Question

Applying forward bias to p-n junction, the potential barrier ______.

• A. increases.
• B. decreases.
• C. remains unchanged.
• D. becomes zero.

Hint:

Forward Bias $\rightarrow$ Pushes holes and electrons TOWARD the junction $\rightarrow$ Shrinks the depletion region $\rightarrow$ Decreases potential barrier $\rightarrow$ Current flows easily! Reverse bias does the exact opposite.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
We need to state the physical effect that applying a forward bias voltage has on the internal built-in potential barrier of a standard p-n junction diode.

Step 2: Detailed Explanation:
In an unbiased p-n junction, a depletion region forms naturally at the interface. This creates a built-in electric field and a corresponding "potential barrier" ($V_0$) that opposes the further diffusion of majority charge carriers.
Forward Bias Configuration:
Forward biasing means connecting the positive terminal of the external battery to the p-type region (anode) and the negative terminal to the n-type region (cathode).
Effect on the Potential Barrier:
The external voltage ($V_{ext}$) applied in forward bias creates an electric field that points in the exact opposite direction to the diode's internal built-in electric field.
These two opposing fields partially cancel each other out.
Therefore, the effective net potential barrier height is reduced to $(V_0 - V_{ext})$.
Because the barrier is lowered, majority carriers (holes from p-side and electrons from n-side) have enough thermal energy to easily cross the junction, resulting in a large forward current.

Step 3: Final Answer:
The potential barrier decreases, matching option (b).