  18. In-Plane Electronic Anisotropy of Underdoped ___122___ Fe-Arsenide Superconductors Revealed by Measurements of Detwinned Single Crystals

    Energy Technology Data Exchange (ETDEWEB)

    Fisher, Ian Randal

    2012-05-08

    The parent phases of the Fe-arsenide superconductors harbor an antiferromagnetic ground state. Significantly, the Neel transition is either preceded or accompanied by a structural transition that breaks the four fold symmetry of the high-temperature lattice. Borrowing language from the field of soft condensed matter physics, this broken discrete rotational symmetry is widely referred to as an Ising nematic phase transition. Understanding the origin of this effect is a key component of a complete theoretical description of the occurrence of superconductivity in this family of compounds, motivating both theoretical and experimental investigation of the nematic transition and the associated in-plane anisotropy. Here we review recent experimental progress in determining the intrinsic in-plane electronic anisotropy as revealed by resistivity, reflectivity and ARPES measurements of detwinned single crystals of underdoped Fe arsenide superconductors in the '122' family of compounds.

  19. Thermo-chemical properties and electrical resistivity of Zr-based arsenide chalcogenides

    Directory of Open Access Journals (Sweden)

    A. Schlechte, R. Niewa, M. Schmidt, G. Auffermann, Yu. Prots, W. Schnelle, D. Gnida, T. Cichorek, F. Steglich and R. Kniep

    2007-01-01

    Full Text Available Ternary phases in the systems Zr–As–Se and Zr–As–Te were studied using single crystals of ZrAs1.40(1Se0.50(1 and ZrAs1.60(2Te0.40(1 (PbFCl-type of structure, space group P4/nmm as well as ZrAs0.70(1Se1.30(1 and ZrAs0.75(1Te1.25(1 (NbPS-type of structure, space group Immm. The characterization covers chemical compositions, crystal structures, homogeneity ranges and electrical resistivities. At 1223 K, the Te-containing phases can be described with the general formula ZrAsxTe2−x, with 1.53(1≤x≤1.65(1 (As-rich and 0.58(1≤x≤0.75(1 (Te-rich. Both phases are located directly on the tie-line between ZrAs2 and ZrTe2, with no indication for any deviation. Similar is true for the Se-rich phase ZrAsxSe2−x with 0.70(1≤x≤0.75(1. However, the compositional range of the respective As-rich phase ZrAsx−ySe2−x (0.03(1≤y≤0.10(1; 1.42(1≤x≤1.70(1 is not located on the tie-line ZrAs2–ZrSe2, and exhibits a triangular region of existence with intrinsic deviation of the composition towards lower non-metal contents. Except for ZrAs0.75Se1.25, from the homogeneity range of the Se-rich phase, all compounds under investigation show metallic characteristics of electrical resistivity at temperatures >20 K. Related uranium and thorium arsenide selenides display a typical magnetic field-independent rise of the resistivity towards lower temperatures, which has been explained by a non-magnetic Kondo effect. However, a similar observation has been made for ZrAs1.40Se0.50, which, among the Zr-based arsenide chalcogenides, is the only system with a large concentration of intrinsic defects in the anionic substructure.

  20. Monopole Charge Domain in High-Gain Gallium Arsenide Photoconductive Switches

    Institute of Scientific and Technical Information of China (English)

    施卫; 陈二柱; 张显斌; 李琦

    2002-01-01

    Considering that semi-insulating gallium arsenide photoconductive switches can be triggered into the high gain mode and no reliable theories can account for the observed transient characteristics, we propose the monopole charge domain model to explain the peculiar switching phenomena occurring in the high gain mode and we discuss the requirements for the lock-on switching. During operation on this mode, the applied field across the switch and the lock-on field are all larger than the Gunn threshold field. Our developed monopole charge domain is based on the transferred-electron effect, but the domain is only composed of large numbers of electrons piled up due to the negative differential mobility. Using the model and taking the physical mechanism of the avalanche impact ionization and recombination radiation into consideration, we interpret the typical phenomena of the lock-on effect, such as the time delay between the beginning of optical illumination and turning-on of the switch, and the conduction mechanism of the sustaining phase. Under different conditions of bias field intensity and incident light energy, the time delay of the switching is calculated. The results show that the physical mechanisms of impact ionization and recombination radiation occurring in the monopole charge domain are responsible for the lock-on switching.

  1. Transport-reaction model for defect and carrier behavior within displacement cascades in gallium arsenide

    Energy Technology Data Exchange (ETDEWEB)

    Wampler, William R.; Myers, Samuel Maxwell,

    2014-02-01

    A model is presented for recombination of charge carriers at displacement damage in gallium arsenide, which includes clustering of the defects in atomic displacement cascades produced by neutron or ion irradiation. The carrier recombination model is based on an atomistic description of capture and emission of carriers by the defects with time evolution resulting from the migration and reaction of the defects. The physics and equations on which the model is based are presented, along with details of the numerical methods used for their solution. The model uses a continuum description of diffusion, field-drift and reaction of carriers and defects within a representative spherically symmetric cluster. The initial radial defect profiles within the cluster were chosen through pair-correlation-function analysis of the spatial distribution of defects obtained from the binary-collision code MARLOWE, using recoil energies for fission neutrons. Charging of the defects can produce high electric fields within the cluster which may influence transport and reaction of carriers and defects, and which may enhance carrier recombination through band-to-trap tunneling. Properties of the defects are discussed and values for their parameters are given, many of which were obtained from density functional theory. The model provides a basis for predicting the transient response of III-V heterojunction bipolar transistors to pulsed neutron irradiation.

  2. Nonlinear radiation response of n-doped indium antimonide and indium arsenide in intense terahertz field

    Science.gov (United States)

    Gong, Jiao-Li; Liu, Jin-Song; Chu, Zheng; Yang, Zhen-Gang; Wang, Ke-Jia; Yao, Jian-Quan

    2016-10-01

    The nonlinear radiation responses of two different n-doped bulk semiconductors: indium antimonide (InSb) and indium arsenide (InAs) in an intense terahertz (THz) field are studied by using the method of ensemble Monte Carlo (EMC) at room temperature. The results show that the radiations of two materials generate about 2-THz periodic regular spectrum distributions under a high field of 100 kV/cm at 1-THz center frequency. The center frequencies are enhanced to about 7 THz in InSb, and only 5 THz in InAs, respectively. The electron valley occupancy and the percentage of new electrons excited by impact ionization are also calculated. We find that the band nonparabolicity and impact ionization promote the generation of nonlinear high frequency radiation, while intervalley scattering has the opposite effect. Moreover, the impact ionization dominates in InSb, while impact ionization and intervalley scattering work together in InAs. These characteristics have potential applications in up-convension of THz wave and THz nonlinear frequency multiplication field. Project supported by the National Natural Science Foundation of China (Grant Nos. 11574105 and 61177095), the Natural Science Foundation of Hubei Province, China (Grant Nos. 2012FFA074 and 2013BAA002), the Wuhan Municipal Applied Basic Research Project, China (Grant No. 20140101010009), and the Fundamental Research Funds for the Central Universities, China (Grant Nos. 2013KXYQ004 and 2014ZZGH021).

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

    Science.gov (United States)

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

    1992-07-01

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

  4. On the understanding of irradiation effects in germanium, silicon and gallium arsenide semi-conductors

    International Nuclear Information System (INIS)

    We have studied the behaviour of germanium, silicon and gallium arsenide semiconductors irradiated by different projectiles (heavy ions, protons, electrons and fullerenes). At low doses, thanks to deep level transient spectroscopy (DLTS) and Hall effect electrical measurements, we were able to explicit the nature of the defects present in germanium after irradiation at room temperature. For different projectiles, we have determined the defect creation kinetics. At higher doses, the electrical measurements have brought to the fore the presence of a specific defect created only after an heavy ion (or proton) irradiation. Moreover, positron annihilation spectroscopy (PAS) measurements show that size of this specific defect increases with the fluence. The damage has also been quantified by channeling Rutherford backscaterring (RBS-C) measurements. At first sight, the obtained defect creation rates are normalized by the nuclear collisions. This normalization is also present in the inverse of the gain evolution in silicon bipolar transistors. Meanwhile, an extensive study shows an efficiency decrease of the defect creation at intermediate values of the electronic energy loss Se, then, at the opposite, an increasing at higher values of Se. In the three semiconductors, we have observed track formation after fullerenes irradiation. These tracks are amorphous cylinders which have been characterized by transmission and high resolution electronic microscopy. They are due to the very high values of the electronic energy density which can be deposited by fullerenes owing to their low velocity. (author)

  5. Coherent detection of THz waves based on THz-induced time-resolved luminescence quenching in bulk gallium arsenide.

    Science.gov (United States)

    Chu, Zheng; Liu, Jinsong; Wang, Kejia

    2012-05-01

    A kind of photoluminescence quenching, in which the time-resolved photoluminescence is modulated by a THz pulse, has been theoretically investigated by performing the ensemble Monte Carlo method in bulk gallium arsenide (GaAs) at room temperature. The quenching ratio could reach up to 50% under a strong THz field (100  kV/cm). The range in which luminescence quenching is linearly proportional to the THz field could be over 60  kV/cm. On the basis of these results, a principle for THz modulation and coherent detection is proposed. PMID:22555695

  6. Indium gallium arsenide imaging with smaller cameras, higher-resolution arrays, and greater material sensitivity

    Science.gov (United States)

    Ettenberg, Martin H.; Cohen, Marshall J.; Brubaker, Robert M.; Lange, Michael J.; O'Grady, Matthew T.; Olsen, Gregory H.

    2002-08-01

    Indium Gallium Arsenide (InGaAs) photodiode arrays have numerous commercial, industrial, and military applications. During the past 10 years, great strides have been made in the development of these devices starting with simple 256-element linear photodiode arrays and progressing to the large 640 x 512 element area arrays now readily available. Linear arrays are offered with 512 elements on a 25 micron pitch with no defective pixels, and are used in spectroscopic monitors for wavelength division multiplexing (WDM) systems as well as in machine vision applications. A 320 x 240 solid-state array operates at room temperature, which allows development of a camera which is smaller than 25 cm3 in volume, weighs less than 100 g and uses less than 750 mW of power. Two dimensional focal plane arrays and cameras have been manufactured with detectivity, D*, greater than 1014 cm-(root)Hz/W at room temperature and have demonstrated the ability to image at night. Cameras are also critical tools for the assembly and performance monitoring of optical switches and add-drop multiplexers in the telecommunications industry. These same cameras are used for the inspection of silicon wafers and fine art, laser beam profiling, and metals manufacturing. By varying the Indium content, InGaAs photodiode arrays can be tailored to cover the entire short-wave infrared spectrum from 1.0 micron to 2.5 microns. InGaAs focal plane arrays and cameras sensitive to 2.0 micron wavelength light are now available in 320 x 240 formats.

  7. Investigation on properties of ultrafast switching in a bulk gallium arsenide avalanche semiconductor switch

    International Nuclear Information System (INIS)

    Properties of ultrafast switching in a bulk gallium arsenide (GaAs) avalanche semiconductor switch based on semi-insulating wafer, triggered by an optical pulse, were analyzed using physics-based numerical simulations. It has been demonstrated that when a voltage with amplitude of 5.2 kV is applied, after an exciting optical pulse with energy of 1 μJ arrival, the structure with thickness of 650 μm reaches a high conductivity state within 110 ps. Carriers are created due to photons absorption, and electrons and holes drift to anode and cathode terminals, respectively. Static ionizing domains appear both at anode and cathode terminals, and create impact-generated carriers which contribute to the formation of electron-hole plasma along entire channel. When the electric field in plasma region increases above the critical value (∼4 kV/cm) at which the electrons drift velocity peaks, a domain comes into being. An increase in carrier concentration due to avalanche multiplication in the domains reduces the domain width and results in the formation of an additional domain as soon as the field outside the domains increases above ∼4 kV/cm. The formation and evolution of multiple powerfully avalanching domains observed in the simulations are the physical reasons of ultrafast switching. The switch exhibits delayed breakdown with the characteristics affected by biased electric field, current density, and optical pulse energy. The dependence of threshold energy of the exciting optical pulse on the biased electric field is discussed

  8. Phase diagram of (Li(1-x)Fe(x))OHFeSe: a bridge between iron selenide and arsenide superconductors.

    Science.gov (United States)

    Dong, Xiaoli; Zhou, Huaxue; Yang, Huaixin; Yuan, Jie; Jin, Kui; Zhou, Fang; Yuan, Dongna; Wei, Linlin; Li, Jianqi; Wang, Xinqiang; Zhang, Guangming; Zhao, Zhongxian

    2015-01-14

    Previous experimental results have shown important differences between iron selenide and arsenide superconductors which seem to suggest that the high-temperature superconductivity in these two subgroups of iron-based families may arise from different electronic ground states. Here we report the complete phase diagram of a newly synthesized superconducting (SC) system, (Li1-xFex)OHFeSe, with a structure similar to that of FeAs-based superconductors. In the non-SC samples, an antiferromagnetic (AFM) spin-density-wave (SDW) transition occurs at ∼127 K. This is the first example to demonstrate such an SDW phase in an FeSe-based superconductor system. Transmission electron microscopy shows that a well-known √5×√5 iron vacancy ordered state, resulting in an AFM order at ∼500 K in AyFe2-xSe2 (A = metal ions) superconductor systems, is absent in both non-SC and SC samples, but a unique superstructure with a modulation wave vector q = (1)/2(1,1,0), identical to that seen in the SC phase of KyFe2-xSe2, is dominant in the optimal SC sample (with an SC transition temperature Tc = 40 K). Hence, we conclude that the high-Tc superconductivity in (Li1-xFex)OHFeSe stems from the similarly weak AFM fluctuations as FeAs-based superconductors, suggesting a universal physical picture for both iron selenide and arsenide superconductors.

  9. Revealing the optoelectronic and thermoelectric properties of the Zintl quaternary arsenides ACdGeAs2 (A = K, Rb)

    International Nuclear Information System (INIS)

    Highlights: • Zintl tetragonal phase ACdGeAs2 (A = K, Rb) are chalcopyrite and semiconductors. • Their direct band gap is suitable for PV, optolectronic and thermoelectric applications. • Combination of DFT and Boltzmann transport theory is employed. • The present arsenides are found to be covalent materials. - Abstract: Chalcopyrite semiconductors have attracted much attention due to their potential implications in photovoltaic and thermoelectric applications. First principle calculations were performed to investigate the electronic, optical and thermoelectric properties of the Zintl tetragonal phase ACdGeAs2 (A = K, Rb) using the full potential linear augmented plane wave method and the Engle–Vosko GGA (EV–GGA) approximation. The present compounds are found semiconductors with direct band gap and covalent bonding character. The optical transitions are investigated via the dielectric function (real and imaginary parts) along with other related optical constants including refractive index, reflectivity and energy-loss spectrum. Combining results from DFT and Boltzmann transport theory, we reported the thermoelectric properties such as the Seebeck’s coefficient, electrical and thermal conductivity, figure of merit and power factor as function of temperatures. The present chalcopyrite Zintl quaternary arsenides deserve to be explored for their potential applications as thermoelectric materials and for photovoltaic devices

  10. Revealing the optoelectronic and thermoelectric properties of the Zintl quaternary arsenides ACdGeAs{sub 2} (A = K, Rb)

    Energy Technology Data Exchange (ETDEWEB)

    Azam, Sikander; Khan, Saleem Ayaz [New Technologies—Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Goumri-Said, Souraya, E-mail: Souraya.Goumri-Said@chemistry.gatech.edu [School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA 30332-0400 (United States)

    2015-10-15

    Highlights: • Zintl tetragonal phase ACdGeAs{sub 2} (A = K, Rb) are chalcopyrite and semiconductors. • Their direct band gap is suitable for PV, optolectronic and thermoelectric applications. • Combination of DFT and Boltzmann transport theory is employed. • The present arsenides are found to be covalent materials. - Abstract: Chalcopyrite semiconductors have attracted much attention due to their potential implications in photovoltaic and thermoelectric applications. First principle calculations were performed to investigate the electronic, optical and thermoelectric properties of the Zintl tetragonal phase ACdGeAs{sub 2} (A = K, Rb) using the full potential linear augmented plane wave method and the Engle–Vosko GGA (EV–GGA) approximation. The present compounds are found semiconductors with direct band gap and covalent bonding character. The optical transitions are investigated via the dielectric function (real and imaginary parts) along with other related optical constants including refractive index, reflectivity and energy-loss spectrum. Combining results from DFT and Boltzmann transport theory, we reported the thermoelectric properties such as the Seebeck’s coefficient, electrical and thermal conductivity, figure of merit and power factor as function of temperatures. The present chalcopyrite Zintl quaternary arsenides deserve to be explored for their potential applications as thermoelectric materials and for photovoltaic devices.

  11. Development of devices and systems of growth of gallium arsenide ingots for micro, nano electronics and photovoltaics

    Directory of Open Access Journals (Sweden)

    A. P. Oksanich

    2013-09-01

    Full Text Available Gallium arsenide is a perspective semiconductor, the need for which is constantly increasing. This is associated with the development of electronic components operating in excess of the high frequency range and development of terrestrial photovoltaics based on gallium arsenide solar cells. Increase in diameter of grown ingots leads to a deterioration in their performance, which is caused by the imperfection of growing technology. The paper presents the results of the development of systems and devices which help to improve existing technology to produce GaAs ingots and wafers with a diameter of 100 mm with the best technical parameters. Developed a system to manage growing GaAs ingot. As a sensor of diameter ingot it uses a weighting method provides a measurement error in the process of growing ± 1,0 mm. The system allows to grow GaAs ingots with an error of ± 2 mm. For the formation of temperature gradients developed thermal unit, which provides a gradient of 51 .. 53 K cm in growing of ingots with diameter of 100 mm. For adjusting the process parameters were developed measuring device of the internal stresses that are generated in the ingot during the growth of the GaAs ingot. Presented in paper technical solutions provided a silicon ingot with a diameter of 100 mm. with mobility, cm2 V-1 s-1 - 2500 ÷ 3500, the charge carrier density, cm-3 - 5x1017 ÷ 5x1018; dislocation density, cm-2 - to 8x104.

  12. Phase diagram of (Li(1-x)Fe(x))OHFeSe: a bridge between iron selenide and arsenide superconductors.

    Science.gov (United States)

    Dong, Xiaoli; Zhou, Huaxue; Yang, Huaixin; Yuan, Jie; Jin, Kui; Zhou, Fang; Yuan, Dongna; Wei, Linlin; Li, Jianqi; Wang, Xinqiang; Zhang, Guangming; Zhao, Zhongxian

    2015-01-14

    Previous experimental results have shown important differences between iron selenide and arsenide superconductors which seem to suggest that the high-temperature superconductivity in these two subgroups of iron-based families may arise from different electronic ground states. Here we report the complete phase diagram of a newly synthesized superconducting (SC) system, (Li1-xFex)OHFeSe, with a structure similar to that of FeAs-based superconductors. In the non-SC samples, an antiferromagnetic (AFM) spin-density-wave (SDW) transition occurs at ∼127 K. This is the first example to demonstrate such an SDW phase in an FeSe-based superconductor system. Transmission electron microscopy shows that a well-known √5×√5 iron vacancy ordered state, resulting in an AFM order at ∼500 K in AyFe2-xSe2 (A = metal ions) superconductor systems, is absent in both non-SC and SC samples, but a unique superstructure with a modulation wave vector q = (1)/2(1,1,0), identical to that seen in the SC phase of KyFe2-xSe2, is dominant in the optimal SC sample (with an SC transition temperature Tc = 40 K). Hence, we conclude that the high-Tc superconductivity in (Li1-xFex)OHFeSe stems from the similarly weak AFM fluctuations as FeAs-based superconductors, suggesting a universal physical picture for both iron selenide and arsenide superconductors. PMID:25532066

  13. Characterization of solar cells for space applications. Volume 14: Electrical characteristics of Hughes liquid phase epitaxy gallium arsenide solar cells as a function of intensity, temperature and irradiation

    Science.gov (United States)

    Anspaugh, B. E.; Downing, R. G.; Miyahira, T. F.; Weiss, R. S.

    1981-01-01

    Electrical characteristics of liquid phase epitaxy, P/N gallium aluminum arsenide solar cells are presented in graphical and tabular format as a function of solar illumination intensity and temperature. The solar cells were exposed to 1 MeV electron fluences of, respectively, 0, one hundred trillion, one quadrillion, and ten quadrillion e/sq cm.

  14. Pixel x-ray detectors in epitaxial gallium arsenide with high-energy resolution capabilities (Fano factor experiment determination)

    International Nuclear Information System (INIS)

    Gallium Arsenide pixel detectors with an area of 170 x 320 microm2 and thickness of 5 microm, realized by molecular beam epitaxy, have been designed and tested with X- and γ rays. No significant charge trapping effects have been observed, and a charge collection efficiency of 100% has been measured. At room temperature an energy resolution of 671 eV full width at half maximum (FWHM) at 59.54 keV has been obtained, with an electronic noise of 532 eV FWHM. With the detector cooled to 243 K, the electronic noise is reduced to 373 eV FWHM, and the Kα and Kβ lines of the 55Fe spectrum can be resolved. The Fano factor for GaAs has been measured at room temperature with 59.5 keV photons yielding F = 0.12 ± 0.01

  15. Study of the structure of a thin aluminum layer on the vicinal surface of a gallium arsenide substrate by high-resolution electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Lovygin, M. V., E-mail: lemi@miee.ru; Borgardt, N. I. [National Research University of Electronic Technology “MIET” (Russian Federation); Seibt, M. [Universität Göttingen, IV Physikalisches Institut (Germany); Kazakov, I. P.; Tsikunov, A. V. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)

    2015-12-15

    The results of electron-microscopy studies of a thin epitaxial aluminum layer deposited onto a misoriented gallium-arsenide substrate are reported. It is established that the layer consists of differently oriented grains, whose crystal lattices are coherently conjugated with the substrate with the formation of misfit dislocations, as in the case of a layer on a singular substrate. Atomic steps on the substrate surface are visualized, and their influence on the growth of aluminum crystal grains is discussed.

  16. Electron tunneling transport across heterojunctions between europium sulfide and indium arsenide

    Science.gov (United States)

    Kallaher, Raymond L.

    This dissertation presents research done on utilizing the ferromagnetic semiconductor europium sulfide (EuS) to inject spin polarized electrons into the non-magnetic semiconductor indium arsenide (InAs). There is great interest in expanding the functionality of modern day electronic circuits by creating devices that depend not only on the flow of charge in the device, but also on the transport of spin through the device. Within this mindset, there is a concerted effort to establish an efficient means of injecting and detecting spin polarized electrons in a two dimensional electron system (2DES) as the first step in developing a spin based field effect transistor. Thus, the research presented in this thesis has focused on the feasibility of using EuS, in direct electrical contact with InAs, as a spin injecting electrode into an InAs 2DES. Doped EuS is a concentrated ferromagnetic semiconductor, whose conduction band undergoes a giant Zeeman splitting when the material becomes ferromagnetic. The concomitant difference in energy between the spin-up and spin-down energy bands makes the itinerant electrons in EuS highly spin polarized. Thus, in principle, EuS is a good candidate to be used as an injector of spin polarized electrons into non-magnetic materials. In addition, the ability to adjust the conductivity of EuS by varying the doping level in the material makes EuS particularly suited for injecting spins into non-magnetic semiconductors and 2DES. For this research, thin films of EuS have been grown via e-beam evaporation of EuS powder. This growth technique produces EuS films that are sulfur deficient; these sulfur vacancies act as intrinsic electron donors and the resulting EuS films behave like heavily doped ferromagnetic semiconductors. The growth parameters and deposition procedures were varied and optimized in order to fabricate films that have minimal crystalline defects. Various properties and characteristics of these EuS films were measured and compared to

  17. Point defects and electric compensation in gallium arsenide single crystals; Punktdefekte und elektrische Kompensation in Galliumarsenid-Einkristallen

    Energy Technology Data Exchange (ETDEWEB)

    Kretzer, Ulrich

    2007-12-10

    In the present thesis the point-defect budget of gallium arsenide single crystals with different dopings is studied. It is shown, in which way the concentration of the single point defects depende on the concentration of the dopants, the stoichiometry deviation, and the position of the Fermi level. For this serve the results of the measurement-technical characterization of a large number of samples, in the fabrication of which these parameters were directedly varied. The main topic of this thesis lies in the development of models, which allow a quantitative description of the experimentally studied electrical and optical properties of gallium arsenide single crystals starting from the point-defect concentrations. Because from point defects charge carriers can be set free, their concentration determines essentially the charge-carrier concentration in the bands. In the ionized state point defects act as scattering centers for free charge carriers and influence by this the drift mobility of the charge carriers. A thermodynamic modeling of the point-defect formation yields statements on the equilibrium concentrations of the point defects in dependence on dopant concentration and stoichiometry deviation. It is show that the electrical properties of the crystals observed at room temperature result from the kinetic suppression of processes, via which the adjustment of a thermodynamic equilibrium between the point defects is mediated. [German] In der vorliegenden Arbeit wird der Punktdefekthaushalt von Galliumarsenid-Einkristallen mit unterschiedlichen Dotierungen untersucht. Es wird gezeigt, in welcher Weise die Konzentration der einzelnen Punktdefekte von der Konzentration der Dotierstoffe, der Stoechiometrieabweichung und der Lage des Ferminiveaus abhaengen. Dazu dienen die Ergebnisse der messtechnischen Charakterisierung einer grossen Anzahl von Proben, bei deren Herstellung diese Parameter gezielt variiert wurden. Der Schwerpunkt der Arbeit liegt in der Entwicklung

  18. Non-local exchange correlation functionals impact on the structural, electronic and optical properties of III-V arsenides

    KAUST Repository

    Anua, N. Najwa

    2013-08-20

    Exchange correlation (XC) energy functionals play a vital role in the efficiency of density functional theory (DFT) calculations, more soundly in the calculation of fundamental electronic energy bandgap. In the present DFT study of III-arsenides, we investigate the implications of XC-energy functional and corresponding potential on the structural, electronic and optical properties of XAs (X = B, Al, Ga, In). Firstly we report and discuss the optimized structural lattice parameters and the band gap calculations performed within different non-local XC functionals as implemented in the DFT-packages: WIEN2k, CASTEP and SIESTA. These packages are representative of the available code in ab initio studies. We employed the LDA, GGA-PBE, GGA-WC and mBJ-LDA using WIEN2k. In CASTEP, we employed the hybrid functional, sX-LDA. Furthermore LDA, GGA-PBE and meta-GGA were employed using SIESTA code. Our results point to GGA-WC as a more appropriate approximation for the calculations of structural parameters. However our electronic bandstructure calculations at the level of mBJ-LDA potential show considerable improvements over the other XC functionals, even the sX-LDA hybrid functional. We report also the optical properties within mBJ potential, which show a nice agreement with the experimental measurements in addition to other theoretical results. © 2013 IOP Publishing Ltd.

  19. CO{sub 2} laser-based dispersion interferometer utilizing orientation-patterned gallium arsenide for plasma density measurements

    Energy Technology Data Exchange (ETDEWEB)

    Bamford, D. J.; Cummings, E. A.; Panasenko, D. [Physical Sciences Inc., 6652 Owens Drive, Pleasanton, California 94588 (United States); Fenner, D. B.; Hensley, J. M. [Physical Sciences Inc., 20 New England Business Center, Andover, Massachusetts 01810 (United States); Boivin, R. L.; Carlstrom, T. N.; Van Zeeland, M. A. [General Atomics, P.O. Box 85608, San Diego, California 92186 (United States)

    2013-09-15

    A dispersion interferometer based on the second-harmonic generation of a carbon dioxide laser in orientation-patterned gallium arsenide has been developed for measuring electron density in plasmas. The interferometer includes two nonlinear optical crystals placed on opposite sides of the plasma. This instrument has been used to measure electron line densities in a pulsed radio-frequency generated argon plasma. A simple phase-extraction technique based on combining measurements from two successive pulses of the plasma has been used. The noise-equivalent line density was measured to be 1.7 × 10{sup 17} m{sup −2} in a detection bandwidth of 950 kHz. One of the orientation-patterned crystals produced 13 mW of peak power at the second-harmonic wavelength from a carbon dioxide laser with 13 W of peak power. Two crystals arranged sequentially produced 58 mW of peak power at the second-harmonic wavelength from a carbon dioxide laser with 37 W of peak power.

  20. A final report for Gallium arsenide P-I-N detectors for high-sensitivity imaging of thermal neutrons

    CERN Document Server

    Vernon, S M

    1999-01-01

    This SBIR Phase I developed neutron detectors made FR-om gallium arsenide (GaAs) p-type/ intrinsic/n-type (P-I-N) diodes grown by metalorganic chemical vapor deposition (MOCVD) onto semi-insulating (S1) bulk GaAs wafers. A layer of isotonically enriched boron-10 evaporated onto the FR-ont surface serves to convert incoming neutrons into lithium ions and a 1.47 MeV alpha particle which creates electron-hole pairs that are detected by the GaAs diode. Various thicknesses of ''intrinsic'' (I) undoped GaAs were tested, as was use of a back-surface field (BSF) formed FR-om a layer of Al sub x Ga sub 1 sub - sub x As. Schottky-barrier diodes formed FR-om the same structures without the p+ GaAs top layer were tested as a comparison. After mesa etching and application of contacts, devices were tested in visible light before application of the boron coating. Internal quantum efficiency (IQE) of the best diode near the GaAs bandedge is over 90%. The lowest dark current measured is 1 x 10 sup - sup 1 sup 2 amps at -1 V o...

  1. The effect of hydrostatic pressure on the physical properties of magnesium arsenide in cubic and hexagonal phases

    Science.gov (United States)

    Mokhtari, Ali; Sedighi, Matin

    2010-04-01

    Full potential-linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT) was applied to study the structural and electronic properties of the magnesium arsenide in both cubic and hexagonal phases. The exchange-correlation functional was approximated as a generalized gradient functional introduced by Perdew-Burke-Ernzerhof (GGA96) and Engel-Vosko (EV-GGA). The lattice parameters, bulk modulus and its pressure derivative, cohesive energy, band structures and effective mass of electrons and holes (EME and EMH) were obtained and compared to the available experimental and theoretical results. A phase transition was predicted at pressure of about 1.63 GPa from the cubic to the hexagonal phase. The effect of hydrostatic pressure on the behavior of the electronic properties such as band gap, valence bandwidths, anti-symmetry gap (the energy gap between two parts of the valence bands), EME and EMH were investigated using both GGA96 and EV-GGA methods. High applied pressure can decrease (increase) the holes mobility of cubic (hexagonal) phase of this compound.

  2. Development of a unique laboratory standard: Indium gallium arsenide detector for the 500-1700 nm spectral region

    Science.gov (United States)

    1987-01-01

    A planar (5 mm diameter) indium gallium arsenide detector having a high (greater than 50 pct) quantum efficiency from the visible into the infrared spectrum (500 to 1700 nm) was fabricated. Quantum efficiencies as high as 37 pct at 510 nm, 58 pct at 820 nm and 62 pct at 1300 nm and 1550 nm were measured. A planar InP/InGaAs detector structure was also fabricated using vapor phase epitaxy to grow device structures with 0, 0.2, 0.4 and 0.6 micrometer thick InP caps. Quantum efficiency was studied as a function of cap thickness. Conventional detector structures were also used by completely etching off the InP cap after zinc diffusion. Calibrated quantum efficiencies were measured. Best results were obtained with devices whose caps were completely removed by etching. Certain problems still remain with these detectors including non-uniform shunt resistance, reproducibility, contact resistance and narrow band anti-reflection coatings.

  3. High-performance organic/inorganic hybrid heterojunction based on Gallium Arsenide (GaAs) substrates and a conjugated polymer

    Science.gov (United States)

    Jameel, D. A.; Felix, J. F.; Aziz, M.; Al Saqri, N.; Taylor, D.; de Azevedo, W. M.; da Silva, E. F.; Albalawi, H.; Alghamdi, H.; Al Mashary, F.; Henini, M.

    2015-12-01

    In this paper, we present an extensive study of the electrical properties of organic-inorganic hybrid heterojunctions. Polyaniline (PANI) thin films were deposited by a very simple technique on (1 0 0) and (3 1 1)B n-type Gallium Arsenide (GaAs) substrates to fabricate hybrid devices with excellent electrical properties. The hybrid devices were electrically characterized using current-voltage (I-V), capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements in the temperature range 20-440 K. The analysis of I-V characteristics based on the thermionic emission mechanism has shown a decrease of the barrier height and an increase of the ideality factor at lower temperatures for both hybrid devices. The interface states were analyzed by series resistance obtained using the C-G-V methods. The interface state density (Dit) of PANI/(1 0 0) GaAs devices is approximately one order of magnitude higher than that of PANI/(3 1 1)B GaAs devices. This behaviour is attributed to the effect of crystallographic orientation of the substrates, and was confirmed by DLTS results as well. Additionally, the devices show excellent air stability, with rectification ratio values almost unaltered after two years of storage under ambient conditions, making the polyaniline an interesting conductor polymer for future devices applications.

  4. A novel three-jet microreactor for localized metal-organic chemical vapour deposition of gallium arsenide: design and simulation

    Science.gov (United States)

    Konakov, S. A.; Krzhizhanovskaya, V. V.

    2016-08-01

    We present a novel three-jet microreactor design for localized deposition of gallium arsenide (GaAs) by low-pressure Metal-Organic Chemical Vapour Deposition (MOCVD) for semiconductor devices, microelectronics and solar cells. Our approach is advantageous compared to the standard lithography and etching technology, since it preserves the nanostructure of the deposited material, it is less time-consuming and less expensive. We designed two versions of reactor geometry with a 10-micron central microchannel for precursor supply and with two side jets of a dilutant to control the deposition area. To aid future experiments, we performed computational modeling of a simplified-geometry (twodimensional axisymmetric) microreactor, based on Navier-Stokes equations for a laminar flow of chemically reacting gas mixture of Ga(CH3)3-AsH3-H2. Simulation results show that we can achieve a high-rate deposition (over 0.3 μm/min) on a small area (less than 30 μm diameter). This technology can be used in material production for microelectronics, optoelectronics, photovoltaics, solar cells, etc.

  5. Light-trapping and recycling for extraordinary power conversion in ultra-thin gallium-arsenide solar cells.

    Science.gov (United States)

    Eyderman, Sergey; John, Sajeev

    2016-01-01

    We demonstrate nearly 30% power conversion efficiency in ultra-thin (~200 nm) gallium arsenide photonic crystal solar cells by numerical solution of the coupled electromagnetic Maxwell and semiconductor drift-diffusion equations. Our architecture enables wave-interference-induced solar light trapping in the wavelength range from 300-865 nm, leading to absorption of almost 90% of incoming sunlight. Our optimized design for 200 nm equivalent bulk thickness of GaAs, is a square-lattice, slanted conical-pore photonic crystal (lattice constant 550 nm, pore diameter 600 nm, and pore depth 290 nm), passivated with AlGaAs, deposited on a silver back-reflector, with ITO upper contact and encapsulated with SiO2. Our model includes both radiative and non-radiative recombination of photo-generated charge carriers. When all light from radiative recombination is assumed to escape the structure, a maximum achievable photocurrent density (MAPD) of 27.6 mA/cm(2) is obtained from normally incident AM 1.5 sunlight. For a surface non-radiative recombination velocity of 10(3) cm/s, this corresponds to a solar power conversion efficiency of 28.3%. When all light from radiative recombination is trapped and reabsorbed (complete photon recycling) the power conversion efficiency increases to 29%. If the surface recombination velocity is reduced to 10 cm/sec, photon recycling is much more effective and the power conversion efficiency reaches 30.6%. PMID:27334045

  6. Light-trapping and recycling for extraordinary power conversion in ultra-thin gallium-arsenide solar cells

    Science.gov (United States)

    Eyderman, Sergey; John, Sajeev

    2016-01-01

    We demonstrate nearly 30% power conversion efficiency in ultra-thin (~200 nm) gallium arsenide photonic crystal solar cells by numerical solution of the coupled electromagnetic Maxwell and semiconductor drift-diffusion equations. Our architecture enables wave-interference-induced solar light trapping in the wavelength range from 300–865 nm, leading to absorption of almost 90% of incoming sunlight. Our optimized design for 200 nm equivalent bulk thickness of GaAs, is a square-lattice, slanted conical-pore photonic crystal (lattice constant 550 nm, pore diameter 600 nm, and pore depth 290 nm), passivated with AlGaAs, deposited on a silver back-reflector, with ITO upper contact and encapsulated with SiO2. Our model includes both radiative and non-radiative recombination of photo-generated charge carriers. When all light from radiative recombination is assumed to escape the structure, a maximum achievable photocurrent density (MAPD) of 27.6 mA/cm2 is obtained from normally incident AM 1.5 sunlight. For a surface non-radiative recombination velocity of 103 cm/s, this corresponds to a solar power conversion efficiency of 28.3%. When all light from radiative recombination is trapped and reabsorbed (complete photon recycling) the power conversion efficiency increases to 29%. If the surface recombination velocity is reduced to 10 cm/sec, photon recycling is much more effective and the power conversion efficiency reaches 30.6%. PMID:27334045

  7. Light-trapping and recycling for extraordinary power conversion in ultra-thin gallium-arsenide solar cells

    Science.gov (United States)

    Eyderman, Sergey; John, Sajeev

    2016-06-01

    We demonstrate nearly 30% power conversion efficiency in ultra-thin (~200 nm) gallium arsenide photonic crystal solar cells by numerical solution of the coupled electromagnetic Maxwell and semiconductor drift-diffusion equations. Our architecture enables wave-interference-induced solar light trapping in the wavelength range from 300-865 nm, leading to absorption of almost 90% of incoming sunlight. Our optimized design for 200 nm equivalent bulk thickness of GaAs, is a square-lattice, slanted conical-pore photonic crystal (lattice constant 550 nm, pore diameter 600 nm, and pore depth 290 nm), passivated with AlGaAs, deposited on a silver back-reflector, with ITO upper contact and encapsulated with SiO2. Our model includes both radiative and non-radiative recombination of photo-generated charge carriers. When all light from radiative recombination is assumed to escape the structure, a maximum achievable photocurrent density (MAPD) of 27.6 mA/cm2 is obtained from normally incident AM 1.5 sunlight. For a surface non-radiative recombination velocity of 103 cm/s, this corresponds to a solar power conversion efficiency of 28.3%. When all light from radiative recombination is trapped and reabsorbed (complete photon recycling) the power conversion efficiency increases to 29%. If the surface recombination velocity is reduced to 10 cm/sec, photon recycling is much more effective and the power conversion efficiency reaches 30.6%.

  8. A final report for: Gallium arsenide P-I-N detectors for high-sensitivity imaging of thermal neutrons

    International Nuclear Information System (INIS)

    This SBIR Phase I developed neutron detectors made FR-om gallium arsenide (GaAs) p-type/ intrinsic/n-type (P-I-N) diodes grown by metalorganic chemical vapor deposition (MOCVD) onto semi-insulating (S1) bulk GaAs wafers. A layer of isotonically enriched boron-10 evaporated onto the FR-ont surface serves to convert incoming neutrons into lithium ions and a 1.47 MeV alpha particle which creates electron-hole pairs that are detected by the GaAs diode. Various thicknesses of ''intrinsic'' (I) undoped GaAs were tested, as was use of a back-surface field (BSF) formed FR-om a layer of AlxGa1-xAs. Schottky-barrier diodes formed FR-om the same structures without the p+ GaAs top layer were tested as a comparison. After mesa etching and application of contacts, devices were tested in visible light before application of the boron coating. Internal quantum efficiency (IQE) of the best diode near the GaAs bandedge is over 90%. The lowest dark current measured is 1 x 10-12 amps at -1 V on a 3mm x 3mm diode, or a density of 1.1 x 10-11 amps cm-2, with many of the diode structures tested having nearly similar results. The PIN diodes were significantly better than the Schottky barrier device, which had six orders of magnitude higher dark current. Diodes were characterized in terms of their current-mode response to 5.5 MeV alpha particles FR-om 241-Americium. These radiation-induced currents were as high as 9.78 x 10-7 A cm-1 on a PIN device with an AlxGa1-xAs BSF. Simple PIN diodes had currents as high as 2.44 x 10-7 A cm-2, with thicker undoped layers showing better sensitivity. Boron coatings were applied, and response to neutrons tested at University of Michigan by Dr. Doug McGregor. Devices with PIN and Schottky barrier designs showed neutron detection efficiencies as high as 2% on 5 (micro)m thick devices, with no need for external bias voltages. PIN diodes showed higher breakdown voltages and lower noise characteristics than did the Schottky barrier design. Uniformity of

  9. Ternary arsenides based on platinum–indium and palladium–indium fragments of the Cu{sub 3}Au-type: Crystal structures and chemical bonding

    Energy Technology Data Exchange (ETDEWEB)

    Zakharova, Elena Yu.; Andreeva, Natalia A.; Kazakov, Sergey M. [Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1-3, GSP-1, 119991 Moscow (Russian Federation); Kuznetsov, Alexey N., E-mail: alexei@inorg.chem.msu.ru [Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1-3, GSP-1, 119991 Moscow (Russian Federation); N.S. Kurnakov Institute of General and Inorganic Chemistry of Russian Academy of Sciences, Leninskii pr. 31, 119991 Moscow (Russian Federation)

    2015-02-05

    Highlights: • Three metal-rich platinum–indium and palladium–indium arsenides were synthesized. • Their crystal structures were determined from powder XRD. • Electronic structures and bonding were studied using DFT/FP-LAPW calculations. • Multi-centered Pt–In or Pd–In bonding was revealed using ELF and ELI-D analysis. • Extra pairwise Pt–Pt interactions are observed only for Pt-based compounds. - Abstract: Three metal-rich palladium–indium and platinum–indium arsenides, Pd{sub 5}InAs, Pt{sub 5}InAs, and Pt{sub 8}In{sub 2}As, were synthesized using a high-temperature ampoule technique. Their crystal structures were determined from Rietveld analysis of powder diffraction data. All the compounds crystallize in tetragonal system with P4/mmm space group (Pd{sub 5}InAs: a = 3.9874(1) Å, c = 6.9848(2) Å, Z = 1, R{sub p} = 0.053; R{sub b} = 0.013; Pt{sub 5}InAs: a = 3.9981(2) Å, c = 7.0597(4) Å, Z = 1, R{sub p} = 0.058, R{sub b} = 0.016; Pt{sub 8}In{sub 2}As: a = 3.9872(3) Å, c = 11.1129(7) Å, Z = 1, R{sub p} = 0.047; R{sub b} = 0.014). The first two compounds belong to the Pd{sub 5}TlAs structure type, while the third one is isotypic with the recently discovered Pd{sub 8}In{sub 2}Se. Main structural units in all arsenides are indium-centered [TM{sub 12}In] cuboctahedra (TM = Pd, Pt) of the Cu{sub 3}Au type, single- and double-stacked along the c axis in TM{sub 5}InAs and Pt{sub 8}In{sub 2}As, respectively, alternating with [TM{sub 8}As] rectangular prisms. DFT electronic structure calculations predict all three compounds to be 3D metallic conductors and Pauli-like paramagnets. According to the bonding analysis based on the electron localization function and electron localizability indicator topologies, all compounds feature multi-centered interactions between transition metal and indium in their heterometallic fragments. Additionally, pairwise interactions between platinum atoms are also observed, indicating a somewhat more localized bonding

  10. Study of current instabilities in high resistivity gallium arsenide; Etude des instabilites de courant dans l'arseniure de gallium de haute resistivite

    Energy Technology Data Exchange (ETDEWEB)

    Barraud, A. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1968-07-01

    We have shown the existence and made a study of the current oscillations produced in high-resistivity gallium arsenide by a strong electric field. The oscillations are associated with the slow travelling of a region of high electrical field across the whole sample. An experimental study of the properties of these instabilities has made it possible for us to distinguish this phenomenon from the Gunn effect, from acoustic-electric effects and from contact effects. In order to account for this type of instability, a differential trapping mechanism involving repulsive impurities is proposed; this mechanism can reduce the concentration of charge carriers in the conduction band at strong electrical fields and can lead to the production of a high-field domain. By developing this model qualitatively we have been able to account for all the properties of high-resistance gallium arsenide crystals subjected to a strong electrical field: increase of the Hall constant, existence of a voltage threshold for these oscillations, production of domains of high field, low rate of propagation of these domains, and finally the possibility of inverting the direction of the propagation of the domain without destroying the latter. A quantitative development of the model makes it possible to calculate the various characteristic parameters of these instabilities. Comparison with experiment shows that there is a good agreement, the small deviations coming especially from the lack of knowledge concerning transport properties in gallium arsenide subjected to high fields. From a study of this model, it appears that the instability phenomenon can occur over a wide range of repulsive centre concentrations, and also for a large range of resistivities. This is the reason why it appears systematically in gallium arsenide of medium and high resistivity. (authors) [French] Nous avons mis en evidence et etudie des oscillations de courant qui se produisent a champ electrique eleve dans l

  11. Superconductivity in Ti-doped iron-arsenide compound Sr4Cr0.8Ti1.2O6Fe2As2

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Superconductivity was achieved in Ti-doped iron-arsenide compound Sr4Cr0.8Ti1.2O6Fe2As2 (abbreviated as Cr-FeAs-42622). The X-ray diffraction measurement shows that this material has a layered structure with the space group of P4/nmm,and with the lattice constants a = b = 3.9003  and c = 15.8376 . Clear diamagnetic signals in ac susceptibility data and zero-resistance in resistivity data were detected at about 6 K,confirming the occurrence of bulk superconductivity. Meanwhile we observed a supercon-ducting transition in the resistive data with the onset transition temperature at 29.2 K,which may be induced by the nonuniform distribution of the Cr/Ti content in the FeAs-42622 phase.

  12. One watt gallium arsenide class-E power amplifier with a thin-film bulk acoustic resonator filter embedded in the output network

    Directory of Open Access Journals (Sweden)

    Kyle Holzer

    2015-05-01

    Full Text Available Integration of a class-E power amplifier (PA and a thin-film bulk acoustic wave resonator (FBAR filter is shown to provide high power added efficiency in addition to superior out-of-band spectrum suppression. A discrete gallium arsenide pseudomorphic high-electron-mobility transistor is implemented to operate as a class-E amplifier from 2496 to 2690 MHz. The ACPF7041 compact bandpass FBAR filter is incorporated to replace the resonant LC tank in a traditional class-E PA. To reduce drain voltage stress, the supply choke is replaced by a finite inductance. The fabricated PA provides up to 1 W of output power with a peak power added efficiency (PAE of 58%. The improved out-of-band spectrum filtering is compared to a traditional class-E with discrete LC resonant filtering. Such PAs can be combined with linearisation techniques to reduce out-of-band emissions.

  13. Indium Arsenide Nanowires

    DEFF Research Database (Denmark)

    Madsen, Morten Hannibal

    This thesis is about growth of Au-assisted and self-assisted InAs nanowires (NWs). The wires are synthesized using a solid source molecular beam epitaxy (MBE) system and characterized with several techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ...

  14. Gallium arsenide pixel detectors

    Energy Technology Data Exchange (ETDEWEB)

    Bates, R.; DaVia, C.; O`Shea, V.; Raine, C.; Smith, K. [Glasgow Univ. (United Kingdom). Dept. of Physics and Astronomy; Campbell, M.; Cantatore, E.; Heijne, E.M.; Middelkamp, P.; Ropotar, I.; Scharfetter, L.; Snoeys, W. [CERN, ECP Div., CH-1211 Geneva 23 (Switzerland); D`Auria, S.; Papa, C. del [Department of Physics, University of Udine and INFN Trieste, Via delle Scienze 208, I-33100 Udine (Italy); RD8 Collaboration

    1998-06-01

    GaAs detectors can be fabricated with bidimensional single-sided electrode segmentation. They have been successfully bonded using flip-chip technology to the Omega-3 silicon read-out chip. We present here the design features of the GaAs pixel detectors and results from a test performed at the CERN SpS with a 120 GeV {pi}{sup -} beam. The detection efficiency was 99.2% with a nominal threshold of 5000 e{sup -}. (orig.) 10 refs.

  15. Atmospheric pressure chemical vapour deposition of vanadium arsenide thin films via the reaction of VCl4 or VOCl3 with tBuAsH2

    International Nuclear Information System (INIS)

    Thin films of vanadium arsenide were deposited via the dual-source atmospheric pressure chemical vapour deposition reactions of VCl4 or VOCl3 with tBuAsH2. Using the vanadium precursor VCl4, films were deposited at substrate temperatures of 550–600 °C, which were black-gold in appearance and were found to be metal-rich with high levels of chlorine incorporation. The use of VOCl3 as the vanadium source resulted in films being deposited between 450 and 600 °C and, unlike when using VCl4, were silver in appearance. The films deposited using VOCl3 demonstrated vanadium to arsenic ratios close to 1:1, and negligible chlorine incorporation. Films deposited using either vanadium precursor were identified as VAs using powder X-ray diffraction and possessed borderline metallic/semiconductor resistivities. - Highlights: • Formation of VAs films via atmospheric pressure chemical vapour deposition. • Films formed using VCl4 or VOCl3 and tBuAsH2. • Powder X-ray diffraction showed that crystalline VAs films were deposited. • Films from VOCl3 had a V:As ratio close to 1 with negligible Cl incorporation. • Films were silver and possessed borderline metallic/semiconductor resistivities

  16. Note: All solid-state high repetitive sub-nanosecond risetime pulse generator based on bulk gallium arsenide avalanche semiconductor switches

    Science.gov (United States)

    Hu, Long; Su, Jiancang; Ding, Zhenjie; Hao, Qingsong; Fan, Yajun; Liu, Chunliang

    2016-08-01

    An all solid-state high repetitive sub-nanosecond risetime pulse generator featuring low-energy-triggered bulk gallium arsenide (GaAs) avalanche semiconductor switches and a step-type transmission line is presented. The step-type transmission line with two stages is charged to a potential of 5.0 kV also biasing at the switches. The bulk GaAs avalanche semiconductor switch closes within sub-nanosecond range when illuminated with approximately 87 nJ of laser energy at 905 nm in a single pulse. An asymmetric dipolar pulse with peak-to-peak amplitude of 9.6 kV and risetime of 0.65 ns is produced on a resistive load of 50 Ω. A technique that allows for repetition-rate multiplication of pulse trains experimentally demonstrated that the parallel-connected bulk GaAs avalanche semiconductor switches are triggered in sequence. The highest repetition rate is decided by recovery time of the bulk GaAs avalanche semiconductor switch, and the operating result of 100 kHz of the generator is discussed.

  17. Generation System of Concentrator Photovoltaic Based on Gallium Arsenide Cells%基于砷化镓电池的聚光光伏发电系统

    Institute of Scientific and Technical Information of China (English)

    宁铎; 王辉辉; 黄建兵; 李明勇

    2011-01-01

    Solar photovoltaic power generation system for the problem of low utilization, a generation system of concentrator photovoltaic (CPV) based on gallium arsenide (GaAs) cells can be designed. The system consists of concentrating power modules, solar tracking module, inverter module. Fresnel lens concentrator power generation module 400 times by concentrating light in lcm2 GaAs after the battery,the realization of power function; sun-tracking modules and optical sensors from the head to ensure that the basic vertical sunlight through the Fresnel lens; GaAs inverter module converts DC battery AC issued. After testing, the system reached 20. 2% conversion efficiency of solar, inverter part of the realization of the exchange function of the DC variable.%针对光伏发电系统中太阳能利用率低的问题,设计了一种基于砷化镓(GaAs)电池的聚光光伏(CPV)发电系统;该系统由聚光发电模块、太阳跟踪模块和逆变模块组成;聚光发电模块采用菲涅尔透镜400倍聚光以后照射在1Cmz的砷化镓电池上,实现发电功能;太阳跟踪模块由云台和光电传感器组成,保证太阳光基本垂直通过菲涅尔透镜,逆变模块将砷化镓电池发出的直流电转换成交流电;经过测试.该系统太阳能转换效率达到20.2%,逆变部分实现了直流变交流功能.

  18. Superconducting properties of iron–platinum–arsenides Ca{sub 10}(Pt{sub n}As{sub 8})(Fe{sub 2−x}Pt{sub x}As{sub 2}){sub 5} (n = 3, 4)

    Energy Technology Data Exchange (ETDEWEB)

    Tamegai, T., E-mail: tamegai@ap.t.u-tokyo.ac.jp [Department of Applied Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Ding, Q.P.; Taen, T.; Ohtake, F.; Inoue, H.; Tsuchiya, Y.; Mohan, S.; Sun, Y.; Nakajima, Y.; Pyon, S. [Department of Applied Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Kitamura, H. [Radiation Measurement Research Section, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555 (Japan)

    2013-11-15

    Highlights: •Iron–platinum arsenides Ca{sub 10}(Pt{sub n}As{sub 8})(Fe{sub 2−x}Pt{sub x}As{sub 2}){sub 5} (n = 3, 4) have been grown and characterized. •Due to modest electromagnetic anisotropy, resistive transition shows broadening. •Magneto-optical imaging confirm homogeneous superconducting states. •Proton irradiation into n = 3 compound leads to T{sub c} suppression by ∼2 K and J{sub c} enhancement by a factor of three. -- Abstract: High-quality single crystals of iron–platinum arsenides Ca{sub 10}(Pt{sub n}As{sub 8})(Fe{sub 2−x}Pt{sub x}As{sub 2}){sub 5} (n = 3, 4) have been grown and their superconducting properties are characterized. The n = 4 and n = 3 compounds have T{sub c}’s ∼ 30 K and 13 K, respectively. Reflecting a modest anisotropy of the system, resistive transition for H//c-axis shows modest broadening in both systems. Magneto-optical imaging shows that superconductivity in both compounds is rather homogeneous, with the critical current density, J{sub c}, ∼1 × 10{sup 5} A/cm{sup 2} at 5 K under self-field. Proton irradiation up to 4 × 10{sup 16} cm{sup −2} into n = 3 compound is found to have T{sub c} suppression by ∼2 K and J{sub c} enhancement by a factor of three at low temperatures.

  19. Growing Gallium Arsenide On Silicon

    Science.gov (United States)

    Radhakrishnan, Gouri

    1989-01-01

    Epitaxial layers of high quality formed on crystal plane. Present work reports successful growth of 1- and 2-micrometer thick layers of n-type, 7-ohms per cm, 2-inch diameter, Si substrate. Growth conducted in Riber-2300(R) MBE system. Both doped and undoped layers of GaAs grown. Chamber equipped with electron gun and camera for in-situ reflection high-energy-electron diffraction measurements. RHEED patterns of surface monitored continuously during slow growth stage.

  20. Barium iron arsenide, barium cobalt arsenide, barium nickel arsenide single crystals and superconductivity upon cobalt doping

    Energy Technology Data Exchange (ETDEWEB)

    Ronning, Filip [Los Alamos National Laboratory; Sefat, A S [ORNL; Mcguire, M M [ORNL; Sales, B [ORNL; Jin, R [ORNL; Mandrus, D [ORNL

    2009-01-01

    The crystal structure and physical properties of BaFe{sub 2}As{sub 2}, BaCo{sub 2}As{sub 2}, and BaNi{sub 2}As{sub 2} single crystals are surveyed. BaFe{sub 2}As{sub 2} gives a magnetic and structural transition at T{sub N} = 132(1) K, BaCo{sub 2}As{sub 2} is a paramagnetic metal, while BaNi{sub 2}As{sub 2} has a structural phase transition at T{sub 0} = 131 K, followed by superconductivity below {Tc} = 0.69 K. The bulk superconductivity in Co-doped BaFe{sub 2}As{sub 2} below {Tc} = 22 K is demonstrated by resistivity, magnetic susceptibility, and specific heat data. In contrast to the cuprates, the Fe-based system appears to tolerate considerable disorder in the transition metal layers. First principles calculations for BaFe{sub 1.84}Co{sub 0.16}As{sub 2} inter-band scattering due to Co is weak.

  1. Non-stoichiometric nickel arsenides in nature: The structure of orcelite, Ni{sub 5−x}As{sub 2} (x = 0.25), from the Bon Accord oxide body, South Africa

    Energy Technology Data Exchange (ETDEWEB)

    Bindi, Luca, E-mail: luca.bindi@unifi.it [Dipartimento di Scienze della Terra, Università degli Studi di Firenze, via La Pira 4, I-50121 Firenze (Italy); Tredoux, Marian [Department of Geology, University of the Free State, Bloemfontein 9300 (South Africa); Zaccarini, Federica [Department of Applied Geosciences and Geophysics, University of Leoben, Peter Tunner str. 5, A-8700 Leoben (Austria); Miller, Duncan E. [Department of Geology, University of the Free State, Bloemfontein 9300 (South Africa); Garuti, Giorgio [Department of Applied Geosciences and Geophysics, University of Leoben, Peter Tunner str. 5, A-8700 Leoben (Austria)

    2014-07-15

    Highlights: • The structure of natural orcelite has been solved for the first time. • The non-stoichiometry for orcelite previously reported was confirmed. • Non-stoichiometry could cause disorder phenomena during the crystal growth. - Abstract: The crystal structure of the mineral orcelite, a rare nickel arsenide reported in the literature with the formula Ni{sub 5−x}As{sub 2} (with x = 0.23), was refined using intensity data collected from a crystal from the Bon Accord body, South Africa. This study revealed that the structure is hexagonal, space group P6{sub 3}mc, with a = 6.7922(2), c = 12.4975(5) Å, and V = 499.31(3) Å{sup 3}. The refinement of an anisotropic model led to an R index of 0.028 for 412 independent reflections. The orcelite structure can be described as a distorted variant of the Pd{sub 5}Sb{sub 2} structure. The smaller As atoms are in the centres of distorted tetragonal antiprisms, formed by only Ni atoms. The coordination sphere is completed with two additional Ni atoms opposite to the rectangular faces. Electron microprobe data carried out on the same crystal used for the structural study point to the following formula [on the basis of Σ(As + Fe + Sb)=2]: Ni{sub 4.75}(As{sub 1.93}Fe{sub 0.05}Sb{sub 0.02}). According to the high-quality structure refinement, the minor elements were found to replace As in the structure. An atomic position for Ni was found to be partially occupied (75%), thus confirming the non-stoichiometry for the mineral orcelite previously reported in literature. Such a deviation from the stoichiometry could represent the driving force favouring disorder phenomena during the growth of the mineral.

  2. Efficient injection of spin-polarized electrons from manganese arsenide contacts into aluminum gallium arsenide/gallium arsenide spin LEDs

    Science.gov (United States)

    Schweidenback, Lars

    In this thesis we describe two spectroscopic projects project on semiconductor heterostructures, as well as putting together and testing a micro-photoluminescence/7 tesla magnet system for the study of micron size two-dimensional crystals. Below we discuss the three parts in more detail. i) MnAs-based spin light emitting diodes. We have studied the injection of spin-polarized electrons from a ferromagnetic MnAs contact into an AlGaAs(n)/GaAs(i)/AlGaAs(p) n-i-p light emitting diode. We have recorder the emitted electroluminescence as function of magnetic field applied at right angles to the device plane in the 7-300 K temperature range. It was found that at 7 Kelvin the emitted light is circularly polarized with a polarization that is proportional to the MnAs contact magnetization with a saturation value of 26% for B > 1.25 tesla. The polarization persists up to room temperature with a saturation value of 6%. ii) Optical Aharonov-Bohm effect in InGaAs quantum wells. The excitonic photoluminescence intensity from InGaAs quantum wells as function of magnetic field exhibits two local maxima superimposed on a decreasing background. The maxima are attributed to the optical Aharonov-Bohm effect of electrons orbiting around a hole localized at the center of an Indium rich InGaAs islands detected by cross sectional scanning tunneling microscopy. Analysis of the position of the maxima yields a value of the electron orbit radius. iii) Micro-Photoluminescence. We have put together a micro-photoluminescence /7 tesla system for the study of two dimensional crystals. The samples are placed inside a continuous flow cryostat whose tail is positioned in the bore of the 7 tesla magnet. A microscope objective is used to focus the exciting laser light and collect the emitted photoluminescence. The system was tested by recording the photoluminescence spectra of WS2 and WSe 2 monolayers at T = 77 K.

  3. Nonlocal ordinary magnetoresistance in indium arsenide

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Pan [School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021 (China); Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Yuan, Zhonghui; Wu, Hao; Ali, S.S. [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Wan, Caihua, E-mail: wancaihua@iphy.ac.cn [Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Ban, Shiliang, E-mail: slban@imu.edu.cn [School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021 (China)

    2015-07-01

    Deflection of carriers by Lorentz force results in an ordinary magnetoresistance (OMR) of (μB){sup 2} at low field. Here we demonstrate that the OMR in high mobility semiconductor InAs could be enhanced by measurement geometry where two probes of voltmeter were both placed on one outer side of two probes of current source. The nonlocal OMR was 3.6 times as large as the local one, reaching 1.8×10{sup 4}% at 5 T. The slope of the linear field dependence of the nonlocal OMR was improved from 12.6 T{sup −1} to 45.3 T{sup −1}. The improvement was ascribed to polarity-conserved charges accumulating on boundaries in nonlocal region due to Hall effect. This InAs device with nonlocal geometry could be competitive in B-sensors due to its high OMR ratio, linear field dependence and simple structure. - Highlights: • Ordinary magnetoresistance could be enhanced by nonlocal geometry by 3.6 times. • Linear field dependence at high field could be realized in nonlocal geometry. • Nonlocal MR was realized by polarity-conserved accumulating charges on boundaries • Nonlocal MR in InAs reached 1.8×10{sup 4}% at 5 T. • Nonlocal MR devices could be used in high-field sensing applications.

  4. Nonlocal ordinary magnetoresistance in indium arsenide

    International Nuclear Information System (INIS)

    Deflection of carriers by Lorentz force results in an ordinary magnetoresistance (OMR) of (μB)2 at low field. Here we demonstrate that the OMR in high mobility semiconductor InAs could be enhanced by measurement geometry where two probes of voltmeter were both placed on one outer side of two probes of current source. The nonlocal OMR was 3.6 times as large as the local one, reaching 1.8×104% at 5 T. The slope of the linear field dependence of the nonlocal OMR was improved from 12.6 T−1 to 45.3 T−1. The improvement was ascribed to polarity-conserved charges accumulating on boundaries in nonlocal region due to Hall effect. This InAs device with nonlocal geometry could be competitive in B-sensors due to its high OMR ratio, linear field dependence and simple structure. - Highlights: • Ordinary magnetoresistance could be enhanced by nonlocal geometry by 3.6 times. • Linear field dependence at high field could be realized in nonlocal geometry. • Nonlocal MR was realized by polarity-conserved accumulating charges on boundaries • Nonlocal MR in InAs reached 1.8×104% at 5 T. • Nonlocal MR devices could be used in high-field sensing applications

  5. Phonon heat transport in gallium arsenide

    Indian Academy of Sciences (India)

    Richa Saini; Vinod Ashokan; B D Indu; R Kumar

    2012-03-01

    The lifetimes of quantum excitations are directly related to the electron and phonon energy linewidths of a particular scattering event. Using the versatile double time thermodynamic Green’s function approach based on many-body theory, an ab-initio formulation of relaxation times of various contributing processes has been investigated with newer understanding in terms of the linewidths of electrons and phonons. The energy linewidth is found to be an extremely sensitive quantity in the transport phenomena of crystalline solids as a collection of large number of scattering processes, namely, boundary scattering, impurity scattering, multiphonon scattering, interference scattering, electron–phonon processes and resonance scattering. The lattice thermal conductivities of three samples of GaAs have been analysed on the basis of modified Callaway model and a fairly good agreement between theory and experimental observations has been reported.

