Radiation Testing of Trimetal Infrared Detectors

Long wavelength infrared PbSnTe and short wavelength infrared HgCdTe photovoltaic detector arrays representative of recent technology have been radiation tested in a steady-state gamma flux, total dose, electron fluence, neutron fluence, and pulsed ionization environments. The transient response of both types of detectors to a steady-state gamma flux results in three interrelated effects, the production of individual pulses, an increased leakage current, and an increased rms noise. The volume of the devices responsible for most of the response is that within a diffusion length of the junction. This results in a relatively large response in PbSnTe devices on a substrate of PbTe (which has a large, ~100 μm diffusion length). Permanent degradation in both types of detectors is dominated by the surface, interface, or insulator effects. In HgCdTe detectors, the mechanism appears to be the inversion of the substrate surface adjacent to the mesa area of the detectors. The measured effects in both types of detectors were an increased leakage current and a decreased zerobias resistance. In addition, the optical response of the HgCdTe detectors increased because of the effective increase in device area, and the reverse breakdown voltage of the PbSnTe devices decreased. The surface effect damage seems to be produced most effectively by exposure to an environment that simultaneously produces both ionization and displacement effects.