Comparison of the Properties of Sputtered and Glow Discharge a-Ge:H Films

Abstract

ABSTRACTUndoped a-Ge:H films have been made both by sputtering and by glow discharge under various combinations of deposition parameters, and characterized structurally, electrically, and optically. A detailed comparison of subband gap spectra of sputtered and glow discharge samples has been carried out using photothermal deflection spectroscopy and the constant photocurrent method. The results show subband gap absorption in a-Ge:H to be an order of magnitude larger than in device-quality a-Si:H. For some of the films the absorption spectra deduced from transmission and PDS fit very well onto the absorption spectra inferred from CPM measurements, while for others it is clear that the match is very poor. We infer that the photoconductivity-derived spectrum does not necessarily reflect the dominant absorption process, and that this is related to the existence of a two-phase structure clearly observed by transmission and scanning electron microscopy.