P. Babu DayalTokyo Institute of Technology,

Japan.

E-mail: babudayal.p.aa@m.titech.ac.jp

MicrosystemResearch Center

Light emitting devices: Fundamentals and Applications

JSPS Science DialogueIwata Minami High School

Shizouka, Japan27th Sep. 2007

Contents

India in Brief….

Semiconductors

Light Emitting Diode

LASERs

VCSELs

Applications

Fundamentals &

Examples

Part-IA brief introduction to India

Where are we?

INDIA

JAPAN

(Bharat)

(Nippon)

Humble Greetings

NAMASTE Koninchiwa

India Japan

2007 : India - Japan Friendship Year !!

Excellent Indo - Japan relations (Aug. 2007)

Dr. Manmohan SinghPrime Minister-India

Mr. Shinzo AbeFormer Prime Minister-Japan Eenadu daily

India

Largest democracy in the world7th Largest country in the world

My Country

India in brief…

Population : 1.12 billion(1,129,866,154 on July 2007)

Capital : New Delhi

Literacy : 61% (M-73.4% & F-47.8%)

States & Union Territories : 28 & 7

National Language : Hindi & English

Official Languages : 22

Currency : Indian Rupee (INR)

Life expectancy : 68.59 (M-66.28 & F-71.17)

Official languages of India (22) !!

Dravidian Indo-Aryan

Tamil, Telugu,

Kannada , and Malayalam

Assamese, Bengali, Bodo, Dogri, Gujarati,

Hindi, Kashmiri, Konkani, Maithili, Manipuri, Marathi,

Nepali, Oriya, Punjabi, Rajasthani, Santhali, Sindhi

and Urdu.

Sanskrit Based

Nepal NepaliUrdu PakistanBengali Bangladesh

Neighboring NationsOfficial languages

Diversity

Hindu80.46%

Muslim13.43%

Christian2.34%

Sikh1.87%

Buddhist0.77%

Jain0.41%

Others0.65%

India

Multiple Religions (% of population)

Unity

Population on July 2007 1,129,866,154

My City-Rajahmundry with Godavari River

My home town: DowlaiswaramSir Aurthor Cotton Barrage for Irrigation of crops

Ancient Indian MathematicsFrom 2600 BC to 18th century AD

Decimal number system 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9

Positive and negative numbers +6 , -9 etc.

Arithmetic, Algebra, Trigonometry, Geometry, Calculus, etc…..

Important contributions were made by scholars like Aryabhata, Brahmagupta, and Bhaskara II.

= 3.14159 26535 89793 23846 26433 83279 50288 41971 69399 37510

Originated in

INDIA !!

Lord Buddha originated from India (563 to 483 B.C)

Statue of Buddha in Gupta’s period

Original Bodhi Tree in Bodhgayain Bihar, India

Takshila, Nalanda university(First centers of higher learning in the world, 300 BC)

Nalanda was not a formal college or university. Instead there were renownedteachers who taught various subjects like medicine, astronomy, astrology,

Commerce, accountancy, law, magic, music, painting, crafts, archery and the study of the Vedas. Students sought admission when they were about 16.

Taj Mahal (1632-1648)

Day light Full moon light

Built by Emperor Shah Jahan for the memory of his wife Mumtaz Mahal

A symbol of love !!

Wonder of the world !!

Popular Arts

Kuchipudi, the traditional dance of

Andhara pradesh

Bharatanatyam-Indian Classical Dance

Masako Ono

(Japanese National)

During Odyssey Show in India

Typical food of India

South Indian meals North Indian meals

Historical Places

Pink City -JaipurTirumala-Andhra Pradesh Kajhuraho-MP

Kutub Minar-Delhi Gate way of India-Mumbai Charminar-Hyd

Srinagar-Jammu & KashmirMinakshi temple-Madurai

India Gate-Delhi

RABINDRANATHTAGORE (1913-Literature)

CHANDRASHEKAR VENKATA RAMAN

(1930-Physics) HARGOBIND KHORANA

(1968-Medicine)

SUBRAMANIAN CHANDRASHEKAR

(1983-Physics) AMARTYA SEN

(1998-Economics)

Nobel Prize Winners from India

MOTHER TERESA(1979-Peace)

V. S. NeiPaul(2001-Literature)

Brand

IIT

Higher Education (Engineering & Technology)

IITs – 1 out of 200 applicants gets admitted !!

