Defect creation kinetics in amorphous silicon thin film transistors

The rate of defect creation in amorphous silicon thin film transistors, under gate bias stress, is proportional to N _BT ^α t ^β−1, where N _BT is the bandtail carrier density. Experimentally α is 1.5–1.9, while β is 0.5–0.6. We have developed a model to account for this dependence, based on an exponential distribution of barriers to defect creation. The key new feature of our model is that we include the backward reaction, as well as the forward reaction, and also the effect of the charge-state of the formed defects. Considering the forward reaction only, leads to α= β, while a full analysis leads to the simple new result that α≈3 β, which is in excellent agreement with experiments.