A Study on the Refractive Index of Sol-Gel Ba1-xGdxTiO3 Thin Films Using Spectroscopic Ellipsometry

Ba1-xGdxTiO3 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-xGdxTiO3 films on a silicon substrate is characterized using Spectroscopic Ellipsometry (SE), where the ellipsometry angles ? and ? 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 temperature. 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-xGdxTiO3 thin films as AR coating for solar cells.