Comprehensive model for photo-degradation in a-Si:H

It has been speculated that a-Si:H can undergo degradation in material properties by a charged dangling bond state trapping a carrier and changing to a neutral dangling bond which is a more effective electron recombination center. They show in this paper that such a phenomenon does occur, and develop a kinetic model for trapping-induced creation of recombination centers. The model uses only three adjustable parameters, the initial trap density, the initial dangling bond density, and a ratio of cross-sections. Using this model, they can fit the experimental photodegradation data of several groups. They show that the kinetic behavior of trap-induced degradation is very different from that of degradation due to bond-breaking, and that it tends to saturate rapidly in time. They thus show that there are two different degradation mechanisms in a-Si:H, one controlled by impurity-induced deep traps, and one controlled by bond breaking, probably of poly-silane bonds