Modulation spectroscopy of semiconductors and semiconductor microstructures.
Item
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Title
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Modulation spectroscopy of semiconductors and semiconductor microstructures.
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Identifier
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AAI9207079
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identifier
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9207079
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Creator
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Hang, Zhijiang.
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Contributor
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Adviser: Fred H. Pollak
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Date
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1991
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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 | Physics, Optics
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Abstract
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The electronic properties of semiconductors and semiconductor microstructures have been studied by electromodulation spectroscopy. Since the derivative nature of Photoreflectance (PR) provides maximum sensitivity to interband electronic transitions, it was used to measure the optical spectra of the direct gap (E{dollar}\sb0{dollar}) of III-V semiconductors such as GaAs, InP, GaAlAs and InGaAs in a wide temperature range up to 600{dollar}\sp\circ{dollar}C. We have evaluated the parameters which describe the dependency of the energy gap E{dollar}\sb0{dollar} and broadening parameters of E{dollar}\sb0{dollar} on temperature. We have concluded that both electron-optic and electron-acoustic phonon interactions as well as the thermal expansion contribute to the energy shifts of the band gap (E{dollar}\sb0{dollar}) of InP and In{dollar}\sb{lcub}\rm x{rcub}{dollar}Ga{dollar}\sb{lcub}\rm 1-x{rcub}{dollar}As (x = 0.06 and 0.15). It is mainly electron-optical phonon interaction which contributes to the broadening (E{dollar}\sb0{dollar}) of the energy gaps.;We have made considerable progress in developing PR as an in-situ monitoring/control method for semiconductor growth. Measurements have been performed in an actual metalorganic chemical vapor deposition (MOCVD) reactor. We found a systematic difference between the temperature of the GaAs substrate and a thermocouple not in contact with the sample. Also, it is now possible to evaluate Aluminum composition in GaAlAs during actual growth. A major step forward has been a substantial reduction in data acquisition time to 30 seconds so that real-time measurements are now feasible.;Photoreflectance also has been used to study alternating composition layers of multiple quantum wells (MQW) both lattice-matched (Ga{dollar}\sb{lcub}\rm 1-x{rcub}{dollar}Al{dollar}\sb{lcub}\rm x{rcub}{dollar}As/GaAs MQW) and lattice-mismatched or strained (In{dollar}\sb{lcub}\rm x{rcub}{dollar}Ga{dollar}\sb{lcub}\rm 1-x{rcub}{dollar}As/GaAs and GaSb/AlSb MQW) systems. The rich spectra were observed at room temperature, and they consisted of both symmetry allowed and forbidden confined (CT) and unconfined (UT) transitions. Both the CT and UT exhibited coupling effects between wells (miniband dispersion). With this information we can examine existing theories, such as Bastard Model theory (31,32), and also experimentally determine the following: (1) the band alignment of the heterostructure (band offset); (2) the alloy composition of Ga{dollar}\sb{lcub}\rm 1-x{rcub}{dollar}Al{dollar}\sb{lcub}\rm x{rcub}{dollar}As or In{dollar}\sb{lcub}\rm x{rcub}{dollar}Ga{dollar}\sb{lcub}\rm 1-x{rcub}{dollar}As epliayers; and the thickness of wells and barriers.;In addition, an investigation of the strained-layer systems enables us to determine the strain distribution. We also use Franz-Keldysh Oscillation (FKO) to study the effects of various conditions (UHV, air, temperature, light intensity) on surface photovoltage (V{dollar}\sb{lcub}\rm s{rcub}{dollar}) effects on the determination of Fermi level pining (V{dollar}\sb{lcub}\rm s{rcub}{dollar}) on (100) GaAs.
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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.
