Insights into the mechanisms of light-induced degradation from studies of defects in low Ge fraction a-Si,Ge:H alloys

Abstract

The modulated photocurrent (MPC) method was used to study deep defect creation and annealing in low Ge fraction a-Si,Ge:H alloys (2–10 at.% Ge). These measurements reveal two distinct bands of deep defects in these samples which are identified as neutral Si and neutral Ge dangling bonds. Upon thermal annealing in the dark from a strongly light degraded state, these two defects are found to decrease in a manner which indicates a direct competition between the annealing of the Si and Ge dangling bonds, and therefore implies a global reconfiguration mechanism. Comparing purely thermal annealing with light-induced annealing indicates that the relative anneal rate for the two types of defects is different. This therefore tends to rule out models in which the rate limiting step in the annealing process comes from the release of the mediating entity (hydrogen? strain?) from a remote site.