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  • 1
    Electronic Resource
    Electronic Resource
    Analysis and modeling of AlxGa1−xN-based Schottky barrier photodiodes (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 2081-2091 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Schottky barrier photovoltaic detectors have been fabricated on n-AlxGa1−xN(0≤x≤0.35) and p-GaN epitaxial layers grown on sapphire. Their characteristics have been analyzed and modeled, in order to determine the physical mechanisms that limit their performance. The influence of material properties on device parameters is discussed. Our analysis considers front and back illumination and distinguishes between devices fabricated on ideal high-quality material and state-of-the-art heteroepitaxial AlxGa1−xN. In the former case, low doping levels are advisable to achieve high responsivity and a sharp spectral cutoff. The epitaxial layer should be thin (〈0.5 μm) to optimize the ultraviolet/visible contrast. In present devices fabricated on heteroepitaxial AlxGa1−xN, the responsivity is limited by the diffusion length. In this case, thick AlxGa1−xN layers are advisable, because the reduction in the dislocation density results in lower leakage currents, larger diffusion length, and higher responsivity. In order to improve bandwidth and responsivity, and to achieve good ohmic contacts, a moderate n-type doping level (∼1018 cm−3) is recommended. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1305838
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  • 2
    Electronic Resource
    Electronic Resource
    High-quality visible-blind AlGaN p-i-n photodiodes (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 1171-1173 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the fabrication and characterization of AlxGa1−xN p-i-n photodiodes (0≤x≤0.15) grown on sapphire by low-pressure metalorganic chemical vapor deposition. The devices present a visible rejection of six orders of magnitude with a cutoff wavelength that shifts from 365 to 338 nm. Photocurrent decays are exponential for high load resistances, with a time constant that corresponds to the RC product of the system. For low load resistances, the transient response becomes non-exponential, with a decay time longer than the RC constant. This behavior is justified by the strong frequency dependence of the device capacitance. By an admittance analysis, we conclude that speed is not limited by deep levels, but by substitutional Mg capture and emission time. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123960
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  • 3
    Electronic Resource
    Electronic Resource
    Band-gap narrowing and potential fluctuation in Si-doped GaN (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 102-104 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate the optical properties of two sets of Si-doped GaN epitaxial layers with different degree of compensation. The electron concentration dependence of the band-gap energy measured by photoluminescence is interpreted as band-gap narrowing effect and evaluated by a simple relation. The photoluminescence peak positions of heavily compensated samples are shifted downward with respect to those of moderately compensated samples, and the down shift becomes larger at higher electron density. Based on analysis of photoluminescence spectra, these prominent behaviors are accounted for by band-edge potential fluctuation associated with inhomogeneous residual impurities. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122964
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  • 4
    Electronic Resource
    Electronic Resource
    High-speed, low-noise metal–semiconductor–metal ultraviolet photodetectors based on GaN (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 762-764 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present the fabrication and characterization of nonintentionally doped GaN and GaN:Mg Schottky metal–semiconductor–metal (MSM) photodetectors, grown on sapphire by metalorganic chemical vapor deposition. Low-leakage, Schottky contacts were made with Pt/Au. The devices are visible blind, with an ultraviolet/green contrast of about five orders of magnitude. The response times of the MSM devices were 〈10 ns and about 200 ns for GaN and GaN:Mg, respectively. The noise power spectral density remains below the background level of the system (10−24 A2/Hz) up to 5 V, for the undoped GaN MSM detector. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123303
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  • 5
    Electronic Resource
    Electronic Resource
    Photoconductor gain mechanisms in GaN ultraviolet detectors (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 870-872 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaN photoconductive detectors have been fabricated on sapphire substrates by metal organic vapor phase epitaxy and gas-source molecular beam epitaxy on Si (111) substrates. The photodetectors showed high photoconductor gains, a very nonlinear response with illuminating power, and an intrinsic nonexponential photoconductance recovery process. A novel photoconductor gain mechanism is proposed to explain such results, based on a modulation of the conductive volume of the layer. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119673
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  • 6
    Electronic Resource
    Electronic Resource
