Optical properties of RF magnetron sputtered Ba0.65Sr0.35TiO3 thin films

Ba0.65Sr0.35TiO3 thin films have been prepared by radio frequency (RF) magnetron sputtering on fused quartz at different substrate temperatures. Optical constants (refractive index n, extinction coefficient k) were determined from the optical transmittance spectra using the envelope method. The dispersion relationship of the refractive index versus substrate temperature was also investigated. The refractive index of BST thin films increased from 1.778 to 1.961 (at λ = 650 nm) as deposited temperature increases from 560 to 650 °C. The extinction coefficient of as-deposited BST thin films increased with the increase of the oxygen to argon ratio, which was due to the change of the film stoichiometry, structure and texture of BST thin films. The oxygen to argon ratio also affected the fluorescence spectra. The fluorescence peaks intensity was greatly increased, apparent frequency shift was detected and the linewidth became narrow as the ratio of oxygen to argon increased from 1:4 to 1:1. The fluorescence spectra also indicated the band transition of BST thin films was an indirect gap transition.