Electronic structure, work function and band alignment of low Miller-index β-TaON surfaces; a DFT + U study

Abstract

First principles calculations using GGA + U method have been carried out to study the stability, electronic structure, work function, and band alignment of low Miller-index surfaces of β-TaON. Fifteen possible surface terminations are included in this study. We found that, among all these surfaces, the O-terminated (111) has the lowest surface energy under all growth conditions followed by the O-terminated (100), the (110) and the (101) surfaces, respectively. The calculated band gap values for these surfaces are; 2.30, 2.20, 2.39 and 2.35 eV, respectively. Based on the determined band edges positions and taking into account the effect of surface states, we found that the (111)_O and (011)_O surfaces are appropriate for photo-catalytic splitting of water while the (100)_O and (101) surfaces are only appropriate for oxygen evolution reaction (OER). Furthermore, our results show that the (110) and (011)_TaN surfaces are suitable for hydrogen evolution reaction only. Our results show also that the electron affinity and work function of TaON depend greatly on the nature of surface termination.