Investigation of charge carrier lifetime in high-resistivity semiconductor layers by the method of small charge photocurrent

A method of determination of charge carrier lifetime from experimental data of small charge current transient under constant electric field strength is discussed. On the basis of experimental results on transient of small charge photocurrent of holes and electrons which were obtained at different electric field strengths, an analysis of charge carrier lifetimes in a-Se layer has been performed. For interpretation of experimental results the approximation, according to which photogenerated electrons or holes can be trapped in levels of three types, has been used. We found that the process of localized charge carrier release is influenced by the electric field strength and that in a-Se layer, in the vicinity of the substrate, there is a narrow region where the density of localized states exceeds its mean in a layer.