Relaxation of non-equilibrium charge carriers in the hopping regime

dWe discuss a kinetic model for glass-like relaxation processes in a strongly localized electron system. In our hopping model we assume that the charge carriers can exchange maximally an amount omega of energy in one hop. The investigation of the system shows that the energy scale omega discriminates between two different relaxation modes. If the thermal energy is large compared to omega the relaxation is percolation like. In this regime the relaxation is determined by the same paths as the close-to-equilibrium conductivity in a transport problem. If the thermal energy is small compared to omega then the relaxation becomes Miller-Abraham like. In this relaxation mode the charge carriers always jump to the next closest site. The differences between these transport regimes manifest themselves in the typical time scales governing the relaxation and in the structure of the transport coefficients. To discuss them we focus on energy relaxation processes. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.