Charge carrier

Charge carrier

In physics, a charge carrier is a free (mobile, unbound) particle carrying an electric charge, especially the particles that carry electric currents in electrical conductors. Examples are electrons and ions. In a conducting medium, an electric field can exert force on these free particles, causing a net motion of the particles through the medium; this is what constitutes an electric current. In different conducting media, different particles serve to carry charge:

In metals, the charge carriers are electrons. One or two of the outer valence electrons from each atom is able to move about freely within the crystal lattice of the metal. The free electrons are referred to as conduction electrons, and the cloud of free electrons is called a Fermi gas.

In ionic solutions, such as salt water, the charge carriers are the dissolved cations and anions. Similarly, cations and anions of the dissociated liquid serve as charge carriers in liquids and melted ionic solids (see eg. the Hall-Heroult process for an example of electrolysis of a melt).

In plasma, such as an electric arc, the electrons and cations of ionized gas and vaporized material of electrodes act as charge carriers. (The electrode vaporization occurs in vacuum too, but then the arc is not technically occurring in vacuum, but in low-pressure electrode vapors.)

In vacuum, in an electric arc or in vacuum tubes free electrons act as charge carriers.

In semiconductor physics, two types of charge carriers are recognized. One of them is electrons. In addition, it is convenient to treat the traveling vacancies in the valence-band electron population (holes) as the second type of charge carriers which carry the positive charge.

Free Carrier Concentration

Free carrier concentration is the concentration of free carriers in a doped semiconductor. It is similar to the carrier concentration in a metal and for the purposes of calculating currents or drift velocities can be used in the same way. Free carriers are electrons (or holes) which have been introduced directly into the conduction (valence) band by doping and are not promoted thermally. For this reason electrons (holes) will not act as double carriers by leaving behind holes (electrons) in the other band.

See also

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