Evidence for Photochemical Changes in Traps in CdS Crystals

Abstract

The dependence of trap filling on the intensity, temperature, and wavelength of the photoexcitation has been investigated for trapping centers in S–Se-annealed CdS–CdSe crystals and in crystals of CdS subjected previously to electron radiation damage and photoexcited annealing. For certain traps in both these kinds of crystals, it was found that trap filling was not only critically dependent on the temperature of excitation but also on the wavelength of excitation. In fact, for each process observed, a band of wavelengths is most effective, the maximum wavelength of this band being larger than the wavelength for maximum photoconductivity. This result makes previous attempts to explain this kind of phenomenon in terms of a Coulomb-repulsive trap less acceptable and provides additional evidence for the presence of photochemical changes at and below room temperature in CdS-like materials.