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(a) Measured XRD ω-2θ scan and corresponding fit from as-grown AlGaN/GaN structure. Inset: schematic diagram of the heterostructure stack (UID refers to unintentionally doped; not to scale) and AFM image of surface morphology. (b) Raman spectrum from transferred CVD graphene on AlGaN/GaN substrate (inset), with D, 2D, and G bands indicated.
Schematic diagram showing the structure of the Cr/graphene/AlGaN/GaN structure. In the case of the reference device, the graphene layer is removed. Not to scale.
Current-voltage characteristics of Cr/AlGaN/GaN and Cr/graphene/AlGaN/GaN.
Current-voltage characteristics as a function of temperature (77 to 300 K, 2 × 10−6 Torr) of: (a) Cr/AlGaN/GaN (inset: Schottky diode turn-on at 250 K) and (b) Cr/graphene/AlGaN/GaN.
Schematic energy band diagrams of: (a) Cr/AlGaN/GaN Schottky diode under zero-bias (top) and forward-bias (bottom) conditions, and (b)Cr/graphene/AlGaN/GaN junction (proposed). E C and E F indicate the bottom of the conduction band and the Fermi level, respectively. Dashed lines indicate effective E C for percolative transport.
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