Change in bulk defect density of hydrogenated amorphous silicon by bias stress in thin film transistor structures

The changes in defect density of hydrogenated amorphous silicon (a-Si:H) in thin film transistor (TFT) structures by prolonged bias stress or light soaking have been studied through constant photocurrent method (CPM) measurements. The CPM absorptions due to defect absorptions do not change after positive or negative bias-stress. On the other hand, the CPM absorptions due to dangling bond defects increase remarkably after light soaking. These experimental results demonstrate that the bulk defect density of a-Si:H in TFT structure is not changed after long time bias stress even though the characteristics of the TFT degrade significantly.