Optical and electrical properties of high-quality Ti₂O₃ epitaxial film grown on sapphire substrate

Abstract

Epitaxial film of Ti₂O₃ with high crystalline quality was grown on Al₂O₃ substrate by pulsed laser deposition process using a powder-pressed TiO₂ target in active O₂ flow. X-ray diffraction clearly reveals the (0006) crystalline Ti₂O₃ orientation and its $(10\overline{1} 0)_{{{\text{Ti}}_{ 2} {\text{O}}_{ 3} }} ||(10\overline{1} 0)_{\text{sapphire}}$ in-plane epitaxial relationship with the substrate. Scanning electron microscopy images show that the film grew uniformly on the substrate with a Volmer–Weber mode. High-resolution transmission electron microscopy and selected area electron diffraction further confirm the high crystalline quality of the film. Transmittance spectrum shows that the Ti₂O₃ film is highly transparent in 400–800 nm with the optical band gap estimated to be 3.53 eV by Tauc plot. The temperature-dependent Hall effect measurement indicates that the Ti₂O₃ film appears to be n-type semiconductor with carrier concentration, mobility, and resistivity showing typical temperature-dependent behavior. The donor ionization energy was estimated to be 83.6 meV by linear relationship of conductivity versus temperature.