Indian Institute of Technology-Delhi

•IIT-Bombay •IIT-Delhi•IIT-Guwahati•IIT-Kanpur•IIT-Kharagpur•IIT-Madras•IIT-Roorkee

IIT = MIT + Harvard + Princeton

BBC

Over 1.12 billion population

28 states, 7 union territories

22 official languages

Multiple religions co-exist

1 Country

INDIA"Satyameva Jayate" (Sanskrit)

������� ���� (Devanagari)

"Truth Alone Triumphs"

Part-IILight Emitting Devices

Structure of atom

Fundamental Subatomic Particles

1.008665 amu0 noneutron

1.007276 amu+1 p+proton

0.0005486 amu-1 e-electron

MassChargeSymbol Particle

Carbon atom as an example

Core electrons

Valence electrons

C612 1s2 2s2 2px

1 2py1

Bohr’s Postulates Energy Levels

Electrons can change orbits by radiating (larger to smaller), absorbing radiation (smaller to larger) or by collisions (either larger to smaller or smaller to larger).

Lower

Higher

Abs

orpt

ion

Emis

sion

Dr. Niels Bohr, Denmark (1913)

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

Elements and Periodic Table

www.stanford.edu/class/educ299x/assignment1.html

Different states of matter

Gas Liquid Solid

http://www.chem.purdue.edu/gchelp/liquids/character.html

atoms can move past one another

atoms can move/slide past one another

atoms locked into place

Solids

Metals Semiconductors Insulators

http://www.physics.udel.edu/~watson/ALLSTEL99/sld007.htm

Electronic band structure in solids

Metals, semiconductors and Insulators

CB

VB

Eg

Semimetal Metal Semiconductor Insulator

Energy(eV)

Carbon Gold Silicon SiO2

Filled Band

Empty Band

Resistivity Ohm/cmConductivity Ohm-1/cm-1

Concept of electron and hole

EgEg

Hole: Deficiency or absence of electron

ConductionBand

ValenceBand

Creation of holes

Eg

Conduction e-

Holes

Valence e-

e- hWater drop Air bubble

Motion of electron and hole

Different types of semiconductors

Elemental Si, Ge

Binary GaAs, InP

Ternary AlGaAs

Quartenary InGaAsP

Intrinsic

P-type

N-type

degenerate

Doping

The addition of a small percentage of foreign atoms in the regular crystallattice of intrinsic semiconductors produces dramatic changes in their electrical properties, producing n-type and p-type semiconductors.

GaAsBonding: covalent, partially ionic

SiliconBonding: covalent

Typical Semiconductors

Intrinsic (Un-doped) Semiconductor

Semiconductor Current

Both electrons and holescontribute to current flow in an intrinsic semiconductor.

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

EF

Conduction band

Valence band

Egap (Fermi Level)

No of electrons = No of holes ⇒ No net electric current !!

Ec

Ev

Extrinsic (doped) semiconductors

Si 1s2 2s2.2p6 3s2.3p2

Sn 1s2 2s2.2p6 3s2.3p6 3d10.4s2.4p6 4d10.5s2.5p3

B 1s2 2s2.2p1

n-Type p-Type

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

P-N Junction (Diode)

http://www.mtmi.vu.lt/pfk/funkc_dariniai/diod/index.html

Forward bias - offers low resistance

Reverse bias - offers high resistance

http://links.baruch.sc.edu/scael/personals/pjpb/lecture/spectrum.gif

Light = Photon (γ) = electromagnetic Wave

Wavelength = Distance between crests

Amplitude = Half height of through to crest

Frequency = No of crests passing though a

point in space every second

cE h

cλ

λν

=

=

E = Energy (eV)C = Speed of light

(3x108 m/s)ν = Frequency (Hz)λ = Wavelength (µm)h = Planck’s constant

What is light ?

