First-principles studies of the structural and electronic properties of the (Ga1-xZnx)(N1-xOx) solid solution photocatalyst

Design of visible-light-driven photocatalytic materials has attracted intense interest in recent years in an attempt to enhance photonic efficiencies of hydrogen production via water splitting. Recent studies have shown that a solid solution of GaN and ZnO, (Ga1-xZnx)(N1-xOx), can oxidize water under visible light in the presence of a sacrificial electron acceptor. Here we present a systematic study of the structural and electronic properties of this (Ga1-xZnx)(N1-xOx) solid solution as a function of zinc (oxygen) concentration, x, using density-functional theory (DFT). The DFT+U approach has been adopted, and two different periodic supercells, the 16-atom (Ga8-nZnn)(N8-nOn) and 32-atom (Ga16-nZnn)(N16-nOn), have been used to model this solid solution. Results obtained from both supercells are in qualitative agreement with available experimental findings (in the lower concentration range x < 0.25), although overall the larger 32-atom supercell provides a better description of the (Ga1-xZnx)(N1-xOx) solid solution. Downward bowing of the band gap over the entire composition range has been observed for both supercells, and the minimum "experimental" band gap is estimated to be about 2.29 eV for the intermediate concentration x = 0.525. This suggests that the photocatalytic activity of this solid solution can be improved further by increasing its zinc (oxygen) concentration.