Zener breakdown:
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Zener breakdown
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Zener breakdown is sharper than Avalanche breakdown. Since Zener diode is heavily doped the impurities are so high and hence the depletion layer is very thin. So even for a small reverse voltage they start conducting. When the reverse biased voltage continues to increase the electrons in the depletion region breaks from the covalent bond and thus the depletion region becomes conductive. This is called Zener breakdown and the voltage at which zener breakdown happens is called zener voltage. Zener breakdown happens at lower voltage than Avalanche breakdown.
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Zener breakdown
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Avalanche breakdown:
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Avalanche breakdown
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when it is reversed biased the depletion layer increases and reverse saturation current due to minority carriers will be flowing constantly. When the voltage is increased in the reverse biased condition the minority carriers gains enough kinetic energy and collide with the immobile ions in the depletion region. This results in more free electrons .These free electrons collide with each other forming more free electrons. So this leads to huge free electrons in the depletion region and the whole diodes starts conducting.
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Avalanche breakdown
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