Interaction of optical processes with electronic processes

Optical processes

AbsorptionEmissionReflectionTransmission

Electronic/electrical

CurrentVoltagePowerResistance

Light Electron

Opto-electronics

⇒ Interaction of photons with electrons and holes

e- + h → hν

LED

Optical processes in semiconductor atoms

LASER

hν > Ec-Ev

Ev

Echν ≥ Ec-Ev

e--h annihilated and appears as emitted light

Light emitting devices (Light sources)

At all possible wavelengths in EM spectrum

pn

hν pn

hνhν

LED LASER

ReflectingMirrors

LED Light Emitting DiodeLASER Light Amplification by Stimulated Emission of Radiation

Spontaneous emission Stimulated emission

Light Emitting Diodes (LEDs)

Color Displays

Forward Biased p-n junction

Electroluminescence

electron-hole pair drops into a morestable bound state, emitting

energy in the form of a photons. Source: Encyclopedia RP-Photonics

In-coherentEmission

Optical Mouse

Marine Navigation

Amusement Parks

Airport Runway

Medical DiagnosisHigh resolution

Imaging

Motor lights

Industry lighting

Flash Lights

Remote Control

LED Applications

1921 Albert Einstein first theoretically proposed the Idea1961 First experimental demonstration of Ruby-LASER

Light Amplification of Stimulated Emission of Radiation( LASER )

Major Characteristics of LASER

•Monochromatic (Single wavelength)

•Coherent (All photos have same phase)

•Collimated (Parallel output beam)

Albert Einstein

Structure of LASER

23 4

1

5

1. Source 2. Gain Medium 3 and 4 Reflectors 5. Output

Pump + Gain medium + Resonator

Ruby-LASER

Population Inversion

1960, Dr. Maiman (USA) λ = 694.3 nmHughes Research Laboratories

ASolid State

LASER

First invention of LASER in the world1960

Theodore Harold Maiman

Different types of lasers

• Gas LASERs

• Chemical LASERs

• Solid State LASERs

* Fiber LASERs

* Semiconductor LASERs

• Dye LASERs

•Free electron lasers

He-Ne Gas Laser for barcode reader

1960, Ali Javan, William Bennet Jr.and Donald Herriot, λ = 632.8 nmBell Labs, USA

Nd:Y3Al5O12

1964, Geusic et al. λ = 1064 nmBell Laboratories, USA

Eye cataract surgery, laser hair removal , manufacturing for cutting and welding steel,Dentistry and so on…

Nd: YAG Solid state Laser

Fiber LASER

The Gain medium of the fiber is doped with rare-earth ions Er3+, Nd3+, Yb3+, Tm3+, Pr3+

Corning Inc. : Low loss optical fiber (1970)

Dye (Liquid) Laser

A table-top dye laser based on Rhodamine 6G, emitting at 580 nm (yellow-orange). Orange dye solution pumped by a 514 nm argon laser (blue-green).

The wide bandwidth makes them particularly suitable for tunable lasers and pulsed lasers.

http://www.alspi.com/laser.htm

Cutting Welding

Organic/chemical laser

350 nm-thick layer of spiro material on top of a silicon substrate with a series of etched parallel grooves(a grating).

Cheap and tunable with optical pumping

Advanced Materials 17 31 2005

Free electron laser

FELs use a relativistic electron beam asthe lasing medium, hence the term freeelectron. This gives them the widest

frequency range of any laser type, andmakes many of them widely tunable,

currently ranging in wavelength from microwaves, through terahertz radiationand infrared, to the visible spectrum, to ultraviolet, to soft X-rays.

Semiconductor laser (or) Laser Diode

The most commonly used laser today !!

In their simplest form it consistsof a small rectangular slab of

semiconductor material with two cleaved facets to act as mirrors.

1962 4 different groups

simultaneouslyreported !!

A forward biased p-n junction powered by injected electrical current.

