Abstract <p>Vertical van der Waals heterostructures composed of HfNBr and ZrNBr are designed, and their electronic and optical behaviors are systematically examined under applied biaxial strain and external electric fields. The application of biaxial strain and external electric fields enables effective modulation of the band structure and bandgap in the heterostructures. Specifically, within the strain range of 2 to 8% and the electric field range of 0.2 to 0.8 V/Å, the band structure exhibits a Type-II alignment. Conversely, in the initial state without any applied strain up to a compressive strain of –8%, and within an electric field range down to –0.8 V/Å, the band structure transitions to a Type-I alignment. The calculations of optical properties indicate that HfNBr/ZrNBr vdWHs possess excellent ultraviolet (UV) light absorption capabilities. Compressive strain strengthens the heterostructure’s ability to absorb light in the ultraviolet region; notably, under –8% biaxial strain, the light absorption is significantly enhanced. In contrast, tensile strain weakens the light absorption performance of the heterostructures. Additionally, an external electric field is also capable of fine-tuning the light absorption capability of the heterostructures. Theoretical simulations have verified the dynamic, thermodynamic, and mechanical stability of HfNBr/ZrNBr vdWHs. The proposed theoretical results are expected to provide a theoretical foundation for the application of HfNBr/ZrNBr vertical heterostructures in tunable optoelectronic and strain-sensitive devices.</p>