Luminescence in electron irradiated CdS
Electron irradiation induced changes in both the photo- and cathodo-luminescence spectra of high purity CdS platelets have been monitored over a wavelength range from 4800A to 2 μm. The irradiations were all performed near 10K using beam energies from 100 keV to 1 MeV. By irradiating with electron energies between the cadmium and sulfur displacement thresholds, and above the cadmium displacement threshold, the damage induced luminescence could be assigned to specific sublattices. In the bound exciton spectral region near the band edge, all exciton lines present before irradiation were observed to decrease in intensity with the exception of the emission line at 4867A. This line was observed to grow in absolute intensity for irradiation energies above the sulfur displacement threshold. We attribute the 4867A emission to the decay of an exciton bound to a shallow neutral donor state associated with the sulfur vacancy. The edge emission was found to decay in intensity when observed by photoluminescence but to increase in intensity when excited by 100 keV electrons following an irradiation above the sulfur displacement threshold. Broad band luminescence has also been produced by irradiation at 7200A and 1.03 μm. The 7200 A band is not observed, however, until a thermal anneal is performed above a recovery stage centered at 180 K. The edge emission and bound exciton emission partially recover in this same temperature range. Another annealing stage is observed at 230 K by monitoring the intensity of emission bands at 1.03 and 1.65 μm. The annealing stage at 180 K is associated with sulfur sublattice damage recovery while the stage at 230 K is due to recovery of cadmium sublattice damage.