  6. Optical Spectroscopy of Indium Gallium Arsenide/gallium Arsenide Quantum Wells

    Science.gov (United States)

    Adams, Stephen J. A.

    1992-01-01

    Available from UMI in association with The British Library. In_{rm x}Ga _{rm 1-x}As/GaAs quantum wells have been studied using optical and magneto -optical techniques. Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy have been used to determine the valence band offset in these heterostructures which was found to vary between 0.4 for wells with indium concentration x = 0.08 to 0.2 for wells with x = 0.21. An interband magneto-luminescence oscillation (IMLO) technique has been applied to the study of undoped 'multi-single' quantum well samples and the theoretically predicted peaked nature of the exciton binding energy as a function of well width has been observed for the first time in any material system. The conduction band effective mass was also determined in the same samples using Optically Detected Cyclotron Resonance (ODCR) and found to be constant over the range of well widths studied at a value close to that of the bulk, with a suitable correction for strain effects. This result was then combined with the IMLO data, fitted to the theory of Akimoto and Hasegawa, to deduce the hole mass as a function of well width, which was found to increase significantly in narrower wells. PL and PLE data was also obtained from modulation doped quantum wells. The PL involving transitions from highly populated subbands was found to be much broader than the PLE data from unpopulated subbands, where the transitions were strongly excitonic. Furthermore the PL linewidth in n-type samples was somewhat greater than that in p-type samples because of the difference in particle effective mass. Comparison of the Fermi energy deduced from PL in n-type samples with Hall and Shubnikov-de Haas measurements suggested an enhancement in the density-of -states over the value in undoped wells. Interesting effects were also observed in the quantum well luminescence arising from an interaction with GaAs deep levels in the barrier layers. A novel method was used to determine the effective mass renormalisation due to the presence of a two-dimensional electron gas in modulation-doped quantum wells. The technique took advantage of the presence, in the samples studied, of parity-allowed transitions between the two lowest conduction subbands and the lowest valence subband. Landau splittings were observed in the n_{rm c } = 1 to n_{rm v } = 1 recombination in PL and in the n _{rm c} = 2 to n _{rm v} = 1 recombination in PLE, and a comparison of the reduced masses derived from the two sets of Landau fans allowed the effective mass enhancement to be determined. Enhancements of the order of 20%, independent of magnetic field, have been observed in samples with well sheet carrier density of approximately 10^{12}cm ^{-2}.

  7. Galvanomagnetic Properties and Magnetic Domain Structure of Epitaxial Manganese Arsenide Films on Gallium ARSENIDE(001)

    Science.gov (United States)

    Park, Moon Chan

    We have studied galvanomagnetic properties and magnetic domain structure of epitaxial ferromagnetic MnAs thin films on GaAs(001) substrates by molecular beam epitaxy in the thickness range 20-200nm. Using data reported here on ordinary and extraordinary Hall effect to determine the field required for perpendicular saturation and using saturation magnetizations reported elsewhere, we determined the shape anisotropy constant in the basal plane of the hexagonal structure to be 3.7(0.6)times10 ^5 erg/cm^3 and the surface anisotropy constant to be -1.3(0.4) erg/cm^2. The negative sign indicates thin enough films will be perpendicularly magnetized. By using magnetic force microscopy on a 100 nm type-B MnAs film we found stripe domains with 180^circ Bloch walls parallel to the easy direction, thereby avoiding the hard c-axis, which in type-B is tilted up 39^circ. out of the film plane. The widths of the domains and the walls are 4.0(0.3) μm and 95(6) nm, respectively. Similar MFM results were obtained for a 100 nm type-A MnAs thin film having hard c-axis in plane, with an average domain width of 11.7(1.2) mum. This domain width agrees with a calculated value using the effective anisotropy constant data. Magnetoresistance versus field shows a linear past beyond the coercive field H _{c} (VSM value +/-324Oe) due to s-d electron scattering as explained by N. F. Mott. Peaks occur at the transition region observed in the vicinity of H_ {c} in the VSM hysteresis loop and are centered at about H_{c}. The peaks are attributed to electron scattering from the domain walls. The electrical resistance showed a rapid increase with temperature beginning about 5 degrees below the Curie temperature (40^circ C) caused by the change in crystal structure from hexagonal to orthorhombic. The resistivities are, respectively, 300(24) and 375(30) muOmega -cm. Comparison with bulk values indicates the large lower temperature value is partly due to the presence of some orthorhombic phase observed in x-ray studies.

  8. Clinical evaluation of dentin hypersensitivity treatment with the low intensity Gallium-Aluminum-Arsenide laser - AsGaAl Avaliação clínica do tratamento da hiperestesia dentinária com laser de baixa potência de Arseniato de Gálio-Alumínio - AsGaAl

    Directory of Open Access Journals (Sweden)

    Luciana Chucre Gentile

    2004-12-01

    Full Text Available The dentin hypersensitivity is a painful condition rather prevalent in the general population. There are several ways of treatment for such condition, including the low intensity lasers. The proposal of this study was to verify the effectiveness of the Gallium-Aluminum-Arsenide diode laser in the treatment of this painful condition, using a placebo as control. MATERIALS AND METHODS: Thirty-two patients were selected, 22 females and 10 males, with ages ranging from 20 to 52 years old. The 32 patients were randomly distributed into two groups, treated and control; the sample consisted of 68 teeth, 35 in the treated group and 33 in the control group. The treated group was exposed to six laser applications with intervals from 48 to 72 hours, and the control group received, as placebo, applications of a curing light. RESULTS: A significant reduction was observed in the pain condition between the initial phase and after six laser applications; however, such reduction could also be observed for the control group exposed to the placebo. CONCLUSION: Therapy with the low intensity Gallium-Aluminum-Arsenide laser - AsGaAl induces a statistically significant reduction in the painful condition after each application and between the beginning and end of treatment, although there was no statistically significant difference between the treated group (laser and the control group (placebo at the end of treatment and after the mediate evaluation results (after 6 weeks, this way impairing the real measurement of laser effectiveness and placebo effect.A hiperestesia dentinária trata-se de uma condição dolorosa bastante prevalente nas populações mundiais. Várias são as modalidades de tratamento para tal condição, entre elas, os lasers de baixa potência. A proposta deste estudo foi a de verificar a efetividade do laser de diodo de Arseniato de Gálio-Alumínio no tratamento desta condição dolorosa, utilizando-se um placebo como controle. MATERIAIS E M

  9. Investigation of spin transport and accumulation in aluminum gallium arsenide

    Science.gov (United States)

    Misuraca, Jennifer

    This dissertation describes spin injection, transport, and detection experiments from Fe electrodes into a bulk AlGaAs channel. This semiconducting alloy is one of a class of persistent photoconductors, chosen as the spin transport medium because its carrier density can be tuned in a controlled manner via photoexcitation through the metal to insulator transition (MIT) in situ. This allows one to determine the dependence of spin lifetime on a variety of external parameters including carrier density, all on one sample. This research represents the first electrical spin-dependent measurements in this material and describes the dependence of the Hanle signal size and spin lifetime on bias, temperature, and carrier density. The photoexcitation needed to change the carrier density in this material comes from an infrared light-emitting diode (IR LED). The first step of this project was to characterize the new, highly Si doped Al0.3Ga 0.7As heterostructures, in order to determine how the illumination of the sample will affect the parameters of the material. To complete this study, Hall crosses were fabricated from the AlGaAs material and the transport properties were measured between 350 mK and 165 K. The resistivity, carrier density, and mobility were determined as a function of temperature for a variety of different illumination times. From this data, the MIT, scattering mechanisms, and the shape of the band tail of the density of states (DOS) were investigated. In fact, this is the first work to electrically probe the DOS in AlGaAs. Once the materials were characterized, they were used to fabricate lateral spin transport devices. Spin transport and accumulation were studied in detail via Hanle effect measurements, which measure the dephasing of electron spins in a perpendicular magnetic field. From these measurements, the spin lifetime of the material can be calculated, and is in the nanosecond range for all measured carrier densities. The spin lifetimes are measured using three distinct measurement configurations which all give consistent results. The dependence of spin lifetime and Hanle signal size are reported as a function of bias, temperature, and carrier density. This is the first spin transport experiment using a persistently photoconductive material as the spin transport channel in order to change the carrier density of the material in situ. The research in this dissertation successfully provides a framework for the continuation of spin injection and detection studies in this and other alloy semiconductors, and provides insight into how the spin lifetime depends on the doping levels in semiconductors.

  10. Ion-beam induced isolation of gallium arsenide layers

    Science.gov (United States)

    Sengupta, D.; Zemanski, J. M.; Williams, J. S.; Johnson, S. T.; Pogany, A. P.

    1989-07-01

    Epitaxial (n +-n) layers on semi-insulating GaAs samples were implanted with 60 keV He + ions at elevated temperatures. Samples were analysed to provide sheet resistivity, Hall mobility and carrier depth profiles using electrical measurement techniques and damage distributions using TEM and Rutherford backscattering and channeling. All of the data were correlated to identify the optimum conditions to achieve electrical isolation. Elevated temperature He + implants have been found to create uniform, single step isolation of GaAs layers. Isolation of the GaAs layers can be enhanced and stabilised further by a suitable post-implantation annealing process.

  11. Spontaneous low frequency oscillation studies in gallium arsenide fast photoconductors

    CERN Document Server

    Foulon, F; Brullot, B; Petit, P; Bergonzo, P; Rubbelynck, C

    1999-01-01

    We have investigated the influence of spontaneous low frequency oscillations (LFO, f approx 0.01 Hz) occurring at high electric field (>1 kV/cm) in resistive photoconductors (PCD) made from semi-insulating GaAs on the response of the PCDs under pulsed gamma-ray irradiation (E approx 1.2 MeV, tau sub F sub W sub H sub M =30 ns). The PCDs were fabricated using GaAs from five commercially available sources. The PCDs were irradiated with fission neutrons in order to reduce their response time down to less than 100 ps. The amplitude of the LFOs was found to be related to the carrier lifetime, and thus defect concentration in the GaAs material. It was larger for material exhibiting high carrier lifetime. Increasing the localised defect concentration, such as EL2 type defect, through GaAs irradiation with fission neutrons was found to decrease the amplitude of the LFOs. PCDs irradiated at high neutron doses (>1x10 sup 1 sup 5 neutrons/cm sup 2) showed no LFOs. It is suggested that interactions between the propagatin...

  12. Spontaneous low frequency oscillation studies in gallium arsenide fast photoconductors

    Energy Technology Data Exchange (ETDEWEB)

    Foulon, F.; Flicstein, J.; Brullot, B.; Petit, P.; Bergonzo, P.; Rubbelynck, C

    1999-07-01

    We have investigated the influence of spontaneous low frequency oscillations (LFO, f{approx}0.01 Hz) occurring at high electric field (>1 kV/cm) in resistive photoconductors (PCD) made from semi-insulating GaAs on the response of the PCDs under pulsed gamma-ray irradiation (E{approx}1.2 MeV, {tau}{sub FWHM}=30 ns). The PCDs were fabricated using GaAs from five commercially available sources. The PCDs were irradiated with fission neutrons in order to reduce their response time down to less than 100 ps. The amplitude of the LFOs was found to be related to the carrier lifetime, and thus defect concentration in the GaAs material. It was larger for material exhibiting high carrier lifetime. Increasing the localised defect concentration, such as EL2 type defect, through GaAs irradiation with fission neutrons was found to decrease the amplitude of the LFOs. PCDs irradiated at high neutron doses (>1x10{sup 15} neutrons/cm{sup 2}) showed no LFOs. It is suggested that interactions between the propagating domains and the highly defective GaAs bulk control the LFO characteristics. Gamma-ray sensitivity, in transient mode, versus bias voltage of PCDs was also found to be correlated to LFOs, showing that high-field behavior of GaAs can be used to predict the optimum operating bias of the PCDs.

  13. Spontaneous low frequency oscillation studies in gallium arsenide fast photoconductors

    International Nuclear Information System (INIS)

    We have investigated the influence of spontaneous low frequency oscillations (LFO, f∼0.01 Hz) occurring at high electric field (>1 kV/cm) in resistive photoconductors (PCD) made from semi-insulating GaAs on the response of the PCDs under pulsed gamma-ray irradiation (E∼1.2 MeV, τFWHM=30 ns). The PCDs were fabricated using GaAs from five commercially available sources. The PCDs were irradiated with fission neutrons in order to reduce their response time down to less than 100 ps. The amplitude of the LFOs was found to be related to the carrier lifetime, and thus defect concentration in the GaAs material. It was larger for material exhibiting high carrier lifetime. Increasing the localised defect concentration, such as EL2 type defect, through GaAs irradiation with fission neutrons was found to decrease the amplitude of the LFOs. PCDs irradiated at high neutron doses (>1x1015 neutrons/cm2) showed no LFOs. It is suggested that interactions between the propagating domains and the highly defective GaAs bulk control the LFO characteristics. Gamma-ray sensitivity, in transient mode, versus bias voltage of PCDs was also found to be correlated to LFOs, showing that high-field behavior of GaAs can be used to predict the optimum operating bias of the PCDs

  14. a 9-BIT, Pipelined Gallium Arsenide Analog-Digital Converter

    Science.gov (United States)

    Breevoort, Cornelius Marius

    1992-01-01

    Excellent Short Take-Off and Landing (STOL) performance is achieved by Upper Surface Blowing (USB) aircraft as a result of mounting high by-pass turbofan engines over the forward part of the wing. High lift levels are generated by directing the engine exhaust over the wing upper surface to entrain additional airflow and by using the Coanda effect to turn the exhaust flow downward over a large radius "Coanda" flap. Commercial application of USB technology could reduce airport congestion and community noise if future configurations can be designed with economically acceptable cruise drag levels. An experimental investigation of the high speed aerodynamics of USB aircraft configurations has been conducted to accurately define the magnitude and causes of the powered configuration cruise drag. A highly instrumented wind tunnel model of a realistic USB configuration has been used which permitted parametric variations in the number and spanwise location of the nacelles and accurately modeled the engine power effects with turbofan propulsion simulators. The measured force data provides an accurate definition of the cruise drag penalty associated with each configuration and the constructed pressure contour plots provide detailed insight into their causes. It was found that the high speed aerodynamics of USB configurations is a complex interaction of jet induced and wing transonic flowfields. The presence of the nacelles on the wing upper surface created a severe drag penalty which increased with freestream Mach number, power setting and angle of attack. The more widely spaced two nacelle configurations exhibited improved flowfields at moderate Mach numbers but suffered from drag levels comparable to the baseline configuration for high speed cruise conditions. At high Mach numbers and power settings, all of the tested configurations displayed strong shocks and separated zones in the wing/nacelle junction regions. Detailed discussions of the causes of the cruise drag penalty and recommended future design improvements are presented.

  15. Gallium arsenide based surface plasmon resonance for glucose monitoring

    Science.gov (United States)

    Patil, Harshada; Sane, Vani; Sriram, G.; Indumathi, T. S; Sharan, Preeta

    2015-07-01

    The recent trends in the semiconductor and microwave industries has enabled the development of scalable microfabrication technology which produces a superior set of performance as against its counterparts. Surface Plasmon Resonance (SPR) based biosensors are a special class of optical sensors that become affected by electromagnetic waves. It is found that bio-molecular recognition element immobilized on the SPR sensor surface layer reveals a characteristic interaction with various sample solutions during the passage of light. The present work revolves around developing painless glucose monitoring systems using fluids containing glucose like saliva, urine, sweat or tears instead of blood samples. Non-invasive glucose monitoring has long been simulated using label free detection mechanisms and the same concept is adapted. In label-free detection, target molecules are not labeled or altered, and are detected in their natural forms. Label-free detection mechanisms involves the measurement of refractive index (RI) change induced by molecular interactions. These interactions relates the sample concentration or surface density, instead of total sample mass. After simulation it has been observed that the result obtained is highly accurate and sensitive. The structure used here is SPR sensor based on channel waveguide. The tools used for simulation are RSOFT FULLWAVE, MEEP and MATLAB etc.

  16. Photoinduced Dissociation Of N-alkyl Bromides On Gallium Arsenide(110) And Gallium Arsenide(100) Electron And Fragment Dynamics

    CERN Document Server

    Khan, K A

    1999-01-01

    In this study we investigate the UV-initiated electron transfer and dissociation fragment dynamics of selected n-alkyl bromides physisorbed on single crystals of GaAs. By systematically varying different chemical and structural parameters of the adsorbate/substrate system we explore a number of fundamental questions regarding the basic physics and chemistry of photochemical processes on surfaces. Monolayers of methyl, ethyl and propyl bromide were deposited on the (110), Ga-terminated (100) and As- terminated (100) surfaces of GaAs without thermal decomposition at 80 K. Substrate-mediated electron transfer to the molecule, induced by exposure to UV light at 193, 248 and 351 nm, causes C-Br bond cleavage. The electron transfer dynamics of this mechanism are examined as a function of wavelength and molecular complexity of the adsorbate to better understand the flow of energy and charge across the adsorbate/substrate interface. The photodynamics of the alkyl fragments are studied using mass-, energy- and angle-r...

  17. Substrate engineering for defect reduction and microstructure control in the growth of indium arsenide on (100) gallium arsenide

    Science.gov (United States)

    Ganesan, Suryanarayanan

    The development of devices based on InAs, GaSb, and AlSb, semiconductors that possess narrow band-gaps and 0.61 nm lattice parameters, has been limited by the defects that ensue in epitaxial films that typically are grown on commercial semi-insulating, but 7% lattice-mismatched, GaAs substrates. The studies described in this dissertation investigate the application of a lateral epitaxial overgrowth technique for defect reduction and microstructure control to the InAs/GaAs heteroepitaxial system by exploring the development of microstructure at various stages of island and film growth in conventional and lateral overgrowth epitaxy (that is, on unpatterned and mask-patterned substrates, respectively). For a range of growth conditions, InAs films on unpatterned (100) GaAs substrates exhibit not only the threading dislocations characteristic of largely mismatched epitaxial films, but also systematic tilting within micron-scale InAs domains. Alteration of the pattern and magnitude of the tilt achieved by varying the growth conditions and/or introducing mask-patterned substrates suggest that not only chemical and kinetic, but also physical constraints can direct microstructural evolution during growth. Backscattered electron Kikuchi pattern-based orientation imaging was used to investigate the origin of the improved epitaxial alignment that is realized when InAs films were grown on mask-patterned (100) GaAs substrates. The island size at coalescence was shown to be critical in determining whether a single or two-fold, four-fold or six-fold epitaxial orientation relationship(s) is (are) present in the film. The evolution of tilt with increasing island size is attributed to the particulars of the misfit dislocation network that forms, which appears to evolve in this epitaxial system as the island grows, in accordance with a model proposed by Spencer and Tersoff [1,2]. Sub-micron (˜0.5 mum or less) island sizes at coalescence appear to lead to a single orientation aligned with the GaAs. This work shows that spatial constraints imposed at the early stages of growth, in this case through use of a mask-patterned substrate, can be used to promote coalescence at small island size as an alternative or parallel approach to setting growth conditions (temperature, precursor stoichiometry, etc.) in order to control the defect nucleation and microstructure. References. [1]. B.J. Spencer, and J. Tersoff, Appl. Phys. Lett. 77 (1997) 2533. [2]. B.J. Spencer, and J. Tersoff, Phys. Rev. B63 (2001) 205424.

  18. Chemical mechanical polishing of Indium phosphide, Gallium arsenide and Indium gallium arsenide films and related environment and safety aspects

    Science.gov (United States)

    Matovu, John Bogere

    As scaling continues with advanced technology nodes in the microelectronic industry to enhance device performance, the performance limits of the conventional substrate materials such as silicon as a channel material in the front-end-of-the-line of the complementary metal oxide semiconductor (CMOS) need to be surmounted. These challenges have invigorated research into new materials such as III-V materials consisting of InP, GaAs, InGaAs for n-channel CMOS and Ge for p-channels CMOS to enhance device performance. These III-V materials have higher electron mobility that is required for the n-channel while Ge has high hole mobility that is required for the p-channel. Integration of these materials in future devices requires chemical mechanical polishing (CMP) to achieve a smooth and planar surface to enable further processing. The CMP process of these materials has been associated with environment, health and safety (EH&S) issues due to the presence of P and As that can lead to the formation of toxic gaseous hydrides. The safe handling of As contaminated consumables and post-CMP slurry waste is essential. In this work, the chemical mechanical polishing of InP, GaAs and InGaAs films and the associated environment, health and safety (EH&S) issues are discussed. InP removal rates (RRs) and phosphine generation during the CMP of blanket InP films in hydrogen peroxide-based silica particle dispersions in the presence and absence of three different multifunctional chelating carboxylic acids, namely oxalic acid, tartaric acid, and citric acid are reported. The presence of these acids in the polishing slurry resulted in good InP removal rates (about 400 nm min-1) and very low phosphine generation (surfaces (0.1 nm RMS surface roughness). The optimized slurry compositions consisting of 3 wt % silica, 1 wt % hydrogen peroxide and 0.08 M oxalic acid or citric acid that provided the best results on blanket InP films were used to evaluate their planarization capability of patterned InP-STI structures of 200 mm diameter wafers. Cross sectional scanning electron microscope (SEM) images showed that InP in the shallow trench isolation structures was planarized and scratches, slurry particles and smearing of InP were absent. Additionally, wafers polished at pH 6 showed very low dishing values of about 12-15 nm, determined by cross sectional SEM. During the polishing of blanket GaAs, GaAs RRs were negligible with deionized water or with silica slurries alone. They were relatively high in aq. solutions of H2O2 alone and showed a strong pH dependence, with significantly higher RRs in the alkaline region. The addition of silica particles to aq. H2O2 did not increase the GaAs RRs significantly. The evolution of arsenic trihydride (AsH3) during the dissolution of GaAs in aq. H2O2 solution was similarly higher in the basic pH range than in neutral pH or in the acidic pH range. However, no AsH3 was measured during polishing, evidently because of the relatively high water solubility of AsH3. The work done on InGaAs polishing shows that InGaAs RR trends are different from those observed for InP or GaAs. InGaAs RRs at pH 2 are higher than those at pH 10 and highest at pH 4. Dissolution rates (DRs), Fourier Transform Infrared Spectroscopy (FTIR), contact angles, X-Ray Photoelectron Spectroscopy (XPS), X-Ray Fluorescence Spectroscopy (XRF), zeta potential measurements and calculated Gibbs free energy changes of the reactions involved during polishing and gas formation were used to discuss the observed RRs and hydride gas generation trends and to propose the reaction pathways involved in the material removal and in hydride gas generation mechanisms.

  19. 铟镓砷焦平面阵列在微光夜视应用中的潜力及前景%The Potential and Prospect of Indium Gallium Arsenide Focal Plane Array Applied to Low Light Level Night Vision

    Institute of Scientific and Technical Information of China (English)

    潘京生; 孙建宁; 金戈; 任玲; 毛汉祺; 顾燕; 郭一亮; 苏德坦

    2014-01-01

    得益于夜气辉在短波红外(SWIR)0.9~1.7μm波段的自然辐射数十倍强于夜天空在可见光和近红外(NIR)0.4~0.9μm波段的辐射,SWIR成像成为应用于微光条件下的成像探测的最佳选择,由晶格匹配In0.53Ga0.47As/InP制作InGaAs焦平面阵列(Focal Plane Array,FPA),灵敏于0.9~1.7μm波段,在整个响应波段具有超过70%的量子效率,和室温非制冷工作的极低的暗电流。通过减薄基底,还可将InGaAs FPA的短波限延伸至可见光波段的0.4μm。最近几年,超低暗电流、低读出噪声、大面阵和小像素尺寸的InGaAs FPA的开发取得了实质性的进展,特别是暗电流得到了数量级的降低,InGaAs FPA探测器已经显露出应用于微光夜视的极大潜力,并且还通过采用更复杂的温度相关的非均匀校正算法实现了无TEC的低功耗工作,基于超低噪声的密集阵列InGaAs FPA的SWIR成像技术有望成为新一代夜视技术的一个重要组成部份。%The shortwave infrared(SWIR)spectral irradiance in the 0.9μm to 1.7μm band which caused by night airglow is several ten times stronger than the irradiance in the visible and near infrared realm of 0.4μm to 0.9μm of the night sky, so SWIR imaging is the best choice for the imaging detection under low light level condition. The Indium Gallium Arsenide(InGaAs)focal plane array(FPA)sensors based on lattice matched In0.53Ga0.47As/InP is sensitive to SWIR light whose wavelength is from 0.9μm to 1.7μm, matching the spectral irradiance caused by night airglow, and have exceeded quantum efficiency of 70%over whole response spectral range, as well as with very low dark current while working at room temperature. Removing the InP substrate from the FPA allows extending cutoff wavelength to visible region of 0.4μm. The work on InGaAs FPA with ultra low dark current, low readout noise, large format and small pixel size has been progressing substantially in

  20. Efeito da terapia com laser de arsenieto de gálio e alumínio (660Nm sobre a recuperação do nervo ciático de ratos após lesão por neurotmese seguida de anastomose epineural: análise funcional Effect of gallium-aluminum-arsenide laser therapy (660Nm on recovery of the sciatic nerve in rats following neurotmesis lesion and epineural anastomosis: functional analysis

    Directory of Open Access Journals (Sweden)

    FA Reis

    2008-06-01

    Full Text Available CONTEXTUALIZAÇÃO: As lesões nervosas periféricas podem comprometer atividades diárias de um indivíduo e resultam em perda da sensibilidade e motricidade do território inervado. OBJETIVO: Com o intuito de acelerar os processos regenerativos, objetivou-se analisar a influência da aplicação do laser de arsenieto de gálio e alumínio (AsGaAl, 660Nm sobre a recuperação funcional do nervo ciático de ratos. MATERIAIS E MÉTODOS: O nervo ciático de 12 ratos Wistar foi submetido à lesão por neurotmese e anastomose epineural e divididos em dois grupos: controle e laserterapia. Após a lesão, utilizou-se o laser de GaAlAs, 660Nm, 4J/cm², 26,3mW, feixe de 0,63cm², em três pontos eqüidistantes sobre a lesão, por 20 dias. As impressões das pegadas dos animais foram obtidas antes e após (sete, 14 e 21 dias pós-operatórios o procedimento cirúrgico e calculou-se o índice funcional do ciático (IFC. RESULTADOS: A comparação do IFC não resultou em diferença significante (p>0,05 entre os grupos. CONCLUSÕES: Conclui-se que os parâmetros e métodos empregados na laserterapia demonstram resultados nulos sobre o IFC no período avaliado.CONTEXT: Peripheral nerve injuries result in sensory and motor losses in the innervated area and can hinder individuals’ daily activities. Objective: The objective was to analyze the influence of applying gallium-aluminum-arsenide (GaAlAs laser (660Nm on the functional recovery of the sciatic nerve in rats. METHODS: The sciatic nerve of 12 Wistar rats was subjected to injury consisting of neurotmesis and epineural anastomosis. The rats were divided into two groups: control and laser therapy. After the injury, a GaAlAs laser was used (660Nm, 4J/cm², 26.3mW and 0.63cm² beam at three equidistant points on the injury, for 20 days. Footprint impressions were obtained from the animals before and seven, 14 and 21 days after the surgical procedure and the sciatic functional index (SFI was calculated

  1. Design of Indium Arsenide nanowire sensors for pH and biological sensing and low temperature transport through p-doped Indium Arsenide nanowires

    DEFF Research Database (Denmark)

    Upadhyay, Shivendra

    With the goal of real time electrical detection of chemical and biological species, nanowires have shown great promise with high sensitivity due to their large surface to volume ratio. While the focus of such electrical detection has shifted to one dimensional semiconductor nanostuctures, Silicon...

  2. Molecular beam epitaxial growth of tungsten layers embedded in single crystal gallium arsenide

    Energy Technology Data Exchange (ETDEWEB)

    Harbison, J.P.; Hwang, D.M.; Levkoff, J.; Derkits G.E. Jr.

    1985-12-01

    We have been able to fabricate structures which consist of a thin (approx.10 nm) polycrystalline W film embedded in surrounding single crystalline GaAs by molecular beam epitaxy (MBE) using an electron beam evaporation source to deposit W metal in an ultrahigh vacuum MBE growth chamber. The entire deposition sequence can take place at elevated temperature (625--700 /sup 0/C) due to the nonreactive nature of W with respect to GaAs. Reflective high-energy diffraction and transmission electron microscopy indicate that the single crystal GaAs overgrowth proceeds by seeding from the GaAs layer beneath the W through spontaneously occurring perforations in the W layer.

  3. The scaling of the effective band gaps in indium-arsenide quantum dots and wires.

    Science.gov (United States)

    Wang, Fudong; Yu, Heng; Jeong, Sohee; Pietryga, Jeffrey M; Hollingsworth, Jennifer A; Gibbons, Patrick C; Buhro, William E

    2008-09-23

    Colloidal InAs quantum wires having diameters in the range of 5-57 nm and narrow diameter distributions are grown from Bi nanoparticles by the solution-liquid-solid (SLS) mechanism. The diameter dependence of the effective band gaps (DeltaE(g)s) in the wires is determined from photoluminescence spectra and compared to the experimental results for InAs quantum dots and rods and to the predictions of various theoretical models. The DeltaE(g) values for InAs quantum dots and wires are found to scale linearly with inverse diameter (d(-1)), whereas the simplest confinement models predict that DeltaE(g) should scale with inverse-square diameter (d(-2)). The difference in the observed and predicted scaling dimension is attributed to conduction-band nonparabolicity induced by strong valence-band-conduction-band coupling in the narrow-gap InAs semiconductor.

  4. A customizable commercial miniaturized 320×256 indium gallium arsenide shortwave infrared camera

    Science.gov (United States)

    Huang, Shih-Che; O'Grady, Matthew; Groppe, Joseph V.; Ettenberg, Martin H.; Brubaker, Robert M.

    2004-10-01

    The design and performance of a commercial short-wave-infrared (SWIR) InGaAs microcamera engine is presented. The 0.9-to-1.7 micron SWIR imaging system consists of a room-temperature-TEC-stabilized, 320x256 (25 μm pitch) InGaAs focal plane array (FPA) and a high-performance, highly customizable image-processing set of electronics. The detectivity, D*, of the system is greater than 1013 cm-√Hz/W at 1.55 μm, and this sensitivity may be adjusted in real-time over 100 dB. It features snapshot-mode integration with a minimum exposure time of 130 μs. The digital video processor provides real time pixel-to-pixel, 2-point dark-current subtraction and non-uniformity compensation along with defective-pixel substitution. Other features include automatic gain control (AGC), gamma correction, 7 preset configurations, adjustable exposure time, external triggering, and windowing. The windowing feature is highly flexible; the region of interest (ROI) may be placed anywhere on the imager and can be varied at will. Windowing allows for high-speed readout enabling such applications as target acquisition and tracking; for example, a 32x32 ROI window may be read out at over 3500 frames per second (fps). Output video is provided as EIA170-compatible analog, or as 12-bit CameraLink-compatible digital. All the above features are accomplished in a small volume < 28 cm3, weight < 70 g, and with low power consumption < 1.3 W at room temperature using this new microcamera engine. Video processing is based on a field-programmable gate array (FPGA) platform with a soft-embedded processor that allows for ease of integration/addition of customer-specific algorithms, processes, or design requirements. The camera was developed with the high-performance, space-restricted, power-conscious application in mind, such as robotic or UAV deployment.

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

    DEFF Research Database (Denmark)

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

    1997-01-01

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

  6. Design and implementation of high sensitive CCD on gallium arsenide based miniaturized spectrometer

    Science.gov (United States)

    Zheng, Jiamin; Shen, Jianhua; Guo, Fangmin

    2013-08-01

    In this paper, a method on how to design and implement a miniaturized spectrometer with low-light-level (LLL) CCD on GaAs is introduced. The optical system uses a blazed grating as the dispersive element and a 1×64 CCD on GaAs as the sensor. We apply a highly integrated Cortex-M4 MCU (STM32F407), to build the data acquisition and analysis unit, providing Wi-Fi interface to communicate with the PC software. It can complete the tasks like data acquisition, digital filtering, spectral display, network communication, human-computer interaction etc.

  7. Structural features of indium antimonide quantum dots on the indium arsenide substrate

    Directory of Open Access Journals (Sweden)

    Liliya A. Sokura

    2015-06-01

    Full Text Available The properties of InSb/InAs quantum dots (QDs have been investigated by transmission electron microscopy (TEM. Specific features of diffraction contrast were discovered in plan-view TEM images of big (9–10 nm in height and 38–50 nm in diameter InSb QDs. To understand the origin of such distortions, a model of an InSb QD on InAs substrate containing a partial Frank dislocation (FD was developed and used for calculations of the displacement field and the subsequent diffraction image simulation of an InSb QD for the first time. The shape of the QD was established to have an insignificant influence on the magnitude of radial displacements. The insertion of a misfit defect (a partial Frank dislocation into the QD reduces the strain at the edges of the QD almost by 30%. The comparison of experimental and simulated data allowed us to explain the observed features of the moiré pattern in the image of a big InSb QD by the presence of a misfit defect at the QD-substrate interface.

  8. Planar Gallium arsenide nanowire arrays for nanoelectronics: Controlled growth, doping, characterization, and devices

    Science.gov (United States)

    Dowdy, Ryan Stewart

    The Vapor-Liquid-Solid (VLS) mechanism is a bottom-up approach to produce onedimensional semiconductor structures, or nanowires. VLS nanowires are formed via a chemical or physical deposition process, where a metallic nanoparticle (seed) facilitates the growth. Nanowire growth diameter is strongly correlated to seed size, therefore top-down patterning can control site location and diameter of nanowire growth. Nanowires are sought after for their potential use as a manageable way produce small dimensioned semiconductor features without the need of expensive lithographic techniques. VLS nanowires commonly grow out-of-plane with respect to their growth substrate, resulting in difficulty with integrating VLS nanowires into existing device processing which is intended for planar geometries. Nanowires are typically removed from the substrate, which requires painstaking and uneconomical methods to pattern and align the nanowires. Planar nanowires are a potential solution to this issue; they grow in-plane on the substrate surface, epitaxially attached along its entire axis. Planar nanowires, as is, can be integrated into any preexisting planar semiconductor process, combining the advantages of nanowires with increased manufacturability. In this dissertation, planar GaAs nanowires are grown using metal organic chemical vapor deposition (MOCVD) with Au nanoparticles as the liquid metal seed. Growth occurs across multiple substrates to elucidate the mechanism behind planar nanowire growth direction. Knowledge gained by observing planar nanowire growth is used to precisely control nanowire growth direction. Subsequently the doping of planar nanowires is explored and unique phenomena related to the p-type doping of planar nanowires are investigated and discussed. The advantages of using planar nanowires are demonstrated through the controlled growth and doping of planar nanowires, and ultimately fabrication of electronic devices using conventional planar process techniques without the need for vertical nanowire processes or nanowire transferring. Devices are characterized and results are presented with discussion. The next steps for the future of planar nanowires are presented with initial results highlighting future applications and issues that must be solved. Chapter 1 is an introduction to the history of Vapor-Liquid-Solid nanowires, and as well as a brief overview of the accomplishments of the field and highlighting unsolved issues. Chapter 2 introduces the planar nanowire and discusses the motivation behind researching planar nanowires as a potential solution to the fundamental problems with vertical VLS nanowires. Chapter 3 gives a short background into VLS nanowire growth and properties, introduction to MOCVD growth and reactor design, and material properties of GaAs, the semiconductor material of interest in this dissertation. Chapter 4 presents the experimental details of planar GaAs nanowire growth on various substrates and the concept of projection theory to determined planar nanowire growth direction, as well as intrinsic growth phenomena. Chapter 5 delves into the doping of planar nanowires, both n-type and p-type. The morphological changes and perturbations to planar nanowire that are caused by p-type dopants are discussed. Chapter 6 demonstrates electrical devices such as MESFETS, inverting amplifiers and p-n diodes fabricated using planar GaAs nanowires as the active structure. Devices performance and metrics are discussed in this chapter. Chapter 7 outlines several future directions for planar nanowires and presents initial results in a variety of areas such as potential devices, modeling opportunities and fundamental issues that need to be solved.

  9. Soft-mask fabrication of gallium arsenide nanomembranes for integrated quantum photonics

    CERN Document Server

    Midolo, Leonardo; Kiršanskė, Gabija; Stobbe, Søren

    2015-01-01

    We report on the fabrication of quantum photonic integrated circuits based on suspended GaAs membranes. The fabrication process consists of a single lithographic step followed by inductively-coupled-plasma dry etching through an electron-beam-resist mask and wet etching of a sacrificial layer. This method does not require depositing, etching, and stripping a hard mask, greatly reducing fabrication time and costs, while at the same time yielding devices of excellent structural quality. We discuss in detail the procedures for cleaning the resist residues caused by the plasma etching and present a statistical analysis of the etched feature size after each fabrication step.

  10. Gallium Arsenide detectors for X-ray and electron (beta particle) spectroscopy

    Science.gov (United States)

    Lioliou, G.; Barnett, A. M.

    2016-11-01

    Results characterizing GaAs p+-i-n+ mesa photodiodes with a 10 μm i layer for their spectral response under illumination of X-rays and beta particles are presented. A total of 22 devices, having diameters of 200 μm and 400 μm, were electrically characterized at room temperature. All devices showed comparable characteristics with a measured leakage current ranging from 4 nA/cm2 to 67 nA/cm2 at an internal electric field of 50 kV/cm. Their unintentionally doped i layers were found to be almost fully depleted at 0 V due to their low doping density. 55Fe X-ray spectra were obtained using one 200 μm diameter device and one 400 μm diameter device. The best energy resolution (FWHM at 5.9 keV) achieved was 625 eV using the 200 μm and 740 eV using the 400 μm diameter device, respectively. Noise analysis showed that the limiting factor for the energy resolution of the system was the dielectric noise; if this noise was eliminated by better design of the front end of the readout electronics, the achievable resolution would be 250 eV. 63Ni beta particle spectra obtained using the 200 μm diameter device showed the potential utility of these detectors for electron and beta particle detection. The development of semiconductor electron spectrometers is important particularly for space plasma physics; such devices may find use in future space missions to study the plasma environment of Jupiter and Europa and the predicted electron impact excitation of water vapor plumes from Europa hypothesized as a result of recent Hubble Space Telescope (HST) UV observations.

  11. Studies on deep electronic levels in silicon and aluminium gallium arsenide alloys

    International Nuclear Information System (INIS)

    This thesis reports on investigations of the electrical and optical properties of deep impurity centers, related to the transition metals (TMs) Ti, Mo, W, V and Ni, in silicon. Emission rates, capture cross sections and photoionization cross sections for these impurities were determined by means of various Junction Space Charge Techniques (JSCTs), such as Deep Level Transient Spectroscopy (DLTS), dark capacitance transient and photo capacitance transient techniques. Changes in Gibbs free energy as a function of temperature were calculated for all levels. From this temperature dependence, the changes in enthalpy and entropy involved in the electron and hole transitions were deduced. The influence of high electric fields on the electronic levels in chalcogen-doped silicon were investigated using the dark capacitance transient technique. The enhancement of the electron emission from the deep centers indicated a more complex field enhancement model than the expected Poole-Frenkel effect for coulombic potentials. The possibility to determine charge states of defects using the Poole-Frenkel effect, as often suggested, is therefore questioned. The observation of a persistent decrease of the dark conductivity due to illumination in simplified AlGaAs/GaAs high Electron Mobility Transistors (HEMTs) over the temperature range 170K< T<300K is reported. A model for this peculiar behavior, based on the recombination of electrons in the two-dimensional electron gas (2DEG) located at the AlGaAs/GaAs interface with holes generated by a two-step excitation process via the deep EL2 center in the GaAs epilayer, is put forward

  12. Size-effects in indium gallium arsenide nanowire field-effect transistors

    Science.gov (United States)

    Zota, Cezar B.; Lind, E.

    2016-08-01

    We fabricate and analyze InGaAs nanowire MOSFETs with channel widths down to 18 nm. Low-temperature measurements reveal quantized conductance due to subband splitting, a characteristic of 1D systems. We relate these features to device performance at room-temperature. In particular, the threshold voltage versus nanowire width is explained by direct observation of quantization of the first sub-band, i.e., band gap widening. An analytical effective mass quantum well model is able to describe the observed band structure. The results reveal a compromise between reliability, i.e., VT variability, and on-current, through the mean free path, in the choice of the channel material.

  13. Electroreflectance of indium gallium arsenide phosphide lattice matched to indium phosphide

    International Nuclear Information System (INIS)

    We report the first systematic measurement of the electroreflectance spectra of In/sub u/Ga/sub 1-u/P/sub v/As/sub 1-v/ over the range of compositions that lattice-match InP substrates, at room temperature and for energies between 0.7 and 3.5 eV. Analysis of the spectra has enabled us to determine the composition dependence of E0, E0+Δ0, E1, E1+Δ1, Δ0, and Δ1. Experimentally determined values of E0, E0+Δ0, and m*/m0 have been used to predict the values of the g factors for these compounds

  14. The electronic and structural properties of the silicon-gallium arsenide(110) interface

    Science.gov (United States)

    Dunstan, P. R.; Wilks, S. P.; Burgess, S. R.; Pan, M.; Williams, R. H.; Cammack, D. S.; Clark, S. A.

    1998-01-01

    The passivation properties of the Sisbnd GaAs(110) interface have been studied using scanning tunnelling microscopy/spectroscopy (STM/STS) and soft X-ray photoemission spectroscopy (SXPS). Silicon has been deposited at room temperature and STM images show the sub-monolayer growth of silicon islands on the GaAs substrate. The electrical properties of these islands together with the clean surface have been investigated using scanning tunnelling spectroscopy (STS). The spectroscopy clearly illustrates the difference in electrical properties between atomically flat regions of GaAs as compared to those containing defects or steps, i.e. where surface band bending occurs. We have investigated the use of sub-monolayer Si coverages to modify the electronic structure of the surface. Height variations of 3-4Åacross Si islands and 2Åacross steps on the GaAs surface have also been observed using the STM. STS spectra, collected simultaneously with the STM image, showed the Si to have semiconducting properties differing from that of crystalline Si and the GaAs substrate. Comparisons between the STM and STS results together with SXPS have provided a correlation between the structural, electrical and chemical nature of the Si/GaAs(110) interface.

  15. Spatially resolved localized vibrational mode spectroscopy of carbon in liquid encapsulated Czochralski grown gallium arsenide wafers

    International Nuclear Information System (INIS)

    Substitutional carbon on an arsenic lattice site is the shallowest and one of the most dominant acceptors in semi-insulating Liquid Encapsulated Czochralski (LEC) GaAs. However, the role of this acceptor in determining the well known ''W'' shape spatial variation of neutral EL2 concentration along the diameter of a LEC wafer is not known. In this thesis, we attempt to clarify the issue of the carbon acceptor's effect on this ''W'' shaped variation by measuring spatial profiles of this acceptor along the radius of three different as-grown LEC GaAs wafers. With localized vibrational mode absorption spectroscopy, we find that the profile of the carbon acceptor is relatively constant along the radius of each wafer. Average values of concentration are 8 x 10E15 cm-3, 1.1 x 10E15 cm-3, and 2.2 x 10E15 cm-3, respectively. In addition, these carbon acceptor LVM measurements indicate that a residual donor with concentration comparable to carbon exists in these wafers and it is a good candidate for the observed neutral EL2 concentration variation. 22 refs., 39 figs

  16. Low-noise gallium-arsenide field-effect transistor preamplifiers for stochastic beam cooling systems

    International Nuclear Information System (INIS)

    The present noise performance, bandwidth capability and gain stability of bipolar and field-effect transistors, parametric amplifier, Schottky diode mixer and maser are summarized and compared in the 100 MHz to 40 GHz frequency range for stochastic beam cooling systems. Stability factor of GaAs FET's as a function of ambient temperature is presented and discussed. Performance data of several low-noise wide-band cryogenically cooled preamplifiers are presented including one with a noise figure of 0.35 dB over a bandwidth range of 150500 MHz operating at ambient temperature of 200K. Also, data are given on a broadband 1-2 GHz preamplifier having a noise figure of approximately 0.2 dB. The gain, operating noise temperature, stability, gain nonuniformity and phase-shift as function of frequency of interest for beam cooling systems are discussed

  17. Structural and Magnetic Phase Transitions in Manganese Arsenide Thin-Films Grown by Molecular Beam Epitaxy

    Science.gov (United States)

    Jaeckel, Felix Till

    Phase transitions play an important role in many fields of physics and engineering, and their study in bulk materials has a long tradition. Many of the experimental techniques involve measurements of thermodynamically extensive parameters. With the increasing technological importance of thin-film technology there is a pressing need to find new ways to study phase transitions at smaller length-scales, where the traditional methods are insufficient. In this regard, the phase transitions observed in thin-films of MnAs present interesting challenges. As a ferromagnetic material that can be grown epitaxially on a variety of technologically important substrates, MnAs is an interesting material for spintronics applications. In the bulk, the first order transition from the low temperature ferromagnetic alpha-phase to the beta-phase occurs at 313 K. The magnetic state of the beta-phase has remained controversial. A second order transition to the paramagnetic gamma-phase takes place at 398 K. In thin-films, the anisotropic strain imposed by the substrate leads to the interesting phenomenon of coexistence of alpha- and beta-phases in a regular array of stripes over an extended temperature range. In this dissertation these phase transitions are studied in films grown by molecular beam epitaxy on GaAs (001). The films are confirmed to be of high structural quality and almost purely in the A0 orientation. A diverse set of experimental techniques, germane to thin-film technology, is used to probe the properties of the film: Temperature-dependent X-ray diffraction and atomic-force microscopy (AFM), as well as magnetotransport give insights into the structural properties, while the anomalous Hall effect is used as a probe of magnetization during the phase transition. In addition, reflectance difference spectroscopy (RDS) is used as a sensitive probe of electronic structure. Inductively coupled plasma etching with BCl3 is demonstrated to be effective for patterning MnAs. We show that the evolution of electrical resistivity in the coexistence regime of alpha- and beta-phase can be understood in terms of a simple model. These measurements allow accurate extraction of the order-parameter "phase fraction" and thus permit us to study the hysteresis of the phase transition in detail. Major features in the hysteresis can be correlated to the ordering observed in the array of alpha- and beta-stripes. As the continuous ferromagnetic film breaks up into isolated stripes of alpha-phase, a hysteresis in the out-of-plane magnetization is detected from measurements of the anomalous Hall effect. The appearance of out-of-plane domains can be understood from simple shape-anisotropy arguments. Remarkably, an anomaly of the Hall effect at low fields persists far into the beta-phase. Signatures of the more elusive beta- to gamma-transition are found in the temperature-dependence of resistivity, the out-of-plane lattice constant, and reflectance difference spectra. The transition temperature is significantly lowered compared to the bulk, consistent with the strained state of the material. The negative temperature coefficient of resistivity, as well as its anisotropic changes, lend support to the idea of an antiferromagnetic order within the beta-phase.

  18. Lattice constant variation and complex formation in zincblende gallium manganese arsenide

    Science.gov (United States)

    Schott, G. M.; Faschinger, W.; Molenkamp, L. W.

    2001-09-01

    We perform high resolution x-ray diffraction on GaMnAs mixed crystals as well as on GaMnAs/GaAs and GaAs/MnAs superlattices for samples grown by low-temperature molecular-beam epitaxy under different growth conditions. Although all samples are of high crystalline quality and show narrow rocking curve widths and pronounced finite thickness fringes, the lattice constant variation with increasing manganese concentration depends strongly on the growth conditions: For samples grown at substrate temperatures of 220 and 270 °C, the extrapolated relaxed lattice constant of Zincblende MnAs is 0.590 nm and 0.598 nm, respectively. This is in contrast to low-temperature GaAs, for which the lattice constant decreases with increasing substrate temperature.

  19. Lattice constant variation and complex formation in zincblende Gallium Manganese Arsenide

    OpenAIRE

    Schott, G. M.; Faschinger, W.; Molenkamp, L.W.

    2001-01-01

    We perform high resolution X-ray diffraction on GaMnAs mixed crystals as well as on GaMnAs/GaAs and GaAs/MnAs superlattices for samples grown by low temperature molecular beam epitaxy under different growth conditions. Although all samples are of high crystalline quality and show narrow rocking curve widths and pronounced finite thickness fringes, the lattice constant variation with increasing manganese concentration depends strongly on the growth conditions: For samples grown at substrate te...

  20. Ferromagnetism in indium manganese arsenide magnetic semiconductor thin films deposited by metalorganic vapor phase epitaxy

    Science.gov (United States)

    Blattner, Aaron J.

    The structure-property relationships of (In,Mn)As magnetic semiconductor thin films have been investigated to elucidate the mechanism of ferromagnetism and to assess its viability for use in spintronic device applications. Single phase, epitaxial (In,Mn)As films were deposited for the first time using atmospheric pressure metalorganic vapor phase epitaxy. The microstructure and phase composition of these films were determined using X-ray diffraction, transmission electron microscopy, and extended x-ray absorption fine structure measurements. Magnetic properties of the films were examined using superconducting quantum interference device magnetometery. Room temperature ferromagnetism was observed in single-phase In1-xMn xAs films with x ≤ 0.10. Magnetization measurements indicated that these (In,Mn)As samples had a transition temperature of 298--333 K. The Curie temperature was effectively independent of Mn concentration over the range of 1--10%. The temperature dependent magnetization along with the magnitude of the saturation magnetization and microstructural analysis indicated that the source of the high-temperature ferromagnetism in single-phase films is not attributable to MnAs nanoprecipitates. The Curie temperatures for these films are nearly constant for hole concentrations of 8 x 1017--1.6 x 1018 cm -3. In addition, the hole concentration is at least two orders of magnitude smaller than what is required under the conventional hole-mediated theory of ferromagnetism to obtain room-temperature ferromagnetism. Consequently, this model in its current form is not sufficient to describe the ferromagnetism in (In,Mn)As deposited using MOVPE. A model based upon interacting atomic scale ferromagnetic clusters was developed. The ferromagnetic coupling between these clusters may be a hole-mediated mechanism. This model of interacting ferromagnetic clusters was very successful in describing both the temperature and field dependence of the magnetization. In addition, this model is able to explain the high Curie temperatures and the Mn concentration independence of the Curie temperature in these (In,Mn)As films. This work has shown that the MOVPE deposited (In,Mn)As films are significantly different than those obtained by molecular beam epitaxy. The higher deposition temperature has been shown to significantly improve Mn solubility and allow for the formation of atomic scale clusters as predicted by recent theoretical calculations. These clusters stabilize the ferromagnetism to much higher temperatures than was previously observed in (In,Mn)As with random Mn substitution.

  1. Manipulating the magnetic anisotropy in the ferromagnetic semiconductor Gallium Manganese Arsenide

    OpenAIRE

    Casiraghi, Arianna

    2012-01-01

    Since its first successful growth in 1996, the ferromagnetic semiconductor (Ga,Mn)- As has had a great inuence on the research field of semiconductor spintronics. Among the outstanding characteristics of this material the large spin-orbit interaction for the holes in the valence band plays a major role, since it is responsible for some of the most interesting properties of (Ga,Mn)As, like the magnetocrystalline anisotropy, the magnetoelastic coupling and the extraordinary contributions to ...

  2. Formation of defects at high temperature plastic deformation of gallium arsenide

    Energy Technology Data Exchange (ETDEWEB)

    Mikhnovich, V.V.

    2006-03-14

    The purpose of the present thesis consists in acquiring more concrete information concerning the mechanism of the movement of dislocations and types of defects that appear during the process of dislocation motion on the basis of systematic experimental studies of the GaAs deformation. Experimental studies concerning the dependence of the stress of the samples from their deformation at different values of the deformation parameters (like temperature and deformation speed) were conducted in this paper. To determine the concentration of defects introduced in samples during the deformation process the positron annihilation spectroscopy (PAS) method was used. The second chapter of this paper deals with models of movement of dislocations and origination of defects during deformation of the samples. In the third chapter channels and models of positron annihilation in the GaAs samples are investigated. In the forth chapter the used experimental methods, preparation procedure of test samples and technical data of conducted experiments are described. The fifth chapter shows the results of deformation experiments. The sixth chapter shows the results of positron lifetime measurements by the PAS method. In the seventh chapter one can find analyses of the values of defects concentration that were introduced in samples during deformation. (orig.)

  3. Origin of optical losses in gallium arsenide disk whispering gallery resonators

    CERN Document Server

    Parrain, David; Wang, Guillaume; Guha, Biswarup; Santos, Eduardo Gil; Lemaitre, Aristide; Senellart, Pascale; Leo, Giuseppe; Ducci, Sara; Favero, Ivan

    2015-01-01

    Whispering gallery modes in GaAs disk resonators reach half a million of optical quality factor. These high Qs remain still well below the ultimate design limit set by bending losses. Here we investigate the origin of residual optical dissipation in these devices. A Transmission Electron Microscope analysis is combined with an improved Volume Current Method to precisely quantify optical scattering losses by roughness and waviness of the structures, and gauge their importance relative to intrinsic material and radiation losses. The analysis also provides a qualitative description of the surface reconstruction layer, whose optical absorption is then revealed by comparing spectroscopy experiments in air and in different liquids. Other linear and nonlinear optical loss channels in the disks are evaluated likewise. Routes are given to further improve the performances of these miniature GaAs cavities.

  4. Indium arsenide as a material for biological applications: Assessment of surface modifications, toxicity, and biocompatibility

    Science.gov (United States)

    Jewett, Scott A.

    III-V semiconductors such as InAs have recently been employed in a variety of applications where the electronic and optical characteristics of traditional, silicon-based materials are inadequate. InAs has a narrow band gap and very high electron mobility in the near-surface region, which makes it very attractive for high performance transistors, optical applications, and chemical sensing. However, InAs forms an unstable surface oxide layer in ambient conditions, which can corrode over time and leach toxic indium and arsenic components. Current research has gone into making InAs more attractive for biological applications through passivation of the surface by adlayer adsorption. In particular, wet-chemical methods are current routes of exploration due to their simplicity, low cost, and flexibility in the type of passivating molecule. This dissertation focuses on surface modifications of InAs using wet-chemical methods in order to further its use in biological applications. First, the adsorption of collagen binding peptides and mixed peptide/thiol adlayers onto InAs was assessed. X-ray photoelectron spectroscopy (XPS) along with atomic force microscopy (AFM) data suggested that the peptides successfully adsorbed onto InAs, but were only able to block oxide regrowth to a relatively low extent. This low passivation ability is due to the lack of covalent bonds of the peptide to InAs, which are necessary to effectively block oxide regrowth. The addition of a thiol, in the form of mixed peptide/thiol adlayers greatly enhanced passivation of InAs while maintaining peptide presence on the surface. Thiols form tight, covalent bonds with InAs, which prevents oxide regrowth. The presence of the collagen-binding peptide on the surface opens the door to subsequent modification with collagen or polyelectrolyte-based adlayers. Next, the stability and toxicity of modified InAs substrates were determined using inductively coupled plasma mass spectrometry (ICP-MS) and zebrafish studies. InAs substrates modified with a poly(ethylene glycol) (PEG) based adlayer showed the highest stability in physiological conditions by leaching the lowest amounts of indium and arsenic. Modified substrates also showed no toxicity to zebrafish after incubation for 120 hours. Overall, these findings suggest that a variety of adlayers can be functionalized onto InAs surfaces and successfully passivate the surface, along with decreasing InAs toxicity. Finally, we demonstrate how surface modifications can be applied to a different III-V semiconductor, GaN, in order to modulate cellular adhesion. Modification of GaN with a laminin-derived peptide increases the adhesion of PC12 neuronal cells and alters the physical morphology of the adhered cells. Additionally, no toxicity to cells is observed, further demonstrating the potential for employing III-V semiconductors in biological applications.

  5. Dual-band technology on indium gallium arsenide focal plane arrays

    Science.gov (United States)

    Dixon, Peter; Hess, Cory D.; Li, Chuan; Ettenberg, Martin; Trezza, John

    2011-06-01

    While InGaAs-based SWIR imaging technology has been improved dramatically over the past 10 years, the motivation remains to reduce Size Weight and Power (SWaP) for applications in Intelligence Surveillance and Reconnaissance (ISR). Goodrich ISR Systems, Princeton (Sensors Unlimited, Inc.) has continued to improve detector sensitivity. Additionally, SUI is working jointly with DRS-RSTA to develop innovative techniques for manufacturing dual-band focal planes to provide next generation technology for not only reducing SWaP for SWIR imagers, but also to combine imaging solutions for providing a single imager for Visible Near-SWIR (VNS) + LW imaging solutions. Such developments are targeted at reducing system SWaP, cost and complexity for imaging payloads on board UASs as well as soldier deployed systems like weapon sights. Our motivation is to demonstrate capability in providing superior image quality in fused LWIR and SWIR imaging systems, while reducing the total system SWaP and cost by enabling Short Wave and Thermal imaging in a single uncooled imager. Under DARPA MTO awarded programs, a LW bolometer (DRS-RSTA) is fabricated on a Short Wave (SW) InGaAs Vis-SWIR (SUI-Goodrich) Imager. The combined imager is a dual-band Sensor-Chip Assembly which is capable of imaging in VIS-SWIR + LW. Both DRS and Goodrich have developed materials and process enhancements to support these dual-band platform investigations. The two imagers are confocal and coaxial with respect to the incident image plane. Initial work has completed a single Read Out Integrated Circuit (ROIC) capable of running both imagers. The team has hybridized InGaAs Focal planes to 6" full ROIC wafers to support bolometer fabrication onto the SW array.

  6. Superconductivity around quantum critical point in P-doped iron arsenides

    Energy Technology Data Exchange (ETDEWEB)

    Cao Guanghan, E-mail: ghcao@zju.edu.c [Department of Physics, Zhejiang University, Hangzhou 310027 (China); Jiang Shuai; Wang Cao; Li Yuke; Ren Zhi; Tao Qian; Dai Jianhui; Xu Zhuan [Department of Physics, Zhejiang University, Hangzhou 310027 (China)

    2010-12-15

    We demonstrate that, by the P/As substitution-without doping of charge carriers-in a FeAs-layer-based parent compound, superconductivity can be universally introduced. The maximum superconducting critical temperature (T{sub c}) of BaFe{sub 2}(As{sub 1-x}P{sub x}){sub 2} achieves 30 K. The P doping in LnFeAsO system (Ln = La and Sm) produces superconductivity below 11 K. The normal-state resistivity obeys linear temperature dependence and the normal-state Hall coefficient shows strong temperature dependence. These non-Fermi liquid behaviors suggest magnetic quantum criticality. The maximum T{sub c} values in different systems correlates strongly with the diagonal bondangle of Fe-As-Fe, implying the important role of the next-nearest-neighbor magnetic exchange coupling in iron pnictide superconductors.

  7. Gallium arsenide integrated circuits for professional broadband applications up to 3 GHz approximately

    Science.gov (United States)

    Weidlich, H.; Pettenpaul, E.; Petz, F. A.

    1983-03-01

    A GaAs-FET-technology for the manufacture of fast GaAs broadband IC's was developed with: local ion implantation for the channel and the contact region; Si3N4 cap for annealing and in process surface protection; gold based metallizations in a modified lift-off technique; and a second Si3N4 layer on top of the metallizations for safe enclosure of the active areas and as dielectric for metal insulator metal coupling capacitors. The gains with this technology approximate those of the silicon planar technology. An antenna amplifier with 20 dB gain from 40 to 1000 MHz and a noise figure of about 4 dB was tested in different modifications with integrated load transistors and with external load inductors. The stages are cascadable without matching, so higher gains are possible. An amplifier for measurement equipment with 2 GHz bandwidth and 16 dB gain was constructed with selected antenna amplifier samples using real load resistors. Monolithic integrated differential amplifier stages show gain factors of up to 35 dB with 22 MHz 3 dB-bandwidth suitable for a 2 stage operational amplifier with dB gain and 14 MHz bandwidth.

  8. Hot-Electron Degradation of Gallium Arsenide Metal-Semiconductor Field-Effect Transistors.

    Science.gov (United States)

    Tkachenko, Yevgeniy A.

    1995-01-01

    The physical mechanism of gradual degradation of GaAs MESFETs during RF overdrive is investigated in detail. A hot-electron effect was found responsible for this so-called "power slump" problem. Hot electrons produced by a large drain-gate voltage swing, tunnel from the MESFET channel and get trapped in SiN. These trapped electrons (i) increase surface depletion, hence reduce maximum channel current, transconductance and transistor gain, (ii) increase knee voltage through an increase in series channel resistance, (iii) relax gate-drain field distribution, thereby suppressing avalanche breakdown, (iv) decrease gate-drain capacitance, hence rm S_{22} under open-channel condition, and (v) increase surface leakage through trap hopping in SiN. The damage to SiN can only be partially recovered by deep UV illumination or 200^circrm C anneal. The evidence supports that trapping occurs in the bulk SiN, instead of at the GaAs/SiN interface. The possible chemical reaction responsible for this trap formation is breaking of the Si-H bond in SiN. An analytical theory of hot-electron effects, which combines hot-electron trapping with gate-drain breakdown and pinched-channel electro-luminescence, was developed and verified using experimental data and numerical simulations. Based on this theory, the rate of hot electron trapping was obtained and the threshold energy for trap formation was determined. The square-root time dependence given by the theory and the threshold energy of 1.9 eV were found consistent with gate current and electro-luminescence measurements. Numerical analysis was consistent with a trap density of the order of 5times10^{12}/rm cm^2 over a distance of approximately 0.1 murm m from the gate toward the drain, and it predicted the experimentally observed open-channel current reduction and gate-drain field relaxation. The spatial distribution of trapped electrons was directly observed by a novel high-voltage electron-beam-induced -current imaging technique. It confirmed the model's prediction. These results can be incorporated into large-signal transistor models for computer-aided circuit design. Such models would quantify trade-off between performance and reliability. An accelerated qualification procedure for the hot-electron-induced degradation trend is devised. This is based on the high-frequency waveform probing and high -sensitivity electro-luminescence measurements. Hot-electron-induced degradation was also found to take place in pseudomorphic high-electron-mobility transistors (PHEMT). The basic signatures of PHEMT degradation are similar to those of MESFETs, however some differences exist due to the structural differences between them. For PHEMT, in addition to SiN surface passivation, hot-electron traps may be formed in the AlGaAs layer under the gate. In addition, various temperature-activated degradation modes are more strongly coupled in the case of PHEMT, which requires analyzing them separately from the field-activated mode.

