LOW-TEMPERATURE TRANSPORT AND RECOMBINATION IN A-SI-H

The d.c. photoconductivity σph and the photoluminescence intensity Ipl of a-Si:H have been studied concomitantly as a function of temperature (10-100 K) and electric fields (up to 2x 105 Vcm-1). The defect density Nd was varied by electron bombardment and subsequent annealing in the range 3xl015-5 x 1017 cm-3. The results cannot be explained in a geminate-pair model. The general behaviour suggests that the strongly superohmic I-Vcharacteristics are not caused by the field-dependent generation of free carriers but by a field dependence of the transport itself. It is argued that the photocurrent arises predominantly from carrier displacement during the thermalization by hopping in the band-tail states. © 1990 Taylor & Francis Ltd.