Deviation from the Einstein relation: mobility of unrelaxed carriers

The relation between the drift mobility and the diffusion coefficient of ch arge carriers in one-dimensional systems with energy disorder is investigat ed. By using the effective medium approximation, we derived expressions for these transport coefficients. The analytical results verified by computer simulations demonstrate that the Einstein relation is invalid during the en ergy relaxation of the charge carriers. Our findings suggest that under typ ical experimental conditions, the time-of-flight mobility of charge carrier s is independent of the field strength and decreases with the sample thickn ess according to the power law. (C) 1999 Elsevier Science B.V. All rights r eserved.