Editing Charge carrier (section)

==In conductors==
In conducting mediums, particles serve to carry charge. In many [[metal]]s, the charge carriers are [[electron]]s. One or two of the [[valence electron]]s from each atom are able to move about freely within the [[crystal structure]] of the metal.<ref>{{cite web
 |url=http://hyperphysics.phy-astr.gsu.edu/hbase/electric/conins.html#c1
 |title=Conductors and Insulators
 |access-date=April 30, 2021
 |first=R.
 |last=Nave}}</ref> The free electrons are referred to as [[conduction band|conduction electron]]s, and the cloud of free electrons is called a [[Fermi gas]].<ref>{{cite web
 |url=https://farside.ph.utexas.edu/teaching/sm1/lectures/node86.html
 |title=Conduction electrons in a metal
 |date=February 2, 2002
 |access-date=April 30, 2021
 |first=Richard
 |last=Fitzpatrick}}</ref><ref name="halbleiter-fundamentals" /> Many metals have electron and hole bands.  In some, the majority carriers are holes.{{citation needed|date=April 2021}}

In [[electrolytes]], such as [[Saline water|salt water]], the charge carriers are [[ion]]s,<ref name="halbleiter-fundamentals" /> which are atoms or molecules that have gained or lost electrons so they are electrically charged. Atoms that have gained electrons so they are negatively charged are called [[anion]]s, atoms that have lost electrons so they are positively charged are called [[cation]]s.<ref>{{cite web
 |url=https://www.technologynetworks.com/analysis/articles/cation-vs-anion-definition-chart-and-the-periodic-table-322863
 |title=Cation vs Anion: Definition, Chart and the Periodic Table
 |date=August 15, 2019
 |access-date=April 30, 2021
 |first=Karen
 |last=Steward}}</ref> Cations and anions of the dissociated liquid also serve as charge carriers in melted [[ionic compound|ionic solid]]s (see e.g. the [[Hall–Héroult process]] for an example of electrolysis of a melted ionic solid). [[Proton conductor]]s are electrolytic conductors employing positive hydrogen ions as carriers.<ref>{{cite web
 |author=Ramesh Suvvada
 |date=1996
 |title=Lecture 12: Proton Conduction, Stoichiometry
 |url=http://www.life.illinois.edu/crofts/bioph354/lect12.html
 |publisher=[[University of Illinois at Urbana–Champaign]]
 |access-date=April 30, 2021
 |archive-date=May 15, 2021
 |archive-url=https://web.archive.org/web/20210515080504/https://www.life.illinois.edu/crofts/bioph354/lect12.html
 |url-status=dead
 }}</ref>

In a [[Plasma (physics)|plasma]], an electrically charged gas which is found in [[electric arc]]s through air, [[neon sign]]s, and the sun and stars, the electrons and cations of ionized gas act as charge carriers.<ref>{{cite web
 |url=https://www.physics.muni.cz/~dorian/Soucek_Difuze.pdf
 |title=Plasma conductivity and diffusion
 |date=October 24, 2011
 |access-date=April 30, 2021
 |first=Pavel
 |last=Souček}}</ref>

In a [[vacuum]], free electrons can act as charge carriers. In the electronic component known as the [[vacuum tube]] (also called ''valve''), the mobile electron cloud is generated by a heated metal [[cathode]], by a process called [[thermionic emission]].<ref>{{cite web
 |url=https://www.engineering.com/story/vacuum-tubes-the-world-before-transistors
 |title=Vacuum Tubes: The World Before Transistors
 |date=January 19, 2018
 |access-date=April 30, 2020
 |first=Michael|last=Alba}}</ref> When an electric field is applied strongly enough to draw the electrons into a beam, this may be referred to as a [[cathode ray]], and is the basis of the [[cathode-ray tube]] display widely used in televisions and computer monitors until the 2000s.<ref>{{cite web
 |url=https://courses.lumenlearning.com/introchem/chapter/cathode-rays/
 |title=Cathode Rays {{!}} Introduction to Chemistry
 |access-date=April 30, 2021}}</ref>

In [[semiconductor]]s, which are the materials used to make electronic components like [[transistor]]s and [[integrated circuit]]s, two types of charge carrier are possible. In p-type semiconductors, "[[Quasiparticle|effective particles]]" known as [[Electron hole|electron holes]] with positive charge move through the crystal lattice, producing an electric current. The "holes" are, in effect, electron vacancies in the [[valence band|valence-band electron]] population of the semiconductor and are treated as charge carriers because they are mobile, moving from atom site to atom site. In n-type semiconductors, electrons in the conduction band move through the crystal, resulting in an electric current.

In some conductors, such as ionic solutions and plasmas, positive and negative charge carriers coexist, so in these cases an electric current consists of the two types of carrier moving in opposite directions. In other conductors, such as metals, there are only charge carriers of one polarity, so an electric current in them simply consists of charge carriers moving in one direction.