Editing Gallium arsenide (section)

===Light-emission devices===
[[File:Bandstruktur GaAs en.svg|thumb|Band structure of GaAs. The direct gap of GaAs results in efficient emission of infrared light at 1.424 eV (~870 nm).]]

GaAs has been used to produce near-infrared laser diodes since 1962.<ref>{{cite journal |last=Hall |first=Robert N. |author-link=Robert N. Hall |author2=Fenner, G. E. |author3=Kingsley, J. D. |author4=Soltys, T. J. |author5=Carlson, R. O. |year=1962 |title=Coherent Light Emission From GaAs Junctions |journal=Physical Review Letters |volume=9 |issue=9 |pages=366–369 |bibcode=1962PhRvL...9..366H |doi=10.1103/PhysRevLett.9.366 |doi-access=free}}</ref> It is often used in alloys with other semiconductor compounds for these applications.

''N''-type GaAs doped with silicon donor atoms (on Ga sites) and boron acceptor atoms (on As sites) responds to ionizing radiation by emitting scintillation photons. At cryogenic temperatures it is among the brightest scintillators known<ref name="Derenzo, S. 2018">{{cite journal |last1=Derenzo |first1=S. |last2=Bourret |first2=E. |last3=Hanrahan |first3=S. |last4=Bizarri |first4=G. |date=2018-03-21 |title=Cryogenic scintillation properties of n -type GaAs for the direct detection of MeV/c2 dark matter |journal=Journal of Applied Physics |volume=123 |issue=11 |page=114501 |arxiv=1802.09171 |bibcode=2018JAP...123k4501D |doi=10.1063/1.5018343 |issn=0021-8979 |s2cid=56118568}}</ref><ref name="Vasiukov, S. 2019">{{cite journal |last1=Vasiukov |first1=S. |last2=Chiossi |first2=F. |last3=Braggio |first3=C. |last4=Carugno |first4=G. |last5=Moretti |first5=F. |last6=Bourret |first6=E. |last7=Derenzo |first7=S. |display-authors=3 |year=2019 |title=GaAs as a Bright Cryogenic Scintillator for the Detection of Low-Energy Electron Recoils From MeV/c<sup>2</sup> Dark Matter |journal=IEEE Transactions on Nuclear Science |publisher=Institute of Electrical and Electronics Engineers (IEEE) |volume=66 |issue=11 |pages=2333–2337 |bibcode=2019ITNS...66.2333V |doi=10.1109/tns.2019.2946725 |issn=0018-9499 |s2cid=208208697}}</ref><ref name="Derenzo, S. 2021">{{cite journal |last1=Derenzo |first1=S. |last2=Bourret |first2=E. |last3=Frank-Rotsch |first3=C. |last4=Hanrahan |first4=S. |last5=Garcia-Sciveres |first5=M. |date=2021 |title=How silicon and boron dopants govern the cryogenic scintillation properties of N-type GaAs |journal=Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment |volume=989 |page=164957 |arxiv=2012.07550 |bibcode=2021NIMPA.98964957D |doi=10.1016/j.nima.2020.164957 |s2cid=229158562}}</ref> and is a promising candidate for detecting rare electronic excitations from interacting dark matter,<ref>S.E. Derenzo (2024), "Monte Carlo calculations of cryogenic photodetector readout of scintillating GaAs for dark matter detection", arXiv: 2409.00504, Nuclear Instr. and Methods in Physics Research, A1068 169791</ref> due to the following six essential factors:
# Silicon donor electrons in GaAs have a binding energy that is among the lowest of all known ''n''-type semiconductors. Free electrons above {{val|8|e=15}} per cm<sup>3</sup> are not “frozen out" and remain delocalized at cryogenic temperatures.<ref>{{cite journal |last1=Benzaquen |first1=M. |last2=Walsh |first2=D. |last3=Mazuruk |first3=K. |date=1987-09-15 |title=Conductivity of n -type GaAs near the Mott transition |journal=Physical Review B |volume=36 |issue=9 |pages=4748–4753 |bibcode=1987PhRvB..36.4748B |doi=10.1103/PhysRevB.36.4748 |issn=0163-1829 |pmid=9943488}}</ref>
# Boron and gallium are group III elements, so boron as an impurity primarily occupies the gallium site. However, a sufficient number occupy the arsenic site and act as acceptors that efficiently trap ionization event holes from the valence band.