Figure 4: Influence of Cu doping on the surface potential.

(a) Band bending as a function of doping level. To numerically determine the band bending, we used the distance determined by ab initio simulations of 0.254 nm. (b) Schematic showing the surface potential dependence on doping. In Cu-doped samples, more of the bulk conduction band is below the Fermi energy, providing enough carriers to screen the band bending.