Why is carbon an insulator while silicon and germanium are semiconductors?
**Types of semiconductors** elemental Si, Ge group IV with 4 valence electrons, compound GaAs, InP etc. Intrinsic has n_e = n_h, extrinsic doped with pentavalent donors (P, As) gives n-type excess electrons, trivalent acceptors (B, Al) gives p-type excess holes, resistivity range semiconductors 10⁻⁵ to 10⁶ Ω·m vs insulators 10¹¹ Ω·m. Carbon (diamond) has a large energy gap (5.4 eV), preventing electron excitation at room temperature, while Si (1.1 eV) and Ge (0.7 eV) have smaller gaps, allowing thermal excitation and conduction. Substituting values gives Carbon has a larger energy gap, which m
Ref: NCERT > Physics Book > Electronic Devices > Semiconductors, Types and Energy Bands