A study on the refractive index of sol-gel Ba1-xGdxTiO3 thin films using spectroscopic ellipsometry

Ba 1-x Gd x TiO 3 thin films have been fabricated at different Gd 3+ ionic concentrations, film thicknesses, and anneal - ing temperatures using the sol-gel method. The refractive index of the Ba 1-x Gd x TiO 3 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 Gd 3+ 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 Gd 3+ doping. The relatively high refractive index of the samples supports the possibility of using Ba 1-x Gd x TiO 3 thin films as AR coating for solar cells.