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. Sn (tin) has an energy gap of 0 eV, typical of metals with overlapping bands, unlike Si (1.1 eV) and Ge (0.7 eV), which are semiconductors. Substituting values gives Sn, which matches expected behaviour for this semiconductor device configuration, confirming doping, depletion and rectifier principles.