Charge carrier
Encyclopedia
In physics
, a charge carrier is a free (mobile, unbound) particle carrying an electric charge
, especially the particles that carry electric current
s in electrical conductor
s. Examples are electron
s and ion
s. 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 metal
s, the charge carriers are electron
s. One or two of the outer valence electron
s 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 tube
s free electrons act as charge carriers.
In semiconductor physics, two types of charge carriers
are recognized. One of them is electron
s. 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.
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.
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, a charge carrier is a free (mobile, unbound) particle carrying an electric charge
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
, especially the particles that carry electric current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
s in electrical conductor
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
s. Examples are electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s and ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s. In a conducting medium, an electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
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 metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
s, the charge carriers are electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s. One or two of the outer valence electron
Valence electron
In chemistry, valence electrons are the electrons of an atom that can participate in the formation of chemical bonds with other atoms. Valence electrons are the "own" electrons, present in the free neutral atom, that combine with valence electrons of other atoms to form chemical bonds. In a single...
s 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
Fermi gas
A Fermi gas is an ensemble of a large number of fermions. Fermions, named after Enrico Fermi, are particles that obey Fermi–Dirac statistics. These statistics determine the energy distribution of fermions in a Fermi gas in thermal equilibrium, and is characterized by their number density,...
.
In ionic solutions, such as salt water
Saline water
Saline water is a general term for water that contains a significant concentration of dissolved salts . The concentration is usually expressed in parts per million of salt....
, 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
Hall-Héroult process
The Hall–Héroult process is the major industrial process for the production of aluminium. It involves dissolving alumina in molten cryolite, and electrolysing the molten salt bath to obtain pure aluminium metal.-Process:...
for an example of electrolysis of a melt).
In plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...
, such as an electric arc
Electric arc
An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. A synonym is arc discharge. An arc discharge is characterized by a lower voltage than a glow discharge, and relies on...
, 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
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
, in an electric arc
Vacuum arc
A vacuum arc can arise when the surfaces of metal electrodes in contact with a good vacuum begin to emit electrons either through heating or via an electric field that is sufficient to cause field electron emission...
or in vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
s free electrons act as charge carriers.
In semiconductor physics, two types of charge carriers
Charge carriers in semiconductors
There are two recognized types of charge carriers in semiconductors. One of them is electrons, which carry negative electric charge. In addition, it is convenient to treat the traveling vacancies in the valence-band electron population as the second type of charge carriers, which carry a positive...
are recognized. One of them is electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s. In addition, it is convenient to treat the traveling vacancies in the valence-band electron population (holes
Electron hole
An electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics, chemistry, and electrical engineering. The concept describes the lack of an electron at a position where one could exist in an atom or atomic lattice...
) as the second type of charge carriers which carry the positive charge.
Free Carrier Concentration
Free carrier concentration is the concentrationConcentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume 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
Electron hole
An electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics, chemistry, and electrical engineering. The concept describes the lack of an electron at a position where one could exist in an atom or atomic lattice...
) which have been introduced directly into the conduction (valence
Valence band
In solids, the valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature....
) 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.