Post on 08-Apr-2018
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Solid State Lighting
James S. Speck
Materials Department
University of California
Santa Barbara, CA
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Outline
Brief primer on light and lightingImpact of solid state lightingTechnology and economics of solid state lightingHighlights of UCSB efforts in solid state lighting
Special thanks to M. Krames (Soraa) and D. Feezell (UCSB) for slides
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Light and Lighting
First a few definitions (I know its confusing!)
Candela (cd): Luminous intensity from ~1 candle*
Luminous intensity Iv(), radiant intensity I()
includes the human eye response V()!
Iv() = 683 V() I()
Lumen (lm):Luminous flux = Luminous intensity x solid angle
e.g., sphere 4 sr
A candle: 1 cd x 4 sr = 12.6 lm
100 W lightbulb: ~1000 lmi.e, 10 lm/W
*formally: luminous intensity at 555 nm of a source
with a radiant intensity I() of 1.46 x 10-3 W/sr
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Human Eye ResponseDaylight (Photopic Cones)
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More on Light
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More on White Light
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Conventional Light Sources
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LED Retrofit Lamps Today
after Krames, CLEO Presentation, June 2009.
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Lighting Efficiency
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Electricity Consumption in CA by End Use
Lighting accounts for34.5% of electricity consumption in CA!
10
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Impact of Solid State Lighting
US Electricity Use:20-25% for Lighting
2030 Energy Savings from SSL in the U.S.
190 TW-hrs
= 24 GW power plants= 31.4 tons CO2
http://www1.eere.energy.gov/buildings/ssl
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Monocrystalline atomic arrangement determines semiconductor bandgap Specifies optical properties
Impurity doping provides p- and n-type regions At forward bias, injected electrons and holes recombine Energy may be released radiatively (light) or non-radiatively (heat) Fundamentally non-destructive
What is a Light Emitting Diode?
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(Al,Ga)InP system offers red (~650 nm) to yellow (~580 nm) emission (In,Ga)N system offers UV-A (~ 380 nm) to green (~550 nm) emission
III-V Materials Systems for SSL
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UCSBmGaNLED(60millionatomdataset)
InGaNQuantumWells
GaNBarrierLayers
AlGaNEBLnGaN pGaNDopedMg
Real Atomic Scale Structure of an LED!
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Example Approaches to Solid State Lighting
Mixing
Optics
RYGB
LEDs
RYGB White
Mixing
Optics
RYGB
LEDs
RYGB White
Multi-Primary Color Mixing Color tuning option Requires color control Requires color mixing optics
Down-Conversion Materials Typically inorganic phosphors Disadvantage: Stokes shift Advantage: integrated color mixing
after Mueller-Mach et al.,phys. stat. sol. (a) 202, 1727 (2005)
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Largest segment in 2010 was mobile (cell phones, mobile computing, mp3) Fastest growing segment was TV and monitor back lighting General lighting expected to drive the market by 2015 Total available SSL market in 2020: ~$50B - $100B
High Brightness LED Market
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LuminousE
fficacy,
lm/W
Commercial
LEDProducts
27004100K
HID
TUBEFL
COMPACTFL
WHALOGEN
INCANDESCENTW
0
50
100
150
200
2003 2007 2011 2015 2019
Emerging ~ 70-80 lm/W warm white power LEDs (2700-4100K) Expect > 150 lm/W power LED performance in the future
*U.S. Dept. of EnergyMulti-Year Plan
LEDs
Timeline for SSL
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SSL Economics our Sunshot!
