Giant Enhancement and Directional Second Harmonic Emission from Monolayer WS₂ on Silicon Substrate via Fabry-Pérot Micro-Cavity

Abstract

Two-dimensional transition metal dichalcogenides (TMDs) possess large second-order optical nonlinearity, making them ideal candidates for miniaturized on-chip frequency conversion devices, all-optical interconnection, and optoelectronic integration components. However, limited by subnanometer thickness, the monolayer TMD exhibits low second harmonic generation (SHG) conversion efficiency (<0.1%) and poor directionality, which hinders their practical applications. Herein, we proposed a Fabry-Pérot (F–P) cavity formed by coupling an atomically thin WS2 film with a silicon hole matrix to enhance the SH emission. A maximum enhancement (∼1580 times) is achieved by tuning the excitation wavelength to be resonant with the microcavity modes. The giant enhancement is attributed to the strong electric field enhancement in the F–P cavity and the oscillator strength enhancement of excitons from suspended WS2. Moreover, directional SH emission (divergence angle ∼5°) is obtained benefiting from the resonance of the F–P microcavity. Our research results can provide a practical sketch to develop both high-efficiency and directional nonlinear optical devices for silicon-based on-chip integration optics.

Giant Out-of-Plane Exciton Emission Enhancement in Two-Dimensional Indium Selenide via a Plasmonic Nanocavity

“…These results vigorously validate that the plasmonic nanogap mode enhances the absorption of InSe and the 800 nm excitation wavelength can achieve the effective exciton–photon interaction required for optimal excitation of OP excitons. For a system with a specific resonance wavelength, resonant excitation can yield the best optical performance, − demonstrated in plasmonic Raman enhancement , and second-harmonic emission. − The increased local density of states in the plasmonic nanocavity results in the suppression of the nonradiative recombination and the shortening of the spontaneous radiative lifetime of the dielectric layer via the Purcell effect, − which has also been applied to upconversion emission , and quantum dot lasing . The time-resolved photoluminescence (TRPL) is measured to obtain the lifetimes of InSe in and off cavity and analyzed through biexponential fitting (Supplementary Figure 7).…”

Deep ultraviolet optical limiting materials: 2D Ti3C2 and Ti3AlC2 nanosheets

“…TMDs are arguably the most widely studied class of 2D layered materials other than graphene. TMDs exhibit typical layer-dependent tunable band gaps ranging from 1 eV (bulk) to 3 eV (monolayer), 19–22 but their larger band gaps are not suitable for mid- and far-infrared bands. 23 Black phosphorus has been regarded as the 2D material closest to graphene, and also has a thickness-dependent band gap (from 0.3 eV to 2 eV).…”

“…23 Black phosphorus has been regarded as the 2D material closest to graphene, and also has a thickness-dependent band gap (from 0.3 eV to 2 eV). 22–26 Nevertheless, monolayer and few-layer black phosphorus are extremely unstable in air, which limits its application in devices. 27,28 TIs have great modulation depth, but the fabrication process is complicated and the cost is high.…”

Giant enhancement of second-harmonic generation of indium selenide on planar Au

“…16,17 Recently, coating quantum dots onto 2D monolayers has enhanced SHG by over three orders of magnitude by energy transfer, yet it is easy to pollute 2D monolayer materials. 18 Photonic structures, such as photonic crystals, 30,31 and optical microcavities, [32][33][34] promote the SHG efficiency via increasing electromagnetic wave density; however, the response spectral range is limited in a very narrow bandwidth around the resonance frequency. 20,21,24 Plasmonic nanostructures can extensively boost the local electric field in a wide spectral range due to surface plasmon resonance, leading to a pronounced enhancement factor (EF) of up to 10 3 at hot spots.…”