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Electronic Structure of Divalent Defects in Tetrahedrally Bonded Amorphous Materials

Published online by Cambridge University Press:  28 February 2011

S. Y. Lin ,
G. Lucovsky ,
S. Guha  and
J. S. Payson
S. Y. Lin
Affiliation:
Department of Physics, N.C. State University, Raleigh N.C. 27965-8202
G. Lucovsky
Affiliation:
Department of Physics, N.C. State University, Raleigh N.C. 27965-8202
S. Guha
Affiliation:
Energy Conversion Devices, Inc., Troy, ML 48084
J. S. Payson
Affiliation:
Department of Physics, N.C. State University, Raleigh N.C. 27965-8202
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Abstract

This paper describes a calculation of twofold-coordinated (or divalent) intrinsic bonding defects in a-SiSn:H alloy films. The motivation for this study comes from experimental studies of the electronic and optical properties of a- Si, Sn:H alloys which indicate dramatic changes in the electronic and photoelectronic properties for small concentrations of Sn (approximately 1–2 at. %). We have used a cluster Bethe lattice structural model and an empirical tight-binding Hamiltonian to investigate the electronic properties of tetrahedrally bonded Sn atoms and neutral Sn defect centers (T2o and T3o) and in an a-Si host. We find that: (C) fourfoldcoordinated Sn atoms simply promote a reduction in the optical bandgap, with the energy gap disappearing for Sn concentrations of about 20 to 30 at. %; (2) neutral dangling bonds (T2o) or threefold-coordinated Sn atoms generate a localized state in the gap that is iower in energy than the corresponding neutral Si atom dangling bond; and (3) divalent (T2o) or twofold-coordinated Sn atoms give rise to two states in the gap, an occupied state that is lower in energy that either the Sn or Si dangling bond, and an empty state that is just below the conduction band edge. We show that the electronic and optical properties of the a-SiSn:H alloys can be understood in terms of a model in which there are relatively high densities of unhydrogenated Sn divalent sites and/or Sn dangling bonds.

Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 70: Symposium E – Materials Issues in Amorphous-Semiconductor Technology , 1986 , 107
Copyright
Copyright © Materials Research Society 1986

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References

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