Spectroscopic ellipsometry characterization of amorphous and crystalline TiO2 thin films grown by atomic layer deposition at different temperatures

•Refractive index was found to be increased from amorphous to the nanocrystalline films.•Refractive index was found to be inversely proportional with growth per cycle.•Large-grained anatase films showed lower refractive indices than the amorphous films.•Roughness was taken into consideration due to the columnar growths of crystalline films. TiO2 thin films of widely different structural and morphological characteristics were grown on Si (100) substrates using Atomic Layer Deposition (ALD) by varying the substrate temperature (Ts) in a wide range (50°C≤Ts≤400°C). Spectroscopic ellipsometry (SE) measurements were carried out to investigate the effect of growth temperature on the optical properties of the films. Measured SE data were analyzed by considering double layer optical model for the sample together with the single oscillator Tauc-Lorentz dispersion relation. Surface roughness was taken into consideration due to the columnar growths of grains in crystalline films. The refractive index was found to be increased from amorphous (Ts≤150°C) to the nanocrystalline films (2500