Origin of the low-temperature drift mobility increase in a-Si: H

Abstract

The low-temperature rise in drift mobility in a-Si: H is interpreted in terms of a hopping model. The model predicts a critical temperature above which the transport level is pinned at the conduction band edge giving an activated behaviour of the drift mobility and below which the transport level falls in the gap leading to non-dispersive transport. It also predicts the rise of the drift mobility below the critical temperature when the transport level falls faster than k _b T.

In conclusion, we have shown that (1) hopping can account for the observed low-temperature drift-mobility behaviour if one properly takes into account the position of the dominant transport level and if one applies the calculations to a density of states with a sharp drop, and that (2) the mobility rise is the result of the fast decrease of the hopping activation energy that accompanies the lowering of the temperature.