Transient Photoconductivity from the Steady State in Undoped Amorphous Silicon

In this study, experimental results of transient photoconductivity decay from the steady state in undoped amorphous silicon are presented. The results are explained within the framework of a theory of multiple trapping. It is found that the occupation function of electrons into the gap behaves as a quasi-Fermi distribution whose quasi-Fermi level moves from its steady-state position to the middle of the gap as time progresses. The rate equation for the free carrier density is numerically solved and compared with the experimental results. A good fit is obtained if one assumes the existence of a peak in the density of states.