66844793 Nhom 30 Firegoats LED

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REPORT

Themes: “LED’s structure and principles”

Group number 30: FireGoats.

September 27, 2011

Members:

- Tr ần Văn Sáng.

- Hoàng Minh Tân.

- Phạm Hùng Cườ ng



Report: LED’s structure and principles

Group number 30: FireGoats C h a p t

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Contents

INTRODUCTION .............................................................................................................................................. 3

I. GENERAL KNOWLEDGE ABOUT LED ..................................................................................................... 4

CLASSIFICATION: ................................................................................................................................................... 4

a. Low/Medium power LEDs. ................................................................................................................. 4

b. Power LEDs: ......................................................................................................................................... 5

II. STRUCTURE OF LED ............................................................................................................................... 5

1. STRUCTURE OF LIGHT-EMITTING DIODES (LEDS) .............................................................................................. 5

i. Classification ........................................................................................................................................ 5

ii. Foundation .......................................................................................................................................... 6

iii. Composition ........................................................................................................................................ 6

iv. Material ................................................................................................................................................ 8

III. OPERATION PRINCIPLES OF LED ........................................................................................................... 9

1. COMMON PRINCIPLES................................................................................................................................... 9

Electromagnetic spectrum: ............................................................................................................... 11

2. ENERGY BAND GAP:.................................................................................................................................... 12

IV. THE DIVERSITY OF LEDS’ COLOURS. ................................................................................................... 14

RED-GREEN-BLUE LIGHT-EMITTING DIODE (RGB LED)........................................................................................... 14

V. CONCLUSION....................................................................................................................................... 15

APPENDIX...................................................................................................................................................... 17

REFERENCE ......................................................................................................................................................... 17





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Introduction

From the ancient past, the Lord said "light go out."

And the light appears, because all things cannot live with thenight. This is a fact or just a myth entirely upon the

individual's faith. But there’s a certainty that to own the kind

of light as we have today, it took many thousands of years to

understand the laws of nature for the invention and creation.

Humans will not exist and did not evolve if there is no light.

Human discovered the fire, created the fire and using fire as

a light source in the distant prehistoric times. Prior to

electrification, over thousands of years and until the 70s of last century people are still using the oil lamp, or to the lamp

a little closure glow-fired steam oil to drive away the night.

Late 19th century, Thomas Edison created a revolution in the "light" through the

invention and fluorescent lamp completion by dint of the light of a resistor heated when

an electrical current across. Quantum mechanics appeared 100 years ago has changed

the understanding of the physics of the microscopic world. In the field of luminescence,

this subject tell us that the quantum leap in energy, the movement of electrons and the

existence of photons (light particles). As a result, one can produce light without burning or

heating a material object to. The fluorescence of neon

mercury vapor to all brightly colored in the capital city

prosperous place at night, are revolutionizing the light a

second time thanks to quantum mechanics. Television

screen using cathode pole was developed based on the

principles of fluorescence. Luminescence does not stop there. Thin liquid crystal display

(liquid crystal) used for computer and television screens are replacing the traditional

cathode pole used to be big, heavy and high energy consumption. Human are still not

satisfied. The curious addition of human need is a cause motivates people to seek

luminescent materials more efficiently. Then this liquid crystal display will be replaced with

the screen taking advantage of luminescent organic materials, very thin and less energy

consumption.

In this article we take a look how the second light revolutionary with the lamps used in

semiconductor have been implemented.





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I. General knowledge about LED

LED, full word is ―light-emitting diode‖, in

1962, was invented on electroluminescence

(the principle of electrical luminescence - EL –

optical phenomenon and electrical

phenomenon). Known as ―diode‖ because the

light emitting parts are composed by electron-

rich semiconductor connected to the other

hole-rich one, the hole can be viewed as

positively charged particles.

LEDs exploit the characteristics of a particular material (semiconductor) that, if conveniently treated, can transmit light when it’s passed through by an electrical

current (electronic light). For their structure they belong to the SSL family (Solid State

Lighting), that means they work with no need for cruets containing gas mixtures, which

are required by most traditional light sources (filament bulbs, fluorescent and

discharge lamps, etc.).

Nowadays, LEDs are semiconductor light source used as indicator lamps in many

devices and are increasingly used for other lighting with the variability across the

visible, ultraviolet and infrared wavelengths, and very high

brightness.

