Mobility field dependence in a-Ge:H, a-SiGe:H, compensated a-Si: H, amorphous multilayer Si/SiGe/Si and the long-range potential fluctuation model

Abstract

The electric field dependence of the mobility is surveyed by time-of-flight (TOF) experiments on a-Ge: H, a-SiGe: H, compensated a-Si: H, and amorphous multilayer Si/SiGe/Si specimens. For all samples, the mobility was found to have very weak field enhancement by the electric field, less than 60% at 2 × 10⁵ V cm⁻¹. This result is inconsistent with predictions of a long-range potential fluctuation (LRPF) model and questions the validity of the LRPF model in explaining the low mobility in these materials. The rnultilayer specimens are constructed with an a-SiGe: H layer (layers) embedded in an a-Si:H matrix in order to create band edge fluctuations. The multilayer structure is confirmed by a Rutherford backscattering (RBS) experiment. TOF measurements on these samples reveal no change in electron and hole mobilities and the mobility activation energy from that of undoped a-Si: H. This result indicates that the carrier transport behaviour in the presence of long range potential fluctuations may not fit the current LRPF model.