THE EMISSION AND ABSORPTION CHARACTERISTICS OF CHALCOGENIDE SEMICONDUCTORS USING STEADY STATE AND TIME RESOLVED PICOSECOND SPECTROSCOPY.
Item
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Title
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THE EMISSION AND ABSORPTION CHARACTERISTICS OF CHALCOGENIDE SEMICONDUCTORS USING STEADY STATE AND TIME RESOLVED PICOSECOND SPECTROSCOPY.
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Identifier
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AAI8302552
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identifier
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8302552
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Creator
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YAO, SHING SHWANG.
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Contributor
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R. R. Alfano
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Date
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1982
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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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In this thesis, two chalcogenide semiconductors were studied by optical spectroscopy: a ferromagnetic semiconductor cadmium chromium selenide(CdCr(,2)Se(,4)) with a Curie temperature 130K and a nonmagnetic layered semiconductor gallium selenide(GaSe).;Using steady state and time resolved picosecond emission spectroscopy, the fundamental energy gap between the S-conduction band and P-valence band has been determined in CdCr(,2)Se(,4). The steady state photoluminescence spectra at low temperatures consists of two bands with an energy difference of 3.5 mev. This splitting was attributed to the exchange effect between the S-conduction electrons and the localized magnetic moments. From the theory of Nolting and Oles, the exchange constant was estimated to be 2.3 mev. The temperature dependence of the relaxation decay time and the steady state integrated intensity of the photoluminescence from CdCr(,2)Se(,4) was explained by the relationship that the photoluminescence intensity is nearly proportional to the square power of the excitation intensity. CdCr(,2)Se(,4) was determined to be a direct bandgap semiconductor from the analysis of the spectral profiles of the electron-hole plasma emission from CdCr(,2)Se(,4).;Using time resolved picosecond absorption spectroscopy, hot photogenerated carriers in GaSe were found to relax to the sample temperature by the emissions of nonpolar optical phonons A'(,1)('(1)) (16.7 mev) which were related to the lattice vibration modes perpendicular to the layers. When the density of photogenerated carriers increased, the relaxation process of hot carriers decreased because the risetime increased from within our resolution to 100ps when the carrier density increased to 1.5 x 10('19)cm('-3) in the time resolved emission spectroscopy. This was attributed to the screening effect on the emissions of nonpolar optical phonons A'(,1)('(1)) from relaxing holes. From the analysis of time integrated emission spectra from GaSe excited by picosecond laser pulses, the transition from exciton-carrier scattering emission to electron-hole plasma emission was observed at carrier density (TURN)3 x 10('17) cm('-3).
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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
