RESIDUAL CONDUCTIVITY OF STRESSED GE-GA PHOTOCONDUCTORS AFTER LOW-DOSE GAMMA-IRRADIATION

Experimental results and a plausible physical model of the gamma-induc ed conductivity changes in stressed Ge:Ga photoconductive detectors ar e presented. Detector samples with boron-implanted contacts operated u nder conditions of low-temperatures 1.6-2.3 K and low photon backgroun ds 10(6)-10(8) cm(-2) s(-1) showed a long-term increase of conductivit y and a decrease of the breakdown field after being exposed to 1 MeV g amma-quanta for a total dose <4 rad. The radiation-induced changes of the parameters are entirely suppressed by a temperature increase to 4. 2 K, while an increase of the electric field above breakdown restores the parameters only partially. The effects are explained in terms of a change of the effective compensation ratio of the samples due to rech arging of the donor and acceptor impurities by electrons and holes gen erated under the gamma-irradiation, as well as taking into account tha t the boron-implanted contacts block minority carriers (electrons) in the semiconductor bulk and prevent their sweepout from the detector. ( C) 1997 American Institute elf Physics.