Engineering bright directional emission from 2D semiconductor in double resonance metal-dielectric metasurface cavity

Controlling directionality and efficiency of light emission from quantum emitters is crucial for a wide range of applications including display, laser, and single photon source. Recently, two-dimensional transition metal dichalcogenides have emerged as key materials to realize quantum light sources, while resonant metasurfaces have attracted considerable attention due to their unprecedented ability to modify optical properties such as polarization, phase, directivity, Purcell factor, and spectrum. In this study, we propose a novel design method of light emitting metasurface to engineer double resonances for enhancement of directional photoluminescence from a monolayer WS2. By integrating a monolayer WS2 film on sapphire with a hybrid metal-dielectric metasurface resonator, the structure supports double resonances at the pump and emission wavelengths, at the same time. The hybrid metasurface resonator consists of silicon nanograting overlaid with a low index spacer and a silver mirror on top. In the proposed hybrid structure, the metallic mirror is incorporated to support Fabry-Pérot (FP) cavity resonances while the silicon nanograting serves as the main resonator to concentrate electromagnetic energy and transfer it to the WS2 layer below the nanograting. This design enables coupling between the five modes: two FP resonances, Mie-resonance, Rayleigh-Wood anomaly, and the exciton resonance of a monolayer WS2. The high directivity of emitted PL primarily attributes to the Rayleigh-Wood anomaly, while the total emission enhancement arises from the double resonance induced by hybridization of the five resonances. Therefore, we numerically demonstrate the emission enhancement exceeding 56-fold, assuming a collection numerical aperture of 0.1.