Exploring strain-induced variations in electronic structure and optical properties of MoSi₂N₄/WSSe heterostructure

The development of two-dimensional van der Waals heterostructures for optoelectronic and photocatalytic applications demands precise control over band alignment and light absorption. This study addresses the challenge of engineering strain-tunable electronic properties in the MoSi₂N₄/WSSe heterostructure, a system exhibiting intrinsic type-I band alignment and a direct band gap of 1.850 eV. We demonstrate that interfacial charge transfer of 0.0831 |e| from MoSi₂N₄ to WSSe generates a robust internal electric field, significantly enhancing charge separation and transport. Crucially, compressive strain induces reversible transitions between type-I and type-II band alignments and between direct and indirect band gaps, enabling dynamic modulation of carrier dynamics. At -4% and -5% strain, the charge transfer aligns with the Z-scheme characteristics, and band edges positions precisely match the water redox potentials. Compared with its individual monolayer components, the heterostructure demonstrates enhanced optical absorption across both visible and ultraviolet spectral regions. Tensile strain markedly enhances light absorption, with the absorption coefficient peak increasing from 5.4 to 28.5%, and induces a redshift of the absorption peak in the visible light range. These findings confirm that the MoSi₂N₄/WSSe heterostructure, with its excellent tunability, holds considerable promise for applications in optoelectronic and photocatalytic devices based on thermodynamic band alignment.

All calculations were performed using the Vienna ab initio Simulation Package (VASP) within the framework of density functional theory. The PBE-GGA functional was chosen as the main exchange-correlation functional, while the HSE06 hybrid functional was used to carry out all electronic and optical property calculations. van der Waals interactions were incorporated via the Grimme-D3 correction. Key computational parameters included a plane-wave kinetic energy cutoff of 520 eV, a total energy convergence threshold of 10^-8 eV, a force convergence threshold of 0.01 eV/Å, and a 5 × 5 × 1 Monkhorst-Pack k-point mesh. A vacuum spacing of 20 Å along the z-axis was applied to eliminate interlayer interactions. Phonon dispersion curves were computed using the Phonopy code.