MOTION OF LOCALIZED CARRIERS IN A STRONG ELECTRIC-FIELD

Localized carriers can contribute to charge transport in a weak electr ic field through thermally activated hopping. If the electric field is sufficiently strong, the potential barrier vanishes and the transport acquires band-like character. In the case of small polarons this corr esponds to their dissociation. We propose a phenomenological model whi ch describes this transition. This model is based on the assumption th at charged classical particles, which are localized in a potential wel l, can be thermally excited by phonons, and dissipate their acquired k inetic energy. Taking the particles' inertia into account we find a de crease in the strength of the above-mentioned transition field and a h ysteresis in the current-voltage relation for certain parameter ranges .