The Transition Region in an Open Circuited p-n Junction

Introduction:
A p-n junction is a type of semiconductor junction formed by the contact between a p-type and an n-type semiconductor material. The p-type material has an excess of holes, while the n-type material has an excess of free electrons. When the two materials are brought into contact, a diffusion of charge carriers occurs, resulting in the formation of a depletion region, also known as a transition region. In this region, the concentration of free electrons and holes is reduced, leading to a low conductivity.

Contents:

- What is the Transition Region?
- Open Circuited p-n Junction
- Uncovered Immobile Impurity Ions

What is the Transition Region?
The transition region is a region in a p-n junction where the concentration of free electrons and holes is reduced due to the diffusion of charge carriers. This region is also known as a depletion region because of the reduced carrier concentration. The width of the transition region depends on the doping concentration of the p-type and n-type materials and the applied voltage across the junction.

Open Circuited p-n Junction:
When a p-n junction is open circuited, no external current flows through the junction. However, there is a small amount of current that flows due to the thermal generation of electron-hole pairs in the transition region. The magnitude of this current is very small and is known as the reverse saturation current.

Uncovered Immobile Impurity Ions:
When a p-n junction is formed, impurity atoms are introduced into the semiconductor material to create the p-type and n-type materials. These impurity atoms may not be completely ionized, leading to the formation of uncovered immobile impurity ions in the transition region. These impurity ions create a fixed electric field in the transition region, which opposes the diffusion of charge carriers and contributes to the width of the depletion region.

Conclusion:
In conclusion, the transition region in an open circuited p-n junction contains both free electrons and holes as well as uncovered immobile impurity ions. The concentration of free electrons and holes is reduced in this region, leading to a low conductivity. The width of the depletion region depends on the doping concentration and applied voltage across the junction.

Anwer is D