Mechanisms for the anomalous dependence of carrier lifetime on injection level and photoconductance on light intensity

Recent experiments indicated an anomalous dependence of carrier lifetime on injection level and of photoconductance on carrier photogeneration rate. In this work mechanisms for these phenomena are proposed which are based on the effects of anomalous increase of carrier lifetime and filling of the defect level by minority carriers, respectively. Distinct from previously known mechanisms, which considered two types of deep defects, traps and recombination centers, our mechanism may take place in semiconductors containing only one type of deep defect, which is a recombination center. It was shown that the anomalous injection-level dependence of lifetime occurs only when the semiconductor is exactly compensated by recombination centers. This conclusion differs from that of the previous model, which concluded that carrier trapping is responsible for the earlier phenomenon. It is shown that the injection-level dependence of carrier lifetime can be used as an experimental tool to determine the deep defect concentration.