Question

Distinguish between Avalanche breakdown and Zener breakdown.

Answer 1

Avalanche breakdown	Zener breakdown
i) When both sides of the PN junction are lightly doped and the depletion layer becomes large, Avalanche breakdown takes place.	i) When both sides of the PN junction are heavily doped, consequently the depletion layer is narrow and zener breakdown takes place.
ii) The electric field across the depletion layer is not so strong.	ii) When a small reverse bias is applied, a very strong electric field is produced.
iii) Due to the collision with valence electrons, covalent bonds are broken and electron hole are generated.	iii) The field breaks the covalent bonds, extremely large number of electrons and holes are produced.
iv) These charge carriers acquired energy from the applied potential and in turn produce more and more carriers. This cumulative process is called avalanche multiplication and the breakdown is called avalanche breakdown.	iv) The electrons and holes thus give rise to the reverse saturation current (Zener current) Zener current is independent of applied voltage.