Proton irradiation results for long-wave HgCdTe infrared detector arrays for Near-Earth Object Camera

HgCdTe detector arrays with a cutoff wavelength of ∼10  μm intended for the Near-Earth Object Camera (NEOCam) space mission were subjected to proton-beam irradiation at the University of California Davis Crocker Nuclear Laboratory. Three arrays were tested—one with 800-μm substrate intact, one with 30-μm substrate, and one completely substrate-removed. The CdZnTe substrate, on which the HgCdTe detector is grown, has been shown to produce luminescence in shorter wave HgCdTe arrays that causes an elevated signal in nonhit pixels when subjected to proton irradiation. This testing was conducted to ascertain whether or not full substrate removal is necessary. At the dark level of the dewar, we detect no luminescence in nonhit pixels during proton testing for both the substrate-removed detector array and the array with 30-μm substrate. The detector array with full 800-μm substrate exhibited substantial photocurrent for a flux of 103  protons/cm2 s at a beam energy of 18.1 MeV (∼750  e−/s) and 34.4 MeV (∼65  e−/s). For the integrated space-like ambient proton flux level measured by the Spitzer Space Telescope, the luminescence would be well below the NEOCam dark current requirement of <200  e−/s, but the pattern of luminescence could be problematic, possibly complicating calibration.