What is p-n junction diode ? Define depletion region.

P-N Junction Diode

A P-N junction diode is a semiconductor device formed by joining two types of semiconductor materials: p-type and n-type. The p-type semiconductor is rich in holes (positive charge carriers), while the n-type semiconductor has an abundance of free electrons (negative charge carriers). When these two materials are joined, a junction is formed, resulting in a P-N junction diode.

At the junction of the p-type and n-type semiconductors, a region is formed where the free electrons from the n-type side combine with the holes from the p-type side. This results in a depletion layer in pn junction where no free charge carriers are present. This depletion region is crucial for the functionality of the diode, as it creates a barrier that prevents the flow of charge carriers under normal conditions.

Depletion Layer in P-N Junction

The depletion layer in pn junction is a narrow region located on either side of the junction between the p-type and n-type materials. It forms due to the diffusion of charge carriers—electrons from the n-type region and holes from the p-type region—into the opposite side. As these carriers recombine, they leave behind immobile ions, creating an electric field that opposes further movement of charge carriers across the junction.

This depletion layer in pn junction acts as an insulator, preventing current from flowing freely when no external voltage is applied. However, when an external voltage is applied in the forward bias direction (positive to p-side and negative to n-side), the electric field in the depletion region is weakened, allowing current to flow. On the other hand, when the diode is reverse biased, the depletion layer becomes wider, increasing the resistance and preventing current flow.

In conclusion, the depletion layer in pn junction plays a key role in controlling the current flow in a P-N junction diode, making it an essential component in many electronic devices such as rectifiers, light-emitting diodes (LEDs), and solar cells.