Optical properties of epitaxially grown zinc oxide films on sapphire by pulsed laser deposition

ZnO thin films were epitaxially grown on c-sapphire substrates by pulsed laser deposition at substrate temperatures of 500–800 °C. The crystal structure of ZnO films follow the epitaxial relationship of ${\text{(0001)}}_{\mathrm{ZnO}}{\text{∥(0001)}}_{{\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}}{\text{(101̄0)}}_{\mathrm{ZnO}}{\text{∥(112̄0)}}_{{\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}}.$ Both room temperature and cryogenic temperature photoluminescence showed a remarkable band-edge transition, and clear excitonic structures could be seen at cryogenic temperature. The optical refractive index was measured in the range of 375–900 nm by varying angle spectroscopic ellipsometry. The simulation was carried out using a Sellmeier equation.