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Due to its high charge carrier mobility, broadband light absorption, andultrafast carrier dynamics, graphene is a promising material for thedevelopment of high-performance photodetectors. Graphene-based photodetectorshave been demonstrated to date using monolayer graphene operating inconjunction with either metals or semiconductors. Most graphene devices arefabricated on doped Si substrates with SiO2 dielectric used for back gating.Here, we demonstrate photodetection in graphene field effect phototransistorsfabricated on undoped semiconductor (SiC) substrates. The photodetectionmechanism relies on the high sensitivity of the graphene conductivity to thelocal change of the electric field that can result from the photo-excitedcharge carriers produced in the back-gated semiconductor substrate. We alsomodeled the device and simulated its operation using the finite element methodto validate the existence of the field induced photoresponse mechanism andstudy its properties. Our graphene phototransistor possesses a room-temperaturephotoresponsivity as high as ~ 7.4 A/W, higher than the requiredphotoresponsivity (1 A/W) in most practical applications. The lightpower-dependent photocurrent and photoresponsivity can be tuned by thesource-drain bias voltage and back-gate voltage. Graphene phototransistorsbased on this simple and generic architecture can be fabricated by depositinggraphene on a variety of undoped substrates, and are attractive for manyapplications in which photodetection or radiation detection is sought.

Gate-tunable and high responsivity graphene phototransistors on undoped semiconductor substrates