Drift and Diffusion Current in p-n Junction – Rankers Physics

Properties of Semiconductors: Practice Problem & Solution

Assertion (A): The drift current in a p-n junction is from n-side to p-side. Reason (R): The diffusion current in a p-n junction is from p-side to n-side.  
Both (A) & (R) are true and the (R) is the correct explanation of the (A)
Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(A) is true but (R) is false
Both (A) and (R) are false

Solution Explained:

To solve this problem, we apply the core principles of Properties of Semiconductors. Understanding the underlying formula is key to arriving at the correct answer below:

In a p-n junction, the built-in electric field points from the n-side to the p-side, causing drift current to flow from n-side to p-side. Thus, Assertion (A) is true. Due to concentration gradients, diffusion current arises from the movement of majority carriers, resulting in a net diffusion current from p-side to n-side. Thus, Reason (R) is also true.


These are two distinct current mechanisms, and R does not explain A.

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