The temperature and excitation power density dependent photoluminescence study of Ga-doped ZnO thin films

Temperature and excitation power density dependent photoluminescence (PL) studies were performed on Ga-doped ZnO (GZO) thin films grown on a-(11 (2) over bar0) and c-(0001) sapphire substrates by Molecular Beam Epitaxy (MBE). The observed PL spectra are dominated by excitonic as well as defect related transitions. The origins of the emission bands were determined by applying the Gaussian fit to 10K PL spectra and discussed and compared with those available in literature. The shape of the temperature dependence of the PL spectra did show any discernable dependence on the substrate orientation used. The peak energies of excitonic transitions redshifted with increasing temperature with a total shift of about 70 meV (from 10K to 300 K). From the temperature activation energies of 6 and 40 meV were obtained from a bi-exponential empirical equation fitting. The excitation power density dependence of total integrated PL intensities and the ratio of peak intensities of the excitonic transition to yellow luminescence revealed that they follow a power law in the form of IT or I-ex/I-YL oc P-E(k), where P-E is the excitation power density and k is the power factor.