PREPARATION AND CHARACTERIZATION OF HYDROGENATED AMORPHOUS CARBON FILMS: ELECTRICAL AND OPTICAL PROPERTIES.
Item
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Title
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PREPARATION AND CHARACTERIZATION OF HYDROGENATED AMORPHOUS CARBON FILMS: ELECTRICAL AND OPTICAL PROPERTIES.
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Identifier
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AAI8112760
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identifier
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8112760
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Creator
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MEYERSON, BERNARD STEELE.
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Contributor
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Frederick W. Smith
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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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There is considerable interest at present in the development of novel semiconducting materials, with the goal of establishing their potential usuefulness in future device applications. Toward this end, a study has been undertaken to determine the properties of a material not widely regarded as interesting in terms of its properties as a semiconductor, ie. carbon in the form of thin amorphous films.;Semiconducting films of hydrogenated amorphous carbon(a-C:H) were prepared via the dc glow discharge of acetylene, at deposition temperatures T(,d) between 25 and 375C. The optical absorption (1.65 to 3.6eV) and electrical conductivity (25 to 350C) were measured. The electrical conductivity was not simply activated for samples with T(,d) < 300C, and varied by over 10 orders of magnitude as a function of T(,d). Optical energy gaps inferred from optical absorption data lay between 0.9 and 2.1 eV, decreasing with increasing T(,d). It has also been deduced from these measurements that these a-C:H films will be graphitic in their electrical and optical properties for T(,d) (GREATERTHEQ) 425C.;Doped a-C:H films prepared via the incorporation of diborane or phosphine gas into the discharge have been studied. For a-C:H films deposited at T(,d) = 250C, room temperature conductivity increased from 10('-12) to 10('-7) ohm('-1)-cm('-1) when either 1% phosphine or 10% diborane was added to the discharge gas. A shift of the Fermi level E(,F) of about 0.7 eV was inferred from changes in the activation energy of conduction. The doping efficiency achieved here was comparable to that obtained in a-Si:H films produced in a like manner. Further verification of doping was obtained from measurements of the thermopower S performed on heavily doped samples ((TURN)1% dopant) prepared at T(,d) = 325C. S was found to be positive for B doped samples, and negative for P doped samples. The magnitude of S, (TURN)30uV/K, was indicative of a hopping transport mechanism, and such an interpretation is discussed in light of the result that S was found to be a nearly linearly increasing function of T (300 < T < 550K) for these samples.;As a result of the properties displayed by the a-C:H films studied here, one may arrive at the conclusion that this material holds promise for eventual use in the field of device technology.
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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
