Question

In a p-n junction diode, what happens to the width of the depletion layer under reverse bias?

• A. It decreases
• B. It increases
• C. It remains constant
• D. It becomes zero

Hint:

Forward bias → depletion region decreases. Reverse bias → depletion region increases.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
A p-n junction features a depletion layer where mobile charge carriers have recombined, leaving behind uncovered immobile ions. A built-in electric field exists across this layer.
Step 2: Key Formula or Approach:
The approach is to analyze the direction of the applied electric field compared to the built-in field. In reverse bias, the p-side is connected to the negative terminal and the n-side to the positive terminal.
Step 3: Detailed Explanation:
When reverse bias is applied, the external battery creates an electric field that points in the same direction as the built-in electric field of the depletion region.
The negative terminal of the battery attracts the holes (majority carriers in the p-region) away from the junction.
Simultaneously, the positive terminal attracts the electrons (majority carriers in the n-region) away from the junction.
Because the majority carriers are pulled away from both sides of the junction, a larger region of immobile ions is left uncovered.
Consequently, the width of the depletion layer increases, preventing any significant current flow across the junction.
Step 4: Final Answer:
The correct option is (B).