Terahertz Detection Using Enhanced Two-Step Absorption in Photoconductive Metasurfaces Gated at λ = 1.55 μm

摘要

Superior ultrafast photoconductive properties make low temperature grown(LT) GaAs one of the best materials for photoconductive terahertz (THz)detection. However, the large bandgap of LT-GaAs limits its operation togating at wavelengths shorter than 870 nm. Here, it is demonstrated forthe first time that nanostructuring the LT-GaAs into a highly absorbingmetasurface enables THz photoconductive detection with a pulsed laser atλ = 1.55 μm. The very weak sub-bandgap absorption mediated by midgapstates in LT-GaAs is strongly enhanced using the concept of perfect absorptionvia degenerate critical coupling. Integrated with a THz antenna, theLT-GaAs metasurface enables high sensitivity THz detection with a highdynamic range of 60 dB and large bandwidth up to 4.5 THz. The LT-GaAsmetasurface has the potential to serve as a universal ultrafast switchingelement for THz applications, enabling low-cost, turn-key THz systems for avariety of real-world applications.