Concept:Doping tetravalent silicon with pentavalent atoms introduces extra valence electrons that are easily excited into the conduction band, creating an N-type semiconductor.
Formula:$$n_n \approx N_D \gg p_n$$
Solution:- Pentavalent atoms (e.g., \( \text{P, As, Sb} \)) possess five valence electrons.
- Four of these electrons form covalent bonds with adjacent silicon atoms, leaving the fifth electron loosely bound.
- Thermal energy at room temperature frees these fifth electrons into the conduction band, making electrons the majority carriers in N-type material.
Why other options are incorrect:- Option B: P-type semiconductors are formed by doping with trivalent impurities (e.g., \( \text{B, Ga, In} \)), which create holes as majority carriers.
- Option C: Positive donor ions are fixed in the lattice and do not act as mobile charge carriers.
- Option D: P-type material has holes as majority carriers; electrons are minority carriers.
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