Growth characteristics, phase composition and optical properties of Ti–Sc–O thin films synthesized by atomic layer deposition

Ti–Sc–O thin films were synthesized at 300°C by atomic layer deposition (ALD) via alternating between the reaction cycles with metal precursors and HO as co-reactant. By varying the cycle ratio, the materials of [Sc]/([Ti] + [Sc]) = 13, 25, 44, 64, 82% were obtained. The films were examined via spectral and single wave null ellipsometry, X-ray photoelectron spectroscopy, scanning electron microscopy and X-ray diffraction. The formation of the material was demonstrated to be substrate-inhibited and to occur within the “temperature window” of ALD. As a result of Ti2p and Sc2p XPS spectra analysis, the oxidation states of the metals are Ti and Sc. At low Sc concentrations (up to [Sc]/([Ti] + [Sc]) = 25%) the film crystallization into anatase phase observed for individual TiO film is suppressed. In the range of [Sc]/([Ti] + [Sc]) = 44–100% the materials of various cubic crystal structure types are formed: with the increase of scandium concentration the structure changes from disordered fluorite ScTiO to cubic ScO-based solid solution. The refractive indices (), extinction coefficients () and optical bandgap values are well described by the Tauc-Lorentz model. They vary between the corresponding parameters of the individual oxides depending on the composition, which is relevant for current problems of optics, photonics, solar energy and photocatalysis.