Tailoring light absorption in Si ₂ XY (X, Y = P, As, Sb, Bi) Janus monolayers via strain engineering

Two-dimensional (2D) Janus materials, characterized by their inherent structural asymmetry, are attracting significant research interest for their exceptional electronic and optical properties, positioning them as promising candidates for next-generation optoelectronic applications. This study employs first-principles calculations to investigate a new class of 2D Janus materials: Si 2 XY (X, Y [Formula: see text] P, As, Sb, Bi) monolayers. The Si 2 XY all systems are mechanically stable, as confirmed by their elastic constants, Young’s modulus, and Poisson’s ratio. Furthermore, the covalent bonding in these systems is confirmed by the electron localization function (ELF) analysis. The Si 2 XY systems exhibit indirect bandgaps ranging from 0.473 eV to 2.009 eV, except for Si 2 AsBi, which possesses a direct bandgap of 0.816 eV using the Heyd–Scuseria–Ernzerhof (HSE06) method. The optical properties of these materials were investigated by calculating the dielectric function and absorption coefficient. Our findings reveal that the Si 2 XY systems exhibit significant optical spectra activity across the visible and ultraviolet (UV) spectral regions. Specifically, a pronounced absorption coefficient of [Formula: see text] [Formula: see text]cm[Formula: see text] is observed at a photon energy of at 4.88 eV, alongside a relatively lower value of [Formula: see text] [Formula: see text]cm[Formula: see text] observed at 4.68[Formula: see text]eV. Crucially, our findings demonstrate that the optical properties of these Janus Si 2 XY monolayers can be tuned by biaxial strain. This tunability underscores their significant potential for incorporation into high-performance optoelectronic devices.