Sigma Percentile
LEVELJEE Main

Animated Solution for Physics - Semiconductor Electronics: When - junction diode is forward biased, then

Select Answer:

Visualized Solution

- \text{ Junction at Equilibrium}

\text{Forward Biasing}

  • \text{Forward Bias: } p \rightarrow +ve, n \rightarrow -ve

\text{External Electric Field}

  • E_{\text{ext}} \text{ opposes } E_{\text{int}}

\text{Carrier Motion}

  • \text{Majority carriers pushed towards junction}

\text{Depletion Region Narrows}

  • \text{Recombination increases} \implies W \downarrow

\text{Barrier Height Reduces}

  • V_{\text{eff}} = V_B - V \implies \text{Barrier Height } \downarrow

\text{Conclusion}

  • \text{Result: Both } W \text{ and } V_B \text{ are reduced.}

The Sigma Insight: p-n Junction Diode

Solution Diagram

Introduction to the - Junction

Imagine you are looking at a pristine - junction diode at equilibrium. Before we connect any external battery, a fascinating natural phenomenon occurs. Electrons from the -side diffuse into the -side, and holes from the -side diffuse into the -side. This creates a central zone completely devoid of free charge carriers, aptly named the depletion region.
Because of this charge migration, an internal electric field is established, creating a built-in barrier potential (). This barrier acts like a hill that prevents any further flow of majority charge carriers. The diode is essentially in a state of standoff.

Applying the Forward Bias

Now, what exactly does forward biasing mean? It means we connect the -side of the diode to the positive terminal of an external battery, and the -side to the negative terminal.
Look closely at the physics of this setup. The positive terminal of the battery exerts a strong repulsive force on the holes in the -region. Simultaneously, the negative terminal repels the electrons in the -region.

The Collapse of the Barrier

Because of this intense repulsion, the majority charge carriers—holes from the left and electrons from the right—are pushed aggressively towards the central junction. As they flood into the depletion region, they begin to recombine with each other. Because the battery provides a continuous supply of these carriers, the width of the depletion region () is significantly reduced.
Simultaneously, the external voltage () creates an electric field that directly opposes the built-in potential. This means the effective barrier height that the charges need to overcome is reduced to . The 'hill' has been flattened!

Conclusion

So, the final takeaway is crystal clear: in forward bias, both the depletion region and the barrier height are reduced, allowing a large current to flow easily through the diode. This perfectly matches our option (c).