Grundlagen der LED Technik

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www.osram-os.com Grundlagen der LED Technik Dr. Berthold Hahn 8.3.

1 Grundlagen der LED Technik Dr. Berthold Hahn Ilmenau 1 Dateienname ORG CODE Initiale Titel/Veranstaltung TT/MM/JJJJ

2 Grundlagen der LED Technik 1. Einführung 2. Lichterzeugung im Halbleiter 3. Weisses Licht 4. Zusammenfassung 2

3 Key Markets of OSRAM Opto Semiconductors Automotive Consumer Forward Lighting Safety Projection Tablets I Monitors I TV Industry General Lighting Video Walls Transportation Outdoor Lighting Residential Lighting 3

4 Potential of today s lighting technologies LED is already the most efficient technology * 4

5 Drivers for LED adaption 5

6 Incandescent and Semiconductor Light Sources 40% 60% 6

7 Semiconductors and LEDs: an introduction pn-junction n-doped p-doped 7

8 Semiconductors and LEDs: an introduction pn-junction n-doped p-doped - + Applying E-field 8

9 Semiconductors and LEDs: an introduction pn-junction n-doped p-doped Energy = Light - recombination + Applying E-field Wavelength is defined by band gap energy Egap=hc/l; 2,8eV=445nm Material defines wavelength!!! Voltage Egap =2,8V at 445nm (blue) 9

Material systems for high brigthness LEDs 4,0 3,5 3,0 2,5 2,0 1,5 1,0 6,2 SiC AlN GaN InN InGaN 13 27.0 Al Aluminium 3p 1 31 69.

10 Material systems for high brigthness LEDs 4,0 3,5 3,0 2,5 2,0 1,5 1,0 6,2 SiC AlN GaN InN InGaN Al Aluminium 3p Ga Gallium 4p In Indium 5p N Nitrogen 2p P Phosphorous 3p 3 AlP Ga P 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 6,5 lattice parameter [A] InGaAlP GaAs InP

11 The Green Gap Efficacy Gap (520 nm nm) between InGaN and InGaAlP InGaN max. Efficiency max. Efficacy ~ 420 nm ~ 530 nm Loss of Efficiency: Efficiency (l) Vf(l) ~ const InGaAlP max Efficiency > 615 nm max. Efficacy > 615 nm Loss of Efficiency: Carrier Confinement 11

12 Epilayer design: substrate buffer layer (Al)GaN:Si InGaN-QWs GaN-barriers electron blocking Layer AlGaN:Mg n-gan:si p-gan:mg TEM image 20 nm n-side (1-2 µm) active layer (30 nm) growth direction p-side (300 nm) 12

13 InGaN LED: Model optical output power [a.u.] E-3 Model of MQW LED: 1E-5 1E-5 1E-4 1E I n 1 I n 2 n = carrier density Current Density [ka/cm²] I n 3 e Piezo-Electric Fields Radiative Recombination (~n²) Non-Radiative Recombination (~n) Auger Losses (~n³) ee e Conduction Band n Valence Band e p p E [a.u.]

14 Brightness Temperature Stability: Root Cause Current Dependence: Internal Quantum Efficiency Ldom=440nm non-radiative Losses T-dependent! Droop T-independent! typical operating conditions IQE: Small Current = Operating C 14

15 B10 and B50 for different temperatures (100mA(350MA) 100,0% 95,0% 90,0% 85,0% 80,0% 75,0% 70,0% 65,0% 60,0% Tj=55 C Tj=85 C Tj=125 C Tj=150 C 55,0% 50,0%

16 B10 and B50 for different temperatures (10mA/350mA) 100,0% 95,0% 90,0% 85,0% Tj=55 C Tj=85 C Tj=125 C 80,0% 75,0% 70,0% 65,0% 60,0% 55,0% 50,0%

17 ThinGaN principle 2 extraction cones (8% of radiation) 1. thin active layer (optically thin) 2. highly reflective mirror 3. rough or tapered surface: angles of total internal reflection are randomized by the surface structure 17

