Question: Q. 5. Explain briefly with the help of necessary diagrams, the forward and the reverse biasing of a pn junction diode. Also draw their characteristic curves in the two cases.

U[Delhi III 2017]

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Solution:

Ans. Circuit diagrams of pn Junction under forward bias reverse bias

1/2+1/2

Explanation of pn junction working for forward and reverse bias

Characteristic curves for the two cases

In forward bias, applied voltage does not support potential barrier. As a result, the depletion layer width decreases and barrier height is reduced. Due to the applied voltage, electrons from n side cross the depletion region and reach p side. Similarly holes from p side cross the junction and reach the n side. The motion of charge carriers, on either side, give rise to current. In reverse bias, applied voltage support potential barrier. As a result, barrier height is increased, depletion layer widens. This suppresses the flow of electrons from np and holes from pn, thereby decrease the diffusion current. 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 drift of carriers give rise to the current called reverse current.

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