The diffusion potential across a P-N junction

A zener diode works on the principle of

The depletion capacitance, C_J, of an abrupt P-N junction with constant doping on either side varies with reverse bias, V_R , as

In a P-type silicon sample, the hole concentration is $$2.25\times10^{15}/cm^3$$. If the intrinsic carrier concentration is $$1.5\times10^{15}/cm^3$$ , the electron concentration is