Tuning electronic and optical properties of narrow band gap 2D WSn2X4 (X=P, As) materials

Since the successful synthesis of MoSi${}_2$N${}_4$ (Hong et al., 2020), the ”MA${}_2$Z${}_4$ family” has emerged as highly promising class of materials for next-generation optoelectronic applications. In this study, we employ first-principles calculations to investigate the structural, electronic, and optical properties of two-dimensional WSn${}_2$X${}_4$ (X = P, As) monolayers. The ground-state energies, elastic constants, and phonon calculations confirm that these materials satisfy the energetic, mechanical, and dynamical stability criteria, indicating their feasibility for experimental synthesis. Ab initio molecular dynamics simulations further indicate that the WSn${}_2$X${}_4$ monolayers can sustain stability at high temperature. Our results reveals that the WSn${}_2$P${}_4$ exhibits metallic behavior at the PBE level, while the HSE06 functional opens a bandgap of 0.12 eV. Similarly, the narrow bandgap of WSn${}_2$As${}_4$ (0.05 eV at the PBE level) is enhanced to 0.32 eV with the HSE06 functional. Furthermore, the optical response of these narrow-bandgap monolayers demonstrates optical bandgaps in the infrared (IR) range, making them promising candidates for infrared detectors. We also investigate the impact of biaxial strain on the electronic and optical properties of WSn${}_2$X${}_4$ (X = P, As) monolayers. Our findings reveal significant changes in both their electronic structure and optical spectra under strain. The bandgap can be tuned, enabling a semiconductor-to-metal transition under biaxial strain. Additionally, the light absorption characteristics and the positions of the absorption peaks can be finely adjusted via biaxial strain, allowing for tailored optical properties in the infrared region. These results provide valuable insights into the intrinsic electronic and optical properties of these 2D materials and their modulation through biaxial strain, highlighting their potential for applications in terahertz devices, nanoelectronics, and optoelectronics.