For an extrinsic semiconductor, mark the donor and acceptor levels on an energy-band diagram.

The energy gaps in $\mathrm{Ge}$, $\mathrm{Si}$ and diamond are $0.7, 1.1$ and $7 \mathrm{eV}$ respectively. Compare their conductivities at absolute zero and at room temperature.

Explain that the energy of a hole deep in the valence band is high.

Draw separate energy-level bands for conductors, semiconductors and insulators and label each of them to illustrate the behaviour of a conductor.