Broadband Visible and Near-Infrared Absorbers Implemented with Planar Nanolayered Stacks

Broadband light absorbers are highly desirable in various applications including solar-energy harvesting, thermo-photovoltaics, and photon detection. Fabry-Perot (F-P) cavity comprising metal-insulator-metal (MIM) layers has attracted enormous interest as a lithography-free structure for realizing planar super absorbers. However, typical F-P cavity exhibits a narrow absorption band, and efforts have thus been made to increase the absorption bandwidth. This study demonstrates that near-perfect absorption over a broad spectral range can be obtained from the MIM structure by using thermally evaporated Ag and Au thin films whose dielectric and optical properties are much different from bulk-state properties owing to their nanoscale features. A 55-nm-thick SiO2 spacer sandwiched between a 10-nm Ag top layer and a 100-nm Al back reflector exhibits absorption > 95% in the visible range of 400-700 nm. The broad absorption band shifts to a near-infrared range of 650-1000 nm by replacing the top layer with a 10-nm-...