Structural and Optical Properties of PECVD TiO2–SiO2 Mixed Oxide Films for Optical Applications

TiO2–SiO2 mixed oxide films with variable compositions are deposited from oxygen/titanium tetraisopropoxide/hexamethyldisiloxane (HMDSO) inductively coupled radiofrequency plasmas at low temperature and pressure. The related structure, morphology, and optical properties are investigated. Results show that the [Si]/[Ti + Si] concentration ratio in the film is increased sharply from 0 (pure TiO2) to 0.48 by adding a small amount of HMDSO. The mixed films are in amorphous phase, and the formation of TiOSi is revealed. With an increase of Si content: the columnar structure of TiO2 disappears, the whole film seems to be homogeneous and more compact, the grain size decreases and the top surface becomes smoother; both the refractive index and extinction coefficient are decreased, while the bandgap is increased. The composition‐dependent properties of TiO2–SiO2 mixed oxide films deposited by PECVD are investigated. By incorporating SiO bonds in the TiO2 network, the columnar morphology is removed and the film homogeneity can be improved, meanwhile, the polycrystalline structure is transformed into amorphous. Although the refractive index is decreased, the films with a good compromise of properties which can fulfil the requirements for optical waveguide applications.