Study of the crystal structure, band gap and dispersion evolution in titanium oxide thin films

Abstract

Titanium oxide (TiO2) thin films were prepared by electron-beam evaporation (EBE) method on crystal silicon, and were thermally treated by rapid thermal annealing (RTA) process. X-ray diffraction (XRD) and variable angle spectroscopic ellipsometry (VASE) were used to analyze the crystal structure, band gap, and optical constants evolution of the investigated films. The strongest diffraction peaks in XRD patterns were found to shift to higher 2θ angle with an increase of film thickness. The lattice spacing decreases and the average grain size increases, indicating the improvement of crystal quality by increasing film thickness. The band gap from well-fitted Forouhi–Bloomer (FB) dispersion model in VASE decreases with an increase of thickness, and one-dimensional quantum confinement effect and disorder effect have been introduced to explain this relation. The refractive indices of TiO2 thin film decrease monotonically with an increase in film thickness in the spectral range from 230 to 800 nm, which can be attributed to the contribution of compressive stress effect.