The Concept of P-N Junction

Introduction

The P-N junction is a junction formed by the combination of P-type and N-type semiconductor materials. The junction is critical in the development of the diode, which is the foundation of most semiconductor devices such as transistors, BJTs, solar cells, and integrated circuits.

When one side of the junction is doped with acceptor impurity (trivalent) in the P-region and the other side is doped with donor (pentavalent) impurity in the N-region, a P-N junction is formed.

The junction, also known as the semiconductor boundary, is the region where both N-type and P-type materials are joined together.

In the P region, the majority of charge carriers are holes, whereas the majority of charge carriers in the N region are electrons.

When the junction is formed, the holes in the P region diffuse into the N-region, leaving the negative charge in the P region behind, which then recombines with electrons, resulting in negatively charged ions in the P-region.

What is P-N Junction?

A P-N junction is created by embedding both the P-type and N-type into the same semiconductor crystal. The majority of charge carriers in the P-type are positively charged holes, while the majority of charge carriers in the N-type are negatively charged electrons.

To maintain a neutral charge condition around the junction due to the electron-hole pair, the overall charge on both sides of a P-N Junction must be equal and opposite. The depletion region is the layer between the P-type and N-type where the charge carriers are replicated multiple times.

There is no conduction at the P-N junction in the equilibrium state. The majority charge carriers diffusion and minority charge carriers drift are involved in the conduction of a P-N junction. Conduction of electrical current in a P-N junction involves both the conduction and valence bands.

Once the external battery is connected, electrons flow in the conduction band and holes flow in the valence band.

Built in Potential of P-N Junction

Majority charge carriers in the N-type region, such as electrons, can cross the junction and recombine with majority charge carriers in the P-type region, such as holes. As a result of the trivalent impurity boron atoms having a static negative charge as they unleash a positively-charged hole in the valence band, a negative static space charge accumulates in the P-type region.

In the N-type region, a positive space charge forms for the same reasons. The space charge zone or depletion zone is the small volume where this space charge is created. At thermal equilibrium, the density of free charge carriers is negligible due to the strong electric field in this small volume.

As the P-type and N-type semiconductors get closer, a potential barrier forms at the depletion layer. In fact, static space charges accumulate at the P-N junction’s borders, positive charges in the N-type region and negative charges in the P-type region, resulting in an electrical field that ranges from N-type to P-type, preventing diffusion and added recombination of electrons and holes.

How is a P-N Junction Formed?

A P-N junction is formed in a single semiconductor crystal by doping one side with acceptor impurity atoms to make it P-type and the opposite side with donor impurity atoms to make it N-type. The P-N junction is the point at which the P-type and N-type converge.

The electrons in the N-type material scatter the junction and combine with the holes in the P-type material in the P-N junction region. For the reason that electrons are attracted by holes, the region of P-type material close to the junction in the semiconductor takes on a negative charge.

As electrons leave the N-type region, they take on a positive charge. As a result, at the junction, there is a tendency for free electrons to diffuse into the P-type region and holes to diffuse into the N-type region, a process known as diffusion.

What is Depletion region?

Depletion, in general, refers to a reduction or decrease in the quantity of something. Oil depletion, for example, refers to a decrease in oil production from a specific oil well, region, or geographic area over a given time period. Similarly, in semiconductor physics, a depletion region is defined as a region in which the flow of charge carriers decreases over time, eventually resulting in empty mobile charge carriers or a region full of immobile charge carriers.

Conclusion

The P-N junction is a junction formed by the combination of P-type and N-type semiconductor materials. When one side of the junction is doped with acceptor impurity in the P-region and the other side is doped with donor impurity in the N-region, a P-N junction is formed. The junction, also known as the semiconductor boundary, is the region where both N-type and P-type materials are joined together. In the P region, the majority of charge carriers are holes, whereas the majority of charge carriers in the N region are electrons. When the junction is formed, the holes in the P region diffuse into the N-region, leaving the negative charge in the P region behind, which then recombines with electrons, resulting in negatively charged ions in the P-region.