Excitonic quantum confinement modified optical conductivity of monolayer and few-layered MoS₂

Optical conductivity plays an important role in characterizing the optoelectronic properties of two-dimensional materials. Here we derive the complex optical conductivities for monolayer and few-layered MoS₂ films from their reflectance and transmittance responses. We show that the excitonic quantum confinement effect significantly modifies both the peak energy and magnitude of their optical conductivity, manifested by a gradual blueshift in energy (consistent with two well-known models for quantum well systems) and exponential attenuation in magnitude with decreasing layer number. More importantly, the C excition induced optical conductivity peak exhibits the strongest dependence on the MoS₂ layer number because of its largest Bohr radius among the A, B and C excitons. This unambiguously confirms the strong influence of quantum confinement effect in the optical conductivity of MoS₂, shedding important insights into understanding its rich exciton-related optical properties and therefore facilitating potential applications in optoelectronic devices.