Terahertz Detection With a Low-Cost Packaged GaAs High-Electron-Mobility Transistor

We present experimental results of an investigation into the performance of a commercial, packaged GaAs high-electron-mobility transistor (HEMT) as a detector of terahertz (THz) radiation in the frequency ranges 0.22-0.32 and 0.520-0.650 THz. Enclosed in a standard ceramic housing and without a dedicated antenna for radiation coupling, the transistor is capable of sensitive direct detection (power detection) of THz radiation at room temperature. The device responsivity shows a strong variation with wavelength, indicating that various device features (transistor metallization, contact pads, wires) act as an effective THz antenna. With the THz radiation focused with a parabolic mirror (and without a substrate lens), the maximum responsivity reaches 2.5 and 0.72 V/W with values of the minimum optical noise-equivalent power (NEP) of 1.4 and 2.5 nW/√(Hz) at the sensitivity peaks at 0.271 and 0.632 THz, respectively. The performance of the HEMT, in comparison with antenna-coupled FET detectors optimized for THz detection (TeraFETs), can be assessed better if the responsivity and the NEP are referred to the effective antenna cross-section determined experimentally for the device. We arrive at a cross-sectional responsivity of 42 V/W (1.6 V/W) and a cross-sectional NEP of 135 pW/√(Hz) (1250 pW/√(Hz)) at 0.271 THz (0.632 THz), for measurements through the ceramic cap. The cross-sectional NEP values are about one order of magnitude at 0.271 THz and two orders of magnitude at 0.632 THz higher than those achieved with the best TeraFETs, yet in a range where they enable many practical applications at low cost for the detector.