Journal
ACS APPLIED NANO MATERIALS
Volume 3, Issue 3, Pages 2978-2986Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsanm.0c00265
Keywords
perfect absorber; Fabry-Perot cavity; metal-insulator-metal structure; dielectric function; planar thin-film stack
Funding
- R&D convergence program of the National Research Council of Science & Technology of the Republic of Korea [CAP-16-10-KIMS]
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Broadband light absorbers are highly desirable in various applications including solar-energy harvesting, thermo-photovoltaics, and photon detection. The 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 because of 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 thick Au film and increasing the SiO2 spacer thickness to 115 nm. The experimental results are supported by finite-difference time-domain simulation. The large absorption bandwidth is attributed to the lossy nature of the nanostructured top metallic layer combined with the resonant absorption of the MIM cavity.
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