Figure 5. Band alignment at aluminium–BP interface.

Schematic band diagrams based on previously calculated E_V and E_C (ref. 3) for (a) few layer (3 nm) and (b) thick BP flakes with Al contacts (13–15 nm). The insensitivity of E_C to thickness change and makes Al a great n-type contact but very high-resistance p-type contact with a large depletion width (w_d) for thin BP. Thicker samples have small Schottky barriers for both n and p-transport, permitting ambipolar operation.