Ultra-thin UV-visible all-dielectric broadband metasurface absorber with resonant coupling of cavity effect.

All-dielectric metasurface perfect absorbers (DMPAs) have shown tremendous potential in applications such as optoelectronic detection and solar energy harvesting. However, the realization of broadband absorption in DMPAs remains challenging due to the harsh coupling conditions of the resonance absorption enhancement effect. Here, we proposed an ultra-thin, broadband DMPA. Our design leverages the broadband anti-reflection capability enabled by the cavity effect of the Ge-SiO₂-Ge structure coupled with a top Ge metasurface resonant layer, which enables highly efficient absorption across the ultraviolet (UV) to visible region (330-700 nm), with an average absorptivity of 97.3%. Additionally, the absorber's ultra-thin overall thickness of 175 nm (0.35 λ) and its absorption spectrum being independent of the metasurface geometry demonstrates excellent fabrication tolerance. This study provides valuable insights into the design of ultra-thin, broadband all-dielectric absorbers and their potential applications in detectors and beyond.