Carbon (diamond) and silicon have the same four-covalent-bond lattice structure. Why is diamond an insulator while Si is an intrinsic semiconductor?
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Question

Carbon (diamond) and silicon have the same four-covalent-bond lattice structure. Why is diamond an insulator while Si is an intrinsic semiconductor?

G1 Physics · Accepted Answer

Carbon bonding electrons lie in a more tightly bound second shell (n = 2) while silicon valence electrons are in the third shell (n = 3). Diamond has a much larger band gap (~5.5 eV) than Si (~1.1 eV). At room temperature Si can thermally generate carriers whereas diamond remains insulating. Final answer: Option C.