Structural and optoelectrical properties of Nb-TiO2 films fabricated by low-energy magnetron sputtering and post-annealing

Abstract

Nb-doped TiO2 (NTO) films have potential to replace indium tin oxide (ITO) as transparent conducting material. However, costly substrates with a specific orientation such as sapphire must be used to avoid formation of the rutile phase and to obtain transparent and conductive NTO films. Furthermore, scaling up is difficult thus hampering commercialization. Herein, in order to control the crystal orientation of TiO2, two-step preparation is described. An amorphous NTO film is first prepared on the economical soda-lime glass substrate by low-energy magnetron sputtering and the sample is annealed in Ar with 5 at% H2 at 400 °C to crystallize the amorphous structure into anatase (101) and anatase (004). The morphology, structure, and optoelectrical properties of the NTO films and relationship with film thickness are studied. The resistivity decreases to 8.1 × 10−4 Ω·cm for a thickness of 320 nm and the average transmittance in the visible region increases monotonically to 73% as the thickness is reduced from 400 nm to 280 nm. The good conductivity and transmittance suggest potential application to smart windows and solar cells.