0.2-4.0 THz broadband terahertz detector based on antenna-coupled AlGaN/GaN HEMTs arrayed in a bow-tie pattern

To satisfy the demand for broadband and high-sensitivity terahertz detectors, we designed and verified a broadband terahertz detector built with antenna-coupled AlGaN/GaN high-electron-mobility transistors (HEMTs). Eighteen pairs of dipole antennas with different center frequency from 0.24 to 7.4 THz are arrayed into a bow-tie pattern. The corresponding eighteen transistors have common a source and a drain but different gated channels coupled by the corresponding antennas. The photocurrents generated by each gated channel are combined in the drain as the output port. With incoherent terahertz radiation from a hot blackbody in a Fourier-transform spectrometer (FTS), the detector exhibits a continuous response spectrum from 0.2 to 2.0 THz at 298 K and from 0.2 to 4.0 THz at 77 K, respectively. The results agree well with simulations taking into account the silicon lens, antenna and blackbody radiation law. The sensitivity is characterized under coherent terahertz irradiation, the average noise-equivalent power (NEP) is about 188 pW/Hz at 298 K and 19 pW/Hz at 77 K from 0.2 to 1.1 THz, respectively. A maximum optical responsivity of 0.56 A/W and a minimum NEP of 7.0 pW/Hz at 0.74 THz are achieved at 77 K. The blackbody response spectrum is divided by the blackbody radiation intensity to obtain a performance spectrum, which is calibrated by measuring coherence performance from 0.2 to 1.1 THz to evaluate detector performance at frequencies above 1.1 THz. At 298 K, the NEP is about 1.7 nW/Hz at 2.0 THz. At 77 K, the NEP is about 3 nW/Hz at 4.0 THz. For further improvements in sensitivity and bandwidth, high-bandwidth coupling components, smaller series resistance, smaller gate lengths and high-mobility materials need to be considered.