In this paper, the geometric structures and electron-optical properties of AlAs/GaS heterojunctions and Se-doped AlAs/GaS heterojunctions are calculated based on first-principles of density functional theory (DFT). At the same time, the influence of the AlAs layer's 5° rotation stacking method on the AlAs/GaS heterojunction is discussed. The results show that the AlAs/GaS heterojunction is a type-II van der Waals heterojunction (vdWH) with a direct bandgap of 0.974 eV, and the Z-scheme electron transfer mechanism is more conducive to the separation of photogenerated electrons and holes. Both semiconductor-to-metal transitions can be achieved by applying an external electric field and strain. Under the action of an external electric field and uniaxial strain, AlAs/GaS maintains the type-II energy band alignment throughout the process. When biaxial strain is applied, the heterojunction is accompanied by a direct–indirect bandgap transition. It is worth mentioning that the optical absorption of the AlAs/GaS heterojunction is significantly higher than that of the two monolayers, and the absorption range is wider. The above characteristics indicate that the AlAs/GaS heterojunction has wider applications in fields such as photodetectors.
