CHARGED AND NEUTRAL DEFECT STATES IN A-SI-H DETERMINED FROM IMPROVED ANALYSIS OF THE CONSTANT PHOTOCURRENT METHOD

In order to obtain information about the density of localized gap stat es in a-Si:H, i.e., the valence band tail, the integrated defect densi ty, the energetic defect distribution and the charge state of the defe ct states, a numerical model has been developed to simulate constant p hotocurrent method spectra. It takes into account the full set of opti cal transitions between localized and extended states under sub-bandga p 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 sta te 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.