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  • 11
    Electronic Resource
    Electronic Resource
    Optical quenching of the photoconductivity in n-type GaN (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 3404-3408 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results of optical quenching of photoconductivity measurements in undoped n-type and Se-doped GaN epitaxial thin films are presented. The spectral distribution of quenching phenomena shows a broadband centered around 1.26 eV. Transient changes in photoconductivity on application or removal of the quenching radiation are shown to exhibit a metastable behavior. The results reveal that the origin of the optical quenching phenomena is closely related to the defects corresponding to the persistent photoconductivity effects and the yellow luminescence band observed in most n-type GaN. In addition, this result indicates that these defects can have multiple charge states. It is found that the quenching ratio increases with increasing Se-doping concentration. We point out that the origin of the defects responsible for the optical quenching can be attributed to nitrogen antisite and/or Ga vacancy. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372358
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  • 12
    Electronic Resource
    Electronic Resource
    Growth and photoluminescence study of ZnTe quantum dots (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 4694-4696 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: ZnTe quantum dots embedded in ZnS were grown successfully by controlling the flow duration in a metalorganic chemical vapor deposition system. Blueshift as large as 250 meV was observed in photoluminescence measurement, and the emission persists up to room temperature. The amount of blueshift decreases with increasing quantum dot size and for large quantum dots, no photoluminescence could be detected. From studying the temperature-dependent integrated intensity of the emission spectra, it is found that the activation energy for the quenching of photoluminescence increases with decreasing quantum dot size, and is identified as the binding energy of exciton in ZnTe quantum dot. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371422
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  • 13
    Electronic Resource
    Electronic Resource
    Optical properties of Si-doped GaN films (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 6124-6127 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results of the front-side and back-side photoluminescence (PL) measurements in a set of Si-doped GaN epifilms are presented. From the back-side PL spectrum, the enhancement of the yellow emission implies that most of the intrinsic defects responsible for the yellow band exist mainly near the interface between the buffer layer and the epilayer. We also found that the intensity of the yellow luminescence decreases with increasing Si dopants, which is consistent with the fact that the microscopic origin of the yellow emission can be attributed to gallium vacancies VGa. In additions, our investigations reveal that the potential fluctuations, that give rise to the effect of band-gap narrowing and linewidth broadening, are mainly caused by randomly distributed doping impurities instead of other defects. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371662
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  • 14
    Electronic Resource
    Electronic Resource
    Apparatus for measuring the curvature of spherical and cylindrical surfaces (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1688-1689 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An apparatus, which is comprised of four equal ball feet forming a square on the same plane of the support plate and a plunger in the square and acts as a probe for determining the sagittal depth, can be used to measure the curvature of spherical as well as cylindrical surfaces. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146865
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  • 15
    Electronic Resource
    Electronic Resource
    Enhancement of conduction-band effective mass in III–V semiconductor alloys induced by chemical disorder (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6761-6765 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The conduction-band effective masses in InxGa1−xAs with a complete range of composition, and InAlGaAs and InGaAsP alloys covering the complete range of lattice matched to InP have been determined by far-infrared optically detected cyclotron resonance and magnetophotoconductivity measurements. It is found that the measured effective masses as a function of alloy composition are heavier than the values predicted from the five-band k⋅p theory. We show that this discrepancy can be resolved by including the effect of disorder-induced potential fluctuations that causes the wave function mixing between conduction and valence bands. We find that the strength of the potential fluctuations can be well described in terms of the Phillips electronegativity difference related to chemical disorder. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363804
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  • 16
    Electronic Resource
    Electronic Resource