  9. Growth and characterization of epitaxial aluminum layers on gallium-arsenide substrates for superconducting quantum bits

    Science.gov (United States)

    Tournet, J.; Gosselink, D.; Miao, G.-X.; Jaikissoon, M.; Langenberg, D.; McConkey, T. G.; Mariantoni, M.; Wasilewski, Z. R.

    2016-06-01

    The quest for a universal quantum computer has renewed interest in the growth of superconducting materials on semiconductor substrates. High-quality superconducting thin films will make it possible to improve the coherence time of superconducting quantum bits (qubits), i.e., to extend the time a qubit can store the amplitude and phase of a quantum state. The electrical losses in superconducting qubits highly depend on the quality of the metal layers the qubits are made from. Here, we report on the epitaxy of single-crystal Al (011) layers on GaAs (001) substrates. Layers with 110 nm thickness were deposited by means of molecular beam epitaxy at low temperature and monitored by in situ reflection high-energy electron diffraction performed simultaneously at four azimuths. The single-crystal nature of the layers was confirmed by ex situ high-resolution x-ray diffraction. Differential interference contrast and atomic force microscopy analysis of the sample’s surface revealed a featureless surface with root mean square roughness of 0.55 nm. A detailed in situ study allowed us to gain insight into the nucleation mechanisms of Al layers on GaAs, highlighting the importance of GaAs surface reconstruction in determining the final Al layer crystallographic orientation and quality. A highly uniform and stable GaAs (001)-(2× 4) reconstruction reproducibly led to a pure Al (011) phase, while an arsenic-rich GaAs (001)-(4× 4) reconstruction yielded polycrystalline films with an Al (111) dominant orientation. The near-atomic smoothness and single-crystal character of Al films on GaAs, in combination with the ability to trench GaAs substrates, could set a new standard for the fabrication of superconducting qubits.

  10. Distribution of elastic strains appearing in gallium arsenide as a result of doping with isovalent impurities of phosphorus and indium

    Energy Technology Data Exchange (ETDEWEB)

    Pavlov, D. A. [Nizhni Novgorod Lobachevsky State University (Russian Federation); Bidus, N. V. [Nizhny Novgorod State University, Physicotechnical Research Institute (Russian Federation); Bobrov, A. I., E-mail: bobrov@phys.unn.ru [Nizhni Novgorod Lobachevsky State University (Russian Federation); Vikhrova, O. V. [Nizhny Novgorod State University, Physicotechnical Research Institute (Russian Federation); Volkova, E. I. [Nizhni Novgorod Lobachevsky State University (Russian Federation); Zvonkov, B. N. [Nizhny Novgorod State University, Physicotechnical Research Institute (Russian Federation); Malekhonova, N. V.; Sorokin, D. S. [Nizhni Novgorod Lobachevsky State University (Russian Federation)

    2015-01-15

    The distribution of elastic strains in a system consisting of a quantum-dot layer and a buried GaAs{sub x}P{sub 1−x} layer is studied using geometric phase analysis. A hypothesis is offered concerning the possibility of controlling the process of the formation of InAs quantum dots in a GaAs matrix using a local isovalent phosphorus impurity.

  11. 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.

  12. Boron, bismuth co-doping of gallium arsenide and other compounds for photonic and heterojunction bipolar transistor devices

    Science.gov (United States)

    Mascarenhas, Angelo

    2015-07-07

    Isoelectronic co-doping of semiconductor compounds and alloys with acceptors and deep donors is sued to decrease bandgap, to increase concentration of the dopant constituents in the resulting alloys, and to increase carrier mobilities lifetimes. For example, Group III-V compounds and alloys, such as GaAs and GaP, are isoelectronically co-doped with, for example, B and Bi, to customize solar cells, and other semiconductor devices. Isoelectronically co-doped Group II-VI compounds and alloys are also included.

  13. Development of a unique laboratory standard indium gallium arsenide detector for the 500 to 1700 micron spectral region, phase 2

    Science.gov (United States)

    Ban, Vladimir S.; Olsen, Gregory H.

    1990-01-01

    In the course of this work, 5 mm diameter InGaAs pin detectors were produced which met or exceeded all of the goals of the program. The best results achieved were: shunt resistance of over 300 K ohms; rise time of less than 300 ns; contact resistance of less than 20 ohms; quantum efficiency of over 50 percent in the 0.5 to 1.7 micron range; and devices were maintained and operated at 125 C without deterioration for over 100 hours. In order to achieve the goals of this program, several major technological advances were realized, among them: successful design, construction and operation of a hydride VPE reactor capable of growing epitaxial layers on 2 inch diameter InP substrates with a capacity of over 8 wafers per day; wafer processing was upgraded to handle 2 inch wafers; a double layer Si3N4/SiO2 antireflection coating which enhances response over the 0.5 to 1.7 micron range was developed; a method for anisotropic, precisely controlled CH4/H2 plasma etching for enhancement of response at short wavelengths was developed; and electronic and optical testing methods were developed to allow full characterization of detectors with size and spectral response characteristics. On the basis of the work and results achieved in this program, it is concluded that large size, high shunt resistance, high quantum efficiency InGaAs pin detectors are not only feasible but also manufacturable on industrial scale. This device spans a significant portion of visible and near infrared spectral range and it will allow a single detector to be used for the 0.5 to 1.7 micron spectral region, rather than the presently used silicon (for 0.5 to 1.1 microns) and germanium (0.8 to 1.7 microns).

  14. Superconductivity at 36 K in gadolinium-arsenide oxides GdO1-xFxFeAs

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    In this paper we report the fabrication and superconducting properties of GdO1-xFxFeAs. It was found that when x is equal to 0.17, GdO0.83F0.17FeAs is a su-perconductor with the onset transition temperature Tcon ≈ 36.6 K. Resistivity anomaly near 130 K was observed for all samples up to x = 0.17, and such a phenomenon is similar to that of LaO1-xFxFeAs. Hall coefficient indicates that GdO1-xFxFeAs is conducted by electron-like charge carriers.

  15. Ohmic contact formation process on low n-type gallium arsenide (GaAs) using indium gallium zinc oxide (IGZO)

    International Nuclear Information System (INIS)

    Highlights: • We propose a method to fabricate non-gold Ohmic contact on low n-type GaAs with IGZO. • 0.15 A/cm2 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/cm2 on-current density and 1.5 on/off-current ratio is achieved on n-type GaAs

  16. Low-noise gallium-arsenide field-effect transistor preamplifiers for stochastic beam-cooling systems

    International Nuclear Information System (INIS)

    The present noise performance, bandwidth capability and gain stability of bipolar and field-effect transistors, parametric amplifier, Schottky diode mixer and maser are summarized and compared in the 100 MHz to 40 GHz frequency range for stochastic beam cooling systems. Stability factor of GaAs FET's as a function of ambient temperature is presented and discussed. Performance data of several low-noise wide-band cryogenically cooled preamplifiers are presented including one with a noise figure of 0.35 dB over a bandwidth range of 150 to 500 MHz operating at ambient temperature of 200K. Also, data are given on a broadband 1 to 2 GHz preamplifier having a noise figure of approximately 0.2 dB. The gain, operating noise temperature, stability, gain nonuniformity and phase-shift as function of frequency of interest for beam cooling systems are discussed

  17. Metal-insulator transitions in two dimensions at zero magnetic field in a p-type gallium arsenide heterostructure

    Science.gov (United States)

    Dultz, Shane Cole

    Presented in this work is a comparative study of two different two dimensional systems in GaAs heterostructures. In the two dimensional hole system, electron-electron interactions are strong and possibly the reason for an anomolous temperature dependence in the resistivity that is reminiscent of metallic behavior which is known not to exist in a non-interacting two dimensional Fermi gas. The other system is an electron system where interactions are much weaker and whose properties have been understood in the context of Fermi liquid theory. In the first set of experiments, the delocalized states of the two dimensional hole system in a p-type GaAs heterostructure are tracked in density-magnetic field parameter space to find qualitatively very different behavior from what is found in the weakly interacting electron system. The lowest delocalized state which corresponds to the lowest Landau level in high magnetic fields, is found to float up in energy as the magnetic field is reduced to zero for the electron system. We found that there is an absence of this floating for the hole system and discuss this in the context of the recently discovered metal-insulator transition at B = 0. We further investigate the high temperature properties of the hole system by analyzing the resistivity to temperatures as high as 120 K to see how well the strongly interacting hole system fits what is expected from acoustic and optical phonon scattering. This is done over a wide range of densities and temperatures so that we could understand what sort of temperature dependence is truly considered anomolous in low temperatures. Finally, the compressibility of both systems is studied. An unequivocal signature for a phase transition is found in the compressibility measurements for the hole system with a temperature independent crossing point in the resistance of the gas occurring at the minimum of the inverse compressibility signal as a function of density (disorder). Differences in the way the compressibilities of the two systems go to zero at low densities is examined. The evolution of the compressibility in a magnetic field is studied in the hole system and compared to what one expects from transport measurements. The magnetic field studies show an evolution between the Hall insulator to quantum Hall liquid transition at high fields to the transition at B = 0 which is being called the metal to insulator transition.

  18. Synergic phototoxic effect of visible light or Gallium-Arsenide laser in the presence of different photo-sensitizers on Porphyromonas gingivalis and Fusobacterium nucleatum

    Directory of Open Access Journals (Sweden)

    Habibollah Ghanbari

    2015-01-01

    Conclusion: Within the limitations of this study, the synergic phototoxic effect of visible light in combination with each of the photosensitizers on P. gingivalis and F. nucleatum. However, the synergic phototoxic effect of laser exposure and hydrogen peroxide and curcumin as photosensitizers on F. nucleatum was not shown.

  19. Molecular beam epitaxy of gallium arsenide antimonide-based ultra-high-speed double heterojunction bipolar transistors and light emitting transistors

    Science.gov (United States)

    Wu, Bing-Ruey

    In this work, GaAsSb-based double heterojunction bipolar transistors (DHBTs) and light emitting transistors (LETs) are grown using gas source molecular beam epitaxy (GSMBE). High-speed GaAs0.5Sb0.5/InP DHBTs are developed through the exercise of GSMBE growth optimization, device fabrication, and characterization. By adjusting the growth temperature and V/III flux ratio, the optimal conditions for growing GaAs0.5Sb0.5 base are found to be at high growth temperature and low V/III ratio. The switching sequence is also optimized so that the Sb segregation effect is minimized. By using GaAs0.5Sb0.5-In0.2Ga0.8As 0.7Sb0.3 compositional grading in the base of the GaAsSb/InP DHBT, a significant improvement of fT from 380 GHz to 500 GHz was achieved compared to a uniform GaAs0.5Sb 0.5 DHBT, while maintaining a high breakdown voltage BVCEO ˜ 4V. The cutoff frequency---breakdown voltage product, fT·BVCEO, of over 2000 GHz-V, is the record value for DHBTs of any material system. Incorporating graded InAs-InGaAs emitter contact layer is also shown to effectively reduce the total emitter resistance, further improving the DHBT high speed performance. LET characteristics with quantum wells (QWs) inserted into the base region of GaAsSb/InP DHBTs are also investigated and the preliminary results are presented. An LET with a tensile strained InGaAsSb/GaAs0.65Sb 0.35 DQW in the base was designed and achieved the emission wavelength of ˜1.6 mum, despite of its low light output intensity. The potential and limitation of realizing a transistor laser with an emission wavelength of 1.55 mum using GaAsSb/InP material system will be discussed.

  20. Anisotropy of iron-platinum-arsenide Ca10(PtnAs8)(Fe2-xPtxAs2)5 single crystals

    Science.gov (United States)

    Yuan, F. F.; Sun, Y.; Zhou, W.; Zhou, X.; Ding, Q. P.; Iida, K.; Hühne, R.; Schultz, L.; Tamegai, T.; Shi, Z. X.

    2015-07-01

    The upper critical field Hc2 anisotropy of Ca10(PtnAs8)(Fe2-xPtxAs2)5 (n = 3, 4) single crystals with long FeAs interlayer distance (d) was studied by angular dependent resistivity measurements. A scaling of the angular dependent resistivity was realized for both single crystals using the anisotropic Ginzburg-Landau (AGL) approach with an appropriate anisotropy parameter γ. The AGL scaling parameter γ increases with decreasing temperature and reaches a value of about 10 at 0.8Tc for both single crystals. These values are much larger than those of other iron-based superconductors (FeSCs). Remarkably, the values of γ2 show an almost linear increase with the FeAs/FeSe interlayer distance d for FeSCs. Compared to cuprates, FeSCs are less anisotropic, indicating that two dimensionality of the superconductivity is intrinsically weak.

  1. Characterization of YBaCuO and ErBaCuO thin films deposited on silicon and gallium arsenide substrates

    International Nuclear Information System (INIS)

    YBaCuO and ErBaCuO films have been deposited on Si substrates with and without a ZrO/sub 2/ buffer layer and on GaAs substrates by RF diode sputtering from stoichiometric oxide targets. The films and interface between the films and semiconductor substrates are analyzed by Rutherford backscattering spectrometry (RBS), X-ray fluorescence spectroscopy (XRF), Auger electron spectroscopy (AES), energy dispersive X-ray spectrometry (EDAX), and scanning electron microscopy (SEM). The films grown on Si substrates with a ZrO/sub 2/ buffer layer show superconductivity above 65 K and no significant interaction at the interface is observed. High-T/sub c/ films can be obtained either by slow furnace annealing or by rapid heat-pulse annealing. No significant interaction is observed between YBaCuO (ErBaCuO) and GaAs after rapid thermal annealing at temperatures below 7500C

  2. Measurement and comparison of AC parameters of silicon (BSR and BSFR) and gallium arsenide (GaAs/Ge) solar cells used in space applications

    Energy Technology Data Exchange (ETDEWEB)

    Anil Kumar, R.; Suresh, M.S. [ISRO Satellite Centre, ISRO, Bangalore 560, 017 Kolhapur (India); Nagaraju, J. [Department of Instrumentation, Indian Institute of Science, Bangalore 560, 012 Kolhapur (India)

    2000-01-15

    The AC parameters of silicon (BSR and BSFR) solar cells and GaAs/Ge solar cell have been measured using impedance spectroscopy. Each cell capacitance, dynamic resistance and series resistance were measured and compared. GaAs/Ge solar cell has shown only the transition capacitance throughout its operating range while silicon (BSR and BSFR) solar cells exhibited both transition and diffusion capacitance. The theoretical and experimental values of dynamic resistance were compared and found in good agreement while the diode factor in silicon solar cells varies from 2 to 1, where as in GaAs/Ge solar cell it varies from 4 to 2 to 1.

  3. Estimation of various scattering parameters and 2-DEG mobilities from electron mobility calculations in the three conduction bands , L and X of gallium arsenide

    Indian Academy of Sciences (India)

    Sonal Singhal; A K Saxena; S Dasgupta

    2007-10-01

    The electron drift mobility in conduction band of GaAs has been calculated before, but for the first time, we have made attempts to estimate the electron mobilities in higher energy L and X minima. We have also calculated the value of mobility of two-dimensional electron gas needed to predict hetero-structure device characteristics using GaAs. Best scattering parameters have been derived by close comparison between experimental and theoretical mobilities. Room temperature electron mobilities in , L and X valleys are found to be nearly 9094, 945 and 247 cm2 /V-s respectively. For the above valleys, the electron masses, deformation potentials and polar phonon temperatures have been determined to be (0.067, 0.22, 0.39m 0 ), (8.5, 9.5, 6.5 eV), and (416, 382, 542 K) as best values, respectively. The 2-DEG electron mobility in minimum increases to 1.54 × 106 from 1.59 × 105 cm2 /V-s (for impurity concentration of 1014 cm-3) at 10 K. Similarly, the 2-DEG electron mobility values in L and X minima are estimated to be 2.28 × 105 and 1.44 × 105 cm2 /V-s at 10 K, which are about ∼ 4.5 and ∼ 3.9 times higher than normal value with impurity scattering present.

  4. Optical and transient capacitance study of EL2 in the absence and presence of other midgap levels. [in gallium arsenide crystals

    Science.gov (United States)

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

    1986-01-01

    A high-resolution optical study was carried out on GaAs crystals grown by horizontal Bridgman and liquid-encapsulated-Czochralski methods. An excellent correlation was found between the intensity of the 1.039-eV no-phonon line and the characteristic absorption of EL2, the major deep donor level in GaAs. A correlation was also found between the characteristic optical absorption of EL2 and its concentration as determined by junction capacitance measurements. The presence of EL0, another midgap level contained in heavily oxygen-doped crystals at concentration always less than those of EL2, had no effect on the optical spectra, but altered the capacitance measurements. Accordingly, an accurate calibration for the determination of EL2 by optical absorption was obtained from capacitance measurements on crystals containing only EL2; in this way the uncertainties introduced by other midgap levels were eliminated.

  5. Etch rates for (100) gallium arsenide using aqueous H2SO4:H2O2 and aqua regia based etchants

    International Nuclear Information System (INIS)

    Etch rate experiments were carried out for (100) GaAs using etching solutions of H2SO4 :H2O2 :H2 O (3:1:1, 3:1:15), HCl:HNO3 (3:1), HCl:HNO3 :H2 O (1:1:1) and HCl:HNO3 :glycerol (with various dilutions of glycerol). Several differences were seen for the (100) plane compared to previous results for other crystal orientations. The sulphuric acid solutions showed much lower activation energies for etching the (100) plane. The HCl:HNO3 :glycerol solutions showed considerably lower etch rates for the (100) plane, probably indicating that they etch GaAs anisotropically. For a 1:1:2 solution of HCl:HNO3 :glycerol a decrease in the etch rate of (100) GaAs was observed in the presence of stirring. This is the opposite result to what is commonly assumed for this polishing etchant. It indicates that the main polishing process attributed to this etchant is not present, and in fact, the polishing quality of the etchant is probably limited by the etching process which is present. 14 refs., 8 figs

  6. Inflammatory process decrease by gallium-aluminium-arsenide (GaAlAs) low intensity laser irradiation on postoperative extraction of impacted lower third molar

    International Nuclear Information System (INIS)

    This study aimed the observation of inflammatory process decrease by the use of GaAlAs Low Intensity Laser (λ=830 nm; 40 mW) irradiation. Five patients were selected and submitted to surgery of impacted lower third molars, both right and left sides at different occasions. On a first stage, a tooth of a random chosen side - right or left - was extracted by conventional surgery, without LILT. The inflammatory process was measured at postoperative on the first, third and seventh days. This side was then called 'control side'. After 21 days, period in which the inflammatory process of the first surgery was terminated, the other side surgery took place, this time using LILT (4 J at four spots) at postoperative, first and third days. As the previous surgery, the inflammatory process was also measured at postoperative on the first, third and seventh days. This side was called 'experimental or lased side'. The inflammatory process was evaluated by measuring its four characteristic signs: swelling, pain, color and temperature. It was clearly observed a decrease for swelling, pain and color on the lased side which presented significant inference and descriptive statistics. It can be concluded that GaAlAs Low Intensity Laser (λ=830 nm) can surely be used as an additional and important anti-inflammatory source on impacted lower third molar surgeries. (author)

  7. Magnetic and transport properties of iron-platinum arsenide Ca10(Pt4-δAs8)(Fe2-xPtxAs2)5 single crystal

    Science.gov (United States)

    Ding, Qing-Ping; Tsuchiya, Yuji; Mohan, Shyam; Taen, Toshihiro; Nakajima, Yasuyuki; Tamegai, Tsuyoshi

    2012-03-01

    We report superconducting properties of single crystalline Ca10(Pt4-δAs8)(Fe2-xPtxAs2)5 by x-ray diffraction, magnetization, resistivity, and magneto-optical imaging measurements. The magnetization measurements reveal a fish-tail hysteresis loop and relatively high critical current density Jc ˜ 0.8 × 105 A/cm2 at low temperatures. The exponential temperature dependence of Jc, which arises from the nonlinear effective flux-creep activation energy, has been observed. The upper critical field determined by resistive transition shows a relatively large anisotropy. The magneto-optical images reveal a homogenous current flow within the crystal.

  8. Thin films of gallium arsenide on low-cost substrates. Quarterly technical progress report No. 8 and topical report No. 3, April 2-July 1, 1978

    Energy Technology Data Exchange (ETDEWEB)

    Ruth, R.P.; Dapkus, P.D.; Dupuis, R.D.; Johnson, R.E.; Manasevit, H.M.; Moudy, L.A.; Yang, J.J.; Yingling, R.D.

    1978-07-01

    The seventh quarter of work on the contract is summarized. The metalorganic chemical vapor deposition (MO-CVD) technique has been applied to the growth of thin films of GaAs and GaAlAs on inexpensive polycrystalline or amorphous substrate materials (primarily glasses and metals) for use in fabrication of large-area low-cost photovoltaic device structures. Trimethylgallium (TMG), arsine (AsH/sub 3/), and trimethylaluminum (TMAl) are mixed in appropriate concentrations at room temperature in the gaseous state and pyrolyzed at the substrate, which is heated in a vertical reactor chamber to temperatures of 725 to 750/sup 0/C, to produce the desired film composition and properties. The technical activities during the quarter were concentrated on (1) a continuing evaluation of various graphite materials as possible substrates for MO-CVD growith of the polycrystalline GaAs solar cells; (2) attempts to improve the quality (especially the grain size) of polycrystalline GaAs films on Mo sheet and Mo/glass substrates by using HCl vapor during the MO-CVD growith process; (3) further studies of the transport properties of polycrystalline GaAs films, wth emphasis on n-type films; (4) continuing investigations of the properties of p-n junctions in polycrystalline GaAs, with emphasis on the formation and properties of p/sup +//n/n/sup +/ deposited structures; and (5) assembling apparatus and establishing a suitable technique for producing TiO/sub 2/ layers for use as AR coatings on GaAs cells. Progress is reported. (WHK)

  9. Inelastic Neutron Scattering Study of a Nonmagnetic Collapsed Tetragonal Phase in Nonsuperconducting CaFe2As2: Evidence of the Impact of Spin Fluctuations on Superconductivity in the Iron-Arsenide Compounds

    Science.gov (United States)

    Soh, J. H.; Tucker, G. S.; Pratt, D. K.; Abernathy, D. L.; Stone, M. B.; Ran, S.; Bud'ko, S. L.; Canfield, P. C.; Kreyssig, A.; McQueeney, R. J.; Goldman, A. I.

    2013-11-01

    The relationship between antiferromagnetic spin fluctuations and superconductivity has become a central topic of research in studies of superconductivity in the iron pnictides. We present unambiguous evidence of the absence of magnetic fluctuations in the nonsuperconducting collapsed tetragonal phase of CaFe2As2 via inelastic neutron scattering time-of-flight data, which is consistent with the view that spin fluctuations are a necessary ingredient for unconventional superconductivity in the iron pnictides. We demonstrate that the collapsed tetragonal phase of CaFe2As2 is nonmagnetic, and discuss this result in light of recent reports of high-temperature superconductivity in the collapsed tetragonal phase of closely related compounds.

  10. Investigation of the current break-down phenomena in solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, S.K.; Srinivasamurthy, N.; Agrawal, B.L. [Power Systems Group, ISRO Satellite Centre, Bangalore (India)

    1996-08-15

    Observed reverse current-voltage characteristics of the single crystal silicon and gallium arsenide solar cells have been analyzed. Physical mechanisms behind the junction break-down in silicon cells and current break-down in gallium arsenide cells have been identified. Preliminary estimates of the diffusion capacitance in GaAs cells have been presented

  11. NREL preprints for the 23rd IEEE Photovoltaic Specialists Conference

    Energy Technology Data Exchange (ETDEWEB)

    Fitzgerald, M. [ed.

    1993-05-01

    Topics covered include various aspects of solar cell fabrication and performance. Aluminium-gallium arsenides, cadmium telluride, amorphous silicon, and copper-indium-gallium selenides are all characterized in their applicability in solar cells.

  12. Activities of the Solid State Physics Research Institute

    Science.gov (United States)

    1985-01-01

    Topics addressed include: muon spin rotation; annealing problems in gallium arsenides; Hall effect in semiconductors; computerized simulation of radiation damage; single-nucleon removal from Mg-24; and He-3 reaction at 200 and 400 MeV.

  13. Highly strained InAs quantum wells on InP substrates for mid-IR emission

    Science.gov (United States)

    Kim, Sangho; Kirch, Jeremy; Mawst, Luke

    2010-04-01

    Optical emission characteristics of indium arsenide (InAs) quantum wells were studied using organometallic vapor phase epitaxy (OMVPE). Low growth temperature (DQW) in a separate confinement hetero-structure (SCH) structure.

  14. Pulse transformer for GaAs laser

    Science.gov (United States)

    Rutz, E. M.

    1976-01-01

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

  15. NASA-OAST photovoltaic energy conversion program

    Science.gov (United States)

    Mullin, J. P.; Loria, J. C.

    1984-01-01

    The NASA program in photovoltaic energy conversion research is discussed. Solar cells, solar arrays, gallium arsenides, space station and spacecraft power supplies, and state of the art devices are discussed.

  16. POLLUTION PREVENTION IN THE SEMICONDUCTOR INDUSTRY THROUGH RECOVERY AND RECYCLING OF GALLIUM AND ARSENIC FROM GAAS POLISHING WASTES

    Science.gov (United States)

    A process was developed for the recovery of both arsenic and gallium from gallium arsenide polishing wastes. The economics associated with the current disposal techniques utilizing ferric hydroxide precipitation dictate that sequential recovery of toxic arsenic and valuble galliu...

  17. Performance of a Double Gate Nanoscale MOSFET (DG-MOSFET) Based on Novel Channel Materials

    OpenAIRE

    Rakesh Prasher; Devi Dass; Rakesh Vaid

    2013-01-01

    In this paper, we have studied a double gate nanoscale MOSFET for various channel materials using simulation approach. The device metrics considered at the nanometer scale are subthreshold swing (SS), drain induced barrier lowering (DIBL), on and off current, carrier injection velocity (vinj), etc. The channel materials studied are Silicon (Si), Germanium (Ge), Gallium Arsenide (GaAs), Zinc Oxide (ZnO), Zinc Sulfide (ZnS), Indium Arsenide (InAs), Indium Phosphide (InP) and Indium Antimonide (...

  18. Inflammatory process decrease by gallium-aluminium-arsenide (GaAlAs) low intensity laser irradiation on postoperative extraction of impacted lower third molar; Reducao de processo inflamatorio com aplicacao de laser de arseneto de galio aluminio ({lambda}=830 nm) em pos-operatorio de exodontia de terceiros molares inferiores inclusos ou semi-inclusos

    Energy Technology Data Exchange (ETDEWEB)

    Atihe, Mauricio Martins

    2002-07-01

    This study aimed the observation of inflammatory process decrease by the use of GaAlAs Low Intensity Laser ({lambda}=830 nm; 40 mW) irradiation. Five patients were selected and submitted to surgery of impacted lower third molars, both right and left sides at different occasions. On a first stage, a tooth of a random chosen side - right or left - was extracted by conventional surgery, without LILT. The inflammatory process was measured at postoperative on the first, third and seventh days. This side was then called 'control side'. After 21 days, period in which the inflammatory process of the first surgery was terminated, the other side surgery took place, this time using LILT (4 J at four spots) at postoperative, first and third days. As the previous surgery, the inflammatory process was also measured at postoperative on the first, third and seventh days. This side was called 'experimental or lased side'. The inflammatory process was evaluated by measuring its four characteristic signs: swelling, pain, color and temperature. It was clearly observed a decrease for swelling, pain and color on the lased side which presented significant inference and descriptive statistics. It can be concluded that GaAlAs Low Intensity Laser ({lambda}=830 nm) can surely be used as an additional and important anti-inflammatory source on impacted lower third molar surgeries. (author)

  19. Semiconducting III-V compounds

    CERN Document Server

    Hilsum, C; Henisch, Heinz R

    1961-01-01

    Semiconducting III-V Compounds deals with the properties of III-V compounds as a family of semiconducting crystals and relates these compounds to the monatomic semiconductors silicon and germanium. Emphasis is placed on physical processes that are peculiar to III-V compounds, particularly those that combine boron, aluminum, gallium, and indium with phosphorus, arsenic, and antimony (for example, indium antimonide, indium arsenide, gallium antimonide, and gallium arsenide).Comprised of eight chapters, this book begins with an assessment of the crystal structure and binding of III-V compounds, f

  20. Film germanium strain gauges for cryogenic temperatures

    International Nuclear Information System (INIS)

    Strain-measuring characteristics of strain gauges (SG) based on germanium films on gallium arsenide designed for operation in 4-100 K temperature interval and strain range ε∼(±0.3%) are presented. SG are characterized by weak temperature dependences of resistance and strain sensitivity in the temperature range measured. It is shown that in the low-temperature region SG based on heteroepitaxial germanium films on gallium arsenide are no worse than the best domestic and foreign semiconducting and metal SG and are perspective for cryogenic object diagnostics under magnetic field effect

  1. Observation of the Spin Hall Effect in Semiconductors

    Science.gov (United States)

    Kato, Y. K.; Myers, R. C.; Gossard, A. C.; Awschalom, D. D.

    2004-12-01

    Electrically induced electron-spin polarization near the edges of a semiconductor channel was detected and imaged with the use of Kerr rotation microscopy. The polarization is out-of-plane and has opposite sign for the two edges, consistent with the predictions of the spin Hall effect. Measurements of unstrained gallium arsenide and strained indium gallium arsenide samples reveal that strain modifies spin accumulation at zero magnetic field. A weak dependence on crystal orientation for the strained samples suggests that the mechanism is the extrinsic spin Hall effect.

  2. Preliminary materials assessment for the Satellite Power System (SPS)

    Energy Technology Data Exchange (ETDEWEB)

    Teeter, R.R.; Jamieson, W.M.

    1980-01-01

    Presently, there are two SPS reference design concepts (one using silicon solar cells; the other using gallium arsenide solar cells). A materials assessment of both systems was performed based on the materials lists set forth in the DOE/NASA SPS Reference System Report: Concept Development and Evaluation Program. This listing identified 22 materials (plus miscellaneous and organics) used in the SPS. Tracing the production processes for these 22 materials, a total demand for over 20 different bulk materials (copper, silicon, sulfuric acid, etc.) and nealy 30 raw materials (copper ore, sand, sulfur ore, etc.) was revealed. Assessment of these SPS material requirements produced a number of potential material supply problems. The more serious problems are those associated with the solar cell materials (gallium, gallium arsenide, sapphire, and solar grade silicon), and the graphite fiber required for the satellite structure and space construction facilities. In general, the gallium arsenide SPS option exhibits more serious problems than the silicon option, possibly because gallium arsenide technology is not as well developed as that for silicon. Results are presented and discussed in detail. (WHK)

  3. IMPATT diodes. Citations from the NTIS data base

    Science.gov (United States)

    Reed, W. E.

    1980-04-01

    Government sponsored research reports are cited covering the design, characterization, and applications of IMPATT diodes. Topics include reliability, power handling, properties, noise, fabrication, and radiation effects. The use of silicon and gallium arsenide IMPATT diodes for microwave generation and amplification is included. This updated bibliography contains 182 abstracts, 14 of which are new entries to the previous edition.

  4. Advanced infrared photomultiplier

    Science.gov (United States)

    Sonnenberg, H.; Taynal, J. D.

    1972-01-01

    Photocathode for the 8500 angstrom through 9000 angstrom range, improving efficiency by an order of magnitude, is achieved with a gallium arsenide cesium oxide photocathode. Protection of the GaAs surface from contamination during bake-out is another important function.

  5. Low temperature transport in p-doped InAs nanowires

    DEFF Research Database (Denmark)

    Upadhyay, Shivendra; Jespersen, Thomas Sand; Madsen, Morten Hannibal;

    2013-01-01

    We present low temperature electrical measurements of p-type Indium Arsenide nanowires grown via molecular beam epitaxy using Beryllium as a dopant. Growth of p-type wires without stacking faults is demonstrated. Devices in field-effect geometries exhibit ambipolar behavior, and the temperature...

  6. Efficient frequency comb generation in AlGaAs-on-insulator

    DEFF Research Database (Denmark)

    Pu, Minhao; Ottaviano, Luisa; Semenova, Elizaveta;

    2016-01-01

    The combination of nonlinear and integrated photonics enables Kerr frequency comb generation in stable chip-based microresonators. Such a comb system will revolutionize applications, including multi-wavelength lasers, metrology, and spectroscopy. Aluminum gallium arsenide (AlGaAs) exhibits very h...

  7. Scratch encourages selective doping

    Science.gov (United States)

    Hawrylo, F. Z.; Kressel, H.

    1980-01-01

    Dislocations induced by scratching produce deep narrow spikes of zinc diffused in gallium arsenide. Density of defects formed locally increases zinc diffusion coefficient. Enhancements by factor of 6 have been observed. Technique works for other dopants than zinc and for other semiconductors besides GaAs.

  8. Satellite Power System Concept Development and Evaluation Program, Critical Supporting Investigations. Summary

    Science.gov (United States)

    Seyl, J. W.

    1980-01-01

    Investigations in critical technology of the solar power satellite (SPS) concept development program are summarized. Studies of the potential application of fiber optics transmission links across the SPS one kilometer antenna and evaluation of gallium arsenide field effect transistors and their associated power amplifier circuitry are discussed in more detail.

  9. Suitability of integrated protection diodes from diverse semiconductor technologies

    NARCIS (Netherlands)

    Wanum, M. van; Lebouille, T.T.N.; Visser, G.C.; Vliet, F.E. van

    2009-01-01

    In this article diodes from three different semiconductor technologies are compared based on their suitability to protect a receiver. The semiconductor materials involved are Silicon, Gallium Arsenide and Gallium Nitride. The diodes in the diverse semiconductor technologies themselves are close in p

  10. Simple intrinsic defects in InAs :

    Energy Technology Data Exchange (ETDEWEB)

    Schultz, Peter Andrew

    2013-03-01

    This Report presents numerical tables summarizing properties of intrinsic defects in indium arsenide, InAs, as computed by density functional theory using semi-local density functionals, intended for use as reference tables for a defect physics package in device models.

  11. Modeling of High Efficiency Solar Cells Under Laser Pulse for Power Beaming Applications

    Science.gov (United States)

    Jain, Raj K.; Landis, Geoffrey A.

    1994-01-01

    Solar cells may be used as receivers for laser power beaming. To understand the behavior of solar cells when illuminated by a pulsed laser, the time response of gallium arsenide and silicon solar cells to pulsed monochromatic input has been modeled using a finite element solar cell model.

  12. Heat load of a GaAs photocathode in an SRF electron gun

    Institute of Scientific and Technical Information of China (English)

    王尔东; 赵夔; JSrg Kewisch; Ilan Ben-Zvi; Andrew Burrill; Trivini Rao; 吴琼; Animesh Jain; Ramesh Gupta; Doug Holmes

    2011-01-01

    A great deal of effort has been made over the last decades to develop a better polarized electron source for high energy physics. Several laboratories operate DC guns with a gallium arsenide photocathode, which yield a highly polarized electron beam. Howe

  13. InP solar cell with window layer

    Science.gov (United States)

    Jain, Raj K. (Inventor); Landis, Geoffrey A. (Inventor)

    1994-01-01

    The invention features a thin light transmissive layer of the ternary semiconductor indium aluminum arsenide (InAlAs) as a front surface passivation or 'window' layer for p-on-n InP solar cells. The window layers of the invention effectively reduce front surface recombination of the object semiconductors thereby increasing the efficiency of the cells.

  14. Fast Clock Recovery for Digital Communications

    Science.gov (United States)

    Tell, R. G.

    1985-01-01

    Circuit extracts clock signal from random non-return-to-zero data stream, locking onto clock within one bit period at 1-gigabitper-second data rate. Circuit used for synchronization in opticalfiber communications. Derives speed from very short response time of gallium arsenide metal/semiconductor field-effect transistors (MESFET's).

  15. High-temperature optically activated GaAs power switching for aircraft digital electronic control

    Science.gov (United States)

    Berak, J. M.; Grantham, D. H.; Swindal, J. L.; Black, J. F.; Allen, L. B.

    1983-01-01

    Gallium arsenide high-temperature devices were fabricated and assembled into an optically activated pulse-width-modulated power control for a torque motor typical of the kinds used in jet engine actuators. A bipolar heterojunction phototransistor with gallium aluminum arsenide emitter/window, a gallium arsenide junction field-effect power transistor and a gallium arsenide transient protection diode were designed and fabricated. A high-temperature fiber optic/phototransistor coupling scheme was implemented. The devices assembled into the demonstrator were successfully tested at 250 C, proving the feasibility of actuator-located switching of control power using optical signals transmitted by fibers. Assessments of the efficiency and technical merits were made for extension of this high-temperature technology to local conversion of optical power to electrical power and its control at levels useful for driving actuators. Optical power sources included in the comparisons were an infrared light-emitting diode, an injection laser diode, tungsten-halogen lamps and arc lamps. Optical-to-electrical power conversion was limited to photovoltaics located at the actuator. Impedance matching of the photovoltaic array to the load was considered over the full temperature range, -55 C to 260 C. Loss of photovoltaic efficiency at higher temperatures was taken into account. Serious losses in efficiency are: (1) in the optical source and the cooling which they may require in the assumed 125 C ambient, (2) in the decreased conversion efficiency of the gallium arsenide photovoltaic at 260 C, and (3) in impedance matching. Practical systems require improvements in these areas.

  16. Development of electrochemical photovoltaic cells. Third technical progress report, November 1, 1979-January 31, 1980

    Energy Technology Data Exchange (ETDEWEB)

    Byker, H.J.; Schwerzel, R.E.; Wood, V.E.; Austin, A.E.; Brooman, E.W.

    1980-03-07

    The development of stable, efficient, electrochemical photovoltaic cells based on silicon and gallium arsenide in non-aqueous electrolyte systems is being investigated. The effect of surface condition of silicon electrodes on electrochemical and physical characteristics has been studied. An electrode-supporting electrolyte interaction in acetonitrile has been identified which leads to etching of the surface. Improved performance can result, which has practical significance. Gallium arsenide electrodes have been electrochemically characterized in cells containing propylene carbonate with a ferrocene/ferricenium redox additive. Degradation of the ferricenium salt under illumination has been investigated. Other redox couples studied to date have not given promising results. Long-term stability experiments have been deferred while a better understanding of electrode behavior is being obtained.

  17. Electron correlations in Mn(x)Ga(1-x)A(s)as seen by resonant electron spectroscopy and dynamical mean field theory.

    Science.gov (United States)

    Di Marco, I; Thunström, P; Katsnelson, M I; Sadowski, J; Karlsson, K; Lebègue, S; Kanski, J; Eriksson, O

    2013-01-01

    After two decades since the discovery of ferromagnetism in manganese-doped gallium arsenide, its origin is still debated, and many doubts are related to the electronic structure. Here we report an experimental and theoretical study of the valence electron spectrum of manganese-doped gallium arsenide. The experimental data are obtained through the differences between off- and on-resonance photo emission data. The theoretical spectrum is calculated by means of a combination of density-functional theory in the local density approximation and dynamical mean field theory, using exact diagonalization as impurity solver. Theory is found to accurately reproduce measured data and illustrates the importance of correlation effects. Our results demonstrate that the manganese states extend over a broad range of energy, including the top of the valence band, and that no impurity band splits-off from the valence band edge, whereas the induced holes seem located primarily around the manganese impurity.

  18. Multi-spectral optical absorption in substrate-free nanowire arrays

    International Nuclear Information System (INIS)

    A method is presented of fabricating gallium arsenide (GaAs) nanowire arrays of controlled diameter and period by reactive ion etching of a GaAs substrate containing an indium gallium arsenide (InGaP) etch stop layer, allowing the precise nanowire length to be controlled. The substrate is subsequently removed by selective etching, using the same InGaP etch stop layer, to create a substrate-free GaAs nanowire array. The optical absorptance of the nanowire array was then directly measured without absorption from a substrate. We directly observe absorptance spectra that can be tuned by the nanowire diameter, as explained with rigorous coupled wave analysis. These results illustrate strong optical absorption suitable for nanowire-based solar cells and multi-spectral absorption for wavelength discriminating photodetectors. The solar-weighted absorptance above the bandgap of GaAs was 94% for a nanowire surface coverage of only 15%.

  19. Structural and magnetic phase transitions in triclinic Ca10(FeAs)10(Pt3As8).

    Science.gov (United States)

    Stürzer, T; Friederichs, G M; Luetkens, H; Amato, A; Klauss, H-H; Johrendt, Dirk

    2013-03-27

    We report the structural and magnetic phase transitions of triclinic Ca10(FeAs)10(Pt3As8), which is the parent compound of the 1038-type iron-arsenide superconductors. High-resolution x-ray diffraction reveals splitting of the in-plane (a,b) lattice parameters at T(s) ≈ 120 K. Platinum-doping weakens the distortion and shifts the transition temperature to 80 K in Ca10(Fe(1-x)Pt(x)As)10(Pt3As8) with x = 0.03. μSR experiments show the onset of magnetic order near T and a broad magnetic phase transition. The structural transition involves no reduction of the space group symmetry in contrast to the other parent compounds of iron-arsenide superconductors; nevertheless the local fourfold symmetry of the FeAs-layers in Ca10(FeAs)10(Pt3As8) is broken.

  20. Magnetic and Ising quantum phase transitions in a model for isoelectronically tuned iron pnictides

    Science.gov (United States)

    Wu, Jianda; Si, Qimiao; Abrahams, Elihu

    2016-03-01

    Considerations of the observed bad-metal behavior in Fe-based superconductors led to an early proposal for quantum criticality induced by isoelectronic P for As doping in iron arsenides, which has since been experimentally confirmed. We study here an effective model for the isoelectronically tuned pnictides using a large-N approach. The model contains antiferromagnetic and Ising-nematic order parameters appropriate for J1-J2 exchange-coupled local moments on an Fe square lattice, and a damping caused by coupling to itinerant electrons. The zero-temperature magnetic and Ising transitions are concurrent and essentially continuous. The order-parameter jumps are very small, and are further reduced by the interplane coupling; consequently, quantum criticality occurs over a wide dynamical range. Our results reconcile recent seemingly contradictory experimental observations concerning the quantum phase transition in the P-doped iron arsenides.

  1. Coherent Cancellation of Photothermal Noise in GaAs/Al$_{0.92}$Ga$_{0.08}$As Bragg Mirrors

    CERN Document Server

    Chalermsongsak, Tara; Cole, Garrett D; Follman, David; Seifert, Frank; Arai, Koji; Gustafson, Eric K; Smith, Joshua R; Aspelmeyer, Markus; Adhikari, Rana X

    2015-01-01

    Thermal noise is a limiting factor in many high-precision optical experiments. A search is underway for novel optical materials with reduced thermal noise. One such pair of materials, gallium arsenide and aluminum-alloyed gallium arsenide (collectively referred to as AlGaAs), shows promise for its low Brownian noise when compared to conventional materials such as silica and tantala. However, AlGaAs has the potential to produce a high level of thermo-optic noise. We have fabricated a set of AlGaAs crystalline coatings, transferred to fused silica substrates, whose layer structure has been optimized to reduce thermo-optic noise by inducing coherent cancellation of the thermoelastic and thermorefractive effects. By measuring the photothermal transfer function of these mirrors, we find evidence that this optimization has been successful.

  2. Performance measurement of low concentration ratio solar array for space application

    Science.gov (United States)

    Mills, M. W.

    1984-01-01

    The measured performance of a silicon and a gallium arsenide low concentration ratio solar array (LCRSA) element is presented. The element characteristics measured in natural sunlight are off pointing performance and response to mechanical distortions. Laboratory measurements of individual silicon and gallium-arsenide solar cell assemblies are also made. The characteristics measured in the laboratory involved responses to temperature and intensity variations as well as to the application of reverse bias potentials. The element design details covered include the materials, the solar cells, and the rationale for selecting these specific characteristics. The measured performance characteristics are contrasted with the predicted values for both laboratory testing and high altitude natural sunlight testing. Excellent agreement between analytical predictions and measured performance is observed.

  3. Modelling and fabrication of GaAs photonic-crystal cavities for cavity quantum electrodynamics.

    Science.gov (United States)

    Khankhoje, U K; Kim, S-H; Richards, B C; Hendrickson, J; Sweet, J; Olitzky, J D; Khitrova, G; Gibbs, H M; Scherer, A

    2010-02-10

    In this paper, we present recent progress in the growth, modelling, fabrication and characterization of gallium arsenide (GaAs) two-dimensional (2D) photonic-crystal slab cavities with embedded indium arsenide (InAs) quantum dots (QDs) that are designed for cavity quantum electrodynamics (cQED) experiments. Photonic-crystal modelling and device fabrication are discussed, followed by a detailed discussion of different failure modes that lead to photon loss. It is found that, along with errors introduced during fabrication, other significant factors such as the presence of a bottom substrate and cavity axis orientation with respect to the crystal axis, can influence the cavity quality factor (Q). A useful diagnostic tool in the form of contour finite-difference time domain (FDTD) is employed to analyse device performance.

  4. Direct imaging of the structural domains in the iron pnictides AFe2As2 (A=Ca, Sr, Ba)

    International Nuclear Information System (INIS)

    The parent compounds of recently discovered iron-arsenide superconductors, AFe2As2 with alkaline earth A=Ca,Sr,Ba, undergo simultaneous structural and magnetic phase transitions at a temperature TSM. Using a combination of polarized light microscopy and spatially resolved high-energy synchrotron x-ray diffraction we show that the orthorhombic distortion leads to the formation of 45o-type structural domains in all parent compounds. Domains penetrate through the sample thickness in the c direction and are not affected by crystal imperfections such as growth terraces. The domains form regular stripe patterns in the plane with a characteristic dimension of 10--50 μm. The direction of the stripes is fixed with respect to the tetragonal (100) and (010) directions but can change by 90o on thermal cycling through the transition. This domain pattern may have profound implications for intrinsic disorder and anisotropy of iron arsenides.

  5. Solar-Electrochemical Power System for a Mars Mission

    Science.gov (United States)

    Withrow, Colleen A.; Morales, Nelson

    1994-01-01

    This report documents a sizing study of a variety of solar electrochemical power systems for the intercenter NASA study known as 'Mars Exploration Reference Mission'. Power systems are characterized for a variety of rovers, habitation modules, and space transport vehicles based on requirements derived from the reference mission. The mission features a six-person crew living on Mars for 500 days. Mission power requirements range from 4 kWe to 120 kWe. Primary hydrogen and oxygen fuel cells, regenerative hydrogen and oxygen fuel cells, sodium sulfur batteries advanced photovoltaic solar arrays of gallium arsenide on germanium with tracking and nontracking mechanisms, and tent solar arrays of gallium arsenide on germanium are evaluated and compared.

  6. Pseudogap and its critical point in the heavily doped Ba(Fe1-xCox)2As2 from c -axis resistivity measurements

    Science.gov (United States)

    Tanatar, M. A.; Ni, N.; Thaler, A.; Bud'Ko, S. L.; Canfield, P. C.; Prozorov, R.

    2010-10-01

    Temperature-dependent interplane resistivity, ρc(T) , was used to characterize the normal state of the iron-arsenide superconductor Ba(Fe1-xCox)2As2 over a broad doping range 0≤xTCG , vanishes at xCG≃0.30 , paving the way to metallic, T linear, ρc(T) close to xCG and superlinear T dependence for x>xCG . None of these features are evident in the in-plane resistivity ρa(T) . For doping levels xxCG . These features are consistent with the existence of a charge gap, accompanying formation of the magnetic pseudogap, and its critical suppression with doping. The inferred c -axis charge gap reflects the three-dimensional character of the electronic structure and of the magnetism in the iron arsenides.

  7. Transient Processes in the GaAs-Based Microwave-PIN-Diodes

    Science.gov (United States)

    Ayzenshtat, G. I.; Yushchenko, A. Yu.; Bozhkov, V. G.

    2015-04-01

    The results of studies of transient characteristics of microwave-pin-diodes based on gallium arsenide are presented. It is shown that in these diodes, a transient process occurs in two stages resulting in a complicated pulse shape during the diode switching. The dependences of the effective lifetime on the diode radius and forward current value are measured. It is experimentally established that the effective lifetime in the diodes depends on the radius of the active region.

  8. Laser therapy in the treatment of nonspecific lung diseases in children.

    OpenAIRE

    Lola Muhamadieva

    2010-01-01

    Endobronchial laser therapy was used in children with nonspecific lung diseases. Effectiveness of laser therapy was evaluated by use of cytogram of bronchoalveolar lavage fluid (BALF). There was observation of 29 children with nonspecific lung diseases: they had been performed endobronchial laser therapy with use of gallium arsenide laser. This investigation has proved the effectiveness of laser therapy, and the method is recommended for treatment of nonspecific lung diseases in children.

  9. Thin film solar cells. (Latest citations from the NTIS bibliographic database). Published Search

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1997-11-01

    The bibliography contains citations concerning research and development of high-efficiency and low-cost thin film solar cells. References discuss the design and fabrication of silicon, gallium arsenide, copper selenide, indium selenide, cadmium telluride, and copper indium selenide solar cells. Applications in space and utilities are examined. Government projects and foreign technology are also reviewed. (Contains 50-250 citations and includes a subject term index and title list.) (Copyright NERAC, Inc. 1995)

  10. Experimental '' of As at 170, 200, 250 and 300 K from the Bijvoet pairs of GaAs

    Indian Academy of Sciences (India)

    G Raja Sudha; K Vimala Devi; D Arthi; S Prasanna Subramanian; N Srinivasan; R Saravanan

    2002-08-01

    Anomalous dispersion effects lead to the modification of the measured X-ray structure factors. In this work, we have determined the imaginary part of the anomalous dispersion correction terms ('' ) of arsenide atom (As), through the X-ray data collected using spherical single crystal of GaAs, at various temperatures, i.e. 170, 200, 250 and 300 K. It is stressed that more measurements of '' of the elements are needed to confirm the theoretical calculations.

  11. Determination of the effective mechanism of chemically stimulated diffusion in semiconductors at their interaction with an atomic hydrogen

    International Nuclear Information System (INIS)

    Paper is devoted to calculate coefficients of chemically stimulated diffusion (CSD) of some impurities in near-the-surface layers of germanium and gallium arsenide following well-known mechanisms to determine governing mechanism of CSD depending on type of diffusing impurity and conditions to carry out experiment. Calculation results of CSD coefficients following the mentioned mechanisms for copper in germanium showed that their efficiency was rather unimpressive in contrast to CSD mechanisms associated with energy transfer to crystal atomic subsystem

  12. Small Business Innovations (Photodetector)

    Science.gov (United States)

    1991-01-01

    Epitaxx, Inc. of Princeton, NJ, developed the Epitaxx Near Infrared Room Temperature Indium-Gallium-Arsenide (InGaAs) Photodetector based on their Goddard Space Flight Center Small Business Innovation Research (SBIR) contract work to develop a linear detector array for satellite imaging applications using InGaAs alloys that didn't need to be cooled to (difficult and expensive) cryogenic temperatures. The photodetectors can be used for remote sensing, fiber optic and laser position-sensing applications.

  13. Textural, mineralogical and stable isotope studies of hydrothermal alteration in the main sulfide zone of the Great Dyke, Zimbabwe and the precious metals zone of the Sonju Lake Intrusion, Minnesota, USA

    Science.gov (United States)

    Li, C.; Ripley, E.M.; Oberthur, T.; Miller, J.D., Jr.; Joslin, G.D.

    2008-01-01

    Stratigraphic offsets in the peak concentrations of platinum-group elements (PGE) and base-metal sulfides in the main sulfide zone of the Great Dyke and the precious metals zone of the Sonju Lake Intrusion have, in part, been attributed to the interaction between magmatic PGE-bearing base-metal sulfide assemblages and hydrothermal fluids. In this paper, we provide mineralogical and textural evidence that indicates alteration of base-metal sulfides and mobilization of metals and S during hydrothermal alteration in both mineralized intrusions. Stable isotopic data suggest that the fluids involved in the alteration were of magmatic origin in the Great Dyke but that a meteoric water component was involved in the alteration of the Sonju Lake Intrusion. The strong spatial association of platinum-group minerals, principally Pt and Pd sulfides, arsenides, and tellurides, with base-metal sulfide assemblages in the main sulfide zone of the Great Dyke is consistent with residual enrichment of Pt and Pd during hydrothermal alteration. However, such an interpretation is more tenuous for the precious metals zone of the Sonju Lake Intrusion where important Pt and Pd arsenides and antimonides occur as inclusions within individual plagioclase crystals and within alteration assemblages that are free of base-metal sulfides. Our observations suggest that Pt and Pd tellurides, antimonides, and arsenides may form during both magmatic crystallization and subsolidus hydrothermal alteration. Experimental studies of magmatic crystallization and hydrothermal transport/deposition in systems involving arsenides, tellurides, antimonides, and base metal sulfides are needed to better understand the relative importance of magmatic and hydrothermal processes in controlling the distribution of PGE in mineralized layered intrusions of this type. ?? Springer-Verlag 2007.

  14. Anisotropic magnetocapacitance in ferromagnetic-plate capacitors

    Science.gov (United States)

    Haigh, J. A.; Ciccarelli, C.; Betz, A. C.; Irvine, A.; Novák, V.; Jungwirth, T.; Wunderlich, J.

    2015-04-01

    The capacitance of a parallel-plate capacitor can depend on the applied magnetic field. Previous studies have identified capacitance changes induced via classical Lorentz force or spin-dependent Zeeman effects. Here we measure a magnetization direction-dependent capacitance in parallel-plate capacitors where one plate is a ferromagnetic semiconductor, gallium manganese arsenide. This anisotropic magnetocapacitance is due to the anisotropy in the density of states dependent on the magnetization through the strong spin-orbit interaction.

  15. On-Chip Picosecond Pulse Detection and Generation Using Graphene Photoconductive Switches

    OpenAIRE

    Hunter, Nicholas; Mayorov, Alexander S.; Christopher D. Wood; Russell, Christopher; Li, Lianhe; Linfield, Edmund H.; Davies, A. Giles; Cunningham, John E.

    2015-01-01

    We report on the use of graphene for room temperature on-chip detection and generation of pulsed terahertz (THz) frequency radiation, exploiting the fast carrier dynamics of light-generated hot carriers, and compare our results with conventional low-temperature-grown gallium arsenide (LT-GaAs) photoconductive (PC) switches. Coupling of picosecond-duration pulses from a biased graphene PC switch into Goubau line waveguides is also demonstrated. A Drude transport model based on the transient ph...

  16. The growth of materials processing in space - A history of government support for new technology

    Science.gov (United States)

    Mckannan, E. C.

    1983-01-01

    Development of a given technology for national defense and large systems developments when the task is too large or risky for entrepreneurs, yet is clearly in the best interest of the nation are discussed. Advanced research to identify areas of interest was completed. Examples of commercial opportunities are the McDonnell-Douglas Corporation purification process for pharmaceutical products and the Microgravity Research Associates process for growing gallium arsenide crystals in space.

  17. Potential means of support for materials processing in space. A history of government support for new technology

    Science.gov (United States)

    Mckannan, E. C.

    1983-01-01

    Development of a given technology for national defense and large systems developments when the task is too large or risky for entrepreneurs, yet is clearly in the best interest of the nation are discussed. Advanced research to identify areas of interest was completed. Examples of commercial opportunities are the McDonnell-Douglas Corporation purification process for pharmaceutical products and the Microgravity Research Associates process for growing gallium arsenide crystals in space.

  18. High T(c) electron doped Ca10(Pt3As8)(Fe2As2)5 and Ca10(Pt4As8)(Fe2As2)5 superconductors with skutterudite intermediary layers.

    Science.gov (United States)

    Ni, Ni; Allred, Jared M; Chan, Benny C; Cava, Robert Joseph

    2011-11-01

    It has been argued that the very high transition temperatures of the highest T(c) cuprate superconductors are facilitated by enhanced CuO(2) plane coupling through heavy metal oxide intermediary layers. Whether enhanced coupling through intermediary layers can also influence T(c) in the new high T(c) iron arsenide superconductors has never been tested due the lack of appropriate systems for study. Here we report the crystal structures and properties of two iron arsenide superconductors, Ca(10)(Pt(3)As(8))(Fe(2)As(2))(5) (the "10-3-8 phase") and Ca(10)(Pt(4)As(8))(Fe(2)As(2))(5) (the "10-4-8 phase"). Based on -Ca-(Pt(n)As(8))-Ca-Fe(2)As(2)- layer stacking, these are very similar compounds for which the most important differences lie in the structural and electronic characteristics of the intermediary platinum arsenide layers. Electron doping through partial substitution of Pt for Fe in the FeAs layers leads to T(c) of 11 K in the 10-3-8 phase and 26 K in the 10-4-8 phase. The often-cited empirical rule in the arsenide superconductor literature relating T(c) to As-Fe-As bond angles does not explain the observed differences in T(c) of the two phases; rather, comparison suggests the presence of stronger FeAs interlayer coupling in the 10-4-8 phase arising from the two-channel interlayer interactions and the metallic nature of its intermediary Pt(4)As(8) layer. The interlayer coupling is thus revealed as important in enhancing T(c) in the iron pnictide superconductors.

  19. Use of accelerated helium-3 ions for determining oxygen and carbon impurities in some pure materials

    Science.gov (United States)

    Aleksandrova, G. I.; Borisov, G. I.; Demidov, A. M.; Zakharov, Y. A.; Sukhov, G. V.; Shmanenkova, G. I.; Shchelkova, V. P.

    1978-01-01

    Methods are developed for the determination of O impurity in Be and Si carbide and concurrent determination of C and O impurities in Si and W by irradiation with accelerated He-3 ions and subsequent activity measurements of C-11 and F-18 formed from C and O with the aid of a gamma-gamma coincidence spectrometer. Techniques for determining O in Ge and Ga arsenide with radiochemical separation of F-18 are also described.

  20. Satellite power system: Concept development and evaluation program, reference system report

    Science.gov (United States)

    1979-01-01

    The Satellite Power System (SPS) Reference System is discussed and the technical and operational information required in support of environmental, socioeconomic, and comparative assessment studies are emphasized. The reference System concept features a gallium-aluminum-arsenide, and silicon solar cell options. Other aspects of an SPS are the construction of bases in space, launch and mission control bases on earth, and fleets of various transportation vehicles to support the construction and maintenance operations of the satellites.

  1. Monolithic AlGaAs second-harmonic nanoantennas

    CERN Document Server

    Gili, V F; Locatelli, A; Rocco, D; Finazzi, M; Ghirardini, L; Favero, I; Gomez, C; Lemaître, A; Celebrano, M; De Angelis, C; Leo, G

    2016-01-01

    We demonstrate monolithic aluminum gallium arsenide (AlGaAs) optical anoantennas. Using a selective oxidation technique, we fabricate such epitaxial semiconductor nanoparticles on an aluminum oxide substrate. Second harmonic generation from an AlGaAs nanocylinder of height h=400 nm and varying radius pumped with femtosecond pulses delivered at 1554-nm wavelength has been measured, revealing a peak conversion efficiency exceeding 10-5 for nanocylinders with an otpimized geometry.

  2. Sulfide-driven arsenic mobilization from arsenopyrite and black shale pyrite

    Science.gov (United States)

    Zhu, W.; Young, L.Y.; Yee, N.; Serfes, M.; Rhine, E.D.; Reinfelder, J.R.

    2008-01-01

    We examined the hypothesis that sulfide drives arsenic mobilization from pyritic black shale by a sulfide-arsenide exchange and oxidation reaction in which sulfide replaces arsenic in arsenopyrite forming pyrite, and arsenide (As-1) is concurrently oxidized to soluble arsenite (As+3). This hypothesis was tested in a series of sulfide-arsenide exchange experiments with arsenopyrite (FeAsS), homogenized black shale from the Newark Basin (Lockatong formation), and pyrite isolated from Newark Basin black shale incubated under oxic (21% O2), hypoxic (2% O2, 98% N2), and anoxic (5% H2, 95% N2) conditions. The oxidation state of arsenic in Newark Basin black shale pyrite was determined using X-ray absorption-near edge structure spectroscopy (XANES). Incubation results show that sulfide (1 mM initial concentration) increases arsenic mobilization to the dissolved phase from all three solids under oxic and hypoxic, but not anoxic conditions. Indeed under oxic and hypoxic conditions, the presence of sulfide resulted in the mobilization in 48 h of 13-16 times more arsenic from arsenopyrite and 6-11 times more arsenic from isolated black shale pyrite than in sulfide-free controls. XANES results show that arsenic in Newark Basin black shale pyrite has the same oxidation state as that in FeAsS (-1) and thus extend the sulfide-arsenide exchange mechanism of arsenic mobilization to sedimentary rock, black shale pyrite. Biologically active incubations of whole black shale and its resident microorganisms under sulfate reducing conditions resulted in sevenfold higher mobilization of soluble arsenic than sterile controls. Taken together, our results indicate that sulfide-driven arsenic mobilization would be most important under conditions of redox disequilibrium, such as when sulfate-reducing bacteria release sulfide into oxic groundwater, and that microbial sulfide production is expected to enhance arsenic mobilization in sedimentary rock aquifers with major pyrite-bearing, black

  3. 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.

  4. Terahertz Technology for Defense and Security-Related Applications

    OpenAIRE

    Iwaszczuk, Krzysztof; Jepsen, Peter Uhd; Heiselberg, Henning

    2012-01-01

    Denne afhandling omhandler udvalgte aspekter af terahertz (THz) teknologi med potentiale i forsvars- og sikkerheds-relaterede applikationer. En ny metode til samtidig dataopsamling i tidsopløst THz spektroskopi eksperimenter er blevet udviklet. Denne teknik demonstreres ved bestemmelse af fladekonduktiviteten af fotogenererede ladningsbrere i semiisolerende gallium arsenid. En sammenligning med resultater opnået ved hjælp af en standard dataopsamlingsprocedure viser at den nye metode minimere...

