Annealing effected Nb dopant activation and optoelectronic properties in anatase thin films

Nb-doped anatase (NTO) thin film is a promising alternative to the conventionally used transparent conductors. However, its optoelectronic properties are strongly dependent on the fabrication condition. To this end, here the influence of the post-deposition annealing parameters on the dopant activation and thereby developed optoelectronic properties of these films are studied. In this regard, ~ 130 nm thick NTO films are first deposited on unheated quartz substrates using RF magnetron sputtering and then annealed at a range of temperature and time at ∼ 2.2 × 10^–4 Pa. Though all these post-annealed films crystallized as anatase, their crystallinity, dopant atom activation and optoelectronic properties are significantly influenced by the annealing process parameters. Only at an optimized annealing condition highest crystallinity in the film along with the most effective Nb doping in Ti lattice sites is seen, which eventually yields to the highest carrier concentration of 0.84 × 10²¹ cm⁻³, carrier mobility of 1.86 cm²/V-s and optical bandgap of 3.51 eV. Consequently, this film shows the lowest electrical resistivity of 4.01 × 10^–3 Ω cm. Moreover, in this paper, the mechanism of dopant atom activation as a function of annealing condition and thereby linked altered optoelectronic properties are discussed in detail.