    Transport properties of Tl2Ba2CaCu2O8 weak links on LaAlO3 bicrystal substrates (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 9221-9223 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Josephson junctions and dc superconducting quantum interference devices (SQUIDs) have been fabricated in ex situ epitaxial Tl2Ba2CaCu2O8 films on bicrystal LaAlO3 substrates with symmetric 32° [001] tilt grain boundaries. The critical temperature Tc, of the junctions was in the range 105–107 K and the critical current densities at 77 K varied between 3×102 and 3×104 A/cm2, two or three orders of magnitude less than those of the film. The I–V curves are described by a resistively shunted junction model. Close to Tc, the temperature dependence of the critical current was described by (1−T/Tc)2. The flux noise spectra SΦ(f) of dc SQUIDs were measured in the locked-loop regime with constant current bias at temperatures up to 94 K. The white noise level was 50μΦ0/(square root of)Hz at 77 K. The crossover frequency to 1/f noise was low, about 5 Hz, and the flux noise level at 1 Hz was 440μΦ0/(square root of)Hz. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362595
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  • 17
    Electronic Resource
    Electronic Resource
    Evolution of photoluminescence of porous silicon under light exposure (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5365-5368 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time evolution of the photoluminescence spectra of low current density electrochemically etched porous silicon are studied. When the sample is exposed to light illumination in atmosphere, the luminescence intensity decays initially. However, after a short period of degradation, it starts to enhance gradually. The profiles of the photoluminescence spectra including peak position and line width are very different for the decay and enhancement processes. When the sample is illuminated in vacuum, only a decay process is observed. Infrared spectrum shows that the hydrogen related bonding in the as-anodized sample is replaced by the oxygen related termination. A quantum confinement model together with the activity of nonradiative recombination centers is proposed to explain our observations. After oxidation under light exposure, the intensity of the photoluminescence is strong and stable. Thus, our study also provides a room temperature oxidation method for producing strong and stable luminescent porous silicon. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359291
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  • 18
    Electronic Resource
    Electronic Resource
    Effective mass of two-dimensional electron gas in δ-doped Al0.48In0.52As/Ga0.47In0.53As quantum wells (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 3355-3359 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the lowest two subbands of two-dimensional electron gas in δ-doped AlInAs/GaInAs quantum wells by Shubnikov–de Haas, quantum Hall effect, and cyclotron resonance measurements. The effective masses determined by the field-dependent cyclotron resonance measurements are 0.0576m0 and 0.0483m0 at electron densities of 17.3 and 3.6×1011 cm−2 for the first and second subbands, respectively. It was found that the electron in the first subband has heavier effective mass and shorter quantum lifetime than that in the second subband. Using the band gap of 810 meV and the band-edge mass of 0.042m0 for Ga0.47In0.53As, we calculated the average distance of the two subbands from the conduction band edge to be 150 and 61 meV, respectively. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363247
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  • 19
    Electronic Resource
    Electronic Resource
    Effect of disorder-induced band mixing on the conduction-band effective mass of InAlGaAs alloys lattice matched to InP (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1239-1241 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is found that the calculation of the effective mass for InAlGaAs alloys obtained from the five-band k⋅p theory is smaller than the measured value from the optically detected cyclotron resonance reported recently. We point out that the effect of disorder-induced conduction valence band mixing must be considered. This disorder effect which creates potential fluctuations is to reduce the matrix element P2 for the conduction valence band coupling in the k⋅p theoretical expression. The strength of the potential fluctuations can be described in terms of the electronegativity difference related to chemical disorder. The inclusion of the disorder effect in the (In0.53Al0.47As)x(In0.53Ga0.47As)1−x quaternary system gives a very good fit to the measured data. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362862
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  • 20
    Electronic Resource
    Electronic Resource
    Photoluminescence study of highly mismatched In0.53Ga0.47As epilayers grown on InP-coated GaAs substrates (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1040-1042 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoluminescence measurement is used to study the properties of In0.53Ga0.47As epilayers grown on InP-coated GaAs substrates. Several structures are designed to test the qualities of the epilayers. It is shown that device-quality In0.53Ga0.47As on a GaAs substrate can be achieved. The effects of hydrogenation using a photochemical-vapor-deposition system are studied, and an enhancement of the band-edge luminescence intensity by a factor of 4 is observed. The resulting intensity even exceeds that of the film grown directly on a lattice-matched InP substrate. In addition, the emission coming from lattice defects is greatly reduced after hydrogenation. These results not only further support the potential application of using binary buffer layer concepts in large lattice-mismatched systems, but also demonstrate that the photochemical-vapor-deposition system is a useful tool for injecting hydrogen into InGaAs epilayers. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358962
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