Light-induced metastable defect formation and annealing kinetics in a-Si:H

We have investigated the kinetics of creation and annealing of light-induced metastable defects and their effect on photocarrier lifetime in two good quality, hydrogenated amorphous silicon samples using the constant photocurrent method (CPM) and steady state photoconductivity measurements at room temperature. Narrow distributions of annealing activation energies that peaked at about 1 eV, account for the annealing of created metastable defects for both samples. A hysteresis-like relation is observed between light-induced defect density and photoconductivity. This relationship is different for the two samples investigated and also depends on light intensity used for degradation. Calculated distributions of annealing activation energies do not provide additional information in the explanation of the observed differences in the hysteresis-like relationship between the samples. Comparing the deduced annealing activation energies distributions with the one obtained by Zhang et al. [Mater. Res. Soc. Symp. Proc. 336 (1994) 269] we have come to the conclusion that, more stable light-induced defects are created at longer illumination times or at higher light intensities, shifting the peak value of distribution of annealing activation energies from about 1 to 1.1 eV.