Multiple absorption regimes in simple lithography-free structures leading to ultrathin slabs

Electromagnetic absorbers serve as fundamental components for a wide range of applications, encompassing energy and heat management, sensing, and communications. In this study, we explore several complex permittivity combinations for lithography-free material-reflector and material-spacer-reflector configurations that lead to perfect absorption peaks across distinct permittivity regimes and varying thicknesses. We provide an extensive analysis of angle and polarization dependencies, specifically using silicon carbide as an illustrative example. Our findings reveal the potential for harnessing different absorption regimes within a single device, thus enabling the realization of multiband absorption capabilities. Furthermore, we demonstrate perfect absorption linked with extreme values of permittivity, and we find the conditions to get perfect absorption in ultrathin slabs. In addition, we carry out an analysis about the response at oblique incidence, and we identify a particular mode in the negative permittivity region and its hybridization with epsilon-near-zero modes at oblique incidence. This investigation serves as a valuable standardization of absorber design, offering insights to develop perfect absorbers for infrared applications such as thermal emission, communications, and sensing.