Todays chip architectures Reduce Chip cost and efficiency due to

Intransparent substrate Contact Light emission Thin film Thin

sapphire like chips UX3 UX3 - Thinfilm - Larger wafer size and

GaN on Si) offers strong cost-down potential Sapphire UX3 - Can

18 Todays chip architectures Reduce Chip cost and efficiency due to improvement of technology Epi Transparent substrate Intransparent substrate Contact Light emission Thin film Thin film flip-chip Flip-chip (w/o laser lift-off) Sapphire and sapphire like chips UX3 UX3 - Thinfilm - Larger wafer size and substitution of sapphire as wafer material (e.g. GaN on Si) offers strong cost-down potential Sapphire UX3 - Can sapphire technology follow the trend to larger substrates? Si as growth substrate is an absorber. 18

e (mw) - blue 350mA UX:3 Brightness Record Evolution 800 700 600 500 400 300 200 100 ThinGaN 350mA; 1mm chip UX:3 9/2004 2/2011 6/2008 WPE 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0 200 400 600

19 e (mw) - blue 350mA UX:3 Brightness Record Evolution ThinGaN 350mA; 1mm chip UX:3 9/2004 2/2011 6/2008 WPE 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% I (ma) WPE IQE 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% IQE 706mW blue at 350mA at 60% WPE and 83% IQE demonstrated! Optimization program for record values: Epi: - optimized growth condiions Chip: - elimination of absorbers & increase of active area Package: - Reduced light absorption & extraction from package 19

20 Brightness 2mm² compared to 1mm² 180MCd/m² 20

21 Sunlight: The Ultimate Benchmark Source: Alex Ryer, Light measurement handbook 21

22 White Light from LEDs Multiple Chips nm blue chip + converter nm UV chip + converters UV- Chip nm

23 White Light from LEDs Multiple Chips nm blue chip + converter Converter e.g. Phosphor nm UV chip + converters UV- Chip nm

24 White Light by Phosphor Conversion 24

25 Efficacy includes eye sensitivity brightness measure 1000 Eye response curve max.555 nm / 682 lm/w 100 lm / W 10 ultra white warm white Standard White wavelength Efficacy strongly depends on color temperature and color coordinates 26

26 Corresponding Color Temperature (CCT) CCT = 6500 K CCT = 4000 K CCT = 3000 K CCT = 2700 K 27

27 Color Rendering Index CRI Sunlight CRI = 100 Lumilux De Luxe CRI > 90 Lumilux CRI > 80 Halophosphate CRI > 70 Sodium Low Pressure Lamp CRI < 20 28

28 LED Phosphors Different solutions for different applications 29

CRI >90 achievable with extremely high efficacy and very crisp light Technical

29 Light Quality = Color Quality Can we do better? Brilliant Mix Mixing of phosphor-converted mint with direct-emitting red LED + CRI >90 achievable with extremely high efficacy and very crisp light Technical challenges: Light mixing Good color steering Temperature compensation reduced color rendering for CCT >4000 K 30

30 Brilliant Mix: What s new? Brilliant Mix plus ~ 6000 K Tuneable white with arctic white Any CCT value within 2700 K 3000 K, CRI K, CRI 90 31

Simulated Losses in Oslon Race & GD+ @ T=25 C GD+, 3000K,

31 Simulated Losses in Oslon Race & T=25 C GD+, 3000K, Sunrise, LRI CLC, ThinGaN (No, Ldom 444nm, 554mW blue, Ie~ 101, Uf=3,17V) OSLON Race, 3000K, Eos, HRI CLC, Lens 150 LRI, TiO2 25%, UX:3 (Ldom 447nm, I 350mA, Uf=3V, IQE 69.1%)

32 LED - challenges LEDs are semiconductor devices; they need cooling < 200 C LEDs emit only visible light LEDs are diodes non ohmic behavior LEDs are DC LEDs are low voltage/high current LEDs output is highly adjustable standardisation difficult High investment cost for LED systems 33

33 LED - Providing Unique Advantages - Performance, Reliability, Features! High energy efficiency LED efficacies of more than 110 lm/w High system efficiency (directional light) % luminaire efficiency Light where you need it, when you need it! Cold light Long lifetime More than 50,000 hrs of life Design & Aesthetics Freedom of design, high functionality Quality of Light Color quality, component quality and reliability Control: Low voltage, fast switching, instant on 34

34 Thank you for Thank you attention We Shape the Future of Light join 35

High Transmittance Ti doped ITO Transparent Conducting Layer Applying to UV-LED. Y. H. Lin and C. Y. Liu

High Transmittance Ti doped ITO Transparent Conducting Layer Applying to UV-LED Y. H. Lin and C. Y. Liu Department of Chemical Engineering and Materials Engineering, National Central University, Jhongli,