Graphene and Lateral Heterostructure for THz Imaging

We report millimeter-wave and sub-terahertz detection using graphene FETs up to 220 GHz at zero-bias to reduce 1/f noise. Detection leveraged the nonlinearity of the channel resistance through resistive field-effect transistor mixing for high-dynamic range. At a 50-Ω load, measured detection responsivity was 70 V/W at 2 GHz to 33 V/W at 110 GHz. The measured noise power of the graphene FETs was ~7.5 ×10^-18 V²/Hz at zero-bias. Noise equivalent power at 110 GHz was estimated to be ~80 pW/Hz^0.5. A linear dynamic range of > 40 dB was measured, providing 15-20 dB greater linear dynamic range compared to conventional CMOS detectors at the transistor level. The emerging graphene heterostructure diodes offer the RC limited cutoff frequency (f_c) of 2.9 THz with the noise equivalent power of ~ 8 pW/Hz^0.5 at 200 GHz due to its small junction-capacitance and diode nonlinearity.