Biaxial strain-dependent electronic and optical behaviors of WSi ₂ N ₄ /g-GaN heterostructure: A first-principles study

We systematically investigated the electronic, optical, and strain-dependent properties of the WSi 2 N 4 /g-GaN van der Waals heterostructure (vdWH) using first-principles calculations. The heterostructure exhibits an indirect band gap of 1.89 eV with type-I band alignment, indicating its potential for high-performance optoelectronic applications. A net charge transfer of 0.103 |e| from WSi 2 N 4 to g-GaN induces charge redistribution, generating a strong built-in electric field that significantly enhances charge carrier transport. Furthermore, tensile strain can induce a transition from indirect to direct band behavior. Meanwhile, the inherent type-I alignment reversibly transformed to type-II under a small compressive strain of -1% or near-zero tensile strain. Notably, the sharp shift indicates high strain sensitivity, enabling precise control over the transition of band alignment type. The heterostructure demonstrates enhanced absorption in both visible and ultraviolet regions compared to its constituent monolayers. Under tensile strain, the optical absorption coefficient exhibits a systematic enhancement, accompanied by a significant redshift in the absorption peak position and a substantial broadening of the absorption spectrum. Conversely, compressive strain leads to band gap widening and a consequent reduction in optical absorption efficiency. These results collectively highlight the exceptional strain-tunable properties of the WSi 2 N 4 /g-GaN vdWH, making it particularly promising for applications in optoelectronic devices and photocatalytic systems.