Practice question

**Energy bands in semiconductors** consist of valence band filled at 0 K and conduction band empty, gap E_g small ~1 eV (Si 1.1 eV, Ge 0.7 eV), insulators large gap >3 eV (C diamond 5.4 eV), conductors overlapping. Intrinsic semiconductor at 0 K behaves as insulator because no thermal excitation, at T>0 K electrons jump to conduction band leaving holes, conductivity increases with temperature. Semiconductors have intermediate resistivity ( 10⁻⁵ to 10⁶ Ω m ), covalent bonding (e.g., Si, Ge), and conductivity that increases with temperature. High conductivity ( 10² to 10⁸ S m⁻¹ ) is typical of metals, not semiconductors. Substituting values gives High