Concept:Trivalent atoms possess three valence electrons. When substituted into a group-IV semiconductor lattice (which requires four covalent bonds per atom), one bonding electron vacancy (hole) remains for every dopant atom, creating a p-type semiconductor.
Formula:$$\text{Group III Dopant} + \text{Group IV Host} \implies p_h \gg n_e \quad (\text{p-type})$$
Solution:- Trivalent dopants (e.g., \(\text{B}\), \(\text{Al}\), \(\text{Ga}\), \(\text{In}\)) act as acceptors.
- They create an excess of positive mobile charge carriers (holes).
- Hence, the resulting extrinsic material is a p-type semiconductor.
Why other options are incorrect:- Option A: N-type semiconductors are formed by doping with pentavalent impurities (e.g., \(\text{P}\), \(\text{As}\), \(\text{Sb}\)).
- Option B: An intrinsic semiconductor is pure, undoped crystal.
- Option D: Doping increases semiconductor conductivity; it does not produce an insulator.
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