Gallium phosphide

Gallium phosphide (GaP), a phosphide of gallium, is a compound semiconductor material with an indirect band gap of 2.24 eV at room temperature. Impure polycrystalline material has the appearance of pale orange or grayish pieces. Undoped single crystals are orange, but strongly doped wafers appear darker due to free-carrier absorption. It is odorless and insoluble in water.

Gallium phosphide

GaP ingots (impure)

GaP wafer (electronic device quality)
Names
IUPAC name
Gallium phosphide
Other names
Gallium(III) phosphide
gallanylidynephosphane
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.031.858
RTECS number
  • LW9675000
UNII
Properties
GaP
Molar mass 100.697 g/mol[1]
Appearance pale orange solid
Odor odorless
Density 4.138 g/cm3[1]
Melting point 1,457 °C (2,655 °F; 1,730 K)[1]
insoluble
Band gap 2.24 eV (indirect, 300 K)[2]
Electron mobility 300 cm2/(V·s) (300 K)[2]
-13.8×10−6 cgs[2]
Thermal conductivity 0.752 W/(cm·K) (300 K)[1]
2.964 (10 µm), 3.209 (775 nm), 3.590 (500 nm), 5.05 (354 nm)[3]
Structure
Zinc blende
T2d-F-43m
a = 544.95 pm[4]
Tetrahedral
Thermochemistry
Std enthalpy of
formation (ΔfH⦵298)
 −88.0 kJ/mol[5]
Hazards
NFPA 704 (fire diamond)
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
3
0
Flash point 110 °C (230 °F; 383 K)
Related compounds
Other anions
 Gallium nitride
Gallium arsenide
Gallium antimonide
Other cations
 Aluminium phosphide
Indium phosphide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

GaP has a microhardness of 9450 N/mm2, a Debye temperature of 446 K (173 °C), and a thermal expansion coefficient of 5.3 ×10−6 K−1 at room temperature.[4] Sulfur, silicon or tellurium are used as dopants to produce n-type semiconductors. Zinc is used as a dopant for the p-type semiconductor.

Gallium phosphide has applications in optical systems.[6][7][8] Its static dielectric constant is 11.1 at room temperature.[2] Its refractive index varies between ~3.2 and 5.0 across the visible range, which is higher than in most other semiconducting materials.[3]

Light-emitting diodes

Gallium phosphide has been used in the manufacture of low-cost red, orange, and green light-emitting diodes (LEDs) with low to medium brightness since the 1960s. It has a relatively short life at higher current and its lifetime is sensitive to temperature. It is used standalone or together with gallium arsenide phosphide.

Pure GaP LEDs emit green light at a wavelength of 555 nm. Nitrogen-doped GaP emits yellow-green (565 nm) light, zinc oxide doped GaP emits red (700 nm).

Gallium phosphide is transparent for yellow and red light, therefore GaAsP-on-GaP LEDs are more efficient than GaAsP-on-GaAs.

At temperatures above ~900 °C, gallium phosphide dissociates and the phosphorus escapes as a gas. In crystal growth from a 1500 °C melt (for LED wafers), this must be prevented by holding the phosphorus in with a blanket of molten boric oxide in inert gas pressure of 10–100 atmospheres. The process is called liquid encapsulated Czochralski (LEC) growth, an elaboration of the Czochralski process used for silicon wafers.

References
  1. Haynes, p. 4.63
  2. Haynes, p. 12.85
  3. Haynes, p. 12.156
  4. Haynes, p. 12.80
  5. Haynes, p. 5.20
  6. Wilson, Dalziel J.; Schneider, Katharina; Hönl, Simon; Anderson, Miles; Baumgartner, Yannick; Czornomaz, Lukas; Kippenberg, Tobias J.; Seidler, Paul (January 2020). "Integrated gallium phosphide nonlinear photonics". Nature Photonics. 14 (1): 57–62. doi:10.1038/s41566-019-0537-9. ISSN 1749-4893.
  7. Cambiasso, Javier; Grinblat, Gustavo; Li, Yi; Rakovich, Aliaksandra; Cortés, Emiliano; Maier, Stefan A. (2017-02-08). "Bridging the Gap between Dielectric Nanophotonics and the Visible Regime with Effectively Lossless Gallium Phosphide Antennas". Nano Letters. 17 (2): 1219–1225. doi:10.1021/acs.nanolett.6b05026. ISSN 1530-6984.
  8. Rivoire, Kelley; Lin, Ziliang; Hatami, Fariba; Masselink, W. Ted; Vučković, Jelena (2009-12-07). "Second harmonic generation in gallium phosphide photonic crystal nanocavities with ultralow continuous wave pump power". Optics Express. 17 (25): 22609–22615. doi:10.1364/OE.17.022609. ISSN 1094-4087.

Cited sources
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