Explain zener breakdown and avalanche breakdown.
The Zener Breakdown and Avalanche Breakdown are two different mechanisms by which a PN junction breaks. The Zener and Avalanche breakdown both occur in diode under reverse bias. The avalanche breakdown occurs because of the ionization of electrons and hole pairs whereas the Zener diode occurs because of heavy doping.
Zener Breakdown: The phenomenon of the Zener breakdown occurs in the very thin depletion region. When reverse bias is increased, the electric field across the thin depletion region increases. This high electric field breaks the covalent bonds and a large number of minority carriers are generated. So a large reverse current flows and causes breakdown. This process is known as the Zener breakdown.
Avalanche Breakdown: As the reverse bias increases, the electrical field across the depletion region increases. When the high electric field exists across the depletion, the velocity of minority charge carrier crossing the depletion region increases. These carriers collide with the atoms of the crystal. Because of the violent collision, the charge carrier takes out the electrons from the atom.
These electrons collide with the other atoms of the crystals and release more electrons. The process is continuous, and the electric field becomes so much higher that a large reverse current starts flowing in the PN junction and causes breakdown. The process is known as the Avalanche breakdown.