Consider avalanche breakdown in a silicon p⁺n junction. The n-region is uniformly doped with a donor density N_D. Assume that breakdown occurs when the magnitude of the electric field at any point in the device becomes equal to the critical field E_crit. Assume E_crit to be independent of N_D. If the built-in voltage of the p⁺n junction is much smaller than the breakdown voltage, V_BR, the relationship between V_BR and N_D is given by