Types of Light Emitting Diode

8/8/2019 Types of Light Emitting Diode

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Amit Dhar

Dept:E&TC

8th Sem,Class Roll-15

ID No-110706015


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Introduction to LEDLED is a special type of diode which emits photon in the visible(wavelength 0.39 um-0.77 um) or infrared range (wavelength 0.77 um-1000 um) due to the radiative recombination between electrons andholes when it is biased properly.

Free electrons moving across a diode fall into empty holes from the P-type layer.This results in a release of energy in the form of photons.


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Classification of LED:LED

Depending upon wavelength Depending upon Device structure

VisibleLED

IRLED

SurfaceEmittingLED(SLED)

EdgeEmittingLED(ELED)

SuperLuminationLED(SLLED)

PlanarLED

DomeLED

=Used as Transmitter in Optical Communication

=Can not be used as Transmitter in Optical Communication


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Materials used to fabricate LEDs:Colour Wavelength

(nm)Bandgap(ev) Semeconductor Material

Infrared >760 Eg


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How to choose materials for LED:Suppose we have to choose materials used to fabricate LED which emits Red Light.

The wavelength for Red light is within the range 610nm


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How to find materials for LED(continued):For =610 nm

evevEg 03.2

106.110610

10310626.6

199

834

!

vvv

vvv

!

For =760 nm

evevEg 63.1

106.110760

10310626.6

199

834

!

vvv

vvv

!

So for the fabrication ofLED which emits Red light we have to choosesemiconductor material whose Bandgap is between 1.63 ev 2.03 ev andthats why Aluminium Gallium Arsenide(AlGaAs) and Gallium Arsenide

Phosphide(GaAsP) is used for the above purpose.


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Surf

ace-emitting LED(

SLED):

Surface EmittingLED or Burrus LED

The surface-emitting LED (shown in figure) is also known as the Burrus LEDin honor of C. A. Burrus, its developer. The active region is the portion of theLED where photons are emitted. The primary active region is below the surfaceof the semiconductor substrate perpendicular to the axis of the fiber.


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Edge-emitting LED(ELED):

Figure shows a typical ELED structure. It shows the different layers of semiconductormaterial used in the ELED. The primary active region of the ELED is a narrow stripe,which lies below the surface of the semiconductor substrate. The semiconductorsubstrate is cut or polished so that the stripe runs between the front and back of the

device. The polished or cut surfaces at each end of the stripe are called facets.

Edge-emitting LED


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Planar and Dome LED:

Dome and Planar-LED is used in most display device where the interest is inextracting the maximum amount of light from the device i.e. light is emitted in alldirections and using a lens arrangement to focus the light.


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Some other types of LEDs:1)Organic Light Emitting Diode(OLED):

If the emitting layer material of the LED is an organic compound, it is knownas an organic light emitting diode (OLED). To function as a semiconductor, the

organic emitting material must have conjugated pi bond.The emitting materialcan be a small organic molecule in a crystalline phase, or a Polymer. Polymermaterials can be f lexible; such LEDs are known as PLEDs.

Compared to regularLEDS , OLEDs are lighter but OLEDs operate at substantially lower efficiencythan inorganic (crystalline) LEDs.

2)Quantum dot LEDs:

This type ofLED involves coating a blue LED with Quantum dots that glowwhite in response to the blue light from the LED. Quantum dots aresemiconductor nanocrystals that possess unique optical properties.Quantumdots LEDs can create almost any colour.


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Thank You

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Types of Light Emitting Diode