Gallium Phosphide - Light-emitting Diodes

Light-emitting Diodes

Gallium phosphide is 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.