ABSTRACT
In the disorder formalism, the field dependence of the mobility arises from the fact that a carrier can reach more acceptor or donor sites without thermal activation in the presence of a field than it can in the absence of a field. At high fields, a carrier will gain energy eEp upon jumping from site i to site j separated by an intersite distance p. Therefore the carrier will be able to reach site j at energy €j ^ + eEa without activation, while only site e^ e j would be accessible without activation. This is equivalent to a reduction in width of the hopping site manifold by an amount BeEp, where B is a factor that represents the fraction of hopping sites whose energies are reduced by the field. The reduction in width of the manifold then results in an increase of the mobility. A first order analysis (Bassler, 1984) gives
and K = T0/ct. From Griinewald et al. (1984), K = 7400 K/eV. The basic assumptions involved in Eqs. (7) to (10) are that the self-energies of adjacent sites are uncorrelated and that the jump rates can be described by the Miller-Abrahams (1960) formalism, originally derived to describe low temperature impurity hop ping in semiconductors. A further assumption is that the Boltzmann jump prob ability, exp[—(€j - e^/kT], is unity for e j < € , Downward jumps in energy are assumed not to be impeded by an energy matching condition for dissipating the difference in energy. Finally, it is assumed that polaronic effects can be neglected.
