Lighting Up Si Nanoparticle Arrays by Exploiting the Bound States in the Continuum Formed in a Si/Au Hybrid Nanostructure

Silicon (Si)-based light emitters compatible with the current fabrication technology of Si chips are crucial for realizing all-optical computation. Here, we propose a Si/Au hybrid nanostructure composed of a regular array of Si nanopillars and a thin gold (Au) film. An accidental bound state in the continuum (BIC) originating from the interference of the mirror-image-induced magnetic dipole and the surface plasmon polariton can be achieved in the nanostructure by deliberately designing the structure parameters. Efficient nonlinear optical emission is observed when the nanostructure is excited by using femtosecond laser pulses. The lowest threshold for the burst of luminescence from the Si nanoparticle is observed at the BIC, where the nonlinear optical absorption is greatly enhanced. It is found that the excitation of the surface plasmon polariton is crucial for taking the advantage of the BIC, which is manifested in the low threshold and special radiation pattern. Our findings open new horizons for manipulating light-matter interaction by exploiting the BICs created in dielectric-metal hybrid nanostructures.