A comprehensive model for photo-degradation in a-Si:H

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Abstract
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. We 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, we can fit the experimental photodegradation data of several groups. We 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. We thus show that there are two different degradation mechanisms in a‐Si:H, on controlled by impurity‐induced deep traps, and one controlled by bond breaking, probably of poly‐silane bonds.

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