Question

Explain asymmetrical current flow in a pn- junction diode.​

Answer 1

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(1) When a pn-junction diode is forward biased, the width of barrier potential narrows while in the reverse biased mode, it widens.

(2) Due to reduced barrier width in forward bias, charge carriers find it easy to cross the junction and contribute to the current. Also the charge carriers are forced towards the junction and gain extra energy to cross the junction. Thus, in the forward biased mode, the current through the diode is large. It is of the order of a few milliamperes for a typical diode.

(3) When the diode is reverse biased, the width of the potential barrier increase and the carriers are forced away from the junction so that very few thermally generated carriers can cross the junction and contribute to the current. Thus, a very small current can flow through the diode when reverse biased. The current in a reverse biased diode is of the order of a few microamperes.

(4) The width of the depletion layer decreases with an increase in the application of a forward voltage while it increases when a reverse voltage is applied. On reversing the polarity of bias voltage, the width of the depletion layer changes. This results in asymmetrical current flow in a junction diode.