  5. Embedment of metal nanoparticles in GaAs and Si for plasmonic absorption enhancement in intermediate band solar cells

    OpenAIRE

    Moura Dias Mendes, Manuel Joao de; Hernández Martín, Estela; Tobías Galicia, Ignacio; Martí Vega, Antonio; Luque López, Antonio

    2010-01-01

    The high near-field enhancement occurring in the vicinity of metallic nanoparticles (MNPs) sustaining surface plasmons can only be fully exploited in photovoltaic devices if the MNPs are placed inside their semiconducting material, in the photoactive region. In this work an experimental procedure is studied to embed MNPs in gallium arsenide (GaAs) and silicon (Si), which can be applied to other semiconductor host materials. The approach consists in spin-coating colloidal MNPs dispersed i...

  6. Anisotropic magneto-capacitance in ferromagnetic-plate capacitors

    OpenAIRE

    Haigh, J. A.; Ciccarelli, C; Betz, A. C.; Irvine, A; Novák, V.; Jungwirth, T.; Wunderlich, J.

    2015-01-01

    The capacitance of a parallel plate capacitor can depend on applied magnetic field. Previous studies have identified capacitance changes induced via classical Lorentz force or spin-dependent Zeeman effects. Here we measure a magnetization direction dependent capacitance in parallel-plate capacitors where one plate is a ferromagnetic semiconductor, gallium manganese arsenide. This anisotropic magneto-capacitance is due to the anisotropy in the density of states dependent on the magnetization t...

  7. Modulation of fluorescence signals from biomolecules along nanowires due to interaction of light with oriented nanostructures

    DEFF Research Database (Denmark)

    Frederiksen, Rune Schøneberg; Alarcon-Llado, Esther; Madsen, Morten H.;

    2015-01-01

    High aspect ratio nanostructures have gained increasing interest as highly sensitive platforms for biosensing. Here, well-defined biofunctionalized vertical indium arsenide nanowires are used to map the interaction of light with nanowires depending on their orientation and the excitation waveleng....... We show how nanowires act as antennas modifying the light distribution and the emitted fluorescence. This work highlights an important optical phenomenon in quantitative fluorescence studies and constitutes an important step for future studies using such nanostructures....

  8. Rapid, Sensitive, and Reusable Detection of Glucose by a Robust Radiofrequency Integrated Passive Device Biosensor Chip

    OpenAIRE

    Nam-Young Kim; Kishor Kumar Adhikari; Rajendra Dhakal; Zorigt Chuluunbaatar; Cong Wang; Eun-Soo Kim

    2015-01-01

    Tremendous demands for sensitive and reliable label-free biosensors have stimulated intensive research into developing miniaturized radiofrequency resonators for a wide range of biomedical applications. Here, we report the development of a robust, reusable radiofrequency resonator based integrated passive device biosensor chip fabricated on a gallium arsenide substrate for the detection of glucose in water-glucose solutions and sera. As a result of the highly concentrated electromagnetic ener...

  9. EFFECTS OF OPERATING CONDITIONS ON THE DEPOSITION OF GaAs IN A VERTICAL CVD REACTOR

    OpenAIRE

    JAE-SANG BAEK; JIN-HYO BOO; YOUN-JEA KIM

    2008-01-01

    A numerical study is needed to gain insight into the growth mechanism and improve the reactor design or optimize the deposition condition in chemical vapor deposition (CVD). In this study, we have performed a numerical analysis of the deposition of gallium arsenide (GaAs) from trimethyl gallium (TMG) and arsine in a vertical CVD reactor. The effects of operating parameters, such as the rotation velocity of susceptor, inlet velocity, and inlet TMG fraction, are investigated and presented. The ...

  10. Results from the high efficiency solar panel experiment flown on CRRES

    International Nuclear Information System (INIS)

    This paper presents results from the High Efficiency Solar Panel Experiment (HESP) flown on the Combined Release and Radiation Effects Satellite (CRRES). The on-orbit solar cell degradation is correlated with the proton and electron environments. Comparisons between gallium arsenide germanium (GaAs/Ge) and silicon (Si) solar cells are presented, and results from three different annealing methods of like GaAs solar cells are compared

  11. Improved retrieval of gas abundances from near-infrared solar FTIR spectra measured at the Karlsruhe TCCON station

    OpenAIRE

    Kiel, M.; Wunch, D.; Wennberg, P. O.; Toon, G. C.; Hase, F.; Blumenstock, T.

    2016-01-01

    We present a modified retrieval strategy for solar absorption spectra recorded by the Karlsruhe Fourier Transform Infrared (FTIR) spectrometer, which is operational within the Total Carbon Column Observing Network (TCCON). In typical TCCON stations, the 3800–11 000 cm−1 spectral region is measured on a single extended Indium Gallium Arsenide (InGaAs) detector. The Karlsruhe setup instead splits the spectrum across an Indium Antimonide (InSb) and InGaAs detecto...

  12. Spatial light modulation in compound semiconductor materials

    Science.gov (United States)

    Cheng, Li-Jen (Inventor); Gheen, Gregory O. (Inventor); Partovi, Afshin (Inventor)

    1990-01-01

    Spatial light modulation (22) in a III-V single crystal (12), e.g., gallium arsenide, is achieved using the photorefractive effect. Polarization rotation created by beam coupling is utilized in one embodiment. In particular, information (16)on a control beam (14) incident on the crystal is transferred to an input beam (10), also incident on the crystal. An output beam (18) modulated in intensity is obtained by passing the polarization-modulated input beam through a polarizer (20).

  13. Thermionic photovoltaic energy converter

    Science.gov (United States)

    Chubb, D. L. (Inventor)

    1985-01-01

    A thermionic photovoltaic energy conversion device comprises a thermionic diode mounted within a hollow tubular photovoltaic converter. The thermionic diode maintains a cesium discharge for producing excited atoms that emit line radiation in the wavelength region of 850 nm to 890 nm. The photovoltaic converter is a silicon or gallium arsenide photovoltaic cell having bandgap energies in this same wavelength region for optimum cell efficiency.

  14. The effectiveness of low laser therapy in subacromial impingement syndrome: a randomized placebo controlled double‐blind prospective study

    OpenAIRE

    Sebnem Koldas Dogan; Saime Ay; Deniz Evcik

    2010-01-01

    OBJECTIVES: Conflicting results were reported about the effectiveness of Low level laser therapy on musculoskeletal disorders. The aim of this study was to investigate the effectiveness of 850-nm gallium arsenide aluminum (Ga-As-Al) laser therapy on pain, range of motion and disability in subacromial impingement syndrome. METHODS: A total of 52 patients (33 females and 19 males with a mean age of 53.59±11.34 years) with subacromial impingement syndrome were included. The patients were randoml...

  15. Use of a semiconductor-diode laser in urology

    Science.gov (United States)

    Watson, Graham M.

    1994-05-01

    The gallium arsenide semiconductor laser can emit in the near infrared where the depth of penetration into tissue is great although scattering is less than with the Nd:YAG laser. The laser is highly compact. It runs off a normal electrical outlet with no cooling requirement. It is therefore quiet and convenient. The laser has been assessed in a wide variety of applications in our urological department.

  16. High-Temperature Superconductivity in Doped BaFe2As2

    International Nuclear Information System (INIS)

    This thesis provides a detailed look on the synthesis, structural features and physical properties of iron arsenides. Especially the properties of BaFe2As2 and the solid solutions (Ba1-xKx)Fe2As2, (Ba1-xSrx)Fe2As2 and BaFe2(As1-xPx)2 which were all synthesized by solid state reactions by heating mixtures of the elements, were intensively investigated.

  17. Low temperature transport in p-doped InAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Upadhyay, S.; Jespersen, T. S.; Madsen, M. H.; Krogstrup, P.; Nygård, J. [Center for Quantum Devices and Nano-Science Center, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen (Denmark)

    2013-10-14

    We present low temperature electrical measurements of p-type Indium Arsenide nanowires grown via molecular beam epitaxy using Beryllium as a dopant. Growth of p-type wires without stacking faults is demonstrated. Devices in field-effect geometries exhibit ambipolar behavior, and the temperature dependence of electron and hole field effect mobilities are extracted. At low temperatures, we observe reproducible conductance fluctuations as a result of quantum interference, and magnetoconductance data show weak antilocalization.

  18. A semiconductor laser excitation circuit

    Energy Technology Data Exchange (ETDEWEB)

    Kaadzunari, O.; Masaty, K.

    1984-03-27

    A semiconductor laser excitation circuit is patented that is designed for operation in a pulsed mode with a high pulse repetition frequency. This circuit includes, in addition to a semiconductor laser, a high speed photodetector, a reference voltage source, a comparator, and a pulse oscillator and modulator. If the circuit is built using standard silicon integrated circuits, its speed amounts to several hundred megahertz, if it is constructed using gallium arsenide integrated circuits, its speed is several gigahertz.

  19. Investigation of Microwave Monolithic Integrated Circuit (MMIC) non-reciprocal millimeterwave components

    Science.gov (United States)

    Talisa, S. H.; Krishnaswamy, S. V.; Adam, J. D.; Yoo, K. C.; Doyle, N. J.

    1991-09-01

    Two ferrite film deposition techniques were investigated in this program for possible use in the monolithic integration of Gallium Arsenide electronic and magnetic millimeter-wave devices; (1) spin-spray plating (SSP) of nickel zinc ferrite films, and (2) sputtering of barium hexaferrites with C-axis oriented normally to the film plane. The SSP technique potential for this application was demonstrated. Film structural characteristics were studied, as well as their adhesions to other substrates and the conditions for growth of thicker films. Multilayers totalling 25 microns in thickness were grown on semiconducting substrates. The SSP process occurs at about 100 C and was experimentally demonstrated not to damage Gallium arsenide MMIC devices. The magnetic characteristics of these films were comparable to ceramic materials. A scheme for the monolithic integration of magnetic and Gallium arsenide electronic devices was proposed and its feasibility experimentally demonstrated. The films showed higher dielectric loss than was desirable, possibly owing to high water content. A better drying technique is required. Barium ferrite films with C-axis texture were reproducibly grown on sapphire. Magnetic measurements yielded acceptable saturation magnetization and anisotrophy field. Ferromagnetic resonance was not observed, possibly due to broad linewidths.

  20. Circuit quantum electrodynamics with a spin qubit.

    Science.gov (United States)

    Petersson, K D; McFaul, L W; Schroer, M D; Jung, M; Taylor, J M; Houck, A A; Petta, J R

    2012-10-18

    Electron spins trapped in quantum dots have been proposed as basic building blocks of a future quantum processor. Although fast, 180-picosecond, two-quantum-bit (two-qubit) operations can be realized using nearest-neighbour exchange coupling, a scalable, spin-based quantum computing architecture will almost certainly require long-range qubit interactions. Circuit quantum electrodynamics (cQED) allows spatially separated superconducting qubits to interact via a superconducting microwave cavity that acts as a 'quantum bus', making possible two-qubit entanglement and the implementation of simple quantum algorithms. Here we combine the cQED architecture with spin qubits by coupling an indium arsenide nanowire double quantum dot to a superconducting cavity. The architecture allows us to achieve a charge-cavity coupling rate of about 30 megahertz, consistent with coupling rates obtained in gallium arsenide quantum dots. Furthermore, the strong spin-orbit interaction of indium arsenide allows us to drive spin rotations electrically with a local gate electrode, and the charge-cavity interaction provides a measurement of the resulting spin dynamics. Our results demonstrate how the cQED architecture can be used as a sensitive probe of single-spin physics and that a spin-cavity coupling rate of about one megahertz is feasible, presenting the possibility of long-range spin coupling via superconducting microwave cavities.

  1. Heat load of a GaAs photocathode in an SRF electron gun

    Institute of Scientific and Technical Information of China (English)

    WANG Er-Dong; ZHAO Kui; J(o)rg Kewisch; Ilan Ben-Zvi; Andrew Burrill; Trivini Rao; WU Qiong; Animesh Jain; Ramesh Gupta; Doug Holmes

    2011-01-01

    A great deal of effort has been made over the last decades to develop a better polarized electron source for high energy physics. Several laboratories operate DC guns with a gallium arsenide photocathode, which yield a highly polarized electron beam. However, the beam's emittance might well be improved by using a superconducting radio frequency (SRF) electron gun, which delivers beams of a higher brightness than that from DC guns because the field gradient at the cathode is higher. SRF guns with metal and CsTe cathodes have been tested successfully. To produce polarized electrons, a Gallium-Arsenide photo-cathode must be used: an experiment to do so in a superconducting RF gun is under way at BNL. Since a bulk gallium arsenide (GaAs) photocathode is normal conducting, a problem arises from the heat load stemming from the cathode. We present our measurements of the electrical resistance of GaAs at cryogenic temperatures, a prediction of the heat load and verification by measuring the quality factor of the gun with and without the cathode at 2 K. We simulate heat generation and flow from the GaAs cathode using the ANSYS program. By following the findings with the heat load model, we designed and fabricated a new cathode holder (plug) to decrease the heat load from GaAs.

  2. Reliability of high-power pulsed IMPATT diodes

    Science.gov (United States)

    Ayyagari, M. S.; Heaton, J. L.; Jansen, N.

    1981-11-01

    Because of their present and future use in military systems, particularly missile seekers, high power pulsed IMPATT reliability is of considerable interest. This report is concerned with a reliability study of gallium arsenide double-drift pulsed IMPATTs of the Read doping profile type, that is both n and p active regions and contains avalanche confining doping structures. Both short-term (freak failure region) and long-term reliability testing have been carried out, comparing performance and failure mechanisms of the gallium arsenide devices with a smaller number of silicon flat profile double-drift devices, and Schottky-barrier, single-drift, low-high-low doping profile gallium arsenide devices. In the second phase of testing, devices were stressed under oscillating conditions, with a set of increasing bias current values, until failure occurred. The test was repeated at 16 different pulse widths and duty cycle combinations allowing determination of the most stringent operating conditions, and evaluation of failure mechanisms characteristic of such overstress. The third phase of testing was directed at examination of long-term reliability and wear-out failure mechanisms. Both a high temperature storage step-stress test and a long-term operation constant stress test were carried out.

  3. Nonlinear THz spectroscopy on n-type GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Gaal, Peter

    2008-06-23

    In this thesis, the ultrafast dynamics of conduction band electrons in semiconductors are investigated by nonlinear terahertz (THz) spectroscopy. In particular, n-doped gallium arsenide samples with doping concentrations in the range of 10{sup 16} cm{sup -3} to 10{sup 17} cm{sup -3} are studied. A novel source for the generation of intense THz radiation is developed which yields single-cycle THz transients with field amplitudes of more then 400 kV/cm. The THz source uses ultrashort optical laser pulses provided by a Ti:sapphire oscillator. In addition, a two-color THz-pump mid-infrared-probe setup is implemented, which allows for two-dimensional time-resolved experiments in the far-infrared wavelength range. Field ionization of neutral shallow donors in gallium arsenide with intense, ultrashort THz pulses and subsequent coherent radiative recombination of electrons to impurity ground states is observed at room temperature. The superradiant decay of the nonlinear polarization results in the emission of a coherent signal with picosecond lifetimes. Such nonlinear signals, which exhibit a lifetime ten times longer than in the linear regime are observed for the first time. At low temperatures and THz field strengths below 5 kV/cm, Rabi flopping on shallow donor transitions is demonstrated. For the first time, the polar electron-LO phonon interaction is directly measured in the quantum kinetic transport regime. Quasi-instantaneous acceleration of conduction band electrons in the polar gallium arsenide lattice by the electric field of intense THz pulses and subsequent probing of the mid-infrared transmission reveals a modulation of the transmission along the THz-mid-infrared delay coordinate with the frequency of the LO phonon. These modulations directly display the relative phase between the electron motion and its surrounding virtual phonon cloud. Quantum kinetic model calculations fully account for the observed phenomena. (orig.)

  4. Medical Applications and Toxicities of Gallium Compounds

    Directory of Open Access Journals (Sweden)

    Christopher R. Chitambar

    2010-05-01

    Full Text Available Over the past two to three decades, gallium compounds have gained importance in the fields of medicine and electronics. In clinical medicine, radioactive gallium and stable gallium nitrate are used as diagnostic and therapeutic agents in cancer and disorders of calcium and bone metabolism. In addition, gallium compounds have displayed anti-inflammatory and immunosuppressive activity in animal models of human disease while more recent studies have shown that gallium compounds may function as antimicrobial agents against certain pathogens. In a totally different realm, the chemical properties of gallium arsenide have led to its use in the semiconductor industry. Gallium compounds, whether used medically or in the electronics field, have toxicities. Patients receiving gallium nitrate for the treatment of various diseases may benefit from such therapy, but knowledge of the therapeutic index of this drug is necessary to avoid clinical toxicities. Animals exposed to gallium arsenide display toxicities in certain organ systems suggesting that environmental risks may exist for individuals exposed to this compound in the workplace. Although the arsenic moiety of gallium arsenide appears to be mainly responsible for its pulmonary toxicity, gallium may contribute to some of the detrimental effects in other organs. The use of older and newer gallium compounds in clinical medicine may be advanced by a better understanding of their mechanisms of action, drug resistance, pharmacology, and side-effects. This review will discuss the medical applications of gallium and its mechanisms of action, the newer gallium compounds and future directions for development, and the toxicities of gallium compounds in current use.

  5. Photovoltaics and solar thermal conversion to electricity - Status and prospects

    Science.gov (United States)

    Alper, M. E.

    1979-01-01

    Photovoltaic power system technology development includes flat-plate silicon solar arrays and concentrating solar cell systems, which use silicon and other cell materials such as gallium arsenide. System designs and applications include small remote power systems ranging in size from tens of watts to tens of kilowatts, intermediate load-center applications ranging in size from tens to hundreds of kilowatts, and large central plant installations, as well as grid-connected rooftop applications. The thermal conversion program is concerned with large central power systems and small power applications.

  6. Studies of III-V ferromagnetic semiconductors

    OpenAIRE

    Wang, Mu

    2012-01-01

    The III-V ferromagnetic semiconductor Gallium Manganese Arsenide ((Ga,Mn)As) is one of the most interesting and well studied materials in spintronics research area. The first chapter is a brief introduction to spintronics, the properties of (Ga,Mn)As and the growth technique molecular beam epitaxy (MBE). Then the thesis presents a detailed study of the effect on the Curie temperature (TC) of varying the growth conditions and post-growth annealing procedures for epitaxially grown (Ga,Mn)As ...

  7. Epitaxial growth of single crystal films

    Science.gov (United States)

    Lind, M. D.; Kroes, R. L.; Immorlica, A. A., Jr.

    1981-01-01

    An experiment in gallium arsenide liquid phase epitaxy (LPE) on a flight of the SPAR 6 is described. A general purpose LPE processor suitable for either SPAR or Space Transportation System flights was designed and built. The process was started before the launch, and only the final step, in which the epitaxial film is grown, was performed during the flight. The experiment achieved its objectives; epitaxial films of reasonably good quality and very nearly the thickness predicted for convection free diffusion limited growth were produced. The films were examined by conventional analytical techniques and compared with films grown in normal gravity.

  8. Optical Absorption of Impurities and Defects in Semiconducting Crystals Electronic Absorption of Deep Centres and Vibrational Spectra

    CERN Document Server

    Pajot, Bernard

    2013-01-01

    This book outlines, with the help of several specific examples, the important role played by absorption spectroscopy in the investigation of deep-level centers introduced in semiconductors and insulators like diamond, silicon, germanium and gallium arsenide by high-energy irradiation, residual impurities, and defects produced during crystal growth. It also describes the crucial role played by vibrational spectroscopy to determine the atomic structure and symmetry of complexes associated with light impurities like hydrogen, carbon, nitrogen and oxygen, and as a tool for quantitative analysis of these elements in the materials.

  9. STUDY ON OCCURENCE FORM OF PLATINUM IN XINJIE Cu—Pt DEPOSIT BY NAA AND SCANNING PROTON MICROPROBE

    Institute of Scientific and Technical Information of China (English)

    李晓林; 童纯菡; 等

    1995-01-01

    A combination of NAA and micro-PIXE was used to study concentrations and distributions of platinum group elements (PGE) in ores from Xinjie Cu-Pt deposit.The NAA results of the bulk indicate that the ores belong to the enriched Pt-Pd type.The element concentration maps of scanning micro-PIXE for the ores show that the occurence form of Pt is independent arsenide minerals.No PGE were detected in chalcopyrite of Xinjie Cu-Pt deposit.These information are economically beneficial to the mineral smelting process.

  10. The origin of the Avram Iancu U-Ni-Co-Bi-As mineralization, Băiţa (Bihor) metallogenic district, Bihor Mts., Romania

    Science.gov (United States)

    Zajzon, Norbert; Szentpéteri, Krisztián; Szakáll, Sándor; Kristály, Ferenc

    2015-10-01

    The Băiţa metallogenic district in the Bihor Mountains is a historically important mining area in Romania. Uranium mining took place between 1952 and 1998 from various deposits, but very little is known about the geology and mineralogy of these deposits. In this paper, we describe geology and mineralogy of uranium mineralization of the Avram Iancu uranium mine from waste dump samples collected before complete remediation of the site. Texturally and mineralogically complex assemblages of nickeline, cobaltite-gersdorffite solid solution, native Bi, Bi-sulfosalts, molybdenite, and pyrite-chalcopyrite-sphalerite occur with uraninite, "pitchblende," and brannerite in most of the ore samples. The association of nickel, cobalt, and arsenic with uranium is reminiscent of five-element association of vein type U-Ni-Co-Bi-As deposits; however, the Avram Iancu ores appear to be more replacement-type stratiform/stratabound. Avram Iancu ore samples contain multistage complex, skarn, uranium sulfide, arsenide assemblages that can be interpreted to have been formed in the retrograde cooling stages of the skarn hydrothermal system. This mineralizing system may have built-up along Upper Cretaceous-Paleogene "Banatite" intrusions of diorite-to-granite composition. The intrusions crosscut the underlying uraniferous Permian formations in the stacked NW-verging Biharia Nappe System. The mineralization forms stacked, multilayer replacement horizons, along carbonate-rich lithologies within the metavolcanic (tuffaceous) Muncel Series. Mineral paragenesis and some mineral chemistry suggest moderate-to-high uranium sulfide stage along stratigraphically controlled replacement zones and minor veins. Uranium minerals formed abundantly in this early stage and include botryoidal, sooty and euhedral uraninite, brannerite, and coffinite. Later and/or lower-temperature mineral assemblages include heterogeneous, complexly zoned arsenide-sulfarsenide solid solutions associated with minute but

  11. Cell Libraries

    Science.gov (United States)

    1994-01-01

    A NASA contract led to the development of faster and more energy efficient semiconductor materials for digital integrated circuits. Gallium arsenide (GaAs) conducts electrons 4-6 times faster than silicon and uses less power at frequencies above 100-150 megahertz. However, the material is expensive, brittle, fragile and has lacked computer automated engineering tools to solve this problem. Systems & Processes Engineering Corporation (SPEC) developed a series of GaAs cell libraries for cell layout, design rule checking, logic synthesis, placement and routing, simulation and chip assembly. The system is marketed by Compare Design Automation.

  12. Trends in Space Photovoltaic Technology

    Science.gov (United States)

    Scott-Monck, J. A.

    1984-01-01

    The current status of silicon and gallium arsenide (GaAs) solar cell technology is described, and anticipated near and far term projections of photovoltaic cell performance are provided. It is shown that current ultrathin silicon and near term GaAs solar cells provide substantial enhancement of planar solar array performance. The advantages of utililizing GaAs cells in high concentration arrays is discussed. Evidence is provided to support the view that photovoltaic offers a viable means of supporting long term space objectives.

  13. Radiation tests of semiconductor detectors

    OpenAIRE

    Chmill, Valery

    2006-01-01

    This thesis investigates the response of Gallium Arsenide (GaAs) detectors to ionizing irradiation. Detectors based on π-υ junction formed by deep level centers doping. The detectors have been irradiated with 137Cs γ-rays up to 110 kGy, with 6 MeV mean energy neutron up to approximately 6 · 1014 n/cm2, with protons and mixed beam up to 1015 p/cm2. Results are presented for the effects on leakage currents and charge collection efficiencies for minimum ionizing electrons and alpha particles. Th...

  14. Cameras Reveal Elements in the Short Wave Infrared

    Science.gov (United States)

    2010-01-01

    Goodrich ISR Systems Inc. (formerly Sensors Unlimited Inc.), based out of Princeton, New Jersey, received Small Business Innovation Research (SBIR) contracts from the Jet Propulsion Laboratory, Marshall Space Flight Center, Kennedy Space Center, Goddard Space Flight Center, Ames Research Center, Stennis Space Center, and Langley Research Center to assist in advancing and refining indium gallium arsenide imaging technology. Used on the Lunar Crater Observation and Sensing Satellite (LCROSS) mission in 2009 for imaging the short wave infrared wavelengths, the technology has dozens of applications in military, security and surveillance, machine vision, medical, spectroscopy, semiconductor inspection, instrumentation, thermography, and telecommunications.

  15. Functional and electrophysiological evaluation of the effect of laser therapy in the treatment of peripheral facial paralysis

    Science.gov (United States)

    Ladalardo, Thereza C.; Brugnera, Aldo, Jr.; Takamoto, Marcia; Pinheiro, Antonio L. B.; Campos, Roberto A. d. C.; Castanho Garrini, Ana E.; Bologna, Elisangela D.; Settanni, Flavio

    2001-04-01

    This clinical case report relates to a total of 4 patients, carriers of idiopathic facial paralysis, treated with Low Level Laser Therapy using a Gallium-Aluminum-Arsenide diode laser of 780 nm, 50 mW, continuous wave emission, spot size 3 mm2 and total dosage of 20 joules per session distributed to the peripheral trajectory of the injured nerve in a point by point contact mode. Altogether 24 treatment sessions were performed in a period of 12 consecutive weeks twice a week All treated patients presented recovery signs from the initial degree of paralysis.

  16. Fabrication and characterization of high aspect ratio perpendicular patterned information storage media in an Al2O3/GaAs substrate

    OpenAIRE

    Wong, Joyce; Scherer, Axel; Todorovic, Mladen; Schultz, Sheldon

    1999-01-01

    In a new approach, we have fabricated 6:1 aspect ratio magnetic nanocolumns, 60–250 nm in diameter, embedded in a hard aluminum-oxide/gallium-arsenide (Al2O3/GaAs) substrate. The fabrication technique uses the highly selective etching properties of GaAs and AlAs, and highly efficient masking properties of Al2O3 to create small diameter, high aspect ratio holes. Nickel (Ni) is subsequently electroplated into the holes, followed by polishing, which creates a smooth and hard surface appropriate ...

  17. Reconfigurable hybrid metamaterial waveguide system at terahertz regime.

    Science.gov (United States)

    Zhao, Xiaolei; Zhu, Lin; Yuan, Cai; Yao, Jianquan

    2016-08-01

    We propose an optically controlled reconfigurable hybrid metamaterial waveguide system at terahertz frequencies, which consists of a two dimensional gold cut wire array deposited on top of a dielectric slab waveguide. Numerical findings reveal that this device is able to realize dynamic transformation from double electromagnetically induced transparency like material to ultra-narrow band guided mode resonance (GMR) filter by controlling the optically excited free carriers in gallium arsenide pads inserted between the gold cut wires. During this reconfiguration process of resonance modes, high quality factors up to ~104 and ~118 for the two EIT-like peaks and up to ~578 for the GMR filter are obtained. PMID:27505788

  18. Superconductivity by transition metal doping in Ca10(Fe1-xMxAs)10(Pt3As8) (M = Co, Ni, Cu)

    Science.gov (United States)

    Stürzer, Tobias; Kessler, Fabian; Johrendt, Dirk

    2014-11-01

    We report the successful substitution of cobalt, nickel and copper for iron in the 1038-phase parent compound ? yielding ?, ? and ?), respectively. Superconductivity is induced in Co and Ni doped compounds reaching critical temperatures up to 15 K, similar to known Pt substituted ?), whereas no superconductivity was detected in ?. The obtained ? phase diagrams are very similar to those of other iron arsenide superconductors indicating rather universal behaviour despite the more complex structures of the 1038-type compounds, where the physics is primarily determined by the FeAs layer.

  19. Arsenic-bridged magnetic interactions in an emerging two-dimensional FeAs nanostructure on MnAs

    Science.gov (United States)

    Helman, Christian; Ferrari, Valeria; Llois, Ana Maria

    2015-08-01

    The extreme case of an Fe monolayer deposited onto a manganese arsenide (MnAs) substrate is analyzed using density functional theory. We find that an FeAs quasi-two-dimensional antiferromagnetic surface nanostructure emerges. This nanostructure, which is magnetically nearly decoupled from the substrate, is due to bonding effects arising from the arsenic atoms bridging the Fe magnetic interactions. These interactions are studied and modeled using a Heisenberg-type Hamiltonian. They display an angular dependence which is characteristic of superexchange-like interactions, which are of the same order of magnitude as those appearing in Fe-based pnictides.

  20. The state of the art of thin-film photovoltaics

    International Nuclear Information System (INIS)

    Thin-film photovoltaic technologies, based on materials such as amorphous or polycrystalline silicon, copper indium diselenide, cadmium telluride, and gallium arsenide, offer the potential for significantly reducing the cost of electricity generated by photovoltaics. The significant progress in the technologies, from the laboratory to the marketplace, is reviewed. The common concerns and questions raised about thin films are addressed. Based on the progress to date and the potential of these technologies, along with continuing investments by the private sector to commercialize the technologies, one can conclude that thin-film PV will provide a competitive alternative for large-scale power generation in the future

  1. Novel deep—submicron x—ray lithography process for T—shaped gate patterns

    Institute of Scientific and Technical Information of China (English)

    XieChangqing; YiFuting; 等

    2001-01-01

    The growing interest in the use of Gallium Arsenids semiconductor materials has presented many opportunities for device operational speed improvements but has also presented many problems for the device maker,A novel deep-submicron x-ray lithography process for T-shaped gate patterns useful for high-electron-mobility transistors(HEMT) is introduced in this work.In the fabrication of T-shaped gate a therr layer resists method is used.The x-ray exposure experiments were finished by Beijing Synchrotron Radiation Facility(BSRF) 3B1A beamline,and good result has been obtained.

  2. Tunable Cobalt Vacancies and Related Properties in LaCoxAs2

    OpenAIRE

    Shen, Shijie; Wang, Gang; Jin, Shifeng; Huang, Qingzhen; Ying, Tianping; Li, Dandan; Lai, Xiaofang; Zhou, Tingting; ZHANG, Han; Lin, Zhiping; Wu, Xiaozhi; Chen, Xiaolong

    2014-01-01

    The origin of transition metal vacancies and their effects on the properties of ThCr2Si2-type compounds have been less studied and poorly understood. Here we carefully investigate the structure, physical properties, and electronic structure for a series of lanthanum cobalt arsenides with nominal composition of LaCoxAs2 (1.6 < = x < = 2.1). It is revealed that the occupancy of Co can be tuned between 1.98(1) and 1.61(1). The structural analyses based on X-ray and neutron diffractions show the ...

  3. Infrared and millimeter waves v.14 millimeter components and techniques, pt.V

    CERN Document Server

    Button, Kenneth J

    1985-01-01

    Infrared and Millimeter Waves, Volume 14: Millimeter Components and Techniques, Part V is concerned with millimeter-wave guided propagation and integrated circuits. In addition to millimeter-wave planar integrated circuits and subsystems, this book covers transducer configurations and integrated-circuit techniques, antenna arrays, optoelectronic devices, and tunable gyrotrons. Millimeter-wave gallium arsenide (GaAs) IMPATT diodes are also discussed. This monograph is comprised of six chapters and begins with a description of millimeter-wave integrated-circuit transducers, focusing on vario

  4. Low-level laser therapy affects osseointegration in titanium implants: resonance frequency, removal torque, and histomorphometric analysis in rabbits

    OpenAIRE

    Kim, Jong-Ryoul; Kim, Sung-Hee; Kim, In-Ryoung; Park, Bong-Soo; Kim, Yong-Deok

    2016-01-01

    Objectives The purpose of this study was to investigate the effects of low-level laser therapy (LLLT) with a diode gallium-aluminum-arsenide (Ga-Al-As) low-level laser device on the healing and attachment of titanium implants in bone. Materials and Methods Thirteen New Zealand white male rabbits weighing 3.0±0.5 kg were used for this study. Dental titanium implants (3.75 mm in diameter and 8.5 mm in length, US II RBM plus fixture; Osstem, Seoul, Korea) were implanted into both femurs of each ...

  5. A W-band RF-MEMS switched LNA in a 70 nm mHEMT process

    OpenAIRE

    Reyaz, Shakila; Gustafsson, Andreas; Samuelsson, Carl; Malmqvist, Robert; Grandchamp, Brice; Rantakari, Pekka; Vaha-Heikkila, Tauno

    2015-01-01

    This work presents a monolithic integrated reconfigurable active circuit consisting of a W-band RF micro-electro-mechanical-systems (MEMS) Dicke switch network and a wideband low-noise amplifier (LNA) realized in a 70 nm gallium arsenide (GaAs) metamorphic high electron mobility transistor process technology. The RF-MEMS LNA has a measured gain of 10.2-15.6 dB and 1.3-8.2 dB at 79-96 GHz when the Dicke switch is switched ON and OFF, respectively. Compared with the three-stage LNA used in this...

  6. Raman spectroscopy and electrical properties of InAs nanowires with local oxidation enabled by substrate micro-trenches and laser irradiation

    CERN Document Server

    Tanta, R; Liao, Z; Krogstrup, P; Vosch, T; Nygard, J; Jespersen, T S

    2016-01-01

    The thermal gradient along indium-arsenide nanowires was engineered by a combination of fabricated micro- trenches in the supporting substrate and focused laser irradiation. This allowed local control of thermally activated oxidation reactions of the nanowire on the scale of the diffraction limit. The locality of the oxidation was detected by micro-Raman mapping, and the results were found consistent with numerical simulations of the temperature profile. Applying the technique to nanowires in electrical devices the locally oxidized nanowires remained conducting with a lower conductance as expected for an effectively thinner conducting core.

  7. GaAs/Ge solar cell AC parameters at different temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, R. Anil; Suresh, M.S. [ISRO Satellite centre, ISRO, Bangalore 560 017 (India); Nagaraju, J. [Department of Instrumentation, Indian Institute of Science, Bangalore 560 012 (India)

    2003-05-15

    The AC parameters of Gallium Arsenide (GaAs/Ge) solar cell were measured at different cell temperatures (198-348K) by varying the cell bias voltage (forward and reverse) under dark condition using impedance spectroscopy technique. It was found that the cell capacitance increases with the cell temperature where as the cell resistance decreases, at any bias voltage. The measured cell parameters were used to calculate the intrinsic concentration of electron-hole pair, cell material relative permittivity and its band gap energy. The diode factor and the cell dynamic resistance at the corresponding maximum power point decrease with the cell temperature.

  8. Diffusion length variation and proton damage coefficients for InP/In(x)Ga(1-x)As/GaAs solar cells

    Science.gov (United States)

    Jain, R. K.; Weinberg, I.; Flood, D. J.

    1993-01-01

    Indium phosphide solar cells are more radiation resistant than gallium arsenide and silicon solar cells, and their growth by heteroepitaxy offers additional advantages leading to the development of lighter, mechanically strong and cost-effective cells. Changes in heteroepitaxial InP cell efficiency under 0.5 and 3 MeV proton irradiations are explained by the variation in the minority-carrier diffusion length. The base diffusion length versus proton fluence is calculated by simulating the cell performance. The diffusion length damage coefficient K(L) is plotted as a function of proton fluence.

  9. Growth and characterization of Cd3-xZnxAs2 undoped and Se-doped films

    International Nuclear Information System (INIS)

    For preparation of Cd3-xZnxAs2 films vapour condensation in vacuum as the one that is broadly applied to obtain films and epitaxial layer of semiconductors was chosen. The films have been grown and subsequently subjected to the evaporation of copper contact by means of vacuum evaporation system. The initial material was made of single crystals grown by the Bridgman method. Preliminary calculations of the evaporation flux density and the condensation of Cd3-xZnxAs2 alloys were made by the known equations for the pressures of zinc and cadmium arsenides saturated steam and sufficiently agree with experimentally obtained data.

  10. Comparative High Field Magneto-transport Of Rare Earth Oxypnictides With Maximum Transition Temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Balakirev, Fedor F [Los Alamos National Laboratory; Migliori, A [MPA-NHMFL; Riggs, S [NHMFL-FSU; Hunte, F [NHMFL-FSU; Gurevich, A [NHMFL-FSU; Larbalestier, D [NHMFL-FSU; Boebinger, G [NHMFL-FSU; Jaroszynski, J [NHMFL-FSU; Ren, Z [CHINA; Lu, W [CHINA; Yang, J [CHINA; Shen, X [CHINA; Dong, X [CHINA; Zhao, Z [CHINA; Jin, R [ORNL; Sefat, A [ORNL; Mcguire, M [ORNL; Sales, B [ORNL; Christen, D [ORNL; Mandrus, D [ORNL

    2008-01-01

    We compare magnetotransport of the three iron-arsenide-based compounds ReFeAsO (Re=La, Sm, Nd) in very high DC and pulsed magnetic fields up to 45 and 54 T, respectively. Each sample studied exhibits a superconducting transition temperature near the maximum reported to date for that particular compound. While high magnetic fields do not suppress the superconducting state appreciably, the resistivity, Hall coefficient, and critical magnetic fields, taken together, suggest that the phenomenology and superconducting parameters of the oxypnictide superconductors bridges the gap between MgB{sub 2} and YBCO.

  11. Nitrogen incorporation into GaAs lattice as a result of the surface cavitation effect

    Energy Technology Data Exchange (ETDEWEB)

    Savkina, R K; Smirnov, A B, E-mail: r_savkina@lycos.co [V. Lashkaryov Institute of Semiconductor Physics at NAS of Ukraine, pr. Nauki 41, 03028 Kiev (Ukraine)

    2010-10-27

    Semi-insulating gallium arsenide was exposed to cavitation impact initiated by focusing a high-frequency acoustic wave into liquid nitrogen. Optical and atomic force microscopy methods were used for the analysis of surface morphology. Formation of microstructures as well as change in the chemical composition of the surface are observed. The morphology of the structures is highly dependent on the acoustic parameters. Raman spectroscopy data have confirmed the incorporation of nitrogen atoms into the GaAs lattice and Ga-N bond formation in the region of maximal structural change due to the cavitation impact.

  12. Ordered arrangements of selective-area grown MnAs nanoclusters as components for novel, planar magneto-electronic devices

    OpenAIRE

    Fischer, Martin

    2015-01-01

    Novel concepts such as racetrack memory devices or planar logic elements based on ferromagnetic materials are subject of today’s research. However, there are certain limits which will have to be faced by the established technology. A very attractive model kit for planar magneto-electronic devices can be found in Manganese arsenide (MnAs ) nanoclusters grown by selective-area metal-organic vapor-phase epitaxy (SA-MOVPE). MnAs exposes ferromagnetism at room temperature and below, and the growt...

  13. Low-Concentration-Ratio Solar-Cell Arrays

    Science.gov (United States)

    Biss, M. S.; Reed, David A., Jr.

    1986-01-01

    Paper presents design concept for mass-producible arrays of solar electric batteries and concentrators tailored to individual requirements. Arrays intended primarily for space stations needing about 100 kW of power. However, modular, lightweight, compact, and relatively low-cost design also fulfill requirements of some terrestrial applications. Arrays built with currently available materials. Pultrusions, injectionmolded parts, and composite materials used extensively to keep weight low. For added flexibility in design and construction, silicon and gallium arsenide solar-cell panels interchangeable.

  14. Microwave monolithic integrated circuit development for future spaceborne phased array antennas

    Science.gov (United States)

    Anzic, G.; Kascak, T. J.; Downey, A. N.; Liu, D. C.; Connolly, D. J.

    1984-01-01

    The development of fully monolithic gallium arsenide (GaAs) receive and transmit modules suitable for phased array antenna applications in the 30/20 gigahertz bands is presented. Specifications and various design approaches to achieve the design goals are described. Initial design and performance of submodules and associated active and passive components are presented. A tradeoff study summary is presented, highlighting the advantages of a distributed amplifier approach compared to the conventional single power source designs. Previously announced in STAR as N84-13399

  15. Inherent polarization entanglement generated from a monolithic semiconductor chip

    DEFF Research Database (Denmark)

    Horn, Rolf T.; Kolenderski, Piotr; Kang, Dongpeng;

    2013-01-01

    Creating miniature chip scale implementations of optical quantum information protocols is a dream for many in the quantum optics community. This is largely because of the promise of stability and scalability. Here we present a monolithically integratable chip architecture upon which is built...... a photonic device primitive called a Bragg reflection waveguide (BRW). Implemented in gallium arsenide, we show that, via the process of spontaneous parametric down conversion, the BRW is capable of directly producing polarization entangled photons without additional path difference compensation, spectral...... as a serious contender on which to build large scale implementations of optical quantum processing devices....

  16. Raman spectroscopy of boron carbides and related boron-containing materials

    International Nuclear Information System (INIS)

    Raman spectra of crystalline boron, boron carbide, boron arsenide (B12As2), and boron phosphide (B12P2) are reported. The spectra are compared with other boron-containing materials containing the boron icosahedron as a structural unit. The spectra exhibit similar features some of which correlate with the structure of the icosahedral units of the crystals. The highest Raman lines appear to be especially sensitive to the B-B distance in the polar triangle of the icosahedron. Such Raman structural markers are potentially useful in efforts to tailor electronic properties of these high temperature semiconductors and thermoelectrics

  17. LLE Review Quarterly Report (April-June 1986). Volume 27

    Energy Technology Data Exchange (ETDEWEB)

    Yaakobi, B. [Univ. of Rochester, NY (United States)

    1986-06-01

    This volume of the LLE Review, covering the period April-June 1986, contains reports on GDL and OMEGA laser activities; analysis of neutron diagnostic methods of compressed laser targets; modeling of non-local heat flow in laser-heated plasmas; and development~ in advanced technology areas at LLE: protective polymeric coatings for nonlinear optical materials, time-resolved observation of electron-phonon relaxation in copper, and non-contact electro-optic sampling of high-speed electrical wave forms with a gallium-arsenide injection laser. Finally, the National Laser Users Facility activities for this period are summarized.

  18. Molecular beam epitaxy

    CERN Document Server

    Pamplin, Brian R

    1980-01-01

    Molecular Beam Epitaxy introduces the reader to the use of molecular beam epitaxy (MBE) in the generation of III-V and IV-VI compounds and alloys and describes the semiconductor and integrated optics reasons for using the technique. Topics covered include semiconductor superlattices by MBE; design considerations for MBE systems; periodic doping structure in gallium arsenide (GaAs); nonstoichiometry and carrier concentration control in MBE of compound semiconductors; and MBE techniques for IV-VI optoelectronic devices. The use of MBE to fabricate integrated optical devices and to study semicond

  19. Absence of phase-dependent noise in time-domain reflectivity studies of impulsively excited phonons

    KAUST Repository

    Hussain, A.

    2010-06-17

    There have been several reports of phase-dependent noise in time-domain reflectivity studies of optical phonons excited by femtosecond laser pulses in semiconductors, semimetals, and superconductors. It was suggested that such behavior is associated with the creation of squeezed phonon states although there is no theoretical model that directly supports such a proposal. We have experimentally re-examined the studies of phonons in bismuth and gallium arsenide, and find no evidence of any phase-dependent noise signature associated with the phonons. We place an upper limit on any such noise at least 40–50 dB lower than previously reported.

  20. Plating on difficult-to-plate metals: what's new

    International Nuclear Information System (INIS)

    Some of the changes since 1970 in procedures for plating on such materials as titanium, molybdenum, silicon, aluminum, and gallium arsenide are summarized. While basic procedures for plating some of these materials were developed as many as 30 to 40 years ago, changes in the end uses of the plated products have necessitated new plating processes. In some cases, vacuum techniques - such as ion bombardment, ion implantation, and vacuum metallization - have been introduced to improve the adhesion of electrodeposits. In other cases, these techniques have been used to deposit materials upon which electrodeposits are required

  1. Local quantum criticality of an iron-pnictide tetrahedron.

    Science.gov (United States)

    Ong, T Tzen; Coleman, Piers

    2012-03-01

    Motivated by the close correlation between transition temperature (T(c)) and the tetrahedral bond angle of the As-Fe-As layer observed in the iron-based superconductors, we study the interplay between spin and orbital physics of an isolated iron-arsenide tetrahedron embedded in a metallic environment. Whereas the spin-Kondo effect is suppressed to low temperatures by Hund's coupling, the orbital degrees of freedom are expected to quantum mechanically quench at high temperatures, giving rise to an overscreened, non-Fermi liquid ground state. Translated into a dense environment, this critical state may play an important role in the superconductivity of these materials.

  2. Raman spectroscopy and electrical properties of InAs nanowires with local oxidation enabled by substrate micro-trenches and laser irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Tanta, R.; Krogstrup, P.; Nygård, J.; Jespersen, T. S., E-mail: tsand@fys.ku.dk [Center for Quantum Devices and Nano Science Center, Niels Bohr Institute, University of Copenhagen, Copenhagen 2100 (Denmark); Madsen, M. H. [Danish Fundamental Metrology, Matematiktorvet 307, Kgs. Lyngby 2800 (Denmark); Liao, Z.; Vosch, T. [Nano-Science Center, Department of Chemistry, University of Copenhagen, Copenhagen 2100 (Denmark)

    2015-12-14

    The thermal gradients along indium arsenide nanowires were engineered by a combination of fabricated micro-trenches in the supporting substrate and focused laser irradiation. This allowed local spatial control of thermally activated oxidation reactions of the nanowire on the scale of the diffraction limit. The locality of the oxidation was detected by micro-Raman mapping, and the results were found to be consistent with numerical simulations of the temperature profile. Applying the technique to nanowires in electrical devices the locally oxidized nanowires remained conducting with a lower conductance as expected for an effectively thinner conducting core.

  3. Raman spectroscopy and electrical properties of InAs nanowires with local oxidation enabled by substrate micro-trenches and laser irradiation

    Science.gov (United States)

    Tanta, R.; Madsen, M. H.; Liao, Z.; Krogstrup, P.; Vosch, T.; Nygârd, J.; Jespersen, T. S.

    2015-12-01

    The thermal gradients along indium arsenide nanowires were engineered by a combination of fabricated micro-trenches in the supporting substrate and focused laser irradiation. This allowed local spatial control of thermally activated oxidation reactions of the nanowire on the scale of the diffraction limit. The locality of the oxidation was detected by micro-Raman mapping, and the results were found to be consistent with numerical simulations of the temperature profile. Applying the technique to nanowires in electrical devices the locally oxidized nanowires remained conducting with a lower conductance as expected for an effectively thinner conducting core.

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

    Science.gov (United States)

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

    2016-05-01

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

  5. Study of the background noise in microwave GaAsFET devices

    Energy Technology Data Exchange (ETDEWEB)

    Serrano S, A. (Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, B.C. (Mexico))

    1984-01-01

    One of the most important properties of the gallium arsenide field effect transistor is its low noise figure in the microwave frequency range (approx. 1 dB, 4 GHz). The applications of this device in components and systems in the high frequency range require analysis of background noise in terms of basic static and dynamic properties of the device. The purpose of this paper is to review GaAsFET noise properties; from this review, a description of precise noise measurement techniques is made. Some experimental and theoretical results on the minimum noise figure are shown for several GaAsFET devices.

  6. An interim report on the NTS-2 solar cell experiment

    Science.gov (United States)

    Statler, R. L.; Walker, D. H.

    1979-01-01

    Data obtained from the fourteen solar cell modules on the NTS-2 satellite are presented together with a record of panel temperature and sun inclination. The following flight data are discussed: (1) state of the art solar cell configurations which embody improvements in solar cell efficiency through new silicon surface and bulk technology, (2) improved coverslip materials and coverslip bonding techniques, (3) short and long term effects of ultraviolet rejection filters vs. no filters on the cells, (4) degradation on a developmental type of liquid epitaxy gallium-aluminum-arsenide solar cell, and (5) space radiation effects.

  7. Synthese und Eigenschaften von Trimethylsilylarsanen (Trimethylsilylverbindungen der Vb-Elemente ; 1)

    OpenAIRE

    Becker, Gerd; Gutekunst, Gerhard; Wessely, Hans Jürgen

    1980-01-01

    Aus Natrium-Kalium-Legierung und pulverisiertem Arsen in Dimethoxyäthan dargestelltes „Na3As/K3As” setzt sich mit Trimethylchlorsilan in 80 bis 90%iger Ausbeute zu Tris(trimethylsilyl)arsan 4 um. 4 reagiert mit Methyllithium in THF oder Dimethoxyäthan zu Lithiumbis(trimethylsilyl)arsenid 5, das mit zwei Molekülen THF – 5a – oder einem Molekül Dimethoxyäthan – 5b – pro Formeleinheit kristallisiert. Das Dimethoxyäthan-Addukt ist dimer in Benzol. Die Umsetzung von 5 mit primären und sekundären A...

  8. Use of a semiconductor diode laser in urology

    Science.gov (United States)

    Watson, Graham M.; Anson, K.

    1993-05-01

    The gallium arsenide semiconductor laser at 805 nm has been used with a variety of delivery fibers to produce actions varying from incision to interstitial coagulation. Clinical experience at this early stage suggests that the laser can be used to cut skin and connective tissue efficiently in air. It may prove at least as effective as the neodymium YAG laser for interstitial coagulation of tumors or prostate. Further efforts are required to promote its action cutting underwater and as a coagulator both in air and water.

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

    CERN Multimedia

    Stolwijk, N

    2002-01-01

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

  10. Self-contained sub-millimeter wave rectifying antenna integrated circuit

    Science.gov (United States)

    Siegel, Peter H. (Inventor)

    2004-01-01

    The invention is embodied in a monolithic semiconductor integrated circuit in which is formed an antenna, such as a slot dipole antenna, connected across a rectifying diode. In the preferred embodiment, the antenna is tuned to received an electromagnetic wave of about 2500 GHz so that the device is on the order of a wavelength in size, or about 200 microns across and 30 microns thick. This size is ideal for mounting on a microdevice such as a microrobot for example. The antenna is endowed with high gain in the direction of the incident radiation by providing a quarter-wavelength (30 microns) thick resonant cavity below the antenna, the cavity being formed as part of the monolithic integrated circuit. Preferably, the integrated circuit consists of a thin gallium arsenide membrane overlying the resonant cavity and supporting an epitaxial Gallium Arsenide semiconductor layer. The rectifying diode is a Schottky diode formed in the GaAs semiconductor layer and having an area that is a very small fraction of the wavelength of the 2500 GHz incident radiation. The cavity provides high forward gain in the antenna and isolation from surrounding structure.

  11. Arsenic speciation in sinter mineralization from a hydrothermal channel of El Tatio geothermal field, Chile

    Science.gov (United States)

    Alsina, Marco A.; Zanella, Luciana; Hoel, Cathleen; Pizarro, Gonzalo E.; Gaillard, Jean-François; Pasten, Pablo A.

    2014-10-01

    El Tatio geothermal field is the principal natural source of arsenic for the Loa River, the main surface water resource in the hyper-arid Atacama Desert (Antofagasta Region, Northern Chile). Prior investigations by bulk X-ray absorption spectroscopy have identified hydrous ferric oxides as the principal arsenic-containing phase in sinter material from El Tatio, suggesting sorption as the main mechanism for arsenic scavenging by the solid phases of these hot spring environments. Here we examine siliceous sinter material sampled from a hydrothermal channel using synchrotron based X-ray micro-probe techniques, including As and Fe Kα X-ray fluorescence (μ-XRF), As K-edge X-ray absorption near edge structure (μ-XANES), and X-ray diffraction (μ-XRD). Least-squares linear fitting of μ-XANES spectra shows that arsenic is predominantly present as arsenate sorbed on hydrous ferric oxides (63% molar proportion), but we also identify nodular arsenide micro-mineralizations (37% molar proportion) similar to loellingite (FeAs2), not previously detected during bulk-scale analysis of the sinter material. Presence of arsenide mineralizations indicates development of anoxic environments on the surface of the siliceous sinter, and suggests a more complex biogeochemistry for arsenic than previously observed for circum-neutral pH brine hot spring environments.

  12. Generalized Synthesis of EAs [E = Fe, Co, Mn, Cr] Nanostructures and Investigating Their Morphology Evolution

    Directory of Open Access Journals (Sweden)

    P. Desai

    2015-01-01

    Full Text Available This paper illustrates a novel route for the synthesis of nanostructured transition metal arsenides including those of FeAs, CoAs, MnAs, and CrAs through a generalized protocol. The key feature of the method is the use of one-step hot-injection and the clever use of a combination of precursors which are low-melting and highly reactive such as metal carbonyls and triphenylarsine in a solventless setup. This method also facilitates the formation of one-dimensional nanostructures as we move across the periodic table from CrAs to CoAs. The chemical basis of this reaction is simple redox chemistry between the transition metals, wherein the transition metal is oxidized from elemental state (E0 to E3+in lieu of reduction of As3+ to As3−. While the thermodynamic analysis reveals that all these conversions are spontaneous, it is the kinetics of the process that influences morphology of the product nanostructures, which varies from extremely small nanoparticles to nanorods. Transition metal pnictides show interesting magnetic properties and these nanostructures can serve as model systems for the exploration of their intricate magnetism as well as their applications and can also function as starting materials for the arsenide based nanosuperconductors.

  13. Strongly correlated electron phenomena in Pr-based filled skutterudite compounds

    International Nuclear Information System (INIS)

    Recent experiments on the Pr-based filled skutterudite arsenides and antimonides PrOs4Sb12, Pr(Os1-xRux)4Sb12, Pr1-xNdxOs4Sb12, PrFe4As12, PrRu4As12, and PrOs4As12 are reviewed. The heavy fermion compound PrOs4Sb12 exhibits unconventional strong-coupling superconductivity below Tc=1.85K that breaks time reversal symmetry, apparently consists of several distinct superconducting phases, and may involve triplet spin pairing of electrons. Studies of the alloy systems Pr(Os1-xRux)4Sb12 and Pr1-xNdxOs4Sb12 revealed rich T-x phase diagrams and a strong suppression of the high field ordered phase and the unconventional superconductivity of PrOs4Sb12 with Ru substitution. Among the three Pr-based filled skutterudite arsenides, PrFe4As12 has a ferromagnetic ground state, PrRu4As12 exhibits conventional BCS superconductivity, and PrOs4As12 is an antiferromagnet

  14. Strongly correlated electron phenomena in Pr-based filled skutterudite compounds

    Energy Technology Data Exchange (ETDEWEB)

    Maple, M.B. [Department of Physics and Institute for Pure and Applied Physical Sciences, University of California, San Diego, La Jolla, CA (United States)]. E-mail: mbmaple@physics.ucsd.edu; Henkie, Z. [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Wroclaw (Poland); Yuhasz, W.M. [Department of Physics and Institute for Pure and Applied Physical Sciences, University of California, San Diego, La Jolla, CA (United States); Ho, P.-C. [Department of Physics and Institute for Pure and Applied Physical Sciences, University of California, San Diego, La Jolla, CA (United States); Yanagisawa, T. [Department of Physics and Institute for Pure and Applied Physical Sciences, University of California, San Diego, La Jolla, CA (United States); Sayles, T.A. [Department of Physics and Institute for Pure and Applied Physical Sciences, University of California, San Diego, La Jolla, CA (United States); Butch, N.P. [Department of Physics and Institute for Pure and Applied Physical Sciences, University of California, San Diego, La Jolla, CA (United States); Jeffries, J.R. [Department of Physics and Institute for Pure and Applied Physical Sciences, University of California, San Diego, La Jolla, CA (United States); Pietraszko, A. [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Wroclaw (Poland)

    2007-03-15

    Recent experiments on the Pr-based filled skutterudite arsenides and antimonides PrOs{sub 4}Sb{sub 12}, Pr(Os{sub 1-x}Ru{sub x}){sub 4}Sb{sub 12}, Pr{sub 1-x}Nd{sub x}Os{sub 4}Sb{sub 12}, PrFe{sub 4}As{sub 12}, PrRu{sub 4}As{sub 12}, and PrOs{sub 4}As{sub 12} are reviewed. The heavy fermion compound PrOs{sub 4}Sb{sub 12} exhibits unconventional strong-coupling superconductivity below T{sub c}=1.85K that breaks time reversal symmetry, apparently consists of several distinct superconducting phases, and may involve triplet spin pairing of electrons. Studies of the alloy systems Pr(Os{sub 1-x}Ru{sub x}){sub 4}Sb{sub 12} and Pr{sub 1-x}Nd{sub x}Os{sub 4}Sb{sub 12} revealed rich T-x phase diagrams and a strong suppression of the high field ordered phase and the unconventional superconductivity of PrOs{sub 4}Sb{sub 12} with Ru substitution. Among the three Pr-based filled skutterudite arsenides, PrFe{sub 4}As{sub 12} has a ferromagnetic ground state, PrRu{sub 4}As{sub 12} exhibits conventional BCS superconductivity, and PrOs{sub 4}As{sub 12} is an antiferromagnet.

  15. Experimental discovery of a topological Weyl semimetal state in TaP.

    Science.gov (United States)

    Xu, Su-Yang; Belopolski, Ilya; Sanchez, Daniel S; Zhang, Chenglong; Chang, Guoqing; Guo, Cheng; Bian, Guang; Yuan, Zhujun; Lu, Hong; Chang, Tay-Rong; Shibayev, Pavel P; Prokopovych, Mykhailo L; Alidoust, Nasser; Zheng, Hao; Lee, Chi-Cheng; Huang, Shin-Ming; Sankar, Raman; Chou, Fangcheng; Hsu, Chuang-Han; Jeng, Horng-Tay; Bansil, Arun; Neupert, Titus; Strocov, Vladimir N; Lin, Hsin; Jia, Shuang; Hasan, M Zahid

    2015-11-01

    Weyl semimetals are expected to open up new horizons in physics and materials science because they provide the first realization of Weyl fermions and exhibit protected Fermi arc surface states. However, they had been found to be extremely rare in nature. Recently, a family of compounds, consisting of tantalum arsenide, tantalum phosphide (TaP), niobium arsenide, and niobium phosphide, was predicted as a Weyl semimetal candidates. We experimentally realize a Weyl semimetal state in TaP. Using photoemission spectroscopy, we directly observe the Weyl fermion cones and nodes in the bulk, and the Fermi arcs on the surface. Moreover, we find that the surface states show an unexpectedly rich structure, including both topological Fermi arcs and several topologically trivial closed contours in the vicinity of the Weyl points, which provides a promising platform to study the interplay between topological and trivial surface states on a Weyl semimetal's surface. We directly demonstrate the bulk-boundary correspondence and establish the topologically nontrivial nature of the Weyl semimetal state in TaP, by resolving the net number of chiral edge modes on a closed path that encloses the Weyl node. This also provides, for the first time, an experimentally practical approach to demonstrating a bulk Weyl fermion from a surface state dispersion measured in photoemission. PMID:26702446

  16. Design of Ceramic Springs for Use in Semiconductor Crystal Growth in Microgravity

    Science.gov (United States)

    Kaforey, M. F.; Deeb, C. W.; Matthiesen, D. H.

    1999-01-01

    Segregation studies can be done in microgravity to reduce buoyancy driven convection and investigate diffusion-controlled growth during the growth of semiconductor crystals. During these experiments, it is necessary to prevent free surface formation in order to avoid surface tension driven convection (Marangoni convection). Semiconductor materials such as gallium arsenide and germanium shrink upon melting, so a spring is necessary to reduce the volume of the growth chamber and prevent the formation of a free surface when the sample melts. A spring used in this application must be able to withstand both the high temperature and the processing atmosphere. During the growth of gallium arsenide crystals during the GTE Labs/USAF/NASA GaAs GAS Program and during the CWRU GaAs programs aboard the First and Second United States microgravity Laboratories, springs made of pyrolytic boron nitride (PBN) leaves were used. The mechanical properties of these PBN springs have been investigated and springs having spring constants ranging from 0.25 N/mm to 25 N/mm were measured. With this improved understanding comes the ability to design springs for more general applications, and guidelines are given for optimizing the design of PBN springs for crystal growth applications.

  17. Configuration dependence of band-gap narrowing and localization in dilute GaAs1 -xBix alloys

    Science.gov (United States)

    Bannow, Lars C.; Rubel, Oleg; Badescu, Stefan C.; Rosenow, Phil; Hader, Jörg; Moloney, Jerome V.; Tonner, Ralf; Koch, Stephan W.

    2016-05-01

    Anion substitution with bismuth (Bi) in III-V semiconductors is an effective method for experimental engineering of the band gap Eg at low Bi concentrations (≤2 % ), in particular in gallium arsenide (GaAs). The inverse Bi-concentration dependence of Eg has been found to be linear at low concentrations x and dominated by a valence band defect level anticrossing between As and Bi occupied p levels. Predictive models for the valence band hybridization require a first-principle understanding which can be obtained by density functional theory with the main challenges being the proper description of Eg and the spin-orbit coupling. By using an efficient method to include these effects, it is shown here that at high concentrations Eg is modified mainly by a Bi-Bi p orbital interaction and by the large Bi atom-induced strain. In particular, we find that at high concentrations, the Bi-Bi interactions depend strongly on model periodic cluster configurations, which are not captured by tight-binding models. Averaging over various configurations supports the defect level broadening picture. This points to the role of different atomic configurations obtained by varying the experimental growth conditions in engineering arsenide band gaps, in particular for telecommunication laser technology.

  18. The quantum Hall effect branches out

    International Nuclear Information System (INIS)

    It is surprising when five theoretical papers all concerned with a single experimental result appear in the same journal. It is perhaps even more surprising when the topic is the quantum Hall effect - a phenomenon that is now over two decades old and has already yielded two Nobel prizes. The great excitement stems from the fact that this experiment and the new theories elegantly intertwine the quantum Hall effect with ferromagnetism, Bose condensation, superfluidity and the Josephson effect. Last year our group at the California Institute of Technology teamed up with Loren Pfeiffer and Ken West of Bell Labs to study how electrons tunnel between two parallel 2-D electron gases. These electrons reside in a semiconductor heterostructure consisting of two thin layers of gallium arsenide separated by a barrier layer of aluminium gallium arsenide. Surprisingly, we observed a huge enhancement in the tunnelling current when just the right magnetic field was applied perpendicular to the 2-D planes in which the electrons were confined (I B Spielman et al. 2000 Phys. Rev. Lett. 84 5808). In the June issue of Physics World, James P Eisenstein of the California Institute of Technology, USA, describes the experiment and explains where it may lead. (U.K.)

