Optical properties of oxygen-implanted CdS:O layers in terms of band anticrossing theory

The microcathodoluminescence (MCL) and photoreflection spectra of CdS:O layers implanted with oxygen ions to 4 $\times$ 10$^{20}$ cm$^{-3}$ are investigated. Used method of MCL spectroscopy yields information only about the implanted-layer volume. Exciton MCL spectra, which allow one to determine the concentration of dissolved oxygen in the CdS:O layers and the influence of deviation of the substrates from stoichiometry, are recorded. The homogeneity of the ion-implanted layers is studied by cathodoluminescence (CL) scanning electron microscopy. The relationship between light-emitting areas and the luminescence band at $\sim$ 630 nm is established. The reason for enhancement of this band upon radiation annealing is revealed and its nature as the luminescence of F$^+$ centers in CdS is confirmed. New photoreflection spectroscopy data are obtained, which describe the specific behavioral features of oxygen on the layer surface as an isoelectronic impurity in highly mismatched alloys (HMAs). It is shown that sulfur completely bonds and removes oxygen from CdS:O. Oxygen-free CdS remains on the surface in the form of nanoparticles, the size of which depends on the oxygen concentration in the CdS:O layer bulk. The results obtained are in agreement with the predictions of band anticrossing theory.