Photoluminescence of nanocoral ZnO films

Photoluminescence studies of nanocoral ZnO nanostructures, fabricated using magnetron sputter deposition of porous Zn films with subsequent oxidation by RTP annealing at 400-800 °C is presented. Structural characterization of the films performed using electron microscopy techniques show the nanocoral morphology of the films with individual coral branches constituting of bunched single crystal ZnO grains of 30-100 nm in dimensions. High resolution images confirm the high quality of individual grains. The features in the photoluminescence spectra are identified using temperature-dependent and power-dependent measurements, with rich features observed in the excitonic region at 5 K, as well as zinc vacancy lines and surface-state recombination lines being present. It is found, that the spectra significantly depend on the annealing temperatures of the samples, with the spectra acquired for the sample annealed at 800 °C exhibiting stronger excitonic emission by 2 orders of magnitude than any other features, thus proving the highest structural quality of the nanostructures.