Editing Charge carrier (section)

===Carrier generation and recombination===
{{main|Carrier generation and recombination}}
When an electron meets with a hole, they [[carrier generation and recombination|recombine]] and these free carriers effectively vanish.<ref>{{cite web
 |url=https://ecee.colorado.edu/~bart/book/book/chapter2/ch2_8.htm
 |title=Carrier recombination and generation
 |date=2011
 |access-date=May 1, 2021
 |first=B.
 |last=Van Zeghbroeck
 |archive-date=May 1, 2021
 |archive-url=https://web.archive.org/web/20210501181954/https://ecee.colorado.edu/~bart/book/book/chapter2/ch2_8.htm
 |url-status=dead
 }}</ref> The energy released can be either thermal, heating up the semiconductor (''thermal recombination'', one of the sources of [[waste heat]] in semiconductors), or released as [[photon]]s (''optical recombination'', used in [[light-emitting diode|LEDs]] and [[laser diode|semiconductor laser]]s).<ref>{{cite web
 |url=https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-720j-integrated-microelectronic-devices-spring-2007/lecture-notes/lecture4.pdf
 |title=Lecture 4 - Carrier generation and recombination
 |date=February 12, 2007
 |access-date=May 2, 2021
 |first=Jesús
 |last=del Alamo
 |page=3
 |publisher=MIT Open CourseWare, Massachusetts Institute of Technology}}</ref> The recombination means an electron which has been excited from the valence band to the conduction band falls back to the empty state in the valence band, known as the holes. The holes are the empty states created in the valence band when an electron gets excited after getting some energy to pass the energy gap.