Charged and neutral defect states in a-Si:H determined from improved analysis of the constant photocurrent method

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. 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 we compare simulated and measured spectra. In the annealed state the defect absorption of undoped, n- and p-type a-Si:H is dominated by a charged defect states. In undoped material the defect density increases upon light soaking but the charged-to-neutral defect ratio does not change