Optical Bias Control of Dispersive Relaxations ina-Si: H

Relaxation of the photoinduced ir absorption band in $a$-Si: H was studied in the microsecond time domain as a function of cw bias illumination. The decays follow a power law $t^{-\alpha }$ where the dispersion parameter $\alpha$ increases with bias illumination. At low temperatures, $\alpha$ increases linearly with the steady-state carrier density while at high temperatures it saturates at high illumination levels. These results are interpreted as evidence for the bias-controlled tunneling process at low temperatures and multiple trapping process with tail states under the saturation condition at high temperatures.