Anatase phase stability and doping concentration dependent refractivity in codoped transparent conducting TiO₂ films

Nb_0.06Sn_xTi_0.94−xO₂ (x ≤ 0.3) thin films were grown by a pulsed-laser deposition method with varying Sn concentration. Through a combinatorial technique, we find that Sn concentration can reach a maximum of about x = 0.3 while maintaining the stable anatase phase and epitaxy. A doping concentration dependence of the refractivity is revealed, in which refractivity reduction at a wavelength of λ = 500 nm is estimated to be 12.4% for Nb_0.06Sn_0.3 Ti_0.64O₂ thin film. Sn doping induced band-gap blue shift can be contributed to the mixing of extended Sn 5s orbitals with the conduction band of TiO₂. Low resistivity on the order of 10⁻⁴ Ω cm at room temperature and high internal transmittance of more than 95% in the visible light region are exhibited for Nb_0.06Sn_x Ti_0.94−xO₂ thin films (x ≤ 0.2). Optical and transport analyses demonstrate that doping Sn into Nb_0.06 Ti_0.94O₂ can reduce the refractivity while maintaining low resistivity and high transparency.