Optical studies on the influence of annealing temperature of TiO2 seed layer to the growth of ZnO nanostructures

In this present work, zinc oxide (ZnO) nanostructures were successfully grown on titanium dioxide (TiO₂) seed layer. To prepare a suitable site for ZnO nanostructures to grow, the TiO₂ seed layer was pre-coated on glass substrate by sol-gel spin-coating. The coated TiO₂ thin films were heated at different annealing temperatures; 350, 400, 450, 500 and 550 C for 2 hours in order to determine the best optical quality of the seed layer film for growth of ZnO nanostructures by solution-immersion method. The optical properties of the TiO₂: ZnO thin films, as a function of TiO₂ annealing temperature have been studied by Photoluminescence (PL) spectroscopy and UV-Vis (Ultraviolet Visible) spectroscopy. Compared to as-grown TiO₂ seed layer, red shift was observed on the PL emission peaks of annealed TiO₂ seed layer in visible region. This is due to the presence of interstitial oxygen (O_i^-). To determine the optical quality and stoichiometric properties of the films, the ratio of the UV emission peak intensity and the visible emission peak intensity, I_UV/I_VIS were calculated to be 0.32, 0.77, 0.88, 1.50, 1.05 and 0.36 for as-grown, 350, 400, 450, 500 and 550 C, respectively. The higher the intensity of the ratio I_UV/I_VIS, the better the optical quality of the thin films is. UV-Vis spectra showed that the thin films exhibited high transparency in visible region and high absorption properties in the UV region.