ELECTROTRANSPORT IN IONIC-CRYSTALS .2. A DYNAMICAL MODEL

A microscopic model of electrotransport in semiconducting ionic crystals is described, which is based on electrostatically interacting hopping charge carriers (cation vacancies and electron holes). Formulating rate equations for the thermally activated motion of electronic and ionic defects in external fields allows for the calculation of stationary charge distributions. In the case of large differences in the mobilities of both defects an adiabatic approximation can be introduced which allows to separate the motion of electron holes and vacancies. The formal problem is identical to the solution of the Poisson-Boltzmann equation for large defect concentrations. An expression for the charge of transport is derived which is equivalent to the Debye-Huckel expression for the relaxation effect but includes distinct geometrical positions around a central point charge.