Question

Explain the formation of depletion region and barrier potential in PN junction diode.

Answer 1

      Schematic representation

       Circuit symbol

1. A p-n junction diode is formed when the p-type semiconductor is fused with an N-type semiconductor.

2. A p-n junction diode is formed when the p-type semiconductor is fused with an N-type semiconductor.

• Forward bias
• Forward bias

a. Forward bias:

1. If the positive terminal of the external voltage source is connected to the p-side and the negative terminal to the n-side forward bias takes place.
2. Electron moves to n-side holes move to the p side Recombination takes place near the junction and reduces depletion region.
3. Electron from n-side accelerates towards p side it experiences reduced potential barrier at the junction.
4. Applied voltage is increased, the width of the depletion region and barrier potential further reduced.
5. So a large number of electrons pass through the junction.

b. Reverse bias:

1. If the positive terminal of the external voltage source is connected to the p-side and the negative terminal to the n-side reverse bias takes place.
2. Depletion region is increased potential barrier is also increased.
3. Majority of charge carriers from both sides experience a great barrier to cross the junction. So diffusion current reduces.
4. The current flows under reverse bias are called reverse saturation current I_s.