Les LEDs à Base de l Oxyde de Zinc D. Rogers : Nanovation & Universite de Technologie de Troyes F. Hosseini Teherani : Nanovation, France

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1 Les LEDs à Base de l Oxyde de Zinc D. Rogers : Nanovation & Universite de Technologie de Troyes F. Hosseini Teherani : Nanovation, France OUTLINE 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

2 1. Problems with Todays White LEDs White LED Efficiency vs Lighting Alternatives Source : Compound Semiconductor Commercial White LED

3 Problems for LEDs in the General Lighting Market CFL < 10% of general lighting market after 20 years Better Efficiency & Lifetime is Not Enough!!!! Source : Sandia National Labs Problems 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 bulbs Source : Compound Semiconductor

4 Need Very Efficient UV LEDs For General Lighting Applications Need: -UVElectroluminescence (EL) : preferably < 350nm lm/w (Optoelectronics Industry Development Association) LED Target Efficiency For General Lighting Source : Compound Semiconductor OIDA General Lighting Target Commercial White LED

5 2. ZnO vs GaN? ZnO Publications Number of Publications in Applied Physics Letters vs Year Number of Publications SiC GaN ZnO Year

6 Some Key ZnO Properties GaN and ZnO: very similar Chen et al.: Materials Science and Engineering B75 (2000) Nanovation

7 Product : thin films of zinc oxide (ZnO) ZnO Substrate SAW Devices 300nm Bottom-up nano ZnO Top-down Photonic Crystal type nanostructures UV Homojunction LEDs UV ZnO/GaN LEDs UV GaN/ZnO LEDs

8 Positioning in the LED Fabrication Chain Systemization Encapsulation Chips Active Layer Substrate Positioning in the LED Fabrication Chain Systemization Encapsulation Chips Active Layer HIGHER PERFORMANCE LED Lead Product Substrate

9 Positioning in the LED Fabrication Chain Systemization Follow-up Products Encapsulation DISRUPTIVE TECHNOLOGY ALLOW LEDs TO ATTACK Chips LIGHTING MARKET Active Layer Substrate 4. ZnO Buffer Layers for GaN

10 Main 2 Substrates Currently Used for GaN Silicon Carbide conducting opaque ~ $500 (2 inch) Cree, Osram Sapphire insulating transparent ~ $40 (2 inch) Nichia, Toyoda Gosei, Lumileds, Osram + Electrode Ga N p GaN n + Electrode Ga N p GaN n - Electrode Silic on Ca rb ide Sapphire - Electrode ZnO as a Substrate for GaN: Theory g ZnO less lattice & thermal mismatch than sapphire or SiC Fukuda et al.: SOXESS ZnO workshop 2003

11 ZnO as a Substrate for GaN: Theory Li et al.: Proc. of SPIE (2006) GaN on ZnO compressive strain reduced cracking Thin Film Growth GaN MOVPE ZnO PLD c-al 2 O 3 Substrate

12 FEG-SEM Image of FIB Cross-section Pt coating for charge dissipation GaN & ZnO continuous Smooth interface & surface So What?

13 Problems 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 conducting substrate Problems of Current GaN based LEDs Substrate electrically & thermally insulating Heating Current crowding Dynamic resistance Want GaN on conducting substrate

14 Sacrificial Etching of ZnO Chemical Lift-off of GaN GaN Lift-off Wafer Bonding ZnO GaN GaN Insulating Sapphire Insulating Sapphire Transparent Conducting Substrate GaN/ZnO Summary Successfully grew wurzite GaN on ZnO/cAl 2 O 3 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.

15 5. ZnO LEDs Some Key ZnO Properties GaN and ZnO: very similar Chen et al.: Materials Science and Engineering B75 (2000) ZnO has more Light emitting potential!

16 6. Future Perspectives History of Red LEDs Haitzs Law 1.Improving LED Performance 2. Reducing LED Costs 1000 Performance (lm/package) Cost ($/lm) & Cost ($/lm) Performance (lm/package) Year Source: Physics today & Lumileds

17 Haitz Law for GaN White LEDs? Source : Compound Semiconductor OIDA Target Haitz Law Future Commercial GaN LED ZnO Based Future? Source : Compound Semiconductor OIDA Target ZnO LED? Commercial GaN LED

18 High quality 2 inch ZnO epiwafers Now Commercially Available!! Now looking for investors & development partners PARTNERS