A model of weak-field quasi-equilibrium hopping transport in disordered materials

An analytical treatment of quasi-equilibrium carrier transport in disordered materials at moderate electric fields is presented. The transport equation derived has the form of a conventional Fokker-Plank equation with drift, diffusion and field-assisted diffusion terms. General formulae are obtained for drift mobility as well as for the coefficients of conventional and field-assisted diffusion. The temperature dependences of these quantities are considered for different energy distributions of localized states.