Direct growth of transparent conducting Nb-doped anatase TiO2 polycrystalline films on glass

This paper proposes a novel sputter-based method for the direct growth of transparent conducting Ti1-xNbxO2 (TNO) polycrystalline films on glass, without the need for any postdeposition treatments, by the use of an initial seed-layer. Anatase TNO epitaxial films grown on LaAlO3 (100) substrates under a reducing atmosphere exhibited a low resistivity (rho) of (3-6) x 10(-4) Omega cm. On glass, however, highly resistive rutile phase polycrystalline films (rho similar to 100 Omega cm) formed preferentially under the same conditions. These results suggest that epitaxial stabilization of the oxygen-deficient anatase phase occurs on lattice-matched substrates. To produce a similar effect on a glass surface, we deposited a seed-layer of anatase TNO with excellent crystallinity under an increased oxygen atmosphere. As a result, anatase phase TNO polycrystalline films could be grown even under heavily reducing atmospheres. An optimized film exhibited rho = 1.1 x 10(-3) Omega cm and optical absorption lower than 10% in the visible region. This rho value is more than one order of magnitude lower than values reported for directly deposited TNO polycrystalline films. This indicates that the seed-layer method has considerable potential for producing transparent conducting TNO polycrystalline films on glass. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3148267]