Atomic layer growth of epitaxial TiO2 thin films from TiCl4 and H2O on α-Al2O3 substrates

Atomic layer deposition of TiO2 thin films on single crystal alpha-Al2O3(1 (1) over bar 02) (sapphire) substrates was studied and compared with that on Si(100) and amorphous SiO2. The TiCl4-H2O process allowed epitaxial growth of rutile on alpha-Al2O3(1 (1) over bar 02) at 425degreesC and higher temperatures. In the epitaxial films, the (101) plane of rutile was parallel to the (1 (1) over bar 02) plane of alpha-Al2O3 and the in-plane orientational relationship was determined to be [10 (1) over bar ]rutile parallel to[1 (1) over bar 01]alpha-Al2O3. Although no epitaxial films were obtained at lower temperatures, the refractive indices of films deposited on alpha-Al2O3(1 (1) over bar 02) substrates were higher than the corresponding values of crystalline films grown on SiO2 under similar conditions. The refractive index values measured at the wavelength of 580 nm were 2.4-2.7 and 2.80-2.82 in the case of non-epitaxial and epitaxial films, respectively, grown on alpha-Al2O3. The band gap of epitaxial rutile was determined to be 3.16eV. (C) 2002 Elsevier Science B.V. All rights reserved.