RECOMBINATION IN DISORDERED SOLIDS

Abstract
The main point of this article is to present a simple physical picture of the recombination process of a carrier hopping in a disordered solid in the presence of molecular recombination centers (rc). First, an exact (asymptotic) calculation of the entire time dependence of the transient photocurrent (TP) and the number of surviving carriers n(t) is carried out for a suitable model system. It is shown that the t^-(1-α) → t^-(1+α) transition does exist in the TP however the transition occurs in over two decades in time (for α=0.5). Further, the time t_r corresponding to the intersection of the two slopes in the log(TP)-log(t) plot is the same as the median time for the n(t) decay. The t_r is next shown to have an alternate simple interpretation. In the low rc concentration limit, t_r is determined from a calculation of the number of distinct sites visited by the hopping carrier, as a function of time (t) and electric field (E). The results are compared to recent measurements in a-Si : H.