Effect of annealing on structure and properties of Ta–O–N films prepared by high power impulse magnetron sputtering

Abstract High power impulse magnetron sputtering of a Ta target in various Ar + O 2 + N 2 gas mixtures was utilized to prepare amorphous tantalum oxynitride (Ta–O–N) films with a finely controlled elemental composition in a wide range. We investigate the effect of film annealing at 900 ° C in vacuum on structure and properties of the films. We show that the finely tuned elemental composition in combination with the annealing enables the preparation of crystalline Ta–O–N films exhibiting a single TaON phase with a monoclinic lattice structure, refractive index of 2.65 and extinction coefficient of 2.0 × 10 2 (both at the wavelength of 550 nm ), optical band gap width of 2.45 eV (suitable for visible light absorption up to 505 nm ), low electrical resistivity of 0.4 Ω cm (indicating enhanced charge transport in the material as compared to the as-deposited counterpart), and appropriate alignment of the band gap with respect to the redox potentials for water splitting. These films are therefore promising candidates for application as visible-light-driven photocatalysts for water splitting.