CARRIER TRANSPORT IN AMORPHOUS SILICON UTILIZING PICOSECOND PHOTOCONDUCTIVITY.
Item
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Title
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CARRIER TRANSPORT IN AMORPHOUS SILICON UTILIZING PICOSECOND PHOTOCONDUCTIVITY.
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Identifier
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AAI8203292
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identifier
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8203292
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Creator
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JOHNSON, ANTHONY MICHAEL.
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Contributor
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David H. Auston | Robert R. Alfano
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Date
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1981
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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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The development of a new, high-speed electronic measurement capability has permitted the direct observation of the transient photoresponse of amorphous silicon (a-Si) with a time resolution of approximately 10ps. We have used this technique to measure the initial mobility of photogenerated (2.1eV) free carriers in three types of a-Si having widely different densities of structural defects (i.e., as prepared by: (1) rf glow discharge (a-Si:H), (2) chemical vapor deposition, and (3) evaporation in ultra-high vacuum). In all three types of a-Si, we find the same initial mobility of approximately 1 cm('2)/Vs at room temperature. This result tends to confirm the often-made suggestion that the free carrier mobility is determined by the influence of shallow states associated with the disorder in the random atomic network, and is an intrinsic property of a-Si which is unaffected by the method of preparation. The rate of decay of the photocurrent correlates with the density of structural defects and varies from 4ps to 200ps for the three types of a-Si investigated. The initial mobility of a-Si:H was found to be thermally activated with an activation energy of approximately 58 meV and a preexponential factor of 8 cm('2)/Vs consistent with theoretical estimates of the free carrier mobility above the mobility edge. We discuss the possible application of extended state transport controlled by multiple trapping and small polaron formation.
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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
