Ultra-broadband terahertz perfect absorber

We propose three kinds of ultra-broadband terahertz (THz) perfect absorbers by fabricating gratings on heavily boron-doped silicon substrate. By optimizing the doping density, the absorption bandwidths are 1 THz, 1.5 THz, and 2.0 THz, respectively, with absorbance above 95%. The fundamental principles are mainly attributed to the antireflection effects, the grating diffractions and the air gap-mode resonance.