Concept:Trivalent dopant atoms (such as boron) share covalent bonds with neighboring silicon atoms by accepting an electron, becoming negatively charged immobile ions (\( N_A^- \)).
Formula:$$B + e^- \to B^- \quad (\text{Fixed negative acceptor ion})$$
Solution:- In the neutral P-region, negative acceptor ions are balanced by mobile holes.
- As holes diffuse across the junction into the N-region, they leave behind uncompensated negative acceptor ions.
- These fixed acceptor ions form a negative space-charge layer on the P-side of the depletion region.
Why other options are incorrect:- Option A: Diffusing electrons recombine with holes to fill covalent bonds rather than accumulating as a free electron gas.
- Option B: Atomic nuclei do not exchange protons; charge transfer involves valence electrons.
- Option D: Dopant ions are fixed in the crystal lattice and do not migrate across the junction.
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