Abstract
Localized carriers can contribute to charge transport in a weak electric 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 corresponds to their dissociation. We propose a phenomenological model which describes this transition. This model is based on the assumption that charged classical particles, which are localized in a potential well, can be thermally excited by phonons, and dissipate their acquired kinetic energy. Taking the particles' inertia into account we find a decrease in the strength of the above-mentioned transition field and a hysteresis in the current-voltage relation for certain parameter ranges.
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