New Lamps for Old: How LEDs are Revolutionizing Lighting Applications

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New Lamps for Old: How LEDs are Revolutionizing Lighting Applications. New Lamps for Old. Light Emitting Diode. Lighting applications presently consume about 20% of all electricity generated worldwide. Getting Started. What is light? What kind of light can we ‘see’? - PowerPoint PPT Presentation

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New Lamps for Old: How LEDs are Revolutionizing

Lighting Applications

New Lamps for Old

Light Emitting

Diode

Lighting applications presently consume about 20% of all electricity generated worldwide.

Getting Started

• What is light?

• What kind of light can we ‘see’?

• How is light produced?

• How does an incandescent light bulb work?

high energy low energy

Infrared Radiation

Ultraviolet Radiation

Visible Spectrum

Light Spectrum

700 nm

~ 1.8 eV

400 nm

~ 3.0 eV

white light sources

0

200

400

600

800

1000

1200

1400

1600

1800

350 400 450 500 550 600 650 700 750 800 850

wavelength (nm)

inte

ns

ity

incandescent

candle

fluorescent

1/3 mm

reflector cup

red light emitted

LED diesemiconductor

material

gold wire contact

The “gap” energy (Eg) is the key!

Eg = 0 eV metal

Eg > 4 eV insulator

Eg > 4 eV

0 < Eg < 4 eV semiconductor

Eg < 4 eV

UV ~ 3.2 eV ~ 1.9 eV IR

350 nm 750 nm

Emission of Light from a Semiconductor

gE

A.

~30 nm

B.

wavelength

rela

tive

inte

nsity

Semiconductors

F

I

Pb AtAu

B

Al

Ga

In

Tl

C

Si

Ge

Sn

N

P

As

Sb

Bi

O

S

Se

Te

Po

Cl

BrCu

Ag

Zn

Cd

Hg

11 12

13 14 15 16 17

Similar shading indicates complementary pairs that preserve the total valence electron count for AZ stoichiometry.

Band Gap and Periodic Properties

Element Eg , eV (, nm)

C 5.5 (230)Si 1.1 (1100)Ge 0.66 (1900)

-Sn < 0.1 (12,000)

Semiconductors

F

I

Pb AtAu

B

Al

Ga

In

Tl

C

Si

Ge

Sn

N

P

As

Sb

Bi

O

S

Se

Te

Po

Cl

BrCu

Ag

Zn

Cd

Hg

11 12

13 14 15 16 17

Similar shading indicates complementary pairs that preserve the total valence electron count for AZ stoichiometry.

Band Gap and Periodic Properties

Material Eg , eV (, nm)

Ge 0.66 (1900)GaAs 1.42 (890)ZnSe 2.70 (460)CuBr 2.91 (430)

LEDs and Color

In

Ga

N

P

AsGe

Al electrons held tightlyGa P

As electrons held loosely

LEDs from Red to Green

In

Ga

N

P

AsGe

Al

Red

GreenGa P

As

0.0A Z 1.00.2A Z 0.80.4A Z 0.60.6A Z 0.40.8A Z 0.21.0A Z 0.0

Solid Solutions

Periodic Properties ReviewAtomic size As the size of atoms increases, the electrons are held more or less tightly?

 

Electronegativity is defined as the pull or attraction for electrons in a bond.

• From left to right across the periodic table, the electronegativity of atoms ______________.

• From top to bottom down a group of the periodic table, the electronegativity of atoms ______________.

• Arrange the following bonds in order of increasing difference in electronegativity? GaN GaAs GaP

Making Observations and Measurements GaPxAs1–x composition

Measured voltage

GaP0.40As0.60      

GaP0.65As0.35      

GaP0.85As0.15      

GaP1.00As0.00      

Ga0.95In0.05N      

Color emitted

Observations with liquid nitrogen dipping

AcknowledgmentsHope College

Lawrence UniversityAppleton Area School District

NSF-MRSEC

Karen Nordell PearsonArthur Ellis

George LisenskyMike CondrenConnie RoopBrian Bartel

http://www.mrsec.wisc.edu/nano