Post-deposition annealing effect on RF-sputtered TiO sub(2) thin-film properties for photonic applications

Titanium dioxide (TiO sub(2)) thin films were grown on glass substrates at room temperature using RF magnetron sputtering technique. Effect of the post-annealing for 1 h at 400-600 degree C on the structural, morphological, optical and waveguide properties was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-visible spectrophotometry and m-lines spectroscopy (MLS). XRD studies show that as-grown and post-annealed TiO sub(2) films exhibit (101) XRD peak corresponding to the anatase phase of TiO sub(2). Higher annealing temperatures result in a significant increase in crystallinity. The grain size values were calculated and found to be about 15-37 nm. From the analyses made on the SEM micrographs and AFM images, it was revealed that the morphology and surface roughness of the thin films were influenced by the heat treatment temperature. The UV-visible spectroscopy analyses show that as-grown TiO sub(2) films were transparent in the visible region with an average transmittance of more than 75 % and the transmittance decreases slightly with an increase in annealing temperature. Annealed TiO sub(2) films also exhibit an increase in the values of direct optical band gap. MLS measurements at 633-nm wavelength put into evidence that TiO sub(2) planar waveguides demonstrate a well-guided fundamental mode for both transverse electric and transverse magnetic polarized light. Moreover, the refractive index was found to increase with temperature and to approach to the anatase TiO sub(2) single-crystal value for the TiO sub(2) film annealed at 600 degree C.