With the help of circuit diagrams, briefly explain the forward biasing and the reverse biasing of a p-n junction diode.
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A simple memory trick: "Forward" bias connects Positive to P-type and Negative to N-type (P-P, N-N). "Reverse" bias connects them oppositely (P-N, N-P).
Concept: • A p-n junction diode is a two-terminal semiconductor device that allows electric current to flow predominantly in one direction.
• Its behavior changes dramatically depending on the polarity of the external voltage applied across it, a process known as biasing.
Step 1: Explain Forward Biasing
When the positive terminal of an external battery is connected to the p-type semiconductor and the negative terminal to the n-type semiconductor, the junction is said to be forward biased.
Circuit Diagram: A battery connected with its positive terminal to the P-side (triangle base) of a diode symbol and negative terminal to the N-side (straight line).
In this configuration, the applied external voltage creates an electric field that opposes the built-in potential barrier of the depletion region.
Because the applied voltage opposes the barrier, the effective barrier height is reduced, and the width of the depletion layer decreases.
Majority charge carriers (holes from the p-side and electrons from the n-side) are pushed towards the junction, easily crossing it.
This results in a significant forward current flowing through the diode due to the continuous recombination of majority carriers at the junction.
Step 2: Explain Reverse Biasing
When the positive terminal of an external battery is connected to the n-type semiconductor and the negative terminal to the p-type semiconductor, the junction is reverse biased.
Circuit Diagram: A battery connected with its positive terminal to the N-side (straight line) of a diode symbol and negative terminal to the P-side (triangle base).
In this configuration, the applied external voltage creates an electric field that perfectly aligns with the built-in potential barrier.
This alignment increases the effective barrier height and significantly widens the depletion layer.
Majority charge carriers are pulled away from the junction by the external battery, effectively stopping the flow of majority current.
Only a very tiny leakage current (reverse saturation current) flows due to the minority charge carriers generated by thermal agitation.
Step 3: Conclusion
Forward biasing reduces the depletion region and allows heavy current flow, acting like a closed switch. Reverse biasing widens the depletion region and blocks current flow, acting like an open switch.
