Single photon emitters in monolayer semiconductors coupled to transition metal dichalcogenide nanoantennas on silica and gold substrates

Abstract: Transition metal dichalcogenide (TMD) single photon emitters (SPEs) offer numerous advantages to quantum information applications, such as high single photon purity and deterministic positioning. Strain in the host monolayer, induced by underlying dielectric Mie resonators, is known to localize their formation to positions co-located with near-field photonic hotspots providing further control over their optical properties. However, traditional materials used for the fabrication of nanoresonators, such as silicon or gallium phosphide (GaP), often require a high refractive index substrate resulting in losses of the emitted light and limited photonic enhancement. Here, we use nanoantennas (NAs) fabricated from multilayer TMDs, which allow complete flexibility with the choice of substrate due to the adhesive van der Waals forces, enabling high refractive index contrast or the use of highly reflective metallic surfaces. We demonstrate the localized formation of SPEs in WSe$_2$ monolayers transferred onto WS$_2$ NAs on both SiO$_2$ and Au substrates, enabling strong photonic enhancements and increased single photon collection. We provide evidence for enhanced quantum efficiencies (QE) reaching an average value of 43% (7%) for SPEs on WS$_2$ NAs on a SiO$_2$ (Au) substrate. We further combine the advantages offered by both dielectric and metallic substrates to numerically simulate an optimized NA geometry for maximum WSe$_2$ single photon excitation, emission, collection. Thus, the fluorescence is enhanced by a factor of over 4 orders of magnitude compared to vacuum and 5 orders of magnitude compared to a flat SiO$_2$/Si surface. Our work showcases the advantages offered by employing TMD material nanoresonators on various substrates for SPE formation and photonic enhancement.