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

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 x 10(5) 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 multilayer 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.