Enhanced Light Emission in MoSe₂-WSe₂ Lateral Heterostructures in the Electron-Hole Plasma Regime

Two-dimensional (2D) transition metal dichalcogenide (TMD) semiconductors exhibit interesting many-body effects even above room temperature due to their strong electron-hole interactions. For instance, low excitation densities lead to the well investigated exciton formation in these 2D TMDs and their heterostructures. The confinement of the moiré excitons and the delocalization of the interlayer excitons are among the novel excitonic phenomena presented by TMD-based heterostructures. However, the high excitation density responses of these 2D semiconductors and their heterostructures still lack solid understanding. In this work, we investigate the electron-hole plasma photoluminescence generated by high excitation densities in 2D MoSe₂-WSe₂ lateral heterostructures. Photoluminescence mapping and spectroscopy measurements at high pumping regimes reveal an enhanced light emission at the lateral heterojunctions. Ab initio calculations for a MoSe₂-WSe₂ lateral heterostructure with an alloyed interface of approximately the size of the heterojunctions of the experimental samples show good agreement with the experimental data. Additionally, the theoretical results provide an explanation for the observed enhancement of the photoluminescence at the heterojunctions and for the role of interfacial alloying in increasing the overlap of electron and hole wave functions at the interface. These observations reveal the localized character of the optical effects at heterojunctions of lateral TMD-based heterostructures under high excitation densities.