Towards sensitive terahertz detection via thermoelectric manipulation using graphene transistors

Graphene has been highly sought after as a potential candidate for hot-electron terahertz (THz) detection benefiting from its strong photon absorption, fast carrier relaxation, and weak electron-phonon coupling. Nevertheless, to date, graphene-based thermoelectric THz photodetection is hindered by low responsivity owing to relatively low photoelectric efficiency. In this work, we provide a straightforward strategy for enhanced THz detection based on antenna-coupled CVD graphene transistors with the introduction of symmetric paired fingers. This design enables switchable photodetection modes by controlling the interaction between the THz field and free hot carriers in the graphene-channel through different contacting configurations. Hence a novel “bias-field effect” can be activated, which leads to a drastic enhancement in THz detection ability with maximum responsivity of up to 280 V/W at 0.12 THz relative to the antenna area and a Johnson-noise limited minimum noise-equivalent power (NEP) of 100 pW/Hz0.5 at room temperature. The mechanism responsible for the enhancement in the photoelectric gain is attributed to thermophotovoltaic instead of plasma self-mixing effects. Our results offer a promising alternative route toward scalable, wafer-level production of high-performance graphene detectors. Controlling how finger-like electrodes are positioned on graphene transistors makes it simpler to detect terahertz radiation for applications including medical diagnostics. When photons strike graphene sheets, multiple electrons with high kinetic energy are released. Changlong Liu at the Chinese Academy of Sciences, Shanghai, and coworkers have exploited these electrons to improve detection of terahertz light, which is useful for seeing features underneath human skin. The team’s device places single-layer graphene into a channel flanked by two microscale antennas, and then adds a pair of thin metal fingers on top of the 2D carbon film. By manipulating the separation of the finger contacts, the team unlocked an enhanced response to terahertz light at room temperature. Experiments and simulations revealed that temperature gradients between contact points generated a terahertz-sensitive photocurrent through conversion of heat into electricity. Graphene is very promising for THz application, especially in the fields desiring fast THz imaging, like security screening, communication, biomedical and pharmacy control. However, current graphene-based THz detectors are severely hindered by its poor switching behavior, and lack of internal gain to boost up the responsivity in the framework of plasma-wave self-mixing or thermoelectric detections. A proper means to selectively trigger the photoelectric conversion is highly desirable for practical applications. This work offers alternative way for room temperature THz detection via manipulating the hot carriers either electrically and electromagnetically. Internal photoelectric gain is achieved via the bias-field effect, which leads to the giant enhancement of graphene-based detector’s responsivity over 200 V/W. Furthermore, switching behavior between photoconductive and photovoltaic modes can be given rise in a single device, being promising for scalable THz imaging.