Excitation intensity dependence of photoluminescence from monolayers of MoS₂ and WS₂/MoS₂ heterostructures

Adetailed study of the excitation dependence of the photoluminescence (PL) frommonolayers of MoS₂ and WS₂/MoS₂ heterostructures grown by chemical vapor deposition on Si substrates has revealed that the luminescence from band edge excitons from MoS₂ monolayers shows a linear dependence on excitation intensity for both above band gap and resonant excitation conditions. In particular, a band separated by ∼55 meV from the Aexciton, referred to as the Cband, shows the same linear dependence on excitation intensity as the band edge excitons. A band similar to the Cband has been previously ascribed to a trion, a charged, three-particle exciton. However, in our study the Cband does not show the 3/2 power dependence on excitati on intensity as would be expected for a three-particle exciton. Further, the PL from the MoS₂ monolayer in a bilayer WS₂/MoS₂ heterostructure, under resonant excitation conditionswhere only the MoS₂ absorbs the laser energy, also revealed a linear dependence on excitation intensity for the Cband, confirming that its origin is not due to a trion but instead a bound exciton, presumably of an unintentional impurity or a native point defect such as a sulfur vacancy. The PL fromthe WS₂/MoS₂ heterostructure, under resonant excitation conditions also showed additional featureswhich are suggested to arise fromthe interface states at the heteroboundary. Further studies are required to clearly identify the origin of these features.