an electron in metals and semiconductors whose energy lies in a partially filled energy band (the conduction band; seeSOLID). At a temperature of absolute zero there are no electrons in the conduction band of dielectrics and semiconductors. Electrons appear with increased temperature, upon illumination and the introduction of impurities, and under the influence of other external influences.
Conduction electrons always exist in metals, where their concentration is high. When T = 0°K, conduction electrons in metals occupy all the states having energies less than the Fermi energy. It is convenient to describe their characteristics in terms of the kinetic theory of gases by utilizing the concepts of mean free path and frequency of collisions, among others. In semiconductors, where the number of conduction electrons is relatively small, the gas is well described by the classical Boltzmann statistics. In metals, the conduction electrons form a degenerate Fermi liquid.