The diode which have lesser doping undergo avalanche breakdown when high reverse voltage is applied. The lesser doping means the depletion width is large and so electric field within depletion region is not so high. Hence the electric field would not be able to pull out electrons from the outer shell of atoms and breakdown doesn’t occur in depletion region. But as the depletion region is large and hence when the minority charge carriers move through the depletion region, they get accelerated by the electric field and that even for larger time (as distance through which acceleration is provided is large). Hence minority charge carriers acquire high velocity and so high kinetic energy. When these charge carriers strike with atoms in the n-type and p-type regions, the high kinetic energy gets converted to thermal energy and hence due to this energy electrons from the outermost shell are pulled out and large current starts flowing. This type of breakdown is called avalanche breakdown.
But due to the high thermal energy, the temperature rises and diode gets burned. Due to this reason the simple diodes (where avalanche breakdown occurs) is not used in the applications and instead Zener diode is used in the application circuits of breakdown diodes such as regulating power supply.
Differences between Zener breakdown and Avalanche breakdown:
Zener breakdown Avalanche breakdown
- The Zener breakdown occurs in HIGH 1. The avalanche breakdown occurs in LOW doping diodes. doping diodes.
- The breakdown occurs within the 2. The breakdown occurs outside the depletion depletion region. region.
- The breakdown voltage is lesser than 3. The breakdown voltage is more than zener that of avalanche breakdown. breakdown voltage.
As Zener breakdown voltage is less than that of avalanche breakdown voltage, hence Zener breakdown is said to occur before the avalanche breakdown.
Hence we can say if we increase the doping of a diode, the chances of zener breakdown increases and hence breakdown voltage decreases