The nature of the defect states above midgap and their role in the light-induced metastability of a-Si:H

Defect states of a-Si:H above midgap, with which the electrons interact through trapping and thermal release and make an important contribution to the imaginary (Y) term of the modulated photocurrent, are determined. Analysis of the ‘transition’ region between the low- and high-frequency regimes enables the densities and capture coefficients of defect states to be probed. A reasonable fit to the data is obtained by assuming three defect states, and it is suggested that the defects with the higher capture probability are hydrogen-related centers that are removed during the initial stage of light degradation.