Question

Explain the working of a P-N junction diode in forward and reverse biased mode.

Answer 1

Hint: In the forward biased mode, the P side of the P-N junction diode is connected to the positive terminal of the battery and the N side is connected to the negative terminal whereas in reverse biased mode, the P side is connected to the negative terminal of the battery and the N side is connected to the positive terminal.

Complete step by step answer:
A P-N junction diode is forward biased when the P side and the N side are connected to the positive and negative terminals of a battery respectively while in reverse bias, they are connected to the opposite terminals.
When a P-N junction diode is forward biased the electrons from the negative end of the battery travel into the N side of the diode and cross over to the P side and combine with the holes. Electrons are also emitted from the P side into the positive terminal of the battery producing more free holes that can travel over to the N side and combine with the electrons. Thus, the depletion layer along with the barrier potential of the junction decreases, decreasing the overall resistance of the diode.
When the diode is reverse biased, the battery attracts and pulls out the majority charge carriers from each side of the junction diode, that is, holes from the P side and electrons from the N side. The holes from the P side enter the negative terminal of the battery and the electrons go into the positive terminal of the battery. This widens the depletion region at the junction and increases the barrier potential. Hence, it becomes more difficult for current to pass through the diode and the resistance of the diode increases very much. In fact, the diode almost acts like a resistor of infinite resistance and it acts like an open circuit.

Note:
This behavior of a P-N junction diode under different kinds of bias is what makes it so unique and useful. This behavior is not possible to be obtained using simple resistors or even capacitors and inductors. Due to this behavior P-N junction diodes find a wide range of practical applications ranging from acting as rectifiers to photovoltaic cells.