Encapsulated Silicon Nitride Nanobeam Cavity for Hybrid Nanophotonics

Most existing implementations of silicon nitride photonic crystal cavities rely on suspended membranes due to their low refractive index. Such floating membranes are not mechanically robust, making them suboptimal for developing a hybrid optoelectronic platform where new materials, such as layered 2D materials, are transferred onto prefabricated optical cavities. To address this issue, we design and fabricate a silicon nitride nanobeam resonator where the silicon nitride membrane is encapsulated by material with a refractive index of ∼1.5, such as silicon dioxide or PMMA. The theoretically calculated quality factor of the cavities can be as large as 105, with a mode-volume of ∼2.5(λ/n)3. We fabricated the cavity and measured the transmission spectrum with the highest quality factor reaching 7000. We also successfully transferred monolayer tungsten diselenide on the encapsulated silicon nitride nanobeam and demonstrated coupling of the cavity with both the monolayer exciton and the defect emissions.