Semimetal

A metal, by contrast, has an appreciable density of states at the Fermi level because the conduction band is partially filled.

To classify semiconductors and semimetals, the energies of their filled and empty bands must be plotted against the crystal momentum of conduction electrons.

According to the Bloch theorem the conduction of electrons depends on the periodicity of the crystal lattice in different directions.

Classification of a material either as a semiconductor or a semimetal can become tricky when it has extremely small or slightly negative band-gaps.

Commonly used experimental techniques to investigate band-gap can be sensitive to many things such as the size of the band-gap, electronic structure features (direct versus indirect gap) and also the number of free charge carriers (which can frequently depend on synthesis conditions).

As semimetals have fewer charge carriers than metals, they typically have lower electrical and thermal conductivities.

The classic semimetallic elements are arsenic, antimony, bismuth, α-tin (gray tin) and graphite, an allotrope of carbon.

Filling of the electronic states in various types of materials at equilibrium . Here, height is energy while width is the density of available states for a certain energy in the material listed. The shade follows the Fermi–Dirac distribution ( black : all states filled, white : no state filled). In metals and semimetals the Fermi level E F lies inside at least one band.
In insulators and semiconductors the Fermi level is inside a band gap ; however, in semiconductors the bands are near enough to the Fermi level to be thermally populated with electrons or holes . "intrin." indicates intrinsic semiconductors .
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This diagram illustrates a direct semiconductor (A), an indirect semiconductor (B), and a semimetal (C).