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  • 1
    Electronic Resource
    Electronic Resource
    Transport properties of silver-doped Y-Ba-Cu-O thin films (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 1538-1542 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transport properties of dilute silver-doped Y-Ba-Cu-O thin films prepared by a laser ablation technique have been investigated. The Hall coefficient and critical current density were measured as a function of temperature and in magnetic field up to 1.0 T. Silver doping is shown to result in significant changes in the temperature- and magnetic-field dependence of the transport properties of these films. The Hall coefficient in silver-doped films shows a clear decrease from that in silver-free films, consistent with an increase in the hole concentration caused by the silver impurities. This result lends a direct support to the observation that dilute silver dopants behave as acceptors but without appreciable influence on the transition temperature. The magnetic-field dependence of the normalized critical current density Jc(H)/Jc(0) is enhanced by silver doping, mainly due to a decrease in the effective weak-link area at the grain boundaries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347245
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  • 2
    Electronic Resource
    Electronic Resource
    Investigation of interfacial roughness of InxGa1−xAs epitaxial layers on GaAs and InP substrates by soft x-ray reflectivity (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 949-953 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The grazing incidence x-ray reflectivity is a nondestructive and sensitive technique for probing the depth profile of electron density in layered structures. This method has been utilized in the soft x-ray regime to determine the roughness of interfaces, and the epilayer thickness in InxGa1−xAs/InP and InxGa1−xAs/GaAs heterostructures, for x=0.57 and x=0.60, grown by molecular beam epitaxy. By fitting the experimental results to our model, assuming uncorrelated interfacial roughness, we conclude that the top surface roughness does not depend on the type of the substrate or presence of stress in the epilayer, and is always smaller than interfacial roughness. The main factors which control the interfacial roughness are the quality of substrate and/or growth conditions rather than strain or lattice mismatch.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347338
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  • 3
    Electronic Resource
    Electronic Resource
    The effect of reduced growth area by substrate patterning on misfit accommodation in molecular beam epitaxially grown InxGa1−xAs/GaAs (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4253-4262 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of reduced growth area on the misfit accommodations of InxGa1−xAs/GaAs grown by molecular beam epitaxy has been studied with cross-sectional transmission electron microscopy (XTEM). Composition grading techniques as well as strained-layer superlattices were used for InxGa1−xAs compositions up to x=0.53 and growth areas which ranged from approximately 10 cm2 (blanket areas) to 4 μm2 squares. Results indicate that the use of step-composition grading and linear-composition grading are particularly effective when combined with reduced growth areas up to 30×30 μm and InxGa1−xAs compositions up to x=0.25. Dislocations which are generated for misfit accommodation during growth are effectively driven to the edges of the patterned growth areas with considerably fewer interactions than dislocations nucleated in blanket areas. XTEM samples prepared from blanket areas were generally found to contain randomly distributed threading dislocation-free regions on the order of 20–30 μm in width bounded by high density dislocation pile-ups. Higher InxGa1−xAs compositions resulted in large densities of threading dislocations with Burgers vectors perpendicular to the growth direction, particularly for step-composition graded layers. We attribute this behavior to roughening of the growth interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348397
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  • 4
    Electronic Resource
    Electronic Resource
    Instability in surface emitting lasers due to external optical feedback (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 16-20 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Instability in the output of dc-biased surface emitting lasers due to an external cavity effect was observed. The output power spectrum exhibited multiple peaks with spacing corresponding to exactly the round-trip delay in silica fibers with length ranging from 2 m to 2 km. The magnitude of the peaks was enhanced in the spectral region centered at the laser relaxation frequency. With increased feedback, the background of the output spectrum was found to increase, indicating the presence of optical chaos. Numerical simulation based on the rate equation analysis was found to agree with the experiment, indicating the surface emitting lasers are well described by the rate equation and are susceptible to feedback as the edge emitting lasers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353880
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  • 5
    Electronic Resource
    Electronic Resource
    A study of the coupling efficiency versus grating periodicity in a normal incident GaAs/AlGaAs multiquantum well infrared detector (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2105-2109 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed study of the dependence of coupling quantum efficiency on the grating periodicity of planar metal grating coupled GaAs/AlGaAs quantum well infrared photodetectors has been made in this work. Five different detector samples with grating periodicities of Λ=1.1, 3.2, 5, 7, and 10 μm have been fabricated for the present study. The results showed that the device with a 5 μm grating periodicity gave the best front-side coupling efficiency, which was in good agreement with our theoretical prediction. A single pass quantum efficiency (η) of 11% was achieved for the front-side illumination at λp=9.8 μm and T=77 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351597
