Comparison Between Avalanche Breakdown & Zener Breakdown :
- Zener breakdown
This form of breakdown occurs in junctions which , being heavily doped ,have narrow depletion layers. The breakdown voltage set up a very strong electric field(about 108 V/m)across this narrow layer. This field is strong enough to break or rupture the covalent bonds there by generating electron-hole pairs. Even a small further increase in reverse voltage is capable of producing large number of current carriers .That is why the junction has very low resistance in the breakdown region.
- Avalanche Breakdown
This form of breakdown occurs in junctions which , being lightly doped , have wide depletion layers where the electric field is not strong enough to produce Zener Breakdown. Instead the minority carriers (accelerated by this field) collide with the semiconductor atoms in depletion region. Due to collision with valence electrons , covalent bonds are broken and electron-hole pairs are generated . The newly generated charge carriers accelerated by the electric field resulting in more collision and hence further production of charge carriers . This leads to an available (or flood) of charge carriers and consequently, to a very low reverse resistance.