An alternative degradation method for amorphous hydrogenated silicon: The constant degradation method

To study the kinetics of metastable defect creation in amorphous hydrogenated silicon we introduce the Constant Degradation Method as a new experimental scheme. In contrast to conventional degradation experiments in which the incident light intensity is constant during light soaking, in this method the photoconductivity of the sample is kept constant by continuously increasing the light intensity. In this case a linear time dependence of the required light intensity and of the resulting defect density is observed experimentally. A detailed analysis of the method shows that the data obtained are in accordance with the assumption of the bond-breaking" model, i.e., the metastable defects are created by bimolecular recombination of localized electron-hole pairs. The observed time dependence is at variance with the stretched exponential time dependence predicted for dispersive transport models. Effects of sample heating due to high light intensities and of Fermi level shifts on the observed time dependence are also discussed.