Editing Semiconductor (section)

=== Doping ===
{{Main article|Doping (semiconductor)}}
[[Image:Silicon doping - Type P and N.svg|thumb|400px|Doping of a pure [[silicon]] array. Silicon based intrinsic semiconductor becomes extrinsic when impurities such as [[Boron]] and [[Antimony]] are introduced.]]
The conductivity of semiconductors may easily be modified by introducing impurities into their [[crystal lattice]]. The process of adding controlled impurities to a semiconductor is known as '''doping'''. The amount of impurity, or dopant, added to an ''[[intrinsic semiconductor|intrinsic]]'' (pure) semiconductor varies its level of conductivity.<ref>{{cite web |url=http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/dope.html |title=Doped Semiconductors |access-date=May 3, 2021 |first=R. |last=Nave}}</ref> Doped semiconductors are referred to as [[extrinsic semiconductor|''extrinsic'']].<ref>{{cite web |url=https://electronicsdesk.com/difference-between-intrinsic-and-extrinsic-semiconductor.html |title=Difference Between Intrinsic and Extrinsic Semiconductors |first=Roshni |last=Y. |date=5 February 2019 |access-date=May 3, 2021}}</ref> By adding impurity to the pure semiconductors, the electrical conductivity may be varied by factors of thousands or millions.<ref>{{cite web |title=Lesson 6: Extrinsic semiconductors |url=https://archive.nptel.ac.in/content/storage2/courses/113106065/Week%203/Lesson6.pdf |archive-url=https://web.archive.org/web/20230128211456/https://archive.nptel.ac.in/content/storage2/courses/113106065/Week%203/Lesson6.pdf |archive-date=January 28, 2023 |access-date=January 28, 2023}}</ref>

A 1&nbsp;cm<sup>3</sup> specimen of a metal or semiconductor has the order of 10<sup>22</sup> atoms.<ref>{{cite web |url=https://www.chemteam.info/Liquids&Solids/WS-unit-cell-AP.html |title=General unit cell problems |access-date=May 3, 2021}}</ref> In a metal, every atom donates at least one free electron for conduction, thus 1&nbsp;cm<sup>3</sup> of metal contains on the order of 10<sup>22</sup> free electrons,<ref>{{cite web |url=http://hydrogen.physik.uni-wuppertal.de/hyperphysics/hyperphysics/hbase/electric/ohmmic.html |title=Ohm's Law, Microscopic View |access-date=May 3, 2021 |first=R. |last=Nave |archive-date=May 3, 2021 |archive-url=https://web.archive.org/web/20210503095813/http://hydrogen.physik.uni-wuppertal.de/hyperphysics/hyperphysics/hbase/electric/ohmmic.html |url-status=dead }}</ref> whereas a 1&nbsp;cm<sup>3</sup> sample of pure germanium at 20{{nbsp}}°C contains about {{val|4.2|e=22}} atoms, but only {{val|2.5|e=13}} free electrons and {{val|2.5|e=13}} holes. The addition of 0.001% of [[arsenic]] (an impurity) donates an extra 10<sup>17</sup> free electrons in the same volume and the electrical conductivity is increased by a factor of 10,000.<ref>{{cite web |url=https://ecee.colorado.edu/~bart/ecen3320/newbook/chapter2/ch2_6.htm |title=Carrier densities |date=2000 |access-date=May 3, 2021 |first=Bart |last=Van Zeghbroeck |archive-date=May 3, 2021 |archive-url=https://web.archive.org/web/20210503141622/https://ecee.colorado.edu/~bart/ecen3320/newbook/chapter2/ch2_6.htm |url-status=dead }}</ref><ref>{{cite web |url=http://www.ioffe.ru/SVA/NSM/Semicond/Ge/bandstr.html |title=Band strcutre and carrier concentration (Ge) |access-date=May 3, 2021}}</ref>

The materials chosen as suitable dopants depend on the atomic properties of both the dopant and the material to be doped. In general, dopants that produce the desired controlled changes are classified as either electron [[acceptor (semiconductors)|acceptors]] or [[donor (semiconductors)|donors]]. Semiconductors doped with ''donor'' impurities are called ''n-type'', while those doped with ''acceptor'' impurities are known as ''p-type''. The n and p type designations indicate which charge carrier acts as the material's [[majority carrier]]. The opposite carrier is called the [[minority carrier]], which exists due to thermal excitation at a much lower concentration compared to the majority carrier.<ref>{{cite web |url=https://www.halbleiter.org/en/fundamentals/doping/ |title=Doping: n- and p-semiconductors |access-date=May 3, 2021}}</ref>

For example, the pure semiconductor [[silicon]] has four valence electrons that bond each silicon atom to its neighbors.<ref>{{cite web |url=http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/sili.html |title=Silicon and Germanium |access-date=May 3, 2021 |first=R. |last=Nave}}</ref> In silicon, the most common dopants are [[Boron group|group III]] and [[group V]] elements. Group III elements all contain three valence electrons, causing them to function as acceptors when used to dope silicon. When an acceptor atom replaces a silicon atom in the crystal, a vacant state (an electron "hole") is created, which can move around the lattice and function as a charge carrier. Group V elements have five valence electrons, which allows them to act as a donor; substitution of these atoms for silicon creates an extra free electron. Therefore, a silicon crystal doped with [[boron]] creates a p-type semiconductor whereas one doped with [[phosphorus]] results in an n-type material.<ref>{{cite web |url=https://www.pveducation.org/pvcdrom/pn-junctions/semiconductor-materials |title=Semiconductor Materials |first1=Christiana |last1=Honsberg |first2=Stuart |last2=Bowden |access-date=May 3, 2021}}</ref>

During [[semiconductor device fabrication|manufacture]], dopants can be diffused into the semiconductor body by contact with gaseous compounds of the desired element, or [[ion implantation]] can be used to accurately position the doped regions.