Classification:

a. Low/Medium power LEDs.

The current used isn’t higher than 150mA,





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mostly used to obtain light signals or decoration.

b. Power LEDs:

They are used to illuminate surfaces and whole

environments.

i.

Single chip Power LEDs

ii. Multi chip Power LEDs

II. Structure of LED

1. Structure of light-emitting diodes (LEDs)

i. Classification

Surface emitting LED structure:

This form of LED structure emits light perpendicular to the plane of the PN junction.

Surface emitting LED structure

Edge emitting LED structure:

This form of LED structure emits light in a plane parallel to the

junction of the PN junction. In this configuration the light can be

confined to a narrow angle

For medium-distance, medium-data-rate systems, ELEDs are preferred.





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ii. Foundation

Size:

In SMD devices (surface mount devices): Most of the size of a

5mm or 3mm indicator LED is the

epoxy package–the actual LED

junction is quite small

SMD

LEDs are available in four sizes,

which are designated 1206, 0805,

0603 and 0402. 0402 is the smallest,

with overall package size of 1.0 mm x

0.5 mm x 0.45 mm (L x W x H). Then

0603 at 1.6 mm x 0.8 mm x 0.6 mm.

0805 are slightly larger, at 2.0 mm x

1.25 mm x 0.8 mm. 1206 are the big

brothers of the family, at 3.2mm x 1.5 mm x 1.1 mm.

Electrical

These aren’t very different from the LEDs you’re used to.

Both of these are rated for a typical forward current of 35mA,

with a typical forward voltage of 3.6V (4.0V max). Where they

stand well apart from the crowd is optically–these are much

wider view angle at 140°. The little guy is rated 200mcd and

the 0805 is rated 120mcd. That may seem low if you’re used

to specs on 5mm LEDs, but remember that luminous

intensity in millicandelas changes as the view angle, so these

have a comparable overall flux

iii.

Composition





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Mold (top of LED) is filled with liquid plastic or epoxy, known

as Epoxy lens/case.

A chip (semiconductor die): bonded into a recess in one half

of the lead frame, is made of semiconducting material doped with

impurities (to create a PN junction). The PN junction can be created

by either impurity diffusion, ion implantation, or it can beincorporated during the epitaxial growth phase

Leadframe: This houses the die and acts as the connection to

it.

Anvil: name to its shape.

Post.

The recess in the anvil is shaped to throw the light radiation

forward.

Reflective cavity: fix light’s direction. Flat spot.

Substrates: common are GaAS, GaP, InP. LEDs are usually

built on an n-type substrate, with an electrode attached to the p-

type layer deposited on its surface. P-type substrates, while less

common, occur as well. Many commercial LEDs, especially

GaN/InGaN, also use sapphire substrate

Electrode:

Anode: usually longer than cathode.





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Cathode: directly connected with die and the anvil, usually

shorter than the former.

iv. Material

The wavelength of the light emitted, and thus its colordepends on the Energy band gap of the materials forming the PN

junction. In silicon or germanium diodes, the electrons and holes

recombine by a non-radiative transition which produces no optical

emission, because these are indirect band gap materials. The

materials used for the LED have a direct band gap with energies

corresponding to near-infrared, visible or near-ultraviolet light.

Conventional LEDs are made from a variety of inorganic

semiconductor materials, producing the following colors:

Order Material Sign Output

1 Aluminum gallium arsenide AlGaAs red and infrared

2 Aluminum gallium phosphide AlGaP green

3 Aluminum gallium indium phosphide AlGaInP high-brightness orange-red, orange,

yellow, and green

4 Gallium arsenide phosphide GaAsP red, orange-red, orange, and yellow

5 Gallium phosphide GaP red, yellow and green

6 Gallium nitride GaN green, pure green (or emerald green),

and blue also white (if it has an AlGaN

Quantum Barrier)

7 Indium gallium nitride InGaN near ultraviolet, bluish-green and blue

8 Silicon carbide SiC as substrate—blue

9 Silicon Si as substrate—blue (under

development)

10 Sapphire Al2O3 as substrate—blue

11 Zinc selenide ZnSe blue

12 Diamond C ultraviolet

13 Aluminum nitride AlN aluminum gallium nitride (AlGaN)—

near to far ultraviolet (down to 210

nanometer (nm)

Most materials used for LED production have very high

refractive indices. This means that much light will be reflected back

into the material at the material/air surface interface. Thus, light

extraction in LEDs is an important aspect of LED production, subject

to much research and development.

