Composition dependence of structural and optical properties for sol-gel derived (100)-oriented Ba1-x Srx Ti O3 thin films

Highly (100) oriented Ba1-x Srx Ti O3 (BST) thin films were grown on LaNi O3 coated silicon substrate by modified sol-gel process. X-ray diffraction analysis shows that the out-of-plane lattice constant decreases linearly with increase of Sr concentration. The energy band gaps (Eg) of BST thin films exhibit strong dependence on Sr content by analyzing the results of the spectroscopic ellipsometer (SE) measurement. The smallest Eg has been obtained at x=0.3, which is at the phase boundary of cube phase and tetragonal phase. The refractive index and thickness of BST thin films were obtained by fitting SE data with a multiphase model.