Synthesis of conductive and transparent Nb-doped TiO2 films: Role of the target material and sputtering gas composition

The authors report a comparative study of the electrical and optical properties of Nb:TiO2 thin films (TNO) in relation with their chemical properties. Two types of niobium containing targets, Nb metal and Nb2O5 oxide were employed simultaneously with ceramic TiO2 target for the films growth, in Ar and Ar-O-2 discharge. Niobium is found to incorporate easily and substitutionally into titanium lattice site when deposited from oxide targets in oxygen-deficient discharge (Ar plasma). Consequently, the TNO film exhibits lowest resistivity of 1.4 x 10(-3) Omega cm with optical transparency of more than 80% in the visible region. On the contrary, doping was not effective in case the TNO films were grown from Nb metal and TiO2 targets in Ar and Ar-O-2 plasma, probably due to the growth of niobium sub-oxide phases and lack of oxygen vacancies. The possible reasons of diverse electrical properties are discussed and are link with the growth conditions. Our result indicates that highly conductive and transparentdoped-TiO2 film can be obtained by choosing appropriate target material and sputtering gas. The obtained results can significantly contribute to the development of transparent electrodes by RF sputtering, a suitable technique for coating on large area substrates.