Electrical and optical properties of Nb-doped TiO2 films deposited by dc magnetron sputtering using slightly reduced Nb-doped TiO2-x ceramic targets

Nb-doped anatase TiO2 films were deposited on unheated glass by dc magnetron sputtering using slightly reduced Nb-doped TiO2-x targets (Nb concentration: 3.7 and 9.5 at. %) with various hydrogen or oxygen flow ratios. After postannealing in a vacuum (6x10-4 Pa) at 500 deg. C for 1 h, both films were crystallized into the polycrystalline anatase TiO2 structure. The resistivity decreased from 1.6x10-3 to 6.3x10-4 Ω cm with increasing Nb concentration from 2.8 to 8.0 at. %, where the carrier density increased from 5.4x1020 to 2.0x1021 cm-3 and the Hall mobility was almost constant at 5-7 cm2 V-1 s-1. The films exhibited a high transparency of over 60%-80% in the visible region.