Exciton aggregation induced photoluminescence enhancement of monolayer WS2

Abstract

Defect mediated nonradiative recombination limits the photoluminescence (PL) quantum yield of transition metal dichalcogenide monolayers (MLs). In this work, the enhancement of the PL intensity of ML WS2 is reported in a van der Waals heterostructure of WS2 ML and InGaN quantum dots (QDs) under excitation with photon energy larger than the bandgaps of both WS2 and QDs. The mechanism of this PL enhancement is due to the aggregation of excitons in WS2 ML toward the QD sites to form an interfacial bound state, which effectively mitigates the influence of defects. This exciton aggregation induced enhancement of PL intensity is more pronounced at low temperatures and under low power excitations. The lifetime and diffusion coefficient of the excitons in WS2 ML are also measured to validate the aggregation scenario.