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Light Emitting Diodes
Outline
- Luminescence Spectra of Atoms
- LEDs. p-n Junction
. Light Outcoupling
- Organic LEDs
- Quantum Dots in LEDs
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Characterization of Organic Illumination SystemsApril 1, 1989,
Hamburgen et a l .
Device Under TestThermocouple Probe
Electrode Separation
Electrode #1 Electrode #2Penetration Penetration
DimensionsininchesElectrode Electrode Electrode#1
Electrode#2
SubjectOrientation Separation Penetration Penetration
BokChoy parallel 0.5 0.5 0.5MandarinOrange parallel 0.38 0.38
0.38Cornichon axial 0.5 0.5 0.5
KosherPickle axial 2.5 1.0 1.5DillPickle axial 2.5 1.0 1.5
Electrode Position:
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p-n Junctions and LEDs
High energy electrons (n-type) fall into low energy holes
(p-type)
p-type n-type
ResistorNot
Shown
Power Source
LED
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p-n Junctions and LEDs
Red
Light Yellow
Emitted Light
EmittedSmall Gap
ENERGY
Large Gap
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ANODE CATHODE
Homojunction p-n Light Emitting Diode
Forward Bias condition
Eg
p-n Diode
INJECTED ELECTRONS
p EC
n EV
npELECTRICITY IN LIGHT OUT
+
INJECTED HOLES
Zero bias condition
Eg
NO CHARGE
p INJECTED(NO LIGHT OUT)EC
nEV
PHOTON EMITTED
VoltageDiode Current Across Diode
TemperatureSaturation
Current in Boltzman
Reverse Bias Constant
CURRENT
Forward
Current
VB
VOLTAGE
Breakdown
Voltage
LeakageCurrent
Avalanche
Current
ReverseVoltage
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Extraction Efficiency of Planar LEDs
critical angle of total internal reflection
Problem: Only small fraction of light can escape from
semiconductor.
Above equation gives < 10% extraction efficiency for typical
III-V.
Trapped
light ray
High-index
semiconductor
EscapeCone
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Image in the Public Domai
ArtificialLightingconsumes8%ofUSenergyand22%ofUSelectricityTheenergycostisestimatedat$50Bannuallyor$200percapita
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INSTALLED EFFICIENCY FRACTION
Incandescent 5% 12%
Fluorescent 20% 62%
HID lamps 25% 26%
White LEDs 35% ----
Note: Electric Motor Efficiency is 85%~90%All Images are in the
Public Domain8
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Survey of Lightbulb Technology Performance(using data from
bulbs.com)
Lum
inescence
Efficiency
[lm/W]
60 65 70 75 80 85 90 95 100
Color Rendering Index
QD VISION
NEXXUS 110V LED
COMPACTFLUORESCENT
HALOGEN
INCANDESCENT
CREE
LR6 LED
CREE
LRP38 LED
OTHER LEDTECHNOLOGIES
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OLED: The Green Display
TV and PC Account for 1% each of US Electricity Usage
Plasma
Power
Usage[W/in2]
0.35 LCD
RPTV
0.30
0.14
OLED
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MIT OpenCourseWarehttp://ocw.mit.edu
6.007 Electromagnetic Energy: From Motors to Lasers
Spring 2011
For information about citing these materials or our Terms of
Use, visit: http://ocw.mit.edu/terms.
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