THEORETICAL-STUDIES OF THE LOW-TEMPERATURE DRIFT MOBILITY IN A-SI-H

The drift mobility in a-Si:H observed by Spear and co-workers shows the unexpected feature that the rather high drift mobility at very low temperatures disappears at about 80 K. At about 100 K it rises again steeply from a very low value. A hopping model has been proposed by Spear et al. to explain these findings. In this study we investigate this model in detail and find in fact a rather high mobility at low temperatures, which however, increases monotonically with increasing temperature. We also investigate a multiple-trapping model which as an additional feature has a very narrow band of hopping states on the low-energy side of an exponential tail. This model qualitatively reproduces the behaviour of the drift mobility as found by Spear et al.