Gallium(III) phosphide

Gallium phosphide (GaP), a phosphide of gallium, is a compound semiconductor material with an indirect band gap of 2.26 eV. It is a solid crystalline material with melting point of 1480°C. Its lattice constant is 0.545 nm. Its electron mobility is 110 cm²/V-s and its hole mobility is 75 cm²/V-s. Its CAS number is [12063-98-8]. Multi-crystalline material has the appearance of pale orange pieces. Undoped single crystal wafers appear clear orange, but strongly doped wafers appear darker due to free-carrier absorption. It is odorless and insoluble in water.

Sulfur or tellurium are used as dopants to turn gallium phosphide into an n-type semiconductor. Zinc is used as a dopant for the p-type semiconductor.

Gallium phosphide is also an optical material. Its refractive index is about 3.37 in the visible, but changes substantially with wavelength. At 800nm (IR) the index is lower, about 3.2.

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Light-emitting diodes

Gallium phosphide is used for manufacture of low and standard brightness red, orange, and green light-emitting diodes (LED). It is a low-cost material. GaP has been used as an LED material 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 at yellow-green (565 nm), 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 ~900C Gallium Phosphide dissociates and the phosphorus escapes as a gas. To grow a crystal from a 1500C melt (for LED wafers), this must be prevented by holding the phosphorus in with a blanket of molten Boric Oxide plus surrounding inert gas pressure of 10-100 atmospheres. The process is called Liquid Encapsulated Czochralski growth (typically abbreviated "LEC"), an elaboration of the Czochralski process used for Silicon wafers.

See also

Related materials

• Gallium arsenide
• Gallium nitride
• Indium phosphide

Alloys

• Aluminium gallium indium phosphide
• Indium gallium phosphide
• Gallium arsenide phosphide