Question

In unbiased p-n junction diode

• A. the potential is same everywhere.
• B. there is an electric field at the junction directed from the p-type side to the n-type side.
• C. there is an electric field at the junction directed from the $n$-type side to $p$-type side.
• D. the p-type side is at higher potential than the n-type side.

Hint:

$n$-type has positive ions, $p$-type has negative ions; field always goes $+$ to $-$.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
When a p-n junction is formed, majority charge carriers diffuse across the junction due to concentration gradients.
Electrons diffuse from the n-side to the p-side, and holes diffuse from the p-side to the n-side.
This diffusion leaves behind immobile charged ions near the junction, creating a depletion region and a built-in electric field.
Step 2: Key Formula or Approach:
The n-side loses electrons, leaving positive donor ions.
The p-side loses holes (gains electrons), leaving negative acceptor ions.
Electric field direction is always from positive charges to negative charges.
Step 3: Detailed Explanation:
Let's evaluate each option based on junction physics:
(A) the potential is same everywhere: False. The built-in electric field creates a potential difference (barrier potential) across the junction.
(D) the p-type side is at higher potential than the n-type side: False. The n-side acquires a net positive charge (positive ions) and the p-side acquires a net negative charge. Therefore, the n-side is at a higher potential.
(B) electric field directed from p-type to n-type: False. The p-side has negative ions and the n-side has positive ions.
(C) electric field directed from n-type to p-type: True. The electric field originates from the positive donor ions on the n-side and points towards the negative acceptor ions on the p-side.
Step 4: Final Answer:
There is an electric field directed from the n-type side to the p-type side.