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  • 6
    Electronic Resource
    Electronic Resource
    Characterization of SiO2/Si heterostructures by soft x-ray reflection (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 1631-1642 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Grazing incidence x-ray reflectivity has been used to characterize four as-grown SiO2/Si(100) heterostructures with SiO2 overlayer thicknesses ranging from about 126 to 1100 A(ring). Root-mean-square roughness at both the top surface and buried interface is determined, as is the (complex-valued) x-ray refractive index of the SiO2 heterostructure material for photons in the energy range 400–800 eV. Knowledge of the SiO2 and Si refractive indices allows the oxygen atomic scattering factor to be deduced at these energies. Evidence that one of the four thermally grown structures may consist of more than just a single homogeneous overlayer is also examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347260
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  • 7
    Electronic Resource
    Electronic Resource
    Migration of constituent atoms and interface morphology in a heterojunction between CdS and CuInSe2 single crystals (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 6052-6058 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Angular dependence of x-ray fluorescence (ADXRF), x-ray absorption fine structure (XAFS), and grazing incidence x-ray scattering measurements were carried out using synchrotron radiation for a study of the interface morphology and migration of constituent atoms in a heterojunction formed between CdS and CuInSe2 single crystals. The advantage of using a single crystal for this study is to avoid the usually complicated problems arising from multiple phases of the Cu–In–Se compounds. By a comparison of the results obtained with a bare CuInSe2 single crystal, the changes of interface microstructures in the CdS/CuInSe2 heterojunction system with well-defined stoichiometry can therefore be investigated. Prominent features in the ADXRF data clearly demonstrate that both Cu and Se atoms have migrated into the CdS layer in the heterojunction while In atoms remain intact in the CuInSe2 single crystal. The local structures around Cu in the system also show a significant change after the deposition of CdS, as manifested by the appearance of new Cd near neighbors in the XAFS spectra. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371653
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  • 8
    Electronic Resource
    Electronic Resource
    Antimalarial Constituents of Chinese Drug, Ch'ang Shan, Dichroa febrifuga Lour (1948)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 70 (1948), S. 1765-1767 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja01185a028
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  • 9
    Electronic Resource
    Electronic Resource
    Raman effect in AlGaAs waveguides for subpicosecond pulses (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 2198-2203 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Raman effect in semiconductor waveguides below half-gap is studied both experimentally and numerically. We report the depolarized Raman gain spectra up to 300 cm−1 in Al0.24Ga0.76As at pump wavelengths of 0.515 and 1.55 μm from the measurement of the absolute Raman scattering cross sections using GaAs as a reference scatterer. In addition, the coupled propagation equations for the AlGaAs waveguides are modified to include the Raman effect. By solving the coupled propagation equations numerically, we verify that the energy transfer between two orthogonally polarized pulses demonstrated in previous pump-probe experiments [M. N. Islam et al., J. Appl. Phys. 71, 1927 (1992)] is caused by Raman effect. We also show numerically that the Raman effect induces spectral distortions on the pulses, and the energy transfer is inversely proportional to the pulse widths. The energy transfer results in a severe cross-talk problem for sub-picosecond pulses in AlGaAs waveguides. For example, the energy exchange is about 30% for 300 fs pulses under π phase shift conditions. Therefore, the Raman effect limits the performance of semiconductor waveguides in optical switching applications for sub-picosecond pulses. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360135
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  • 10
    Electronic Resource
    Electronic Resource
    Experimental sensitivity analysis of pseudomorphic InGaAs/AlAs resonant-tunneling diodes (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6305-6317 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Through the use of a novel vertically integrated resonant-tunneling diode (RTD) heterostructure we have established experimentally the relationship between intentional variations in the structural parameters of the pseudomorphic In0.53Ga0.47As/AlAs resonant tunneling diode (i.e., barrier thickness, quantum-well thickness, quantum-well composition, and doping density) and the measured current–voltage characteristics of the device. Based upon the results of these experiments, we have determined that a 1 monolayer increase in AlAs barrier width, InGaAs quantum-well width, or InAs subwell width results in a peak current reduction of 56%±7%, 19%±2%, and 18%±3%, respectively. Further, a 1% decrease in indium mole fraction of the InGaAs quantum well has been found to increase the peak current by 10%±1%. Sensitivity parameters have been tabulated for both the peak current and the peak voltage of the RTD. Through the use of these parameters, the maximum allowed fluctuation in the RTDs structural parameters has been estimated for a given tolerance in the RTDs electrical characteristics. Further, these data can also be used to evaluate the feasibility of in situ epitaxial growth control of resonant tunneling devices. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360511
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