les leds à base de l’oxyde de zinc
TRANSCRIPT
© June 26th 2007
Les LEDs à Base de l’Oxyde de Zinc
D. Rogers : Nanovation & Universite de Technologie de Troyes
F. Hosseini Teherani : Nanovation, France
© June 26th 2007
nanovation
1. Problems with Todays LEDs
2. ZnO vs GaN
3. Nanovation Overview
4. ZnO as a Buffer for GaN
5. ZnO LEDs
6. Future Perspectives
OUTLINE
© June 26th 2007
nanovation
1. Problems with Todays’ WhiteLEDs
© June 26th 2007
nanovationWhite LED Efficiency vs Lighting Alternatives
Commercial
White LED
Source : Compound Semiconductor
© June 26th 2007
nanovationProblems for LEDs in the General Lighting Market
Better Efficiency& Lifetime isNot Enough!!!!
Source : Sandia National Labs
CFL < 10% of general lightingmarket after 20years……
© June 26th 2007
nanovationProblems for LEDs in General Lighting Market
Low Power Rating:• Many LEDs Needed• High Total Cost*
*In $/lm white LEDs cost more than 50x more than incandescent bulbsSource : Compound Semiconductor
© June 26th 2007
Need Very Efficient UV LEDsnanovation
For General Lighting Applications Need:- UV Electroluminescence (EL) : preferably < 350nm- 150 lm/W (Optoelectronics Industry Development Association)
© June 26th 2007
nanovationLED Target Efficiency For General Lighting
Commercial
White LED
OIDA General Lighting Target
Source : Compound Semiconductor
© June 26th 2007
nanovation
2. ZnO vs GaN?
© June 26th 2007
nanovationZnO Publications
N u m b e r o f P u b l i c a t i o n s i n A p p l i e d P h y s i c s L e t t e r s v s Y e a r
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Y e a r
Num
ber
of P
ublic
atio
ns
S iC
ZnO
G a N
© June 26th 2007
nanovationSome Key ZnO Properties
Chen et al.: Materials Science and Engineering B75 (2000) 190–198
GaN and ZnO: very similar
© June 26th 2007
nanovation
3. Nanovation
© June 26th 2007
nanovationProduct : thin films of zinc oxide (ZnO)
Substrate
ZnO
© June 26th 2007
SAW Devices
Top-downPhotonic Crystal
type nanostructures
UV ZnO/GaN LEDsUV GaN/ZnO LEDs
Bottom-upnano ZnO
300nm
UV Homojunction LEDs
© June 26th 2007
Chips
Active Layer
Systemization
Substrate
nanovationPositioning nanovation in the LED Fabrication Chain
Encapsulation
© June 26th 2007
Chips
Active Layer
Systemization
Substrate
nanovationPositioning nanovation in the LED Fabrication Chain
Encapsulation
Lead Product
HIGHERPERFORMANCE
LED
© June 26th 2007
Chips
Active Layer
Systemization
Substrate
nanovationPositioning nanovation in the LED Fabrication Chain
Encapsulation
Follow-up
Products
DISRUPTIVE TECHNOLOGYALLOW LEDs TO ATTACK
LIGHTING MARKET
© June 26th 2007
nanovation
4. ZnO Buffer Layers for GaN
© June 26th 2007
nanovationMain 2 Substrates Currently Used for GaN
Silicon Carbide
Silic on Ca rb ide
- Ele ct rode
+ Ele ct rod e
Ga N p
GaN n
• conducting• opaque• ~ $500 (2 inch)• Cree, Osram
Sapphire
Sa p p h ire
- Ele ct rod e
+ Ele ct rode
Ga N p
GaN n
• insulating• transparent• ~ $40 (2 inch)• Nichia, Toyoda Gosei, Lumileds, Osram
© June 26th 2007
nanovationZnO as a Substrate for GaN: Theory
g
Fukuda et al.: SOXESS ZnO workshop 2003
ZnO � less lattice &thermal mismatch thansapphire or SiC
© June 26th 2007
ZnO as a Substrate for GaN: Theory
Li et al.: Proc. of SPIE (2006)
GaN on ZnO� compressive strain� reduced cracking
© June 26th 2007
c-Al2O3 Substrate
ZnO
nanovationThin Film Growth
PLD
GaN MOVPE
© June 26th 2007
FEG-SEM Image of FIB Cross-section
GaN & ZnO continuousSmooth interface & surface
Pt coating forcharge dissipation
© June 26th 2007
nanovation
So What?
© June 26th 2007
nanovationProblems of Current GaN based LEDs
Substrate electrically & thermally insulating
� Lateral LED� Complex top contacts
Source: Compound Semiconductor, 2006
Top contact issues:� Patent protected� Increased device size
Want GaN on conductingsubstrate
© June 26th 2007
nanovationProblems of Current GaN based LEDs
Substrate electrically &
thermally insulating � Heating
�Current crowding� Dynamic resistance
Want GaN on conductingsubstrate
© June 26th 2007
nanovationSacrificial Etching of ZnO � Chemical Lift-off of GaN
InsulatingSapphire
ZnO
GaN
InsulatingSapphire
GaN
TransparentConductingSubstrate
GaN
Lift-offWafer Bonding
© June 26th 2007
nanovation
Successfully grew wurzite GaN on ZnO/cAl2O3 templates
Achieved chemical lift-off of GaN
Can bond on thermally & electrically conducting substrate
This low-cost approach should allow vertical LEDs with
superior brightness, efficiency & lifetime.
GaN/ZnO Summary
© June 26th 2007
nanovation
5. ZnO LEDs
© June 26th 2007
nanovationSome Key ZnO Properties
Chen et al.: Materials Science and Engineering B75 (2000) 190–198
GaN and ZnO: very similar
ZnO has more Light emitting
potential!
© June 26th 2007
nanovation
6. Future Perspectives
© June 26th 2007
nanovationHistory of Red LEDs � Haitzs’ Law
Source: Physics today & Lumileds
0.001
0.01
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10
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1000
1970 1980 1990 2000 2010
Performance (lm/package)
Per
form
ance
(lm
/pac
kage
)
Year
Cost ($/lm)
& C
ost (
$/lm
)
1.Improving LED Performance 2. Reducing LED Costs
© June 26th 2007
nanovationHaitz Law for GaN White LEDs?
Commercial
GaN LED
Source : Compound Semiconductor
Haitz Law FutureOIDA Target
© June 26th 2007
nanovationZnO Based Future?
Commercial
GaN LED
ZnO LED?
Source : Compound Semiconductor
OIDA Target
© June 26th 2007
High quality 2 inch ZnO epiwafers Now Commercially Available!!
High quality 2 inch ZnO epiwafers Now Commercially Available!!
Now looking for investors & development partners
© June 26th 2007
nanovationPARTNERS