= Solution
\b[A $2.24\,\mathrm{eV}$ <band gap> is consistent with a <semiconductor>.] In pure <gallium phosphide>, the <valence band> is essentially full and the <conduction band> essentially empty at low <temperature>; thermal or optical excitation can produce mobile <electrons> and <electron holes>.
At room <temperature>, $k_BT\approx0.026\,\mathrm{eV}$ is much smaller than the <band gap>, so intrinsic excitation is strongly suppressed. Pure material consequently has a low intrinsic carrier density, while <semiconductor doping> can markedly increase its <electrical conductivity>.
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