The diffusion current in a p-n junction is: - Vidyadip

MCQ

The diffusion current in a $p-n$ junction is:

A
From the n-side to the $p-$side.
✓
From the $p-$side to the $n-$side.
C
From the $n-$side to the p-side if the junction is forward$-$biased and in the opposite direction if it is reverse$-$biased.
D
From the $p-$side to the $n-$side if the junction is forward$-$biased and in the opposite direction if it is reverse$-$biased.

✓

Answer

Correct option: B.

From the $p-$side to the $n-$side.

When a $p‒n$ junction is formed then because of the difference in the concentration of charge carriers in the two regions, electrons from the $n$ region move to the $p$ region and holes from the $p$ region move to the $n$ region. Since the direction of the current is always opposite to the motion of electron, the direction of the current is from the $p$ side to the n side.
Similarly, when the junction is forward biassed, the positive terminal of the battery is connected to the pside of the $p‒n$ junction and the negative terminal of the battery is connected to the n side of the $p‒n$junction. As a result, electrons in the n side of the $p‒n$ junction are repelled by the negative terminal of the battery and they move to the $p$ side, where the positive terminal of the battery attracts them. Similarly, holes from the $p$ side of the $p‒n$ junction are repelled by the positive terminal of the battery and they move to the $n$ side, where the negative terminal of the battery attracts them. Thus, they give diffusion current from the $p$ side to the $n$ side across the $p‒n$ junction.
In reverse biassing, there is no flow of majority carriers across the junction; hence, there is not diffusion current. Here, the flow of majority carriers is opposed by the applied voltage.

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