Light Emitting Diode (LED)
Principle:
It’s a
device used to convert the electrical energy into light energy.
When it
is forward biased, the majority charge carriers of electrons from n-type and
holes from p-type are diffuse into each other.
At the
junction the electron hole recombination process takes place and energy is
emitting in the form of visible light and IR region.
Construction:
The light
emitting diode is made by Gallium Arsenide semiconductors. First the PN
Junction is formed by epitaxial growth technique. Si+Ga=n-type; Si+As=p-type.
The
thickness of the n-layer is always larger than the p-layer, because of
increasing the radiative recombination.
Proper
electric connection (forward bias) given to the semiconductor through
aluminiumcontact. P-jn is slightly open for outcoming light rays.
Working:
When the
p-n junction diode is forward biased, the barrier width is reduced, raising the
potential energy on the n-side and lowering that on the p-side.
The free
electrons and holes have sufficient energy to move into the junction region. If
a free electron meets a hole, it recombines and releases a photon.
Thus,
light radiation from the LED is caused by the recombination of holes and
electrons that are injected into the junction by a forward bias voltage.
Advantages of LED
1. Very
small in size
2. Less cost
and long life time.
3. It needs
less voltage for operate
Disadvantages of LED
1. It
requires high power.
2. Its
preparation cost is high.
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