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.