LEDs for Visible Spectrum of Light.

The operating principle, fabrication and application of LEDs are outlined. Light emission is induced by the radiative recombination of minority charge carriers injected via a PN junction. Most LEDs are made of gallium phosphide and mixed crystals composed of gallium arsenide phosphide doped to emit red, yellow or green light according to need. For the quantity production of LEDs intended as discrete indicators and for incorporation in seven-segment digital displays and alphanumeric matrix displays it has been necessary to develop new crystal growth and epitaxial technologies.