From indirect to direct and back: Band gap evolution in strained Z-type AlN/B2SSe heterostructures for water splitting

In this article, we constructed an AlN/B2SSe heterostructure using B2SSe and AlN. Using first -principles calculations, we calculated the stability, electronic structure, optical properties, and photocatalytic properties of the AlN/B2SSe heterostructure. Firstly, we consider four high -symmetry stacking configurations of the AlN/B2SSe heterostructure: Model I, Model II, Model III, and Model IV. After analysis, Model III and Model IV have the lower binding energy. The stability of the Model III and Model IV of AlN/B2SSe heterostructure was determined through phonon spectra. Secondly, the band structure, charge density, work function, and difference charge density of the AlN/B2SSe heterostructure were calculated using the HSE06 hybrid density functional. Model III is an indirect bandgap semiconductor with a bandgap of 1.89/3.03 eV at the PBE/HSE06 level, meanwhile, Model IV is also an indirect bandgap semiconductor with a bandgap of 1.47/2.60 eV at the PBE/HSE06 level. The work functions (phi) of B2SSe, AlN, Model III, and Model IV are 6.31 eV, 5.81 eV, 6.02 eV, and 6.08 eV, respectively. This also means that during the heterojunction formation between B2SSe and AlN, electrons will transfer from the AlN layer to the B2SSe layer until the Fermi level reaches dynamic equilibrium, which creates a built-in electric field between the B2SSe and AlN layers. The presence of the built-in electric field promotes the separation of electron -hole pairs. Additionally, applying strain to the AlN/B2SSe heterostructure further broadened the range of the optical absorption spectrum. The light absorption range of Model III is extended to 557 nm, and the light absorption range of Model IV is extended to 683 nm. Therefore, the photocatalytic efficiency of AlN/ B2SSe heterostructure is improved under strain. Finally, the AlN/B2SSe heterostructure exhibited good hydrogen evolution efficiency, as observed through HER. These characteristics make the AlN/B2SSe heterostructure promising for photocatalytic water -splitting applications.