Effect of embedded microcrystallites on the light-induced degradation of hydrogenated amorphous silicon

We have studied the degradation kinetics of undoped hydrogenated amorphous silicon $(a-\mathrm{S}\mathrm{i}:\mathrm{H})$ samples, in which a small fraction of microcrystallites is embedded. We find that the defect density increases with an unusually slow initial pace, which is then followed by the “normal” $t^{1/3}$ law and the subsequent saturation. The corresponding photoconductivity shows a remarkable initial stability. We present a model that reproduces the experimental results, and relates the structural and degradation anomalies. The measured defect density is interpreted as a superposition of contributions from a defective layer that wraps the microcrystallites and a high-quality amorphous matrix.