Determination of refractive indices and thicknesses of Ba_(0.7)Sr_(0.3)TiO_3 films with and without MgO (001) buffer layer on silicon substrate

摘要

Ba_(0.7)Sr_(0.3)TiO_3 (BST30) thin films, deposited on single crystal Si (100) substrates with or without a MgO(001) buffer layer by the sol-gel method, have been investigated for their optical properties with a visible reflection spectrophotometer. An improved simplex numerical optimization method based on the reflectance spectra fitting is utilized to obtain the refractive indices and thicknesses of the thin films. Two models for the refractive index variations of the films (with or without a MgO buffer layer) together with a resemble double-layer structure are used to describe the films. The crystallization and microstructure of the films are characterized by the field emission scanning electron microscopy, which indicates that the MgO(001) buffer layer can significantly hold up the interdiffusion between the BST30 layer and the Si substrate, acuminate the interfaces, and improve the crystallinity of the BST thin film deposited on it. Furthermore, due to the large difference between the refractive index of the BST30 thin film and that of the MgO(001) buffer layer, which results in a strong beam confinement, a desirable waveguide structure could be constructed.