Room-temperature, low-impedance and high-sensitivity terahertz direct detector based on bilayer graphene field-effect transistor

Abstract We report a room-temperature, low-impedance and high-sensitivity terahertz direct detector based on bilayer graphene field-effect transistor (GFET). Epitaxially grown on silicon carbide, the bilayer graphene had an as-grown carrier mobility of 3000 cm 2 /Vs. The source/drain contacts were formed on the freshly cleaned graphene sheet to minimize the contact resistance and served also as terahertz antennas. The gate and the dielectric layer underneath with a length of 145 nm and a gap of 203 nm to the source/drain antennas were formed in a self-alignment process. Although the carrier mobility in the GFET was reduced to about 405 cm 2 /Vs, the high-quality ohmic contacts and the short graphene channel delivered an overall source-drain resistance less than 203 Ω. A voltage responsivity of 30 V/W and a noise-equivalent power of 51 pW/Hz 1/2 were estimated in direct detection at 0.33 THz. By using the GFET detector as a two-terminal detector, i.e., with the gate floating, a transmission-type terahertz imaging was demonstrated. Such a low-impedance GFET detector is ready to be matched to a commercial 50-Ω low-noise radio/microwave frequency amplifier allowing for high-speed homodyne detection and heterodyne detection in a quasi-optical configuration.