Pump–probe pulse transient photoconductivity study in amorphous and microcrystalline Si:H

Transient photoconductivity of disordered Si:H is studied using pump–probe technique. PC transients due to a weak probe pulse are controlled by the Si dangling bond defects in defective samples. In these samples including microcrystalline Si:H, a strong amplification of the probe pulse photoconductivity transient takes place by cw or pulse bias light. In annealed a-Si:H at low temperature the effect is opposite (reduction). The amplification becomes evident when the photocarriers created by the pump pulse approach the number of defects in the sample. The amplification decays slowly up to milliseconds after the pump pulse and is related to states distributed between 0.4 and 0.6 eV. Several scenarios including an interplay between the carriers trapped into different gap states, defect relaxation, and the dependence of capture coefficients on the occupancy of the tail states are considered.