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New Lamps for Old: How LEDs are Revolutionizing Lighting Applications
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
