Waveguide-coupled heterodyne terahertz detector based on AlGaN/GaN high-electron-mobility transistor

We report a room-temperature, low output impedance, broad intermediate-frequency (IF) bandwidth field-effect terahertz detector based on an AlGaN/GaN high-electron-mobility transistor (HEMT) integrated in a metal waveguide. The waveguide detector equips a pair of quasi-Yagi antenna probes that are used to couple the terahertz energy to the HEMT channel. The gate is configured as an asymmetric edge-coupled coplanar waveguide transmission line. This terahertz electric field is asymmetrically distributed in the channel along the edges of the transmission lines. The responsivity and noise for direct and heterodyne detections are characterized and analyzed at different local oscillator (LO) powers. The noise-equivalent power in direct detection is below 189 pW/${\text{Hz}}^{1/2}$ . Operated in a heterodyne mode with a LO power of −3 dBm, the detector offers a conversion loss less than 55 dB in a frequency band of 320–340 GHz. The channel in a form of transmission line performs the broad IF bandwidth, which is increased to gigahertz range (3 GHz), and reduces the output impedance to 377 Ω which is about 20 times lower than previously reported. The transmission-line impedance could be optimized together with the distribution of the terahertz electric field in the gated channel to reduce the conversion loss.