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

Abstract

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 (ρ) of (3–6)×10−4Ωcm. On glass, however, highly resistive rutile phase polycrystalline films (ρ∼100Ωcm) 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 ρ=1.1×10−3Ωcm and optical absorption lower than 10% in the visible region. This ρ 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.