Ultra-broadband near-perfect absorber based on a single-layer Ge-assisted metasurface

We demonstrate a single-layer metasurface structure to achieve broadband near-perfect absorption at visible light to near-infrared wavelengths. The nanoposts with two different sizes in one unit cell excite the Mie resonances, thereby causing incident light to be efficiently coupled to the loss substrate and further enhance absorption. The metasurface and the supporting substrate are composed of the homogeneous material germanium. Broadband absorption can be achieved due to the coupling and overlapping of different orders of Mie resonances. The average absorption is 96% at wavelengths ranging from 400 to 1300 nm. The structure is polarization independent due to its C 4 symmetry. Our proposed structure also achieves an average absorption efficiency of 92% when the incident angle is up to 50°. This work may provide a paradigm for designing high-performance single-layer perfect absorbers, which is potentially applicable in advanced optical capture, integrated photon systems, and optoelectronic devices.