Evidence for the Mott Model of Hopping Conduction in the Anneal Stable State of Amorphous Silicon

The temperature dependence of the dc conductivity and the room-temperature optical absorption were measured for a series of vacuum-evaporated amorphous Si films. Both properties were strongly dependent on annealing up to about 400°C, but insensitive from 400 to 600°C. We find a $\ln \left(\sigma \sqrt{T}\right)\propto T^{\frac{-1\mathrm{}}{4}}$ behavior which gives reasonable parameters for Mott's localized-state model for conductivity by hopping only for films that have been annealed at least to 400°C.