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Defect Thermodynamics, Inhomogeneity, and the Density of Gap States in Hydrogenated Amorphous Silicon

Published online by Cambridge University Press:  25 February 2011

Howard M. Branz  and
Marvin Silver
Howard M. Branz
Affiliation:
Solar Energy Research Institute, 1617 Cole Boulevard, Golden, CO 80401
Marvin Silver
Affiliation:
Dept. of Physics, Univ. of N. Carolina, Chapel Hill, NC 27599
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Abstract

A new hydrogenated amorphous silicon (a-Si:H) density of states (d.O.s.) in+cluding the transition levels of both neutral (T3o) and charged (T3+ and T3−) dangling-bond defects is proposed. We derive closed-form and numerical solutions for the d.o.s. from a thermodynamic equilibrium theory of defect concentrations in which material inhomogeneity is assumed to give rise to ∼1020 cm−3 of electrostatic potential fluctuations. The connection between thermodynamic transition level energy and defect formation energy implicit in this and other “defect pool” models is included explicitly in the calculation. We calculate the d.o.s. for a range of parameters and for different values of Fermi energy. We apply the calculated d.o.s. to explain and unify various experimental results in a-Si:H. In particular, we reconcile recent depletion-width-modulated ESR data with the near-perfect Curie law T-dependence of the dangling-bond spin density observed by several groups. It is seen +that the depletion results in roughly equal numbers of T3−T3–>° and T3°–>T3+ transitions despite the positive value of effective correlation energy. We also discuss possible sources of the short-to-medium range potential fluctuations in amorphous silicon.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 192: Symposium O – Amorphous Silicon Technology - 1990 , 1990 , 261
Copyright
Copyright © Materials Research Society 1990

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