Annealing effect on the near-band edge emission of ZnO

ZnO thin films have been grown on the sapphire (с-Al2O3) substrates at the temperature of 250 °C by means of the direct current (DC) magnetron sputtering technique. The crystal structure and surface morphology of the deposited films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). The optical transmission, reflection and luminescence spectra at 300 K were analyzed for both the as-grown and post-annealed ZnO films. Using the λ-modulation method gives the possibility to reveal the main features of the energy band structure and the nature of the radiative transitions causing the ultraviolet (UV) luminescence.

► λ-modulation method allows to reveal details of the band structure of ZnO.
► Annealing at 600–900 °C causes the appearance of intense luminescence of ZnO.
► Near band edge emission peak consists of three bands formed by local centers.