Stability and electro-optical properties of two-dimensional magnesium sulfide under strain and buckling

Exploring two-dimensional sulfur-based materials with remarkable properties is particularly significant for advancing applications in optoelectronics. Here, we explore a hexagonal magnesium sulfide (h-MgS) monolayer using PBE + G₀W₀ + BSE calculations, uncovering its desirable properties under strain and buckling. The pristine h-MgS monolayer shows slight instability and a moderate indirect bandgap. A small biaxial tensile strain of +0.5% or a buckling height of 0.25 Å can significantly enhance its stability. Interestingly, applied biaxial tensile strain and buckling can modify its bandgap by more than 1 eV, while the buckling itself can transform the nature of the indirect gap. In addition, the h-MgS monolayer demonstrates substantial light absorption (>10⁵ cm^-1) for near-ultraviolet light. Increased tensile strain and buckling height can induce a prominent red-shift in the optical spectrum and significantly boost visible and near-infrared light absorption. The exciton binding energy can also exceed 1 eV under the observed biaxial tensile strains and buckling heights. These findings indicate that the h-MgS monolayer could be a promising candidate for optoelectronic devices.