Density of localized states in low-mobility materials: A numerical study

Abstract

We describe a procedure for extracting the density of localized states in the gap of low-mobility materials from transient photocurrent measurements. We base our analysis on the multiple-trapping transport model, and present a deconvolution scheme which determines, for each discrete trap level, a set of time-temperature combinations which optimizes the information that can be extracted for this level. The density of states is then obtained from the currents using a numerical technique suitable for overdetermined linear systems. We apply our procedure to signals generated on the computer using, as a starting point, an exponential band tail, appropriate to amorphous semiconductors, as well as a delta-like distribution, either singly or doubly peaked, appropriate to doped crystalline systems. The deconvoluted distributions of states are in all cases found to be in excellent agreement with the original ones. We indicate how our method could be extended to the analysis of real data, currently not available in the time-temperature regime appropriate to our procedure.