  19. Performance of a Double Gate Nanoscale MOSFET (DG-MOSFET Based on Novel Channel Materials

    Directory of Open Access Journals (Sweden)

    Rakesh Prasher

    2013-03-01

    Full Text Available In this paper, we have studied a double gate nanoscale MOSFET for various channel materials using simulation approach. The device metrics considered at the nanometer scale are subthreshold swing (SS, drain induced barrier lowering (DIBL, on and off current, carrier injection velocity (vinj, etc. The channel materials studied are Silicon (Si, Germanium (Ge, Gallium Arsenide (GaAs, Zinc Oxide (ZnO, Zinc Sulfide (ZnS, Indium Arsenide (InAs, Indium Phosphide (InP and Indium Antimonide (InSb. The results suggest that InSb and InAs materials have highest Ion and lowest Ioff values when used in the channel of the proposed MOSFET. Besides, InSb has the highest values for Ion / Ioff ratio, vinj, transconductance (gm and improved short channel effects (SS = 59.71 and DIBL = 1.14, both are very close to ideal values. More results such as effect of quantum capacitance verses gate voltage (Vgs, drain current (Ids vs. gate voltage and drain voltage (Vds, ratio of transconductance (gm and drain current (Id vs. gate voltage, average velocity vs. gate voltage and injection velocity (Vinj for the mentioned channel materials have been investigated. Various results obtained indicate that InSb and InAs as channel material appear to be suitable for high performance logic and even low operating power requirements for future nanoscale devices as suggested by latest ITRS reports.

  20. Voltage adjusting characteristics in terahertz transmission through Fabry-Pérot-based metamaterials

    Directory of Open Access Journals (Sweden)

    Jun Luo

    2015-10-01

    Full Text Available Metallic electric split-ring resonators (SRRs with featured size in micrometer scale, which are connected by thin metal wires, are patterned to form a periodically distributed planar array. The arrayed metallic SRRs are fabricated on an n-doped gallium arsenide (n-GaAs layer grown directly over a semi-insulating gallium arsenide (SI-GaAs wafer. The patterned metal microstructures and n-GaAs layer construct a Schottky diode, which can support an external voltage applied to modify the device properties. The developed architectures present typical functional metamaterial characters, and thus is proposed to reveal voltage adjusting characteristics in the transmission of terahertz waves at normal incidence. We also demonstrate the terahertz transmission characteristics of the voltage controlled Fabry-Pérot-based metamaterial device, which is composed of arrayed metallic SRRs. To date, many metamaterials developed in earlier works have been used to regulate the transmission amplitude or phase at specific frequencies in terahertz wavelength range, which are mainly dominated by the inductance-capacitance (LC resonance mechanism. However, in our work, the external voltage controlled metamaterial device is developed, and the extraordinary transmission regulation characteristics based on both the Fabry-Pérot (FP resonance and relatively weak surface plasmon polariton (SPP resonance in 0.025-1.5 THz range, are presented. Our research therefore shows a potential application of the dual-mode-resonance-based metamaterial for improving terahertz transmission regulation.

  1. Rapid Progress of High Speed Short Haul Optical Interconnections in Optical Communication Systems

    Directory of Open Access Journals (Sweden)

    Ahmed Nabih Zaki Rashed

    2012-06-01

    Full Text Available This paper has proposed the new progress of optical interconnections is processed, taking into account the following items such as its ultimate device bandwidth, its available transmission bit rates based on either soliton or maximum time division multiplexing (MTDM transmission techniques, its ultimate transmission link bandwidth, and the product of the link bandwidth and its transmission length. Two items of special emphasis in the basic design of optical interconnection are: aluminum gallium arsenide (AlGaAs and Barium Fluoride (BaF2 waveguides, and the optical source cast as Vertical Cavity Surface Emitting Laser Diodes (VCSELD, made of either AlGaAs at operating wavelength of 0.85 µm or indium gallium arsenide phosphors (InGaAsP at operating wavelength of 0.65 µm, special emphasis is focused on the both above two items under different operating conditions including both the thermal and electrical effects. The optical interconnect is built up on the bases of two VCSELD and one optical link where thermal effects of both diodes and links are included. The good performance of the optical interconnect is deeply and parametrically investigated under wide ranges of the affecting parameters. The high speed performance is processed through three different effects, namely the device 3-dB bandwidth, and the link dispersion characteristics.

  2. Transformational III-V Electronics

    KAUST Repository

    Nour, Maha A.

    2014-04-01

    Flexible electronics using III-V materials for nano-electronics with high electron mobility and optoelectronics with direct band gap are attractive for many applications. This thesis describes a complementary metal oxide semiconductor (CMOS) compatible process for transforming traditional III-V materials based electronics into flexible one. The thesis reports releasing 200 nm of Gallium Arsenide (GaAs) from 200 nm GaAs / 300 nm Aluminum Arsenide (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 that contributes to the better transparency (45 % at 724 nm wavelengths) observed. Fabrication of metal oxide semiconductor capacitor (MOSCAPs) on GaAs is followed by releasing it to have devices on flexible 200 nm GaAs. Similarly, flexible GaSb and InP fabrication process is also reported to transform traditional electronics into large-area flexible electronics.

  3. Growth of 1.5 micron gallium indium nitrogen arsenic antimonide vertical cavity surface emitting lasers by molecular beam epitaxy

    Science.gov (United States)

    Wistey, Mark Allan

    Fiber optics has revolutionized long distance communication and long haul networks, allowing unimaginable data speeds and noise-free telephone calls around the world for mere pennies per hour at the trunk level. But the high speeds of optical fiber generally do not extend to individual workstations or to the home, in large part because it has been difficult and expensive to produce lasers which emitted light at wavelengths which could take advantage of optical fiber. One of the most promising solutions to this problem is the development of a new class of semiconductors known as dilute nitrides. Dilute nitrides such as GaInNAs can be grown directly on gallium arsenide, which allows well-established processing techniques. More important, gallium arsenide allows the growth of vertical-cavity surface-emitting lasers (VCSELs), which can be grown in dense, 2D arrays on each wafer, providing tremendous economies of scale for manufacturing, testing, and packaging. Unfortunately, GaInNAs lasers have suffered from what has been dubbed the "nitrogen penalty," with high thresholds and low efficiency as the fraction of nitrogen in the semiconductor was increased. This thesis describes the steps taken to identify and essentially eliminate the nitrogen penalty. Protecting the wafer surface from plasma ignition, using an arsenic cap, greatly improved material quality. Using a Langmuir probe, we further found that the nitrogen plasma source produced a large number of ions which damaged the wafer during growth. The ions were dramatically reduced using deflection plates. Low voltage deflection plates were found to be preferable to high voltages, and simulations showed low voltages to be adequate for ion removal. The long wavelengths from dilute nitrides can be partly explained by wafer damage during growth. As a result of these studies, we demonstrated the first CW, room temperature lasers at wavelengths beyond 1.5mum on gallium arsenide, and the first GaInNAs(Sb) VCSELs beyond 1

  4. Scanning near-field infrared microscopy on semiconductor structures

    Energy Technology Data Exchange (ETDEWEB)

    Jacob, Rainer

    2011-01-15

    literature. While the structures of the first system were in the micrometer regime, the capability to probe buried nanostructures is demonstrated at a sample of indium arsenide quantum dots. Those dots are covered by a thick layer of gallium arsenide. For the first time ever, it is shown experimentally that transitions between electron states in single quantum dots can be investigated by near-field microscopy. By monitoring the near-field response of these quantum dots while scanning the wavelength of the incident light beam, it was possible to obtain characteristic near-field signatures of single dots. Near-field contrasts up to 30 % could be measured for resonant excitation of electrons in the conduction band of the indium arsenide dots. (orig.)

  5. Interaction of coal-derived synthesis gas impurities with solid oxide fuel cell metallic components

    Science.gov (United States)

    Marina, Olga A.; Pederson, Larry R.; Coyle, Christopher A.; Edwards, Danny J.; Chou, Yeong-Shyung; Cramer, Carolyn N.

    Oxidation-resistant alloys find use as interconnect materials, heat exchangers, and gas supply tubing in solid oxide fuel cell (SOFC) systems, especially when operated at temperatures below ∼800 °C. If fueled with synthesis gas derived from coal or biomass, such metallic components could be exposed to impurities contained in those fuel sources. In this study, coupons of ferritic stainless steels Crofer 22 APU and SS 441, austenitic nickel-chromium superalloy Inconel 600, and an alumina-forming high nickel alloy alumel were exposed to synthesis gas containing ≤2 ppm phosphorus, arsenic and antimony, and reaction products were tested. Crofer 22 APU coupons coated with a (Mn,Co) 3O 4 protective layer were also evaluated. Phosphorus was found to be the most reactive. On Crofer 22 APU, the (Mn,Cr) 3O 4 passivation layer reacted to form an Mn-P-O product, predicted to be manganese phosphate from thermochemical calculations, and Cr 2O 3. On SS 441, reaction of phosphorus with (Mn,Cr) 3O 4 led to the formation of manganese phosphate as well as an Fe-P product, predicted from thermochemical calculations to be Fe 3P. Minimal interactions with antimony or arsenic in synthesis gas were limited to Fe-Sb and Fe-As solid solution formation. Though not intended for use on the anode side, a (Mn,Co) 3O 4 spinel coating on Crofer 22 APU reacted with phosphorus in synthesis gas to produce products consistent with Mn 3(PO 4) 2 and Co 2P. A thin Cr 2O 3 passivation layer on Inconel 600 did not prevent the formation of nickel phosphides and arsenides and of iron phosphides and arsenides, though no reaction with Cr 2O 3 was apparent. On alumel, an Al 2O 3 passivation layer rich in Ni did not prevent the formation of nickel phosphides, arsenides, and antimonides, though no reaction with Al 2O 3 occurred. This work shows that unprotected metallic components of an SOFC stack and system can provide a sink for P, As and Sb impurities that may be present in fuel gases, and thus complicate

  6. Scanning near-field infrared microscopy on semiconductor structures

    International Nuclear Information System (INIS)

    literature. While the structures of the first system were in the micrometer regime, the capability to probe buried nanostructures is demonstrated at a sample of indium arsenide quantum dots. Those dots are covered by a thick layer of gallium arsenide. For the first time ever, it is shown experimentally that transitions between electron states in single quantum dots can be investigated by near-field microscopy. By monitoring the near-field response of these quantum dots while scanning the wavelength of the incident light beam, it was possible to obtain characteristic near-field signatures of single dots. Near-field contrasts up to 30 % could be measured for resonant excitation of electrons in the conduction band of the indium arsenide dots. (orig.)

  7. III - V semiconductor structures for biosensor and molecular electronics applications

    Energy Technology Data Exchange (ETDEWEB)

    Luber, S.M.

    2007-01-15

    The present work reports on the employment of III-V semiconductor structures to biosensor and molecular electronics applications. In the first part a sensor based on a surface-near two dimensional electron gas for a use in biological environment is studied. Such a two dimensional electron gas inherently forms in a molecular beam epitaxy (MBE) grown, doped aluminum gallium arsenide - gallium arsenide (AlGaAs-GaAs) heterostructure. Due to the intrinsic instability of GaAs in aqueous solutions the device is passivated by deposition of a monolayer of 4'-substituted mercaptobiphenyl molecules. The influence of these molecules which bind to the GaAs via a sulfur group is investigated by Kelvin probe measurements in air. They reveal a dependence of GaAs electron affinity on the intrinsic molecular dipole moment of the mercaptobiphenyls. Furthermore, transient surface photovoltage measurements are presented which demonstrate an additional influence of mercaptobiphenyl chemisorption on surface carrier recombination rates. As a next step, the influence of pH-value and salt concentration upon the sensor device is discussed based on the results obtained from sensor conductance measurements in physiological solutions. A dependence of the device surface potential on both parameters due to surface charging is deduced. Model calculations applying Poisson-Boltzmann theory reveal as possible surface charging mechanisms either the adsorption of OH- ions on the surface, or the dissociation of OH groups in surface oxides. A comparison between simulation settings and physical device properties indicate the OH- adsorption as the most probable mechanism. In the second part of the present study the suitability of MBE grown III-V semiconductor structures for molecular electronics applications is examined. In doing so, a method to fabricate nanometer separated, coplanar, metallic electrodes based on the cleavage of a supporting AlGaAs-GaAs heterostructure is presented. This is followed

  8. (CaFeAs)10PtzAs8 superconductors and related compounds

    International Nuclear Information System (INIS)

    The main topic of this dissertation is the identification of new compounds, structure determination, and substitution dependent investigation of properties in this new branch of the family of iron arsenide superconductors (Chapter 2). Chapter 2.1 presents the identification of the superconducting compounds and the corresponding structure elucidation identifying two dif-ferent species (CaFeAs)10Pt3As8 and (CaFeAs)10Pt4As8 in this family (abbreviated as 1038 and 1048 according to their stoichiometry). However, a closer look revealed a more challenging structure chemistry which is covered in Chapter 2.2. The following two Chapters 2.3 and 2.4 are devoted to (CaFeAs)10Pt3As8 and more detailed investigations on this parent compound of the new superconductor family. Furthermore, transition metal substitution series (CaFe1-xMxAs)10Pt3As8 were synthesized to investigate the resemblance to model systems Ba(Fe1-xMx)2Asx and LaO(Fe1-xMx)As in the scope of structural changes and superconductivity as described in Chapter 2.5. Initially amazing differences in superconducting properties com-paring 1038 and 1048 compounds are analyzed in Chapter 2.6 establishing an universal dop-ing model in the (CaFe1-xMxAs)10PtzAs8 family. Additionally substituent dependent properties upon rare earth substitution in electron doped (Ca1-yREyFeAs)10Pt3As8 are investigated in Chapter 2.7, while a detailed study of superconducting properties and magnetism in (Ca1-yLayFeAs)10Pt3As8 by the local μSR technique is presented in Chapter 2.8. In Chapter 2.9 a comparison of direct and electron doping is discussed based on codoping experiments in (Ca1-yLayFe1-xPtxAs)10Pt3As8 and (CaFe1-xPtxAs)10Pt4As8. Finally, in Chapter 2.10 electron doping in stoichiometric 1048 is studied by charge compensation experiments in (Ca1-yNayFeAs)10Pt4As8. Chapter 3 is dedicated to a new family of calcium iron arsenides featuring frameworks of interconnected iron arsenide layers. The first subchapter presents the structure

  9. Organic semiconductors in a spin

    CERN Document Server

    Samuel, I

    2002-01-01

    A little palladium can go a long way in polymer-based light-emitting diodes. Inorganic semiconductors such as silicon and gallium arsenide are essential for countless applications in everyday life, ranging from PCs to CD players. However, while they offer unrivalled computational speed, inorganic semiconductors are also rigid and brittle, which means that they are less suited to applications such as displays and flexible electronics. A completely different class of materials - organic semiconductors - are being developed for these applications. Organic semiconductors have many attractive features: they are easy to make, they can emit visible light, and there is tremendous scope for tailoring their properties to specific applications by changing their chemical structure. Research groups and companies around the world have developed a wide range of organic-semiconductor devices, including transistors, light-emitting diodes (LEDs), solar cells and lasers. (U.K.)

  10. Transient-Grating Study of Electron and Hole Diffusion in (Ga,Mn)As

    Science.gov (United States)

    Kittlaus, Eric

    2011-11-01

    Dilute magnetic semiconductors are a class of materials exhibiting both semiconducting and ferromagnetic properties while being chemically similar to traditional semiconductors. This dual nature presents the opportunity for new ``spintronic'' devices, with the caveat that current dilute magnetic semiconductors are only ferromagnetic above their subzero Curie temperature, Tc. In order to develop new materials functional at room temperature, it is necessary to develop a better theoretical understanding of how such materials become magnetic, a result of microscopic electronic processes. One of the most common dilute magnetic semiconductors, (Ga,Mn)As, is produced by doping Gallium Arsenide with manganese. We use a laser-based experiment, transient-grating spectroscopy, to measure the diffusive motion of electrons and holes in (Ga,Mn)As, which provides information related to the processes which control magnetism in these materials. We present preliminary data and calculations and discuss further improvements in experimental design that will provide unprecedented insight into the microscopic workings of dilute magnetic semiconductors.

  11. Semiconductor Nanomembranes for Quantum Photonics: Quantum Light Sources and Optomechanics

    DEFF Research Database (Denmark)

    Liu, Jin

    This thesis describes the fabrication and characterizations of semiconductor nanomembranes, i.e., gallium arsenide (GaAs) photonic crystal (PC) and optomechanical nanomemebranes. Processing techniques are developed and optimized in order to fabricate PC membranes for quantum light sources...... and optomechanical nanomembranes for cavity cooling experiments. For PC cavities, several important processes have been extensively optimized such as the inductively coupled plasma (ICP) dry etch, the release of the membranes and the post-cleaning of the samples. GaAs optomechanical nanomembranes with a world......-record mechanical Q-factor up to 1 million have been fabricated with two step selective wet etches. These optomechanical naonmembranes exhibit superb performances in cavity optomechanical cooling experiments in which a mechanical mode has been cooled from room temperature to 4 K. The interaction between single...

  12. Inorganic Photovoltaics Materials and Devices: Past, Present, and Future

    Science.gov (United States)

    Hepp, Aloysius F.; Bailey, Sheila G.; Rafaelle, Ryne P.

    2005-01-01

    This report describes recent aspects of advanced inorganic materials for photovoltaics or solar cell applications. Specific materials examined will be high-efficiency silicon, gallium arsenide and related materials, and thin-film materials, particularly amorphous silicon and (polycrystalline) copper indium selenide. Some of the advanced concepts discussed include multi-junction III-V (and thin-film) devices, utilization of nanotechnology, specifically quantum dots, low-temperature chemical processing, polymer substrates for lightweight and low-cost solar arrays, concentrator cells, and integrated power devices. While many of these technologies will eventually be used for utility and consumer applications, their genesis can be traced back to challenging problems related to power generation for aerospace and defense. Because this overview of inorganic materials is included in a monogram focused on organic photovoltaics, fundamental issues and metrics common to all solar cell devices (and arrays) will be addressed.

  13. Characterization of InGaAs linear array for applications to remote sensing

    Science.gov (United States)

    Garcia, Christopher S.; Refaat, Tamer F.; Farnsworth, Glenn R.; Abedin, M. N.; Elsayed-Ali, Hani E.

    2005-05-01

    An Indium Gallium Arsenide linear photodiode array in the 1.1-2.5 μm spectral range was characterized. The array has 1024X1 pixels with a 25 μm pitch and was manufactured by Sensors Unlimited, Inc. Characterization and analysis of the electrical and optical properties of a camera system were carried out at room temperature to obtain detector performance parameters. The signal and noise were measured while the array was uniformly illuminated at varying exposure levels. A photon transfer curve was generated by plotting noise as a function of average signal to obtain the camera gain constant. The spectral responsivity was also measured, and the quantum efficiency, read noise and full-well capacity were determined. This paper describes the characterization procedure, analyzes the experimental results, and discusses the applications of the InGaAs linear array to future earth and planetary remote sensing mission.

  14. Integrated three-dimensional photonic nanostructures for achieving near-unity solar absorption and superhydrophobicity

    Science.gov (United States)

    Kuang, Ping; Hsieh, Mei-Li; Lin, Shawn-Yu

    2015-06-01

    In this paper, we proposed and realized 3D photonic nanostructures consisting of ultra-thin graded index antireflective coatings (ARCs) and woodpile photonic crystals. The use of the integrated ARC and photonic crystal structure can achieve broadband, broad-angle near unity solar absorption. The amorphous silicon based photonic nanostructure experimentally shows an average absorption of ˜95% for λ = 400-620 nm over a wide angular acceptance of θ = 0°-60°. Theoretical studies show that a Gallium Arsenide (GaAs) based structure can achieve an average absorption of >95% for λ = 400-870 nm. Furthermore, the use of the slanted SiO2 nanorod ARC surface layer by glancing angle deposition exhibits Cassie-Baxter state wetting, and superhydrophobic surface is obtained with highest water contact angle θCB ˜ 153°. These properties are fundamentally important for achieving maximum solar absorption and surface self-cleaning in thin film solar cell applications.

  15. Plasmonic Light Trapping in an Ultrathin Photovoltaic Layer with Film-Coupled Metamaterial Structures

    CERN Document Server

    Wang, Hao

    2014-01-01

    A film-coupled metamaterial structure is numerically investigated for enhancing the light absorption in an ultrathin photovoltaic layer of crystalline gallium arsenide (GaAs). The top subwavelength concave grating and the bottom metallic film could not only effectively trap light with the help of wave interference and magnetic resonance effects excited above the bandgap, but also practically serve as electrical contacts for photon-generated charge collection. The energy absorbed by the active layer is greatly enhanced in the film-coupled metamaterial structure, resulting in significant enhancement on the short-circuit current density by three times over a free-standing GaAs layer at the same thickness. The results would facilitate the development of next-generation ultrathin solar cells with lower cost and higher efficiency.

  16. Electrical tuning of Rashba spin-orbit interaction in multigated InAs nanowires

    Science.gov (United States)

    Scherübl, Zoltán; Fülöp, Gergő; Madsen, Morten H.; Nygârd, Jesper; Csonka, Szabolcs

    2016-07-01

    Indium arsenide nanowires (NWs) are a promising platform to fabricate quantum electronic devices, among other advantages they have strong spin-orbit interaction (SOI). The controlled tuning of the SOI is desired in spin-based quantum devices. In this study we investigate the possibility of tuning the SOI by electrostatic fields generated by a back gate and two side gates placed on the opposite sides of the NW. The strength of the SOI is analyzed by weak anti-localization effect. We demonstrate that the strength of the SOI can be strongly tuned up to a factor of 2 with the electric field across the NW, while the average electron density is kept constant. Furthermore, a simple electrostatic model is introduced to calculate the expected change of the SOI. Good agreement is found between the experimental results and the estimated Rashba-type SOI generated by the gate-induced electric field.

  17. Photonic crystals possessing multiple Weyl points and the experimental observation of robust surface states

    Science.gov (United States)

    Chen, Wen-Jie; Xiao, Meng; Chan, C. T.

    2016-01-01

    Weyl points, as monopoles of Berry curvature in momentum space, have captured much attention recently in various branches of physics. Realizing topological materials that exhibit such nodal points is challenging and indeed, Weyl points have been found experimentally in transition metal arsenide and phosphide and gyroid photonic crystal whose structure is complex. If realizing even the simplest type of single Weyl nodes with a topological charge of 1 is difficult, then making a real crystal carrying higher topological charges may seem more challenging. Here we design, and fabricate using planar fabrication technology, a photonic crystal possessing single Weyl points (including type-II nodes) and multiple Weyl points with topological charges of 2 and 3. We characterize this photonic crystal and find nontrivial 2D bulk band gaps for a fixed kz and the associated surface modes. The robustness of these surface states against kz-preserving scattering is experimentally observed for the first time. PMID:27703140

  18. Fabrication and characterization of a microaccelerometer based on resonant-tunneling diodes

    Science.gov (United States)

    Li, Mengwei; Deng, Tao; Du, Kang; Chu, WeiHang; Liu, Jun; Chen, Houjin; Liu, Zewen

    2016-01-01

    A microaccelerometer based on gallium arsenide (GaAs) resonant-tunneling diodes (RTDs) is demonstrated. The input acceleration signal can be transformed into an output electrical signal using the meso-piezoresistive effects of the RTDs located at the root of the detection beams. Finite element simulations were performed to design, analyze, and optimize the structures of the accelerometer. The accelerometer was fabricated using a combination of GaAs IC surface and bulk micromachining techniques. Vibrating tests and shock tests were conducted to investigate the accelerometer characteristics. The experimental results revealed that the sensitivity of the RTD accelerometer was 7.91 mV/g. The noise resolution was ˜1.264 mg/√Hz, and the working frequency was up to 3 kHz.

  19. Low-energy laser treatment of rheumatic diseases: a long-term study

    Science.gov (United States)

    Antipa, Ciprian; Moldoveanu, Vladimir; Rusca, Nicolae; Bruckner, Ion I.; Podoleanu, Adrian Gh.; Stanciulescu, Viorica

    1995-05-01

    We tried to establish the efficiency of low energy (power) lasers (LEL), in various inflammatory and noninflammatory rheumatic diseases during five years. We treated 514 patients with osteoarthrosis, 326 patients with nonarticular rheumatism and 82 patients with inflammatory rheumatism, in four different ways: only with Galium-Aluminum-Arsenide (GaAs) infrared lasers; both GaAs lasers and Helium neon (HeNe) lasers; with placebo laser; with classical anti-inflammatory therapy. The results were analyzed using local objective improvements and the score obtained from a pain scale before and after the treatments. We also note some preliminary results obtained by the computer analysis of the evocated potentials after laser irradiation. We conclude that LEL (especially HeNe with GaAs) is obviously more efficient than placebo laser therapy and also had better or at least similar results, in most of the cases, than classical anti-inflammatory therapy.

  20. Scanning tunnelling microscopy and spectroscopy on organic PTCDA films deposited on sulfur passivated GaAs(001)

    International Nuclear Information System (INIS)

    Deposition of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) on sulfur passivated gallium arsenide S-GaAs(001) surfaces is investigated by scanning tunnelling microscopy and scanning tunnelling spectroscopy. The surface morphology and the film structure are studied for the multilayer growth of the organic molecules. Spectroscopic results for both clean substrate and ordered areas of PTCDA are shown in this work. We have measured I-V plots at different tip-sample distances, avoiding deformation of the organic layer. Under proper experimental conditions, a gap value of 2.2eV has been measured on PTCDA crystals, in good agreement with the expected value for PTCDA (2.2-2.55eV)

  1. Alteration zones around Kupferschiefer-type base metal mineralization in West Germany

    Science.gov (United States)

    Schmidt, F.-P.

    1987-07-01

    Several occurrences of red-colored rocks, which represent an unusual species within the lower Zechstein sediments as well as siderite ribbons and kaolinization have been reported from the West German lower Zechstein sequence. The red-colored rocks had been classified into two types, i.e., the stratiform red layers (SRL) and the Rote Fäule (RF). With regard to the gray beds, both types are characterized by enrichments and depletions of certain elements. As a result, ore-related Rote Fäule could be distinguished from insignificant stratiform red layers. Whereas Rote Fäule, which represents the alteration zone around diagenetic Kupferschiefer-type deposits, is chiefly characterized by apparent red coloring and enrichment in sulfate S, both the siderite ribbons and kaolinization of feldspars refer to formation of Cu-As sulfides and arsenides due to a hydrothermal, epigenetic process. Formation under more oxidizing, synsedimentary conditions is presumed for the stratiform red layers.

  2. Influence of photon recycling effects in the operation and design of GaAs solar cells; Influencia del reciclaje de fotones en el funcionamiento y del diseno de las celulas solares de Arsenico de Galio

    Energy Technology Data Exchange (ETDEWEB)

    Balenzategui Manzanares, J. L.

    2005-07-01

    Photon recycling (PR) is the process by which photons internally emitted in a semiconductor can be re-absorbed by the material, giving as result new electron-hole pairs. Although this process has been receiving some international research from the Sixties, because their effects revealed as relevant in certain devices and materials (as in gallium arsenide), its influence in the operation of solar cells has been scarcely considered in the past. Thus deposited it has been demonstrated that one of its major effects is an enhancement of the radiative carrier lifetine, photon recycling is not usually taken into account in photovoltaic, neither in device modelling and simulation, nor from the perspective of taking advantage of the phenomenon to improve the efficiency of solar cells. This work describes the results of our investigations in the field of photon recycling. (Author)

  3. Geometrical shape design of nanophotonic surfaces for thin film solar cells.

    Science.gov (United States)

    Nam, W I; Yoo, Y J; Song, Y M

    2016-07-11

    We present the effect of geometrical parameters, particularly shape, on optical absorption enhancement for thin film solar cells based on crystalline silicon (c-Si) and gallium arsenide (GaAs) using a rigorous coupled wave analysis (RCWA) method. It is discovered that the "sweet spot" that maximizes efficiency of solar cells exists for the design of nanophotonic surfaces. For the case of ultrathin, rod array is practical due to the effective optical resonances resulted from the optimum geometry whereas parabola array is viable for relatively thicker cells owing to the effective graded index profile. A specific value of thickness, which is the median value of other two devices tailored by rod and paraboloid, is optimized by truncated shape structure. It is therefore worth scanning the optimum shape of nanostructures in a given thickness in order to achieve high performance. PMID:27410892

  4. The Unexpected Influence of Precursor Conversion Rate in the Synthesis of III-V Quantum Dots.

    Science.gov (United States)

    Franke, Daniel; Harris, Daniel K; Xie, Lisi; Jensen, Klavs F; Bawendi, Moungi G

    2015-11-23

    Control of quantum dot (QD) precursor chemistry has been expected to help improve the size control and uniformity of III-V QDs such as indium phosphide and indium arsenide. Indeed, experimental results for other QD systems are consistent with the theoretical prediction that the rate of precursor conversion is an important factor controlling QD size and size distribution. We synthesized and characterized the reactivity of a variety of group-V precursors in order to determine if precursor chemistry could be used to improve the quality of III-V QDs. Despite slowing down precursor conversion rate by multiple orders of magnitude, the less reactive precursors do not yield the expected increase in size and improvement in size distribution. This result disproves the widely accepted explanation for the shortcoming of current III-V QD syntheses and points to the need for a new generalizable theoretical picture for the mechanism of QD formation and growth.

  5. Universal Test Facility

    Science.gov (United States)

    Laughery, Mike

    A universal test facility (UTF) for Space Station Freedom is developed. In this context, universal means that the experimental rack design must be: automated, highly marketable, and able to perform diverse microgravity experiments according to NASA space station requirements. In order to fulfill these broad objectives, the facility's customers, and their respective requirements, are first defined. From these definitions, specific design goals and the scope of the first phase of this project are determined. An examination is first made into what types of research are most likely to make the UTF marketable. Based on our findings, the experiments for which the UTF would most likely be used included: protein crystal growth, hydroponics food growth, gas combustion, gallium arsenide crystal growth, microorganism development, and cell encapsulation. Therefore, the UTF is designed to fulfill all of the major requirements for the experiments listed above. The versatility of the design is achieved by taking advantage of the many overlapping requirements presented by these experiments.

  6. Increasing the effective aperture of a detector and enlarging the receiving field of view in a 3D imaging lidar system through hexagonal prism beam splitting.

    Science.gov (United States)

    Lee, Xiaobao; Wang, Xiaoyi; Cui, Tianxiang; Wang, Chunhui; Li, Yunxi; Li, Hailong; Wang, Qi

    2016-07-11

    The detector in a highly accurate and high-definition scanning 3D imaging lidar system requires high frequency bandwidth and sufficient photosensitive area. To solve the problem of small photosensitive area of an existing indium gallium arsenide detector with a certain frequency bandwidth, this study proposes a method for increasing the receiving field of view (FOV) and enlarging the effective photosensitive aperture of such detector through hexagonal prism beam splitting. The principle and construction of hexagonal prism beam splitting is also discussed in this research. Accordingly, a receiving optical system with two hexagonal prisms is provided and the splitting beam effect of the simulation experiment is analyzed. Using this novel method, the receiving optical system's FOV can be improved effectively up to ±5°, and the effective photosensitive aperture of the detector is increased from 0.5 mm to 1.5 mm. PMID:27410800

  7. The social costs of solar energy: A study of photovoltaic energy systems

    Science.gov (United States)

    Neff, T. L.

    An extensive analysis of the social costs of photovoltaic energy systems shows that there are potentially significant hazards associated with the manufacture and use of such technologies as large-crystal silicon, cadmium sulfide, and gallium arsenide solar cell arrays. The categories of applications considered were (1) decentralized residential installations, (2) decentralized neighborhood, commercial or industrial installations, and (3) central station plants. Summary and conclusion statements are presented for occupational health, public health, environmental impacts, labor, materials and energy impacts, and implications for technological development. It is thought in overview that there are reasons for optimism about the ability of photovoltaics to improve the balance of social costs and benefits in the energy sector.

  8. Structural and magnetic phase transitions in NdCoAsO under high pressures

    International Nuclear Information System (INIS)

    We have investigated structural and magnetic phase transitions under high pressures in a quaternary rare-earth transition-metal arsenide oxide NdCoAsO compound that is isostructural to the high temperature superconductor parent phase NdFeAsO. The four-probe electrical resistance measurements carried out in a designer diamond anvil cell show that the ferromagnetic Curie temperature and antiferromagnetic Neel temperature increase with an increase in pressure. High pressure x-ray diffraction studies using a synchrotron source show a structural phase transition from a tetragonal phase to a new crystallographic phase at a pressure of 23 GPa at 300 K. The NdCoAsO sample remained antiferromagnetic and non-superconducting down to 10 K and up to the highest pressure achieved in this experiment, 53 GPa. A P-T phase diagram for NdCoAsO is presented from ambient conditions to P = 53 GPa and T = 10 K.

  9. Numerical simulation and analysis of electrical and optical properties of Al(x)Ga(1-x)As / GaAs

    Science.gov (United States)

    Eschrich, Heinz

    A numerical algorithm for description of gallium arsenide solar cells behavior with photovoltaic active window layer is developed. A partial nonlinear differential equation system, based on current, balance and Poisson equations, was solved using finite difference method. Spatial distributions of charge carrier concentration and potential were calculated using a recursive and iterative solution algorithm. Reflexion losses at all phase boundaries were determined using a matrix method. Solution algorithm was tested considering results of an analytical model of a solar cell with abrupt pn transition. From results of analytic optimization calculations, an improved structure was obtained, with a thinner emitter of 820 nm. The influence of surface and boundary recombination, diffusion length and cell geometry on spectral internal quantum efficiency was simulated.

  10. Mechanism for explaining differences in the order parameters of FeAs-based and FeP-based pnictide superconductors.

    Science.gov (United States)

    Thomale, Ronny; Platt, Christian; Hanke, Werner; Bernevig, B Andrei

    2011-05-01

    We put forward a scenario that explains the difference between the order-parameter character in arsenide (As) and phosphorous (P) iron-based superconductors. Using functional renormalization group to analyze it in detail, we find that nodal superconductivity on the electron pockets (hole pocket gaps are always nodeless) can naturally appear when the hole pocket at (π,π) in the unfolded Brillouin zone is absent, as is the case in LaOFeP. There, electron-electron interactions render the gap on the electron pockets softly nodal (of s(±) form). When the pocket of d(xy) orbital character is present, intraorbital interactions with the d(xy) part of the electron Fermi surface drives the superconductivity nodeless.

  11. Transition from three-dimensional anisotropic spin excitations to two-dimensional spin excitations by electron doping the FeAs-based BaFe1.96Ni0.04As2 superconductor.

    Science.gov (United States)

    Harriger, Leland W; Schneidewind, Astrid; Li, Shiliang; Zhao, Jun; Li, Zhengcai; Lu, Wei; Dong, Xiaoli; Zhou, Fang; Zhao, Zhongxian; Hu, Jiangping; Dai, Pengcheng

    2009-08-21

    We use neutron scattering to study the effect of electron doping on the structural or magnetic order in BaFe2As2. In the undoped state, BaFe2As2 exhibits simultaneous structural and magnetic phase transitions below 143 K. Upon electron doping to form BaFe1.96Ni0.04As2, the system first displays the lattice distortion near approximately 97 K, and then orders antiferromagnetically at 91 K before developing weak superconductivity below approximately 15 K. The effect of electron doping is to reduce the c-axis exchange coupling in BaFe2As2 and induce quasi-two-dimensional (2D) spin excitations. These results suggest that the transition from 3D spin waves to quasi-2D spin excitations by electron doping is important for the separated structural and magnetic phase transitions in iron arsenides.

  12. Superconductivity and ferromagnetism in hole-doped RbEuFe4As4

    Science.gov (United States)

    Liu, Yi; Liu, Ya-Bin; Tang, Zhang-Tu; Jiang, Hao; Wang, Zhi-Cheng; Ablimit, Abduweli; Jiao, Wen-He; Tao, Qian; Feng, Chun-Mu; Xu, Zhu-An; Cao, Guang-Han

    2016-06-01

    We discover a robust coexistence of superconductivity and ferromagnetism in an iron arsenide RbEuFe4As4 . The new material crystallizes in an intergrowth structure of RbFe2As2 and EuFe2As2 , such that the Eu sublattice turns out to be primitive instead of being body-centered in EuFe2As2 . The FeAs layers, featured by asymmetric As coordinations, are hole doped due to charge homogenization. Our combined measurements of electrical transport, magnetization, and heat capacity unambiguously and consistently indicate bulk superconductivity at 36.5 K in the FeAs layers and ferromagnetism at 15 K in the Eu sublattice. Interestingly, the Eu-spin ferromagnetic ordering belongs to a rare third-order transition, according to the Ehrenfest classification of phase transitions. We also identify an additional anomaly at ˜5 K, which is possibly associated with the interplay between superconductivity and ferromagnetism.

  13. Nanostructured semiconductor solar absorbers with near 100% absorption and related light management picture

    Science.gov (United States)

    Li, Yali; Gao, Pingqi; Chen, Qiang; Yang, Jiaming; Li, Junshuai; He, Deyan

    2016-06-01

    Optical behaviors of both polycrystalline silicon (Si) and gallium arsenide (GaAs) nanocone (NC)-capped nanowire (NW) arrays are systematically investigated and a full light management picture is presented. The study demonstrates that compared to shape- and environment-sensitive optical resonance modes, including leaky modes and guided longitudinal resonances, optimization of light harvesting based on light scattering is more operable to guide related device fabrication. Under this consideration, near 100% absorption above the bandgap energy is realized for GaAs NC-capped NW arrays with an effective thickness of only ~1000 nm through balancing antireflection and light scattering in the optical systems. Further study under oblique incidence shows that light absorption for the optimized NC-capped NW arrays is almost insensitive to the incident angle, indicating excellent omnidirectional light management in the NC-capped NW configuration.

  14. Surface impedance of BaFe2-xNixAs2 in the radio frequency range

    Directory of Open Access Journals (Sweden)

    Abbassi Abdellatif

    2012-08-01

    Full Text Available We report measurements of the temperature dependence of the surface impedance in superconducting BaFe1.93Ni0.07As2 crystals using the radiofrequency reflection technique in the 5arsenide superconductors BaFe2-xNixAs2 has attracted much interest. For a Ni doping level of 7% the superconducting phase transition is found around 20K. The temperature dependence of the superconducting penetration depth was determined.

  15. Detrapping and retrapping of free carriers in nominally pure single crystal GaP, GaAs and 4H-SiC semiconductors under light illumination at cryogenic temperatures

    CERN Document Server

    Mouneyrac, David; Floch, Jean-Michel Le; Tobar, Michael E; Cros, Dominique; Krupka, Jerzy

    2010-01-01

    We report on extremely sensitive measurements of changes in the microwave properties of high purity non-intentionally-doped single-crystal semiconductor samples of gallium phosphide, gallium arsenide and 4H-silicon carbide when illuminated with light of different wavelengths at cryogenic temperatures. Whispering gallery modes were excited in the semiconductors whilst they were cooled on the coldfinger of a single-stage cryocooler and their frequencies and Q-factors measured under light and dark conditions. With these materials, the whispering gallery mode technique is able to resolve changes of a few parts per million in the permittivity and the microwave losses as compared with those measured in darkness. A phenomenological model is proposed to explain the observed changes, which result not from direct valence to conduction band transitions but from detrapping and retrapping of carriers from impurity/defect sites with ionization energies that lay in the semiconductor band gap. Detrapping and retrapping relax...

  16. Amorphous metallic films in silicon metallization systems

    Science.gov (United States)

    So, F.; Kolawa, E.; Nicolet, M. A.

    1985-01-01

    Diffusion barrier research was focussed on lowering the chemical reactivity of amorphous thin films on silicon. An additional area of concern is the reaction with metal overlays such as aluminum, silver, and gold. Gold was included to allow for technology transfer to gallium arsenide PV cells. Amorphous tungsten nitride films have shown much promise. Stability to annealing temperatures of 700, 800, and 550 C were achieved for overlays of silver, gold, and aluminum, respectively. The lower results for aluminum were not surprising because there is an eutectic that can form at a lower temperature. It seems that titanium and zirconium will remove the nitrogen from a tungsten nitride amorphous film and render it unstable. Other variables of research interest were substrate bias and base pressure during sputtering.

  17. Optical and interfacial electronic properties of diamond-like carbon films

    Science.gov (United States)

    Woollam, J. A.; Natarajan, V.; Lamb, J.; Khan, A. A.; Bu-Abbud, G.; Banks, B.; Pouch, J.; Gulino, D. A.; Domitz, S.; Liu, D. C.

    1984-01-01

    Hard, semitransparent carbon films were prepared on oriented polished crystal wafers of silicon, indium phosphide and gallium arsenide, as well as on KBr and quartz. Properties of the films were determined using IR and visible absorption spectrocopy, ellipsometry, conductance-capacitance spectroscopy and alpha particle-proton recoil spectroscopy. Preparation techniques include RF plasma decomposition of methane (and other hydrocarbons), ion beam sputtering, and dual-ion-beam sputter deposition. Optical energy band gaps as large as 2.7 eV and extinction coefficients lower than 0.1 at long wavelengths are found. Electronic state densities at the interface with silicon as low as 10 to the 10th states/eV sq cm per were found.

  18. AlGaAs-On-Insulator Nonlinear Photonics

    CERN Document Server

    Pu, Minhao; Semenova, Elizaveta; Yvind, Kresten

    2015-01-01

    The combination of nonlinear and integrated photonics has recently seen a surge with Kerr frequency comb generation in micro-resonators as the most significant achievement. Efficient nonlinear photonic chips have myriad applications including high speed optical signal processing, on-chip multi-wavelength lasers, metrology, molecular spectroscopy, and quantum information science. Aluminium gallium arsenide (AlGaAs) exhibits very high material nonlinearity and low nonlinear loss when operated below half its bandgap energy. However, difficulties in device processing and low device effective nonlinearity made Kerr frequency comb generation elusive. Here, we demonstrate AlGaAs-on-insulator as a nonlinear platform at telecom wavelengths. Using newly developed fabrication processes, we show high-quality-factor (Q>100,000) micro-resonators with integrated bus waveguides in a planar circuit where optical parametric oscillation is achieved with a record low threshold power of 3 mW and a frequency comb spanning 350 nm i...

  19. Effect of tensile stress on the in-plane resistivity anisotropy in BaFe2As2

    International Nuclear Information System (INIS)

    The effect of uniaxial tensile stress and the resultant strain on the structural/magnetic transition in the parent compound of the iron arsenide superconductor BaFe2As2 is characterized by temperature-dependent electrical resistivity, x-ray diffraction, and quantitative polarized light imaging. We show that strain induces a measurable uniaxial structural distortion above the first-order magnetic transition and significantly smears the structural transition. This response is different from that found in another parent compound, SrFe2As2, where the coupled structural and magnetic transitions are strongly first order. This difference in the structural responses explains the in-plane resistivity anisotropy above the transition in BaFe2As2. This conclusion is supported by the Ginzburg-Landau-type phenomenological model for the effect of the uniaxial strain on the resistivity anisotropy.

  20. The Laser MicroJet (LMJ): a multi-solution technology for high quality micro-machining

    Science.gov (United States)

    Mai, Tuan Anh; Richerzhagen, Bernold; Snowdon, Paul C.; Wood, David; Maropoulos, Paul G.

    2007-02-01

    The field of laser micromachining is highly diverse. There are many different types of lasers available in the market. Due to their differences in irradiating wavelength, output power and pulse characteristic they can be selected for different applications depending on material and feature size [1]. The main issues by using these lasers are heat damages, contamination and low ablation rates. This report examines on the application of the Laser MicroJet(R) (LMJ), a unique combination of a laser beam with a hair-thin water jet as a universal tool for micro-machining of MEMS substrates, as well as ferrous and non-ferrous materials. The materials include gallium arsenide (GaAs) & silicon wafers, steel, tantalum and alumina ceramic. A Nd:YAG laser operating at 1064 nm (infra red) and frequency doubled 532 nm (green) were employed for the micro-machining of these materials.

  1. Effect of hydrogen on change carrier dissipation in 60Co irradiated by γ-quanta and non-alloyed n-type GaAs

    International Nuclear Information System (INIS)

    The pretreatment in hydrogen plasma (the hydrogenation) influences on the charge carrier dissipation processes in the non-alloyed gallium arsenide of n-type with no = (5...7) centre dot 1015 cm-3 and μo = (5...6) centre dot 10 13 cm2 / (V centre dot c) irradiated by γ-quantum 60Co was studied. The comparison of experimental dependence μ (T) with the designed one in the temperature range 77...291 K for non-hydrogenized and hydrogenized non irradiated and γ-quantum irradiated crystals was carried out. It is shown that the main dissipative mechanism that determine the charged carrier mobility in the non hydrogenized material is the dissipation on the charged centers - the radiation defects in the γ-quantum irradiated GaAs; the presence of double ionized defects is possible

  2. Cell membrane conformation at vertical nanowire array interface revealed by fluorescence imaging

    Science.gov (United States)

    Berthing, Trine; Bonde, Sara; Rostgaard, Katrine R.; Hannibal Madsen, Morten; Sørensen, Claus B.; Nygård, Jesper; Martinez, Karen L.

    2012-10-01

    The perspectives offered by vertical arrays of nanowires for biosensing applications in living cells depend on the access of individual nanowires to the cell interior. Recent results on electrical access and molecular delivery suggest that direct access is not always obtained. Here, we present a generic approach to directly visualize the membrane conformation of living cells interfaced with nanowire arrays, with single nanowire resolution. The method combines confocal z-stack imaging with an optimized cell membrane labelling strategy which was applied to HEK293 cells interfaced with 2-11 μm long and 3-7 μm spaced nanowires with various surface coatings (bare, aminosilane-coated or polyethyleneimine-coated indium arsenide). We demonstrate that, for all commonly used nanowire lengths, spacings and surface coatings, nanowires generally remain enclosed in a membrane compartment, and are thereby not in direct contact with the cell interior.

  3. Enhancing Solar Cell Efficiency Using Photon Upconversion Materials

    Directory of Open Access Journals (Sweden)

    Yunfei Shang

    2015-10-01

    Full Text Available Photovoltaic cells are able to convert sunlight into electricity, providing enough of the most abundant and cleanest energy to cover our energy needs. However, the efficiency of current photovoltaics is significantly impeded by the transmission loss of sub-band-gap photons. Photon upconversion is a promising route to circumvent this problem by converting these transmitted sub-band-gap photons into above-band-gap light, where solar cells typically have high quantum efficiency. Here, we summarize recent progress on varying types of efficient upconversion materials as well as their outstanding uses in a series of solar cells, including silicon solar cells (crystalline and amorphous, gallium arsenide (GaAs solar cells, dye-sensitized solar cells, and other types of solar cells. The challenge and prospect of upconversion materials for photovoltaic applications are also discussed

  4. X-ray imaging with photon counting hybrid semiconductor pixel detectors

    CERN Document Server

    Manolopoulos, S; Campbell, M; Snoeys, W; Heijne, Erik H M; Pernigotti, E; Raine, C; Smith, K; Watt, J; O'Shea, V; Ludwig, J; Schwarz, C

    1999-01-01

    Semiconductor pixel detectors, originally developed for particle physics experiments, have been studied as X-ray imaging devices. The performance of devices using the OMEGA 3 read-out chip bump-bonded to pixellated silicon semiconductor detectors is characterised in terms of their signal-to-noise ratio when exposed to 60 kVp X-rays. Although parts of the devices achieve values of this ratio compatible with the noise being photon statistics limited, this is not found to hold for the whole pixel matrix, resulting in the global signal-to-noise ratio being compromised. First results are presented of X-ray images taken with a gallium arsenide pixel detector bump-bonded to a new read-out chip, (MEDIPIX), which is a single photon counting read-out chip incorporating a 15-bit counter in every pixel. (author)

  5. X-ray imaging with photon counting hybrid semiconductor pixel detectors

    Energy Technology Data Exchange (ETDEWEB)

    Manolopoulos, S.; Bates, R.; Campbell, M.; Snoeys, W.; Heijne, E.; Pernigotti, E.; Raine, C.; Smith, K. E-mail: k.smith@physics.gla.ac.uk; Watt, J.; O' Shea, V.; Ludwig, J.; Schwarz, C

    1999-09-11

    Semiconductor pixel detectors, originally developed for particle physics experiments, have been studied as X-ray imaging devices. The performance of devices using the {omega}3 read-out chip bump-bonded to pixellated silicon semiconductor detectors is characterised in terms of their signal-to-noise ratio when exposed to 60 kVp X-rays. Although parts of the devices achieve values of this ratio compatible with the noise being photon statistics limited, this is not found to hold for the whole pixel matrix, resulting in the global signal-to-noise ratio being compromised. First results are presented of X-ray images taken with a gallium arsenide pixel detector bump-bonded to a new read-out chip, (MEDIPIX), which is a single photon counting read-out chip incorporating a 15-bit counter in every pixel. (author)

  6. Vertical nanowire arrays as a versatile platform for protein detection and analysis

    DEFF Research Database (Denmark)

    Rostgaard, Katrine R.; Frederiksen, Rune S.; Liu, Yi-Chi;

    2013-01-01

    Protein microarrays are valuable tools for protein assays. Reducing spot sizes from micro- to nano-scale facilitates miniaturization of platforms and consequently decreased material consumption, but faces inherent challenges in the reduction of fluorescent signals and compatibility with complex...... the NWs unnecessary. Fluorescence detection of proteins allows quantitative measurements and spatial resolution, enabling us to track individual NWs through several analytical steps, thereby allowing multiplexed detection of different proteins immobilized on different regions of the NW array. We use NW...... arrays for on-chip extraction, detection and functional analysis of proteins on a nano-scale platform that holds great promise for performing protein analysis on minute amounts of material. The demonstration made here on highly ordered arrays of indium arsenide (InAs) NWs is generic and can be extended...

  7. Lead sulphide nanocrystal photodetector technologies

    Science.gov (United States)

    Saran, Rinku; Curry, Richard J.

    2016-02-01

    Light detection is the underlying principle of many optoelectronic systems. For decades, semiconductors including silicon carbide, silicon, indium gallium arsenide and germanium have dominated the photodetector industry. They can show excellent photosensitivity but are limited by one or more aspects, such as high production cost, high-temperature processing, flexible substrate incompatibility, limited spectral range or a requirement for cryogenic cooling for efficient operation. Recently lead sulphide (PbS) nanocrystals have emerged as one of the most promising new materials for photodetector fabrication. They offer several advantages including low-cost manufacturing, solution processability, size-tunable spectral sensitivity and flexible substrate compatibility, and they have achieved figures of merit outperforming conventional photodetectors. We review the underlying concepts, breakthroughs and remaining challenges in photodetector technologies based on PbS nanocrystals.

  8. Fiber-optic sensor family for the measurement of temperature, vibration, and pressure

    International Nuclear Information System (INIS)

    A family of fiberoptic sensors for measuring temperature, vibration and pressure is described with respect to measurement principle, sensor design and optical construction. Non-coherent optical luminescence phenomena are used as information carriers for the measuring parameters. The sensors contain luminescent materials (gallium arsenide or neodymium-doped glass) and have a mechanical design that is determined by the specific application. The optical design of the system is based on beam splitters with interference filters and other micro-components. Experimental results of present designs are described and the development potential of the sensors is discussed. Finally, an overview of present application areas is given together with results from recent field experiments and reference installations in progress at present. (orig.)

  9. Resonant metallic nanostructure for enhanced two-photon absorption in a thin GaAs p-i-n diode

    International Nuclear Information System (INIS)

    Degenerate two-photon absorption (TPA) is investigated in a 186 nm thick gallium arsenide (GaAs) p-i-n diode embedded in a resonant metallic nanostructure. The full device consists in the GaAs layer, a gold subwavelength grating on the illuminated side, and a gold mirror on the opposite side. For TM-polarized light, the structure exhibits a resonance close to 1.47 μm, with a confined electric field in the intrinsic region, far from the metallic interfaces. A 109 times increase in photocurrent compared to a non-resonant device is obtained experimentally, while numerical simulations suggest that both gain in TPA-photocurrent and angular dependence can be further improved. For optimized grating parameters, a maximum gain of 241 is demonstrated numerically and over incidence angle range of (−30°; +30°).

  10. Manipulation of adsorbed atoms and creation of new structures on room-temperature surfaces with a scanning tunneling microscope.

    Science.gov (United States)

    Whitman, L J; Stroscio, J A; Dragoset, R A; Celotta, R J

    1991-03-01

    A general method of manipulating adsorbed atoms and molecules on room-temperature surfaces with the use of a scanning tunneling microscope is described. By applying an appropriate voltage pulse between the sample and probe tip, adsorbed atoms can be induced to diffuse into the region beneath the tip. The field-induced diffusion occurs preferentially toward the tip during the voltage pulse because of the local potential energy gradient arising from the interaction of the adsorbate dipole moment with the electric field gradient at the surface. Depending upon the surface and pulse parameters, cesium (Cs) structures from one nanometer to a few tens of nanometers across have been created in this way on the (110) surfaces of gallium arsenide (GaAs) and indium antimonide (InSb), including structures that do not naturally occur.

  11. Three Photon Absorption in Optical Parametric Oscillators Based on OP-GaAs

    CERN Document Server

    Heckl, Oliver H; Winkler, Georg; Changala, P Bryan; Spaun, Ben; Porat, 1 Gil; Bui, Thinh Q; Lee, Kevin F; Jiang, Jie; Fermann, Martin; Schunemann, Peter G; Ye, Jun

    2016-01-01

    We report on the first singly-resonant (SR), synchronously pumped optical parametric oscillator (OPO) based on orientation-patterned gallium arsenide (OP-GaAs). Together with a doubly resonant (DR) degenerate OPO based on the same OP-GaAs material, the output spectra cover 3 to 6 ${\\mu}$m within ~3 dB of relative power. The DR-OPO has the highest output power reported to date from a femtosecond, synchronously pumped OPO based on OP-GaAs. We discovered strong three photon absorption with a coefficient of 0.35 ${\\pm}$ 0.06 cm${^3}$/GW${^2}$ for our OP-GaAs sample, which limits the output power of these OPOs as mid-IR light sources. We present a detailed study of the three photon loss on the performance of both the SR and DR-OPOs, and compare them to those without this loss mechanism.

  12. Transient reflectance of photoexcited Cd{sub 3}As{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Weber, C. P., E-mail: cweber@scu.edu; Berggren, Bryan S. [Department of Physics, Santa Clara University, 500 El Camino Real, Santa Clara, California 95053-0315 (United States); Arushanov, Ernest; Nateprov, Alex [Institute of Applied Physics, Academy of Sciences of Moldova, Academiei str. 5, MD 2028 Chisinau (Moldova, Republic of); Hosseini, Tahereh; Kouklin, Nikolai [Departments of Electrical Engineering and Computer Science, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, Wisconsin 53201 (United States)

    2015-06-08

    We report ultrafast transient-grating measurements of crystals of the three-dimensional Dirac semimetal cadmium arsenide, Cd{sub 3}As{sub 2}, at both room temperature and 80 K. After photoexcitation with 1.5-eV photons, charge-carriers relax by two processes, one of duration 500 fs and the other of duration 3.1 ps. By measuring the complex phase of the change in reflectance, we determine that the faster signal corresponds to a decrease in absorption, and the slower signal to a decrease in the light's phase velocity, at the probe energy. We attribute these signals to electrons' filling of phase space, first near the photon energy and later at lower energy. We attribute their decay to cooling by rapid emission of optical phonons, then slower emission of acoustic phonons. We also present evidence that both the electrons and the lattice are strongly heated.

  13. Removal and separation of impurity ions in preparation of high-purity inorganic salts%高纯无机盐制备中杂质离子的去除与分离

    Institute of Scientific and Technical Information of China (English)

    石磊

    2012-01-01

    介绍了在制备高纯无机盐过程中,有害杂质离子——重有色金属离子(Cu、Mg、Zn、Pd、Cd等)、铁离子、砷化物的去除与分离方法:氧化-还原法、难溶金属氢氧化物沉淀法、硫化物沉淀法.%Introduced in the preparation of high purity inorganic salt process, harmful impurity ion-heavy non-ferrous metal ion (Cu,Mg,Zn,Pd,CDS,etc. ) ,iron ion,arsenide in removing and separation methods : oxidation-reduction method and difficult to thick metal hydroxide precipitation, sulfide precipitation.

  14. Resonance-like tunneling across a barrier with adjacent wells

    Indian Academy of Sciences (India)

    S Mahadevan; P Prema; S K Agarwalla; B Sahu; C S Shastry

    2006-09-01

    We examine the behavior of transmission coefficient across the rectangular barrier when attractive potential well is present on one or both sides and also the same is studied for a smoother barrier with smooth adjacent wells having Woods–Saxon shape. We find that presence of well with suitable width and depth can substantially alter at energies below the barrier height leading to resonant-like structures. In a sense, this work is complementary to the resonant tunneling of particles across two rectangular barriers, which is being studied in detail in recent years with possible applications in mind. We interpret our results as due to resonant-like positive energy states generated by the adjacent wells. We describe in detail the possible potential application of these results in electronic devices using n-type oxygen-doped gallium arsenide and silicon dioxide. It is envisaged that these results will have applications in the design of tunneling devices.

  15. Scanning SQUID microscopy on polycrystalline SmFeAsO_{0.85} and NdFeAsO_{0.94}F_{0.06}

    Energy Technology Data Exchange (ETDEWEB)

    Hicks, Clifford W.; Lippman, Thomas M.; Moler, Kathryn A.; /Stanford U., Geballe Lab.; Huber, Martin E.; /Colorado U.; Ren, Zhi-An; Zhao, Zhong-Xian; /Beijing, Inst. Phys.

    2009-01-08

    The order parameter of the recently-discovered ferric arsenide family of superconductors remains uncertain. Some early experiments on polycrystalline samples suggested line nodes in the order parameter, however later experiments on single crystals have strongly supported fully-gapped superconductivity. An absence of nodes does not rule out unconventional order: {pi} phase shifts between the separate Fermi sheets and time-reversal symmetry-breaking components in the order parameter remain possibilities. One test for unconventional order is scanning magnetic microscopy on well-coupled polycrystalline samples: d- or p-wave order would result in orbital frustration, leading to spontaneous currents and magnetization in the superconducting state. We have performed scanning SQUID microscopy on SmFeAsO{sub 0.85} and NdFeAsO{sub 0.94}F{sub 0.06}, and in neither material do we find spontaneous orbital currents, ruling out p- or d-wave order.

  16. Buffer layer between a planar optical concentrator and a solar cell

    International Nuclear Information System (INIS)

    The effect of inserting a buffer layer between a periodically multilayered isotropic dielectric (PMLID) material acting as a planar optical concentrator and a photovoltaic solar cell was theoretically investigated. The substitution of the photovoltaic material by a cheaper dielectric material in a large area of the structure could reduce the fabrication costs without significantly reducing the efficiency of the solar cell. Both crystalline silicon (c-Si) and gallium arsenide (GaAs) were considered as the photovoltaic material. We found that the buffer layer can act as an antireflection coating at the interface of the PMLID and the photovoltaic materials, and the structure increases the spectrally averaged electron-hole pair density by 36% for c-Si and 38% for GaAs compared to the structure without buffer layer. Numerical evidence indicates that the optimal structure is robust with respect to small changes in the grating profile

  17. Evaluation of DAST and zinc telluride nonlinear crystals for efficient terahertz generation

    International Nuclear Information System (INIS)

    Terahertz (THz) signal is generated from 4-N, N-dimethylamino-4’-N’-methyl-stilbazolium tosylate (i.e. DAST Crystal) and Zinc telluride (ZnTe) nonlinear crystals by employing 140 fs laser pulses at 800 nm with 80 MHz repetition rate. The semi insulating gallium arsenide photoconductive stripline antennas (gap =5 µm, length = 20 µm) is used as a Terahertz detector. The detected temporal profile of Terahertz radiation generated from DAST crystal is high as compared to ZnTe crystal in terms of amplitude. THz effective bandwidths of these crystals are extended up to 1.1 THz range. The potential of THz generation of DAST and ZnTe crystals are evaluated with respect to incident laser power

  18. First tests of a Medipix-1 pixel detector for X-ray dynamic defectoscopy

    CERN Document Server

    Vavrik, D; Visschers, J; Pospísil, S; Ponchut, C; Zemankova, J

    2002-01-01

    Recent theoretical damage material models describe the dynamic development of voids and microcracks in materials under plastic deformation. For these models, experimental verification is needed. We propose direct and non-destructive observation of the propagation of material damage by measuring changes in transmission of X-rays penetrating a stressed material, using a photon-counting X-ray imager. The present contribution aims to demonstrate the applicability of silicon and gallium-arsenide devices for X-ray transmission measurements with a specimen of high-ductile aluminium alloy under study. The first experiments to determine the resolution and the sensitivity of the proposed method with the Medipix-1 pixel detector are presented.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-09-01

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

  20. 1.95  μm-pumped OP-GaAs optical parametric oscillator with 10.6  μm idler wavelength.

    Science.gov (United States)

    Wueppen, Jochen; Nyga, Sebastian; Jungbluth, Bernd; Hoffmann, Dieter

    2016-09-15

    We report on an optical parametric oscillator that generates output idler wavelengths around 10.6 μm. On the basis of orientation-patterned gallium arsenide (OP-GaAs) as a nonlinear medium and a 1.95 μm ns-pulsed pump laser, a signal-resonant bow-tie resonator was designed in order to maximize the output power at moderate intensities well below the damage threshold of the optical components. With this setup, the average idler output power at 50 kHz and 100 ns idler pulse length was more than 800 mW, which corresponds to a pulse energy of 16 μJ. The maximum quantum conversion efficiency of 36.8% is the highest value measured so far for comparable setups to the best of our knowledge.

  1. Morphology and composition of oxidized InAs nanowires studied by combined Raman spectroscopy and transmission electron microscopy

    Science.gov (United States)

    Tanta, Rawa; Kanne, Thomas; Amaduzzi, Francesca; Liao, Zhiyu; Madsen, Morten H.; Alarcón-Lladó, Esther; Krogstrup, Peter; Johnson, Erik; Morral, Anna Fontcuberta i.; Vosch, Tom; Nygård, Jesper; Jespersen, Thomas S.

    2016-07-01

    Any device exposed to ambient conditions will be prone to oxidation. This may be of particular importance for semiconductor nanowires because of the high surface-to-volume ratio and only little is known about the consequences of oxidation for these systems. Here, we study the properties of indium arsenide nanowires which were locally oxidized using a focused laser beam. Polarization dependent micro-Raman measurements confirmed the presence of crystalline arsenic, and transmission electron microscopy diffraction showed the presence of indium oxide. The surface dependence of the oxidation was investigated in branched nanowires grown along the [0001] and [01\\bar{1}0] wurtzite crystal directions exhibiting different surface facets. The oxidation did not occur at the [01\\bar{1}0] direction. The origin of this selectivity is discussed in terms transition state kinetics of the free surfaces of the different crystal families of the facets and numerical simulations of the laser induced heating.

