Physics Electronics PMDC Conceptual Practice
PMDC Verified Question 349 of 494
Why is a practical \( \text{P-N} \) junction manufactured within a single continuous semiconductor crystal rather than by mechanically pressing separate P-type and N-type blocks together?
A
Mechanical contact generates excessive thermal noise that destroys the semiconductor
B
Microscopic surface irregularities and oxide layers prevent continuous atomic lattice alignment
C
Separate blocks cause majority carriers to spontaneously annihilate before crossing
D
Mechanical pressing alters the bandgap energy of silicon from \( 1.1\text{ eV} \) to zero
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Microscopic surface irregularities and oxide layers prevent continuous atomic lattice alignment
Concept:

A functional \( \text{P-N} \) junction requires an uninterrupted crystal lattice across the boundary so that charge carriers can cross via quantum-mechanical diffusion.

Formula:

Qualitative concept / No formula required.

Solution:

  • Mechanically pressing two distinct pieces creates an interface with surface roughness, air gaps, and oxide layers.


  • These surface defects disrupt the crystal lattice and create interface states that prevent the formation of a uniform depletion layer.


  • Therefore, junctions are fabricated within a single crystal using methods such as diffusion, ion implantation, or epitaxy.


Why other options are incorrect:

  • Option A: The primary limitation is structural interface defects and oxidation, not thermal noise generation.
  • Option C: Majority carriers cross via diffusion once a continuous junction forms; they do not annihilate without interacting.
  • Option D: Mechanical contact does not alter the fundamental bandgap energy (\( E_g \)) of the bulk semiconductor material.

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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