Official Correct Choice:
Option B: They recombine near the interface, exposing uncompensated, immobile positive and negative ions
Concept:When mobile electrons and holes cross the junction, they recombine and eliminate each other as free carriers, exposing the fixed donor and acceptor ions that form the depletion layer.
Formula:$$e^- + h^+ \longrightarrow \text{Recombination (annihilation of mobile carriers near interface)}$$
Solution:- Diffusing electrons from the N-side recombine with holes on the P-side.
- This recombination leaves behind fixed positive donor ions (\( N_D^+ \)) on the N-side and fixed negative acceptor ions (\( N_A^- \)) on the P-side.
- The resulting space-charge layer creates the built-in potential barrier \( V_0 \).
Why other options are incorrect:- Option A: Carriers recombine rather than scattering elastically back to their origin.
- Option C: Recombination releases low-energy phonons or optical photons (in direct bandgap materials), not gamma rays.
- Option D: Carrier diffusion establishes an internal electrostatic field, not a magnetic field.
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