Built-in potential ($V_b$)

The built-in potential of a p-n junction is the electrostatic potential difference established when carrier diffusion exposes ionized dopants until the opposing drift and diffusion currents balance. The equilibrium electrochemical potential is constant even though the electric potential and band edges vary. In a nondegenerate homojunction with neutral-edge majority densities $p_p,n_n$, $e{V}_b=k_{B}T\log (p_p{n}_n/n_i^2)$. This is band bending within the same material, not necessarily a discontinuous offset of different materials' band edges.