Fig. 5
a–c Schematics of the device structure of a top-contacted h-BN/Gr/h-BN sample, b edge-contacted h-BN/Gr/h-BN sample, and c h-BN/Gr/few-layer h-BN/Gr/h-BN vertical-tunnel-junction sample. d, e Photographs of d top-contact and e edge-contact h-BN/Gr/h-BN devices. Dashed lines outline the location of graphene. Scale bars are 10 μm. g, h Resistance data as a function of carrier density of Gr for the devices shown in d and e, respectively; conductivity data is shown in the insets. In g, data shown in red and blue indicates the resistance value of left and right graphene in d, respectively. f Photograph of h-BN/Gr/few-layer h-BN/Gr/h-BN vertical-tunnel-junction device. Solid and dashed red lines indicate the bottom and top graphene, respectively. The white line indicates the thin h-BN tunnel barrier. The thickness of few-layer h-BN is determined via AFM to be about 1.5 nm. Scale bar is 10 μm. i Current–voltage characteristics of the device shown in c at 3 K
