What is Zener Breakdown?

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Quantum mechanical tunneling of carriers through the bandgap is the dominant breakdown mechanism for the highly doped p-n junction. In zener breakdown mechanism, the electric field becomes as high as $${ 10 }^{ 7 }$$ V/m in the depletion layer with only a small applied reverse bias voltage. In this process, it becomes possible for some electrons to jump across the barrier from the valence band in p-material to some of the unfilled conduction band in n-material. This process is known as zener breakdown. In this process, the junction is not damaged. The junctions regain its original position when the reverse voltage is removed. This process is used in the zener diodes. The embedded graph below roughly defines zener breakdown.

However, if the number of electrons jumping across the barrier (i.e. flow of current) increases beyond the rated capacity of the zener diode, then avalanche breakdown takes place which destroys the junction.

The tunneling probability equals:

The tunneling current is obtained from the product of the carrier density. The velocity equals the Richardson velocity, the velocity with which on average the carriers approach the barrier while the carrier density equals the density of available electrons multiplied by the tunneling probability, yielding:

$${ J }_{ n }=q{ v }_{ R }n\quad \Theta$$

The tunneling current therefore depends exponentially on the bandgap energy to the $$\frac { 3 }{ 2 }$$ power.

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