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+O2+N2 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 2.0×102 (both at the wavelength of 550nm), optical band gap width of 2.45eV (suitable for visible light absorption up to 505nm), low electrical resistivity of 0.4Ωcm (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.