Thickness dependent optical properties of titanium oxide thin films

TiO2 thin films of different thickness were prepared by the Electron Beam Evaporation (EBE) method on crystal silicon. A variable angle spectroscopic ellipsometer (VASE) was used to determine the optical constants and thickness of the investigated films in the spectral range from 300 to 800 nm at incident angles of 60A degrees, 70A degrees, and 75A degrees, respectively. The whole spectra have been fitted by Forouhi-Bloomer (FB) model, whose best-fit parameters reveal that both electron lifetime and band gap of TiO2 thin film have positive correlation to the film thickness. The refractive indices of TiO2 thin film increase monotonically with an increase in film thickness in the investigated spectral range. The refractive index spectra of TiO2 thin films have maxima at around 320 nm and the maxima exhibit a marginally blue-shift from 327.9 to 310.0 nm with an increase in film thickness. The evolution of structural disorder in the TiO2 thin film growth can be used to explain these phenomena.