Color Sensitive Response of Graphene/Graphene Quantum Dot Phototransistors

We present the fabrication and characterization of all-carbon phototransistors made of graphene three terminal devices, coated with atomically precise graphene quantum dots (GQD). Chemically synthesized GQDs are the light absorbing materials, while the underlying chemical vapor deposition (CVD)-grown graphene layer acts as the charge transporting channel. We investigated three types of GQDs with different sizes and edge structures, having distinct and characteristic optical absorption in the UV-vis range. The photoresponsivity exceeds 106 A/W for vanishingly small incident power (<10-12 W), comparing well with state of the art sensitized graphene photodetectors. More importantly, the photoresponse is determined by the specific absorption spectrum of each GQD, exhibiting the maximal responsivity at the wavelengths corresponding to the absorption maxima. Overall this behavior can be ascribed to the efficient and selective absorption of light by the GQDs, followed by a charge transfer to graphene, a mechanism known as the photogating effect. Our results suggest the use of graphene/GQD devices as valuable photodetectors for application where color sensitivity is required.