  2. Non-destructive analysis of European cobalt blue glass trade beads

    International Nuclear Information System (INIS)

    Chemical analyses were made of royal blue glass trade beads from two early 17th century, archaeological sites in southern Ontario, Canada and from a glass beadmaking house in Amsterdam, The Netherlands. The results confirm that these beads were all mixed alkali - lime - silica glasses, coloured with Co and with opaque varients opacificed with Sn. The groupings by chemistry tend to segregate by bead shapes, so that oval beads group together and circular shaped beads group together. Although the 2 Canadian sites are about 190 km apart, they produced 2 different sets of oval beads of similar chemistry, possibly helping confirm the contemporaneity of the people at both sites. An As/Co atomic ratio of about two may fit with the possible source of Co as a cobalt-arsenide ore (of common name smaltite) from the Hartz Mountains of eastern Germany, a source not far from either Amsterdam or Venice, both well known glass beadmaking centres of the period. (author)

  3. Structural and magnetic phase transitions in NdCoAsO under high pressures

    Energy Technology Data Exchange (ETDEWEB)

    Uhoya, Walter; Tsoi, Georgiy M.; Vohra, Yogesh K.; McGuire, Michael A.; Sefat, Athena S.; Sales, Brian C.; Mandrus, David; Weir, Samuel T. (UAB); (ORNL); (LLNL)

    2010-05-04

    We have investigated structural and magnetic phase transitions under high pressures in a quaternary rare-earth transition-metal arsenide oxide NdCoAsO compound that is isostructural to the high temperature superconductor parent phase NdFeAsO. The four-probe electrical resistance measurements carried out in a designer diamond anvil cell show that the ferromagnetic Curie temperature and antiferromagnetic Neel temperature increase with an increase in pressure. High pressure x-ray diffraction studies using a synchrotron source show a structural phase transition from a tetragonal phase to a new crystallographic phase at a pressure of 23 GPa at 300 K. The NdCoAsO sample remained antiferromagnetic and non-superconducting down to 10 K and up to the highest pressure achieved in this experiment, 53 GPa. A P-T phase diagram for NdCoAsO is presented from ambient conditions to P = 53 GPa and T = 10 K.

  4. Structural and magnetic phase transitions in NdCoAsO under high pressures

    Energy Technology Data Exchange (ETDEWEB)

    Uhoya, Walter [University of Alabama, Birmingham; Tsoi, Georgiy [University of Alabama, Birmingham; Vohra, Y. K. [University of Alabama, Birmingham; McGuire, Michael A [ORNL; Sefat, A. S. [Oak Ridge National Laboratory (ORNL); Sales, Brian C [ORNL; Mandrus, David [ORNL; Weir, S. T. [Lawrence Livermore National Laboratory (LLNL)

    2010-01-01

    We have investigated structural and magnetic phase transitions under high pressures in a quaternary rare-earth transition-metal arsenide oxide NdCoAsO compound that is isostructural to the high temperature superconductor parent phase NdFeAsO. The four-probe electrical resistance measurements carried out in a designer diamond anvil cell show that the ferromagnetic Curie temperature and antiferromagnetic Neel temperature increase with an increase in pressure. High pressure x-ray diffraction studies using a synchrotron source show a structural phase transition from a tetragonal phase to a new crystallographic phase at a pressure of 23 GPa at 300 K. The NdCoAsO sample remained antiferromagnetic and non-superconducting down to 10 K and up to the highest pressure achieved in this experiment, 53 GPa. A P-T phase diagram for NdCoAsO is presented from ambient conditions to P = 53 GPa and T = 10 K.

  5. Mechanical design of a low concentration ratio solar array for a space station application

    Science.gov (United States)

    Biss, M. S.; Hsu, L.

    1983-01-01

    This paper describes a preliminary study and conceptual design of a low concentration ratio solar array for a space station application with approximately a 100 kW power requirement. The baseline design calls for a multiple series of inverted, truncated, pyramidal optical elements with a geometric concentration ratio (GCR) of 6. It also calls for low life cycle cost, simple on-orbit maintainability, 1984 technology readiness date, and gallium arsenide (GaAs) of silicon (Si) solar cell interchangeability. Due to the large area needed to produce the amount of power required for the baseline space station, a symmetrical wing design, making maximum use of the commonality of parts approach, was taken. This paper will describe the mechanical and structural design of a mass-producible solar array that is very easy to tailor to the needs of the individual user requirement.

  6. Low concentration ratio solar array for low Earth orbit multi-100kW application. Volume 2: Drawings

    Science.gov (United States)

    Nalbandian, S. J.; French, E. P.

    1982-01-01

    A preliminary design effort directed toward a low concentration ratio photovoltaic array system based on 1984 technology and capable of delivering multi-hundred kilowatts (300 kW to 100 kW range) in low Earth orbit. The array system consists of two or more array modules each capable of delivering between 113 kW to 175 kW using silicon solar cells or gallium arsenide solar cells, respectively. The array module deployed area is 1320 square meters and consists of 4356 pyramidal concentrator elements. The module, when stowed in the Space Shuttle's payload bay, has a stowage volume of a cube with 3.24 meters on a side. The concentrator elements are sized for a geometric concentration ratio (GCR) of six with an aperture area of 0.5 meters x 0.5 meters. Drawings for the preliminary design configuration and for the test hardware that was fabricated for design evaluation and test are provided.

  7. Nanowire Growth for Photovoltaics

    DEFF Research Database (Denmark)

    Holm, Jeppe Vilstrup

    the light. The concentration and light trapping means that single junction nanowire solar cells have a higher theoretical maximum efficiency than equivalent planar solar cells. We have demonstrated the built-in light concentration of nanowires, by growing, contacting and characterizing a solar cell...... consisting of a single, vertical, gallium arsenide(GaAs) nanowire grown on silicon with a radial p-i-n-junction. The average concentration was ~8, and the peak concentration was ~12. By increasing the number of junctions in solar cells, they can extract more energy per absorbed photon. In ideal multi......Solar cells commercial success is based on an efficiency/cost calculation. Nanowire solar cells is one of the foremost candidates to implement third generation photo voltaics, which are both very efficient and cheap to produce. This thesis is about our progress towards commercial nanowire solar...

  8. Optical, thermal, and electrical performance of low-CR solar arrays. [Concentration Ratio

    Science.gov (United States)

    French, E. P.; Mills, M. W.; Backovsky, Z.

    1983-01-01

    This paper describes the analysis and testing of a photovoltaic low-CR concentrator shaped like a truncated pyramid with an aperture of 0.5 m on a side and a geometric concentration ratio of six. The truncated base plane is covered by either silicon (Si) or gallium arsenide (GaAs) solar cells. Ray-trace analysis of the concentrator predicts a peak optical efficiency of 0.77, which falls off only gradually with pointing error. A coupled thermal-electrical analysis of the system shows that the moderately nonuniform illumination produced by the concentrator does not result in significant mismatch losses, provided the solar cells are connected in parallel groups. The results of ground tests involving a full-scale prototype concentrator conform well with theoretical predictions.

  9. Resonantly enhanced second-harmonic generation using III-V semiconductor all-dielectric metasurfaces

    CERN Document Server

    Liu, Sheng; Keeler, Gordon A; Sinclair, Michael B; Yang, Yuanmu; Reno, John; Pertsch, Thomas; Brener, Igal

    2016-01-01

    Nonlinear optical phenomena in nanostructured materials have been challenging our perceptions of nonlinear optical processes that have been explored since the invention of lasers. For example, the ability to control optical field confinement, enhancement, and scattering almost independently, allows nonlinear frequency conversion efficiencies to be enhanced by many orders of magnitude compared to bulk materials. Also, the subwavelength length scales render phase matching issues irrelevant. Compared with plasmonic nanostructures, dielectric resonator metamaterials show great promise for enhanced nonlinear optical processes due to their larger mode volumes. Here, we present, for the first time, resonantly enhanced second-harmonic generation (SHG) using Gallium Arsenide (GaAs) based dielectric metasurfaces. Using arrays of cylindrical resonators we observe SHG enhancement factors as large as 104 relative to unpatterned GaAs. At the magnetic dipole resonance we measure an absolute nonlinear conversion efficiency o...

  10. Performance evaluation of a lossy transmission lines based diode detector at cryogenic temperature

    Science.gov (United States)

    Villa, E.; Aja, B.; de la Fuente, L.; Artal, E.

    2016-01-01

    This work is focused on the design, fabrication, and performance analysis of a square-law Schottky diode detector based on lossy transmission lines working under cryogenic temperature (15 K). The design analysis of a microwave detector, based on a planar gallium-arsenide low effective Schottky barrier height diode, is reported, which is aimed for achieving large input return loss as well as flat sensitivity versus frequency. The designed circuit demonstrates good sensitivity, as well as a good return loss in a wide bandwidth at Ka-band, at both room (300 K) and cryogenic (15 K) temperatures. A good sensitivity of 1000 mV/mW and input return loss better than 12 dB have been achieved when it works as a zero-bias Schottky diode detector at room temperature, increasing the sensitivity up to a minimum of 2200 mV/mW, with the need of a DC bias current, at cryogenic temperature.

  11. Review of wide band-gap semiconductors technology

    Directory of Open Access Journals (Sweden)

    Jin Haiwei

    2016-01-01

    Full Text Available Silicon carbide (SiC and gallium nitride (GaN are typical representative of the wide band-gap semiconductor material, which is also known as third-generation semiconductor materials. Compared with the conventional semiconductor silicon (Si or gallium arsenide (GaAs, wide band-gap semiconductor has the wide band gap, high saturated drift velocity, high critical breakdown field and other advantages; it is a highly desirable semiconductor material applied under the case of high-power, high-temperature, high-frequency, anti-radiation environment. These advantages of wide band-gap devices make them a hot spot of semiconductor technology research in various countries. This article describes the research agenda of United States and European in this area, focusing on the recent developments of the wide band-gap technology in the US and Europe, summed up the facing challenge of the wide band-gap technology.

  12. PDT in non-surgical treatment of periodontitis in kidney transplanted patients: a split-mouth, randomized clinical trial

    Science.gov (United States)

    Marinho, Kelly C. T.; Giovani, Elcio M.

    2016-03-01

    This study was to evaluate clinical and microbiological effectiveness of photodynamic therapy (PDT) in the treatment of periodontal disease in kidney-transplanted patients. Eight kidney transplanted patients treated at Paulista University were arranged in two groups: SRP performed scaling and root planning by ultrasound; SRP+PDT- in the same patient, which was held to PDT in the opposite quadrant, with 0.01% methylene blue and red laser gallium aluminum arsenide, wavelength 660 nm, power 100 mW. There was reduction in probing pocket depth after 45 days and 3 months regardless the group examined; plaque and bleeding index showed improvement over time, regardless the technique used, and bleeding index in the SRP+PDT group was lower when compared with the baseline the other times. There was no difference in the frequency of pathogens. Photodynamic therapy may be an option for treatment of periodontal disease in renal-transplanted patients and its effectiveness is similar to conventional therapy.

  13. Angle-resolved cathodoluminescence imaging polarimetry

    CERN Document Server

    Osorio, Clara I; Brenny, Benjamin; Polman, Albert; Koenderink, A Femius

    2015-01-01

    Cathodoluminescence spectroscopy (CL) allows characterizing light emission in bulk and nanostructured materials and is a key tool in fields ranging from materials science to nanophotonics. Previously, CL measurements focused on the spectral content and angular distribution of emission, while the polarization was not fully determined. Here we demonstrate a technique to access the full polarization state of the cathodoluminescence emission, that is the Stokes parameters as a function of the emission angle. Using this technique, we measure the emission of metallic bullseye nanostructures and show that the handedness of the structure as well as nanoscale changes in excitation position induce large changes in polarization ellipticity and helicity. Furthermore, by exploiting the ability of polarimetry to distinguish polarized from unpolarized light, we quantify the contributions of different types of coherent and incoherent radiation to the emission of a gold surface, silicon and gallium arsenide bulk semiconductor...

  14. GaAs epitaxy on Si substrates: modern status of research and engineering

    Energy Technology Data Exchange (ETDEWEB)

    Bolkhovityanov, Yu B; Pchelyakov, O P [Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk (Russian Federation)

    2008-05-31

    While silicon and gallium arsenide are dominant materials in modern micro- and nanoelectronics, devices fabricated from them still use Si and GaAs substrates only separately. Integrating these materials on the (highest effeciency) substrate of Si has been the subject of much research effort for more than twenty years. This review systematizes and generalizes the current understanding of the fundamental physical mechanisms governing the epitaxial growth of GaAs and its related III-V compounds on Si substrates. Basic techniques avilable for improving the quality of such heterostructures are described, and recent advances in fabricating device-quality A{sup III}B{sup V}/Si heterostructures and devices on their bases are also presented. (reviews of topical problems)

  15. Polarized Electron Gun Development at the Brookhaven National Laboratory

    International Nuclear Information System (INIS)

    Development of two different polarized electron guns is ongoing at BNL. One aims at extremely high brightness at a moderate beam current. This design uses a superconducting RF gun and a test setup is built to show that a Gallium-Arsenide cathode with negative affinity has a sufficiently long quantum efficiency lifetime in such an environment. An electron injector using this technology may eliminate the need of the electron damping ring and a long transport line at the International Linear Collider. The other project aims at producing a high beam current with moderate emittance requirements, dubbed the 'Gatling gun'. In this DC gun, bunches are extracted from 20 separate cathodes and merged into a single beam using a rotating magnetic field. Such an electron gun could serve as an injector for the electron-ion collider eRHIC, which is planned at BNL. We will report on the status of these projects.

  16. Neutron scattering studies of structure, magnetism and superconductivity under pressure in AFe2As2 (A=Ca, Ba) under pressure

    International Nuclear Information System (INIS)

    The interplay between superconductivity, magnetism, and structure has become a major theme of research in the iron arsenide families of superconductors. The strong coupling between magnetism and structure, for example, is illustrated by the parent compounds, AEFe2As2 (AE = Ba, Sr, Ca), which manifest simultaneous transitions from a paramagnetic, tetragonal phase to an antiferromagnetically ordered, orthorhombic phase. The coupling between superconductivity and magnetism has been demonstrated by, for example, the suppression of the antiferromagnetic ordering and orthorhombic distortion below the superconducting transition in some electron doped compounds. The elastic and inelastic neutron scattering measurements, under pressure, that have elucidated the nature of the magnetic order and its relationship to the tetragonal-orthorhombic structural transition at ambient pressure, the quenching of magnetism in the cT phase, and the identification of the superconducting phase in CaFe2As2 under applied uniaxial pressure are discussed

  17. Thermally Stable Ohmic Contacts on Silicon Carbide Developed for High- Temperature Sensors and Electronics

    Science.gov (United States)

    Okojie, Robert S.

    2001-01-01

    The NASA aerospace program, in particular, requires breakthrough instrumentation inside the combustion chambers of engines for the purpose of, among other things, improving computational fluid dynamics code validation and active engine behavioral control (combustion, flow, stall, and noise). This environment can be as high as 600 degrees Celsius, which is beyond the capability of silicon and gallium arsenide devices. Silicon-carbide- (SiC-) based devices appear to be the most technologically mature among wide-bandgap semiconductors with the proven capability to function at temperatures above 500 degrees Celsius. However, the contact metalization of SiC degrades severely beyond this temperature because of factors such as the interdiffusion between layers, oxidation of the contact, and compositional and microstructural changes at the metal/semiconductor interface. These mechanisms have been proven to be device killers. Very costly and weight-adding packaging schemes that include vacuum sealing are sometimes adopted as a solution.

  18. Clinical and Experimental Study of Gaalas Phototherapy for Tемрoromandibular Disorders

    Directory of Open Access Journals (Sweden)

    Nencheva-Svechtarova S.

    2014-12-01

    Full Text Available The objective of this study was to test the clinical effectiveness of the gallium-aluminum-arsenide laser (GaAlAs; 785 nm and superluminiscent diodes (633 nm phototherapy (MedX 1100 device for the treatment of patients with temporomandibular disorders and myofascial pain syndrome. The results demonstrated a positive effect in pain relief. A significant reduction (p < 0.05 in the level of pain was observed for the temporomandibular joint and for the masseter muscles using paired samples t-test and Wilcoxon signed rank test. The experimental study on pork muscle samples showed that a the main part of laser radiation is absorbed by the tissue in thin layer of 3-4 mm, b in the spectral region 650-950 nm the intensity of light penetration is about 0.2-0.25 percent of the initial light intensity.

  19. Ion trap in a semiconductor chip

    Science.gov (United States)

    Stick, D.; Hensinger, W. K.; Olmschenk, S.; Madsen, M. J.; Schwab, K.; Monroe, C.

    2006-01-01

    The electromagnetic manipulation of isolated atoms has led to many advances in physics, from laser cooling and Bose-Einstein condensation of cold gases to the precise quantum control of individual atomic ions. Work on miniaturizing electromagnetic traps to the micrometre scale promises even higher levels of control and reliability. Compared with `chip traps' for confining neutral atoms, ion traps with similar dimensions and power dissipation offer much higher confinement forces and allow unparalleled control at the single-atom level. Moreover, ion microtraps are of great interest in the development of miniature mass-spectrometer arrays, compact atomic clocks and, most notably, large-scale quantum information processors. Here we report the operation of a micrometre-scale ion trap, fabricated on a monolithic chip using semiconductor micro-electromechanical systems (MEMS) technology. We confine, laser cool and measure heating of a single 111Cd+ ion in an integrated radiofrequency trap etched from a doped gallium-arsenide heterostructure.

  20. Response of timepix detector with GaAs:Cr and Si sensor to heavy ions

    Science.gov (United States)

    Abu Al Azm, S. M.; Chelkov, G.; Kozhevnikov, D.; Guskov, A.; Lapkin, A.; Leyva Fabelo, A.; Smolyanskiy, P.; Zhemchugov, A.

    2016-05-01

    The response of the Timepix detector to neon ions with kinetic energy 77 and 158.4 MeV has been studied at the cyclotron U-400M of the JINR Flerov Laboratory of Nuclear Reaction. Sensors produced from gallium arsenide compensated by chromium and from silicon are used for these measurements. While in Timepix detector with Si sensor the well-known so-called "volcano effect" observed, in Timepix detector with GaAs:Cr sensor such effect was completely absent. In the work the behavior of the Timepix detector with GaAs:Cr sensor under irradiation with heavy ions is described in comparison with the detector based on Si sensor. Also the possible reason for absence of "volcano" effect in GaAs:Cr detector is proposed.

  1. Focusing effect of bent GaAs crystals for gamma-ray Laue lenses: Monte Carlo and experimental results

    CERN Document Server

    Virgilli, E; Rosati, P; Bonnini, E; Buffagni, E; Ferrari, C; Stephen, J B; Caroli, E; Auricchio, N; Basili, A; Silvestri, S

    2015-01-01

    We report on results of observation of the focusing effect from the planes (220) of Gallium Arsenide (GaAs) crystals. We have compared the experimental results with the simulations of the focusing capability of GaAs tiles through a developed Monte Carlo. The GaAs tiles were bent using a lapping process developed at the cnr/imem - Parma (Italy) in the framework of the laue project, funded by ASI, dedicated to build a broad band Laue lens prototype for astrophysical applications in the hard X-/soft gamma-ray energy range (80-600 keV). We present and discuss the results obtained from their characterization, mainly in terms of focusing capability. Bent crystals will significantly increase the signal to noise ratio of a telescope based on a Laue lens, consequently leading to an unprecedented enhancement of sensitivity with respect to the present non focusing instrumentation.

  2. Shot noise suppression in p-n junctions due to carrier generation-recombination

    Science.gov (United States)

    Maione, I. A.; Pellegrini, B.; Fiori, G.; Macucci, M.; Guidi, L.; Basso, G.

    2011-04-01

    We present a theoretical and experimental investigation of shot noise suppression in gallium arsenide and silicon p-n junctions due the to effect of generation-recombination phenomena. In particular, the availability of the cross-correlation technique and of ultra-low-noise amplifiers has allowed us to significantly extend, down to 10 pA, the range of bias current values for which results were available in the literature. To provide a quantitative understanding of the observed V-shape noise behavior, we have extended the Shockley-Read-Hall model for the trap-assisted generation-recombination mechanism. Such a model has represented the theoretical background for the performed Monte Carlo noise simulations, which have provided good agreement with the experimental results.

  3. The CRRES high efficiency solar panel

    International Nuclear Information System (INIS)

    This paper reports on the High Efficiency Solar Panel (HESP) experiments which is to provide both engineering and scientific information concerning the effects of space radiation on advanced gallium arsenide (GaAs) solar cells. The HESP experiment consists of an ambient panel, and annealing panel and a programmable load. This experiment, in conjunction with the radiation measurement experiments abroad the CREES, provides the first opportunity to simultaneously measure the trapped radiation belts and the results of radiation damage to solar cells. The engineering information will result in a design guide for selecting the optimum solar array characteristics for different orbits and different lifetimes. The scientific information will provide both correlation of laboratory damage effects to space damage effects and a better model for predicting effective solar cell panel lifetimes

  4. Impact of substrate characteristics on performance of large area plasmonic photoconductive emitters.

    Science.gov (United States)

    Yardimci, Nezih T; Salas, Rodolfo; Krivoy, Erica M; Nair, Hari P; Bank, Seth R; Jarrahi, Mona

    2015-12-14

    We present a comprehensive analysis of terahertz radiation from large area plasmonic photoconductive emitters in relation with characteristics of device substrate. Specifically, we investigate the radiation properties of large area plasmonic photoconductive emitters fabricated on GaAs substrates that exhibit short carrier lifetimes through low-temperature substrate growth and through epitaxially embedded rare-earth arsenide (ErAs and LuAs) nanoparticles in superlattice structures. Our analysis indicates that the utilized substrate composition and growth process for achieving short carrier lifetimes are crucial in determining substrate resistivity, carrier drift velocity, and carrier lifetime, which directly impact optical-to-terahertz conversion efficiency, radiation power, radiation bandwidth, and reliability of large area plasmonic photoconductive emitters.

  5. 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.

  6. Effect of InAlAs window layer on efficiency of indium phosphide solar cells

    Science.gov (United States)

    Jain, Raj K.; Landis, Geoffrey A.

    1992-01-01

    Indium phosphide (InP) solar cell efficiencies are limited by surface recombination. The effect of a wide bandgap, lattice-matched indium aluminum arsenide (In(0.52)Al(0.48)As) window layer on the performance of InP solar cells was investigated by using the numerical code PC-1D. The p(+)n InP solar cell performance improved significantly with the use of the window layer. No improvement was seen for the n(+)p InP cells. The cell results were explained by the band diagram of the heterostructure and the conduction band energy discontinuity. The calculated current voltage and internal quantum efficiency results clearly demonstrated that In(0.52)Al(0.48)As is a very promising candidate for a window layer material for p(+)n InP solar cells.

  7. Effect of InAlAs window layer on the efficiency of indium phosphide solar cells

    Science.gov (United States)

    Jain, R. K.; Landis, G. A.

    1991-01-01

    Indium phosphide (InP) solar cell efficiencies are limited by surface recombination. The effect of a wide-bandgap lattice-matched indium aluminum arsenide (In0.52Al0.48As) window layer on the performance of InP solar cells was investigated using a numerical code PC-1D. The p(+)n InP solar cell performance improves significantly with the use of a window layer. No improvement is seen for n(+)p InP cells. Cell results are explained by the band diagram of the heterostructure and the conduction-band energy discontinuity. The calculated I-V and internal quantum efficiency results clearly demonstrate that In0.52Al0.48As is a promising candidate as a window layer material for p(+)n InP solar cells.

  8. Micro-cooler enhancements by barrier interface analysis

    Energy Technology Data Exchange (ETDEWEB)

    Stephen, A.; Dunn, G. M. [Department of Physics, University of Aberdeen, King' s College, AB24 3UE Aberdeen (United Kingdom); Glover, J.; Oxley, C. H. [Department of Engineering, De Montfort University, Gateway, LE1 9BH Leicester (United Kingdom); Bajo, M. Montes; Kuball, M. [Center for Device Thermography and Reliability, H. H. Wills Physics Laboratory, University of Bristol, BS8 1TL Bristol (United Kingdom); Cumming, D. R. S.; Khalid, A. [School of Engineering, University of Glasgow, Rankine Building, G12 8LT Glasgow (United Kingdom)

    2014-02-15

    A novel gallium arsenide (GaAs) based micro-cooler design, previously analysed both experimentally and by an analytical Heat Transfer (HT) model, has been simulated using a self-consistent Ensemble Monte Carlo (EMC) model for a more in depth analysis of the thermionic cooling in the device. The best fit to the experimental data was found and was used in conjunction with the HT model to estimate the cooler-contact resistance. The cooling results from EMC indicated that the cooling power of the device is highly dependent on the charge distribution across the leading interface. Alteration of this charge distribution via interface extensions on the nanometre scale has shown to produce significant changes in cooler performance.

  9. Temperature mapping of operating nanoscale devices by scanning probe thermometry

    Science.gov (United States)

    Menges, Fabian; Mensch, Philipp; Schmid, Heinz; Riel, Heike; Stemmer, Andreas; Gotsmann, Bernd

    2016-03-01

    Imaging temperature fields at the nanoscale is a central challenge in various areas of science and technology. Nanoscopic hotspots, such as those observed in integrated circuits or plasmonic nanostructures, can be used to modify the local properties of matter, govern physical processes, activate chemical reactions and trigger biological mechanisms in living organisms. The development of high-resolution thermometry techniques is essential for understanding local thermal non-equilibrium processes during the operation of numerous nanoscale devices. Here we present a technique to map temperature fields using a scanning thermal microscope. Our method permits the elimination of tip-sample contact-related artefacts, a major hurdle that so far has limited the use of scanning probe microscopy for nanoscale thermometry. We map local Peltier effects at the metal-semiconductor contacts to an indium arsenide nanowire and self-heating of a metal interconnect with 7 mK and sub-10 nm spatial temperature resolution.

  10. Terahertz Technology for Defense and Security-Related Applications

    DEFF Research Database (Denmark)

    Iwaszczuk, Krzysztof

    This thesis deals with chosen aspects of terahertz (THz) technology that have potential in defense and security-related applications. A novel method for simultaneous data acquisition in time-resolved THz spectroscopy experiments is developed. This technique is demonstrated by extracting the sheet...... conductivity of photoexcited charge carriers in semi-insulating gallium arsenide. Comparison with results obtained using a standard data acquisition scheme shows that the new method minimizes errors originating from uctuations in the laser system output and timing errors in the THz pulse detection. Furthermore......, a new organic material, BNA, is proved to be a strong and broadband THz emitter which enables spectroscopy with a bandwidth twice as large as conventional spectroscopy in the eld. To access electric elds allowing exploration of THz nonlinear phenomena, eld enhancement properties of tapered parallel...

  11. Visible and Near-Infrared Contrast of Faculae in Active Region NOAA 8518

    Institute of Scientific and Technical Information of China (English)

    Yan Xu; Guo Yang; Jiong Qiu; Tom J. Spirock; Ju Jing; Carsten Denker; Haimin Wang

    2004-01-01

    We compare the contrast of faculae, in visible light and in the near infrared (NIR), that were associated with the active region NOAA 8518 which crossed the solar disk from April 19 to 27, 1999. We obtained NIR continuum images at 1.6μm at the Big Bear Solar Observatory (BBSO) with an Indium Gallium Arsenide (In Ga As) NIR digital camera. We also obtained high-resolution longitudinal magnetograms and visible light filtergrams at 610.3 nm with the newly developed Digital Vector Magnetograph (DVMG). Our data show that the contrast of faculae has the same sign in both the visible and the NIR. We did not find any so-called "dark faculae", faculae that are bright in the visible and simultaneously dark in the NIR.We determined a threshold magnetic flux density that separates pores from faculae.

  12. Development and commercialization of mode-locked VECSELs

    Science.gov (United States)

    Hempler, Nils; Bialkowski, Bartlomiej; Hamilton, Craig J.; Maker, Gareth T.; Malcolm, Graeme P. A.

    2015-03-01

    This paper will describe the current state-of-the-art in commercial mode-locked Vertical External Cavity Surface Emitting Lasers (VECSEL) and demonstrate their efficacy in key applications. Based on indium gallium arsenide quantum well gain structures, our systems operate between 920 nm - 1050 nm with >1 W output powers, 200 MHz pulse repetition rate and duration. Crucially, the development issues that have been overcome to bring this promising technology to market will be discussed. These include: thermal management challenges, electronic control system development and robust mechanical design requirements. Having the potential to replace more conventional titanium sapphire laser technology where wavelength flexibility can be traded off against a significantly lower cost point and form factor, we will discuss the use of VECSELs in key applications such as nonlinear microscopy.

  13. A simple model of space radiation damage in GaAs solar cells

    Science.gov (United States)

    Wilson, J. W.; Stith, J. J.; Stock, L. V.

    1983-01-01

    A simple model is derived for the radiation damage of shallow junction gallium arsenide (GaAs) solar cells. Reasonable agreement is found between the model and specific experimental studies of radiation effects with electron and proton beams. In particular, the extreme sensitivity of the cell to protons stopping near the cell junction is predicted by the model. The equivalent fluence concept is of questionable validity for monoenergetic proton beams. Angular factors are quite important in establishing the cell sensitivity to incident particle types and energies. A fluence of isotropic incidence 1 MeV electrons (assuming infinite backing) is equivalent to four times the fluence of normal incidence 1 MeV electrons. Spectral factors common to the space radiations are considered, and cover glass thickness required to minimize the initial damage for a typical cell configuration is calculated. Rough equivalence between the geosynchronous environment and an equivalent 1 MeV electron fluence (normal incidence) is established.

  14. Superconducting properties and pseudogap from preformed Cooper pairs in the triclinic (CaFe1-xPtxAs ) 10Pt3As8

    Science.gov (United States)

    Surmach, M. A.; Brückner, F.; Kamusella, S.; Sarkar, R.; Portnichenko, P. Y.; Park, J. T.; Ghambashidze, G.; Luetkens, H.; Biswas, P. K.; Choi, W. J.; Seo, Y. I.; Kwon, Y. S.; Klauss, H.-H.; Inosov, D. S.

    2015-03-01

    Using a combination of muon-spin relaxation (μ SR ) , inelastic neutron scattering (INS), and nuclear magnetic resonance (NMR), we investigated the novel iron-based superconductor with a triclinic crystal structure (CaFe1-xPtxAs ) 10Pt3As8 (Tc=13 K), containing platinum-arsenide intermediary layers. The temperature dependence of the superfluid density obtained from the μ SR relaxation-rate measurements indicates the presence of two superconducting gaps, Δ1≫Δ2 . According to our INS measurements, commensurate spin fluctuations are centered at the (π ,0 ) wave vector, like in most other iron arsenides. Their intensity remains unchanged across Tc, indicating the absence of a spin resonance typical for many Fe-based superconductors. Instead, we observed a peak in the spin-excitation spectrum around ℏ ω0=7 meV at the same wave vector, which persists above Tc and is characterized by the ratio ℏ ω0/kBTc≈6.2 , which is significantly higher than typical values for the magnetic resonant modes in iron pnictides (˜4.3 ) . The temperature dependence of magnetic intensity at 7 meV revealed an anomaly around T*=45 K related to the disappearance of this new mode. A suppression of the spin-lattice relaxation rate, 1 /T1T , observed by NMR immediately below T* without any notable subsequent anomaly at Tc, indicates that T* could mark the onset of a pseudogap in (CaFe1-xPtxAs ) 10Pt3As8 , which is likely associated with the emergence of preformed Cooper pairs.

  15. Arsenic (III, V), indium (III), and gallium (III) toxicity to zebrafish embryos using a high-throughput multi-endpoint in vivo developmental and behavioral assay.

    Science.gov (United States)

    Olivares, Christopher I; Field, Jim A; Simonich, Michael; Tanguay, Robert L; Sierra-Alvarez, Reyes

    2016-04-01

    Gallium arsenide (GaAs), indium gallium arsenide (InGaAs) and other III/V materials are finding increasing application in microelectronic components. The rising demand for III/V-based products is leading to increasing generation of effluents containing ionic species of gallium, indium, and arsenic. The ecotoxicological hazard potential of these streams is unknown. While the toxicology of arsenic is comprehensive, much less is known about the effects of In(III) and Ga(III). The embryonic zebrafish was evaluated for mortality, developmental abnormalities, and photomotor response (PMR) behavior changes associated with exposure to As(III), As(V), Ga(III), and In(III). The As(III) lowest observable effect level (LOEL) for mortality was 500 μM at 24 and 120 h post fertilization (hpf). As(V) exposure was associated with significant mortality at 63 μM. The Ga(III)-citrate LOEL was 113 μM at 24 and 120 hpf. There was no association of significant mortality over the tested range of In(III)-citrate (56-900 μM) or sodium citrate (213-3400 μM) exposures. Only As(V) resulted in significant developmental abnormalities with LOEL of 500 μM. Removal of the chorion prior to As(III) and As(V) exposure was associated with increased incidence of mortality and developmental abnormality suggesting that the chorion may normally attenuate mass uptake of these metals by the embryo. Finally, As(III), As(V), and In(III) caused PMR hypoactivity (49-69% of control PMR) at 900-1000 μM. Overall, our results represent the first characterization of multidimensional toxicity effects of III/V ions in zebrafish embryos helping to fill a significant knowledge gap, particularly in Ga(III) and In(III) toxicology. PMID:26824274

  16. Arsenic (III, V), indium (III), and gallium (III) toxicity to zebrafish embryos using a high-throughput multi-endpoint in vivo developmental and behavioral assay.

    Science.gov (United States)

    Olivares, Christopher I; Field, Jim A; Simonich, Michael; Tanguay, Robert L; Sierra-Alvarez, Reyes

    2016-04-01

    Gallium arsenide (GaAs), indium gallium arsenide (InGaAs) and other III/V materials are finding increasing application in microelectronic components. The rising demand for III/V-based products is leading to increasing generation of effluents containing ionic species of gallium, indium, and arsenic. The ecotoxicological hazard potential of these streams is unknown. While the toxicology of arsenic is comprehensive, much less is known about the effects of In(III) and Ga(III). The embryonic zebrafish was evaluated for mortality, developmental abnormalities, and photomotor response (PMR) behavior changes associated with exposure to As(III), As(V), Ga(III), and In(III). The As(III) lowest observable effect level (LOEL) for mortality was 500 μM at 24 and 120 h post fertilization (hpf). As(V) exposure was associated with significant mortality at 63 μM. The Ga(III)-citrate LOEL was 113 μM at 24 and 120 hpf. There was no association of significant mortality over the tested range of In(III)-citrate (56-900 μM) or sodium citrate (213-3400 μM) exposures. Only As(V) resulted in significant developmental abnormalities with LOEL of 500 μM. Removal of the chorion prior to As(III) and As(V) exposure was associated with increased incidence of mortality and developmental abnormality suggesting that the chorion may normally attenuate mass uptake of these metals by the embryo. Finally, As(III), As(V), and In(III) caused PMR hypoactivity (49-69% of control PMR) at 900-1000 μM. Overall, our results represent the first characterization of multidimensional toxicity effects of III/V ions in zebrafish embryos helping to fill a significant knowledge gap, particularly in Ga(III) and In(III) toxicology.

  17. A natural analogue for copper waste canisters: The copper-uranium mineralised concretions in the Permian mudrocks of south Devon, United Kingdom

    Energy Technology Data Exchange (ETDEWEB)

    Milodowski, A.E.; Styles, M.T.; Hards, V.L. [Natural Environment Research Council (United Kingdom). British Geological Survey

    2000-08-01

    mineralisation and alteration that can be related to the burial and diagenetic history of the Permian strata. The native copper mineralisation exhibits close temporal association with the formation of uraniferous and vanadiferous concretions (known as 'fish-eyes') in the same rocks. Petrographical relationships indicate that both the copper and the 'fish-eye' concretions formed during burial diagenesis but before the maximum compaction of the host mudstone and siltstone. The regional burial history Wessex Basin, indicates that the maximum compaction of the Permian strata would have been achieved by at least the end of the Lower Jurassic (possibly even in the Triassic). Therefore, the native copper mineralisation is older than 176 Ma. The native copper sheets display a complex sequence of alteration and subsequent mineral growth of minerals on their surfaces. The earliest alteration was to copper oxides - principally cuprite with minor tenorite, indicating a change to more oxidising groundwater conditions. The dissolution of native silver and the growth of fringes of copper arsenides followed this. Nickel arsenides and chalcocite, associated with the precipitation of uranium silicates occurred in the later stages of alteration. This suggests a return to a more reducing pore water environment. Again, petrographical relationships indicate that this alteration and subsequent mineralisation is geologically old (i.e. Lower Jurassic or older). Secondary malachite, intimately intergrown copper sulphate and copper oxides, copper chloride, copper-uranium arsenate and uranium vanadates have formed as late-stage alteration products of the native copper and earlier diagenetic cuprite, chalcocite, copper-nickel arsenide and uranium silicate alteration and mineralisation. This latest stage alteration is most probably attributable to near-surface weathering processes. Although the native copper is affected by corrosion, the study has shown that a significant proportion (30

  18. (CaFeAs){sub 10}Pt{sub z}As{sub 8} superconductors and related compounds

    Energy Technology Data Exchange (ETDEWEB)

    Stuerzer, Tobias

    2015-04-13

    The main topic of this dissertation is the identification of new compounds, structure determination, and substitution dependent investigation of properties in this new branch of the family of iron arsenide superconductors (Chapter 2). Chapter 2.1 presents the identification of the superconducting compounds and the corresponding structure elucidation identifying two dif-ferent species (CaFeAs){sub 10}Pt{sub 3}As{sub 8} and (CaFeAs){sub 10}Pt{sub 4}As{sub 8} in this family (abbreviated as 1038 and 1048 according to their stoichiometry). However, a closer look revealed a more challenging structure chemistry which is covered in Chapter 2.2. The following two Chapters 2.3 and 2.4 are devoted to (CaFeAs){sub 10}Pt{sub 3}As{sub 8} and more detailed investigations on this parent compound of the new superconductor family. Furthermore, transition metal substitution series (CaFe{sub 1-x}M{sub x}As){sub 10}Pt{sub 3}As{sub 8} were synthesized to investigate the resemblance to model systems Ba(Fe{sub 1-x}M{sub x}){sub 2}As{sub x} and LaO(Fe{sub 1-x}M{sub x})As in the scope of structural changes and superconductivity as described in Chapter 2.5. Initially amazing differences in superconducting properties com-paring 1038 and 1048 compounds are analyzed in Chapter 2.6 establishing an universal dop-ing model in the (CaFe{sub 1-x}M{sub x}As){sub 10}Pt{sub z}As{sub 8} family. Additionally substituent dependent properties upon rare earth substitution in electron doped (Ca{sub 1-y}RE{sub y}FeAs){sub 10}Pt{sub 3}As{sub 8} are investigated in Chapter 2.7, while a detailed study of superconducting properties and magnetism in (Ca{sub 1-y}La{sub y}FeAs){sub 10}Pt{sub 3}As{sub 8} by the local μSR technique is presented in Chapter 2.8. In Chapter 2.9 a comparison of direct and electron doping is discussed based on codoping experiments in (Ca{sub 1-y}La{sub y}Fe{sub 1-x}Pt{sub x}As){sub 10}Pt{sub 3}As{sub 8} and (CaFe{sub 1-x}Pt{sub x}As){sub 10}Pt{sub 4}As{sub 8}. Finally, in Chapter 2

  19. Investigation of the physics potential and detector development for the ILC

    Energy Technology Data Exchange (ETDEWEB)

    Ohlerich, Martin

    2010-02-15

    interaction point and surrounding the beam pipe. Due to its location, a lot of beamstrahlung pair particles will hit this calorimeter, representing a challenge for the operational reliability of the sensors under such harsh radiation conditions. We investigated single-crystal and polycrystalline CVD diamond, gallium arsenide and radiation-hard silicon as sensor candidates for their radiation hardness and found that diamond and gallium arsenide are promising. We used a 10 MeV electron beam of few nA to irradiate the samples under investigation up to doses of 5 MGy for diamond, up to about 1.5 MGy for gallium arsenide and up to about 90 kGy for silicon. We measured in regular periods the CCD to characterize the impact of the absorbed dose on the size of the signal, which is generated by electrons of a {sup 90}Sr source crossing the sensor. Additional measurements such as the dark current and the CCD as functions of the voltage completed the characterization of the sensor candidates. For the single-crystal CVD diamond, also the termally stimulated current was measured to determine amongst others the defect density created by irradiation. In the diamond samples, evidence for strong polarization effects inside the material was found and investigated in more detail. A phenomenological model based on semi-conductor physics was developed to describe the sensor properties as a function of the applied electric field, the dose and the dose rate. Its predictions were compared with the results of the measurements. Several parameters such as time scales and cross-sections were determined using this model, which led to ongoing investigations. (orig.)

  20. Time-resolved X-ray diffraction with accelerator- and laser-plasma-based X-ray sources

    Energy Technology Data Exchange (ETDEWEB)

    Nicoul, Matthieu

    2010-09-01

    Femtosecond X-ray pulses are a powerful tool to investigate atomic motions triggered by femtosecond pump pulses. This thesis is dedicated to the production of such pulses and their use in optical pump - X-ray probe measurement. This thesis describes the laser-plasma-based sources available at the University of Duisburg-Essen. Part of it consists of the description of the design, built-up and characterization of a new ''modular'' X-ray source dedicated to optimize the X-ray flux onto the sample under investigation. The acoustic wave generation in femtosecond optically excited semiconductor (gallium arsenide) and metal (gold) was performed using the sources of the University of Duisburg-Essen. The physical answer of the material was modeled by a simple strain model for the semiconductor, pressure model for the metal, in order to gain information on the interplay of the electronic and thermal pressures rising after excitation. Whereas no reliable information could be obtain in gallium arsenide (principally due to the use of a bulk), the model for gold achieved very good agreement, providing useful information. The relaxation time of the electron to lattice energy was found to be (5.0{+-}0.3) ps, and the ratio of the Grueneisen parameters was found to be {gamma}{sub e} / {gamma}{sub i} = (0.5{+-}0.1). This thesis also describes the Sub-Picosecond Pulse Source (SPPS) which existed at the (formally) Stanford Linear Accelerator Center, an accelerator-based X-ray source, and two measurements performed with it. The first one is the detailed investigation of the phonon softening of the A{sub 1g} mode launch in bismuth upon fluence excitation. Detailed information concerning the new equilibrium position and phonon frequency were obtained over extended laser pump fluences. The second measurement concerned the study of the liquid phase dynamics in a newly formed liquid phase following ultrafast melting in indium antimonide. The formation of the liquid phase

  1. Orogenic-type copper-gold-arsenic-(bismuth) mineralization at Flatschach (Eastern Alps), Austria

    Science.gov (United States)

    Raith, Johann G.; Leitner, Thomas; Paar, Werner H.

    2015-10-01

    Structurally controlled Cu-Au mineralization in the historic Flatschach mining district (Styria, Austria) occurs in a NE-SW to NNE-WSW oriented vein system as multiple steep-dipping calcite-(dolomite)-quartz veins in amphibolite facies metamorphic rocks (banded gneisses/amphibolites, orthogneisses, metagranitoids) of the poly-metamorphosed Austroalpine Silvretta-Seckau nappe. Vein formation postdated ductile deformation events and Eoalpine (Late Cretaceous) peak metamorphism but predated Early to Middle Miocene sediment deposition in the Fohnsdorf pull-apart basin; coal-bearing sediments cover the metamorphic basement plus the mineralized veins at the northern edge of the basin. Three gold-bearing ore stages consist of a stage 1 primary hydrothermal (mesothermal?) ore assemblage dominated by chalcopyrite, pyrite and arsenopyrite. Associated minor minerals include alloclasite, enargite, bornite, sphalerite, galena, bismuth and matildite. Gold in this stage is spatially associated with chalcopyrite occurring as inclusions, along re-healed micro-fractures or along grain boundaries of chalcopyrite with pyrite or arsenopyrite. Sericite-carbonate alteration is developed around the veins. Stage 2 ore minerals formed by the replacement of stage 1 sulfides and include digenite, anilite, "blue-remaining covellite" (spionkopite, yarrowite), bismuth, and the rare copper arsenides domeykite and koutekite. Gold in stage 2 is angular to rounded in shape and occurs primarily in the carbonate (calcite, Fe-dolomite) gangue and less commonly together with digenite, domeykite/koutekite and bismuth. Stage 3 is a strongly oxidized assemblage that includes hematite, cuprite, and various secondary Cu- and Fe-hydroxides and -carbonates. It formed during supergene weathering. Stage 1 and 2 gold consists mostly of electrum (gold fineness 640-860; mean = 725; n = 46), and rare near pure gold (fineness 930-940; n = 6). Gold in stage 3 is Ag-rich electrum (fineness 350-490, n = 12), and has a

  2. Photonic Crystal Microcavities for Quantum Information Science

    Science.gov (United States)

    Hagemeier, Jenna Nicole

    Quantum information science and technology is a broad and fascinating field, encompassing diverse research areas such as materials science, atomic physics, superconductors, solid-state physics, and photonics. A goal of this field is to demonstrate the basic functions of information initialization, manipulation, and read-out in systems that take advantage of quantum physics to greatly enhance computing performance capabilities. In a hybrid quantum information network, different systems are used to perform different functions, to best exploit the advantageous properties of each system. For example, matter quantum bits (qubits) can be used for local data storage and manipulation while photonic qubits can be used for long-distance communication between storage points of the network. Our research focuses on the following two solid-state realizations of a matter qubit for the purpose of building such a hybrid quantum network: the electronic spin of a self-assembled indium arsenide quantum dot and the electronic spin of a nitrogen-vacancy defect center in diamond. Light--matter interactions are necessary to transfer the information from the matter qubit to the photonic qubit, and this interaction can be enhanced by embedding the spin system in an optical cavity. We focus on photonic crystal microcavities for this purpose, and we study interactions between the optical cavity modes and incorporated spin systems. To improve the performance of this spin--photon interface, it is important to maximize the coupling strength between the spin and photonic systems and to increase the read-out efficiency of information stored in the cavity. In this thesis, we present our work to deterministically couple a nitrogen-vacancy center in diamond to a photonic crystal microcavity in gallium phosphide. This is achieved by nanopositioning a pre-selected diamond nanocrystal in the intensity maximum of the optical cavity mode. We also present an optimized design of a photonic crystal

  3. Crystal chemical aspects of superconductivity in BaFe2As2 and related compounds

    Science.gov (United States)

    Johrendt, Dirk

    2010-03-01

    BaFe2As2 is the parent compound of the 122-type iron arsenides.^1 Superconductivity can be induced by several kinds of doping^2-4 or by pressure.^5 It is widely accepted that superconductivity in iron arsenides is unconventional and a number of experiments agree with the s±-scenario.^6 The latter relies on Fermi surface nesting which depends on both the electron count and the lattice. However, the coincidence of doping and pressure effects on the structure of BaFe2As2 supports the role of the structure.^7 Another open issue is the co-existence of superconductivity and AF magnetic ordering. Our ^57Fe-M"ossbauer experiments with underdoped Ba0.8K0.2Fe2As2 (Tc = 24 K) revealed full magnetic splitting, which indicates such a co-existence.^8 Compounds like Sr2VO3FeAs (Tc = 37-45 K) are promising candidates for higher Tc, but their crystal chemistry is not yet understood. In non-superconducting Sr2CrO3FeAs, we have detected a non-stoichiometry of the Fe-site (Fe0.93(1)Cr0.07(1)) and C-type AF ordering of the Cr^3+-layers.^9 The Cr-doping of the FeAs layer is probably detrimental to superconductivity in Sr2CrO3FeAs, but a similar non-stoichiometry may play a vital role in Sr2VO3FeAs.-^1 M. Rotter, M. Tegel, I. Schellenberg, et al., Phys. Rev. B 78, 020503 (2008).^2 M. Rotter, M. Tegel, and D. Johrendt, Phys. Rev. Lett. 101, 107006 (2008).^3 S. Jiang, C. Wang, Z. Ren, et al., J. Phys.: Condens. Matter 21, 382203 (2009).^4 A. S. Sefat, R. Jin, M. A. McGuire, et al., Phys. Rev. Lett. 101, 117004 (2008).^5 P. L. Alireza, Y. T. C. Ko, J. Gillett, et al., J. Phys.: Condens. Matter 21, 012208 (2009).^6 I. Mazin, D. J. Singh, M. D. Johannes, et al., Phys. Rev. Lett. 101, 057003 (2008).^7 M. Rotter, M. Pangerl, M. Tegel, et al., Angew. Chem. Int. Ed. 47, 7949 (2008).^8 M. Rotter, M. Tegel, I. Schellenberg, et al., New J. Phys. 11, 025014 (2009).^9 M. Tegel, Y. Su, F. Hummel, et al., arXiv0911.0450.

  4. Time-resolved X-ray diffraction with accelerator- and laser-plasma-based X-ray sources

    International Nuclear Information System (INIS)

    Femtosecond X-ray pulses are a powerful tool to investigate atomic motions triggered by femtosecond pump pulses. This thesis is dedicated to the production of such pulses and their use in optical pump - X-ray probe measurement. This thesis describes the laser-plasma-based sources available at the University of Duisburg-Essen. Part of it consists of the description of the design, built-up and characterization of a new ''modular'' X-ray source dedicated to optimize the X-ray flux onto the sample under investigation. The acoustic wave generation in femtosecond optically excited semiconductor (gallium arsenide) and metal (gold) was performed using the sources of the University of Duisburg-Essen. The physical answer of the material was modeled by a simple strain model for the semiconductor, pressure model for the metal, in order to gain information on the interplay of the electronic and thermal pressures rising after excitation. Whereas no reliable information could be obtain in gallium arsenide (principally due to the use of a bulk), the model for gold achieved very good agreement, providing useful information. The relaxation time of the electron to lattice energy was found to be (5.0±0.3) ps, and the ratio of the Grueneisen parameters was found to be γe / γi = (0.5±0.1). This thesis also describes the Sub-Picosecond Pulse Source (SPPS) which existed at the (formally) Stanford Linear Accelerator Center, an accelerator-based X-ray source, and two measurements performed with it. The first one is the detailed investigation of the phonon softening of the A1g mode launch in bismuth upon fluence excitation. Detailed information concerning the new equilibrium position and phonon frequency were obtained over extended laser pump fluences. The second measurement concerned the study of the liquid phase dynamics in a newly formed liquid phase following ultrafast melting in indium antimonide. The formation of the liquid phase and its development for excitations close to the

  5. Iron pnictide superconductors

    International Nuclear Information System (INIS)

    The scope of this dissertation therefore has not only been the synthesis of various new superconducting and non-superconducting iron pnictides of several structural families but also their in-depth crystallographic and physical characterisation. In Chapters 3 - 6, the family of the ZrCuSiAs-type (1111) compounds is subject of discussion. The solid solution series La(CoxFe1-x)PO is analysed regarding magnetic and superconducting properties and the new compounds EuMnPF and REZnPO, as well as the new superconductor parent compound SrFeAsF are presented. Chapters 7 - 9 are dedicated to the new iron arsenide superconductors of the ThCr2Si2-type (122 family). Therein, also the discovery of the first superconductor in this structural family, Ba0.6K0.4Fe2As2, is unveiled. A detailed examination of the complete solid solution series (Ba1-xKx)Fe2As2 is presented. Moreover, the crystallographic phase transitions of the closely related compounds SrFe2As2 and EuFe2As2 are characterised and the superconductors Sr1-xKxFe2As2 and Ca1-xNaxFe2As2 are examined for magnetic and phononic excitations. In Chapter 10, the redetermined crystal structure of the superconductor Fe(Se1-xTex) (11-type) is presented from a chemist's point of view. Chapters 11 - 14 look into the superconducting and non-superconducting iron arsenides of more complex structural families (32522-type and 21311-type). Therein, crystallographic and magnetic details of Sr3Sc2O5Fe2As2 are presented and Ba2ScO3FeAs and Sr2CrO3FeAs, the first two members of the new 21311-type are portrayed. Sr2CrO3FeAs is looked at in close detail with various methods, so e.g. the spin structure of the magnetically ordered compound is solved and a possible reason for the absence of superconductivity in this compound is given. Finally, the superconductor Sr2VO3FeAs is scrutinised and necessary prerequisites for superconductivity in this compound are suggested. (orig.)

  6. Evaluation of critical materials for five advanced design photovoltaic cells with an assessment of indium and gallium

    Energy Technology Data Exchange (ETDEWEB)

    Watts, R.L.; Gurwell, W.E.; Jamieson, W.M.; Long, L.W.; Pawlewicz, W.T.; Smith, S.A.; Teeter, R.R.

    1980-05-01

    The objective of this study is to identify potential material supply constraints due to the large-scale deployment of five advanced photovoltaic (PV) cell designs, and to suggest strategies to reduce the impacts of these production capacity limitations and potential future material shortages. This report presents the results of the screening of the five following advanced PV cell designs: polycrystalline silicon, amorphous silicon, cadmium sulfide/copper sulfide frontwall, polycrystalline gallium arsenide MIS, and advanced concentrator-500X. Each of these five cells is screened individually assuming that they first come online in 1991, and that 25 GWe of peak capacity is online by the year 2000. A second computer screening assumes that each cell first comes online in 1991 and that each cell has 5 GWe of peak capacity by the year 2000, so that the total online cpacity for the five cells is 25 GWe. Based on a review of the preliminary basline screening results, suggestions were made for varying such parameters as the layer thickness, cell production processes, etc. The resulting PV cell characterizations were then screened again by the CMAP computer code. Earlier DOE sponsored work on the assessment of critical materials in PV cells conclusively identtified indium and gallium as warranting further investigation as to their availability. Therefore, this report includes a discussion of the future availability of gallium and indium. (WHK)

  7. The effects of low-level laser on muscle damage caused by Bothrops neuwiedi venom

    Directory of Open Access Journals (Sweden)

    DM Dourado

    2008-01-01

    Full Text Available The present study aimed to assess the effects of low-level laser (660 nm on myonecrosis caused by the insertion of Bothrops neuwiedi venom in the gastrocnemius muscle of rats. Male Wistar rats were divided into three groups (n = 24 each: Group S (0.9% saline solution; Group V (venom and Group VLLL (venom plus low-level laser. These categories were subdivided into four additional groups (n = 6 based on the euthanasia timing (3 hours, 24 hours, 3 days and 7 days. The groups V and VLLL were inoculated with 100 µL of concentrated venom (40 µg/mL in the gastrocnemius muscle. The muscle was irradiated using a gallium-aluminum-arsenide laser (GaAlAs at 35 mW power and 4 J/cm² energy density for 3 hours, 24 hours, 3 days or 7 days after venom inoculation. To evaluate the myotoxic activity of the venom, CK activity was measured and the muscle was histologically analyzed. The low-level laser reduced venom-induced CK activity in the groups euthanized at 3 hours, 24 hours and 3 days (p < 0.0001. Histological analysis revealed that low-level laser reduced neutrophilic inflammation as well as myofibrillar edema, hemorrhage and myonecrosis following B. neuwiedi envenomation. These results suggest that low-level laser can be useful as an adjunct therapy following B. neuwiedi envenomation.

  8. Low-level laser therapy: Case-control study in dogs with sterile pyogranulomatous pododermatitis

    Directory of Open Access Journals (Sweden)

    Roberta Perego

    2016-08-01

    Full Text Available Aim: Low-level laser therapy (LLLT is a therapeutic photobiostimulation with properties in reducing swelling, inflammation, and promoting tissue healing. The objective of this pilot study was to evaluate LLLT in sterile pyogranulomatous pododermatitis in five dogs. Materials and Methods: In each dog, one lesion was designated as the control (treated with a 0.0584% hydrocortisone aceponate spray, and one or more other lesions were treated with a gallium aluminum arsenide-laser, daily for 5 days. Lesions were scored before treatment (D0, at the end (D4, 16 days after the last laser treatment (D20, and after 2 months (D65. Results: Comparing the treated lesion group with the control lesion group, the clinical score was similar at D0, whereas there was a statistically significant difference at D4 and D20; in the treated group over time, there was a statistically significant improvement between D0, D4, and D20. Lesion recurrence was absent in more than 50% of the treated lesions at D65. No adverse reactions were reported. Conclusion: Given the positive results of this first clinical study, it would be interesting to extend the study to confirm the validity of this type of therapy in sterile pyogranulomatous pododermatitis in the dog.

  9. Different doses of low-level laser irradiation modulate the in vitro response of osteoblast-like cells

    Science.gov (United States)

    Incerti Parenti, Serena; Checchi, Luigi; Fini, Milena; Tschon, Matilde

    2014-10-01

    Because osteoblasts play a key role in bone remodeling and the influence of low-level laser therapy on this process is not clear, Saos-2 human osteoblast-like cells were irradiated by a gallium-aluminum-arsenide diode laser (915 nm) for 10, 48, 96, 193, and 482 s using doses 1, 5, 10, 20, and 50 J/cm2, respectively. A control group was not irradiated. Morphology, viability, and cytotoxicity analyses were carried out after 1 hr, 1 day, and 3 days. Deoxyribose nucleic acid (DNA) content and release of vascular endothelial growth factor (VEGF), receptor activator of nuclear factor kappa B ligand (RANKL), and osteoprotegerin (OPG) were evaluated. Viability was modulated by laser irradiation in a dose-dependent manner, with 10 J/cm2 inducing a biostimulatory response and 20 to 50 J/cm2 determining a bioinhibitory and cytotoxic effect. Accordingly, DNA content was generally increased for the 10 J/cm2 dose and decreased for the 50 J/cm2 dose. A rapid and transitory trend toward increased RANKL/OPG ratio and a tendency toward a delayed increase in VEGF release for doses of 1 to 10 J/cm2 was found. Further investigations using the biostimulatory dose of 10 J/cm2 emerged from this study are needed to establish the ideal treatment regimens in the laboratory as well as in clinical practice.

  10. 1983 Annual progress report

    International Nuclear Information System (INIS)

    This report is concerned with the whole activities of the LETI (Laboratoire d'Electronique et de Technologie de l'Informatique) during 1983. They defined three sections wich are ''materials'', ''electronic components'' and the one called ''instrumentation and systems''. Among the magnetic materials, materials for magnetic bubble memories are concerned. Among semi-conductor materials, first, crystals of gallium arsenide and germanium are peculiarly studied; then researches on crystal growth processes aim at deposition of zinc or cadmium sulfide thin layers in aqueous solutions; and, finally, piezoelectric material researches consisted essentially in developing fabrication processes of lithium niobiate. Materials for infra-red devices are also studied together with materials related to optical microstructures (LNA, MgF2, LiYF4). The section ''Components'' comprises silicium microelectronics (ionic implantation techniques, MOS systems, etc), the magnetic bubble memories, the components related to integrated circuits for infrared imaging or to Josephson effect devices. Display, sensors, optical telecommunications, wiring terminations are also concerned. Physics and medicine instrumentation (magnetometry, time-of-flight positon tomography, X-ray tomography, NMR spectrometry in-vivo), robotics and technology of acquisition and processing of images (in view of an automatic control) are activities of the last section

  11. NREL photovoltaic subcontract reports: Abstracts and document control information, 1 August 1992--31 July 1993

    Energy Technology Data Exchange (ETDEWEB)

    1993-09-01

    This report contains document control information and abstracts for the National Renewable Energy Laboratory (NREL) subcontracted photovoltaic (PV) program publications. It also lists source information on additional publications that describe US Department of Energy (DOE) PV research activities. It is not totally exhaustive, so it lists NREL contacts for requesting further information on the DOE and NREL PV programs. This report covers the period from August 1, 1992, through July 31, 1993. This report is published periodically, with the previous one covering the period from August 1, 1991, through July 31, 1992. The purpose of continuing this type of publication is to help keep people abreast of specific PV interests, while maintaining a balance on the costs to the PV program. The information in this report is organized under PV technology areas: Amorphous Silicon Research; Polycrystalline Thin Films (including copper indium diselenide, cadmium telluride, and thin-film silicon); Crystalline Materials and Advanced Concepts (including silicon, gallium arsenide, and other group III-V materials); PV Manufacturing Technology Development (which may include manufacturing information for various types of PV materials).

  12. Beyond 3rd generation MCT: SXGA QWIP (Invited Paper)

    Science.gov (United States)

    Crawford, Stewart; Skivington, Tracey; Craig, Robert; Haining, Andrew; Costard, Eric; Belhaire, Eric; Bois, Philippe

    2005-05-01

    Successful past experience of implementing long wave MCT 1st and 2nd Generation thermal imagers has demonstrated to THALES Optronics that MCT presents difficult challenges when correcting non-uniformity errors caused by rapidly changing detector element gain and offset drifts. These problems become even more demanding when the move is made from long linear arrays to focal plane arrays due to the significantly larger number of detector elements. Relaxation of these demands would make a significant impact on the price/performance trade which inevitably occurs in a camera development. In recognition of the need to offer UK MOD best value, THALES Optronics has initiated a programme to achieve a SXGA resolution camera and is working with UK MOD, over a two year period, to investigate whether an alternative technology can maintain the high resolution required whilst achieving a downward step change in price. The selected technology is 3rd Generation Gallium Arsenide long wave Quantum Well Infra-red Photodiode (QWIP) chosen because initial indications are that drift rates are orders of magnitude slower than MCT. The programme involves studies to determine effects of defect clusters, bimodalism, non-uniformity correction levels and higher than normal operating temperatures on achieving acceptable performance, including logistics, in user scenarios whilst maximising detector yield. Development of demonstrator IR camera hardware (technology readiness level 6/7) based on a THALES Research & Technology QWIP array is also part of the programme.

  13. The effectiveness of low laser therapy in subacromial impingement syndrome: a randomized placebo controlled double-blind prospective study

    Directory of Open Access Journals (Sweden)

    Sebnem Koldas Dogan

    2010-01-01

    Full Text Available OBJECTIVES: Conflicting results were reported about the effectiveness of Low level laser therapy on musculoskeletal disorders. The aim of this study was to investigate the effectiveness of 850-nm gallium arsenide aluminum (Ga-As-Al laser therapy on pain, range of motion and disability in subacromial impingement syndrome. METHODS: A total of 52 patients (33 females and 19 males with a mean age of 53.59±11.34 years with subacromial impingement syndrome were included. The patients were randomly assigned into two groups. Group I (n = 30, laser group received laser therapy (5 joule/cm² at each point over maximum 5-6 painful points for 1 minute. Group II (n = 22, placebo laser group received placebo laser therapy. Initially cold pack (10 minutes was applied to all of the patients. Also patients were given an exercise program including range of motion, stretching and progressive resistive exercises. The therapy program was applied 5 times a week for 14 sessions. Pain severity was assessed by using visual analogue scale. Range of motion was measured by goniometer. Disability was evaluated by using Shoulder Pain and Disability Index. RESULTS: In group I, statistically significant improvements in pain severity, range of motion except internal and external rotation and SPADI scores were observed compared to baseline scores after the therapy (p0.05. CONCLUSIONS: The Low level laser therapy seems to have no superiority over placebo laser therapy in reducing pain severity, range of motion and functional disability.

