Structural phase-dependent resistivity of intrinsic-extrinsic co-doped transparent titanium dioxide films

The authors report a method of enhancing the conductivity of TiO2 films by controlling their structural phases. Thin films of Nb:TiO2 (TNO) were prepared on glass and silicon substrates by RF sputtering with varying Nb content at 200 °C. It is shown that fine control over the structural phases of TiO2 is critical for achieving low resistivity. The resistivity values of the films doped with oxygen vacancies and Nb+5 decreased from 3.8 × 10−1 to 4.1 × 10−3 Ω cm when the weight percent of rutile in anatase-rutile phase mixture decreases from 52.8% to 32%. Furthermore, the lowest resistivity value of 2.37 × 10−3 Ω cm was obtained for the doped TiO2 films having single phase anatase structure. The physical processes responsible for the diverse electrical properties are discussed and are associated with the growth conditions. Our result indicates that highly conductive doped-TiO2 film can be obtained by controlling the anatase phase formation via the growth temperature. The obtained results can significantly contribute to the development of transparent electrodes by RF sputtering, a suitable technique for coating large area substrates.