Hole drift mobility in amorphous silicon

Abstract

The drift mobility of holes has been measured as a function of temperature for a series of both undoped and doped a-Si films, prepared by the glow-discharge technique. The doped specimens were compensated by incorporating both phosphorus and boron impurities. The room-temperature hole drift mobility is about 10⁻⁴ cm² s⁻¹ V⁻¹ with an activation energy of about 0.43 eV, in general agreement with the work of Moore (1977). The mobility does not depend on acceptor concentration, so that hopping through acceptor states can be excluded. In the light of the known density-of-states distribution for a-Si, it is suggested that a trap-controlled band transport mechanism is the most likely interpretation of the data. Both dispersive and non-dispersive current pulses have been observed. Even the most dispersive transits show an essentially linear dependence of the inverse transit time on the applied potential, in disagreement with the theoretical predictions of Scher and Montroll (1975), but making it possible to define a drift mobility.