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We report on the voltage response of carbon nanotube devices to sub-terahertz (THz) radiation. The devices contain carbon nanotubes (CNTs), which are over their length partially suspended and partially Van der Waals bonded to a SiO 2 substrate, causing a difference in thermal contact. We observe a DC voltage upon exposure to 140 GHz radiation. Based on the observed gate voltage and power dependence, at different temperatures, we argue that the observed signal is both thermal and photovoltaic. The room temperature responsivity in the microwave to THz range exceeds that of CNT based devices reported before. The unique band structure of carbon nanotubes (CNT) makes them good candidates for optoelectronic applications in a wide frequency range. [1][2][3] Due to the quantization of the electron wave vector around the circumference a CNT with n -m 6 ¼ 3i, where i is an integer is a semiconductor with an energy gap e g $ 1/r (with r the radius of the CNT). 4 The optical properties of semiconducting nanotubes, in the visible and near infrared range, have been intensely studied during the last ten years. 1,5,6 It has been shown that they can be used as basic elements for different optoelectronic functions, such as photodetectors 6 or light emitting diodes. 7 Nanotubes, with n -m ¼ 3i, with n 6 ¼ m, are called quasi-metallic, due to their small band gap, which ranges from about 1 to about 30 meV for nanotubes with a diameter of 1-2 nm. 8,9 Socalled armchair CNTs, with n ¼ m, are truly metallic. Quasi-metallic CNTs are potentially very good candidates for optoelectronics in the THz range because their bandgaps fall into the corresponding energy range.Previous research on THz detectors based on CNTs has brought interesting new results. 3,10 Diode type detection and bolometric detection were reported in Refs. 3 and 10. Photonassisted tunneling in the Coulomb blockade regime was reported in Ref. 11. The response of antenna-coupled fully suspended single carbon nanotubes to sub-THz radiation was reported in Ref.12. A power-dependent DC voltage was reported in this work and interpreted as a combined effect of the increased temperature of the electron liquid with respect to the electrodes and requiring an asymmetry in the contact resistances.Here we report on CNT devices, which will have a temperature gradient due to a difference in heat transfer along the CNTs while exposed to radiation. The different heat transfer conditions occur because of a difference in coupling to the substrate along the length. The devices show a DC voltage signal in response to radiation in the sub-THz range in the temperature range from 4.2 to 300 K. We argue that the room temperature response is thermal in origin, similarly to the photoresponse of CNT films reported before, e.g., in Ref. 13. The data obtained at low temperatures indicate contributions of both thermal effects and of photovoltaic effects. While it is not clear if the observed effect can be used to develop efficient THz detectors we note that the responsivity of our devices exceeds that ...

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