Question

How does current flow in a PN junction?

Answer 1

Forward Biased.

1. When the P side and the N side are connected to the positive and negative terminals of a battery, respectively, a PN junction diode is forward-biased.
2. Electrons from the battery's negative end enter a contact diode's N side, pass over to the P side, and merge with the holes when the diode is forward biased.
3. Additionally, electrons are released from the P side into the battery's positive terminal, creating more free holes that can cross to the N side and join the electrons there.
4. Therefore the depletion layer and barrier potential of the junction both decrease, which lowers the diode's overall resistance.

Reverse biased

1. When the P side is connected to the negative terminal and the N side is connected to the positive of a battery, respectively, a PN junction diode is reverse-biased.
2. The battery collects and expels the bulk charge carriers from all sides of the junction diode when the diode is reverse biased.
3. Electrons enter the positive terminal of the battery while holes from the P side, electrons from the N side, and holes from the P side enter the negative terminal.
4. This increases the barrier potential and widens the depletion zone at the junction.
5. Therefore, the resistance of the diode greatly increases, and current flow through the diode becomes more challenging. The diode functions as a circuit and is almost like a resistor with infinite resistance.

Hence, once the barrier voltage is passed in a forward-biased PN junction, it starts to conduct a current. Current flow is made possible by the externally provided voltage, which drives the majority of carriers toward the junction where recombination occurs.