Link between enhanced carrier mobilities and DOS profiles in a-Si:H

Abstract

High carrier mobilities have been reported in a-Si:H samples prepared at high deposition rate and high substrate temperature in an expanding thermal plasma (ETP). Those mobilities were found to be field independent, and subsequent analysis showed that tail-state distributions with a steeper than exponential decrease are required to account for this field independence. Such steeper profile implies an increased ratio of shallow to deep states and, given that the shallow states dominate the carrier mobility, this fact might explain the observed enhanced mobility. Through the use of analytical expressions for the time-of-flight transients, the circumstances whereby the high, field-independent mobility can be achieved are explored. It is found that a prominent feature close to the mobility edge is required to account for the observations.