As we know that, Zener breakdown takes place, when we supply reverse bias voltage to Zener diode. Due to heavily dopping, the electrons in the valence band of
p-type region can jump easily to the conduction band of
n-type region, hence due to high electric field, zener breakdown occur. Thus, there is very high sudden increase in Zener current
(IZ) that is caused by reverse breakdown voltage
(VZ).
Hence, Zener breakdown is easily observed in Zener diode which is heavily doped and having narrow depletion region.