SSL Targets for 2020
$1/klm cost
Industry targets$0.50 light engine$0.50 electronics+base+luminaire
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Major GaN SSL Issues: Droop
Kiopakis and Van de Walle, APL 98, 161107 (2011)
Droop major challenge in LEDs
Droop origin: under investigationUCSB theory: indirect Auger
Experimental verification in progress
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Major GaN SSL Issues: Green Gap
New orientations of GaNPioneered at UCSB
Nonpolar and Semipolar
Promise to fill the green gap ultimate RGB solutions for SSL
0%
10%
20%
30%
40%
50%
60%
350 450 550 650
Peak Wavelength (nm)
ExternalQuantumE
fficiency
InxGa1-xN
UV
(AlxGa1-x).52In.48P
C-plane
IWN06By Nichia
SSLDC 2006
By UCSB
Nonpolar
UCSB
SemipolarUCSB
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1m
Major issue in SSL: Light ExtractionRecent UCSB work on Photonic Crystal LEDS
Rough LED PhC LED
Improvement over rough LED:
25% higher EQE 60% higher vertical output
power (directionality effect)
1.6x
3 m
Rangel et al. APL 98, 081104 (2011)
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High-power LEDs Beginning to enter general lighting Commercial LEDs 70-80 lm/W (warm white) Costs are ~ 75 lm/$ (LED) vs. ~ 5 lm/$ (lamp) Compare to ~ 1000 lm/$ (general incand. bulb)
Adoption Generally slow; slower due to high costs Cost reduction breakthrough is key Green trend / legislation will help New markets have helped LED LCD TV Major driver/barrier: cost our Sunshot: $1/klm
Energy efficiency SSL has the promise to reduce global electricity consumption >10% $100B/yr in energy costs, and > 200 M tonnes per yr of CO2
Prospects
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Extra Slides
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Material systems typically III-V compound semiconductor alloys Layer deposition by metal-organic-chemical-vapor-deposition
(MOCVD)
Similar roadmap as for Si-based integrated circuit technology
LUXEON Rebel
after Krames et al., CLEO Presentation, June 2009
LED Fabrication
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Current Light Source Efficiencies
DOE SSL Multi-Year Program Plan: 2009-2015
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[0001][0001]
a-direction
m-direction
c-direction
Figure: Mel McLaurin
P. Waltereit et al, Nature 406, L1329 (2000).
Wurtzite GaN - Polarization
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EmissionWavelength
CrystalOrientation
Outputpowerat20mA
EQE
1413nm (1011) 20.6mW 33.9%
2433nm (1011) 19.7mW 34.4%
3444nm (1011) 16.2mW 29%
4489nm (1122) 9mW 18%
5519nm (1122) 9mW 18.9%
6562.7nm (1122) 5.9mW 13.4%
1. Tyagietal.Jpn.J.Appl.Phys.46(2007)L129.2. Satoetal.(unpublished)3. Zhongetal.Appl.Phys.Le;.90(2007)2335044. Zhongetal.ElectronicsLe;.43(2007)No.15.5. Satoetal.J.LightandVisEnv.Vol32(2)p107110(2008)6. Satoetal.Appl.Phys.Le;.92(2008)22110
0%
10%
20%
30%
40%
50%
60%
350 450 550 650
Peak Wavelength (nm)
ExternalQu
antumE
fficiency
InxGa1-xN
UV
(AlxGa1-x).52In.48P
C-plane
IWN06
By Nichia
SSLDC 2006
By UCSB
Nonpolar
UCSB
Semipolar
UCSB
SignificantimprovementhasbeenmadeintheefficiencyofsemipolarLEDsoverthelasttwoyears
Summary:
SemipolarLEDshavedemonstratedtremendouspotenOalinsolvingthegreengapproblemExperimentstounderstandtheefficiencydroopiscurrentlyinprogressSemipolarLEDscouldpotenOallybeusedfornextgeneraOonredLEDswithimprovedthermalperformance
24.3mW
43.5%
Semipolar LEDs Solution to Green Gap
S f A G N b d LED P f
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State-of-Art GaN-based LED Performance
> 60% peak external quantum efficiency ~ 80% peak internal quantum efficiency Slope efficiency up to 1.7 Watts/amp (blue), but decreases with drive current
after Krames et al., CLEO Presentation, June 2009
O S ff
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Overall System Efficiency
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Cree (2010)