Solving the Mystery of B-Peak Emission in Monolayer Transition Metal Dichalcogenides

We survey a large number of monolayer TMDs to better understand the conditions responsible for various emission characteristics that have been reported in literature. We find that the intensities for both A- and B-peak emission vary widely as a result of sample-to-sample variations. However, a measurable B-peak intensity is evident in all samples. There is a clear linear relationship between the two peak intensities. The emission from the dominant A-peak is commonly several orders of magnitude higher than B-peak emission, resulting in B/A-intensity ratios well below 1%. Yet, as the A-peak intensity decreases, the ratio of B/A monotonically increases, and we observe a B/A ratio up to 30% in monolayer MoS₂. The A-excitonic emission is further quenched when MoS₂ is incorporated into an MoS₂/MoSe₂ heterostructure, where we observe comparable A- and B-peak intensities. We attribute these variations to differences in exciton recombination times, allowing us to clarify contradictory reports regarding the feasibility and significance of B-peak emission.