Practice question

**Semiconductor properties** distinguish from conductors and insulators by temperature dependence and doping response. At 0 K intrinsic acts as insulator, conductivity due to thermally generated electron-hole pairs, number of outer electrons 4 for Si/Ge forming covalent bonds, each atom shares electrons, crystal with N atoms has 4N valence electrons, 2N bonds. The threshold voltage for a germanium diode, where forward current increases significantly, is approximately 0.2 V, lower than silicon due to its smaller energy gap. Substituting values gives 0.2 V, which matches expected behaviour for this semiconductor device configuration, confirming doping, depletion and rectifier principles.