nakamuraWhat Are the Limits for SSL

DOE Solid-State Lighting R&D Workshop, February 2-4, 2010, Raleigh, NC
SSLEC Faculty
Shuji Nakamura -GaN blue LED & laser -Solar cell James Speck -MBE/TEM -LED and Solar Steven DenBaars -MOCVD -LED & Laser -Solar Cell Chris Van de Walle -Elec. Theory -ZnO & Solar Umesh Mishra -Device fab -Solar cells -Power Switching
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Reduction of polarization‐related electric fields – Increased overlap of the electron and hole wave‐ functions – Increased oscillator strength – Ability to employ thicker quantum well design – Reduce emission wavelength blue‐shift with increasing drive current Anisotropic strain inside QWs – Lower hole effective mass – Polarized light emission
What is Light-Emitting Diode (LED)?
WIDE BANDGAP RANGE
6 5 4 GaN 3 SiC(6H) 2 InN d(MgO) 4 AlP GaP GaAs d(sapphire) 4.5 5 5.5 ZnO AlN BN MgS cubic-GaN ZnS MgSe UV ZnSe AlAs InP 6 6.5 blue green red IR Direct Eg Indirect
Pierre Petroff -QDots
Fred Lange -ZnO
Ram Seshadri -inorganic phosphors -high refractive index mtl
Claude Weisbuch Photonic Crystal
Contents 1. Introduction 2. For the High Efficiency of SSL 3. Internal Quantum Efficiency 4. Light Extraction Efficiency 5. Phosphor Quantum Efficiency 6. Efficiency Droop 7. Bulk GaN Growth by Ammonothermal Method 8. Summary
hv
ηint
ηLext =
h+ h+ h+ h+
P / (h ) = Pint / (h )
Usually, the efficiency of LED is regarded as ηEQE
For Luminous Efficacy (ηL) : 200 lm/W
ηint ηLext
Current Status of EQE = 60~95% (1~10A/cm ) ηEQE =50%~75% = 60~80%
ηinj =1
e- e- e-
overflow
e- e- e- ee- e- e-
Pint / (h ) = I /e
# of photons emitted into free space per second # of photons emitted from active region per second
2008 DOE Roadmap 4100K-6500K 70-80 CRI
2015
Current GaN LED EQE Status
Transparent LED
80 70 60
EQE(%)
Roughened, VLED
PSS2
50 40 30 20 10 0 1998 2000 2002 2004 Year 2006 2008 2010
2
1. High Efficient White LED
ηint
ηLext
η Phosphor EQE
a) Non-polar GaN substrate a) Patterned Sapphire Substrate b) Semi-polar GaN substrate b) µCone LEDs c) Photonic Crystals
GaAsP
0.1 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Time (years)
“The Promise” Energy Usage Comparison
LEDs Save 53Watts
60 50 40
Power Used (Watts)
wk.baidu.com
The Power Consumption E26 60W equivalent: 6.9W, 82.6 lm/W E17 40W equivalent: 5.5W The product released on Oct. 21, 2009
Toshiba LED Bulb Lamp
Components of the LED Bulb Lamp
Ban the Light Bulb
• • “Ban the Incandescent Light Bulb” gaining momentum California Legislator Lloyd Levine introduces bill to ban the incandescent light bulb – February 1, 2007 • Australia passes legislation to ban the
L u m in o u s E ffic ie n c y (lm /W )
100
Fluorescent Compact Fluorescent
Cree 186lm/W CCT 4577K in Dec 2009 CRI ??
10
1
AlInGaP/GaP (red, orange) Incandescent bulb AlGaAs/GaAs (red) GaAsP:N (red, yellow) InGaN InGaN (green) (blue) Thomas Edison’s first bulb GaP,Zn:O InGaN (blue) SiC (blue)
light bulb by 2010 – February 21, 2007
• •
EU to ban light bulbs – March 9, 2007 United States
LED CFL
Panasonic LED Bulb Lamp
E26LED bulb Lamp
Dimmer-Compatible 60W-, 40WEquivalent E26. E-17 LED Lamps
60W Bulb Compact Fluor. LED
30 20 10 0
Light Source If a 150 lm/Watt Solid State White LED source was deployed Globally then: We would realize savings of $100 Billion/year Alleviate the need of 380 new power stations!*
Eg(InN)~0.7
1 2.5 3
InN
3.5
Lattice Constant (A)
Roadmap for the SSL at UCSB
Comparison of Luminous Efficacies for Various Light Sources
UCSB SSLEC Roadmap CCT ? CRI ?
Std Flip Chip PSS
GaN LED Historical Development
U
150 lm/W with 3.6V DC 168 lm/W pulsed 193 lm/W with 2.8V, 20mA? CCT 4002K by UCSB in 2007 CRI?? AlInGaP/GaP (red, orange, yellow)
Nonpolar, semipolar GaN: Electrons and holes recombine more efficiently to make light
Advantages of Nonpolar and Semipolar GaN
polar nonpolar semipolar
What Are the Limits for SSL?
Shuji Nakamura
Solid State Lighting and Energy Center Materials and ECE Departments University of California, Santa Barbara
Definitions : External Quantum Efficiency
ηEQE = ηinj(≈ 1) x ηint x ηLext
ηinj = ηint =
fraction of electrons that Recombine in active region
≈1
# of photons emitted from active region per second # of electrons injected into LED per second
LED Package
Natural white: 810 lm, 93 lm/W, CRI = 70, Warm white: 600 lm, CRI=80 The Power Consumption: 8.7W (equivalent 60W incandesent bulb lamp) The product is released on Oct. 16, 2009
Contents 1. Introduction 2. For the High Efficiency of SSL 3. Internal Quantum Efficiency 4. Light Extraction Efficiency 5. Phosphor Quantum Efficiency 6. Efficiency Droop 7. Bulk GaN Growth by Ammonothermal Method 8. Summary
= ηabsorption QE x ηint
a) New Phosphor b) Placement
2. Efficiency Droop (Output Power Saturation) - Auger recombination ∝ n3 - Carrier Overflow ∝ n1
Contents 1. Introduction 2. For the High Efficiency of SSL 3. Internal Quantum Efficiency 4. Light Extraction Efficiency 5. Phosphor Quantum Efficiency 6. Efficiency Droop 7. Bulk GaN Growth by Ammonothermal Method 8. Summary
How to make White Color
White light based on LEDs. - Three dominant ways to produce white light based on LEDs. - Comparison of the spectrum of ideal sunlight with two LED-based white-light sources.
Polar vs. Nonpolar/Semipolar GaN QWs
• Quantum Wells on polar GaN: energy bands distorted, ‘red shift’ of emitted light
Polar (c-plane)
Nonpolar, Semipolar