A COMPARISON OF COHERENT POTENTIAL AND RANDOM WALK METHODS FOR CALCULATING THE TRANSPORT PROPERTIES OF AMORPHOUS SEMICONDUCTORS

Abstract

The motion of particles between discrete localised states is studied in terms of two types of approximation to the solution of the appropriate rate equations. The first of these involves an extension of the decoupling of configurational averages from which the usual continuous time random walk (CTRW) approximation can be derived to define a CTRW(n) approximation. The other approach, which is presented in some detail, is based on a modification of the homomorphic cluster extension of the coherent potential approximation (HCCPA). A comparison of the results of these methods for the diffusion coefficient in some model systems indicates that all these methods give the same results at high frequencies. At intermediate frequencies the results of the CTRW(2) method are much closer than those of the CTRW(l) method to those of the HCCPA, but at low frequencies the results of both these CTRW methods differ appreciably from those of the HCCPA method