Hot pixel annealing behavior in CCDs irradiated at -84°C

A Hubble space telescope wide field camera 3 e2v CCD was irradiated while operating at -84°C and the dark current studied as a function of temperature while the charge coupled device was warmed to a sequence of temperatures up to a maximum of +30°C. The device was then cooled back down to -84° and remeasured. Hot pixel populations were tracked during the warm up and cool down. Hot pixel annealing began below -40°C and the anneal process was largely completed by the time the detector reached +20°C. There was no apparent sharp annealing temperature. Although a large fraction of the hot pixels fell below the threshold to be counted as a hot pixel, they nevertheless sustained a higher leakage rate than the remaining population. The mechanism for hot pixel annealing is not presently understood. Room temperature irradiations do not adequately characterize the hot pixel distributions for cooled applications.