What do you mean by zener breakdown and avalanche breakdown?

Answer Posted / nilesh mangalhara

Avalanche Breakdown:
When in a normally doped p-n juction diode, a high
potential in reverse bias configuration is introduced, the
minority charge carriers(let us take electrons in p type Si
material for explanation)get high Kinetic Energy due to
which they collide with the covalent bonds of Si atoms. The
reaction takes place like an avalanche an one electron
excites two others of the covalent bond. Due to the fast
moving electrons from p to n and holes from n to p in the
avalanche, the potential barrier between the p and n type
material is destroyed. Ths point of time at which the
avalanche takes place is called the AVALANCHE BREAKDOWN.
Also there is a hysteresis effect,once avalanche breakdown
has occurred, the material will continue to conduct if the
voltage across it drops below the breakdown voltage.
Whereas this is not the case in Zener diode.

Zener Breakdown:
Zener Diode has a special configuration. It is a heavily
doped p-n junction diode. In zener diode when we increase
the voltage in reverse bias configuration, a point comes
when a high electric field developes at the junction with
positive polarity on the p side and negative polarity at
the n side. This electric field attracts the minority
charge carriers on either side(take electrons on p side) to
move to the other side. Thus electrons on p side move to n
side with high velocity but due to heavy doping, the
electron jumps the juntion. Although the high speed breaks
the boundries of the junction. This point is known as the
ZENER BREAKDOWN. As we know that in Zener breakdown, the
junction does not breaks, it leads to the result that when
the voltage is decreased(less than the zener voltage) in
reverse bias, the zener diode stops acting as a conductor.

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