Strain-Induced Modulation of the Electronic and Optical Properties of Janus MoSSe Monolayer: A First-principles Study

This study investigates the strain-dependent electronic and optical properties of a Janus MoSSe monolayer using first-principles density functional theory calculations incorporating spin-orbit coupling (SOC). In the unstrained structure, the monolayer is a direct-band-gap semiconductor with a PBE+SOC band gap of 1.47 eV at the K point. The valence band exhibits a pronounced SOC-induced splitting of 0.169 eV, substantially larger than the 0.013 eV splitting in the conduction band. Biaxial strain modifies both the band-gap magnitude and the locations of the band edges, producing distinct responses under compression and tension. Under compressive strain, the band gap varies non-monotonically, reaching a maximum at −2% strain, while the conduction-band minimum shifts away from K towards the K–Γ direction and the valence-band maximum moves from K to M at larger compressive strains. Under tensile strain, the valence-band maximum shifts to Γ, whereas the conduction-band minimum remains at K. The band gap decreases monotonically with increasing tensile strain and closes at +10%, indicating a strain-induced semiconductor-to-metal transition supported by the calculated density of states and optical response. The frequency-dependent dielectric function, refractive index, extinction coefficient, absorption coefficient, and reflectivity exhibit corresponding changes with strain. In addition, the static dielectric constant follows an inverse relationship with the band gap, consistent with the Penn model. These findings demonstrate how biaxial strain can modify the electronic band-edge configuration and optical response of Janus MoSSe, highlighting its potential for strain-mediated control of optoelectronic properties.