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  • 1
    Electronic Resource
    Electronic Resource
    Determination of the local Al concentration in AlxGa1−xAs-GaAs quantum well structures using the (200) diffraction intensity obtained with a 10 A(ring) electron beam (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 1454-1456 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel method for determining the local concentration of Al in the AlxGa1−xAs layer of AlxGa1−xAs-GaAs multiple quantum well structures is reported. By scanning a 10 A(ring) electron beam across the interface, the (200) dark-field scanning transmission electron microscopy (STEM) image shows the contrast of the AlxGa1−xAs-GaAs multilayer since the intensity of the (200) diffraction is sensitive to the Al concentration. The line scan intensity profile of the (200) diffraction, along a uniform specimen region of known thickness, shows the intensity variation of the (200) diffraction and reflects the local content of Al in each region. The simulation of the nanodiffraction patterns produces a chart of the (200) diffraction intensity versus the Al concentration for the determination of the local change of the Al concentration. A molecular beam epitaxy grown AlxGa1−xAs-GaAs specimen (x=0.57 as determined from Raman spectroscopy) is tested and the dark-field STEM studies show two thin layers of x=0.46 at the 1/3 and 2/3 height level within every AlxGa1−xAs layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100695
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  • 2
    Electronic Resource
    Electronic Resource
    Theoretical study of time-resolved Raman scattering profiles of hot electrons in semiconductors (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 4325-4335 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A comprehensive time-resolved electronic Raman scattering theory for nonequilibrium carrier excitations in semiconductors is presented. The following are simultaneously taken into account: (i) the effects of the ultrashort laser pulse for probing the excited carrier distribution function; (ii) the fact that the fluctuation-dissipation theorem is not valid under conditions of nonequilibrium carrier distributions; (iii) the effects of quasiparticle life time via a finite collision time in the Raman scattering cross section; and (iv) the effect of the time-dependent resonant enhancement factor due to the band structure. The single-particle scattering spectra for spin-density fluctuation contribution is found to be significantly broadened by an ultrashort laser pulse, but is substantially narrowed by the finite collision time. The effect of the time-dependent resonant enhancement factor has been demonstrated to broaden the line shape of single-particle scattering spectra for the spin-density fluctuation contribution as the probe photon energy increases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352196
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis of the single-particle scattering spectra for spin-density fluctuations of electrons in n-GaAs at T=300 K (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3023-3027 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The line shapes of single-particle scattering spectra for spin-density fluctuations of electrons in n-GaAs with carrier concentrations ranging from 5×1015 to 7×1017 cm−3 have been analyzed. We have found that the Raman line shapes can be very well explained by a theory developed by Hamilton and McWhorter which takes into account both the band-structure effects in semiconductors and the effects of carrier collision in a relaxation time approximation. For carrier concentration n≥2×1016 cm−3, the effects of finite collision time has been demonstrated to be very important and these effects must be properly taken into account in order to satisfactorily interpret the line shapes of single-particle scattering spectra for spin-density fluctuations in n-GaAs at T=300 K. We show that although Lindhard–Mermin's expression for dielectric constant as well as Hamilton and McWhorter's theory fit the Raman line shapes equally well for carrier density n=7×1017 cm−3, neglect of band-structure effects of the former tends to underestimate the carrier collision time. An interpretation of the deduced collision time in terms of electron-electron, electron-impurity, and electron-phonon scattering is also given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353008
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  • 4
    Electronic Resource
    Electronic Resource
    Critical analysis of the band-shape function of a molecular system imbedded in a host crystal: Application to F centers (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 7574-7585 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present an investigation of the accuracy of the saddle-point method in application to band-shape functions and find that it gives excellent results for most commonly encountered situations. We also present a comparison with a new improved short-time approximation which shows promise in applications. We use this new method to examine the behavior of the band-shape function in a distorted oscillator model. As an application, we have used these methods to explain the absorption and emission spectra of an F-center defect (a prototype defect system) in four different host crystals KCl, KI, KBr, and NaCl.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465687
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  • 5
    Electronic Resource
    Electronic Resource
