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Gallium phosphide (GaP), a phosphide of gallium, is a compound semiconductor material with an indirect band gap of 2.24 eV at room temperature. The 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.jpg
GaP ingots
IUPAC name
3D model (JSmol)
ECHA InfoCard 100.031.858
RTECS number LW9675000
Molar mass 100.70 g/mol[1]
Appearance pale orange solid
Odor odorless
Density 4.13 g/cm3[1]
Melting point 1,480 °C; 2,690 °F; 1,750 K[1]
Band gap 2.24 eV (indirect, 300 K)[2]
Electron mobility 300 cm2/(V·s) (300 K)[2]
-13.8×106 cgs[2]
Thermal conductivity 0.752 W/(cm·K) (300 K)[1]
3.02 (2.48 µm), 3.19 (840 nm), 3.45 (550 nm), 4.30 (262 nm)
Zinc blende
a = 549.05 pm[1]
NFPA 704
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 codeNFPA 704 four-colored diamond
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

Sulfur 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. Its refractive index is between 4.30 at 262 nm (UV), 3.45 at 550 nm (green) and 3.19 at 840 nm (IR)[3], which is higher than in most known materials, including diamond (2.4).


Light-emitting diodesEdit

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.


  1. ^ a b c d e Haynes, p. 12.81
  2. ^ a b c Haynes, p. 12.86
  3. ^ GaP.

Cited sourcesEdit

  • Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. ISBN 1439855110.

External linksEdit