Room-Temperature High-Gain Long-Wavelength Photodetector via Optical-Electrical Controlling of Hot Carriers in Graphene

Photodetectors exploiting photoejected hot electrons have the potential to achieve ultrahigh sensitivity and broadband detection capabilities, which are controlled by the structure of the device rather than the bandgap of the employed materials. However, the achievement of photodetectors of long-wavelength photons with both high responsivity and bandwidth is still challenging. Here, a novel class of high-gain photodetectors based on the manipulation of intrinsic hot carriers by exploiting the electromagnetic engineering of a graphene-based active channel is presented. Light field is focused in a split-finger gated structure to create a potential gradient in the channel, which is able to trap and detrap the charges laterally transferred from low resistive Au-graphene interface, finally leading to a high photoconductive gain. Correspondingly, the device activity can be easily switched from photovoltaic to photoconductive, depending on the photoinduced hot-carrier distribution, just by controlling the electric field. The device shows tunable sensitivity, higher energy efficiency, and photoconductive gain. In particular, the responsivity (0.6-6.0 kV W-1) and the noise-equivalent power (less than 0.1 nW Hz(-0.5) at room temperature) are significantly improved even at low-energy terahertz band with respect to state-of-the-art devices based on extrinsically coupled hot carriers operating in the near infrared.