HOPPING IN EXPONENTIAL BANDTAILS IN HIGH ELECTRIC-FIELDS AND TRANSPORT MODELS IN AMORPHOUS-SILICON

A calculation of electrical transport during the thermalization of exc ess carrier hopping between states of an exponential bandtail is prese nted. The calculation is based on a typical rate approximation. For sm all electric fields the calculation reproduces multiple-trapping dispe rsion, in agreement with prior research. For high electric fields elec trical transport becomes nonlinear, primarily due to an electric-field -induced increase in the dispersion parameter. The calculation should be contrasted to recent work of Esipov which extended bandtail multipl e-trapping to incorporate tunnelling to a transport edge; in his calcu lation nonlinear transport set in without changes in the dispersion. W e suggest that these results discriminate between hopping and mobility -edge models for electron thermalization measurements in a-Si: H.