Materials with refractive index that could allow light to get

out.





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III. Operation principles of LED

1. Common principles.

LEDs give off lights on the principle of electrical luminescence known as

electroluminescence - EL classified into optical phenomenon and electrical

phenomenon.

Electroluminescence

Luminescence occurs when electrical current flows across a diode, an

electron (negative charge) will be combined with a hole (+); the

combination will make the electron jump from one energy level high to a

lower energy. The process of jumping from high to low gives an excess

energy. This energy, depending on the energy band gap of the

semiconductor environment, will be spread out as infrared, visible light and

ultraviolet light (also known as UV).

When the applied forward voltage on the diode of the LED drives the

electrons and holes into the active region between the n-type and p-type

material, forward bias occurs, the energy can be converted into infrared or

visible photons. This implies that the electron-hole pair drops into a more

stable bound state, releasing energy on the order of electron volts by




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emission of a photon. The red extreme of the visible spectrum, 700 nm,

requires an energy release of 1.77eV to provide the quantum energy of the

photon. At the other extreme, 400 nm in the violet, 3.1eV is required.

Conventional LEDs are made from a variety of inorganic semiconductor

materials, the following table shows the available colors with wavelength

range, voltage drop and material:

Order Color Wavelength

(nm)

Voltage (V) Semiconductor material Sign

1 Infrared λ > 760 ΔV < 1.9 Gallium arsenide

Aluminium gallium

arsenide

GaAs,

AlGaAs

2 Red 590 < λ <

610

1.63 < ΔV <

2.03

Aluminium gallium

arsenide

Gallium arsenide

phosphide

Aluminium gallium indium

phosphide

Gallium(III) phosphide

AlGaAs,

GaAsP,

AlGaInP

, GaP

3 Orange 590 < λ <

610

2.03 < ΔV <

2.10

Gallium arsenide

phosphide


phosphide


GaAsP,

AlGaInP

, GaP

4 Yellow 570 < λ <

590

2.10 < ΔV <

2.18

Gallium arsenide

phosphide


phosphide


GaAsP,

AlGaInP

, GaP

5 Green 500 < λ <

570

1.9 < ΔV <

4.0

Indium gallium nitride /

Gallium(III) nitride


Aluminium gallium indiumphosphide

Aluminium gallium

phosphide

InGaN,

GaN,

GaP,

AlGaInP, AlGaP

6 Blue 450 < λ <

500

2.48 < ΔV <

3.7

Zinc selenide

Indium gallium nitride

Silicon carbide as

substrate

Silicon as substrate –

(under development)

ZnSe,

InGaN,

SiC, Si

7 Violet 400 < λ < 2.76 < ΔV < Indium gallium nitride InGaN





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450 4.0

8 Purple multiple types 2.48 < ΔV <

3.7

Dual blue/red LEDs,

blue with red phosphor,

or white with purple

plastic9 Ultraviolet λ < 400 3.1 < ΔV <

4.4

Diamond (235 nm)

Boron nitride (215 nm)

Aluminium nitride

(210 nm)

Aluminium gallium nitride


nitride – (down to

210 nm)

AlN,

AlGaN,

AlGaIn

N

10 White Broad

spectrum

ΔV = 3.5 Blue/UV diode with yellow

phosphor

Electromagnetic spectrum:

The appearance of the visible light will be the results of the overlap integral

between the eye response curve and the spectral power of the device.

Thus, the peak of the luminous curve will not in general be the same as the

peak of the spectral power curve





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2. Energy band gap:

Energy band gap is an important characteristic of the solid.

The band gap is not an abstract concept but a character can be measured.

Solids are set by the superposition of atoms that make up. It is imitated that

per cm3 solid formed by approximately 1022 atoms. During this process

constitutes, according to quantum mechanics, the electronic energy levels

will be formed and the electrons of the atom will occupy these energylevels. Since the atomic number is extremely large, so the energy levels and





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also to gather a range of electronic energy (electronic energy band), similar

to the pages gather into a book.

The formation of solid power band may not be continuous, there will be a

"gap" appears, like the ditch divided into two bands (region) energy. The

space is called a band gap energy. Band gap values are in electron volt (eV- 1eV = 1.602 x 10-12 ERG).

