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(Color online) (a) Optical micrograph of a measured device: Black lines show the edge of bilayer graphene flake. (b) Schematic diagram of our measurement system.
(Color online) (a) Color coded plot of Isd vs. Vtg and Vbg at T = 4.2 K. I-V characteristic of the Nn junction with Vtg = −35 V and Vbg = 80 V (b), Np junction with Vtg = −45 V and Vbg = 55 V (c), Pn junction with Vtg = 20 V and Vbg = −93.45 V (d), respectively. (e) Differential conductance vs. Vsd plotted for a range of back gate voltages with Vtg = 40 V. The back gate voltages correspond to measurements at points on the dotted line in (a). Minimum points are shifted indicating the shift of the quasi-Fermi level. The number attached to each curve shows the applied Vbg value.
(Color online) (a) Schematic of band structure at an interface when the Fermi level is set in the opened bandgap: The differential conductance would show different slopes outside of the gap in the differential conductance curves when carriers are driven by the Vsd voltage. Carrier conduction would be suppressed when carriers experience the opened bandgap. (b) Analysis of a differential conductance curve (Vtg = −40 V, Vbg = 37.5 V): The point at which the slope of derivative conductance starts to change corresponds to the edge of the opened bandgap. The product of difference between 2 inflection points of Vsd and e of elementary charge corresponds to the opened bandgap value. (c) Evaluated bandgap values vs. the applied electric fields. Circles are the evaluated values of our analysis. Squares are the values of previous optical measurements (see Ref. 7) and continuous curve is the theoretical calculation in the previous work (see Ref. 7).
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