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Light Emitting Diode (LED) : Optical Fiber

A Light Emitting Diode (LED) is a type of PN junction diode made from specially doped semiconductors that emit light when forward biased. The operation involves the movement of electrons and holes across a PN junction, resulting in electroluminescence, where energy is released as visible light. LEDs are energy efficient, have a long lifespan, and are used in various applications including lighting, displays, and optical fiber communication.

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43 views4 pages

Light Emitting Diode (LED) : Optical Fiber

A Light Emitting Diode (LED) is a type of PN junction diode made from specially doped semiconductors that emit light when forward biased. The operation involves the movement of electrons and holes across a PN junction, resulting in electroluminescence, where energy is released as visible light. LEDs are energy efficient, have a long lifespan, and are used in various applications including lighting, displays, and optical fiber communication.

Uploaded by

reema2006793
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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College of Electronic Technology

Optical fiber

Light Emitting
Diode
(LED)
Reema Abdallah Abdalgani ALkeesh
What is a Light Emitting Diode
(LED)?

A Light Emitting Diode (LED) is a special type of PN junction diode. The light emitting diode is
specially doped and made of a special type of semiconductor. This diode can emit light when it
is in the forward biased state. Aluminum indium gallium phosphide (AlInGaP) and indium
gallium nitride (InGaN) are two of the most commonly used semiconductors for LED
technologies
_________________________________________________________________________________________

How Does an LED Work?


An LED is made up of semiconductors, materials that can either conduct or
insulate electricity depending on the conditions. The semiconductor material is
typically doped to create two regions:

 A negatively charged N-type region that has excess electrons.


 A positively charged P-type region where electrons are missing and left with

“holes”.
The two types are connected to form a PN junction. The electrons from the N-side
move to the P-side, and holes from the P-side move to the N-side. During this
process, a new region is formed at the interface, called the depletion layer. A PN
junction, when enclosed in a protective casing and has external leads for electrical
connections, forms a PN junction diode.

When an external battery is connected across the diode such that the
positive terminal is connected to the P-side and the negative terminal
to the N-side, electric current flows through the circuit. The electrons
from the N-side and holes from the P-side move, recombine and
release energy in the form of photons, which produce visible light. This
process is known as electroluminescence.
The energy band gap of the semiconductor material governs the energy
required to move electrons and holes across the device. It is defined as
the difference in energy between the valence band (where holes are
normally present) and the conduction band (where electrons can move
freely).

When the electrons recombine with holes, the energy difference is


released as light, and the color (wavelength) of that light depends on the
size of the band gap. The larger the band gap, the higher the energy of
the emitted photons, which corresponds to a shorter wavelength of light
(towards the blue end of the spectrum). A smaller band gap results in
lower energy photons, leading to longer wavelengths (towards the red
end of the spectrum).

Advantages of LEDs:
 Extremely energy efficient.
 Very long lifespan (can exceed 50,000 hours).
 Small in size and easy to integrate into circuits.
 Low heat emission.
 Environmentally friendly, as they do not contain toxic substances
like mercury.

Applications of LEDs :
 Residential and industrial lighting systems.
 Displays (TVs, smartphones, monitors).
 Indicator lights in electronics.
 Traffic lights and automotive lights.
 Optical fiber communication, where LEDs serve as light sources
for data transmission.

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