Ultra-broadband perfect absorber utilizing a multi-size rectangular structure in the UV-MIR range

We propose an ultra-broadband perfect absorber (UBPA) utilizing a multi-size rectangular structure, which consists of multi-layer silicon/iron (Si/Fe) units. A single-layer model is designed based on the theory of dipole equivalent circuit, and a nine-layer model is demonstrated with the FDTD method. Surprisingly, the absorber shows an average absorptivity of over 96% in the range of 300-3000 nm under the normal incident, which covers from the ultraviolet to mid-infrared (UV-MIR) region. A good tolerance of incident angle and polarization state is proved. It is found that the average level of absorption still exceeds 91% at a larger viewing angle of +/- 70 degrees under the TM polarization. The excellent absorption performance is revealed by the slow-wave effect, localized surface plasmon resonance (LSPR), and propagating surface plasmons (PSPs). In addition, both chro-mium and iron films are used in the multi-layer structure to avoid the iron oxidation. Thus, the proposed absorber reduces the cost of actual production and can be applied in many areas, such as solar cells and emitters.