Annealing Effect on DC Magnetron Sputtered TiO₂ Film: Theoretical and Experimental Investigations

In this work, both experimental and theoretical investigations were carried out on TiO₂ thin film deposited on n-Si by a direct current (DC) magnetron sputtering system. Post-deposition annealing of the film was conducted at 500 °C and 800 °C for 90 min using a high temperature furnace. Experimental results, obtained through x-ray diffraction, showed amorphous nature of the as-deposited TiO₂ film. However, after annealing at 500 °C, a diffraction peak corresponding to anatase TiO₂ appeared. Further increasing the annealing temperature to 800 °C resulted in an improvement in the crystallinity of the film. Surface roughness of the TiO₂ film was investigated using atomic force microscope. The root-mean square value of the surface roughness increased with the rise in annealing temperature. The increase in surface roughness was attributed to increase in the crystallite size of the film. The band gap of the TiO₂ was examined using ultraviolet–visible reflectance spectroscopy analysis. The band gap was decreased with the increase of annealing temperature. The electrical resistivity of the film decreased after the annealing. Theoretical investigations revealed tetragonal structure of TiO₂ and a decrease in its band gap with an increase in the annealing temperature which was associated with the quantum size effect in the material. The static refractive index (n_o) for un-annealed and annealed films (500, 800 °C) were found to be 2.48, 2.69 and 3.03 respectively. Similarly, absorption peaks were also affected by the increase in the annealing temperature. The theoretical investigations validated the experimental results of this work.