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

    International Nuclear Information System (INIS)

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

  15. Advances in telecom and datacom optical components

    Science.gov (United States)

    Eldada, Louay A.

    2001-07-01

    We review and contrast key technologies developed to address the optical components market for telecom and datacom applications. We first look at different material systems, compare their properties, and describe the functions achieved to date in each of them. The material systems reviewed include glass fiber, silica on silicon, silicon on insulator, silicon oxynitride, sol-gels, polymers, thin film dielectrics, lithium niobate, indium phosphide, gallium arsenide, magneto-optic materials, and birefringent crystals. We then look at the most commonly used classes of technology and present their pros and cons as well as the functions achieved to date in each. The technologies reviewed include passive, actuation, and active technologies. The passive technologies described include fused fibers, dispersion-compensating fiber, beam steering (e.g., AWG), Bragg gratings, diffraction gratings, holographic elements, thin film filters, photonic crystals, microrings, and birefringent elements. The actuation technologies include thermo-optics, electro-optics, acousto- optics, magneto-optics, liquid crystals, total internal reflection technologies (e.g., bubble technology), and mechanical actuation (e.g., moving fibers and MEMS). We finally describe active technologies including heterostructures, quantum wells, rare earth doping, and semiconductor optical amplifiers. We also investigate the use of different material systems and technologies to achieve building block functions including lasers, amplifiers, detectors, modulators, polarization controllers, couplers, filters, switches, attenuators, nonreciprocal elements (Faraday rotators or nonreciprocal phase shifters) for isolators and circulators, wavelength converters, and dispersion compensators.

  16. Influence of the Thickness of the Barrier Layer in Nanoheterostructures and the Gate-Drain Capacitance on the Microwave and Noise Parameters of Field-Effect AlGaN/GaN HEMT

    Science.gov (United States)

    Mikhaylovich, S. V.; Fedorov, Yu. V.

    2016-07-01

    We perform a computational and analytical study of how the thickness of the barrier layer in nanoheterostructures and the gate-drain capacitance C gd influence the microwave parameters (limiting frequency of current amplification and maximum generation frequency) and noise parameters (noise factor) of a field-effect AlGaN/GaN high electron mobility transistor. The results of complex measurements of the parameters of such transistors based on nanoheterostructures with a barrier layer thickness of 3.5-15.7 nm, which were performed within the framework of four technological routes in the range 0.1-67 GHz, are presented. It is shown that in order to reduce the noise ratio and improve the microwave parameters, it is necessary to optimize both the parameters of nanoheterostructures and the manufacturing techniques. In particular, the thickness of the barrier layer should be reduced, and the gate length should be chosen such as to maximize the product of the squared maximum current amplification frequency in the interior of the transistor and the output impedance between the drain and the source. Additionally, attention should be given to the shape of the gate to reduce the capacitance C gd. Under certain conditions of manufacture of nitride field-effect HEMT, one can achieve a lower noise factor compared with the transistors based on arsenide nanoheterostructures.

  17. Microfabrication of microsystem-enabled photovoltaic (MEPV) cells

    Science.gov (United States)

    Nielson, Gregory N.; Okandan, Murat; Cruz-Campa, Jose L.; Resnick, Paul J.; Wanlass, Mark W.; Clews, Peggy J.; Pluym, Tammy C.; Sanchez, Carlos A.; Gupta, Vipin P.

    2011-02-01

    Microsystem-Enabled Photovoltaic (MEPV) cells allow solar PV systems to take advantage of scaling benefits that occur as solar cells are reduced in size. We have developed MEPV cells that are 5 to 20 microns thick and down to 250 microns across. We have developed and demonstrated crystalline silicon (c-Si) cells with solar conversion efficiencies of 14.9%, and gallium arsenide (GaAs) cells with a conversion efficiency of 11.36%. In pursuing this work, we have identified over twenty scaling benefits that reduce PV system cost, improve performance, or allow new functionality. To create these cells, we have combined microfabrication techniques from various microsystem technologies. We have focused our development efforts on creating a process flow that uses standard equipment and standard wafer thicknesses, allows all high-temperature processing to be performed prior to release, and allows the remaining post-release wafer to be reprocessed and reused. The c-Si cell junctions are created using a backside point-contact PV cell process. The GaAs cells have an epitaxially grown junction. Despite the horizontal junction, these cells also are backside contacted. We provide recent developments and details for all steps of the process including junction creation, surface passivation, metallization, and release.

  18. Octave-wide frequency comb centered at 4 μm based on a subharmonic OPO with Hz-level relative comb linewidth

    Science.gov (United States)

    Smolski, V. O.; Xu, J.; Schunemann, P. G.; Vodopyanov, K. L.

    2016-03-01

    We study coherence properties of a more-than-octave-wide (2.6-7.5 μm) mid-IR frequency comb based on a 2-μm Tmfiber- laser-pumped degenerate (subharmonic) optical parametric oscillator (OPO) that uses orientation-patterned gallium arsenide (OP-GaAs) as gain element. By varying intracavity dispersion, we observed a 'phase' transition from a singlecomb state (at exactly OPO degeneracy) to a two-comb state (near-degenerate operation), characterized by two spectrally overlapping combs (signal and idler) with distinct carrier-envelope offset frequencies. We achieve this by generating a supercontinuum (SC) from the mode-locked Tm laser that spans most of the near-IR range, and observing RF beats between the SC and parasitic sum-frequency light (pump + OPO) that also falls into the near-IR. We found RF linewidth to be pump laser comb is preserved to a high degree in a subharmonic OPO. Transition to a two-comb state was characterized by a symmetric splitting of the RF peak. Low pump threshold (down to 7 mW), high (73 mW) average power and high (up to 90%) pump depletion make this comb source very attractive for numerous applications including trace molecular detection and chemical sensing with massively parallel spectral data acquisition.

  19. Technology development of 3D detectors for high energy physics and medical imaging

    CERN Document Server

    Pellegrini, G

    2003-01-01

    This thesis is concerned with the fabrication, characterisation and simulation of 3D semiconductor detectors. Due to their geometry, these detectors have more efficient charge collection properties than current silicon and gallium arsenide planar detectors. The unit cell of these detectors is hexagonal with a central anode surrounded by six cathode contacts. This geometry gives a uniform electric field with the maximum drift and depletion distance set by electrode spacing, 85m in this project, rather than detector thickness, as in the case of planar detectors (typically 100-300m). This results in lower applied biases (35-40 V in the work of this project) compared to >200 V in typical planar detectors. The reduction in bias offers the possibility of improved detector operation in the presence of bulk radiation damage as lower voltage reduces leakage current which limits the signal to noise ratio and hence the overall detector efficiency. In this work, 3D detectors realised in Si, GaAs and SiC have ...

  20. Relative phase and physical properties of CrN/AlN multilayer: A DFT study

    Science.gov (United States)

    Cudris, E. F.; Díaz F, J. H.; Espita R, M. J.

    2016-08-01

    Using first principles total-energy calculations within the framework of density functional theory, we studied the relative stability and the structural and electronic properties of multilayer CrN/AlN in the sodium chloride (NaCl), cesium chloride (CsCl), nickel arsenide (NiAs), zinc-blende, and wurtzite structures. The calculations were carried out using the method based on pseudopotentials, employed exactly as implemented in Quantum-ESPRESSO code. Based on total energy minimization, we found that the minimum global energy of CrN/AlN is obtained for the zincblende structure. Additionally, at high pressure our calculations show the possibility of a phase transition from the zincblende to NaCl structure. For the zincblende phase, the density of states analysis reveals that the multilayer exhibits a half-metallic behavior with a magnetic moment of 3.0^p/Cr-atom. These properties come essentially from the polarization of Cr-d and N-p states that cross the Fermi level. Due to these properties, the multilayer can potentially be used in the field of spintronics or spin injectors.

  1. Improved combination of scalar diffraction theory and Rayleigh–Rice theory and its application to spectroscopic ellipsometry of randomly rough surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Ohlídal, Ivan, E-mail: ohlidal@physics.muni.cz [Department of Physical Electronics, Faculty of Science, Masaryk University, Kotlářká 2, 611 37 Brno (Czech Republic); Franta, Daniel; Nečas, David [Department of Physical Electronics, Faculty of Science, Masaryk University, Kotlářká 2, 611 37 Brno (Czech Republic); CEITEC — Central European Institute of Technology, Masaryk University, Kamenice 5, 625 00 Brno (Czech Republic)

    2014-11-28

    Expressions for ellipsometric quantities and reflectance presented are based on a heuristic combination of the Rayleigh–Rice theory and the scalar diffraction theory. The latter takes into account the local slopes and shadowing. The second-order Rayleigh–Rice theory is used to express the local electric field on the rough surface and the obtained expressions are then used in the scalar diffraction theory instead of the expressions corresponding to a smooth surface. A numeric method of evaluation of the quadruple integral resulting from this combination of the two theories is developed, utilising a Gauss-like quadrature. The efficiency of the formulae is illustrated by optical characterisation of rough silicon and gallium arsenide surfaces created using anodic and thermal oxidation, respectively, and covered with native oxide layers. The optical characterisation employs variable-angle spectroscopic ellipsometry and spectroscopic reflectometry. - Highlights: • Combination of Rayleigh–Rice theory and scalar diffraction theory is developed. • This combination is applied to randomly rough surfaces. • Slopes and shadowing are included within the scalar diffraction theory. • The combination is proven by measuring rough Si and GaAs surfaces.

  2. Triple-bond reactivity of an AsP complex intermediate: synthesis stemming from molecular arsenic, As(4).

    Science.gov (United States)

    Spinney, Heather A; Piro, Nicholas A; Cummins, Christopher C

    2009-11-11

    While P(4) is the stable molecular form of phosphorus, a recent study illustrated the possibility of P(2) generation for reactions in organic media under mild conditions. The heavier group 15 element arsenic can exist as As(4) molecules, but As(4) cannot be stored as a pure substance because it is both light-sensitive and reverts thermally to its stable, metallic gray form. Herein we report As(4) activation giving rise to a mu-As(2) diniobium complex, serving in turn as precursor to a terminal arsenide anion complex of niobium. Functionalization of the latter provides the new AsPNMes* ligand, which when complexed with tungsten pentacarbonyl elicits extrusion of the (AsP)W(CO)(5) molecule as a reactive intermediate. Trapping reactions of the latter with organic dienes are found to furnish double Diels-Alder adducts in which the AsP unit is embedded in a polycyclic organic framework. Thermal generation of (AsP)W(CO)(5) in the presence of the neutral terminal phosphide complex P identical withMo(N[(i)Pr]Ar)(3) leads to the cyclo-AsP(2) complex (OC)(5)W(cyclo-AsP(2))Mo(N[(i)Pr]Ar)(3). The (AsP)W(CO)(5) trapping products were crystallized and characterized by X-ray diffraction methods, and computational methods were applied for analysis of the As-As and As-P bonds in the complexes. PMID:19842699

  3. The effects of low-level laser on muscle damage caused by Bothrops neuwiedi venom

    International Nuclear Information System (INIS)

    The present study aimed to assess the effects of low-level laser (660 nm) on myonecrosis caused by the insertion of Bothrops neuwiedi venom in the gastrocnemius muscle of rats. Male Wistar rats were divided into three groups (n = 24 each): Group S (0.9% saline solution); Group V (venom) and Group VLLL (venom plus low-level laser). These categories were subdivided into four additional groups (n = 6) based on the euthanasia timing (3 hours, 24 hours, 3 days and 7 days). The groups V and VLLL were inoculated with 100 μL of concentrated venom (40 μg/mL) in the gastrocnemius muscle. The muscle was irradiated using a gallium-aluminum-arsenide laser (GaAlAs) at 35 mW power and 4 J/cm2 energy density for 3 hours, 24 hours, 3 days or 7 days after venom inoculation. To evaluate the myotoxic activity of the venom, CK activity was measured and the muscle was histologically analyzed. The low-level laser reduced venom-induced CK activity in the groups euthanized at 3 hours, 24 hours and 3 days (p < 0.0001). Histological analysis revealed that low-level laser reduced neutrophilic inflammation as well as myofibrillar edema, hemorrhage and myonecrosis following B. neuwiedi envenomation. These results suggest that low-level laser can be useful as an adjunct therapy following B. neuwiedi envenomation. (author)

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

    Directory of Open Access Journals (Sweden)

    Cristina de Freitas Bueno

    2013-01-01

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

  5. Nanoparticles Formed from Bacterial Oxyanion Reduction of Toxic Group 15 and Group 16 Metalloids

    Energy Technology Data Exchange (ETDEWEB)

    Pearce, Carolyn I.; Baesman, Shaun M.; Switzer Blum, Jodi; Fellowes, Jonathan W.; Oremland, Ronald S.

    2012-03-01

    Environmental Significance of Group 15 and 16 Toxic Metalloids Selenium, tellurium, and arsenic are present naturally in aquatic and terrestrial environments and share many similar biogeochemical characteristics. These elements are released into the environment through the weathering and decomposition of minerals contained within a variety of lithologies, with slow release rates resulting in low environmental concentrations. Selenium, tellurium, and arsenic occur in several oxidation states as oxyanions (e.g., selenate [SeO4 2], selenite [SeO3 2], tellurate [TeO4 2], tellurite [TeO3 2], arsenate [HAsO4 2], and arsenite [HAsO3 2]) in their native elemental states [e.g., Se(0), Te(0)] or in their most reduced states as selenide (-II) and telluride (-II) or arsenide/arsines (-III). These elements can be methylated through microbial activity to form compounds such as dimethylselenide (Ehrlich, 2002; Masscheleyn, et al., 1990), dimethyltelluride (Basnayake, et al., 2001; Fleming and Alexander, 1972), and methylarsonous acid (Dopp, et al., 2004) as well as a variety of toxic methylated arsine gases (Yuan, et al., 2008). These elements are also found as analogues of sulfurous proteins such as selenocysteine and selenomethionine (Bock, et al., 1991; Jones, et al., 1979; Stolz, et al., 2006; Zannoni, et al., 2008), tellurocysteine, telluromethionine (Zannoni, et al., 2008), and the arsenic-containing amino acid, arsenomethionine (Dembitsky and Levitsky, 2004).

  6. Lattice vibrations of icosahedral boron-rich solids

    Energy Technology Data Exchange (ETDEWEB)

    Beckel, C.L.; Yousaf, M. (The University of New Mexico, Albuquerque, New Mexico 87131 (United States))

    1991-07-01

    The rhombohedral lattices for {alpha}-boron, boron arsenide, and boron phosphide are each of D{sub 3d} symmetry and have bases that include B{sub 12} icosahedra. Boron carbide with B{sub 4}C stoichiometry has near-D{sub 3d} symmetry and is almost certainly composed of B{sub 11}C icosahedra and C-B-C chains. Comparable classical force field models are applied to each of these crystals to correlate q=0 phonon structure with experimental Raman and IR spectra. We here describe our methods and contrast interaction strengths for different materials. Vibrations are correlated in the different crystals through normal mode eigenvector expansions. Acoustic wave velocities from Brillouin zone dispersion curves in two distinct symmetry-axis directions are presented and contrasted for {alpha}-boron and B{sub 12}As{sub 2}. The origin of lines with anomalous polarization and width in {alpha}-boron, B{sub 12}As{sub 2}, and B{sub 12}P{sub 2} is considered.

  7. Searching for Dark Absorption with Direct Detection Experiments

    CERN Document Server

    Bloch, Itay M; Tobioka, Kohsaku; Volansky, Tomer; Yu, Tien-Tien

    2016-01-01

    We consider the absorption by bound electrons of dark matter in the form of dark photons and axion-like particles, as well as of dark photons from the Sun, in current and next-generation direct detection experiments. Experiments sensitive to electron recoils can detect such particles with masses between a few eV to more than 10 keV. For dark photon dark matter, we update a previous bound based on XENON10 data and derive new bounds based on data from XENON100 and CDMSlite. We find these experiments to disfavor previously allowed parameter space. Moreover, we derive sensitivity projections for SuperCDMS at SNOLAB for silicon and germanium targets, as well as for various possible experiments with scintillating targets (cesium iodide, sodium iodide, and gallium arsenide). The projected sensitivity can probe large new regions of parameter space. For axion-like particles, the same current direction detection data improves on previously known direct-detection constraints but does not bound new parameter space beyond...

  8. Observation of a Hidden Hole-Like Band Approaching the Fermi Level in K-Doped Iron Selenide Superconductor

    Science.gov (United States)

    Sunagawa, Masanori; Terashima, Kensei; Hamada, Takahiro; Fujiwara, Hirokazu; Fukura, Tetsushi; Takeda, Aya; Tanaka, Masashi; Takeya, Hiroyuki; Takano, Yoshihiko; Arita, Masashi; Shimada, Kenya; Namatame, Hirofumi; Taniguchi, Masaki; Suzuki, Katsuhiro; Usui, Hidetomo; Kuroki, Kazuhiko; Wakita, Takanori; Muraoka, Yuji; Yokoya, Takayoshi

    2016-07-01

    One of the ultimate goals of the study of iron-based superconductors is to identify the common feature that produces the high critical temperature (Tc). In the early days, based on a weak-coupling viewpoint, the nesting between hole- and electron-like Fermi surfaces (FSs) leading to the so-called s± state was considered to be one such key feature. However, this theory has faced a serious challenge ever since the discovery of alkali-metal-doped FeSe (AFS) superconductors, in which only electron-like FSs with a nodeless superconducting gap are observed. Several theories have been proposed, but a consistent understanding is yet to be achieved. Here we show experimentally that a hole-like band exists in KxFe2-ySe2, which presumably forms a hole-like Fermi surface. The present study suggests that AFS can be categorized in the same group as iron arsenides with both hole- and electron-like FSs present. This result provides a foundation for a comprehensive understanding of the superconductivity in iron-based superconductors.

  9. Visualizing weakly bound surface Fermi arcs and their correspondence to bulk Weyl fermions

    Science.gov (United States)

    Batabyal, Rajib; Morali, Noam; Avraham, Nurit; Sun, Yan; Schmidt, Marcus; Felser, Claudia; Stern, Ady; Yan, Binghai; Beidenkopf, Haim

    2016-01-01

    Fermi arcs are the surface manifestation of the topological nature of Weyl semimetals, enforced by the bulk-boundary correspondence with the bulk Weyl nodes. The surface of tantalum arsenide, similar to that of other members of the Weyl semimetal class, hosts nontopological bands that obscure the exploration of this correspondence. We use the spatial structure of the Fermi arc wave function, probed by scanning tunneling microscopy, as a spectroscopic tool to distinguish and characterize the surface Fermi arc bands. We find that, as opposed to nontopological states, the Fermi arc wave function is weakly affected by the surface potential: it spreads rather uniformly within the unit cell and penetrates deeper into the bulk. Fermi arcs reside predominantly on tantalum sites, from which the topological bulk bands are derived. Furthermore, we identify a correspondence between the Fermi arc dispersion and the energy and momentum of the bulk Weyl nodes that classify this material as topological. We obtain these results by introducing an analysis based on the role the Bloch wave function has in shaping quantum electronic interference patterns. It thus carries broader applicability to the study of other electronic systems and other physical processes. PMID:27551687

  10. Broken symmetry dielectric resonators for high quality-factor Fano metasurfaces

    CERN Document Server

    Campione, Salvatore; Basilio, Lorena I; Warne, Larry K; Langston, William L; Luk, Ting S; Wendt, Joel R; Reno, John L; Keeler, Gordon A; Brener, Igal; Sinclair, Michael B

    2016-01-01

    We present a new approach to dielectric metasurface design that relies on a single resonator per unit cell and produces robust, high quality-factor Fano resonances. Our approach utilizes symmetry breaking of highly symmetric resonator geoemetries, such as cubes, to induce couplings between the otherwise orthogonal resonator modes. In particular, we design perturbations that couple "bright" dipole modes to "dark" dipole modes whose radiative decay is suppressed by local field effects in the array. Our approach is widely scalable from the near-infrared to radio frequencies. We first unravel the Fano resonance behavior through numerical simulations of a germanium resonator-based metasurface that achieved a quality-factor of ~1300 at ~10.8 um. Then, we present two experimental demonstrations operating in the near-infrared (~1 um): a silicon-based implementation that achieved a quality-factor of ~350; and a gallium arsenide-based structure that achieves a quality-factor of ~600 - the highest near-infrared quality-...

  11. Direct Detection of sub-GeV Dark Matter with Scintillating Targets

    CERN Document Server

    Derenzo, Stephen; Massari, Andrea; Soto, Adrían; Yu, Tien-Tien

    2016-01-01

    We describe a novel search for MeV-to-GeV-mass dark matter, in which the dark matter scatters off electrons in a scintillating target. The excitation and subsequent de-excitation of the electron produces one or more photons, which could be detected with an array of cryogenic low-noise photodetectors, such as transition edge sensors (TES) or microwave kinetic inductance devices (MKID). Scintillators may have distinct advantages over other experiments searching for a low ionization signal from sub-GeV DM. First, the detection of one or a few photons may be technologically easier. Second, since no electric field is required to detect the photons, there may be far fewer dark counts mimicking a DM signal. We discuss various target choices, but focus on calculating the expected dark matter-electron scattering rates in three scintillating crystals, sodium iodide (NaI), cesium iodide (CsI), and gallium arsenide (GaAs). Among these, GaAs has the lowest band gap (1.52 eV) compared to NaI (5.9 eV) or CsI (6.4 eV), allow...

  12. Mission analysis of photovoltaic solar energy conversion. Volume IV. Supplementary studies

    Energy Technology Data Exchange (ETDEWEB)

    Leonard, S. L.; Breisacher, P.; Munjal, P. K.; Neiss, J. A.

    1977-03-01

    A discussion is presented of the most significant problems associated with the production and deployment of photovoltaic arrays. The principal chemical compounds to be used in the manufacture of silicon, gallium arsenide, and cadmium sulfide photovoltaic arrays are discussed with respect to physical and chemical properties, sources of the raw materials required to extract or synthesize these materials, the methods of manufacture, storage and handling in large quantities, transportation restrictions, spills, leaks, ignition and explosion. A discussion of safety hazards associated with the finished products is followed by an analysis of the toxicological properties of all raw, refined, and finished chemical species involved. The principal tool used in the evaluation of incentive strategies was a new Public Utility Financial Analysis and Planning Model which is described in some detail. After adaptation to match the characteristics of photovoltaic plants, it was used in the comparative evaluation of six different incentive strategies. The candidate strategies, the rationale for their selection, and the results of the comparative evaluation are presented. An account is given of an attempt to assess the full non-internalized costs of coal-fired power generation. A detailed description is given of the various damage elements and their associated societal costs for coal production, coal transportation, and coal-fired power generation. (MHR)

  13. Signal transmission techniques for large-scale nuclear fuel reprocessing applications

    International Nuclear Information System (INIS)

    The RCE is currently developing a prototypic microwave-based signal transmission system for reprocessing cell applications. This system, being developed for use in the Advanced Integrated Maintenance System (AIMS), will operate in the 10-GHz frequency range. Provisions are being made for five real-time video channels, three bidirectional data channels at one megabaud data rate each, and two audio channels. The basic utility of the concept has been proven in a laboratory demonstration using gallium arsenide gunn diode transmitter/receivers with horn antennas. Unidirectional transmission of one real-time video channel over a distance of 200 ft was demonstrated. No evidence of multipath interference was detected even when the transmission path was surrounded by metallic reflectors. The microwave signal transmission system for the AIMS application is in final design. Fabrication in the ORNL instrument shops will begin in October 1985, and the system should be operational in the Maintenance Systems Test Area (MSTA) at ORNL in the latter half of 1986

  14. Quantum control in spintronics.

    Science.gov (United States)

    Ardavan, A; Briggs, G A D

    2011-08-13

    Superposition and entanglement are uniquely quantum phenomena. Superposition incorporates a phase that contains information surpassing any classical mixture. Entanglement offers correlations between measurements in quantum systems that are stronger than any that would be possible classically. These give quantum computing its spectacular potential, but the implications extend far beyond quantum information processing. Early applications may be found in entanglement-enhanced sensing and metrology. Quantum spins in condensed matter offer promising candidates for investigating and exploiting superposition and entanglement, and enormous progress is being made in quantum control of such systems. In gallium arsenide (GaAs), individual electron spins can be manipulated and measured, and singlet-triplet states can be controlled in double-dot structures. In silicon, individual electron spins can be detected by ionization of phosphorus donors, and information can be transferred from electron spins to nuclear spins to provide long memory times. Electron and nuclear spins can be manipulated in nitrogen atoms incarcerated in fullerene molecules, which in turn can be assembled in ordered arrays. Spin states of charged nitrogen vacancy centres in diamond can be manipulated and read optically. Collective spin states in a range of materials systems offer scope for holographic storage of information. Conditions are now excellent for implementing superposition and entanglement in spintronic devices, thereby opening up a new era of quantum technologies. PMID:21727123

  15. Mechanical strength and tribological behavior of ion-beam deposited boron nitride films on non-metallic substrates

    International Nuclear Information System (INIS)

    An investigation was conducted to examine the mechanical strength and tribological properties of boron nitride (BN) films ion-beam deposited on silicon (Si), fused silica (SiO2), gallium arsenide (GaAs), and indium phosphide (InP) substrates in sliding contact with a diamond pin under a load. The results of the investigation indicate that BN films on nonmetallic substrates, like metal films on metallic substrates, deform elastically and plastically in the interfacial region when in contact with a diamond pin. However, unlike metal films and substrates, BN films on nonmetallic substrates can fracture when they are critically loaded. Not only does the yield pressure (hardness) of Si and SiO2 substrates increase by a factor of 2 in the presence of a BN film, but the critical load needed to fracture increases as well. The presence of films on the brittle substrates can arrest crack formation. The BN film reduces adhesion and friction in the sliding contact. BN adheres to Si and SiO2 and forms a good quality film, while it adheres poorly to GaAs and InP. The interfacial adhesive strengths were 1 GPa for a BN film on Si and appreciably higher than 1 GPa for a BN film on SiO2

  16. Discriminating a deep gallium antisite defect from shallow acceptors in GaAs using supercell calculations

    Science.gov (United States)

    Schultz, Peter A.

    2016-03-01

    For the purposes of making reliable first-principles predictions of defect energies in semiconductors, it is crucial to distinguish between effective-mass-like defects, which cannot be treated accurately with existing supercell methods, and deep defects, for which density functional theory calculations can yield reliable predictions of defect energy levels. The gallium antisite defect GaA s is often associated with the 78/203 meV shallow double acceptor in Ga-rich gallium arsenide. Within a conceptual framework of level patterns, analyses of structure and spin stabilization can be used within a supercell approach to distinguish localized deep defect states from shallow acceptors such as BA s. This systematic approach determines that the gallium antisite supercell results has signatures inconsistent with an effective mass state and cannot be the 78/203 shallow double acceptor. The properties of the Ga antisite in GaAs are described, total energy calculations that explicitly map onto asymptotic discrete localized bulk states predict that the Ga antisite is a deep double acceptor and has at least one deep donor state.

  17. Updated Results of a Solid-State Sensor Irradiation Study for ILC Extreme Forward Calorimetry

    CERN Document Server

    Courcoubetis, George; Fadeyev, Vitaliy; Fink, Caleb; Guillemaud, Nikolas; Renteria, Cesar Gonzalez; Gruey, Benjamin; LaBarre, Patrick; Martinez-McKinney, Forest; Rischbieter, Greg; Schumm, Bruce A; Spencer, Edwin; Wilder, Max

    2016-01-01

    Detectors proposed for the International Linear Collider (ILC) incorporate a tungsten sampling calorimeter (`BeamCal') intended to reconstruct showers of electrons, positrons and photons that emerge from the interaction point of the collider with angles between 5 and 50 milliradians. For the innermost radius of this calorimeter, radiation doses at shower max are expected to reach 100 Mrad per year, primarily due to minimum-ionizing electrons and positrons that arise in the induced electromagnetic showers of e+e- `beamstrahlung' pairs produced in the ILC beam-beam interaction. However, radiation damage to calorimeter sensors may be dominated by hadrons induced by nuclear interactions of shower photons, which are much more likely to contribute to the non-ionizing energy loss that has been observed to damage sensors exposed to hadronic radiation. We report here on the results of SLAC Experiment T-506, for which several different types of silicon diode and gallium-arsenide sensors were exposed to doses of radiati...

  18. Environmental assessment for the satellite power system concept development and evaluation program: atmospheric effects

    International Nuclear Information System (INIS)

    The US Department of Energy (DOE) has undertaken a preliminary, three-year program to investigate the impacts of the construction and operation of a satellite power system, of unprecedented scale. The Department of Energy's program, titled The Concept Development and Evaluation Program, focused its investigations on a Reference System description that calls for the use of either silicon (Si) or gallium aluminum-arsenide (GaAlAs) photovoltaic cells on 60 satellites to be constructed in GEO over a 30-yr period. Rectennas would be constructed on the ground to receive microwave energy from the satellites. Each satellite-rectenna pair is designed to produce 5 GW of power on an essentially continuous basis for use as a baseload power source for an electric power distribution system. The environmental assessment part of the program was divided into five interdependent task areas. The present document constitutes the final technical report on one of the five task areas, the Assessment of the Atmospheric Effects, and as such presents an in-depth summary of work performed during the assessment program. The issues associated with SPS activities in the troposphere are examined. These include tropospheric weather modification related to rectenna operations and rocket launches, and air quality impacts related to rocketlaunch ground clouds. Then progressing upward through the various levels of the atmosphere, the principal middle and upper atmospheric effects associated with rocket effluents are analyzed. Finally, all of the potential SPS atmospheric effects are summarized

  19. Electronic materials high-T(sub c) superconductivity polymers and composites structural materials surface science and catalysts industry participation

    Science.gov (United States)

    1988-01-01

    The fifth year of the Center for Advanced Materials was marked primarily by the significant scientific accomplishments of the research programs. The Electronics Materials program continued its work on the growth and characterization of gallium arsenide crystals, and the development of theories to understand the nature and distribution of defects in the crystals. The High Tc Superconductivity Program continued to make significant contributions to the field in theoretical and experimental work on both bulk materials and thin films and devices. The Ceramic Processing group developed a new technique for cladding YBCO superconductors for high current applications in work with the Electric Power Research Institute. The Polymers and Composites program published a number of important studies involving atomistic simulations of polymer surfaces with excellent correlations to experimental results. The new Enzymatic Synthesis of Materials project produced its first fluorinated polymers and successfully began engineering enzymes designed for materials synthesis. The structural Materials Program continued work on novel alloys, development of processing methods for advanced ceramics, and characterization of mechanical properties of these materials, including the newly documented characterization of cyclic fatigue crack propagation behavior in toughened ceramics. Finally, the Surface Science and Catalysis program made significant contributions to the understanding of microporous catalysts and the nature of surface structures and interface compounds.

  20. Anomalous magneto-elastic and charge doping effects in thallium-doped BaFe2As2

    Science.gov (United States)

    Sefat, Athena S.; Li, Li; Cao, Huibo B.; McGuire, Michael A.; Sales, Brian; Custelcean, Radu; Parker, David S.

    2016-02-01

    Within the BaFe2As2 crystal lattice, we partially substitute thallium for barium and report the effects of interlayer coupling in Ba1-xTlxFe2As2 crystals. We demonstrate the unusual effects of magneto-elastic coupling and charge doping in this iron-arsenide material, whereby Néel temperature rises with small x, and then falls with additional x. Specifically, we find that Néel and structural transitions in BaFe2As2 (TN = Ts = 133 K) increase for x = 0.05 (TN = 138 K, Ts = 140 K) from magnetization, heat capacity, resistivity, and neutron diffraction measurements. Evidence from single crystal X-ray diffraction and first principles calculations attributes the stronger magnetism in x = 0.05 to magneto-elastic coupling related to the shorter intraplanar Fe-Fe bond distance. With further thallium substitution, the transition temperatures decrease for x = 0.09 (TN = Ts = 131 K), and this is due to charge doping. We illustrate that small changes related to 3d transition-metal state can have profound effects on magnetism.

  1. Ultrahigh bandwidth signal processing

    Science.gov (United States)

    Oxenløwe, Leif Katsuo

    2016-04-01

    Optical time lenses have proven to be very versatile for advanced optical signal processing. Based on a controlled interplay between dispersion and phase-modulation by e.g. four-wave mixing, the processing is phase-preserving, and hence useful for all types of data signals including coherent multi-level modulation formats. This has enabled processing of phase-modulated spectrally efficient data signals, such as orthogonal frequency division multiplexed (OFDM) signals. In that case, a spectral telescope system was used, using two time lenses with different focal lengths (chirp rates), yielding a spectral magnification of the OFDM signal. Utilising such telescopic arrangements, it has become possible to perform a number of interesting functionalities, which will be described in the presentation. This includes conversion from OFDM to Nyquist WDM, compression of WDM channels to a single Nyquist channel and WDM regeneration. These operations require a broad bandwidth nonlinear platform, and novel photonic integrated nonlinear platforms like aluminum gallium arsenide nano-waveguides used for 1.28 Tbaud optical signal processing will be described.

  2. Arsenic in the environment: enrichments in the Slovenian soils

    Directory of Open Access Journals (Sweden)

    Mateja Gosar

    2005-12-01

    Full Text Available Arsenic, a toxic element with metalloid properties, is found in detectable concentrations in environmental samples. In nature it is enriched in metal (sulphide ore deposits, mainly as arsenides of Cu, Ni and Fe. Arsenic compounds are used mainly in agricultureand forestry as pesticides and herbicides. The ecosystem can be contaminated with arsenic via both natural and anthropogenic sources. Uses of arsenic contaminated water present so far the greatest health hazard. Occurrences of mining related arsenic problems havealso been recorded in many parts of the world.The impact of mining and metallurgic industry with regard to arsenic contents in soils in some potentially contaminated areas in Slovenia is discussed. Enriched contents of arsenic were found in Mežica. Arsenic correlates very well with lead, zinc and other heavymetals which are enriched as a result of long lasting lead production in the area. Also in Celje and Jesenice arsenic has the same distribution pattern as other anthropogenically introduced pollutants. In Idrija there are some slightly arsenic enriched areas, but there is no correlation with mercury, so the origin of arsenic in not clear yet.

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

    Science.gov (United States)

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

    2013-12-01

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

  4. Rapid Progress of a Thermal Arrayed Waveguide Grating Module for Dense Wavelength Division Multiplexing Applications

    Directory of Open Access Journals (Sweden)

    Abd ElñNaser A. Mohamed

    2011-09-01

    Full Text Available In the present paper, we have proposed a thermal planar arrayed waveguide grating (AWG module for dense wavelength division multiplexing (DWDM which is composed of one of the following material as a core such as Pure silica glass (SiO2, Lithium niobate (LiNbO3, and gallium aluminum arsenide (Ga(1 xAl(xAs/Polyhexafluoro isopropyl 2-fluoroacrylate dibutyl phathalate (PHFIP 2-FA-DBP used as over cladding material/Polyhexafluoro isopropyl 2-fluoroacrylate (PHFIP 2-FA used as under cladding material, hybrid materials on a silicon substrate has parametrically investigated over wide range of the affecting parameters. multiplexing technique is processed where multi channels in ultra dense wavelength division multiplexing in a thermal AWG module. We have theoretically investigated the temperature dependent wavelength shift of the AWG depends on the refractive indices of the materials and the size of the waveguide. A thermalization of the AWG can be realized by selecting proper values of the material and structural parameters of the device. We have taken into account the increased number of transmitted channels within DWDM technique over a thermal planar AWG of hybrid materials. The thermal effects of different hybrid materials employed in the fabrication of AWG are studied deeply and parametrically for the good performance of such AWG.

  5. Synthesis, crystal structure and magnetism of Eu{sub 3}Sc{sub 2}O{sub 5}Fe{sub 2}As{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Hummel, Franziska; Johrendt, Dirk [Ludwig-Maximilians-Universitaet Muenchen (Germany). Dept. Chemie; Tegel, Marcus [Fraunhofer-Institut fuer Fertigungstechnik und Angewandte Materialforschung (IFAM), Dresden (Germany); Gerke, Birgit; Poettgen, Rainer [Muenster Univ. (Germany). Inst. fuer Anorganische und Analytische Chemie

    2015-11-01

    The iron arsenide Eu{sub 3}Fe{sub 2}O{sub 5}Fe{sub 2}As{sub 2} was synthesized at 1173-1373 K in a resistance furnace and characterized by X-ray powder diffraction with Rietveld analysis: Sr{sub 3}Fe{sub 2}O{sub 5}Cu{sub 2}S{sub 2} type, I4/mmm, a = 406.40(1) pm, c = 2646.9(1) pm. Layers of edge-sharing FeAs{sub 4/4} tetrahedra are separated by perovskite-like oxide blocks. No structural transition occurs in the temperature range from 10 to 300 K. Magnetic measurements have revealed Curie-Weiss behavior with an effective magnetic moment of 7.79 μ{sub B} per europium atom in agreement with the theoretical value of 7.94 μ{sub B} for Eu{sup 2+}. A drop in the magnetic susceptibility at 5 K indicates possible antiferromagnetic ordering. {sup 151}Eu and {sup 57}Fe Moessbauer spectroscopic measurements have confirmed a beginning cooperative magnetic phenomenon by showing significantly broadened spectra at 4.8 K compared to those at 78 K.

  6. Photovoltaics: From the laboratory to the marketplace

    Energy Technology Data Exchange (ETDEWEB)

    Basso, T.S.; Surek, T.; Thornton, J.

    1991-03-01

    Photovoltaics (PV), the direct conversion of sunlight to electricity, is experiencing significant improvements in technology performance and lowered costs. Fostering these improvements, the SERI Photovoltaic Advanced Research and Development (PV AR D) Project supports research and provides services to the US PV industry. This paper presents the recent advances and future direction of the PV project. Research areas are Fundamental and Supporting Research, Advanced Thin-Film Materials, High-Efficiency Materials, Module Development, and Systems Development. Materials of interest include amorphous silicon, copper indium diselenide, cadmium telluride, crystalline silicon, gallium arsenide and related alloys, transparent conductors, antireflection coatings, substrates, and encapsulants. The PV project inherently provides technology transfer that helps industry shorten the time to bring R D advances to the marketplace. SERI annually performs over 10,000 measurements for the entire PV community, participates in collaborative research, and welcomes visiting scientists. Two specific areas of recently increased national focus are: (1) manufacturing processes for cost-effective PV modules, and (2) systems development for high-value utility applications. The SERI research approach is based on facilitating direct contact between industry, electric utilities, and others interested in PV technology. This approach heavily relies on SERI/industry partnerships. The arrangements vary to address generic and company-specific problems to improve the US industry's competitive position and accelerate greater electric utility deployment of PV systems. 5 refs., 5 figs., 6 tabs.

  7. Recent Advances in PV Research and Future Directions

    Science.gov (United States)

    Deb, Satyen K.

    1998-04-01

    The photovoltaic technology is making a major thrust in the commercial arena with 1997 worldwide production of PV modules reaching over 125 MW and growing at the rate of 20-25semiconductor materials and devices are emerging as strong contenders for PV applications even though silicon is still the 'work-horse' of the industry. Ultra-high efficiency solar cells fabricated from gallium arsenide (GaAs) and its ternary alloys like gallium indium phosphide (GaInP2) are finding applications in space technology. Enormous progress has also been made on various thin-film solar cell technologies, which offer the promise for substantially reducing the cost of PV systems. Some of the leading contenders are amorphous and polycrystalline silicon, compound semiconductor thin films such as copper indium diselenide (CuInSe2) based alloys, and cadmium telluride (CdTe) thin films. Exciting new developments are happening in the use of nano-particle semiconductor materials like titanium dioxide (TiO2) for low-cost PV devices. Intense research on these and other materials and devices is making a strong impact on the technology. In this presentation, a brief overview of recent advances in PV research will b e made and the trends and opportunities for future research directions will be identified.

  8. Pretreatment and thiosulfate leaching of refractory gold-bearing arsenosulfide concentrates

    Institute of Scientific and Technical Information of China (English)

    Yuqun Meng

    2005-01-01

    A hydrometallurgical process for refractory gold-bearing arsenosulfide concentrates at ambient temperature and pressure was presented, including fine grinding with intensified alkali-leaching (FGIAL), enhanced agitation alkali-leaching (EAAL), thiosulfate leaching and displacement. Experimental results on a refractory gold concentrate showed that the total consumption of NaOH in alkaline leaching is only 41% of those theoretically calculated under the conditions of full oxidization for the same amount of arsenides and sulfides transformed into arsenates and sulfates, and 72.3% of gold is synchro-dissoluted by thiosulfate self-generated during alkaline leaching. After alkaline leaching, thiosulfate leaching was carried out for 24 h. The dissolution of gold is increased to 91.9% from 4.6% by cyanide without the pretreatment. The displacement of gold by zinc powder in the solution gets to 99.2%. Due to an amount of thiosulfate self-generated during alkaline leaching, the reagent addition in thiosulfate leaching afterwards is lower than the normal.

  9. Laser drilling of via micro-holes in single-crystal semiconductor substrates using a 1070nm fibre laser with millisecond pulse widths

    Science.gov (United States)

    Maclean, Jessica O.; Hodson, Jonathan R.; Voisey, K. T.

    2015-07-01

    Micro-machining of semiconductors is relevant to fabrication challenges within the semiconductor industry. For via holes for solar cells, laser drilling potentially avoids deep plasma etching which requires sophisticated equipment and corrosive, high purity gases. Other applications include backside loading of cold atoms into atom chips and ion traps for quantum physics research, for which holes through the semiconductor substrate are needed. Laser drilling, exploiting the melt ejection material removal mechanism, is used industrially for drilling hard to machine materials such as superalloys. Lasers of the kind used in this work typically form holes with diameters of 100's of microns and depths of a few millimetres in metals. Laser drilling of semiconductors typically uses short pulses of UV or long wavelength IR to achieve holes as small as 50 microns. A combination of material processes occurs including laser absorption, heating, melting, vaporization with vapour and dust particle ejection and resolidification. An investigation using materials with different fundamental material parameters allows the suitability of any given laser for the processing of semiconductors to be determined. We report results on the characterization of via holes drilled using a 2000 W maximum power 1070 nm fibre laser with 1-20 ms pulses using single crystal silicon, gallium arsenide and sapphire. Holes were characterised in cross-section and plan view. Significantly, relatively long pulses were effective even for wide bandgap substrates which are nominally transparent at 1070 nm. Examination of drilled samples revealed holes had been successfully generated in all materials via melt ejection.

  10. Active layer identification of photonic crystal waveguide biosensor chip for the detection of Escherichia coli

    Science.gov (United States)

    Painam, Balveer; Kaler, Rajinder S.; Kumar, Mukesh

    2016-07-01

    This work represents experimental and simulation analysis of photonic crystal waveguide (PCW)-based biosensor structures, which is used for detection of the Escherichia coli (E. coli) cell. A method is adopted for E. coli culture to measure length, diameter, and refractive index to finalize the structural design and to verify the suitability of PCW as a biosensor. This method is tested using DH5α strains of E. coli. The typical precisions of measurements are varied in ranges from 1.132 to 1.825 μm and from 0.447 to 0.66 μm for pathogen's length and diameter, respectively. The measured distribution of samples over length and diameter are in correlation with the measurements performed by scanning electron microscope. After obtaining average length and diameter of cylindrical shaped E. coli cell, we consider these values for simulation analysis of designed PCW biosensor. E. coli cell is trapped in the middle of the PCW biosensor having three different types of waveguides, i.e., gallium arsenide/silicon dioxide (GaAs/SiO2), silicon/silicon dioxide (Si/SiO2), or silicon nitride/silicon dioxide (Si3N4/SiO2) to observe the maximum resonance shift and sensitivity. It is observed from the simulation data analysis that GaAs/SiO2 is the preferred PCW biosensor for the identification of E. coli.

  11. Six-fold hexagonal symmetric nanostructures with various periodic shapes on GaAs substrates for efficient antireflection and hydrophobic properties

    International Nuclear Information System (INIS)

    We fabricated various periodic nanostructures with a six-fold hexagonal symmetry on gallium arsenide (GaAs) substrates using simple process steps, together with a theoretical analysis of their antireflective properties. Elliptical photoresist (PR) nanopillars, which are inevitably generated by the asymmetric intensity distribution of the laser interference, were converted to rounded lens-like patterns by a thermal reflow process without any additional complex optic systems, thus leading to an exact six-fold hexagonal symmetry. Various shaped periodic nanostructures including nanorods, cones, truncated cones, and even parabolic patterns were obtained under different etching conditions using the rounded lens-like PR patterns formed by the reflow process. For the parabolic structure, the calculated lowest average reflectance of ∼ 2.3% was obtained. To achieve better antireflection characteristics, an aluminum-doped zinc oxide (AZO) film was deposited on the GaAs parabolas, which forms an AZO/GaAs parabolic nanostructure. The structure exhibited a low average reflectance of ∼ 1.2% over a wide wavelength region of 350–1800 nm and a hydrophobic surface with a water contact angle of θc ∼ 115°. The calculated reflectances were reasonably consistent with the measured results.

  12. Stable phases in aged type 321 stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Bentley, J.; Leitnaker, J.M.

    1978-01-01

    X-ray diffraction and Analytical Electron Microscopy have been used to characterize the precipitate phases present in type 321 stainless steel after 17 years of service at approximately 600/sup 0/C. The morphology, crystallography, and orientation relationships with the matrix of the precipitates have been determined along with the chemical composition of several of the phases. Long-term aging of type 321 stainless steel indicates TiC, not M/sub 23/C/sub 6/, is the stable carbide phase. A theory is developed to explain appearance of M/sub 23/C/sub 6/ at intermediate times. The theory also indicates the means for preventing M/sub 23/C/sub 6/ formation and hence sensitization of the steel to intergranular corrosion. The amount of sigma found correlates well with results from shorter time studies. Ti/sub 4/C/sub 2/S/sub 2/ and a complex phosphide-arsenide were also present.

  13. Wet etch methods for InAs nanowire patterning and self-aligned electrical contacts

    Science.gov (United States)

    Fülöp, G.; d’Hollosy, S.; Hofstetter, L.; Baumgartner, A.; Nygård, J.; Schönenberger, C.; Csonka, S.

    2016-05-01

    Advanced synthesis of semiconductor nanowires (NWs) enables their application in diverse fields, notably in chemical and electrical sensing, photovoltaics, or quantum electronic devices. In particular, indium arsenide (InAs) NWs are an ideal platform for quantum devices, e.g. they may host topological Majorana states. While the synthesis has been continously perfected, only a few techniques have been developed to tailor individual NWs after growth. Here we present three wet chemical etch methods for the post-growth morphological engineering of InAs NWs on the sub-100 nm scale. The first two methods allow the formation of self-aligned electrical contacts to etched NWs, while the third method results in conical shaped NW profiles ideal for creating smooth electrical potential gradients and shallow barriers. Low temperature experiments show that NWs with etched segments have stable transport characteristics and can serve as building blocks of quantum electronic devices. As an example we report the formation of a single electrically stable quantum dot between two etched NW segments.

  14. Thermal conductivity of III-V semiconductor superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Mei, S., E-mail: song.mei@wisc.edu; Knezevic, I., E-mail: irena.knezevic@wisc.edu [Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

    2015-11-07

    This paper presents a semiclassical model for the anisotropic thermal transport in III-V semiconductor superlattices (SLs). An effective interface rms roughness is the only adjustable parameter. Thermal transport inside a layer is described by the Boltzmann transport equation in the relaxation time approximation and is affected by the relevant scattering mechanisms (three-phonon, mass-difference, and dopant and electron scattering of phonons), as well as by diffuse scattering from the interfaces captured via an effective interface scattering rate. The in-plane thermal conductivity is obtained from the layer conductivities connected in parallel. The cross-plane thermal conductivity is calculated from the layer thermal conductivities in series with one another and with thermal boundary resistances (TBRs) associated with each interface; the TBRs dominate cross-plane transport. The TBR of each interface is calculated from the transmission coefficient obtained by interpolating between the acoustic mismatch model (AMM) and the diffuse mismatch model (DMM), where the weight of the AMM transmission coefficient is the same wavelength-dependent specularity parameter related to the effective interface rms roughness that is commonly used to describe diffuse interface scattering. The model is applied to multiple III-arsenide superlattices, and the results are in very good agreement with experimental findings. The method is both simple and accurate, easy to implement, and applicable to complicated SL systems, such as the active regions of quantum cascade lasers. It is also valid for other SL material systems with high-quality interfaces and predominantly incoherent phonon transport.

  15. Resonantly Enhanced Second-Harmonic Generation Using III-V Semiconductor All-Dielectric Metasurfaces.

    Science.gov (United States)

    Liu, Sheng; Sinclair, Michael B; Saravi, Sina; Keeler, Gordon A; Yang, Yuanmu; Reno, John; Peake, Gregory M; Setzpfandt, Frank; Staude, Isabelle; Pertsch, Thomas; Brener, Igal

    2016-09-14

    Nonlinear optical phenomena in nanostructured materials have been challenging our perceptions of nonlinear optical processes that have been explored since the invention of lasers. For example, the ability to control optical field confinement, enhancement, and scattering almost independently allows nonlinear frequency conversion efficiencies to be enhanced by many orders of magnitude compared to bulk materials. Also, the subwavelength length scale renders phase matching issues irrelevant. Compared with plasmonic nanostructures, dielectric resonator metamaterials show great promise for enhanced nonlinear optical processes due to their larger mode volumes. Here, we present, for the first time, resonantly enhanced second-harmonic generation (SHG) using gallium arsenide (GaAs) based dielectric metasurfaces. Using arrays of cylindrical resonators we observe SHG enhancement factors as large as 10(4) relative to unpatterned GaAs. At the magnetic dipole resonance, we measure an absolute nonlinear conversion efficiency of ∼2 × 10(-5) with ∼3.4 GW/cm(2) pump intensity. The polarization properties of the SHG reveal that both bulk and surface nonlinearities play important roles in the observed nonlinear process. PMID:27501472

  16. Correlation between structural, optical, and electrical properties of self-assembled plasmonic nanostructures on the GaAs surface

    Energy Technology Data Exchange (ETDEWEB)

    Gladskikh, Polina V.; Gladskikh, Igor A.; Toropov, Nikita A., E-mail: nikita.a.toropov@gmail.com; Baranov, Mikhail A.; Vartanyan, Tigran A. [ITMO University (Russian Federation)

    2015-11-15

    Self-assembled silver nanostructures on the industry-grade 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 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 caused by major transformations of the film morphology. While the As prepared films predominantly had a small-scale labyrinth structure, after annealing well-separated silver 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.Graphical Abstract.

  17. Direct investigation of (sub-) surface preparation artifacts in GaAs based materials by FIB sectioning.

    Science.gov (United States)

    Belz, Jürgen; Beyer, Andreas; Torunski, Torsten; Stolz, Wolfgang; Volz, Kerstin

    2016-04-01

    The introduction of preparation artifacts is almost inevitable when producing samples for (scanning) transmission electron microscopy ((S)TEM). These artifacts can be divided in extrinsic artifacts like damage processes and intrinsic artifacts caused by the deviations from the volume strain state in thin elastically strained material systems. The reduction and estimation of those effects is of great importance for the quantitative analysis of (S)TEM images. Thus, optimized ion beam preparation conditions are investigated for high quality samples. Therefore, the surface topology is investigated directly with atomic force microscopy (AFM) on the actual TEM samples. Additionally, the sectioning of those samples by a focused ion beam (FIB) is used to investigate the damage depth profile directly in the TEM. The AFM measurements show good quantitative agreement of sample height modulation due to strain relaxation to finite elements simulations. Strong indications of (sub-) surface damage by ion beams are observed. Their influence on high angle annular dark field (HAADF) imaging is estimated with focus on thickness determination by absolute intensity methods. Data consolidation of AFM and TEM measurements reveals a 3.5nm surface amorphization, negligible surface roughness on the scale of angstroms and a sub-surface damage profile in the range of up to 8.0nm in crystalline gallium arsenide (GaAs) and GaAs-based ternary alloys. A correction scheme for thickness evaluation of absolute HAADF intensities is proposed and applied for GaAs based materials. PMID:26855206

  18. Infrared spectroscopy of rare-earth-doped CaFe2As2

    Science.gov (United States)

    Xing, Zhen; Huffman, T. J.; Xu, Peng; Qazilbash, M. M.; Saha, S. R.; Drye, Tyler; Paglione, J.

    2014-03-01

    Recently, rare-earth doping in CaFe2As2 has been used to tune its electronic, magnetic, and structural properties. The substitution of rare-earth ions at the alkaline-earth sites leads to the suppression of the spin-density wave (SDW) phase transition in CaFe2As2. For example, Pr substitution results in a paramagnetic metal in the tetragonal phase that is susceptible to a low temperature structural transition to a collapsed tetragonal phase. However, La-doped CaFe2As2 remains in the uncollapsed tetragonal structure down to the lowest measured temperatures. Both the uncollapsed and collapsed tetragonal structures exhibit superconductivity with maximum Tc reaching 47 K, the highest observed in inter-metallics albeit with a small superconducting volume fraction. In this work, we perform ab-plane infrared spectroscopy of rare-earth-doped CaFe2As2 at different cryogenic temperatures. Our aim is to ascertain the contributions of electron doping and chemical pressure to the charge and lattice dynamics of this iron-arsenide system.

  19. Effective deleting of residual photoconductivity in high-resistance layers GaAs

    International Nuclear Information System (INIS)

    Full text: The phenomenon of residual photoconductivity as the storage of optical memory (OM) represents practical interest in micro and optoelectronics. The finding - out of the nature OM represents undoubtedly and scientific interest. Now residual photoconductivity (RPC) is explained by potential barriers arising because of non-monocharacteristical of distribution components of the semiconductor or carriers of a current in volume. Depending on a nature non-monocharacteristical the time relaxation RPC changes in a wide limit. The special interest represents RPC created by impurity. In the given work the results of research of a nature RPC created photos by ionization of the filled centres of chrome in compensated epitaxilogic layers arsenide galls are resulted. Epitaxilogic layers were brought up by a vertical method ZFE. Highness was reached (achieved) by special indemnification of the residual donors deep acceptors of chrome. Substrates served n-GoAs. Lassitude of i-layers has made 70-80 microns. Specific resistance of layers has made (1/3) 108 om·sm. (T= 300 K). The structures were photosensitive as at low (T = 77 K) and at room temperatures. The photosensitivity of structures in impurity to a strip of absorption chrome (= 1,4 microns) was comparable (compared) with own. The researches show, that the structures have RPC. Size RPC the greatest ambassador impurity of illumination is carrying out photoionization Cr2 + - of the centres. That is established, RPC impurity of a photocurrent is effectively erased only at certain length of a wave of external illumination

  20. Laser Systems For Use With Airborne Platforms

    Science.gov (United States)

    Jepsky, Joseph

    1984-10-01

    This paper describes a family of airborne laser systems in use for terrain profiling, surveying, mapping, altimetry, collision avoidance and shipboard landing systems using fixed and rotary wing aircraft as the platforms. The laser altimeter has also been used in systems compatible with the Army T-16 and. T-22 carrier missiles (platform). Both pulsed gallium arsenide and Nd:YAG (neodymium-doped, yttrium-aluminum-garnet) laser rangefinders have been used for these applications. All of these systems use ACCI's advanced measurement techniques that permit range accuracies of 8 cm, single shot, 1 cm averaged, to be achieved. Pulse rates up to 4 Khz are employed for airborne profiling. This high data density rate provides 1 data point every 2" along the aircraft flight line at aircraft speed of 500 knots. Scanning modes for some applications are employed. Systems have been integrated with all current inertial navigation systems (Litton, Ferranti and Honeywell), as well as a number of microwave positioning systems. Removal of aircraft motion from the laser range measurements by use of an accelerometer is described. Flight data from a number of program performed by U.S. and Canadian Federal Agencies, in addition to those of commercial surveying and mapping companies are described.

  1. The efficiency limit of CH3NH3PbI3 perovskite solar cells

    Science.gov (United States)

    Sha, Wei E. I.; Ren, Xingang; Chen, Luzhou; Choy, Wallace C. H.

    2015-06-01

    With the consideration of photon recycling effect, the efficiency limit of methylammonium lead iodide (CH3NH3PbI3) perovskite solar cells is predicted by a detailed balance model. To obtain convincing predictions, both AM 1.5 spectrum of Sun and experimentally measured complex refractive index of perovskite material are employed in the detailed balance model. The roles of light trapping and angular restriction in improving the maximal output power of thin-film perovskite solar cells are also clarified. The efficiency limit of perovskite cells (without the angular restriction) is about 31%, which approaches to Shockley-Queisser limit (33%) achievable by gallium arsenide (GaAs) cells. Moreover, the Shockley-Queisser limit could be reached with a 200 nm-thick perovskite solar cell, through integrating a wavelength-dependent angular-restriction design with a textured light-trapping structure. Additionally, the influence of the trap-assisted nonradiative recombination on the device efficiency is investigated. The work is fundamentally important to high-performance perovskite photovoltaics.

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

    Science.gov (United States)

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

    2015-09-16

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

  3. 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.

  4. Effect of Low-Level Laser Therapy on Incorporation of Block Allografts

    Directory of Open Access Journals (Sweden)

    Renato Valiati, Jefferson Viapiana Paes, Aury Nunes de Moraes, Aldo Gava, Michelle Agostini, Anelise Viapiana Masiero, Marilia Gerhardt de Oliveira, Rogério Miranda Pagnoncelli

    2012-01-01

    Full Text Available Objective To assess the effect of low-level laser therapy (LLLT on the incorporation of deep-frozen block allografts in a rabbit model.Background Data Studies have shown that LLLT has beneficial effects on tissue repair and new bone formation.Methods Bone tissue was harvested from two rabbits, processed by deep-freezing and grafted into the calvaria of 12 animals, which were then randomly allocated into two groups: experimental (L and control (C. Rabbits in group L were irradiated with an aluminum gallium arsenide diode laser (AlGaAs; wavelength 830 nm, 4 J/cm2, applied to four sites on the calvaria, for a total dose of 16 J/cm2 per session. The total treatment dose after eight sessions was 128 J/cm2. Animals were euthanized at 35 (n = 6 or 70 days (n = 6 postoperatively.Results Deep-freeze-processed block allografts followed by LLLT showed incorporation at the graft-host interface, moderate bone remodeling, partial filling of osteocyte lacunae, less inflammatory infiltrate in the early postoperative period, and higher collagen deposition than the control group.Conclusion Optical microscopy and scanning electron microscopy showed that allograft bone processed by deep-freezing plus LLLT is suitable as an alternative for the treatment of bone defects. Use of the deep-freezing method for processing of bone grafts preserves the structural and osteoconductive characteristics of bone tissue.

  5. III-V semiconductors for photoelectrochemical applications: surface preparation and characterization

    Energy Technology Data Exchange (ETDEWEB)

    Fertig, Dominic; Schaechner, Birgit; Calvet, Wofram; Kaiser, Bernhard; Jaegermann, Wolfram [TU Darmstadt, Fachbereich Materialwissenschaft, Fachgebiet Oberflaechenforschung (Germany)

    2011-07-01

    III-V semiconductors are promising reference systems for photoelectrochemical energy conversion. Therefore we have studied the influence of different acids and acidic solutions on the etching of p-doped gallium-arsenide and gallium-phosphide single crystal surfaces. From our experiments we conclude, that etching with HCl and subsequent annealing up to 450 C gives the best results for the removal of the carbonates and the oxides without affecting the quality of the sample. By treating the surfaces with ''piranha''-solution (H{sub 2}SO{sub 4}:H{sub 2}O{sub 2}:H{sub 2}O/7:2:1), the creation of an oxide layer with well defined thickness can be achieved. For the creation of an efficient photoelectrochemical cell, Pt nanoparticles have been deposited from solution. These surfaces are then characterized by photoelectron spectroscopy and AFM. Further electrochemical measurements try to correlate the effect of the surface cleaning and the Pt deposition on the photoactivity of the GaAs- and GaP-semiconductors.