    Growth kinetics and morphology of high quality AlN grown on Si(111) by plasma-assisted molecular beam epitaxy (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 4681-4683 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: AlN layers were grown on Si(111) substrates by plasma-assisted molecular beam epitaxy. Crystal quality was assessed by atomic force microscopy and high resolution x-ray diffraction. The III/V ratio and the growth temperature, rather than thickness and growth rate, are found to be critical parameters to achieve good quality AlN layers. III/V ratios close to stoichiometry, and high growth temperatures (≥900 °C) lead to optimal AlN layers. The growth rate is barely modified when growth temperature changes from 780 to 920 °C, but the growth mode and surface roughness are strongly affected. Optimal AlN layers have full-widths at half-maximum values of 10 arcmin, and an average surface roughness of 48 Å. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366208
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  • 7
    Electronic Resource
    Electronic Resource
    On the coherence of incorporation of the fluorovinyl moiety into bioactive organic compounds. Synthesis of an insect juvenile hormone III fluorinated analog
    Amsterdam : Elsevier
    Tetrahedron 44 (1988), S. 5161-5167 
    Details
    ISSN: 0040-4020
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/S0040-4020(01)86022-1
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  • 8
    Electronic Resource
    Electronic Resource
    Operator splitting and upwinding for the Navier-Stokes equations (1997)
    Springer
    Computational mechanics 20 (1997), S. 474-477 
    Details
    ISSN: 1432-0924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We present an operator splitting scheme for the unsteady Navier-Stokes equations for incompressible viscous fluid flow. Like other operator splitting methods applied to these equations, the difficulties associated with the nonlinearity and the incompressibility condition are decoupled. At each time step we obtain two subproblems of Stokes type and a linear one of elliptic type. The linear problem gives us uncoupled scalar problems of transport type; then, we may take advantage of well known upwind techniques for such kind of problems in order to handle large Reynolds numbers flow with coarse meshes. To show the efficiency of the scheme we report numerical results up to Reynolds numbers Re=4000 obtained with very coarse meshes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004660050268
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  • 9
    Electronic Resource
    Electronic Resource
    Vegetative propagation of Colutea arborescens L., a multipurpose leguminous shrub of semiarid climates (1999)
    Springer
    Agroforestry systems 46 (1999), S. 113-121 
    Details
    ISSN: 1572-9680
    Keywords: adventitious rooting ; bladder senna ; IBA ; leafless hardwood stem cuttings ; shrubby legumes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The vegetative propagation of the multipurpose leguminous shrub Colutea arborescens from leafless hardwood cuttings was examined. Specific attention was paid to the factors: 1) cutting origin (apical, medial or basal); 2) indole-3-butyric acid (IBA) treatment (0, 50 or 200 ppm); and 3) relative humidity of the propagation environment (high or low humidity). After 120 days, 67.6% of the C. arborescens cuttings had rooted. The rooting ability of the cuttings was significantly influenced by the cutting origin and hormonal treatment. No effects on rooting percentage were shown by the relative humidity of the propagation environment. The best rooting response (95%) was shown by basal cuttings treated with 200 ppm IBA. Cutting origin, IBA treatment and relative humidity were significantly related to the root number, longest root length and the fresh/dry biomass of roots and leaves. Under conditions of high humidity, basal cuttings treated with 200 ppm IBA gave rise to the most highly developed plants. The positive relationship between sprouting and rooting suggests that successful propagation is related to the shoot formation potential of the cutting's food reserves. These findings were used to propose an efficient method for the vegetative propagation of C. arborescens plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006234909144
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  • 10
    Electronic Resource
    Electronic Resource
    Variation of the electric properties along the diaphysis of bovine femoral bone (1991)
    Springer
    Medical & biological engineering & computing 29 (1991), S. 441-446 
    Details
    ISSN: 1741-0444
    Keywords: Bone conductivity ; Bone impedance ; Bone permittivity ; Cortical bone ; Femoral diaphysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract A preliminary study is presented of the variability of the electric properties, in the axial, tangential and radial directions, as a function of position in the diaphysis of a femoral bovine bone. The measurements were carried out at three frequencies: 100 Hz, 10 kHz and 1 MHz. It is shown that both the conductivity and the permittivity exhibit significant variations along the diaphysis, and increase in magnitude towards the epiphyses. From this study, the variation of the electric properties cannot be clearly and directly ascribed to the longitudinal variability of the total volumetric fluid content of the bone. The results reflect the orthotropic nature of the electric properties, at any given location, and indicate a position-dependent tendency towards axis symmetry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02441667
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