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Electronic States in the Gap of a-Si from Bond Angle Variations

Published online by Cambridge University Press:  25 February 2011

B. N. Davidson  and
G. Lucovsky
B. N. Davidson
Affiliation:
Dept. of Physics, NC State University, Raleigh, NC 27695–8202
G. Lucovsky
Affiliation:
Dept. of Physics, NC State University, Raleigh, NC 27695–8202
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Abstract

We investigate the formation of defect states in the gap of a-Si arising from deviations from the ideal tetrahedral bond angles. The local density of states for Si atoms in disordered environments is calculated using tight-binding parameters for the cluster-Bethe lattice method. The Hamiltonian for a-Si with bond angle distortions is taken as an average over many configurations associated with a random choice of bond angles, weighted by Gaussian distributions with standard deviations between 2°.and 10°. Bond angle deviations in this range generate a density of defect states at the valence band edge that: 1) increases as the average bond angle deviation increases; and 2) is significantly larger than the density of band tail states generated at the conduction band edge. We obtain a shift of the absorption edge from the joint density of states (DOS) as a function of bond angle deviations. In addition, a calculation of the DOS for a distorted tetrahedral cluster embedded in an idealized Bethe lattice yields a threshold bond angle distortion of ±20° for the appearance of a discrete state in the gap near the valence band edge.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 192: Symposium O – Amorphous Silicon Technology - 1990 , 1990 , 279
Copyright
Copyright © Materials Research Society 1990

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References

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