Perfectly absorbing dielectric metasurfaces for photodetection

Perfect absorption of light by an optically thin metasurface is among several remarkable optical functionalities enabled by nanophotonics. This functionality can be introduced into optoelectronic devices by structuring an active semiconductor-based element as a perfectly absorbing all-dielectric metasurface, leading to improved optical properties while simultaneously providing electrical conductivity. However, a delicate combination of geometrical and material parameters is required for perfect absorption, and currently, no general all-dielectric metasurface design fulfills these conditions for a desired semiconductor and operation wavelength. Here, using numerical simulations, we demonstrate that Mie resonators with subwavelength-size interconnecting channels allow this combination of perfect absorption requirements to be satisfied for different wavelengths of operation and different levels of intrinsic material absorption. We reveal the underlying physics and show that interconnecting channels play a critical role in achieving perfect absorption through their effects on the resonant wavelengths and losses for the electric dipole and magnetic dipole modes in Mie resonators. By adjusting only the channel widths, perfect absorption can be achieved for an optically thin GaAs-based metasurface at a desired wavelength of operation in a range from 715 nm to 840 nm, where the intrinsic absorption level in GaAs varies by more than a factor of 2. Optical transmission experiments confirm that these metasurfaces resonantly enhance optical absorption. This work lays out the foundation and guidelines for replacing bulk semiconductors with electrically connected, optically thin, perfectly absorbing metasurfaces in optical detectors.