Light Emitting Diode
The LESD is basically a device which
changes input electrical energy into output optical radiation in the visible or
infrared position of spectrum depending on the semiconductor material used. LEDs
have replaced incandesced lamp in many applications because of low voltage long
life and fast on off switching. He materials used in manufacturing the LEDs are
1. Gallium Arsenide Phosphide
(GaAsP): It provides either red light or yellow light.
2. Gallium Phosphide (GaP): It provides red or green
light.
3. Gallium Arsenide (GaAs): It provides infrared
radiation
Principle: When a P-N junction forward
biased, charge carrier recombination take place at a junction as electron cross
from the n- side and combine with holes on the p- side. Free electrons are in
the conduction band of energy level while holes are in the valence band.