Question

If the given figure, \( V_0 \) is the potential barrier across a p-n junction in an unbiased condition. Which of the following statements is correct ?

• A. Curves 1 and 3 both correspond to forward biasing of p-n junction.
• B. Curve 3 corresponds to forward biasing and Curve 1 corresponds to reverse biasing.
• C. Curve 1 corresponds to forward biasing and Curve 3 corresponds to reverse biasing.
• D. Curves 1 and 3 both correspond to reverse biasing.

Hint:

Visual trick: "Forward" bias pushes charges "forward" over the hill, so it must lower the hill (barrier). "Reverse" bias makes it harder, so the hill (barrier) grows taller.

Answer 1

The Correct Option is B

Concept:
• In a p-n junction diode, a depletion region naturally forms at the junction, creating a built-in potential barrier \( V_0 \).

• When a forward bias is applied (p-side connected to positive, n-side to negative), the external electric field strictly opposes the built-in field.

• This opposition shrinks the depletion region and reduces the height of the potential barrier to \( V_0 - V_{\text{applied}} \).

• Conversely, when a reverse bias is applied, the external electric field aligns with and supports the built-in field.

• This alignment widens the depletion region and increases the height of the potential barrier to \( V_0 + V_{\text{applied}} \).

Step 1: Analyze the given graph for barrier heights
The graph plots electric potential on the y-axis against distance on the x-axis.
Curve 2 represents the reference potential barrier \( V_0 \) in the unbiased equilibrium state.
Curve 3 displays a potential barrier height that is visually lower than \( V_0 \).
Curve 1 displays a potential barrier height that is visually higher than \( V_0 \).

Step 2: Correlate barrier height to biasing conditions
Since a forward bias effectively lowers the barrier height to allow easier flow of majority charge carriers, Curve 3 represents the forward biased condition.
Since a reverse bias effectively raises the barrier height, impeding the flow of majority charge carriers, Curve 1 represents the reverse biased condition.

Step 3: Conclusion
Curve 3 correlates to forward bias, and Curve 1 correlates to reverse bias.
Scanning the given options, statement (B) perfectly describes this conclusion.