LIGHT EMITTING DIODESLIGHT EMITTING DIODES & &

LASER DIODESLASER DIODES

Presentation by A.JOHNY RENOALD M.E.,(Ph.D.,)

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• A light emitting diode (LED) is essentially a PN junction opto-semiconductor that emits a monochromatic (single color) light when operated in a forward biased direction.

• LEDs convert electrical energy into light energy.

About LEDs

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Construction - Light Emitting DiodesConstruction - Light Emitting Diodes

UV – AlGaNBlue – GaN, InGaNRed, green – GaPRed, yellow – GaAsPIR- GaAs

HOW DOES A LED WORK? (1/2)HOW DOES A LED WORK? (1/2)

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• When sufficient voltage is applied to the chip across the leads of the LED, electrons can move easily in only one direction across the junction between the p and n regions.

• When a voltage is applied and the current starts to flow, electrons in the n region have sufficient energy to move across the junction into the p region.

HOW DOES A LED WORK? (2/2)HOW DOES A LED WORK? (2/2)

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When a light-emitting diode is forward biased, electrons are able to recombine with holes within the device, releasing energy in the form of photons.

This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor

HHowow M Muchuch Energy Does an LED Emit? Energy Does an LED Emit?

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• The energy (E) of the light emitted by an LED is related to the electric charge (q) of an electron and the voltage (V) required to light the LED by the expression: E = qV Joules.

• This expression simply says that the voltage is proportional to the electric energy

• The constant q is the electric charge of a single electron, 1.6 x 10-19 Coulomb.

ApplicationsApplications

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• Sensor Applications

• Mobile Applications

• Sign Applications

• Automative Uses

• LED Signals

• Illuminations

• Indicators

SENSOR APPLİCATİONSSENSOR APPLİCATİONS Medical Instrumentation Bar Code Readers Color & Money Sensors Encoders Optical Switches Fiber Optic Communication

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MOBİLE APPLİCATİONSMOBİLE APPLİCATİONS

Mobile Phone PDA's Digital Cameras Lap Tops General Backlighting

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SİGN APPLİCATİONSSİGN APPLİCATİONS

Full Color Video Monochrome Message Boards Traffic/VMS Transportation - Passenger Information

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AUTOMATİVE APPLİCATİONSAUTOMATİVE APPLİCATİONS

Interior Lighting - Instrument Panels & Switches, Courtesy Lighting

Exterior Lighting - CHMSL, Rear Stop/Turn/Tail Truck/Bus Lighting - Retrofits, New Turn/Tail/Marker Lights

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SİGNAL APPİCATİONSSİGNAL APPİCATİONS

Traffic Rail Aviation Tower Lights Runway Lights Emergency/Police Vehicle Lighting

LEDs offer enormous benefits over traditional incandescent lampsincluding:

Energy savings (up to 85% less power than incandescent) Reduction in maintenance costs Increased visibility in daylight and adverse weather conditions

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Illumination (1/2)Illumination (1/2)

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Architectural Lighting Signage (Channel Letters) Machine Vision Retail Displays Emergency Lighting (Exit Signs) Neon Replacement Bulb Replacements Flashlights Outdoor Accent Lighting - Pathway, Marker Lights

INDİCATİONINDİCATİON

Household appliances VCR/ DVD/ Stereo and other audio and video devices Toys/Games Instrumentation Security Equipment Switches

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Colours of LEDs (1/3)Colours of LEDs (1/3)

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• LEDs are available in red, orange, amber, yellow, green, blue and white.

• LEDs are made from gallium-based crystals that contain one or more additional materials such as phosphorous to produce a distinct color.

• Different LED chip technologies emit light in specific regions of the visible light spectrum and produce different intensity levels.

LED - Colors & voltage dropLED - Colors & voltage drop

ColorWavelength

(nm)Voltage (V) Semiconductor Material

Infrared λ > 760 ΔV < 1.9 Gallium arsenide (GaAs) Aluminium gallium arsenide (AlGaAs)

Red 610 < λ < 760

1.63 < ΔV < 2.03

Aluminium gallium arsenide (AlGaAs) Gallium arsenide phosphide (GaAsP) Aluminium gallium indium phosphide (AlGaInP) Gallium(III) phosphide (GaP)

Orange 590 < λ < 610

2.03 < ΔV < 2.10

Gallium arsenide phosphide (GaAsP) Aluminium gallium indium phosphide (AlGaInP)Gallium(III) phosphide (GaP)

Yellow 570 < λ < 590

2.10 < ΔV < 2.18

Gallium arsenide phosphide (GaAsP) Aluminium gallium indium phosphide (AlGaInP) Gallium(III) phosphide (GaP)

Green 500 < λ < 570

1.9 < ΔV < 4.0 Indium gallium nitride (InGaN) / Gallium(III) nitride (GaN) Gallium(III) phosphide (GaP)Aluminium gallium indium phosphide (AlGaInP) Aluminium gallium phosphide (AlGaP)

Blue 450 < λ < 500

2.48 < ΔV < 3.7 Zinc selenide (ZnSe), Indium gallium nitride (InGaN), Silicon carbide (SiC) as substrate, Silicon (Si)

Violet 400 < λ < 450

2.76 < ΔV < 4.0 Indium gallium nitride (InGaN)

Purple multiple types

2.48 < ΔV < 3.7 Dual blue/red LEDs,blue with red phosphor,or white with purple plastic

Ultra-violet

λ < 400 3.1 < ΔV < 4.4 diamond (235 nm), Boron nitride (215 nm) , Aluminium nitride (AlN) (210 nm) Aluminium gallium nitride (AlGaN) (AlGaInN) — (to 210 nm)

White Broad spectrum

ΔV = 3.5 Blue/UV diode with yellow phosphor

Bargraph 7-segment Starburst Dot matrix

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Some Types of LEDs

1.Miniature

2. High power

3.Ac driven

If you wish to have several LEDs on at the same time, connect them in series.

