Zener effect

It occurs in a reverse biased p-n diode when the electric field enables tunneling of electrons from the valence to the conduction band of a semiconductor, leading to numerous free minority carriers which suddenly increase the reverse current.

[2] Sufficiently strong electric fields enable tunneling of electrons across the depletion region of a semiconductor, leading to numerous free charge carriers.

This sudden generation of carriers rapidly increases the reverse current and gives rise to the high slope conductance of the Zener diode.

Avalanche breakdown involves minority carrier electrons in the transition region being accelerated, by the electric field, to energies sufficient for freeing electron-hole pairs via collisions with bound electrons.

[2] The avalanche breakdown occurs in lightly doped junctions, which produce a wider depletion region.