Wafer-Scale Single-Crystalline AB-Stacked Bilayer Graphene

A wafer-scale formation of artificial single-crystalline AB-stacked bilayer grapheme (AB-BLG) via aligned transfer of two single-crystalline monolayers was reported. The AB-BLG was encapsulated between two hexagonal boron nitride (h-BN) flakes which play a role as back and top gate dielectrics. The top gate was swept from 20 to 20 V while applying back gate. from Si substrate. The resistance reaches maximum at highest displacement field region (the top-left and bottom-right), confirming the tunability of bandgap with perpendicular dipole electric field. The on/off ratio was initially 4 but rises to 16 after gating at room temperature. To demonstrate the electrical and stacking-order uniformity on a wafer scale cm in diameter single-crystalline AB-BLG was transferred onto a SiO2/Si substrate, followed by the fabrication of 380 dual-gate devices by standard photolithography processes. The transistor transport characteristics were measured one by one to obtain carrier mobility and on/off ratio of all devices. All the devices show nearly similar on/off ratio near 2.5 before and 8 after opening bandgap. This confi rms the formation of AB-BLG uniformly over the entire area.