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.
Therefore electronics are at place some of its energy is given up in the form of heat and will be emitted and junction becomes light source which called as “Light Emitting Diode”.
Therefore electronics are at place some of its energy is given up in the form of heat and will be emitted and junction becomes light source which called as “Light Emitting Diode”.
Construction and Working
The cross sectional view of a typical
LED is shown in fig (or) the semiconductor material employed is gallium
arsenate or Gallium Arsinatic phosphate or Gallium phosphate. A n type bar is
grown up on a substrate and p region is created by diffusion. Since the charge
carrier recombination occurs in the p-region it must be kept uppermost the
metal film anode connection must be patterned to allow most of the light to be
emitted. A gold film is applied to the bottom of substrate to reflect as much
as possible of the light towards the surface of the device and to provide
cathode connection.
Cross Section View of LED
The below fig shows the circuit symbol of LED. The outward
arrow indicates emission of light and the below fig shows the VI characteristic
of LED. From VI characteristics one can expect a typical the operating voltage
range of LED is from 1.7V to 3.0V.
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Circuit Diagram
V-I Charecteristics of LED
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