PUB - Publikationen an der Universität Bielefeld

In order to obtain information about the density of localized gap states in a-Si:H, i.e., the valence band tail, the integrated defect density, the energetic defect distribution and the charge state of the defect states, a numerical model has been developed to simulate constant photocurrent method spectra. It takes into account the full set of optical transitions between localized and extended states under sub-bandgap illumination, capture, emission and recombination processes as well as the energetic position of the Fermi level. We compare measured and simulated CPM spectra of doped and undoped a-Si:H. In the annealed state the defect absorption of n- and p-type as well as undoped a-Si:H is dominated by a charged defect states. The simulation reveals that in undoped a-Si:H light soaking, causing an enhanced defect density, does not alter the charged-to-neutral defect ratio.