Optical polarization in mono and bilayer MoS₂

Optical anisotropy in monolayer- and bilayer-MoS₂ was investigated by polarization resolved photoluminescence measurements. The photoluminescence of monolayer-MoS₂ is found to be partially polarized at 4.2 K and maintains this polarization characteristic up to room temperature, while the photoluminescence of bilayer-MoS₂ shows no obvious polarization. This polarization anisotropy is due to strain effects at the interface between the MoS₂ layer and the SiO₂ substrate, causing symmetry breaking of the MoS₂ charge distribution. Calculations using density functional theory of the electron density distribution of the monolayer- and bilayer-MoS₂ in the in-plane direction are also presented, giving support to our qualitative analysis.