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

Abstract

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\ifmmode^\circ\else\textdegree\fi{}C, but insensitive from 400 to 600\ifmmode^\circ\else\textdegree\fi{}C. We find a $\mathrm{ln}(\ensuremath{\sigma}\sqrt{T})\ensuremath{\propto}{T}^{\frac{\ensuremath{-}1}{4}}$ 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\ifmmode^\circ\else\textdegree\fi{}C.