Degradation mechanisms of gamma irradiated LWIR HgCdTe photovoltaic detectors

Planar n/sup +/p Hg/sub 1-x/ Cd/sub x/Te (x=0.23) photodiodes passivated with ZnS were irradiated by a Co/sup 60/ gamma source. A strong increase in the reverse dark current was observed for doses above 0.3 Mrad(air). A similar effect is found by exposing the photodiodes to UV illumination from a high-pressure mercury lamp. By filtering the UV light it is shown that the degradation in the performance of the photodiodes is caused by the light or radiation absorbed in the ZnS layer above the implanted n-type region. C-V measurements of irradiated MIS devices showed a significant increase in the fast surface state density. Galvanomagnetic and lifetime measurements made on irradiated p-type HgCdTe layer showed no significant changes in the bulk transport parameters. Based on these findings, a model for the degradation mechanism is proposed. >