Substrate-Induced Photofield Effect in Graphene Phototransistors


A single atomic layer of graphene, integrated onto an undoped bulk substrate in a back-gated transistor configuration, demonstrates stunning strong photoconduction, and however, the physical origin of the photoresponse is not totally understood. Here, we tend to use an in depth computational model to demonstrate that the photoconductivity arises from the electrostatic doping of graphene, induced by the surface accumulation of photogenerated carriers at the graphene/substrate interface. The accumulated charge density depends strongly on the speed of charge transfer between the substrate and the graphene; the suppression of the transfer rate below that of carrier's thermal velocity is a vital prerequisite for a considerable photoinduced doping within the graphene channel under this mechanism. The contact-to-graphene coupling (defined by the ratio of graphene-metal contact capacitance to graphene's quantum capacitance) determines the magnitude of photoinduced doping in graphene at the source/drain contacts. High-performance graphene phototransistors would, therefore, need careful engineering of the graphene-substrate interface and optimization of graphene-metal contacts.

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