Question

In a reversed-biased p-n junction diode, the applied voltage mostly drops across :

• A. p-region only
• B. n-region only
• C. depletion region
• D. the diode

Hint:

In forward bias, applied voltage opposes built-in potential and reduces depletion width. In reverse bias, applied voltage aids built-in potential and widens the depletion layer, dropping almost all voltage across it.

Answer 1

The Correct Option is C

Concept:
• In a p-n junction diode, the depletion region is depleted of mobile charge carriers and consists only of immobile donor and acceptor ions.

• Applying reverse bias increases the width of the depletion layer and raises the potential barrier height.

Step 1: Understanding reverse bias resistance
When a reverse bias voltage is applied across a p-n junction diode, the majority charge carriers are pulled away from the junction.
This widens the depletion layer, rendering it virtually free of mobile charge carriers.
Consequently, the resistance of the depletion region becomes extremely high (order of megaohms) compared to the low resistance of the neutral p-type and n-type bulk regions.

Step 2: Voltage distribution across regions
In a series electrical circuit, voltage drop is proportional to resistance ($V = I R$).
Because almost all the total resistance of a reverse-biased diode resides in the depletion region, virtually the entire external applied voltage drops across the depletion region.

Step 3: Conclusion
The applied reverse voltage drops almost entirely across the depletion region, corresponding to option (C).