Directional broadband resonant fluorescence from Si bullseye resonators on a SiO ₂ /Au heterostructure

Silicon (Si) based light emitters compatible with standard CMOS fabrication are critical for integrated photonics, yet conventional Si nanoparticles suffer from severe dissipation losses under high-density carrier injection that limit directional hot electron luminescence when they act as light sources. Resolving this limitation, we developed optimized Si bullseye resonators on a silica/gold heterostructure substrate that enable broadband directional luminescence through the resonant mechanism of the Bragg gratings. First, the central Si nanopillar is designed for sustaining strong magnetic dipole and mirror-image-induced magnetic dipole resonances, enhancing two-photon absorption photoluminescence (PL) under the excitation of femtosecond laser pulses. Second, laterally propagating surface plasmon polaritons induced by the central nanopillar light source undergo efficient out-coupling via Bragg gratings, generating distinct emitted spectral peaks. Comparative collection efficiency measurements reveal that more than 60% of emitted energy across 470–600 nm is captured within a 29° half-aperture angle using a 0.7 NA oil-immersion objective. Notably, a dominant emission peak covering the 570–590 nm wavelength band concentrates 85% of energy within this angular range. The bullseye resonator concurrently amplifies Si PL at both excitation and emission stages while delivering pronounced mode selectivity and broadband collimation. This work establishes a practical pathway toward CMOS-compatible compact Si light sources.