Employing Monte Carlo techniques, the diffusion and drift of charge carriers within an array of hopping states subject to a Gaussian distribution of site energies of width σ has been studied as a function of σ/kT and electric field. With increasing disorder and field, significant deviations from Einstein’s law are noted. They are shown to be the consequence of anomalous, field-assisted diffusion while the mobility remains constant. The effect can account for anomalous transit-time dispersion observed in polymeric photoconductors exhibiting time independent transport.

• Received 17 November 1988

DOI:https://doi.org/10.1103/PhysRevLett.63.547