Depletion approximation
= Depletion approximation
The <depletion approximation> replaces the junction's transition region by a region without mobile carriers, leaving only fixed ionized dopants. For a uniformly doped abrupt <p-n junction>, $\rho=-eN_A$ on the p side, $\rho=+eN_D$ on the n side and $\rho\simeq0$ outside. <Charge neutrality> gives $N_Ax_p=N_Dx_n$. Integrating <Poisson equation> gives the <electric field> and the electrostatic <band bending>.