Sub-picosecond pulsed THz FET detector characterization in plasmonic detection regime based on autocorrelation technique

Many THz applications require detection of sub-picosecond THz pulses. Electronic detectors, in particular, can address this challenge. We report on the detection of sub-picosecond THz pulses generated by a large-area interdigitated photoconductive antenna using a AlGaN / GaN high electron mobility transistor with integrated bow-tie antenna. We demonstrate that the detectors photoresponse is linear in a wide range of gate bias voltages regarding the available THz radiation power with peak power levels of a few hundreds of milliwatts. We apply an autocorrelation technique to investigate the spectral response of our detector within a bandwidth exceeding 1 THz. We observe an unexpected frequency roll-off of responsivity, which can not be predicted using a framework of standard distributed transmission line theory. However, we show that the data can be understood if one accounts for only partial plasmon screening by the gate electrode, so that the results adhere simply to the distributed resistive mixing approximation, whereby the device suffers from the observed roll-off. This indicates, that for novel detectors and radiation sources, which intend to utilize plasma waves, it is important to ensure efficient screening by the gate electrode.