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  • 1
    Electronic Resource
    Electronic Resource
    Above-barrier states in GaAs–AlGaAs superlattices studied by photoconductivity and photoreflectance (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1460-1462 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report that the quasibound states at the above-barrier region in AlGaAs–GaAs superlattices can be clearly observed at room temperature by photoconductivity as well as photoreflectance measurements. We provide concrete evidence to confirm that free-carrier confinement at barrier layer does exist. It is also found that the barrier-width dependence of the above-barrier transition energies can be described quite well by the modified Messiah's calculation. However, the simple calculation using the constructive interference condition can only explain the transitions at lower energies, and fails with increasing transition energy. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370965
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  • 2
    Electronic Resource
    Electronic Resource
    Properties of the second-order nonlinear optical susceptibility χ(2) in asymmetric undoped AlGaAs/InGaAs double quantum wells (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1467-1471 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The second-order nonlinear optical susceptibility χ(2) for second-harmonic generation is calculated for the 11H transition of a graded double quantum well (DQW) structure of undoped GaAs/AlxGa1−xAs. These results are compared with the single quantum well (QW). Our results show that the values of χ(2) have optimal magnitudes dependent on the width, depth and separation between the QWs in a DQW structure. When the electric field increases, the dipole moment increases due to the increasing separation between the electron and hole wave functions. On the other hand, the oscillator strength of the 11H transition is reduced as a result of the decrease in the overlap of the electron and hole envelope functions. These two competing factors give rise to optimal conditions for the enhancement of the second-order nonlinear susceptibility χ(2). It is demonstrated that χ(2) for the DQW structure is more enhanced than for the biased single QW. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370914
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  • 3
    Electronic Resource
    Electronic Resource
    Electron swarm parameters in SF6/Ne mixtures determined by swarm experiment (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 6611-6612 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electron swarm growth processes in SF6/Ne gas mixtures have been studied by a pulsed Townsend method over the range 8≤E/P≤140 V mm−1 kPa−1, where E is the electric field and P is the gas pressure. The variation patterns as a function of the pressure reduced electric field of the effective ionization coefficient α¯, electron drift velocity, Ve, and longitudinal diffusion coefficient DL in SF6/Ne gas mixtures have been given. The dielectric strength of SF6/Ne gas mixtures has also been determined, which varies linearly with SF6 concentration in the gas mixtures. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371632
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  • 4
    Electronic Resource
    Electronic Resource
    Perpendicular magnetic anisotropy of Co–Ag granular thin films (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5048-5050 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The perpendicular magnetic anisotropy constant in giant magnetoresistive granular Co22Ag78 thin films is found to increase and then decrease with annealing temperature, the maximum being about 5×105 ergs/cc at an annealing temperature of about 600 K. The observation of domain patterns by magnetic force microscopy is consistent with this result. The origin of the perpendicular magnetic anisotropy is not clear, but suggested to be in an anisotropic Co–Co particle distribution and also due to a surface anisotropy of Co particles. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370087
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  • 5
    Electronic Resource
    Electronic Resource
    Saturation of alpha particle driven instability in Tokamak Fusion Test Reactor (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 629-632 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A nonlinear theory of kinetic instabilities near threshold [Berk et al., Plasma Phys. Rep. 23, 842 (1997)] is applied to calculate the saturation level of toroidicity-induced Alfvén eigenmodes (TAE), and to be compared with the predictions of δf method calculations (Y. Chen, Ph.D. thesis, Princeton University, 1998). Good agreement is observed between the predictions of both methods and the predicted saturation levels are comparable to experimentally measured amplitudes of the TAE oscillations in Tokamak Fusion Test Reactor [D. J. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)]. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873216
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  • 6
    Electronic Resource
    Electronic Resource
    Dielectric studies of Zn1−xMnxSe epilayers (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1630-1633 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the dielectric properties of Zn1−xMnxSe(0≤x≤0.78) epilayers, by capacitance and dissipation factor measurements at temperature 5 K〈T〈475 K and frequency 20 Hz〈f〈100 kHz. A Debye-like relaxational contribution to the dielectric response is observed, which requires the presence of charge redistribution. The relaxation is found to be a thermally activated process, and the activation energies obtained from the dissipation factor and capacitance are in good agreement. The capacitance is found to increase with a decrease in test frequency. From our results it is established that the dielectric response is caused by carrier hopping among structural defects. A monotonic variation is found in the relationship between the activation energy and the Mn concentration. This monotonic variation is interpreted in terms of the four-center model, in which the number of Mn atoms appearing in the nearest-neighbor sites of the defect can have four possible configurations. The measured defect behavior reflects the overall average of all energy levels involved in the center, and the result is weighted by the relative concentrations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370938
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  • 7
    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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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Pulsed laser deposition of epitaxial GaNxAs1−x on GaAs (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3951-3953 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial layers of GaNxAs1−x were grown on (001) GaAs substrates by pulsed laser ablation of a GaAs target in an ammonia (NH3) atmosphere. High-resolution x-ray diffraction indicates the existence of a threshold NH3 pressure, above which the incorporated N content x increases linearly with increasing NH3 pressure. The band-gap dependence of GaNxAs1−x on x for x≤2.9% is examined by optical absorption and photoconductivity measurements at room temperature. We found that the band-gap energy reduces with higher N composition, and our results agree approximately with the prediction based on the dielectric model. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124234
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  • 10
    Electronic Resource
    Electronic Resource
    Investigation on Ag/Pb(Zr0.53Ti0.47)O3/YBa2Cu3O7−δ three-terminal system with small gate area (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 2044-2046 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The three-terminal devices Ag/Pb(ZrxTi1−x)O3/YBa2Cu3O7−δ(Ag/PZT/YBCO) have been fabricated onto (100) SrTiO3 by pulsed laser deposition technique and photolithography. For the purpose of application, we specially selected the PZT layer with morphotropic phase boundary composition as the gate to lower the coercive fields and decrease the operating voltage. We tried to minimize the electrode area to 6×10−6 cm2 for deeply investigating the leakage problem and getting sufficient polarization of the PZT gate, also for the high integration in future application. From the process, we obtained the following results at 64 K: the saturation polarization and the remanent polarization reach 60 and 41 μC/cm2, respectively. The coercive field is lower than 37 kV/cm, and the breakdown field is ≥3×105 V/cm. The electric field effect measurement shows that the maximum modulation channel resistance ΔRDS/RDS is 3% under the gate voltage of ±9 V at 64 K (lower than the zero resistance temperature TC0, 70 K), at which the superconducting and normal state transition is driven by channel current IDS(IDS〉Ic, Ic=15 mA). © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123751
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