Concept:At the moment of junction formation, a steep concentration gradient exists across the boundary: high electron concentration on the n-side and high hole concentration on the p-side. This gradient drives the diffusion of majority carriers across the interface.
Formula:$$J_{\text{diff}} = q D_n \frac{dn}{dx} - q D_p \frac{dp}{dx}$$
Solution:- Electrons naturally diffuse from high concentration (n-side) to low concentration (p-side).
- Holes naturally diffuse from high concentration (p-side) to low concentration (n-side).
- This initial diffusion leaves behind unneutralized donor and acceptor ions, establishing the depletion region.
Why other options are incorrect:- Option A: The initial junction formation occurs before any external voltage is applied.
- Option C: Diffusion is driven by concentration gradients, not external radiation.
- Option D: Gravitational forces on atomic charge carriers are negligible compared to electrostatic forces.
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.