MODULATED PHOTOCURRENT SPECTROSCOPY OF DEFECT STATES IN UNDOPED A-SI-H

The modulated photocurrent spectroscopy results obtained for intrinsic , undoped a-Si:H are described. The measured midgap density of states consists of broad bands of neutral and charged defect states, between which there is orders of magnitude difference in carrier capture effic iency. Amplitude of the neutral defect band is considerably larger tha n that of the charged defect band, in both thermally annealed and ligh t soaked states. Implications of these experimental findings are discu ssed in connection with the model of defect structure based on the def ect pool concept.