Physics Electronics PMDC Conceptual Practice
PMDC Verified Question 222 of 494
How does increasing the dopant impurity concentration in a PN junction affect its built-in potential barrier \( V_0 \)?
A
The barrier potential decreases toward zero
B
The barrier potential increases logarithmically
C
The barrier potential remains strictly constant
D
The barrier potential drops to negative values
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: The barrier potential increases logarithmically
Concept:

The built-in potential barrier \( V_0 \) depends logarithmically on the product of the acceptor and donor doping concentrations (\( N_A \) and \( N_D \)).

Formula:

$$V_0 = \frac{k T}{q} \ln\left(\frac{N_A N_D}{n_i^2}\right)$$

Solution:

  • Higher doping levels \( N_A \) and \( N_D \) increase the carrier concentration gradient across the junction.


  • According to the equation, \( V_0 \) increases logarithmically as either \( N_A \) or \( N_D \) increases.


Why other options are incorrect:

  • Option A: Higher doping increases the barrier potential rather than decreasing it.
  • Option C: \( V_0 \) depends directly on the doping concentrations \( N_A \) and \( N_D \).
  • Option D: The equilibrium barrier potential is always positive.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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