  6. Defect effects on THz wave emission induced by ion irradiation

    International Nuclear Information System (INIS)

    Background: As the core component of terahertz system, terahertz source determines the performance of the whole system. The THz wave emission efficiency depends decisively on the THz emitting materials which are usually made of low-temperature-grown gallium arsenide. It is found that through ion irradiation better THz wave emission material can be prepared, which overcomes the poor reproducibility of high quality material prepared by the traditional method. Purpose: In order to find out the best irradiation condition for producing the required photoconductive material, we try to clarify the mechanism of the THz wave emission induced by ion implantation. Methods: Applying Monte Carlo method, we simulated the terahertz emission under different defect conditions, and tested the emission efficiency of GaAs and InP(Fe) irradiated by N ions with the energy of 500 keV and 1.5 MeV, respectively. Results: MC simulation study shows that both capture cross-section and trap density can cause changes in terahertz pulse width and peak intensity. From the experiments conducted on ion irradiated semiconductors we found only the peak intensity changes with the irradiation fluence. Conclusion: It is proposed that intrinsic defects introduced during growth of crystals are the key defects that contribute mainly to the terahertz wave emission behavior, and defects introduced by ion irradiation may only modify the transport property of carriers through scattering in semiconductor, by which it changes the terahertz wave emission performance. (authors)

  7. Visualizing weakly bound surface Fermi arcs and their correspondence to bulk Weyl fermions.

    Science.gov (United States)

    Batabyal, Rajib; Morali, Noam; Avraham, Nurit; Sun, Yan; Schmidt, Marcus; Felser, Claudia; Stern, Ady; Yan, Binghai; Beidenkopf, Haim

    2016-08-01

    Fermi arcs are the surface manifestation of the topological nature of Weyl semimetals, enforced by the bulk-boundary correspondence with the bulk Weyl nodes. The surface of tantalum arsenide, similar to that of other members of the Weyl semimetal class, hosts nontopological bands that obscure the exploration of this correspondence. We use the spatial structure of the Fermi arc wave function, probed by scanning tunneling microscopy, as a spectroscopic tool to distinguish and characterize the surface Fermi arc bands. We find that, as opposed to nontopological states, the Fermi arc wave function is weakly affected by the surface potential: it spreads rather uniformly within the unit cell and penetrates deeper into the bulk. Fermi arcs reside predominantly on tantalum sites, from which the topological bulk bands are derived. Furthermore, we identify a correspondence between the Fermi arc dispersion and the energy and momentum of the bulk Weyl nodes that classify this material as topological. We obtain these results by introducing an analysis based on the role the Bloch wave function has in shaping quantum electronic interference patterns. It thus carries broader applicability to the study of other electronic systems and other physical processes. PMID:27551687

  8. Plasmonic light trapping in an ultrathin photovoltaic layer with film-coupled metamaterial structures

    International Nuclear Information System (INIS)

    A film-coupled metamaterial structure is numerically investigated for enhancing the light absorption in an ultrathin photovoltaic layer of crystalline gallium arsenide (GaAs). The top subwavelength concave grating and the bottom metallic film could not only effectively trap light with the help of wave interference and magnetic resonance effects excited above the bandgap, but also practically serve as electrical contacts for photon-generated charge collection. The energy absorbed by the active layer is greatly enhanced with the help of the film-coupled metamaterial structure, resulting in significant improvement on the short-circuit current density by three times over a free-standing GaAs layer at the same thickness. The performance of the proposed light trapping structure is demonstrated to be little affected by the grating ridge width considering the geometric tolerance during fabrication. The optical absorption at oblique incidences also shows direction-insensitive behavior, which is highly desired for efficiently converting off-normal sunlight to electricity. The results would facilitate the development of next-generation ultrathin solar cells with lower cost and higher efficiency

  9. Nanowire Photovoltaic Devices

    Science.gov (United States)

    Forbes, David

    2015-01-01

    Firefly Technologies, in collaboration with the Rochester Institute of Technology and the University of Wisconsin-Madison, developed synthesis methods for highly strained nanowires. Two synthesis routes resulted in successful nanowire epitaxy: direct nucleation and growth on the substrate and a novel selective-epitaxy route based on nanolithography using diblock copolymers. The indium-arsenide (InAs) nanowires are implemented in situ within the epitaxy environment-a significant innovation relative to conventional semiconductor nanowire generation using ex situ gold nanoparticles. The introduction of these nanoscale features may enable an intermediate band solar cell while simultaneously increasing the effective absorption volume that can otherwise limit short-circuit current generated by thin quantized layers. The use of nanowires for photovoltaics decouples the absorption process from the current extraction process by virtue of the high aspect ratio. While no functional solar cells resulted from this effort, considerable fundamental understanding of the nanowire epitaxy kinetics and nanopatterning process was developed. This approach could, in principle, be an enabling technology for heterointegration of dissimilar materials. The technology also is applicable to virtual substrates. Incorporating nanowires onto a recrystallized germanium/metal foil substrate would potentially solve the problem of grain boundary shunting of generated carriers by restricting the cross-sectional area of the nanowire (tens of nanometers in diameter) to sizes smaller than the recrystallized grains (0.5 to 1 micron(exp 2).

  10. Effectiveness of Gaalas Phototherapy According to Diagnostic Criteria for Tемрoromandibular Disorders

    Directory of Open Access Journals (Sweden)

    Nencheva-Sveshtarova Savina

    2015-11-01

    Full Text Available The objective of this study was to test the clinical effectiveness of the combined gallium-aluminum-arsenide laser (GaAlAs; 785 nm and superluminiscent diods (SLD; 633 nm phototherapy (MedX 1100 device for the treatment of 62 patients with 7 of the most common pain-related temporomandibular disorders with highest sensitivity and specificity according to diagnostic criteria DC/TMD. Using paired samples t-test a positive effect in the pain relief for all tested conditions was demonstrated. The most manifested and statistically significant reduction of pain was found in arthralgia attributed to osteoarthritis and systemic (rheumatoid arthritis (p = 0.0000001, and disc displacement without reduction with limited opening (p = 0.0000002. Similar levels of pain reduction were found in arthralgia attributed to subluxation, myofascial pain with referral, local myalgia (p values vary between 0.000001 and 0.000284; the lowest values were recorded for myofascial pain (p = 0.001789 and hypermobility-related myalgia (p = 0.018443. The combined laser and SLD phototherapy can be defined as very effective treatment option particularly in pain reduction of internal derangement disorders as well as in some myogenic-related pain conditions affected by TMJ dysfunction.

  11. 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.)

  12. Steady thermocapillary-buoyant convection in a shallow annular pool.Part 2: Two immiscible fluids

    Institute of Scientific and Technical Information of China (English)

    You-Rong Li; Shuang-Cheng Wang; Chun-Mei Wu

    2011-01-01

    This work is devoted to the study of steady thermocapillary-buoyant convection in a system of two horizontal superimposed immiscible liquid layers filling a lateral heated thin annular pool.The governing equations are solved using an asymptotic theory for the aspect ratios e → 0.Asymptotic solutions of the velocity and temperature fields are obtained in the core region away from the cylinder walls.In order to validate the asymptotic solutions,numerical simulations are also carried out and the results are compared to each other.It is found that the present asymptotic solutions are valid in most of the core region.And the applicability of the obtained asymptotic solutions decreases with the increase of the aspect ratio and the thickness ratio of the two layers.For a system of gallium arsenide (lower layer) and boron oxide (upper layer),the buoyancy slightly weakens the thermocapillary convection in the upper layer and strengthens it in the lower layer.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-12-15

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

  14. 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.

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

    Science.gov (United States)

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

    2014-12-01

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

  16. The effects of low-level laser on muscle damage caused by Bothrops neuwiedi venom

    Energy Technology Data Exchange (ETDEWEB)

    Dourado, D.M.; Matias, R.; Almeida, M.F.; Paula, K.R. de; Carvalho, P.T.C. [University for the Development of the State and of the Region of Pantanal (UNIDERP), Campo Grande, MS (Brazil). Lab. of Experimental Histopathology]. E-mail: ccfi@uniderp.br; Vieira, R.P. [University of Sao Paulo (USP), SP (Brazil). School of Medicine. Dept. of Pathology and Physical Therapy; Oliveira, L.V.F. [Nove de Julho University (UNINOVE), Sao Paulo, SP (Brazil). Masters Program in Rehabilitation Sciences

    2008-07-01

    The present study aimed to assess the effects of low-level laser (660 nm) on myonecrosis caused by the insertion of Bothrops neuwiedi venom in the gastrocnemius muscle of rats. Male Wistar rats were divided into three groups (n = 24 each): Group S (0.9% saline solution); Group V (venom) and Group VLLL (venom plus low-level laser). These categories were subdivided into four additional groups (n = 6) based on the euthanasia timing (3 hours, 24 hours, 3 days and 7 days). The groups V and VLLL were inoculated with 100 {mu}L of concentrated venom (40 {mu}g/mL) in the gastrocnemius muscle. The muscle was irradiated using a gallium-aluminum-arsenide laser (GaAlAs) at 35 mW power and 4 J/cm{sup 2} energy density for 3 hours, 24 hours, 3 days or 7 days after venom inoculation. To evaluate the myotoxic activity of the venom, CK activity was measured and the muscle was histologically analyzed. The low-level laser reduced venom-induced CK activity in the groups euthanized at 3 hours, 24 hours and 3 days (p < 0.0001). Histological analysis revealed that low-level laser reduced neutrophilic inflammation as well as myofibrillar edema, hemorrhage and myonecrosis following B. neuwiedi envenomation. These results suggest that low-level laser can be useful as an adjunct therapy following B. neuwiedi envenomation. (author)

  17. Hard x-ray broad band Laue lenses (80 - 600 keV): building methods and performances

    CERN Document Server

    Virgilli, E; Rosati, P; Liccardo, V; Squerzanti, S; Carassiti, V; Caroli, E; Auricchio, N; Stephen, J B

    2015-01-01

    We present the status of the laue project devoted to develop a technology for building a 20 meter long focal length Laue lens for hard x-/soft gamma-ray astronomy (80 - 600 keV). The Laue lens is composed of bent crystals of Gallium Arsenide (GaAs, 220) and Germanium (Ge, 111), and, for the first time, the focusing property of bent crystals has been exploited for this field of applications. We show the preliminary results concerning the adhesive employed to fix the crystal tiles over the lens support, the positioning accuracy obtained and possible further improvements. The Laue lens petal that will be completed in a few months has a pass band of 80 - 300 keV and is a fraction of an entire Laue lens capable of focusing X-rays up to 600 keV, possibly extendable down to 20 - 30 keV with suitable low absorption crystal materials and focal length. The final goal is to develop a focusing optics that can improve the sensitivity over current telescopes in this energy band by 2 orders of magnitude.

  18. Estimates of occupational safety and health impacts resulting from large-scale production of major photovoltaic technologies

    Energy Technology Data Exchange (ETDEWEB)

    Owens, T.; Ungers, L.; Briggs, T.

    1980-08-01

    The purpose of this study is to estimate both quantitatively and qualitatively, the worker and societal risks attributable to four photovoltaic cell (solar cell) production processes. Quantitative risk values were determined by use of statistics from the California semiconductor industry. The qualitative risk assessment was performed using a variety of both governmental and private sources of data. The occupational health statistics derived from the semiconductor industry were used to predict injury and fatality levels associated with photovoltaic cell manufacturing. The use of these statistics to characterize the two silicon processes described herein is defensible from the standpoint that many of the same process steps and materials are used in both the semiconductor and photovoltaic industries. These health statistics are less applicable to the gallium arsenide and cadmium sulfide manufacturing processes, primarily because of differences in the materials utilized. Although such differences tend to discourage any absolute comparisons among the four photovoltaic cell production processes, certain relative comparisons are warranted. To facilitate a risk comparison of the four processes, the number and severity of process-related chemical hazards were assessed. This qualitative hazard assessment addresses both the relative toxicity and the exposure potential of substances in the workplace. In addition to the worker-related hazards, estimates of process-related emissions and wastes are also provided.

  19. Natural fracking and the genesis of five-element veins

    Science.gov (United States)

    Markl, Gregor; Burisch, Mathias; Neumann, Udo

    2016-08-01

    Hydrothermal Ag-Co-Ni-Bi-As (five-element vein type) ore deposits show very conspicuous textures of the native elements silver, bismuth, and arsenic indicating formation from a rapid, far-from-equilibrium process. Such textures include up to dm-large tree- and wire-like aggregates overgrown by Co-Ni-Fe arsenides and mostly carbonates. Despite the historical and contemporary importance of five-element vein type deposits as sources of silver, bismuth, and cobalt, and despite of spectacular museum specimens, their process of formation is not yet understood and has been a matter of debate since centuries. We propose, based on observations from a number of classical European five-element vein deposits and carbon isotope analyses, that "natural fracking," i.e., liberation of hydrocarbons or hydrocarbon-bearing fluids during break up of rocks in the vicinity of an active hydrothermal system and mixing between these hydrocarbons (e.g., methane and/or methane-bearing fluids) and a metal-rich hydrothermal fluid is responsible for ore precipitation and the formation of the unusual ore textures and assemblages. Thermodynamic and isotope mixing calculations show that the textural, chemical, and isotopic features of the investigated deposits can entirely be explained by this mechanism.

  20. The efficiency limit of CH3NH3PbI3 perovskite solar cells

    International Nuclear Information System (INIS)

    With the consideration of photon recycling effect, the efficiency limit of methylammonium lead iodide (CH3NH3PbI3) perovskite solar cells is predicted by a detailed balance model. To obtain convincing predictions, both AM 1.5 spectrum of Sun and experimentally measured complex refractive index of perovskite material are employed in the detailed balance model. The roles of light trapping and angular restriction in improving the maximal output power of thin-film perovskite solar cells are also clarified. The efficiency limit of perovskite cells (without the angular restriction) is about 31%, which approaches to Shockley-Queisser limit (33%) achievable by gallium arsenide (GaAs) cells. Moreover, the Shockley-Queisser limit could be reached with a 200 nm-thick perovskite solar cell, through integrating a wavelength-dependent angular-restriction design with a textured light-trapping structure. Additionally, the influence of the trap-assisted nonradiative recombination on the device efficiency is investigated. The work is fundamentally important to high-performance perovskite photovoltaics

  1. Bulk superconductivity at 2.6 K in undoped RbFe{sub 2}As{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Bukowski, Z., E-mail: bukowski@phys.ethz.c [Laboratory for Solid State Physics, ETH Zurich, CH-8093 Zurich (Switzerland); Weyeneth, S., E-mail: wstephen@physik.uzh.c [Physik-Institut der Universitaet Zuerich, Winterthurerstrasse 190, CH-8057 Zuerich (Switzerland); Puzniak, R. [Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02-668 Warsaw (Poland); Karpinski, J.; Batlogg, B. [Laboratory for Solid State Physics, ETH Zurich, CH-8093 Zurich (Switzerland)

    2010-12-15

    The iron arsenide RbFe{sub 2}As{sub 2} with the ThCr{sub 2}Si{sub 2}-type structure is found to be a bulk superconductor with T{sub c}=2.6K. The onset of diamagnetism was used to estimate the upper critical field H{sub c2}(T), resulting in {mu}{sub 0}dH{sub c2}/dT{approx_equal}-1.4T/K and an extrapolated {mu}{sub 0}H{sub c2}(0){approx_equal}2.5T. As a new representative of iron pnictide superconductors, superconducting RbFe{sub 2}As{sub 2} contrasts with BaFe{sub 2}As{sub 2}, where the Fermi level is higher and a magnetic instability is observed. Thus, the solid solution series (Rb, Ba)Fe{sub 2}As{sub 2} is a promising system to study the cross-over from superconductivity to magnetism.

  2. Alteration of uraniferous and native copper concretions in the Permian mudrocks of south Devon, United Kingdom

    International Nuclear Information System (INIS)

    This report presents the results of a study of the mineralogy and alteration characteristics of unusual concretions containing sheets of native copper, and uranium-vanadium mineralised concretions, in mudstones and siltstones of the Pennian Littleham Mudstone Formation, at Littleham Cove, south Devon, England. The main objectives of the study were: 1. To investigate the corrosion characteristics of the native copper as a natural analogue for the long-term behaviour of copper canisters, sealed in a compacted clay (bentonite) backfill, that will be used for the deep geological disposal of spent fuel and high-level radioactive waste (HLW). This study developed from an earlier pilot study, which demonstrated that the alteration of the native copper in the concretions from Littleham Cove was mineralogically and chemically complex. 2. To investigate the alteration and oxidation of minerals containing reduced species (e.g. ferrous iron) within the uranium-rich concretions as a natural analogue for the potential effects of oxidation induced by alpha-radiolysis of water in a HLW repository environment. Native copper-bearing concretions in the Littleham Mudstone Formation are very rare. They occur, as thin lenticular disks developed largely along bedding lamina and thin low-angle fractures cutting the bedding laminae the upper part of the formation, about 10 m below the top of the formation. This part of the sequence comprises laterally discontinuous, fine-grained sheet-flood and channel sandstones and siltstones. Some of these sandstones, are more extensively-cemented by copper sulphides (mainly chalcocite), copper arsenides, cobalt-nickel arsenides, and uranium silicate. The thin permeable sandstones and siltstones, and fractures zones around small faults appear to have acted as the conduits for the movement of mineralising fluids through the mudstones. The native copper sheets all show a similar pattern of corrosion and alteration. However, the intensity of alteration is

  3. Temperature dependence of the band gap of GaSb{sub 1−x}Bi{sub x} alloys with 0 < x ≤ 0.042 determined by photoreflectance

    Energy Technology Data Exchange (ETDEWEB)

    Kopaczek, J.; Misiewicz, J. [Institute of Physics, Wrocław University of Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław (Poland); Kudrawiec, R., E-mail: robert.kudrawiec@pwr.wroc.pl [Institute of Physics, Wrocław University of Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław (Poland); Material Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720 (United States); Linhart, W. M.; Rajpalke, M. K.; Veal, T. D. [Stephenson Institute for Renewable Energy and Department of Physics, School of Physical Sciences, University of Liverpool, Liverpool L69 7ZF (United Kingdom); Yu, K. M. [Material Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720 (United States); Jones, T. S.; Ashwin, M. J. [Department of Chemistry, University of Warwick, Coventry CV4 7AL (United Kingdom)

    2013-12-23

    GaSb{sub 1−x}Bi{sub x} layers with 0 < x ≤ 0.042 have been studied by photoreflectance in 15–290 K temperature range. We found that due to the incorporation of Bi atoms into the GaSb host, the E{sub 0} band gap-related transition redshifts (∼30 meV per 1% Bi) and significantly broadens. The shift of the E{sub 0} transition in the temperature range 10–270 K has been found to be ∼70 meV, very similar to the energy shift in GaSb over the same temperature range. We analyzed the energy and broadening of the E{sub 0} transition using the Varshni and Bose-Einstein formulas and found that the Varshni and Bose-Einstein parameters of GaSb{sub 1−x}Bi{sub x} are similar to those of GaSb. Moreover we concluded that the inhomogeneities in GaSb{sub 1−x}Bi{sub x} alloys is less important than in dilute bismide arsenides since Bi atoms are more similar to Sb atoms (in electronegativities and ionic sizes)

  4. Inverted Metamorphic Multijunction (IMM) Cell Processing Instructions

    Energy Technology Data Exchange (ETDEWEB)

    Duda, A.; Ward, S.; Young, M.

    2012-02-01

    This technical report details the processing schedule used to fabricate Inverted Metamorphic Multijunction (IMM) concentrator solar cells at The National Renewable Energy Laboratory (NREL). These devices are used as experimental test structures to support the research at NREL that is focused on increasing the efficiency of photovoltaic power conversion. They are not intended to be devices suitable for deployment in working concentrator systems primarily because of heat sinking issues. The process schedule was developed to be compatible with small sample sizes and to afford relatively rapid turn-around times, in support of research efforts. The report describes the use of electro deposition of gold for both the back and front contacts. Electro-deposition is used because of its rapid turn around time and because it is a benign metallization technique that is seldom responsible for damage to the semiconductors. The layer transfer technique is detailed including the use of a commercially available adhesive and the etching away of the parent gallium arsenide substrate. Photolithography is used to define front contact grids as well as the mesa area of the cell. Finally, the selective wet chemical etchant system is introduced and its use to reveal the back contact is described.

  5. Epitaxy of (Ga,Mn)As; Epitaxie von (Ga,Mn)As

    Energy Technology Data Exchange (ETDEWEB)

    Utz, Martin

    2012-09-14

    The focus of this work lies on the enhancement of the magnetic properties of the ferromagnetic semiconductor Gallium manganese arsenide (GaMnAs), which is a basic material for the research in spintronics: It is told, how a high sample reproducibility and a strong control over the growth process can be gained by applying band edge spectroscopy and a special procedure for the material flux calibration. Also the most important methods for the electrical characterization of GaMnAs are discussed in a critical manner by showing that the anomalous Hall Effect contributes significantly to the Hall resistance even at room temperature and that Novak's method for the termination of the Curie-temperature provides correct values for layers with low defect concentration. Furthermore it is reported on the considerable enlargement of the useable parameter space of GaMnAs which was enabled by the enhanced control over the growth process: It was possible to grow layers with a very high Manganese content of 22% and Curie temperatures of 172 K and even once were produced which showed a strong magnetic moment despite an insulating behaviour at low temperatures. A last key aspect is the growth and characterization of ultra-thin GaMnAs layers, giving prospects for gating experiments or experiments on the proximity effect as these layers combine high Curie temperatures with insulating behaviour.

  6. Mineral Phases and Release Behaviors of As in the Process of Sintering Residues Containing As at High Temperature

    Directory of Open Access Journals (Sweden)

    Xingrun Wang

    2014-01-01

    Full Text Available To investigate the effect of sintering temperature and sintering time on arsenic volatility and arsenic leaching in the sinter, we carried out experimental works and studied the structural changes of mineral phases and microstructure observation of the sinter at different sintering temperatures. Raw materials were shaped under the pressure of 10 MPa and sintered at 1000~1350°C for 45 min with air flow rate of 2000 mL/min. The results showed that different sintering temperatures and different sintering times had little impact on the volatilization of arsenic, and the arsenic fixed rate remained above 90%; however, both factors greatly influenced the leaching concentration of arsenic. Considering the product’s environmental safety, the best sintering temperature was 1200°C and the best sintering time was 45 min. When sintering temperature was lower than 1000°C, FeAsS was oxidized into calcium, aluminum, and iron arsenide, mainly Ca3(AsO42 and AlAsO4, and the arsenic leaching was high. When it increased to 1200°C, arsenic was surrounded by a glass matrix and became chemically bonded inside the matrix, which lead to significantly lower arsenic leaching.

  7. The contribution of solid-state chemistry in the determination of multicomponent phase diagrams

    Institute of Scientific and Technical Information of China (English)

    Jean Claude Tedenac; Franck Gascoin; Didier Ravot

    2006-01-01

    For a long period of time, the determination of phase diagrams was only supported by experiments related to thermal effects or thermodynamic measurements: thermal analysis, calorimetric measurements, vapor pressures, and EMF measurements. As a matter of fact, solid-solid transformations were not so accurately determined and could not be taken into account in the system's analysis. First, X-ray diffraction methods were used as a support for the thermal analysis. Sec ond, the implementation of novel tools in structural analysis (for example, the Rietveld method) has permitted to increase the knowledge of phase stability. Finally, modeling the phases using a Calphad method needed increasingly more structural results to determine and better understand the phase diagrams. On the other hand, the Calphad method has been widely developed for metallic systems, for oxide systems, and in the past 10 years, for some semi-conductor systems, for example,gallium arsenide, cadmium telluride, and lead telluride systems. In such applications, it is very important to bring point defects in the modeling of the phases to map the defects as a function of the chemical composition. Owing to its complexity,this characteristic, the knowledge of which is crucial for the understanding and the control of potential physical applications, was ignored in the previous assessment of semi-conductor systems.

  8. Review of pulmonary toxicity of indium compounds to animals and humans

    International Nuclear Information System (INIS)

    Due to the increased production of ITO, the potential health hazards arising from occupational exposure to this material have attracted much attention. This review consists of three parts: 1) toxic effects of indium compounds on animals, 2) toxic effects of indium compounds on humans, and 3) recommendations for preventing exposure to indium compounds in the workplace. Available data have indicated that insoluble form of indium compounds, such as ITO, indium arsenide (InAs) and indium phosphide (InP), can be toxic to animals. Furthermore, InP has demonstrated clear evidence of carcinogenic potential in long-term inhalation studies using experimental animals. As for the dangers to humans, some data are available concerning adverse health effects to workers who have been exposed to indium-containing particles. The Japan Society for Occupational Health recommended the value of 3 μg/L of indium in serum as the occupational exposure limit based on biological monitoring to preventing adverse health effects in workers resulting from occupational exposure to indium compounds. Accordingly, it is essential that much greater attention is focused on human exposure to indium compounds, and precautions against possible exposure to indium compounds are most important with regard to health management among indium-handling workers.

  9. Low cost, high concentration ratio solar cell array for space applications

    Science.gov (United States)

    Patterson, R. E.; Rauschenbach, H. S.; Cannady, M. D.; Whang, U. S.; Crabtree, W. L.

    1981-01-01

    A miniaturized Cassegrainian-type concentrator solar array concept for space applications is described. In-orbit cell operating temperatures near 80 C are achieved with purely passive cell cooling and a net concentration ratio of 100. A multiplicity of miniaturized, rigid solar cell concentrator subassemblies are electrically interconnected in conventional fashion and mounted into rigid frames to form concentrator solar panel assemblies approximately 14-mm thick. A plurality of such interconnected panels forms a stowable and deployable solar cell blanket. It is projected that for 20% efficient silicon cells an array of 500 kW beginning-of-life output capability, including orbiter cradle structures, can be transported by a single shuttle orbiter flight into low earth orbit. In-orbit array specific performance is calculated to be approximately 100 W/sq m and 20 W/kg, including all stowage, deployment and array figure control equipment designed for a 30-year orbital life. Higher efficiency gallium arsenide and multiple band gap solar cells will improve these performance factors correspondingly.

  10. Low concentration ratio solar array for low Earth orbit multi-100 kW application. Volume 1: Design, analysis and development tests

    Science.gov (United States)

    1983-01-01

    A preliminary design effort directed toward a low concentration ratio photovoltaic array system capable of delivering multihundred kilowatts (300 kW to 1000 kW range) in low earth orbit is described. The array system consists of two or more array modules each capable of delivering between 113 kW to 175 kW using silicon solar cells or gallium arsenide solar cells, respectively. The array module deployed area is 1320 square meters and consists of 4356 pyramidal concentrator elements. The module, when stowed in the Space Shuttle's payload bay, has a stowage volume of a cube with 3.24 meters on a side. The concentrator elements are sized for a geometric concentration ratio (GCR) of six with an aperture area of .25 sq. m. The structural analysis and design trades leading to the baseline design are discussed. It describes the configuration, as well as optical, thermal and electrical performance analyses that support the design and overall performance estimates for the array are described.

  11. Low concentration ratio solar array for low Earth orbit multi-100 kW application

    Science.gov (United States)

    Nalbandian, S. J.

    1982-01-01

    An ongoing preliminary design effort directed toward a low-concentration-ratio photovoltaic array system based on 1984 technology and capable of delivering multi-hundred kilowatts (300 kW to 1000 kW range) in low earth orbit is described. The array system consists of two or more array modules each capable of delivering between 80 kW to 172 kW using silicon solar cells or gallium arsenide solar cells respectively. The array module deployed area is 1320 square meters and consists of 4356 pryamidal concentrator elements. The module, when stowed in the Space Shuttle's payload bay, has a stowage volume of a cube with 3.24 meters on a side. The concentrator elements are sized for a geometric concentration ratio (GCR) of six with an aperture area of 0.5 meters x 0.5 meters. The structural analysis and design trades leading to the baseline design are discussed. The configuration, as well as optical, thermal and electrical performance analyses that support the design and overall performance estimates for the array are described.

  12. Transurethral diode (810 nm) laser application for treatment of benign prostatic hyperplasia: a clinical study

    Science.gov (United States)

    Pow-Sang, Mariela; Orihuela, Eduardo; Motamedi, Massoud

    1995-05-01

    The objective of this study was to evaluate the effectiveness and safety of diode laser for the treatment of human BPH. The study included 11 patients with significant BPH that were treated with diode laser 15 watts for 180 seconds (Diomed, Inc., Gallium-Aluminum- Arsenide, 810 nm). Mean age was 69 years (range 59 to 84). Mean prostatic volume was 64.5 cc (range 30 to 96). In all cases the procedure was uncomplicated, the blood loss was minimal (< 100 cc) and all patients were discharged within the first 24 hours. On average, patients voided spontaneously after 4 days (range 1 to 11). There were no postoperative complications. At 6 months follow up the mean AUA-7 symptom score decreased from 24.27 to 8.12, the peak flow rate increased from 7.12 cc/sec, to 13.85 cc/sec, and the post void residual diminished from 58.5 cc to 38 cc. Our study suggests that diode laser therapy may offer a safe and effective alternative for the treatment of BPH.

  13. Monte Carlo simulation for the electron cascade due to gamma rays in semiconductor radiation detectors

    International Nuclear Information System (INIS)

    A Monte Carlo code was developed for simulating the electron cascade in radiation detector materials. The electron differential scattering cross sections were derived from measured electron energy-loss and optical spectra, making the method applicable for a wide range of materials. The detector resolution in a simplified model system shows dependence on the bandgap, the plasmon strength and energy, and the valence band width. In principle, these parameters could be optimized to improve detector performance. The intrinsic energy resolution was calculated for three semiconductors: silicon (Si), gallium arsenide (GaAs), and zinc telluride (ZnTe). Setting the ionization thresholds for electrons and holes is identified as a critical issue, as this strongly affects both the average electron-hole pair energy w and the Fano factor F. Using an ionization threshold from impact ionization calculations as an effective bandgap yields pair energies that are well matched to measured values. Fano factors of 0.091 (Si), 0.100 (GaAs), and 0.075 (ZnTe) were calculated. The Fano factor calculated for silicon using this model was lower than some results from past simulations and experiments. This difference could be attributed to problems in simulating inter-band transitions and the scattering of low-energy electrons.

  14. Monte Carlo simulation for the electron cascade due to gamma rays in semiconductor radiation detectors

    Energy Technology Data Exchange (ETDEWEB)

    Narayan, Raman D.; Miranda, Ryan; Rez, Peter [Department of Physics, Arizona State University, Tempe, Arizona 85287-1504 (United States)

    2012-03-15

    A Monte Carlo code was developed for simulating the electron cascade in radiation detector materials. The electron differential scattering cross sections were derived from measured electron energy-loss and optical spectra, making the method applicable for a wide range of materials. The detector resolution in a simplified model system shows dependence on the bandgap, the plasmon strength and energy, and the valence band width. In principle, these parameters could be optimized to improve detector performance. The intrinsic energy resolution was calculated for three semiconductors: silicon (Si), gallium arsenide (GaAs), and zinc telluride (ZnTe). Setting the ionization thresholds for electrons and holes is identified as a critical issue, as this strongly affects both the average electron-hole pair energy w and the Fano factor F. Using an ionization threshold from impact ionization calculations as an effective bandgap yields pair energies that are well matched to measured values. Fano factors of 0.091 (Si), 0.100 (GaAs), and 0.075 (ZnTe) were calculated. The Fano factor calculated for silicon using this model was lower than some results from past simulations and experiments. This difference could be attributed to problems in simulating inter-band transitions and the scattering of low-energy electrons.

  15. The efficiency limit of CH{sub 3}NH{sub 3}PbI{sub 3} perovskite solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Sha, Wei E. I. [Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong (China); The University of Hong Kong Shenzhen Institute of Research and Innovation (HKU-SIRI), Shenzhen 518057 (China); Ren, Xingang; Chen, Luzhou; Choy, Wallace C. H., E-mail: chchoy@eee.hku.hk [Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong (China)

    2015-06-01

    With the consideration of photon recycling effect, the efficiency limit of methylammonium lead iodide (CH{sub 3}NH{sub 3}PbI{sub 3}) perovskite solar cells is predicted by a detailed balance model. To obtain convincing predictions, both AM 1.5 spectrum of Sun and experimentally measured complex refractive index of perovskite material are employed in the detailed balance model. The roles of light trapping and angular restriction in improving the maximal output power of thin-film perovskite solar cells are also clarified. The efficiency limit of perovskite cells (without the angular restriction) is about 31%, which approaches to Shockley-Queisser limit (33%) achievable by gallium arsenide (GaAs) cells. Moreover, the Shockley-Queisser limit could be reached with a 200 nm-thick perovskite solar cell, through integrating a wavelength-dependent angular-restriction design with a textured light-trapping structure. Additionally, the influence of the trap-assisted nonradiative recombination on the device efficiency is investigated. The work is fundamentally important to high-performance perovskite photovoltaics.

  16. The use of laser therapy for dental implant surface decontamination: a narrative review of in vitro studies.

    Science.gov (United States)

    Kamel, Marina Salah; Khosa, Amardeep; Tawse-Smith, Andrew; Leichter, Jonathan

    2014-11-01

    The aim of this narrative review was to critically evaluate in vitro studies assessing the efficacy of lasers in the bacterial decontamination of titanium implant surfaces. The MEDLINE, Web of Knowledge and Embase electronic databases were used to search for articles relating to the use of lasers in the bacterial decontamination of titanium specimen surfaces using predetermined search statements. Clinical studies, case reports, case series, review articles and animal models were excluded. Study selection was carried out independently and then cross-checked by two authors through abstract viewing. Eighteen articles were selected for full-text analysis. Erbium-doped yttrium-aluminium-garnet lasers had a wide range of powers capable of inducing bacterial decontamination. While carbon dioxide and gallium-aluminium-arsenide diode lasers demonstrated the ability to produce bacterial decontamination, the bacterial sensitivity to each varied depending on the species involved. There is no concensus on the laser type or settings that are optimal for bacterial decontamination of titanium implant surfaces as studies employ various test specimens, contamination methodologies, irradiation settings and protocols, and outcome measures resulting in limited study comparability. More investigations are required to provide guidelines for the use of laser therapy in the decontamination of implant surfaces.

  17. Growth and Strain Evaluation of InGaP/InGaAs/Ge Triple-Junction Solar Cell Structures

    Science.gov (United States)

    Alhomoudi, Ibrahim A.

    2016-06-01

    Metalorganic chemical vapor deposition (MOCVD) has been used for development of photovoltaic (PV) structures that enable enhanced efficiency for triple-junction solar cell (TJSC) devices. The in-plane strain, lattice match, surface defects, surface morphology, compositional uniformity, threading dislocations (TDs), and depth profile of each layer of the TJSC structure have been examined. The heteroepitaxial layers were found to be near lattice matched to the substrate with excellent coherence between the layers. The analysis explained that the indium gallium phosphide (InGaP) and indium gallium arsenide (InGaAs) layers on germanium (Ge) substrate are a strained structure with purely tetragonal crystalline phase, which indicates that the TJSC structural layers could maintain high crystalline quality. The biaxial in-plane strain in each layer of the TJSC structure is compressive and varies in magnitude for each layer in the structure, being strongly influenced by the Ge substrate and the multiple epilayers of the PV structure. Transmission electron microscopy (TEM) results show no TDs observed over a region with area of 500 nm2, with surface defect density less than 1 × 108 cm-2. No evidence of stacking faults and no visible defects of antiphase domains (APDs) at interfaces were observed, indicating adequate nucleation of epitaxial layers on the substrate and on subsequent growth layers. Furthermore, secondary-ion mass spectrometry (SIMS) analysis showed no significant Ge diffusion from the substrate into the TJSC structure.

  18. Magnetic and structural properties of AFe4X2 (A = Y, Sc, Lu, and Zr; X = Ge and Si)

    International Nuclear Information System (INIS)

    The compound RFe4Ge2 (R=Dy,Ho,Er,Y) have been reported to crystallize with the tetragonal ZrFe4Si2 structure type and to show interesting magnetic properties. In YFe4Ge2, antiferromagnetic ordering with small ordered moment ∝0.63 μB occurs simultaneously with a large (2.5 %) first order structural distortion from tetragonal to orthorhombic at 43.5 K. The presence of a large structural distortion despite a weak antiferromagnetic ordering with low TN and small moments is reminiscent of observations in Fe-arsenides. Here, we present magnetic and structural properties of AFe4X2 (A=Y, Sc, Lu and Zr; X=Ge and Si) based on magnetic susceptibility, specific heat, resistivity and low temperature X-ray diffractometer measurements. Our results indicate the occurrence of a transition in all compounds at critical temperatures between 30 K and 75 K depending on the compounds. There is no systematic relationship between TN and and the lattice parameters of AFe4X2. However, magnetic order and structural distortion seems generally to be connected. The relation between structural, electronic, and magnetic properties is discussed.

  19. SERC Central Laser Facility annual report 1992

    International Nuclear Information System (INIS)

    In this 1992 Annual Report to the Laser Facility Committee of the Science and Engineering Research Council, the Central Laser Facility at Rutherford Appleton Laboratory, technical progress is described and mid-term organizational goals outlined. Outstanding among recent achievements is the work on plasma heating being undertaken on the Sprite facility using the ultra-bright KrF laser pumped Raman beams. Two-beam operation at power levels approaching 2 TW in 10 ps are hoped for. On a four year timescale the Titania system will provide four Raman beams of exceptional brightness and power up to 20TW in 10ps. The other high power laser facility, Vulcan is also producing exciting work. Progress in nanosecond studies using Raman spectroscopy have produced the first Raman spectrum of solvated Buckmister fullerene and direct observation of the separation of germinate ion pairs, as well as information on the behaviour of a single base in an oligonuclide chain. Phase boundaries for the solidification of a two dimensional electron fluid have been determined in a Gallium Arsenide heterojunction. Despite staff number attrition, operation and development of the facilities have continued successfully. (UK)

  20. Environmental assessment for the satellite power system concept development and evaluation program: atmospheric effects

    Energy Technology Data Exchange (ETDEWEB)

    Rote, D.M.; Brubaker, K.L.; Lee, J.L.

    1980-11-01

    The US Department of Energy (DOE) has undertaken a preliminary, three-year program to investigate the impacts of the construction and operation of a satellite power system, of unprecedented scale. The Department of Energy's program, titled The Concept Development and Evaluation Program, focused its investigations on a Reference System description that calls for the use of either silicon (Si) or gallium aluminum-arsenide (GaAlAs) photovoltaic cells on 60 satellites to be constructed in GEO over a 30-yr period. Rectennas would be constructed on the ground to receive microwave energy from the satellites. Each satellite-rectenna pair is designed to produce 5 GW of power on an essentially continuous basis for use as a baseload power source for an electric power distribution system. The environmental assessment part of the program was divided into five interdependent task areas. The present document constitutes the final technical report on one of the five task areas, the Assessment of the Atmospheric Effects, and as such presents an in-depth summary of work performed during the assessment program. The issues associated with SPS activities in the troposphere are examined. These include tropospheric weather modification related to rectenna operations and rocket launches, and air quality impacts related to rocketlaunch ground clouds. Then progressing upward through the various levels of the atmosphere, the principal middle and upper atmospheric effects associated with rocket effluents are analyzed. Finally, all of the potential SPS atmospheric effects are summarized.

  1. Photomorphogenesis, photosynthesis, and seed yield of wheat plants grown under red light-emitting diodes (LEDs) with and without supplemental blue lighting

    Science.gov (United States)

    Goins, G. D.; Yorio, N. C.; Sanwo, M. M.; Brown, C. S.; Sager, J. C. (Principal Investigator)

    1997-01-01

    Red light-emitting diodes (LEDs) are a potential light source for growing plants in spaceflight systems because of their safety, small mass and volume, wavelength specificity, and longevity. Despite these attractive features, red LEDs must satisfy requirements for plant photosynthesis and photomorphogenesis for successful growth and seed yield. To determine the influence of gallium aluminium arsenide (GaAlAs) red LEDs on wheat photomorphogenesis, photosynthesis, and seed yield, wheat (Triticum aestivum L., cv. 'USU-Super Dwarf') plants were grown under red LEDs and compared to plants grown under daylight fluorescent (white) lamps and red LEDs supplemented with either 1% or 10% blue light from blue fluorescent (BF) lamps. Compared to white light-grown plants, wheat grown under red LEDs alone demonstrated less main culm development during vegetative growth through preanthesis, while showing a longer flag leaf at 40 DAP and greater main culm length at final harvest (70 DAP). As supplemental BF light was increased with red LEDs, shoot dry matter and net leaf photosynthesis rate increased. At final harvest, wheat grown under red LEDs alone displayed fewer subtillers and a lower seed yield compared to plants grown under white light. Wheat grown under red LEDs+10% BF light had comparable shoot dry matter accumulation and seed yield relative to wheat grown under white light. These results indicate that wheat can complete its life cycle under red LEDs alone, but larger plants and greater amounts of seed are produced in the presence of red LEDs supplemented with a quantity of blue light.

  2. Electronic and optoelectronic materials and devices inspired by nature

    Science.gov (United States)

    Meredith, P.; Bettinger, C. J.; Irimia-Vladu, M.; Mostert, A. B.; Schwenn, P. E.

    2013-03-01

    Inorganic semiconductors permeate virtually every sphere of modern human existence. Micro-fabricated memory elements, processors, sensors, circuit elements, lasers, displays, detectors, etc are ubiquitous. However, the dawn of the 21st century has brought with it immense new challenges, and indeed opportunities—some of which require a paradigm shift in the way we think about resource use and disposal, which in turn directly impacts our ongoing relationship with inorganic semiconductors such as silicon and gallium arsenide. Furthermore, advances in fields such as nano-medicine and bioelectronics, and the impending revolution of the ‘ubiquitous sensor network’, all require new functional materials which are bio-compatible, cheap, have minimal embedded manufacturing energy plus extremely low power consumption, and are mechanically robust and flexible for integration with tissues, building structures, fabrics and all manner of hosts. In this short review article we summarize current progress in creating materials with such properties. We focus primarily on organic and bio-organic electronic and optoelectronic systems derived from or inspired by nature, and outline the complex charge transport and photo-physics which control their behaviour. We also introduce the concept of electrical devices based upon ion or proton flow (‘ionics and protonics’) and focus particularly on their role as a signal interface with biological systems. Finally, we highlight recent advances in creating working devices, some of which have bio-inspired architectures, and summarize the current issues, challenges and potential solutions. This is a rich new playground for the modern materials physicist.

  3. Predicting Low Energy Dopant Implant Profiles in Semiconductors using Molecular Dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Beardmore, K.M.; Gronbech-Jensen, N.

    1999-05-02

    The authors present a highly efficient molecular dynamics scheme for calculating dopant density profiles in group-IV alloy, and III-V zinc blende structure materials. Their scheme incorporates several necessary methods for reducing computational overhead, plus a rare event algorithm to give statistical accuracy over several orders of magnitude change in the dopant concentration. The code uses a molecular dynamics (MD) model to describe ion-target interactions. Atomic interactions are described by a combination of 'many-body' and pair specific screened Coulomb potentials. Accumulative damage is accounted for using a Kinchin-Pease type model, inelastic energy loss is represented by a Firsov expression, and electronic stopping is described by a modified Brandt-Kitagawa model which contains a single adjustable ion-target dependent parameter. Thus, the program is easily extensible beyond a given validation range, and is therefore truly predictive over a wide range of implant energies and angles. The scheme is especially suited for calculating profiles due to low energy and to situations where a predictive capability is required with the minimum of experimental validation. They give examples of using the code to calculate concentration profiles and 2D 'point response' profiles of dopants in crystalline silicon and gallium-arsenide. Here they can predict the experimental profile over five orders of magnitude for <100> and <110> channeling and for non-channeling implants at energies up to hundreds of keV.

  4. The study of structural properties of 100 keV hydrogen ion implanted semi-insulating GaAs single crystals

    International Nuclear Information System (INIS)

    100 keV hydrogen ion implantation has been carried out on undoped semi-insulating (1 0 0) gallium arsenide single crystals for various ion doses at room temperature. The structural properties due to high dose, low energy hydrogen ion implantation has been investigated using X-ray double crystal diffractometry (DCD) analysis, Rutherford backscattering spectrometry and channeling (RBS/C) experiments and transmission electron microscopy (TEM) analysis. By using DCD analysis, the value of elastic lattice strain for the ion doses of 1x1016, 1x1018 ions/cm2 has been estimated to be 2.1x10-3 and 3.2x10-3, respectively. The RBS spectra in the channeling mode for the high dose implantations (1017 and 1018 ions/cm2) show a high yield indicating a highly damaged region near the range of the implanted hydrogen ions. Particularly, for the dose 1018 ions/cm2, a heavily damaged region at the surface can be observed. The TEM results evidenced that no amorphization occurred for the dose 1018 ions/cm2. From TEM characterisation, it is also observed that there are no hydrogen bubbles present in the implanted region. But small dislocation loops have been identified. The projected range of implanted hydrogen ions and the thickness of the implanted layer obtained by RBS and TEM analysis are compared with the TRIM calculations. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

  5. The application of the symmetry properties of optical second harmonic generation to studies of interfaces and gases

    International Nuclear Information System (INIS)

    Optical second harmonic generation has proven to be a powerful tool for studying interfaces. The symmetry properties of the process allow for surface sensitivity not available with other optical methods. In this thesis, we take advantage of these symmetry properties SHG to study a variety of interesting systems not previously studied with this technique. We show that optical second harmonic generation is an effective surface probe with a submonolayer sensitivity for media without inversion symmetry. We demonstrate the technique at a gallium arsenide surface, exploiting the different symmetry properties of the bulk and surface of the crystal to isolate the surface contribution. We also demonstrate that optical second harmonic generation can be used to determine the anisotropic orientational distribution of a surface monolayer of molecules. We apply the technique to study homogeneously aligned liquid crystal cells. To further explore the LC-polymer interface, we used SHG to study the surface memory effect. The surface memory effect is the rendering of an isotropic interface anisotropic by putting it in contact with an anisotropic bulk. Last, we describe some preliminary measurements of a time-resolved spectroscopic study of the phenomenon of second harmonic generation in a gas. The construction of a 500 microjoule pulsed, tunable laser source is described

  6. Efficient on-the-fly interpolation technique for Bethe-Salpeter calculations of optical spectra

    Science.gov (United States)

    Gillet, Yannick; Giantomassi, Matteo; Gonze, Xavier

    2016-06-01

    The Bethe-Salpeter formalism represents the most accurate method available nowadays for computing neutral excitation energies and optical spectra of crystalline systems from first principles. Bethe-Salpeter calculations yield very good agreement with experiment but are notoriously difficult to converge with respect to the sampling of the electronic wavevectors. Well-converged spectra therefore require significant computational and memory resources, even by today's standards. These bottlenecks hinder the investigation of systems of great technological interest. They are also barriers to the study of derived quantities like piezoreflectance, thermoreflectance or resonant Raman intensities. We present a new methodology that decreases the workload needed to reach a given accuracy. It is based on a double-grid on-the-fly interpolation within the Brillouin zone, combined with the Lanczos algorithm. It achieves significant speed-up and reduction of memory requirements. The technique is benchmarked in terms of accuracy on silicon, gallium arsenide and lithium fluoride. The scaling of the performance of the method as a function of the Brillouin Zone point density is much better than a conventional implementation. We also compare our method with other similar techniques proposed in the literature.

  7. The Study of 0.34 THz Monolithically Integrated Fourth Subharmonic Mixer Using Planar Schottky Barrier Diode

    Science.gov (United States)

    Tong, Xiaodong; Li, Qian; An, Ning; Wang, Wenjie; Deng, Xiaodong; Zhang, Liang; Liu, Haitao; Zeng, Jianping; Li, Zhiqiang; Tang, Hailing; Xiong, Yong-Zhong

    2015-11-01

    A planar Schottky barrier diode with the designed Schottky contact area of approximately 3 μm2 is developed on gallium arsenide (GaAs) material. The measurements of the developed planar Schottky barrier diode indicate that the zero-biased junction capacitance Cj0 is 11.0 fF, the parasitic series resistance RS is 3.0 Ω, and the cut off frequency fT is 4.8 THz. A monolithically integrated fourth subharmonic mixer with this diode operating at the radio frequency (RF) signal frequency of 0.34 THz with the chip area of 0.6 mm2 is implemented. The intermediate frequency (IF) bandwidth is from DC to 40 GHz. The local oscillator (LO) bandwidth is 37 GHz from 60 to 97 GHz. The RF bandwidth is determined by the bandwidth of the on chip antenna, which is 28 GHz from 322 to 350 GHz. The measurements of the mixer demonstrated a conversion loss of approximately 51 dB.

  8. Field-effect transistors based on cubic indium nitride.

    Science.gov (United States)

    Oseki, Masaaki; Okubo, Kana; Kobayashi, Atsushi; Ohta, Jitsuo; Fujioka, Hiroshi

    2014-02-04

    Although the demand for high-speed telecommunications has increased in recent years, the performance of transistors fabricated with traditional semiconductors such as silicon, gallium arsenide, and gallium nitride have reached their physical performance limits. Therefore, new materials with high carrier velocities should be sought for the fabrication of next-generation, ultra-high-speed transistors. Indium nitride (InN) has attracted much attention for this purpose because of its high electron drift velocity under a high electric field. Thick InN films have been applied to the fabrication of field-effect transistors (FETs), but the performance of the thick InN transistors was discouraging, with no clear linear-saturation output characteristics and poor on/off current ratios. Here, we report the epitaxial deposition of ultrathin cubic InN on insulating oxide yttria-stabilized zirconia substrates and the first demonstration of ultrathin-InN-based FETs. The devices exhibit high on/off ratios and low off-current densities because of the high quality top and bottom interfaces between the ultrathin cubic InN and oxide insulators. This first demonstration of FETs using a ultrathin cubic indium nitride semiconductor will thus pave the way for the development of next-generation high-speed electronics.

  9. Reliability Analysis of III-V Solar Cells Grown on Recycled GaAs Substrates and an Electroplated Nickel Substrate

    Directory of Open Access Journals (Sweden)

    Ray-Hua Horng

    2013-01-01

    Full Text Available This study involved analyzing the reliability of two types of III-V solar cells: (1 III-V solar cells grown on new and recycled gallium arsenide (GaAs substrates and (2 the III-V solar cells transferred onto an electroplated nickel (Ni substrate as III-V thin-film solar cells by using a cross-shaped pattern epitaxial lift-off (CPELO process. The III-V solar cells were grown on new and recycled GaAs substrates to evaluate the reliability of the substrate. The recycled GaAs substrate was fabricated by using the CPELO process. The performance of the solar cells grown on the recycled GaAs substrate was affected by the uneven surface morphology of the recycled GaAs substrate, which caused the propagation of these dislocations into the subsequently grown active layer of the solar cell. The III-V solar cells were transferred onto an electroplated Ni substrate, which was also fabricated by using CPELO technology. The degradation of the III-V thin-film solar cell after conducting a thermal shock test could have been caused by microcracks or microvoids in the active layer or interface of the heterojunction, which resulted in the reduction of the external quantum efficiency response and the increase of recombination loss.

  10. Fast, High-Precision Readout Circuit for Detector Arrays

    Science.gov (United States)

    Rider, David M.; Hancock, Bruce R.; Key, Richard W.; Cunningham, Thomas J.; Wrigley, Chris J.; Seshadri, Suresh; Sander, Stanley P.; Blavier, Jean-Francois L.

    2013-01-01

    The GEO-CAPE mission described in NASA's Earth Science and Applications Decadal Survey requires high spatial, temporal, and spectral resolution measurements to monitor and characterize the rapidly changing chemistry of the troposphere over North and South Americas. High-frame-rate focal plane arrays (FPAs) with many pixels are needed to enable such measurements. A high-throughput digital detector readout integrated circuit (ROIC) that meets the GEO-CAPE FPA needs has been developed, fabricated, and tested. The ROIC is based on an innovative charge integrating, fast, high-precision analog-to-digital circuit that is built into each pixel. The 128×128-pixel ROIC digitizes all 16,384 pixels simultaneously at frame rates up to 16 kHz to provide a completely digital output on a single integrated circuit at an unprecedented rate of 262 million pixels per second. The approach eliminates the need for off focal plane electronics, greatly reducing volume, mass, and power compared to conventional FPA implementations. A focal plane based on this ROIC will require less than 2 W of power on a 1×1-cm integrated circuit. The ROIC is fabricated of silicon using CMOS technology. It is designed to be indium bump bonded to a variety of detector materials including silicon PIN diodes, indium antimonide (InSb), indium gallium arsenide (In- GaAs), and mercury cadmium telluride (HgCdTe) detector arrays to provide coverage over a broad spectral range in the infrared, visible, and ultraviolet spectral ranges.

  11. Superconductivity up to 30 K in the vicinity of the quantum critical point in BaFe{sub 2}(As{sub 1-x}P{sub x}){sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Jiang Shuai; Xing Hui; Xuan Guofang; Wang Cao; Ren Zhi; Dai Jianhui; Xu Zhu' an; Cao Guanghan [Department of Physics, Zhejiang University, Hangzhou 310027 (China); Feng, Chunmu, E-mail: ghcao@zju.edu.c [Test and Analysis Center, Zhejiang University, Hangzhou 310027 (China)

    2009-09-23

    We report bulk superconductivity induced by an isovalent doping of phosphorus in BaFe{sub 2}(As{sub 1-x}P{sub x}){sub 2}. The P-for-As substitution results in shrinkage of the lattice, especially for the FeAs block layers. The resistivity anomaly associated with the spin-density-wave (SDW) transition in the undoped compound is gradually suppressed by the P doping. Superconductivity with a maximum T{sub c} of 30 K emerges at x = 0.32, coinciding with a magnetic quantum critical point (QCP) which is shown by the disappearance of SDW order and the linear temperature-dependent resistivity in the normal state. The T{sub c} values were found to decrease with further P doping and no superconductivity was observed down to 2 K for x>=0.77. The appearance of superconductivity in the vicinity of QCP hints at the superconductivity mechanism in iron-based arsenides. (fast track communication)

  12. III-V aresenide-nitride semiconductor materials and devices

    Science.gov (United States)

    Major, Jo S. (Inventor); Welch, David F. (Inventor); Scifres, Donald R. (Inventor)

    1997-01-01

    III-V arsenide-nitride semiconductor crystals, methods for producing such crystals and devices employing such crystals. Group III elements are combined with group V elements, including at least nitrogen and arsenic, in concentrations chosen to lattice match commercially available crystalline substrates. Epitaxial growth of these III-V crystals results in direct bandgap materials, which can be used in applications such as light emitting diodes and lasers. Varying the concentrations of the elements in the III-V crystals varies the bandgaps, such that materials emitting light spanning the visible spectra, as well as mid-IR and near-UV emitters, can be created. Conversely, such material can be used to create devices that acquire light and convert the light to electricity, for applications such as full color photodetectors and solar energy collectors. The growth of the III-V crystals can be accomplished by growing thin layers of elements or compounds in sequences that result in the overall lattice match and bandgap desired.

  13. Alteration of uraniferous and native copper concretions in the Permian mudrocks of south Devon, United Kingdom

    Energy Technology Data Exchange (ETDEWEB)

    Milodowski, A.E.; Styles, M.T.; Horstwood, M.S.A.; Kemp, S.J. [British Geological Survey, Nottingham (United Kingdom)

    2002-03-01

    This report presents the results of a study of the mineralogy and alteration characteristics of unusual concretions containing sheets of native copper, and uranium-vanadium mineralised concretions, in mudstones and siltstones of the Pennian Littleham Mudstone Formation, at Littleham Cove, south Devon, England. The main objectives of the study were: 1. To investigate the corrosion characteristics of the native copper as a natural analogue for the long-term behaviour of copper canisters, sealed in a compacted clay (bentonite) backfill, that will be used for the deep geological disposal of spent fuel and high-level radioactive waste (HLW). This study developed from an earlier pilot study, which demonstrated that the alteration of the native copper in the concretions from Littleham Cove was mineralogically and chemically complex. 2. To investigate the alteration and oxidation of minerals containing reduced species (e.g. ferrous iron) within the uranium-rich concretions as a natural analogue for the potential effects of oxidation induced by alpha-radiolysis of water in a HLW repository environment. Native copper-bearing concretions in the Littleham Mudstone Formation are very rare. They occur, as thin lenticular disks developed largely along bedding lamina and thin low-angle fractures cutting the bedding laminae the upper part of the formation, about 10 m below the top of the formation. This part of the sequence comprises laterally discontinuous, fine-grained sheet-flood and channel sandstones and siltstones. Some of these sandstones, are more extensively-cemented by copper sulphides (mainly chalcocite), copper arsenides, cobalt-nickel arsenides, and uranium silicate. The thin permeable sandstones and siltstones, and fractures zones around small faults appear to have acted as the conduits for the movement of mineralising fluids through the mudstones. The native copper sheets all show a similar pattern of corrosion and alteration. However, the intensity of alteration is

  14. Analytical study of pulsed laser irradiation on some materials used for photovoltaic cells on satellites

    Science.gov (United States)

    Abd El-Hameed, Afaf M.

    2015-12-01

    The present research concerns on the study of laser-powered solar panels used for space applications. A mathematical model representing the laser effects on semiconductors has been developed. The temperature behavior and heat flow on the surface and through a slab has been studied after exposed to nano-second pulsed laser. The model is applied on two different types of common active semiconductor materials that used for photovoltaic cells fabrication as silicon (Si), and gallium arsenide (GaAs). These materials are used for receivers' manufacture for laser beamed power in space. Various values of time are estimated to clarify the heat flow through the material sample and generated under the effects of pulsed laser irradiation. These effects are theoretically studied in order to determine the performance limits of the solar cells when they are powered by laser radiation during the satellite eclipse. Moreover, the obtained results are carried out to optimize conversion efficiency of photovoltaic cells and may be helpful to give more explanation for layout of the light-electricity space systems.

  15. New VLSI smart sensor for collision avoidance inspired by insect vision

    Science.gov (United States)

    Abbott, Derek; Moini, Alireza; Yakovleff, Andre; Nguyen, X. Thong; Blanksby, Andrew; Kim, Gyudong; Bouzerdoum, Abdesselam; Bogner, Robert E.; Eshraghian, Kamran

    1995-01-01

    An analog VLSI implementation of a smart microsensor that mimics the early visual processing stage in insects is described with an emphasis on the overall concept and the front- end detection. The system employs the `smart sensor' paradigm in that the detectors and processing circuitry are integrated on the one chip. The integrated circuit is composed of sixty channels of photodetectors and parallel processing elements. The photodetection circuitry includes p-well junction diodes on a 2 micrometers CMOS process and a logarithmic compression to increase the dynamic range of the system. The future possibility of gallium arsenide implementation is discussed. The processing elements behind each photodetector contain a low frequency differentiator where subthreshold design methods have been used. The completed IC is ideal for motion detection, particularly collision avoidance tasks, as it essentially detects distance, speed & bearing of an object. The Horridge Template Model for insect vision has been directly mapped into VLSI and therefore the IC truly exploits the beauty of nature in that the insect eye is so compact with parallel processing, enabling compact motion detection without the computational overhead of intensive imaging, full image extraction and interpretation. This world-first has exciting applications in the areas of automobile anti- collision, IVHS, autonomous robot guidance, aids for the blind, continuous process monitoring/web inspection and automated welding, for example.

  16. Depth of penetration of an 850nm wavelength low level laser in human skin.

    Science.gov (United States)

    Esnouf, Alan; Wright, Philip A; Moore, Joan C; Ahmed, Salim

    2007-01-01

    Low Level Laser Therapy is used for a wide variety of conditions including superficial skin sores, musculoskeletal and joint problems, and dentistry. Knowledge of the penetration depth of laser radiation in human skin is an essential prerequisite to identifying its method of action. Mathematical simulations and estimates from the literature suggest that the depth of penetration of laser radiation using wavelengths from 630nm up to 1100nm may be up to 50mm. The aim of this study is to directly measure the penetration depth of a Low Level Laser in human tissue. Human abdominal skin samples up to 0.784mm thickness were harvested by dermatome following abdominoplasty procedures. These samples were irradiated by a Gallium Aluminium Arsenide Laser (Wavelength 850nm near infra-red invisible light, 100mW, 24kHz, 0.28mm diameter probe) and the transmitted radiation measured with an Ophir Optronics 'Nova' external energy meter. The intensity of laser radiation reduced by 66% after being transmitted through a 0.784mm sample of human abdominal tissue. In this study most laser radiation was absorbed within the first 1mm of skin.

  17. Barrier and well-width dependence of optical emission of GaN/AlGaN quantum well nanostructures

    Directory of Open Access Journals (Sweden)

    H. Haratizadeh

    2007-06-01

    Full Text Available Internal polarizations field which take place in quantum structures of group-III nitrides have an important consequence on their optical properties. Optical properties of wurtzite AlGaN/GaN quantum well (QW structures grown by MBE and MOCVD on c-plane sapphire substrates have been investigated by means of photoluminescence (PL and time resolved photoluminescence (TRPL at low-temperature. PL spectra exhibit a blue-shifted emission of AlGaN/GaN quantum well (QW nanostructures by decreasing the barrier width contrary to the arsenide system. The trend of the barrier-width dependence of the internal polarization field is reproduced by using simple electrostatic arguments. In addition the effect of well width variation on the optical transition and decay time of GaN MQWs have been investigated and it has been shown that the screening of the piezoelectric field and the electron-hole separation are strongly dependent on the well thickness and have a profound effect on the optical properties of the GaN/AlGaN MQWs.

  18. A bow-tie photoconductive antenna using a low-temperature-grown GaAs thin-film on a silicon substrate for terahertz wave generation and detection

    International Nuclear Information System (INIS)

    This paper presents heterogeneously integrated bow-tie emitter–detector photoconductive antennas (PCAs) based on low-temperature grown-gallium arsenide (LTG-GaAs) thin-film devices on silicon-dioxide/silicon (SiO2/Si) host substrates for integrated terahertz (THz) systems. The LTG-GaAs thin-film devices are fabricated with standard photolithography and thermal evaporation of metal-contact layers of chromium (Cr), nickel (Ni) and gold (Au). They are etched selectively and separated from their growth GaAs substrate. The LTG-GaAs thin-film devices are then heterogeneously integrated on bow-tie antenna electrodes patterned on the surface of a SiO2/Si host substrate for THz emitters and THz detectors. Cost-effective and selective integration of LTG-GaAs thin-film devices on a Si platform is demonstrated. THz radiation from the fabricated THz PCAs is successfully measured using a pump–probe THz time-domain configuration. The THz temporal duration was measured at full width half maximum of 0.36 ps. Its frequency spectrum exhibits a broadband response with a peak resonant frequency of about 0.31 THz. The demonstration illustrates the feasibility of creating heterogeneously integrated THz systems using separately optimized LTG-GaAs devices and Si based electronics. (paper)

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

    CERN Document Server

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

    2014-01-01

    Semi-insulating Gallium Arsenide (SI-GaAs) samples experimentally show, under high electric fields and even at room temperature, negative differential conductivity in N-shaped form (NNDC). Since the most consolidated model for n-GaAs, namely, "the model", proposed by E. Scholl was not capable to generate the NNDC curve for SI-GaAs, in this work we proposed an alternative model. The model proposed, "the two-valley model" is based on the minimal set of generation recombination equations for two valleys inside of the conduction band, and an equation for the drift velocity as a function of the applied electric field, that covers the physical properties of the nonlinear electrical conduction of the SI-GaAs system. The "two valley model" was capable to generate theoretically the NNDC region for the first time, and with that, we were able to build a high resolution parameter-space of the periodicity (PSP) using a Periodicity-Detection (PD) routine. In the parameter space were observed self-organized periodic structu...

  20. Wireless multi-level terahertz amplitude modulator using active metamaterial-based spatial light modulation.

    Science.gov (United States)

    Rout, Saroj; Sonkusale, Sameer

    2016-06-27

    The ever increasing demand for bandwidth in wireless communication systems will inevitably lead to the extension of operating frequencies toward the terahertz (THz) band known as the 'THz gap'. Towards closing this gap, we present a multi-level amplitude shift keying (ASK) terahertz wireless communication system using terahertz spatial light modulators (SLM) instead of traditional voltage mode modulation, achieving higher spectral efficiency for high speed communication. The fundamental principle behind this higher efficiency is the conversion of a noisy voltage domain signal to a noise-free binary spatial pattern for effective amplitude modulation of a free-space THz carrier wave. Spatial modulation is achieved using an an active metamaterial array embedded with pseudomorphic high-electron mobility (pHEMT) designed in a consumer-grade galium-arsenide (GaAs) integrated circuit process which enables electronic control of its THz transmissivity. Each array is assembled as individually controllable tiles for transmissive terahertz spatial modulation. Using the experimental data from our metamaterial based modulator, we show that a four-level ASK digital communication system has two orders of magnitude improvement in symbol error rate (SER) for a degradation of 20 dB in transmit signal-to-noise ratio (SNR) using spatial light modulation compared to voltage controlled modulation. PMID:27410614