Question

If no external voltage is applied across p-n junction, there would be

• A. no electric field across the junction
• B. an electric field pointing from n-type to p-type side across the junction
• C. an electric field pointing from p-type to n-type side across the junction
• D. a temporary electric field during formation of p-n junction that would subsequently disappear

Hint:

Built-in field opposes further diffusion of majority carriers.

Answer 1

The Correct Option is B

The question pertains to the electric field present across a p-n junction when no external voltage is applied. Understanding the concept of a p-n junction in semiconductor physics is crucial to solving this question.

A p-n junction is formed by joining p-type and n-type semiconductors. On formation, electrons from the n-type side diffuse across the junction into the p-type side, where they recombine with holes. Similarly, holes from the p-type region diffuse into the n-type region. This process creates a region devoid of mobile charge carriers, known as the depletion region, at the interface. The diffusion of charge carriers across the junction leads to the formation of an internal electric field.

This built-in electric field is directed from the n-type to the p-type side, acting as a barrier that opposes further diffusion of charge carriers. It is this electric field that maintains equilibrium within the p-n junction when no external voltage is applied.

Let's examine the options one by one to corroborate our understanding:

1. No electric field across the junction: This is incorrect as an inherent electric field exists due to the diffusion of carriers and formation of the depletion region.
2. An electric field pointing from n-type to p-type side across the junction: This is the correct option, as explained above. The inherent electric field due to the built-in potential barrier indeed points from n-type to p-type side.
3. An electric field pointing from p-type to n-type side across the junction: This is incorrect. The direction is opposite; it points from n-type to p-type.
4. A temporary electric field during formation of p-n junction that would subsequently disappear: This is incorrect. The electric field remains as long as the junction is in equilibrium without any external voltage.

Therefore, the correct answer is: an electric field pointing from n-type to p-type side across the junction.