Ultrafast Spontaneous Emission from a Slot-Antenna Coupled WSe₂ Monolayer

Optical antennas can enhance the spontaneous emission rate from nanoemitters by orders of magnitude, enabling the possibility of an ultrafast, efficient, nanoscale LED. Semiconductors would be the preferred material for such a device to allow for direct high-speed modulation. However, efficient nanoscale devices are challenging to implement because of high surface recombination typical of most III-V materials. Monolayer transition metal dichalcogenides are an attractive alternative to a III-V emitter due to their intrinsically nanoscale dimensions, direct bandgap, and near-ideal surfaces resulting in high intrinsic quantum yield. In this work, we couple a nanostrip (30 nm × 250 nm) monolayer of WSe<sub>2</sub> to a cavity-backed optical slot antenna through a self-aligned fabrication process. Photoluminescence, scattering, and lifetime measurements are used to estimate a radiative spontaneous emission rate enhancement of 318× from WSe<sub>2</sub> monolayers coupled to on-resonance antennas. Finally, such a huge increase in the spontaneous emission rate results in an ultrafast radiative recombination rate and a quantum yield in nanopatterned monolayers comparable to unprocessed exfoliated flakes of WSe<sub>2</sub>.