The interpretation of drift mobility experiments on amorphous silicon

Abstract

A simple analysis is given of the charge displacements expected in a drift mobility experiment from (a) the carrier generation and (b) the subsequent drift of the excess carriers across the specimen. It is then shown that the features of the observed pulses in experiments on a-Si are in quantitative agreement with the predicted behaviour and show a clear transition between events (a) and (b). On the basis of these and of other results it is concluded that, under our experimental conditions, the main component of the observed displacement is associated with the transit of excess electrons, leading to an extended state mobility of about 10cm² V⁻¹ s⁻¹. These conclusions disagree with the recent work of Silver and coworkers and throw considerable doubt on their estimated mobility of 10³cm² V⁻¹ s⁻¹ for a-Si.