Electron Spin Resonance Studies of Trapped Electrons in CdS

A resonance line characterized by g // =1.783 and g ⊥ =1.764 was observed at 1.5°K under irradiation of band gap light in undoped CdS. The resonance signal was greatly diminished by annealing the sample in sulfur vapour and was enhanced by annealing it in cadmium vapour at high temperature (∼800°C). The depencence of the resonance intensity on the wavelength of excitation light was measured. The relevant processes involved in excitation and quenching for the resonance signal are discussed in terms of electron transfer from some electron traps via the conduction band and recombination with holes excited from cadmium vacancies into the valence band by the radiation respectively. As a possible model for the magnetic center responsible for the resonance the sulfur vacancy with an unpaired electron is considered. Some results on ENDOR experiments are presented.