1999 Fiscal Year Final Research Report Summary
Theoretical Study of Bond-Fluctuation in Amorphous Semiconductors
| Project/Area Number |
10640311
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体物性Ⅰ(光物性・半導体・誘電体)
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| Research Institution | Wakayama University (1999)
Yamaguchi University (1998) |
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Principal Investigator |
SHINOZUKA Yuzo Wakayama University, Faculty of Systems Engineering, Professor, システム工学部, 教授 (30144918)
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| Project Period (FY) |
1998 – 1999
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| Keywords | amorphous semiconductor / structural randomness / metastable structure / s-p hybridization / optical absorption / Urbach rule / gap state / selection rule |
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| Research Abstract |
The electronic structure and optical properties of covalent amorphous semiconductors are theoretically studied with special attention to the s-p hybridization in electronic states and the spatial correlation in their mixing. One-dimensional tight binding model is used in which the inter-atomic transfer energy of an electron between nearest neighbor atoms depends linearly on their inter-atomic distance. All the electronic states are numerically calculated for a 150-atom system and the ensemble average is taken over 10 samples. Following results have been obtained.
(1)As the degree of randomness increase, the degree of hybridization decreases and rearrangements in the covalent bonds take place.
(2)The width of the band gap decreases but the gap remains rather long compared to a case where the spatial correlation is neglected.
(3)There appears a characteristic peak in the optical absorption spectrum, which reflects central peaks in the partial (s- or p-) density of states in the valence and conduction bands and is related to an electron localization caused by the spatial correlation.
Since we have used the one-dimensional model, the van Hove singularity appears remarkably at the band edges, and then we cannot directly compare the results with experiments on the absorption spectrum. However, rearrangements of the hybridization and the covalent bond are expected to take place also in three-dimension. This would be important in connection with the stability of so-called weak bond and dangling bond and their metamorphosis. Self-consistent calculations for the distribution of the interatomic distance and the local covalent bond in three-dimensional system are under progress in order to explain a universal value for the steepness parameter of the Urbach tails the absorption spectrum in various amorphous semiconductors.
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