Optical properties of ZrTiO4 films grown by radio-frequency magnetron sputtering

Thin films of zirconium titanate on quartz glass were prepared using radio-frequency magnetron sputter deposition at various substrate temperature (Td from 25 to 450 °C). Crystallinity of the films sets in either at Td=400 °C or after annealing in air up to 650 °C. The refractive index showed monotonic increase with Td from 2.22 to 2.37 at 550 nm while the extinction coefficient ranging from 1.0×10−3 to 4.7×10−3 increased with decreasing Ti/Zr stoichiometric ratio (from 1.08 to 1.03) of the films. The influence of the Ti/Zr ratio on the oxygen deficiency and absorption properties of the films was attributed to the stronger attraction of the Ti4+ ions compared with Zr4+ ions to the condensing oxygen atoms or ions on the surface of growing film. The optical band gap was found to be 3.4 eV of indirect-transition type. A single-oscillator model was used to fit the dispersion of the refractive index with the wavelength, indicating that the amorphous and crystalline ZrTiO4 films are similar in short-range-order structure. The inhomogeneity and packing density of the films were analyzed using well-known relations.