Terahertz detection at 240 GHz with a semiconducting carbon-nanotube field-effect transistor

We report on terahertz detection experiments at 240 GHz using carbon-nanotube field-effect transistors with a single semiconducting single-walled tube as the transistor´s channel. From DC channel resistance measurements, the voltage response is predicted theoretically from the dc transconductance of the devices. Rectification is shown for an electronically applied 2-MHz signal and for free-space illumination at 240 GHz. The measured voltage responses compare well with the theory, however, at 240 GHz an additional gate-bias-dependent contribution to the rectified signal is observed for higher gate voltages.