Photoluminescence and cathodoluminescence studies of stoichiometric and oxygen-deficient ZnO films

Photoluminescence and cathodoluminescence (CL) spectra of stoichiometric and oxygen-deficient ZnO films grown on sapphire were examined. It was found that the intensities of the green and yellow emissions depend on the width of the free-carrier depletion region at the particle surface; the thinner the width, the larger the intensity. Experimental results and spectral analyses suggest that the mechanism responsible for the green (yellow) emission is the recombination of a delocalized electron close to the conduction band with a deeply trapped hole in the single ionized oxygen vacancy $V_o^{+}$ (the single negatively charged interstitial oxygen ion ${\mathrm{O}}_i^{-})$ center in the particle.