Temperature dependence of the electron drift mobility in doped and undoped amorphous silicon

Abstract

We have measured the temperature dependence of the drift mobility of electrons in undoped and phosphorus-doped amorphous-silicon samples by the time-of-flight technique between 300 and 30 K. The drift mobility is nondispersive and thermally activated for both doped and undoped samples up to 200 K. Below 200 K the drift mobility becomes dispersive and, below 140 K, it becomes too small to be measured and remains so down to 30 K. In particular, we do not see the upturn in drift mobility below 100 K as observed by Cloude et al. [Philos. Mag. B 54, L113 (1986)]. This suggests that the low-temperature transport is critically dependent on details of the distribution of states in the band tails.