PN junction diode forward bias operation

PN junction diode is electronic component made up of silicon semiconductor material and widely used in rectifier circuits. To use PN junction diode practically, one must know the forward and reverse bias of this. In this article, i will try to explain the same. PN junction diode forward biases when positive terminal of the power supply is connected to the P-type side, and the negative terminal of the power supply is connected to the N-type side.

·   When a PN junction is forward biased, the holes are repelled from the positive terminal of the battery and are moved towards the junction.

·   Similarly the free electrons are repelled from the negative terminal of the battery and move towards the PN junction. Because of their acquired energy, some of the holes and the free electrons enter into the depletion region and recombine themselves.

·    It reduces the potential barrier and the width of the depleting region.

·    The width of depletion region and the barrier potential reduces with the increase in forward bias.

·   Hence more majority carriers diffuse across the junction and it leads to a large current to flow through the PN junction. This is called forward current.

·    The point from where sharp increase in current starts is called as the “knee” point

·    The PN junction will not allow the current to flow until the external bias voltage overcomes the barrier potential VB. The external bias voltage should be greater than the barrier potential for the current to flow.

PN junction diode reverse biases when positive terminal of the power supply is connected to the N-type side, and the negative terminal of the power supply is connected to the P-type side.

·   When a PN junction is reverse biased, the holes are attracted from the negative terminal of the battery and are moved towards the terminal.

·  Similarly the free electrons are attracted from the positive terminal of the battery and move towards the terminal. It reduces the potential barrier and the width of the depleting region.

·    The width of depletion region and the barrier potential increases with the increase in reverse bias.