Q170 / 180 · COMEDK 2026 (9 May Shift 1) · Physics
In a PN junction diode, the forward bias is increased gradually from 0 Volt to 1 Volt. Which of the following statements is correct?
- AThe depletion width increases, and barrier potential increases
- BThe depletion width decreases, but the electric field inside the junction increases
- CThe depletion width remains unchanged, but current increases
- Correct answerDThe depletion width decreases and barrier potential decreases
Solution
In a PN junction diode, the built-in potential (barrier potential) acts from the n-side to the p-side.
When the diode is forward biased, the applied voltage opposes the built-in potential. The effective barrier potential becomes $V_0 - V_f$, where $V_0$ is the built-in potential and $V_f$ is the applied forward bias voltage. Thus, the barrier potential decreases.
The width of the depletion region is directly proportional to the square root of the effective barrier potential, given by $W \propto \sqrt{V_0 - V_f}$.
As the effective barrier potential decreases with an increase in forward bias, the depletion width also decreases.
Therefore, both the depletion width and the barrier potential decrease.
Answer: The depletion width decreases and barrier potential decreases
When the diode is forward biased, the applied voltage opposes the built-in potential. The effective barrier potential becomes $V_0 - V_f$, where $V_0$ is the built-in potential and $V_f$ is the applied forward bias voltage. Thus, the barrier potential decreases.
The width of the depletion region is directly proportional to the square root of the effective barrier potential, given by $W \propto \sqrt{V_0 - V_f}$.
As the effective barrier potential decreases with an increase in forward bias, the depletion width also decreases.
Therefore, both the depletion width and the barrier potential decrease.
Answer: The depletion width decreases and barrier potential decreases
Hence, the correct answer is option: 'D'.