Features of subthreshold defect formation in CdS and CdS:Cu single crystals subjected to irradiation with X-ray photons

Abstract

Experimental results of the study of the effect of irradiation with 230-keV electrons and with X-ray photons with energies of 8.06 and 17.5 keV and the effect of quenching on the formation and reconstruction of the centers of slow recombination of nonequilibrium charge carriers (the so-called r centers) in nominally undoped and Cu doped (N Cu ∼ 1018 cm−3) CdS single crystals are reported. It is shown that defects in cadmium sublattice in the crystal (specifically, the V Cd vacancies and the CuCd defects with parameters close to those of the above vacancies) are responsible for the r centers. In the case of the X-ray irradiation of both undoped and Cu-doped CdS single crystals, subthreshold defect formation of cadmium vacancies and CuCd defects takes place; this occurs at sites with distorted and weakened interatomic bonds, i.e., at “weak sites” near large structural imperfections of the lattice, of technological or other origin. Starting with a quenching temperature 170°C, the spectrum of slow-recombination centers is appreciably affected by thermally formed vacancies V Cd and secondary defects CuCd. At quenching temperatures higher than 250°C, a significant contribution to the spectrum of optical quenching of photoconductivity is made by thermally introduced free (away from structural imperfections) r centers, i.e., the V Cd and CuCd defects.