Question

what is forward bias and reverse bias

Answer 1

Forward Biased

When we connect p-type region of a junction with the positive terminal of a voltage source and n-type region with the negative terminal of the voltage source, then the junction is said to be forward bias.

Reverse Biased

When positive terminal of a voltage source is connected to the n-type region and the negative terminal of the source is connected to the p-type region then the pn junction is said to be in reverse biased condition.

Answer 2

Hey !!

FORWARD BIAS

1. When a external voltage is applied, where negative of battery is connected to n side while positive of battery is connected to p side, then voltage potential will get reduced and more current can flow across the junction that decreases the pn junction diode width.
2. The positive terminal of battery repels majority carries, holes in p-region while negative terminal repels electrons in n-region which pushes them towards the junction.
3. Here, an increase in concentration of charge carries near the junction is observed, where recombination takes place thereby reducing width of depletion region.
4. Due to rise in forward bias voltage, depletion will continue to reduce its width which results in more and more carries recombination.

REVERSE BIAS

1. If an external voltage is applied in reverse direction where positive of battery is connected to n side while negative of battery is connected to p side, then barrier potential will increase and minority charge carries will flow across junction.
2. In this, the current will be quiet small and is independent of external voltage.
3. Beyond certain voltage, diode will break with Avalanche breakdown mechanism or Zener breakdown mechanism.
4. Here, negative terminal of battery will attract majority carries, holes in p-region and positive terminal attracts electrons in n-region which pulls them away from the junction.
5. As a result of this, there will be decrease in concentration of charge carries near junction which increases the width of depletion region.
6. A small amount of current flow due to minority carries known as reverse bias current or leakage current flows and with rise in reverse bias voltage, depletion region continues to increase in width without any flow of current.

GOOD LUCK !!