Sensitive Room-Temperature Terahertz Detection via Photothermoelectric Effect in Graphene

Due to the weak electron-phonon coupling and strong electron-electron interaction in graphene, the thermoelectric effect provides a highly sensitive detection mechanism for heat absorbed in the electronic system. We present here a bi-metal contacted graphene thermoelectric THz photodetector with sensitivity exceeding 100 V/W at room temperature and noise equivalent power less than 100 pW/Hz$^{1/2}$, competitive with the best room-temperature THz detectors, while time-resolved measurements indicate our graphene detector is eight to nine orders of magnitude faster. We also measured the thermoelectric response to Joule heating, and compare to the thermoelectric response due to optical excitation in the near infrared and at THz frequencies. A simple model of the response, including contact asymmetries reproduces the qualitative features of the data. We also suggest that orders-of-magnitude sensitivity improvements are possible by using local gates to define graphene pn-junctions.