Light-intensity dependence of the steady-state photoconductivity used to estimate the density of states in the gap of intrinsic semiconductors

We present a method to obtain the density of states of photoconductive semiconductors based on the light-intensity dependence of the steady-state photoconductivity. A simple expression-relating the density of states at the electron quasi-Fermi level to measurable quantities-is deduced by performing suitable approximations from the analytical solution of the generalized equations that describe the photoconductivity of semiconductors. The validity of the approximations and the applicability of the final expression are verified from numerical simulations of the process. The usefulness of the method is demonstrated by performing measurements on a standard hydrogenated amorphous silicon sample. (c) 2005 Elsevier B.V. All rights reserved.