Injection laser diodes

Edge emitting lasers

• Double heterostructure lasers

• Separate confinement lasers

• Distributed feedback lasers

1962-1977-after

Edge emittingOR

In-plane lasers

• Quantum well lasers

• Quantum dot lasers

• Quantum wire lasers

Innovative Research and Development over 3 decades

Invention of Surface Emitting Lasers

Prof. Emeritus, Kenichi Iga, 1977Tokyo Institute of Technology

F. Koyama, iNOW-2007, Beijing & Lanzhou, China

Celebrating 30th anniversary of VCSELs !

Comparison between edge emitting VS surface emitting lasers

Active layer volume 60µm3 0.06 µm3

Cavity Length 300µm ≈ 1 µm

Theshold current ≥ mA < µA

Edge emitting lasers Surface emitting lasersFew important parameters

Short-Cavity and Low power consumption causes high performance !!

1 µm = 10-4 cm =1000 nm

H. Li and K. Iga, Vertical Cavity Surface-Emitting Laser Devices, Springer, 2003

Vertical Integration ?

Why surface emitting lasers

Principle of VCSEL

P. L. GourleyNature 371 (1994) 571

Why VCSELs ???

Low power consumptionSmall footprint 2D array integrationWavelength tuning

Wafer level testing

High speed LANOptical interconnectOptical signal processing

Optical sensingHigh power applications

F. Koyama, iNOW-2007, Beijing & Lanzhou, China

Applications of VCSELs

VCSEL Photonics

Datacom

Display

Sensing

Printing

after Novalux

after FujiXerox

after Logitech

Interconnects

after IBM/AgilentF. Koyama, iNOW-2007, Beijing & Lanzhou, China

Mobile PhoneFeaturesFree from EMIHigh speed > 1GbpsLow power consumptionSmall footprint

Optical Interconnections

F. Koyama, iNOW-2007, Beijing & Lanzhou, China

“VCSEL-based Ultra-high Speed Optical Link Technologies”（FY 2006-2011）

VCSEL ArrayLow Power Consumption

Small Footprint

Target：・100Gbps Parallel Link Modules　850nm＆1300nm　wavelength bands・Multi-wavelength Array beyond 100Gbps

（Tokyo Institute of Technology，Fuji Xerox and Furukawa Electric）

Parallel Optical Link

アクセス系LAN

F. Koyama, iNOW-2007, Beijing & Lanzhou, China

International Symposium on Optical CommunicationsNew Green pia Hotel, Tsunan, Niigata, Japan

6th-8th August, 2006

From Left

My selfProf. K. IgaProf. Y. SuematsuProf. F. Koyama

Tokyo Institute of TechnologySuzukakedai Campus

Summer Winter

Part-IIILeadership and Management

Leadership Vs Management

Leader

• Do Right Things

• Coping with Change

• Architects

• Ask why and what?

• Innovative

• Relay on trust

• Long-Range Views

Manager

• Do Things Right

• Coping with Complexity

• Builders

• Ask How and When?

• Administrative

• Relay on Control

• Short-Range Views

Leadership is action, not position.Donald H. McGannon

Marks of a Great LeaderMarks of a Great Leader--11

• Courage and confidence

• Servicing and sacrificing

• Initiating and risk taking

• Needing no credit

• Empowering others

• Clarifying values

• Honest, trustworthy

• Good role model

• Caring

• Committed

Marks of a Great LeaderMarks of a Great Leader--22

To some degree we have all of them!! We must practice these qualities in ourselves if we are to be effective leaders.

• Good listener

• Respectful

• Positive, enthusiastic

• Passionate

Are we born with these qualities or are

they learned behaviors?

The poor man is not he who is without a cent, but he who without a dream. Harry Kemp

http://www.main.nc.us/cartoons/Ihadadream.jpg

Do you have dream??

Scientist

Doctor

Manager

Leader

Teacher

Soldier

Engineer

Conclusions

• India in-brief : Unity in Diversity in the world !!

• Light emitting devices

• LED

• LASER

• Semiconductor LASER

• VCSEL & Optical Communication Applications

• Leadership !!

Acknowledgements

• JSPS, Science Dialogue staff

• Iwata Minami High School SD Organizers

• Prof. Kenichi Iga (JSPS)

• Prof. Fumio Koyama, (Tokyo Tech.)

• Mr. Satoshi Suda, (Tokyo Tech)

• All of you !!