Surface and Bulk GAP States Distributions in Amorphous Silicon Films as Obtained by Optical Methods

Abstract

ABSTRACTThe aim of this work is to achieve detailed information about surface and bulk density of states in device quality a-Si:H films by means of deconvolution of PDS spectra. Unambiguous deconvolution of the spectra has been performed by calculating the first derivative vs. energy of the absorption coefficient of the samples. The results are compared with those obtained by means of the integration rule. Calculations of the density of states carried out on samples having different thickness suggest that the defect distribution differs from surface to bulk. The surface defect peaks are found to lie closer to the corresponding mobility edges, with respect to the bulk defect peaks: these results agree well with those obtained by means of other techniques, like total yield spectroscopy and can be explained in terms of a defect pool model.The present deconvolution procedure when applied to samples having different thickness provides new results about the film's homogeneity in terms of deep defect and valence tail states.