Transient and Permanent Effects of Neutron Bombardment on a Commercially Available N-Buried-Channel CCD

A study of the effects of neutron bombardment on a commercially available n-buried-channel CCD (the Fairchild CCD 321A) has been performed. Both transient and permanent changes in dark current density and charge transfer inefficiency were examined. Considerable shortterm annealing of dark current was observed at room temperature for times up to ~104 sec following pulsed neutron irradiation, but negligible annealing of the transfer inefficiency was noted over the period from 1.5 sec to 1000 hours. This transient annealing difference suggests that transfer inefficiency increases are dominated by isolated, as opposed to clustered, defects under the present experimental conditions. Transfer inefficiency data obtained over the range 208-303° K yield trap energy levels with respect to the conduction band of 0.54 eV before irradiation and 0.33 eV after irradiation. The trap introduction rate was determined to be ~2.6 n-1 cm-1. In studies at cryogenic temperatures, a dependence of transfer inefficiency on clock frequency to the one-half power was noted. This dependence is attributed to a trap-limited diffusion process, with trapping occurring at the As donor level. Neutron irradiation at 77° K caused the transfer inefficiency to decrease, and a qualitative model for such behavior is given.