Investigation of low-dose radiation effects in Ge:Ga far-infrared photoconductors for ASTRO-F

Ge:Ga photoconductive devices are the most sensitive detectors for far-infrared (FIR) satellite instruments; a combination of stressed and unstressed detectors continuously covers the wide wavelength range of 40-200 μm. However, the performance of these detectors is known to be severely influenced by the ionizing radiation environment in space. In order to investigate global properties of low-dose radiation effects, γ-ray irradiation of the Ge:Ga (stressed and unstressed) detectors was performed by using radioactive sources 60Co and 137Cs under various levels of FIR photon conditions. Substantial enhancement in detector responsivity was observed during the irradiation for both types of detectors. After cessation of the irradiation, significant systematic differences were found between the stressed and unstressed detectors in the relaxation rate of the enhanced responsivity and effectiveness of curing procedures. It is concluded that the former is attributed to the difference in the averaged energy of the FIR photons falling on the detector, while the latter is due to the difference in the Ga ionization energy for the stressed and unstressed Ge:Ga.