Broadband absorption in nanostructured cross-shaped metamaterial for visible and infrared wavelengths

The successful implementation of broadband, ultrathin and highly efficient nanostructured plasmonic absorbers is difficult to realize. The performance of the nanoscale metamaterial absorbers is severely restricted due to the multilayer design architecture and difficult fabrication process. So herein a simple and plain nano cross-shaped ring of nickel metal is exploited as a broadband absorber for visible to mid-infrared spectrum. The proposed cross shaped nanoabsorber (CSNA) holds a three layers device configuration with upper and lower layers of plasmonic metal Ni, an insulating dielectric material of aluminium nitride (AlN), which is sandwiched between them. The CSNA reveals an ultrabroadband absorption spectrum operating in the visible and IR wavelengths from 400 to 3000 nm, which exhibits an average absorption value of more than 90%. Moreover, the angular performance analysis is also conducted by considering the incident and polarization angles of the incident optical light. It is noticed that the discussed CSNA manifests polarization insensitive behavior under the rotation of polarization angles and it also shows stable absorption response by exciting different oblique incident angles. The optimal engineering of the design parameters of the proposed CSNA including length of the cross-shaped resonator, spacer thickness and periodicity of the unit cell play a pivotal role in enhancing the absorption window. Additionally, an analytical equivalent circuit modeling approach has been adopted for calculating absorption features and validating it through simulation results. In conclusion, the designed CSNA holds great promise for various applications, such as energy harvesting, optical emission, and thermal photonics.