Effects of intrinsic defects and extrinsic doping on the electronic and photocatalytic properties of Ta3N5

Abstract

Ta₃N₅ is a good candidate for an oxygen evolution photocatalyst or a photoanode for a Z-scheme device due to its n-type feature. In the present work, the formation energies and electronic structures of defects contained in Ta₃N₅ are studied by first principles density functional theory in detail. Our results show that the substitution of O for three-coordinated N in Ta₃N₅ possesses a low formation energy and introduces a shallow donor under both N-rich and N-poor conditions, making a major contribution to the n-type conductivity. By investigation of the optical transition levels, we show that the four-coordinated N vacancy in Ta₃N₅ is responsible for the observed 720 nm sub-band gap optical absorption. In addition, for alkali metal doped Ta₃N₅, our results reveal that the interstitial doping can lead to enhanced conductivity and reduced band gap, and the doping of Na and K in Ta₃N₅ are expected to produce higher photocatalytic activity compared to Rb and Cs. These results are useful to understand the recent experimental observations and provide guidance to engineer Ta₃N₅ with improved photocatalytic efficiency.