Atomic layer deposition of rutile and TiO2-II from TiCl4 and O3 on sapphire: Influence of substrate orientation on thin film structure

Atomic layer deposition of TiO2 from TiCl4 and ozone on single crystal α-Al2O3 substrates was investigated and the possibility to control the phase composition by the substrate orientation was demonstrated. Epitaxial growth of rutile and high-pressure TiO2-II on α-Al2O3(0 0 0 1) and rutile on α-Al2O3(0 1 1̄ 2) were obtained at 400-600 °C. On α-Al2O3(0 0 0 1), the epitaxial relationships were determined to be [0 1 0]R // [2 1̄ 1̄ 0]S and [0 0 1]R // [0 1 1̄ 0]S for rutile and sapphire, and [0 0 1]II // [2 1̄ 1̄ 0]S and [0 1̄ 0]II // [0 1 1̄ 0]S for TiO2-II and sapphire. The TiO2-II concentration up to 50% was obtained in the films deposited at 425-500 °C. On α-Al2O3(0 1 1̄ 2), the epitaxial relationship of rutile was [0 1 0]R // [2 1̄ 1̄ 0]S and [0 0 1]R // [0 1 1̄ 0]S. The densities of epitaxial films reached 4.2-4.3 g/cm3 on substrates with both orientations but the epitaxial quality was markedly higher on α-Al2O3(0 0 0 1).