Avalanche breakdown

Breakdown of the PN Junction diode occurs in the reverse bias condition. As we keep on increasing the reverse bias voltage for the PN junction diode the charge carriers will move away from the depletion region into N side and P side, this will increase the depletion width further. Now during this time the minority carriers which arise in the junction that are resulting in the reverse saturation current due to the generation and recombination of charge carriers. These minority carriers generated in the depletion region will have increased velocity which proportional to the increased reverse bias. At a particular voltage the velocity if these charge carriers is so high that these charge carriers when they hit the atoms or ions present in the depletion region, they liberate or dislodge further charge carriers from the ions/ atoms. (Diode biasing)

This process will continue and looks like multiplication of charge carriers takes place and finally the depletion region behaves as a perfect conductor and this condition is known to be breakdown of the PN junction diode. The device once reaches this condition will lose its properties and is permanently damaged as infinite current flows through the device in a short span. There are special types of diodes designed to operate in the breakdown region such as Zener diode. The PN Junction diode under the breakdown condition are done when the P type and N type semiconductors are lightly doped whereas in case of the zener diode the N Type and P Type are heavily doped.  This is also called as avalanche breakdown.

Avalanche breakdown