Ultra-broadband and polarization-insensitive terahertz metamaterial absorber based on undoped silicon

Terahertz (THz) absorbers with high absorptivity across a wide frequency band have attracted considerable interest. In this paper, we present the design of an ultra-broadband THz metamaterial absorber with high absorptivity based on a single-layer square silicon array and a silicon film backed with metallic gold. It is numerically demonstrated that the absorption exceeds 90% covering the frequency range of 0.62–8.75 THz (with an effective absorption bandwidth of 8.13 THz) when the conductivity of semiconductor (undoped silicon) is 600 S/m. Diffraction and impedance-matched induce strong absorption and the corresponding broad bandwidth. The proposed ultra-broadband THz absorber is polarization-insensitive at normal incidence. It can operate over a rather wide range of incidence angle up to 60 degrees for transverse magnetic (TM) terahertz wave. This work provides a way to achieving ultra-broadband terahertz absorption, which is very useful in the development of terahertz imaging, high sensitivity sensors and detection.