Broadband long-wave infrared metamaterial absorbers based on germanium resonators

The broadband metamaterial perfect absorbers over various incident angles are highly significant in long-wave infrared (LWIR) detection. Previous research on LWIR metamaterial absorbers has mainly focused on metallic resonators. Here, we propose two broadband LWIR metamaterial absorbers that use dielectric resonators instead. The germanium (Ge) resonators on the top layer excite resonance modes that control the equivalent impedance of the structure, which acts on the high-lossy Si 3 N 4 -Ti reflecting layer to assume the absorption. Firstly, we designed a three-layer structure of Ge-Si 3 N 4 -Ti, which achieved a broadband absorption with an average absorptivity of 93.1 % in the 8–12 μm range. The absorption ratio of metal can be effectively reduced by replacing the metal. Then, to further enhance the absorptivity, we inserted a Si 3 N 4 layer into the Ge layer, increasing the 90 % absorption bandwidth to 7.96–14.16 μm and the average absorptivity in 8–14 μm to 96.5 %. Compared to metamaterial absorbers based on metallic resonators, dielectric resonators with a large feature size make fabricating easier. Our proposed metamaterial absorber provides ultra-wideband absorption covering the LWIR range. In addition, it is insensitive to the incident angle, making it a potential candidate for thermal imaging and broadband thermal emission applications.