    Raman scattering by interface phonons in GaAs-AlAs multiple-quantum-well structures: Correlation between Raman and high-resolution electron microscopy results (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 418-421 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of shallow impurity and interface roughness on resonant Raman scattering by interface phonons in GaAs-AlAs multiple quantum-well structures have been studied. By correlating the Raman results with observations by high-resolution electron microscopy, it has been demonstrated that Raman scattering from interface phonons depends strongly on the sample quality. For a relatively smooth interface with about 1–2 monolayers of interface roughness, the Raman signal is governed primarily by the impurity if the impurity concentration inside the GaAs layers is greater than about 2×1016 cm−3. On the other hand, for nominally undoped quantum-well structures, the Raman signal can be dominated by interface roughness if the interfaces are sufficiently distorted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350291
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  • 6
    Electronic Resource
    Electronic Resource
    Observation of electronic Raman scattering from Mg-doped wurtzite GaN (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2889-2891 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electronic Raman scattering experiments have been carried out on both molecular beam epitaxy and metal-organic chemical vapor deposition-grown Mg-doped wurtzite GaN samples. Aside from the expected Raman lines, a broad structure (full width at half maximum≅15 cm−1) observed at around 841 cm−1 is attributed to the electronic Raman scattering from neutral Mg impurities in Mg-doped GaN. Our experimental results demonstrate that the energy between the ground and first excited states of Mg impurities in wurtzite GaN is about one-half of its binding energy. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126507
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  • 7
    Electronic Resource
    Electronic Resource
    Picosecond Raman scattering studies of nonequilibrium electron distributions and energy-loss rate in InxGa1−xAs1−yNy (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 3094-3096 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nonequilibrium electron distributions and energy-loss rate in a metal–organic chemical-vapordeposition-grown InxGa1−xAs1−yNy (x=0.03 and y=0.01) epilayer on a GaAs substrate have been studied by picosecond Raman spectroscopy. It is demonstrated that for electron density n≅1018 cm−3, electron distributions can be described very well by Fermi–Dirac distributions with electron temperatures substantially higher than the lattice temperature. From the measurement of electron temperature as a function of the pulse width of the excitation laser, the energy-loss rate in InxGa1−xAs1−yNy is estimated to be 64 meV/ps. These experimental results are compared with those of GaAs. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1371962
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  • 8
    Electronic Resource
    Electronic Resource
    Electron–phonon interactions in solid C60 studied by transient picosecond Raman spectroscopy (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 1051-1053 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron–phonon interactions in solid C60 have been studied by transient Raman spectroscopy on a picosecond time scale. The electrons were photoinjected into the triply-degenerate states of solid C60 by an ultrashort laser pulse of photon energy (h-dash-bar)ω=2.14 eV. These energetic electrons relax by emitting various phonons. By monitoring the phonon occupations at very low temperatures with anti-Stokes Raman scattering, direct information about the relative strength of the electron–phonon interactions in solid C60 was obtained. Our experimental results demonstrate that electrons interact much more strongly with the low-frequency radial Ag mode than the other phonon modes in solid C60. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116245
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  • 9
    Electronic Resource
    Electronic Resource
    Nonequilibrium electron distributions and phonon dynamics in wurtzite GaN (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2990-2992 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report experimental measurements of nonequilibrium electron distributions as well as phonon dynamics in wurtzite GaN by using subpicosecond time-resolved Raman spectroscopy. Our experimental results have demonstrated that for electron densities n≥5×1017 cm−3, the nonequilibrium electron distributions in wurtzite GaN can be very well described by Fermi–Dirac distribution functions with the temperature of electrons substantially higher than that of the lattice. The population relaxation time of longitudinal optical phonons was directly measured to be τ(approximately-equal-to)5±1 ps at T=25 K. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116673
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  • 10
    Electronic Resource
    Electronic Resource
    Quantitative assessment of the effects of carrier screening on the average electric field in a GaAs-based p–i–n nanostructure under subpicosecond laser excitation (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 406-408 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used electric-field-induced Raman scattering to quantitatively assess the effects of carrier screening on the average electric fields in a GaAs-based p–i–n nanostructure semiconductor under subpicosecond laser photoexcitation. Our experimental results demonstrated that the effects of carrier screening on the average electric field were negligible for a photoexcited electron–hole pair density of n≤1015 cm−3. As the density of photoexcited carriers increased, we observed a significant decrease of the average electric field. In particular, for n=1018 cm−3, a decrease of electric field of about 50% was found. All of these experimental results were explained by ensemble Monte Carlo simulations and very good agreement has been obtained. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364072
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