Band gap determines the electrical conductivity of solids. The electrical

conductivity or not is due to the ability to "jump ditches" of the electrons. If

the electron of the solids cannot jump from low energy to high-energy

region, they are electrical insulators.

i. For example, the band gap of the polymer (plastic) is 3-5eV, the

diamond is 8eV; the "ditch" is too large to electrons can jump in

normal conditions (22 ° C, 1atm). These are excellent insulators.

ii. In contrast, the length of the metal band is zero. Electronic travel

between the two energy freely, conduction occurs. In between these

two extremes is a semiconductor.

iii. Band gap of semiconductors is in the range from 1 to 1.5eV.

As we will see, band gap energy is a very important property of matter not

only for the electrical properties (insulator, conductor or semiconductor),

but also in the design of a material in the applied optics, or optoelectronics

that luminescence is a good example.





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IV. The diversity of LEDs’ colours.

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

Blue and white LEDs are much more expensive than the other colours.

The colour of an LED is determined by the semiconductor material, not by

the colouring of the package (the plastic body). LEDs of all colours are

available in uncoloured packages which may be diffused (milky) or clear(often described as water clear). The coloured packages are also available

as diffused (the standard type) or transparent

Human eye can see light with wavelengths from 380nm (violet light) to

720nm (red light). Waves carry energy and energy is inversely proportional

to wavelength. Thus, the energy of visible light is 1.7eV (720 nm) to 3.3eV

(380 nm). Electromagnetic waves have wavelengths less than 380 nm is

ultraviolet light and is larger than 720 nm infrared (heat). What an

interesting random values of energy band gap of semiconductors andsome insulators, such as conjugated polymer bearing connections, fit in the

area of infrared energy, light visible and ultraviolet light, which relates with

luminescence. When an electron co-ordinates with a hole (+) from high

energy level to drop lower level, then this distance of these two levels is the

energy band gap of the physical environment where collaboration

happens. Put it more simply, if we want the red luminescence we will design

materials whose band gap is in approximately the range 1.7eV. Diamond ’s

band gap value is greater than 5eV, so being fluorescent environment

diamonds will emit UV radiation. Other compound semiconductors of the

gallium (Ga) as GaAs, GaAsP, AlGaP, GAP, InGaN have values in range from

1eV to 3.5eV can emit all colors of visible light.

Red-Green-Blue Light-Emitting Diode (RGB LED)

Embed with intelligent IC, LED can be adjusted the intensity of three basic colours,

red green and blue, to emit diversified colours. For instance, we can build some

circuit like these:





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V. Conclusion.

It’s undeniable that the birth of LEDs in 1927 had been the risk of the extinction of

heating lamps while people increasingly concerned about the economic value,

particularly over the environmental benefits that this discovery brings. They not

only save energy, environmentally friendly, but life for centuries, even decades...

With an incredible speed of technological development as now, then soon, the





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device produced by this technology will flood the market, with super power-saving

lamps, the ultra-thin ultra-stroke screen also features environmentally friendly.

It was a great benefit of not only physics in particular, but also the science in

general.





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Appendix

Reference

1. Electronic Devices and Circuit Theory 7th Edition Floyd.

2.

C. W. Tang and S. A. VanSlyke, Appl. Phys. Lett. 51 (1987) 913.

3. J. H. Burroughes, D. D. C. Bradley,A. R. Brown, R. N. Marks, K. MacKay, R. H. Friend,

P. L. Burn an A. B. Holmes, Nature 347 (1990) 539.

4. M. Berggren, O. Inganäs, G. Gustafsson, J. Rasmusson, M. R. Andersson, T.

Hjertberg and O. Wennerstrom, Nature 372 (1994) 444.

5. "Polymers light up" in Chemistry & Industry, 26 March 2007.

6. http://web.dongtak.net/spip.php?article1553

7. http://led.linear1.org/

8.

http://vietsciences.free.fr/inventions/denphatquang.htm 9. http://vi.wikibooks.org/wiki/%C4%90ai_%E1%BB%90t_Ph%C3%A1t_S%C3%A1ng

10. http://www.youtube.com/watch?v=P3PDLsJQcGI&feature=player_embedded#!

