Modulation spectroscopy of semiconductor microstructures.
Item
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Title
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Modulation spectroscopy of semiconductor microstructures.
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Identifier
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AAI9707119
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identifier
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9707119
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Creator
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Krystek, Wojciech.
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Contributor
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Adviser: Fred H. Pollak
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Date
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1996
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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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With modern thin film growth techniques, such as molecular beam epitaxy, one can design new, complex semiconductor microstructures with almost arbitrary potential profiles. The investigation of the properties of these artificially structured crystals is of considerable interest from both fundamental and applied perspectives. In this thesis we have studied several very important semiconductor microstructures with photoreflectance (PR), contactless electroreflectance (CER) and piezoreflectance modulation spectroscopy techniques.;We have measured the temperature dependence of the direct gaps of ZnSe and {dollar}\rm Z\sb{lcub}0.56{rcub}Cd\sb{lcub}0.44{rcub}Se{dollar} in the temperature range {dollar}\rm 25K< T < 400K{dollar} using CER. The quantities that describe the temperature dependence of the energy (including thermal expansion effects) and broadening function of the band gaps were evaluated. Comparison has been made with corresponding parameters of several other II-VI and III-V materials.;Using CER at 300K we have characterized the potential profile of a pseudomorphic 0.98 {dollar}\mu{dollar}m InGaAs/GaAs/GaAlAs graded index of refraction separate confinement heterostructure laser. Signals were detected from all three relevant portions of the sample. To identify spectral features we have performed computer calculation based on the envelope function approximation, including the effects of strain and electric field. From the period of the observed Franz-Keldysh oscillations from the graded GaAlAs region we have evaluated directly the built-in electric field in the structure.;We have presented the contactless determination of the time constants of the equivalent circuits of both the GaAs collector and GaAlAs emitter portions of a GaAs/GaAlAs heterojunction bipolar transistor (HBT) structure using the modulation frequency dependence (2 {dollar}{lcub}\rm Hz{rcub} < \Omega\sb{lcub}m{rcub} < 100{dollar} kHz) of the in-phase and quadrature PR signals. An analysis of the collector time constant has revealed that the recombination mechanism in the collector-base region is dominated by the hole current and is due to midgap trap states.;We have also presented new results on the illumination dependence of the electric fields deduced from the PR spectra of this GaAs/GaAlAs HBT structure. We have found that doping levels in the emitter/base and collector/base regions can be obtained from the illumination dependence of the observed fields, while the fields themselves can be used to evaluate variations in the doping levels.
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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.
