Structure-related optical properties of Bi_{4 - x}La_xTi₃O₁₂ thin films grown on Pt/Ti/SiO₂/Si substrate

Polycrystalline Bi_{4 - x}La_xTi₃O₁₂ (BLT, x = 0, 0.5, 0.75, and 1.0) thin films have been grown on Pt/Ti/SiO₂/Si substrate by metalorganic decomposition method at 650 °C. The studies of X-ray diffraction patterns and atomic force microscopy images indicate that the crystallization of BLT films was affected by the La substituting concentration. The refractive index and extinction coefficient of BLT thin films were determined by fitting the infrared spectroscopic ellipsometric data using a classical dielectric function formula. In the wavelength range of 2.5-8.0 μm, as the La concentration increases, the refractive index decreases. The refractive index of BLT thin films in the wavelength range of 400-1100 nm, derived from the reflectance spectra, decreases with increasing La concentration. The La concentration dependence of optical constants for BLT films was investigated.