P-N Junction: When p-type semiconductor and n-type semiconductor are joined at a junction, the junction is called p-n Junction.
When a p-type semiconductor is joined with the n-type semiconductor, the free electron from n-side moves (diffuses) into p-side while holes move from p-side to n- side. So the p-side junction contains only negatively charged ions, while n-side near junction contains only positively charged ions. The free electrons and holes after crossing the junction combine respectively with holes and the free electron. This process is called electron-hole recombination.
The completion of free electrons from n-side to holes of p-side produces a narrow region of the junction called depletion layer. The depletion layer has no free electrons or holes as it contains only negatively charged ions in p-side and positively charged ions in n-side. Then an electric field is produced. The electric field opposes the further flow of holes from p-side to n-side. The potential difference produced due to the electric field due to electric field across the junction is called barrier.
Diode: When a p-type semiconductor and n type semi conductor are joined at a junction, a diode is formed. Simply, diode is a two terminal electronic component with asymmetric transfer characteristics with ideally low resistance in one direction called forward direction and high resistance in other direction called reverse direction.
Uses of diode:
- Over volatage protection
- Voltage regulation
- Radio demodulation
- Temperature measurement
- Lighting purposes
- Power conversion etc.