Concept:Trivalent impurity atoms (Group III, such as B, Al, Ga, In) have three valence electrons and create electron vacancies (holes) when substituting into a tetravalent semiconductor lattice, forming a P-type semiconductor.
Formula:$$\text{Group III Dopant (Ga)} + \text{Group IV Host (Ge)} \implies \text{P-type Semiconductor } (p \approx N_A \gg n)$$
Solution:- Gallium has 3 valence electrons and bonds with 4 neighboring Germanium atoms, leaving one covalent bond incomplete.
- This creates a vacancy (hole) in the valence band that can accept an electron, making holes the majority carriers in a P-type material.
Why other options are incorrect:- Option A: N-type semiconductors are formed using pentavalent (Group V) dopants.
- Option C: Doping creates an extrinsic semiconductor, not an intrinsic one.
- Option D: Doping increases semiconductor conductivity rather than forming an insulator.
Quality & Fidelity Assurance:
Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.