Tuning the electronic and optical properties in MoSeS and WSeS monolayers by mechanical strains

Abstract

This study systematically explored the effects of tensile, compressive, and shear strains on the structural parameters, stability, and optoelectronic characteristics of MoSeS and WSeS monolayers, utilising first principles. Phonon spectral analysis confirms the dynamic stability of the MSeS (M=Mo, W) pristine and its biaxial tensile strain systems, and electronic structure calculations show that both MoSeS and WSeS are a type of direct bandgap semiconductor. Further analysis shows that different types of strains significantly affect the band edge, band gap width, band gap type, density of states, and charge density distribution. Uniaxial compressive strain has a greater effect on the electronic structure than uniaxial tensile strain, while the effect of shear strain is intermediate between uniaxial tensile and compressive, and biaxial strain has the greatest effect. The optical properties also get better when the material is strained. For example, under 16 % biaxial compressive strain, the static dielectric constants of MoSeS and WSeS increase by a factor of 6 and 9.6, respectively, which improves the dielectric properties and charge retention. Additionally, strain shifts the absorption band edges to longer wavelengths, expanding the material's response in the infrared and visible ranges. Compressive and shear strains also increase reflectivity, with MoSeS and WSeS reflectivity rising approximately 2.9 and 3.5 times, respectively, under 16 % biaxial compressive strain. These findings provide a theoretical basis for the application of Janus monolayers in novel optoelectronic devices and reveal a new strategy to precisely modulate optoelectronic properties through strain.