Optical Properties of CdS Microcrystallite-Doped SiO₂ Glass Thin Films

The optical properties of SiO 2 glass thin films containing CdS microcrystallites have been investigated. The thin films were deposited onto SiO 2 and GaAs substrates using an rf-sputtering technique. X-ray photoelectron spectroscopy and X-ray diffraction measurement indicated that the Cd and S atoms were doped as CdS with a hexagonal system in SiO 2 glass matrixes. In the optical absorption spectra, the absorption edge of the films with 18.5 at% of CdS clearly exhibited a blue shift by about 0.13 eV in comparison with that of the bulk CdS. In accordance with this result, the photoluminescence spectra of the films exhibited a blue band-edge emission at a higher energy than that of the bulk CdS. The shift to higher energy seems to be a low-dimensional quantum size effect due to confinement of electrons and holes in CdS microcrystallites.