Space charge region of p-n junction diode

[rkgjet]

does np=ni^2 holds even the space charge region of a pn junction diode?

 

[bob012345]

For an unbiased junction with no net carrier recombination or generation I believe it does however most books use the depletion approximation where they assume there are no carriers in the space charge or depletion region and only the ionized donor and acceptor dopant concentrations matter. This graph shows the carrier concentrations to not go to zero in the depletion region.

There is something called the law of the Junction which goes as $np=n_i^2e^{qV_a/kT}$ where $V_a$ is the applied voltage. This is valid throughout the space charge region. For $V_a=0$ the mass action law $np = n_i^2$ is recovered.

https://inst.eecs.berkeley.edu/~ee130/fa13/pnjunctions.pdf