MODULATION AND RAMAN SPECTROSCOPY STUDY OF MICROSTRUCTURAL GEOMETRIES IN SEMICONDUCTORS.
Item
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Title
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MODULATION AND RAMAN SPECTROSCOPY STUDY OF MICROSTRUCTURAL GEOMETRIES IN SEMICONDUCTORS.
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Identifier
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AAI8713797
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identifier
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8713797
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Creator
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SHEN, HONGEN.
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Contributor
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Fred H. Pollak
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Date
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1987
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Condensed Matter
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Abstract
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Microstructural geometries were investigated using photoreflectance (PR), electroreflectance (ER) and Raman scattering. We have demonstrated for the first time that photoreflectance spectra from superlattices can be fit by a third derivative function electromodulation lineshape, thus making it possible to precisely determine energies of the quantum transitions. By employing a detailed lineshape fit, we can detect a barrier height change of several millielectron volts and variations in well width as small as 2A with a spatial resolution about 100{dollar}\mu{dollar}m. For the first time at room temperature, several forbidden transitions from GaAlAs/GaAs superlattices have been clearly observed, which is a strong support to the valence band mixing theory in superlattices.;The Franz-Keldysh theory for modulation spectroscopy has been generalized to involving both dc and ac fields. We have demonstrated, both theoretically and experimentally that provided that ac field is smaller than dc field, Franz-Keldysh oscillations in modulation spectroscopy are related to the dc electric field and not to the ac modulation field.;Photoreflectance study on doping superlattices (nipi) have been performed. For samples with small periodicity, the room temperature spectra showed quantum size effect. For samples with large periodicity, spectra exhibited Franz-Keldysh oscillations. The pump chopping frequency dependence of the PR signal was employed to measure the recombination lifetime of the carriers.;The effect of polish-induced stress on the LO Raman spectra from GaAs and InP have been investigated in detail. The lineshape changes have been quantitatively accounted for by a model based on the convolution of the skin depth of light and the penetration depth of the polish-induced surface strain. The strain penetration depth as well as the surface strain were determined for various polishing conditions.;We demonstrated that Raman scattering can be used to determine the width of the depletion layer as well as carrier concentration for {dollar}{dollar} n-type GaAs (up to n {dollar}\simeq{dollar} {dollar}10\sp{19}{lcub}\rm cm{rcub}\sp{lcub}-3{rcub}).{dollar} The results are correlated with a generalized theory of the depletion width for both degenerate and non-degenerate situation at finite temperatures. We have also obtained the coefficient of electric field induced Raman tensor (both amplitude and phase) as well as impurity induced Raman tensor for {dollar}{dollar} GaAs at 2.7eV (4579A). (Abstract shortened with permission of author.).
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Physics
