First-Principles Study of Band-Gap Evolution in Monolayer MoS₂ under Biaxial Strain

Abstract

Two-dimensional transition-metal dichalcogenides have become important candidate materials for post-silicon semiconductors and optoelectronic devices because of their atomic-scale thickness, tunable band gaps, and good device compatibility. The electronic structure of monolayer MoS₂ is highly sensitive to strain. In-plane biaxial strain can continuously tune both the magnitude and the direct/indirect character of the band gap by changing Mo–S bond lengths and orbital hybridization. Based on density-functional theory, this work systematically performs first-principles calculations on the electronic structure of monolayer 1H-MoS₂ under biaxial strains from −6% to +8% in Quantum ESPRESSO, using the PBE functional and PAW pseudopotentials. At each strain point, ionic relaxation, self-consistent field calculation, and Γ–K–M–Γ band analysis are completed, and the fundamental gap, the K–K direct gap, and the Γ–K indirect gap are extracted simultaneously. The results show that under −2% compressive strain the system exhibits a K–K direct gap with a fundamental gap of 1.890 eV; near zero strain the K–K and Γ–K gaps are nearly degenerate (1.686 eV and 1.667 eV, respectively); after entering the tensile regime, the valence-band maximum shifts to Γ while the conduction-band minimum remains at K, forming a stable indirect gap, and the fundamental gap decreases monotonically from 1.667 eV at 0% to 0.589 eV at +8%. Gaps on the compressive side remain overall larger and reach a maximum of 1.919 eV at −4% within the present scan. This study provides a reproducible strain–band-gap relation and transition criterion, and offers a benchmark for band-gap engineering of two-dimensional MoS₂ and for subsequent higher-accuracy calculations.