Concept of currents in a p-n junction

In a p-n junction, there are two types of current:

• Diffusion current: due to majority carriers moving from high concentration to low concentration.
• Drift current: due to minority carriers moving under the influence of the electric field across the depletion region.

Effect of forward bias

When the junction is forward biased:

• The potential barrier decreases.
• Majority carriers cross the junction more easily.
• Hence, diffusion current increases greatly.
• Drift current remains almost unchanged (it is mainly due to thermally generated minority carriers).

Therefore, under forward bias, $I_{\text{diffusion}} > I_{\text{drift}}$ So, Assertion A is correct.

Check the Reason R

Reason says: Diffusion current in a p-n junction is from the n-side to the p-side if the junction is forward biased.

Under forward bias:

• Electrons diffuse from n-side to p-side.
• Holes diffuse from p-side to n-side.

So diffusion involves majority carriers crossing in both directions for different carriers. The conventional diffusion current direction is taken in the same overall direction across the junction, but the statement as written is incomplete/misleading because diffusion current is not simply described only as from n-side to p-side.

Hence, Reason R is not correct.

Option matching

• Assertion A: Correct
• Reason R: Incorrect

Therefore, the correct option is: $\boxed{\text{B}}$

Comparison with stored answer

Stored correct answer = B

My derived answer = B

Hence, they agree.