Electronic structure and optical property regulation of two-dimensional monolayer FeGa<sub>2</sub>S<sub>4</sub>

This study aims to explore two-dimensional semiconductor materials with superior carrier transport properties to meet the growing demands of high-speed electronics and optoelectronic devices, focusing on evaluating the feasibility of monolayer FeGa<sub>2</sub>S<sub>4</sub> as a candidate material through systematic theoretical investigations. First-principles calculations are used to analyze the exfoliation energy of FeGa<sub>2</sub>S<sub>4</sub> bulk crystal, as well as the structural stability, mechanical properties, and strain-dependent optoelectronic behavior of its monolayer counterpart. Strain engineering strategies, including uniaxial and biaxial strain, are used to assess carrier mobility modulation and spectral response. Our calculation results indicate that monolayer FeGa<sub>2</sub>S<sub>4</sub> is an indirect bandgap semiconductor (<i>E</i><sub>g</sub> = 1.65 eV) with low stiffness (Young’s modulus up to 151.6 GPa) and high flexibility (Poisson’s ratio less than 0.25), demonstrating exceptional thermodynamic stability. Under +5% uniaxial tensile strain, its electron mobilities along <i>x</i> and <i>y</i> directions dramatically increases to 5402.4 cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup> and 4164.0 cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup>, fivefold higher than its hole mobility. Biaxial strain outperforms uniaxial strain in bandgap modulation and induces a systematic redshift in optical spectra, significantly enhancing visible-light harvesting efficiency. This work reveals that monolayer FeGa<sub>2</sub>S<sub>4</sub> is a promising high-mobility photoactive material for next-generation solar cells and optoelectronics. The strain-mediated control of electronic and optical properties provides a theoretical framework for optimizing 2D semiconductors and critical guidance for experimental synthesis and device engineering. These findings highlight the potential of materials in advancing energy conversion technology and photonic applications.