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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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9/29SSLECDOE Solid State Lighting MYP March 2011

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

5/6/11 16

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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)