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(a) A schematic of ohmic metal scheme to graphene, where the graphene channel is n-type. (b) An equivalent circuit for the ohmic contact resistance as series resistor network. (c) AFM scan of 10 × 10 µm2 graphene surface prior to ohmic metal deposition. (d) A SEM image of TLM pattern with 0.5 µm contact separation. (e) The source-drain current of a HFO2/graphene FET with source-drain separation of 2 µm and Vds = 50 mV.
(a) Measured TLM resistance values versus contact separations of 0.25 to 32 µm are plotted. (b) An expanded view of TLM resistance plot over 0.25 to 8 µm is shown. The contact width was 22 µm.
The current-voltage characteristics of the graphene FET is shown with the source-drain current as high as 2.2 A/mm at Vds = 1.5 V with on-resistance of 550 Ω µm. An inset shows a SEM image of a short-channel HFO2/graphene FET, where the source-drain separation is 0.46 µm and the gate length is 0.25 µm. The dotted line represents the source-drain current at the Dirac point where the current is determined by a hole current, rather than an electron current.
(a) A schematic of band alignment at a metal-graphene interface (case of ΦM < ΦG) and associated effective doping of graphene material. (b) Doping density n in graphene as a function of the metal-graphene work function difference and a metal-to-graphene distance d.
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