This prolongs battery life by lighting several LEDs with the same current as just one LED.

The power supply must have sufficient voltage to provide about 2V for each LED (4V for blue and white) plus at least another 2V for the resistor.

To work out a value for the resistor you must add up all the LED voltages and use this for VL.

Connecting LEDs in seriesConnecting LEDs in series

Connecting LEDs in seriesConnecting LEDs in series

Example A red, a yellow and a green LED in series need a supply voltage of at least 3×2V + 2V = 8V, so choose a 9V battery. Adjust the resistor R to have current I=15 mA.

Connecting LEDs in seriesConnecting LEDs in series

Example A red, a yellow and a green LED in series need a supply voltage of at least 3×2V + 2V = 8V, so choose a 9V battery. Adjust the resistor R to have current I=15 mA.

VL = 2V + 2V + 2V = 6V (the three LED voltages added up).

If the supply voltage VS is 9V and the current I must be 15mA = 0.015A,

Resistor R = (VS - VL) / I = (9 - 6) / 0.015 = 3 / 0.015 = 200, so choose R = 220Ω   (the nearest standard value which is greater).

Connecting several LEDs in parallel with just one resistor shared between them is a bad idea.

If the LEDs require slightly different voltages only the lowest voltage LED will light and it may be destroyed by the larger current flowing through it.

If LEDs are in parallel each one should have its own resistor.

Avoid connecting LEDs in parallel!Avoid connecting LEDs in parallel!

LED displays are packages of many LEDs arranged in a pattern, the most familiar pattern being the 7-segment displays for showing numbers (digits 0-9).

LED DisplaysLED DisplaysIt is a common anode display since all anodes are joined together and go to the positive supply.

The cathodes are connected individually to resistors limiting the current through each diode to a safe value.

SPECTRAL LINEWIDTHS

Semiconductor Lasers DiodesSemiconductor Lasers Diodes

Laser diode is similar in principle to an LED.

A laser diode, also known as an injection laser or diode laser, is a semiconductor device that produces coherent radiation (in which the waves are all at the same frequency and phase) in the visible or infrared (IR) spectrum when current passes through it.

IntroductionIntroduction

Semiconductor diode (the first laser diode) was demonstrated in 1962 by two US groups led by Robert N. Hall at the General Electric research center and by Marshall Nathan at the IBM T.J. Watson Research Center

The semiconductor laser is made in mass quantities from wafers of gallium arsenide or similar crystals.

Classification Of Classification Of Semiconductor LaserSemiconductor Laser

Semiconductor Laser

Homojunction Diode Laser

Heterojunction Diode Laser

Double Heterojunction

Diode Laser

Single Heterojunction

Diode Laser

Laser Diode symbolLaser Diode symbol

Homojunction laserHomojunction laser

It is simply a laser diode where the active medium is a semiconductor similar to that found in a light-emitting diode. The most common and practical type of laser diode is formed from a p-n junction and powered by injected electric current

Homojunction Semiconductor LaserHomojunction Semiconductor LaserHomojunction diode lasers are those in which P end and N end of the diode are made of the same semiconductor material.Example : Ga As laserThey use Direct Band Gap Semi- conductor material.P-N Junction act as the active medium.The crystal is cut at a thickness of 0.5 mmApplied voltage is given through metal contacts on both surfaces of the diode.Pulse beam of laser of 8400 Å is produced

Working Working

FORWARD BIASED DIODE LASER

metal contact

Ga –As material on both ends

P end

N end Laser beam +

PPumpingumping When PN junction diode is forward biased, the

electrons from ‘n’ region and holes from ‘p’ region recombine with each other at the junction .

During the recombination process light radiations (photons) is released from certain specified direct band gap semiconductors like Ga-As.

This radiation is called recombination radiation and the corresponding energy is called activation energy.

Heterojunction laserHeterojunction laser

A hetero junction is the interface that occurs between two laser or regions of dissimilar crystalline semiconductors. These semiconducting materials have unequal band gaps as opposed to a homo junction.

Using hetero junctions in lasers was first proposed in 1963 in Herbert Kroemer

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metal contactP end

N end Laser Beam

Ga As

GaAIAs

ComparisionComparisionHOMOJUNCTION DIODE LASER HETEROJUNCTION DIODE LASER

P and N regions are made of the same diode material

Active medium : Single crystal of PN Diode

Pulse beamWavelength : 8300Å-8500ÅExample : GaAs,InP.

P and N regions are made of different diode material

Active Medium : Third layer of p type material among the five layers

Continuous beamWavelength : 8400 ÅExample : GaAIAs, InP/InAIP

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AdvantagesAdvantages They are light weighted and portable.Battery supported ; easily replaceable Small size and low costCompatibility with optical fibres

DisadvantagesDisadvantagesDue to relatively low power production,

these lasers not suited to typical laser applications

The temperature affects greatly the output of the laser

Beam divergence is much greater as compared to all other lasers

Cooling system required in some cases

ApplicationsApplicationsFiber optic communicationsBarcode readersLaser pointersDisc readerLaser printing & scanningDirectional lighting sources

Thank you for your Attention!