Optical properties of RF-sputtered Ba_0.65Sr_0.35TiO₃ thin films

Ba0.65Sr0.35TiO3 (BST) thin Films have been prepared by radio frequency 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 vs. substrate temperature was also investigated. The refractive index of BST thin films increased from 1.778 to 1.961 (at lambda=650 run) as deposited temperature increases from 560 degrees C to 650 degrees 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,really 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.