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. The energy gaps are: C (diamond) = 5.4 eV, Si = 1.1 eV, Ge = 0.7 eV. Ge has the smallest energy gap. Substituting values gives Ge, which matches expected behaviour for this semiconductor device configuration, confirming doping, depletion and rectifier principles.