Van der Waals (vdW) heterostructures assembled from two-dimensional (2D) materials offer a highly versatile platform for developing multifunctional devices. Here we systematically investigate the electronic structure and photocatalytic properties of the $\beta$-$\mathrm{As}\mathrm{P}$/${\mathrm{Mo}\mathrm{Si}}_2{\mathrm{N}}_4$ vdW heterostructure via first-principles calculations. Our results indicate that the heterostructure remains stable at room temperature and possesses an indirect band gap of 1.91 eV. It exhibits a type-II band alignment, along with enhanced electron mobility and optical absorption capacity compared with its constituent monolayers. Notably, compressive strain exceeding 1% induces an indirect-to-direct band gap transition, attributed to the distinct strain responses of the band edges in the individual layers. Furthermore, the band alignment can be reversibly tuned between type I and type II through the application of external strain or an electric field. A particularly promising configuration arises under a tensile strain of 0.43% or an electric field of $-0.25$ V/Å, which results in equal band offsets ($\mathrm{\Delta }{E}_c=\mathrm{\Delta }{E}_v$). Our findings suggest great potential for low-power electronic device applications of 2D materials.

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• Electronic structure
• Optoelectronics
• Photocatalysis
• Heterostructures
• Semiconductor compounds
• van der Waals systems
• Density functional calculations
• Strain engineering