A First-Principles Study on Structural and Optoelectronic Properties of 2D GaN/SnO₂ van der Waals Heterostructures under Biaxial Strain

Two-dimensional GaN/SnO2 van der Waals heterostructures were systematically investigated by using first-principles calculations to explore stacking-dependent optoelectronic properties. Among 24 configurations, the most stable structure exhibited −4.27 eV with an interlayer spacing of 3.67 Å. Biaxial strain engineering revealed distinct responses: compressive strain (0–5%) reduced the top surface work function from 5 to 4.5 eV while stabilizing the bottom surface potential (4.5–5 eV). It enhanced ultraviolet absorption (300–400 nm) but suppressed the visible light response, simultaneously decreasing short-wavelength reflectivity. Tensile strain conversely increased short-wavelength reflectivity. Notably, compressive strain induced type-I band alignment (direct gap, 1.75 eV) favoring light emission, while tensile strain created a type-II heterojunction (indirect gap, 1.5 eV) beneficial for carrier separation. Strain modulation significantly affected carrier dynamics. Compressive strain increased the electron effective mass from 0.35 m0 to 0.45 m0 with reduced carrier mobility, whereas tensile strain improved mobility with effective mass reduction. These strain-dependent transitions between type-I/II heterojunctions and tunable optoelectronic responses provide critical design principles for developing ultrathin photonic devices and strain-engineered sensors. The work establishes fundamental guidelines for manipulating low-dimensional heterostructure functionalities through mechanical deformation, advancing applications in flexible optoelectronics and energy-efficient nanodevices.