11. http://www.kpsec.freeuk.com/components/led.htm

12. http://en.wikipedia.org/wiki/Light-emitting_diode#Colors_and_materials

13. http://en.wikipedia.org/wiki/Electroluminescence

14. http://www.google.com.vn/imgres?q=diode&hl=vi&client=firefox-

a&hs=9eD&sa=X&rls=org.mozilla:en-

US:official&biw=1368&bih=648&tbm=isch&prmd=imvnsr&tbnid=98baqLVb071KiM:&imgrefurl=http://congnghe12.wikispaces.com/%25C4%2590i%25E1%25BB%25

91t%2Bb%25C3%25A1n%2Bd%25E1%25BA%25ABn&docid=vHRmQPvGD_0vDM

&w=325&h=295&ei=LF1_TqWDK-

6jiAeW8rG2Dg&zoom=1&iact=rc&dur=377&page=1&tbnh=128&tbnw=141&star

t=0&ndsp=21&ved=1t:429,r:8,s:0&tx=60&ty=38

15. http://www.google.com.vn/url?sa=t&source=web&cd=5&ved=0CE8QFjAE&url=ht

tp%3A%2F%2Fmaterial.eng.usm.my%2Fstafhome%2Fzainovia%2FEBB424e%2FLED

1.ppt&rct=j&q=LED%20%27s%20principle&ei=4ml_TtavIuiViQes8bjjDg&usg=AFQjCNEwGVsfDqyk15_tYW7JDOetIk9olw&sig2=3c5SBr1MH1TMVrNHRdYMiQ&cad=rj

a

16. http://cantalupiusa.com/led-lighting-principles

17. http://www.madehow.com/Volume-1/Light-Emitting-Diode-LED.html

18. http://en.wikipedia.org/wiki/Diode

19. http://www.newworldencyclopedia.org/entry/LED

20. http://www.radio-electronics.com/info/data/semicond/leds-light-emitting-

diodes/structure-fabrication.php 21. http://www.tpub.com/neets/tm/110-4.htm

http://web.dongtak.net/spip.php?article1553


http://led.linear1.org/


http://vietsciences.free.fr/inventions/denphatquang.htm


http://vi.wikibooks.org/wiki/%C4%90ai_%E1%BB%90t_Ph%C3%A1t_S%C3%A1ng


http://www.youtube.com/watch?v=P3PDLsJQcGI&feature=player_embedded



http://www.kpsec.freeuk.com/components/led.htm



http://en.wikipedia.org/wiki/Light-emitting_diode#Colors_and_materials



http://en.wikipedia.org/wiki/Electroluminescence



http://www.google.com.vn/imgres?q=diode&hl=vi&client=firefox-a&hs=9eD&sa=X&rls=org.mozilla:en-US:official&biw=1368&bih=648&tbm=isch&prmd=imvnsr&tbnid=98baqLVb071KiM:&imgrefurl=http://congnghe12.wikispaces.com/%25C4%2590i%25E1%25BB%2591t%2Bb%25C3%25A1n%2Bd%25E1%25BA%25ABn&docid=vHRmQPvGD_0vDM&w=325&h=295&ei=LF1_TqWDK-6jiAeW8rG2Dg&zoom=1&iact=rc&dur=377&page=1&tbnh=128&tbnw=141&start=0&ndsp=21&ved=1t:429,r:8,s:0&tx=60&ty=38











http://www.google.com.vn/url?sa=t&source=web&cd=5&ved=0CE8QFjAE&url=http%3A%2F%2Fmaterial.eng.usm.my%2Fstafhome%2Fzainovia%2FEBB424e%2FLED1.ppt&rct=j&q=LED%20%27s%20principle&ei=4ml_TtavIuiViQes8bjjDg&usg=AFQjCNEwGVsfDqyk15_tYW7JDOetIk9olw&sig2=3c5SBr1MH1TMVrNHRdYMiQ&cad=rja








http://cantalupiusa.com/led-lighting-principles



http://www.madehow.com/Volume-1/Light-Emitting-Diode-LED.html



http://en.wikipedia.org/wiki/Diode



http://www.newworldencyclopedia.org/entry/LED



http://www.radio-electronics.com/info/data/semicond/leds-light-emitting-diodes/structure-fabrication.php





http://www.tpub.com/neets/tm/110-4.htm



































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22. http://led.linear1.org/surface-mount-leds/

23. http://leds-led-drivers.com/Engineering-Services/what-are-led-lamps.cfm

http://led.linear1.org/surface-mount-leds/



http://leds-led-drivers.com/Engineering-Services/what-are-led-lamps.cfm





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