Concept:Trivalent impurity atoms have three valence electrons. When substituted into a tetravalent semiconductor lattice, one covalent bond remains incomplete, creating a hole.
Formula:$$p_p \approx N_A \gg n_p$$
Solution:- A trivalent atom (e.g., boron) forms covalent bonds with three neighboring silicon atoms.
- The fourth bond lacks an electron, leaving an empty electronic state (a hole) in the valence band.
- This hole can accept an electron from a neighboring bond, allowing positive charge transport through the valence band.
Why other options are incorrect:- Option A: Extra free electrons are provided by pentavalent donor dopants, not trivalent acceptors.
- Option C: Trivalent doping creates an electron vacancy (hole), not an unbonded electron pair.
- Option D: Acceptor atoms become fixed negative ions after accepting an electron; they do not form mobile positive ions.
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