Indirect bandgap MoSe₂ resonators for light-emitting nanophotonics

Bulk transition metal dichalcogenides (TMDs) have an extremely high refractive index of approximately 5 in the visible and IR spectral ranges. This property makes TMDs an excellent medium for nanophotonic structures. However, due to the indirect bandgap of TMDs, most of the attention in the field of nanophotonics has been given to the creation of dielectric nanophotonic structures for light absorption or low-loss nanophotonics. Unfortunately, there have been few studies on light-emitting TMD nanophotonic structures.

In this study, we present a new type of stand-alone TMD nanocavity that serves as a source of excitonic photoluminescence. We created disk whispering-gallery-mode optical nanoresonators using bulk indirect bandgap MoSe₂. To avoid contamination or chemical treatment that could alter the TMD's properties, we employed the novel frictional probe lithography to fabricate the nanoresonators. The resulting nanoresonators exhibited strongly enhanced photoluminescence (by two orders of magnitude) in the range of 850 to 1050 nm. By varying the nanocavity diameter, we can tune the peak positions. This work demonstrates a new approach to fabricating light-emitting nanophotonic devices from indirect bandgap TMDs and paves the way for further research.