Selective phase growth of ultra-smooth Ti2O3 and TiO2 thin films at low growth temperature controlled by the oxygen partial pressure

Abstract

The selective phase growth of Ti-based oxide thin films on sapphire substrates is crucial in controlling the electronic properties, such as the insulator-to-metal transition (IMT). Thin films are generally prepared by pulsed laser deposition under high temperatures, but it is challenging to obtain a smooth surface. In this study, we deposited ultra-smooth epitaxial TiO₂ and Ti₂O₃ thin films with roughnesses below 0.34 Å on sapphire substrates. By controlling the oxygen partial pressure at a relatively low temperature, at 473 K, we obtained highly crystalline thin films with selective growth. The thin films grown at 1 and 10⁻³ Pa exhibited a rutile-type TiO₂ phase, and those grown at 10⁻⁶ Pa exhibited a hexagonal Ti₂O₃ phase. The crystal structures and electronic structures were consistent with the previous reports on TiO₂ and Ti₂O₃ thin films. Moreover, Ti₂O₃ underwent an IMT, whereas TiO₂ was unchanged.