Uncovered charges

The un-neutralised ions in the neighbourhood of the junction are known as uncovered charges. These charges play a crucial role in the behavior of a p-n junction and can affect its electrical characteristics.

Formation of a p-n junction
A p-n junction is formed by bringing a p-type semiconductor in contact with an n-type semiconductor. In the p-type semiconductor, the majority carriers are holes (positive charge carriers), while in the n-type semiconductor, the majority carriers are electrons (negative charge carriers). When these two semiconductors are brought together, the electrons from the n-region diffuse into the p-region and combine with the holes, forming negatively charged ions (uncovered negative charges) in the p-region. Similarly, the holes from the p-region diffuse into the n-region and combine with the electrons, forming positively charged ions (uncovered positive charges) in the n-region.

Uncovered charges near the junction
In the vicinity of the p-n junction, the uncovered positive and negative charges create an electric field. This electric field opposes the further diffusion of charge carriers across the junction. As a result, a region near the junction becomes depleted of majority charge carriers, leading to the formation of a depletion region.

Depletion region and Uncovered charges
The depletion region is a region near the junction where the concentration of charge carriers is significantly reduced. It consists of fixed positive charges (due to uncovered negative ions in the p-region) and fixed negative charges (due to uncovered positive ions in the n-region). These fixed charges in the depletion region create an electric field that prevents the further movement of charge carriers.

Role of Uncovered charges
The uncovered charges near the junction play a crucial role in the behavior of the p-n junction. They create an electric field that establishes a potential barrier, also known as the built-in potential, across the junction. This potential barrier prevents the flow of current in the absence of an external bias.

Conclusion
The un-neutralised ions in the neighbourhood of the junction are known as uncovered charges. They create an electric field and establish a potential barrier near the p-n junction, which affects the electrical characteristics of the junction. Understanding the behavior of these uncovered charges is essential for analyzing the operation of p-n junctions and their applications in electronic devices.