Ba1-x Gdx TiO3 thin films have been fabricated at different Gd3+ ionic concentrations, film thicknesses, and annealing temperatures using the sol-gel method. The refractive index of the Ba1-x Gdx TiO3 films on a silicon substrate is characterized using Spectroscopic Ellipsometry (SE), where the ellipsometry angles Ψ and Δ are fitted very well with the Cauchy dispersion model. The results show that the refractive index at 632.8 nm decreases from 2.18 to 1.892 with the increase of the Gd3+ ratio, while it increases with film thickness and annealing tempera-ture. This trend for refractive index variation is explained based on interatomic spacing and density densification of the films. Using Wemple–Di Domenico (WDD) model shows that the dispersion energy increases with film thickness and annealing temperature and decreases with Gd3+ doping. The relatively high refractive index of the samples supports the possibility of using Ba1-x Gdx TiO3 thin films as AR coating for solar cells.
