Breakdown mechanism

This process is must useful to know about diode function and operate of it .If the reverse bias voltage is made to high ,the current through the PN junction increases rapidly at Vz. The voltage at which this happens is known as Breakdown Voltage or Zener voltage .There are two mechanism which cause this Breakdown .This two mechanism are as followings:
  1. Zener Breakdown
  2. Avalanche Breakdown
When reverse bias voltage is increased the electric field at the junction also increase.At some stage the electric filed becomes so high ,then it breaks the covalent bonds creating electron hole pairs .Thus a large number of carriers are generated . This cause a large number of current to flow .This mechanism is known as Zener breakdown.

At high reverse voltage due to high electric field ,the minorities charge carrier ,While crossing the PN junction acquires very high velocities .These by collision breakdown the covalent bonds generating more charge carriers .A chain reaction is established giving rise to high current .This mechanism is known as Avalanche breakdown.

The covalent bonds where the junction breakdown liberating large number of electron pair .Then the reverse current is increase highly to high amount .This avalanche breakdown may damage the PN junction .This phenomenon is used to zener diode and used in voltage regulator.

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