When a forward bias is applied to a p -n junction. It

Options

A. (a) raises the potential barrier
B. (b) reduces the majority carrier current to zero
C. (c ) lowers the potential barrier
D. (d) All of the above

Explanation

To solve the question "When a forward bias is applied to a p-n junction," we need to analyze the effects of applying a forward bias to a p-n junction diode.

### Step-by-Step Solution:

1. **Understanding the p-n Junction**:
- A p-n junction consists of p-type and n-type semiconductors. The p-type has an abundance of holes (positive charge carriers), while the n-type has an abundance of electrons (negative charge carriers).
- At the junction, a potential barrier is formed due to the diffusion of electrons from the n-side to the p-side and holes from the p-side to the n-side.

2. **Applying Forward Bias**:
- Forward bias means connecting the p-side (anode) to the positive terminal of a voltage source and the n-side (cathode) to the negative terminal.
- This external voltage opposes the built-in potential barrier of the p-n junction.

3. **Effect on the Potential Barrier**:
- When forward bias is applied, the external electric field reduces the potential barrier. This occurs because the positive terminal repels holes towards the junction and the negative terminal attracts electrons towards the junction.
- As a result, the potential barrier decreases, allowing charge carriers to move across the junction more easily.

4. **Current Flow**:
- With the reduction of the potential barrier, majority charge carriers (holes from the p-side and electrons from the n-side) can cross the junction, leading to an increase in current flow through the diode.

5. **Evaluating the Options**:
- **Option A**: Raises the potential barrier – This is incorrect because forward bias reduces the potential barrier.
- **Option B**: Reduces the majority charge carrier current to zero – This is also incorrect; forward bias increases the majority charge carrier current.
- **Option C**: Lowers the potential barrier – This is correct as explained above.
- **Option D**: All of the above – This is incorrect because options A and B are wrong.

### Conclusion:
The correct answer is **C: lowers the potential barrier**.