 Use of the term semimetal, rather than metalloid, has recently been discouraged. This is because the former term 'has a well defined and quite distinct meaning in physics'. In physics, a semimetal is an element or a compound in which the valence band marginally (rather than substantially) overlaps the conduction band. This results in only a small number of effective charge carriers. Thus, the densities of charge carriers in the elemental semimetals carbon (as graphite, in the direction of its planes), arsenic, antimony and bismuth are 3 × 1018 cm − 3, 2 × 1020 cm − 3, 5 × 1019 cm − 3 and 3 × 1017 cm − 3 respectively. In contrast, the room-temperature concentration of electrons in metals usually exceeds 1022 cm − 3.
