TRANSIENT PHOTOCURRENT TECHNIQUES AS A MEANS OF CHARACTERISING AMORPHOUS SEMICONDUCTORS

We describe techniques to study electronic transport and localized state distributions in amorphous semiconductors from their photocurrent response to steady and impulse excitation. The response to impulse excitation contains information on distributions of trapping and release times for localized states in the mobility gap of the material; the problem is to determine a unique density of states (DOS) from such data. One technique is applicable to cases in which both trapping and release processes are significant. A second ‘post-transit’ analysis is restricted to situations where only carrier release processes are significant. In both cases we derive analytical DOS spectroscopies capable of fine energy resolution. We also report on studies of transport and DOS distributions, in thin films of several representative chalcogenides, including recent studies of surface defect states in CdSe nanocrystals in SiOx matrix. We also report on interpretation of steady state and transient measurements on thin film amorphous As2Se3