Determination of the density of states of semiconductors from steady-state photoconductivity measurements

We discuss a method to obtain the density of states of photoconductive semiconductors from the light-intensity-dependence of the steady-state photoconductivity. Considering a material having different species of gap states – i.e., with different capture coefficients – we deduce a simple expression relating the defect density to measurable quantities. We show that the relevant capture coefficient appearing into the formula is that of the states that control the recombination. We check the validity of the approximations and the applicability of the final expression from numerical calculations. We demonstrate the usefulness of the method by performing measurements on a standard hydrogenated amorphous silicon sample.