CPM AND SPECTRAL PHOTOCONDUCTIVITY TECHNIQUES - A CRITICAL ANALYSIS OF THE EXPERIMENTAL RESULTS

The sub-bandgap absorption in intrinsic a-Si:H films has been measured by the constant photocurrent method (CPM) in DC and AC conditions, an d by spectral photoconductivity (SPC) techniques. CPM measurements hav e been performed at different constant values of the photocurrent in o rder to investigate its effect on the spectra. Finally, experimental r esults have been compared with a model of sub-bandgap absorption relyi ng on the hypothesis that a distribution of charged states is present above the valence band.