Low-complexity pixelated terahertz absorber based on a graphene/InSb heterostructure

A low-complexity pixelated terahertz metasurface absorber based on a graphene/indium antimonide (InSb) heterostructure was proposed. The designed 2 × 2 square pixel structure achieved absorptance higher than 90% over 4.68-10.56 THz, corresponding to an effective bandwidth of 5.88 THz and reached a maximum of 99.9997% at 9.56 THz. The structure also exhibited good polarization stability and angular robustness. A CST-assisted semi-analytical multiple-reflection reconstruction reproduced the main absorption characteristics of the full-structure simulation. Together with the impedance-matching analysis, these results indicated that the broadband high-absorptance response could be explained by multiple-reflection interference and impedance matching. The effects of graphene material parameters and the InSb temperature-dependent response were then investigated, confirming the electrical tunability and thermal tunability of the absorber. In addition, the effects of key structural parameters on the absorptance response were also analyzed. Further comparisons among 2 × 2, 3 × 3, and 4 × 4 square pixel arrays were conducted under the investigated material arrangements and geometric conditions. Among these specific configurations, the 2 × 2 array exhibited a more favorable balance among absorption bandwidth, spectral flatness, and structural complexity. Finally, different unit geometries were evaluated within the same 2 × 2 array framework. The triangular unit maintained absorptance above 90% over 4.61-10.92 THz, with an effective bandwidth of 6.31 THz and a shape factor of 0.526, outperforming the other unit geometries overall. The potential fabrication feasibility of the proposed graphene/InSb absorber was also discussed based on reported experimental processes. These results demonstrate that low-complexity, broadband, and high-absorptance terahertz metasurface absorbers can be realized on the graphene/InSb platform by jointly optimizing the material parameters, array complexity, and unit geometry.