Strain-tunable electronic and optical properties of a Z-scheme MoSi2N4/GaN vdW heterojunction

Abstract

In this study, we designed four stacking configurations of MoSi₂N₄/GaN vdW heterojunctions based on the MoSi₂N₄ and GaN monolayers, with the AD-stacking heterojunction (AD-HS) identified as the most stable. Under −2% biaxial strain, AD-HS undergoes a transition from type-I to type-II band alignment, which significantly enhances charge separation and photocatalytic efficiency. Then we investigate the structural, electronic and photocatalytic properties of AD-HS (−2%) using first-principles calculations. Phonon dispersion and ab initio molecular dynamics confirm its dynamic and thermal stability. The bandgap of AD-HS (−2%) calculated by the HSE06 method is 2.66 eV, with its band edges spanning water redox potentials at pH = 0, 7 and 14. Charge density difference and Bader charge analysis reveal electrons transfer from GaN to MoS₂N₄ monolayers at the interface, forming a built-in electric field that promotes carrier separation. It conforms to the Z-scheme carrier transfer mechanism. Band edge energy level analysis shows that AD-HS (−2%) facilitates hydrogen evolution on the GaN monolayer and oxygen evolution on the MoSi₂N₄ monolayer. What's more, the Gibbs free energy changes of elementary reactions are calculated to discuss the spontaneity of the oxygen evolution reaction (OER), and the light absorption coefficients are calculated to evaluate its light-harvesting ability. Taking all factors into consideration, AD-HS (−2%) can be regarded as a potential water splitting photocatalyst in alkaline environments.