A model of anomalous charge-transport behaviour in amorphous materials

Abstract

The model proposed deals with carrier transport controlled by a system of localized levels distributed within a sufficiently wide energy interval in the gap of a semiconductor. Carrier transitions between the localized levels are assumed to play a principal role in the transport behaviour. An injected carrier, captured by the localized level nearest a band of transport states, subsequently makes transitions from one level to another. A succession of such transitions presents a random walk of carriers along the energy axis. During this walk a carrier can sometimes be released to the band of transport states, where it drifts for a short time before the next trapping event. This process is shown to cause the anomalous transit-time dispersion. Finally, we use the above model to analyse the ‘anomalous diffusion’.