Diffusion current in a p-n junction is greater than the drift current in magnitude

Options

A. if the junction is forward-biased
B. if the junction is reverse-biased
C. if the junction is unbiased
D. in no case.

Answer

To determine whether the diffusion current in a p-n junction is greater than the drift current in magnitude, we need to analyze the behavior of the p-n junction under different biasing conditions.

### Step-by-Step Solution:

1. **Understanding the p-n Junction:**
- A p-n junction consists of p-type and n-type semiconductors. The p-side has an abundance of holes (positive charge carriers), while the n-side has an abundance of electrons (negative charge carriers).

2. **Current Components:**
- In a p-n junction, two types of currents can be identified:
- **Diffusion Current:** This occurs due to the movement of charge carriers from a region of high concentration to a region of low concentration. In the p-n junction, holes diffuse from the p-side to the n-side, and electrons diffuse from the n-side to the p-side.
- **Drift Current:** This occurs due to the movement of charge carriers in an electric field. In a p-n junction, the electric field is created by the built-in potential barrier at the junction.

3. **Forward Bias Condition:**
- When the p-n junction is forward biased (positive terminal connected to the p-side and negative terminal to the n-side), the barrier potential is reduced. This allows more holes to move from the p-side to the n-side and more electrons to move from the n-side to the p-side.
- In this condition, the diffusion current is significantly increased because the majority carriers (holes in p-side and electrons in n-side) are pushed across the junction.

4. **Reverse Bias Condition:**
- In reverse bias (positive terminal connected to the n-side and negative terminal to the p-side), the barrier potential is increased, which reduces the movement of majority carriers across the junction. Here, the drift current (due to minority carriers) becomes very small compared to the diffusion current, which is almost negligible.

5. **Unbiased Condition:**
- In an unbiased condition, the p-n junction is at equilibrium. The diffusion current and drift current are equal in magnitude but opposite in direction, resulting in a net current of zero.

6. **Conclusion:**
- The statement "the diffusion current in a p-n junction is greater than the drift current in magnitude" is true when the junction is forward biased. In reverse bias, the drift current is very small, and in unbiased conditions, both currents are equal.

### Final Answer:
The diffusion current in a p-n junction is greater than the drift current in magnitude when the junction is **forward biased**.