Class 12 Physics Semiconductor Electronics Reverse biasing

Reverse biasing

  • If the positive terminal of the external battery is connected to the n-side and the negative terminal of the external battery is connected to the p-side, then the p-n junction is said to be reverse biased

  • The direction of the applied voltage is same as that of the barrier potential
  • As a result, the barrier height increases and the depletion region widens due to change in electric field
  • The effective barrier height is VB + V
  • This suppresses the flow of electrons from n region to p region and holes from the p region to n region. Hence, diffusion current decreases
  • The electric field direction of the junction is such that if electrons on p-side or holes on n-side in their random motion come close to the junction, they will be swept to its majority zone. This gives rise to drift current of order of few µA
  • The diode reverse current is not much dependent on the applied voltage. Even a small voltage is sufficient to sweep the minority carriers from one side of the junction to the other side of the junction
  • The current under reverse bias is essentially voltage independent up to a critical reverse bias voltage, known as breakdown voltage VBE
  • When V = VBE, the diode reverse current increases sharply. If the current is not limited, the p-n junction will get destroyed

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