Question

Application of a forward bias to a p-n junction:

• A. increases the number of donors on the n-side
• B. increases the electric field in the depletion zone
• C. increases the potential difference across the depletion zone
• D. widens the depletion zone

Answer 1

The Correct Option is A

To understand the effect of forward bias on a p-n junction, let's review the basic principles of how a p-n junction works:

• The p-n junction is a fundamental component in semiconductor devices, formed by joining p-type and n-type semiconductors.
• The p-type semiconductor contains an excess of holes (positive charge carriers), while the n-type has an excess of electrons (negative charge carriers).
• At the interface, there is a region called the depletion zone, which is devoid of mobile charge carriers due to the recombination of electrons and holes. This region has a built-in electric field that opposes further movement of charge carriers across the junction.

Now, let's explore what happens when a forward bias is applied:

• Applying forward bias means connecting the p-side to the positive terminal and the n-side to the negative terminal of a voltage source. This reduces the built-in potential barrier.
• The reduction in potential barrier allows more charge carriers to cross the junction. Electrons from the n-side move towards the p-side, and holes from the p-side move towards the n-side.
• This effectively increases the current flow through the junction, as the charge carriers are now provided with sufficient energy to overcome the barrier.
• The width of the depletion zone decreases because the potential barrier is lowered, allowing carriers to neutralize the immobile charges in the depletion region.

Considering the options:

1. Increases the number of donors on the n-side: This statement is incorrect. Forward biasing does not change the number of donor atoms in the n-side. Donors are fixed once the semiconductor is doped.
2. Increases the electric field in the depletion zone: Incorrect, as forward bias actually reduces the electric field in the depletion zone.
3. Increases the potential difference across the depletion zone: Incorrect, since forward bias reduces the potential barrier allowing current to flow more easily across the junction.
4. Widens the depletion zone: Incorrect, as the application of forward bias reduces the width of the depletion zone.

None of the given options is correct considering the context of the question, and it seems there might have been an error in identifying the supposed correct answer.

In conclusion, forward bias decreases the potential barrier and the width of the depletion zone, allowing more charge carriers to participate in conduction.