Optical properties and local atomic bonding in hydrogenated amorphous silicon-carbon alloy films.
Item
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Title
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Optical properties and local atomic bonding in hydrogenated amorphous silicon-carbon alloy films.
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Identifier
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AAI9000014
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identifier
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9000014
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Creator
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Basa, Deepak Kumar.
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Contributor
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Adviser: Frederick W. Smith
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Date
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1989
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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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Thin films of a-Si{dollar}\sb{lcub}\rm 1-x{rcub}{dollar}C{dollar}\sb{lcub}\rm x{rcub}{dollar}:H alloys have been prepared via the rf glow discharge of acetylene and silane and ethylene and silane. The optical constants, optical bandgap E{dollar}\sb{lcub}\rm opt{rcub}{dollar} and the infrared absorption have been determined as functions of composition and annealing temperature in order to understand the effect of the local silicon, carbon, and hydrogen bonding configurations on the optical properties of these alloy films.;The films in this alloy series are proposed to be macroscopically homogeneous, while having a heterogeneous microstructure. A microstructural model, based on four components: amorphous polymeric, amorphous graphitic, amorphous tetrahedral and void, is proposed to model the optical response of these films. This microstructural model gives a good description of the observed dependences of {dollar}\epsilon\sb1{dollar} and {dollar}\epsilon\sb2{dollar} on composition and provides a convincing demonstration that appearance of the amorphous graphitic component in the films limits the attainable value of E{dollar}\sb{lcub}\rm opt{rcub}{dollar} in this alloy series as the carbon content increases. In addition, the model provides strong evidence that complete chemical ordering with homogeneous dispersion exists within the amorphous tetrahedral component across the entire alloy series. Thus we have provided for the first time a new experimental approach to the issue of chemical ordering and have asserted that the optical constants measurements have the potential to be a sensitive probe of film microstructure and of chemical ordering.;The annealing study of these films has enabled us to understand the changes in the local bonding and the structural changes in the network leading to crystallization. It has been established that there is a change from amorphous to microcrystalline and then to crystalline phase with increase in the annealing temperature. In addition this study enables us to resolve conclusively the controversy regarding the assignment of various IR modes of a-Si{dollar}\sb{lcub}\rm 1-x{rcub}{dollar}C{dollar}\sb{lcub}\rm x{rcub}{dollar}:H films.;It is also observed that the optical band gap E{dollar}\sb{lcub}\rm opt{rcub}{dollar} correlates well with the hydrogen concentration. Further, it is established that E{dollar}\sb{lcub}\rm opt{rcub}{dollar} is controlled by the amount of disorder and that the hydrogen affects E{dollar}\sb{lcub}\rm opt{rcub}{dollar} indirectly through its effect on disorder.
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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.
