A study on the refractive index of sol-gel Ba_1-xGd_xTiO₃ thin films using spectroscopic ellipsometry

ABSTRACT

Ba_1-xGd_xTiO₃ 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 Ba_1-xGd_xTiO₃ 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 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 Ba_1-xGd_xTiO₃ thin films as AR coating for solar cells.

Keywords
Ba_1-xGd_xTiO₃; Thin films; Refractive index; Ellipsometry