A DFT study of rotationally twisted 2D ZnO/GaN van der Waals heterostructures: the role of twisting angle on band gap, band edges, and optical absorption

Abstract This work investigates the effect of rotating a monolayer within the ZnO/GaN van der Waals (vdW) heterostructure on key photocatalytic performance for solar water splitting. Using a computationally efficient and validated Perdew–Burke–Ernzerhof generalized gradient approximation with density functional theory+U correction approach, we systematically engineered the heterointerface by rotating the ZnO monolayer at 15 {}^∘ , 30 {}^∘ , and 45 {}^∘ relative to a fixed GaN monolayer. Our results show that rotation induces a superlattice that systematically reduces the band gap from 2.94 eV (non-rotated) to 1.42 eV (45 {}^∘ rotated), while simultaneously broadening optical absorption well into the visible light spectrum. Specifically, we observed enhanced interlayer interactions between Zn and N, and Ga and O atoms, leading to the formation of bonds and pronounced monolayer buckling. Specific rotated configurations, particularly the 15 {}^∘ structure, maintain a type-II band alignment suitable for driving the water redox reactions at pH 0 and pH 7, and retain a significant built-in electric field for efficient charge separation and increase exciton lifetime. This work establishes controlled rotation as a potent strategy for tailoring the electronic and optical properties of vdW heterostructures, providing a clear design principle for developing high-efficiency, solar-driven photocatalysts.