<ref>{{cite journal |last1=Pätzold |first1=O. |last2=Gärtner |first2=G. |last3=Irmer |first3=G. |date=2002 |title=Boron Site Distribution in Doped GaAs |journal=Physica Status Solidi B |volume=232 |issue=2 |pages=314–322 |bibcode=2002PSSBR.232..314P |doi=10.1002/1521-3951(200208)232:2<314::AID-PSSB314>3.0.CO;2-# |issn=0370-1972}}</ref>
# After trapping an ionization event hole from the valence band, the boron acceptors can combine radiatively with delocalized donor electrons to produce photons 0.2 eV below the cryogenic band-gap energy (1.52 eV). This is an efficient radiative process that produces scintillation photons that are not absorbed by the GaAs crystal.<ref name="Vasiukov, S. 2019" /><ref name="Derenzo, S. 2021" />
# There is no afterglow, because metastable radiative centers are quickly annihilated by the delocalized electrons. This is evidenced by the lack of thermally induced luminescence.<ref name="Derenzo, S. 2018" />
# ''N''-type GaAs has a high refractive index (~3.5) and the narrow-beam absorption coefficient is proportional to the free electron density and typically several per cm.<ref>{{cite journal |last1=Spitzer |first1=W. G. |last2=Whelan |first2=J. M. |date=1959-04-01 |title=Infrared Absorption and Electron Effective Mass in n -Type Gallium Arsenide |journal=Physical Review |volume=114 |issue=1 |pages=59–63 |bibcode=1959PhRv..114...59S |doi=10.1103/PhysRev.114.59 |issn=0031-899X}}</ref><ref>{{cite journal |last=Sturge |first=M. D. |date=1962-08-01 |title=Optical Absorption of Gallium Arsenide between 0.6 and 2.75 eV |journal=Physical Review |volume=127 |issue=3 |pages=768–773 |bibcode=1962PhRv..127..768S |doi=10.1103/PhysRev.127.768 |issn=0031-899X}}</ref><ref>{{cite journal |last1=Osamura |first1=Kozo |last2=Murakami |first2=Yotaro |date=1972 |title=Free Carrier Absorption in n -GaAs |journal=Japanese Journal of Applied Physics |volume=11 |issue=3 |pages=365–371 |bibcode=1972JaJAP..11..365O |doi=10.1143/JJAP.11.365 |issn=0021-4922 |s2cid=120981460}}</ref> One would expect that  almost all of the scintillation photons should be trapped and absorbed in the crystal, but this is not the case. Recent Monte Carlo and Feynman path integral calculations have shown that the high luminosity could be explained if most of the narrow beam absorption is not absolute absorption but a '''''novel''''' type of optical scattering from the conduction electrons with a cross section of about 5 x 10<sup>−18</sup> cm<sup>2</sup> that allows scintillation photons to escape total internal reflection.<ref>{{cite journal |last1=Derenzo |first1=Stephen E. |year=2022 |title=Monte Carlo calculations of the extraction of scintillation light from cryogenic ''n''-type GaAs |journal=Nuclear Instruments and Methods in Physics Research Section A |volume=1034 |page=166803 |arxiv=2203.15056 |bibcode=2022NIMPA103466803D |doi=10.1016/j.nima.2022.166803 |s2cid=247779262}}</ref><ref>S. E. Derenzo (2023), “Feynman photon path integral calculations of optical reflection, diffraction, and scattering from conduction electrons,” Nuclear Instruments and Methods, vol. A1056, pp. 168679. arXiv2309.09827</ref> This cross section is about 10<sup>7</sup> times larger than Thomson scattering but comparable to the optical cross section of the conduction electrons in a metal mirror.<ref>M. K. Pogodaeva, S. V. Levchenko, V. P. Drachev, and I. R. Gabitov, 3032, “Dielectric function of six elemental metals,” J. Phys.: Conf. Ser., vol. 1890, pp. 012008.</ref>
# ''N''-type GaAs(Si,B) is commercially grown as 10&nbsp;kg crystal ingots and sliced into thin wafers as substrates for electronic circuits. Boron oxide is used as an encapsulant to prevent the loss of arsenic during crystal growth, but also has the benefit of providing boron acceptors for scintillation.