Greatly Enhanced Photoluminescence From a Si/WS ₂ /Si ₃ N ₄ /Ag Nanocavity by Exploiting the Electron Transfer Induced by Femtosecond Laser Pulses

Monolayer transition metal dichalcogenides hold great potential for quantum photonic devices owing to their unique physical properties. However, the atomically thin nature of these materials fundamentally limits their light absorption, which in turn constrains the efficiency and intensity of exciton emission. Here, we resonantly excited a WS 2 monolayer embedded in a Si/Si 3 N 4 /Ag nanocavity composed of a silicon (Si) nanoparticle and a Si 3 N 4 /Ag heterostructure by using femtosecond laser pulses, strongly enhancing two‐photon absorption in the Si nanoparticle. The generated electrons transfer to the WS 2 monolayer, effectively compensating for its weak optical absorption. We observed a significantly enhanced photoluminescence (PL) intensity of the Si/WS 2 /Si 3 N 4 /Ag nanocavity under femtosecond laser excitation compared to continuous‐wave laser excitation. Simultaneous enhancement of the excitation rate, emission intensity and emission directionality induced by double resonances further boosts the PL intensity in the WS 2 monolayer. The weak coupling between the exciton and magnetic dipole resonance additionally enhances the PL intensity and leads to a redshift in the PL spectrum. We obtain a PL enhancement factor as large as ≈ 13729 in the nanocavity at low laser power. Our findings suggest that the manipulation of carrier dynamics in hybrid nanocavities offers a promising strategy for the development of novel light‐emitting devices.