Tuning and Identification of Interband Transitions in Monolayer and Bilayer Molybdenum Disulfide Using Hydrostatic Pressure

Abstract

Few-layer molybdenum disulfide (MoS₂) is advantageous for application in next-generation electronic and opto­electronic devices. For monolayer MoS₂, it has been established that both the conduction band minimum (CBM) and the valence band maximum (VBM) occur at the K point in the Brillouin zone. For bilayer MoS₂, it is known that the VBM occurs at the Γ point. However, whether the K valley or the Λ valley forms the CBM and the energy difference between them remain disputable. Theoretical calculations have not provided a conclusive answer. In this paper, we demonstrate that a direct K–K to an indirect Λ–K interband transition in bilayer MoS₂ can be optically detected by tuning the hydrostatic pressure. A changeover of the CBM from the K valley to the Λ valley is observed to occur under a pressure of approximately 1.5 GPa. The experimental results clearly indicate that the K valley forms the CBM under zero strain, while the Λ valley is approximately 89 ± 9 meV higher in energy