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Near-infrared free carrier absorption enhancement of heavily doped silicon in all-dielectric metasurface

As the hole mobility increases with free carrier absorption (FCA), heavily doped p-type silicon has emerged as a promising candidate for detecting near-infrared (NIR) light with photonic energy below the semiconductor bandgap, and the hot-carrier photodetector is capable of high responsivity approaching commercially available devices. To enhance performance-related FCA of the semiconductor, here we demonstrate an all-silicon metasurface absorber designed in nanohole arrays and present an in-depth analysis on the electromagnetic resonance mechanism in the NIR spectral of interest. Multipole decomposition under a Cartesian coordinate system reveals that combining with the dielectric loss introduced by the doping, magnetic dipole resonances contribute predominantly to the absorption enhancement. This simple and easy-fabricated architecture has great potential for silicon hot-carrier photodetectors.