The Light Emitting Diodes (LED) The basic operation of the led is as follows: When the device is forwarded biased, electron crosses the PN junction from the N-type material and recombine with holes in the P-type material. Recall that those free electrons band and at a higher energy level then holes in the valance band. When recombination takes place, the recombining electrons release energy in the form of heat and light. A large exposed surface area on one layer of the semiconductor material permits the photons to be emitted as visible light. (a) illustrates this process, which is called electroluminescence. The semiconductor materials used in LEDs are gallium arsenide (GaAs), gallium arsenide phosphide (GaAs), and gallium phosphide (GaP). Silicon and Germanium are not used because they are essentially heated producing material and are very poor at producing light. GaAs LEDs emit infrared (IR) radiation. GaAsP produces either red or yellow light, and...