Photocarrier capture properties of light-induced defects in a-Si:H

Abstract

ABSTRACTLight-induced degradation of photoconductive properties is investigated as a function of lightinduced Si dangling bond defect concentration and subgap absorption. This relation is studied for a variety of sample preparation techniques including a-Si:D, wide range of temperatures during light exposure and annealing, and sample degradation pre-history. Under a given exposure condition, light-induced defects have a fixed effective electron capture coefficient, while its value varies greatly with exposure conditions (temperature during exposure or stepwise anneal) and with sample microstructure. This explains commonly observed non-linear dependences and hysteresis between defect concentration and mobility-lifetime product. Creation efficiency of less-stable defects with large capture coefficients is not influenced by the presence of a large number of stable defects. Structural change accompanying the defect creation, if any, is strongly related to the defect creation and is likely to occur locally around the defects, modifying their capture coefficients. Capture can vary both because of the changes in intrinsic capture probabilities and due to changes in the net defect charge balance. The former may be increased by the presence of H or photocarrier trap (e.g. weak bond tail state) in a close vicinity of Si dangling bond. The latter may be caused by a wide distribution of defect states in the gap or by simultaneous creation of negatively charged floating bond states near VB edge.