Electrically tunable excitonic light-emitting diodes based on monolayer WSe₂ p-n junctions

The development of light-emitting diodes with improved efficiency, spectral properties, compactness and integrability is important for lighting, display, optical interconnect, logic and sensor applications. Monolayer transition-metal dichalcogenides have recently emerged as interesting candidates for optoelectronic applications due to their unique optical properties. Electroluminescence has already been observed from monolayer MoS₂ devices. However, the electroluminescence efficiency was low and the linewidth broad due both to the poor optical quality of the MoS₂ and to ineffective contacts. Here, we report electroluminescence from lateral p-n junctions in monolayer WSe₂ induced electrostatically using a thin boron nitride support as a dielectric layer with multiple metal gates beneath. This structure allows effective injection of electrons and holes, and, combined with the high optical quality of WSe₂, yields bright electroluminescence with 1,000 times smaller injection current and 10 times smaller linewidth than in MoS₂ (refs 17,18). Furthermore, by increasing the injection bias we can tune the electroluminescence between regimes of impurity-bound, charged and neutral excitons. This system has the required ingredients for new types of optoelectronic device, such as spin- and valley-polarized light-emitting diodes, on-chip lasers and two-dimensional electro-optic modulators.