Low-Level Radiation Effects in Extrinsic Infrared Detectors

Experimental data are presented on the effect of gamma irradiation at low dose levels of 10 Rads or less on the responsivity of arsenic-doped extrinsic IR detectors under operating conditions at 4.3 to 12°K. The observed large changes in responsivity under irradiation, and the subsequent transient behavior during a period of less than 1 minute immediately after the radiation is turned off, are strongly dependent on temperature, bias voltage, and IR flux level. The net effect following irradiation is always a responsivity increase; however, under some conditions, the increase can be preceded by a decrease. The responsivity change relaxes slowly, requiring more than one day for complete recovery of the detector to its pre-irradiation condition. The effects anneal rapidly at temperatures over 20°K. The observed phenomena can be explained by radiation-induced changes in the charge state of the levels associated with the majority IR-active dopant and the compensating impurities. The complex dependence of the responsivity changes on the operating conditions is explained in terms of competing processes involved in capture, recombination, and sweepout of radiation-generated electrons and holes. The physical mechanisms and a qualitative model offering a possible explanation of the effect of temperature, bias, and IR flux level are discussed.