郭政達 e-mail: max_kuo@epistar.com.tw 從磊晶看LED發光效率 郭政達 e-mail: max_kuo@epistar.com.tw

Outline LED照明未來預估與市場規模 高功率磊晶技術發展解析 LED發光效率演進動向

Market Demand $20X75/1000=$1.5 (3W)

Luminaire Efficiency 2006 March 2006

Luminaire Efficiency 2006 March 2007

Nichia’s white LED EQE(68%) Nichia’s achieves 150 lm/W white LED (Dec. 2006) Epistar’s blue LED EQE(50%, in production, 58% R&D best performance)

Luminaire Efficiency Source: Multi-year program plan FY’08-FY’13 (DOE)

Lighting Market Source: Nov. 2007 亞洲電子科技雜誌

Only Performance Better Performance for Small LED?

Summary Power LED Small LED High Efficiency High Lumens/Package Low Current Application Flexible Module Design Higher Chip Process Yield Simply Package Structure High Lumens/Package High Current Application Lower Chip Process Yield Complex Package Structure for Heat Dissipation

Application

White LED Performance Improvement 2000 2005 2010 2015 2020 200 150 100 50 Efficacy (lm/W) Japan 21 OIDA / US DOE Production level Lab. level Incandescent / Halogen Compact fluorescent Tube fluorescent HID Source: Nichia/Cree Year White LED @ 20 mA White LED @ 300 mA

Lighting efficacy 40 lm/W Optical Efficiency HID: 100 lm/W 40% Utilization Efficiency Lighting efficacy 40 lm/W 80% Utilization Efficiency 2005 LED: 50 lm/W

Outline LED照明未來預估與市場規模 高功率磊晶技術發展解析 LED發光效率演進動向

磊晶機台簡介 MOCVD (Metal Organic Chemical Vapor Deposition) 有機金屬化學氣相沉積

MOCVD製程上膜形成過程 (i)反應氣體或反應元素因熱裂解由邊界層(boundary layer)向基板表面輸送氣相擴散，入射原子衝撞基板，一部分被反射，其他吸附於基板上。 (ii)基板表面吸附表面擴散，吸附原子於基板表面上擴散，產生原子間之二次衝撞而形成團簇(cluster,原子集合體)，或只在表面上停留某段時間後，再度蒸發解析脫離。 (iii)表面反應，核形成團簇反覆與表面擴散原子衝撞或以單原子再釋出，而當原子數超過某一臨界值後開始成長，與鄰接之團簇聚合而成連續膜，大多為三維團簇，但以二維團簇方式成長情形也有。 (iv)反應生成物之蒸發解析脫離。 (v) 脫離之反應生成物向外擴散（out diffusion)(氣相擴散)。 邊界層 供給 排氣 原料 (i)輸送 (氣相擴散) (ii)吸附 表面擴散 (iii)反應，核形成 horizontal gas flow (iv) 解析脫附 (v) 向外擴散

MOCVD反應原理 何謂MOCVD Ⅲ 族的(CH3)3Ga TMGa (三甲基鎵) 、(CH3)3In TMIn (三甲基銦)等，與Ⅴ族特殊氣體如：AsH3 (arsine) 砷化氫、PH3 (phosphine)磷化氫、NH3等，通過特殊載體氣流送到高溫的GaAs晶片、人造藍寶石等晶片上，在Reactor反應器內的高溫下，這些材料發生化學反應，並使反應物沉積在晶片上，而得到磊晶片上形成一層半導體結晶膜，這樣就能做成半導體發光材料，如發光二極體等 基本化學式： 四元TMGa(g) + AsH3(g) → GaAs(s) +CH4(g) 藍光TMGa(g) + NH3(g) → GaN(s)+CH4(g)+N2(g)+H2(g) MOCVD技術與機台的設計，應用,延伸問題包涵多種學問與原理： 物理、化學、數學、流體力學、熱力學、機械力學、材料學及電磁學等等 Recipe x MOCVD機台 = 磊晶結果

MOCVD設備及系統 Cooling supply 電控系統 E -Control unit power Cooling unit Safety control system 反應腔 Reactor Cooling unit Control computer Heater unit PLC Temp. control unit SLC… Pressure control unit Glovebox 氣體傳輸系統 gas mixing system gas supply 後端管路抽氣系統 Exhaust system Filter Butterfly valve Vacuum Pump 氣體偵測器

MOCVD Reactors – the market

Principle of MOCVD gas blending reactor high purity, precise mixing H , N P=10-200 mbar 2 TMGa, AsH 3 NH TMIn , PH gas blending reactor high purity, precise mixing safety GaAs , InP substrate, T ~ 400 - 1200°C D 100 rpm production oriented low cost of ownership Ga (CH ) + AsH GaAs + 3CH 4 TMAl, sapphire 5 - NH GaN scrubbing system H filter unit vacuum pump throttle valve crystal quality, thickness uniformity, reproducibility

MOCVD growth H N Ga gas phase mass transfer by diffusion CH3 H2 gas phase mass transfer by diffusion boundary layer precursor decomposition -radical H N CH3 Ga CH4 = CH3 + H adsorption CH3 CH3- radical N*+N*=N2 wafer surface surface diffusion and reaction incorporation and growth

MOCVD Growth Criteria Thickness uniformity Composition uniformity Doping concentration uniformity Clean wafer surface On wafer uniformity Wafer to wafer uniformity Run to run stability (reproducibility) Less maintenance (high through-put)

Light Extraction Efficiency

Geometry Effect 1 2 3 4 5 6

Efficiency Droop Problem (IQE) Lm/$ ~ Lm/Package

Recombination Mechanisms

Defect Density Schubert et al. Appl. Phys. Lett. 91, 231114 2007

Piezoeletric Field Effect without piezoelectric field with piezoelectric field I. V. Rozhansky and D. A. Zakheim: phys. stat. sol. (a) 204, No. 1 (2007)

p-MQW LED p n n p I. V. Rozhansky and D. A. Zakheim: phys. stat. sol. (a) 204, No. 1 (2007)

n-p-n LED I. V. Rozhansky and D. A. Zakheim: phys. stat. sol. (a) 204, No. 1 (2007)

Polarization Effect Kim et al. Appl. Phys. Lett. 91, 183507 2007

Polarization Effect Kim et al. Appl. Phys. Lett. 91, 183507 2007

Outline LED照明未來預估與市場規模 高功率磊晶技術發展解析 LED發光效率演進動向

LED發光效率演進動向 Market pull What will happen @ 2 A/mm2? lm/W→ lm/packaged → lm/$ 200 mA/mm2 → 350 mA/mm2 →700 mA/mm2 → 2000 mA/mm2 What will happen @ 2 A/mm2? Current density Heat dispersion Package issue

Current Uniformity – 1 LumiLeds Lighting Nichia

Current Uniformity – 2 Current Uniformity

Thermal Efficiency Lm/$ ~ Lm/Package Source: OIDA / US DOE

Chip Level Improvement Tj = Ta + I * V * Rth ThinGaN Flip Chip

Thermal Resistance Model

Heat Spreading Lm/$ ~ Lm/Package

100W LED Road Test on NTU Campus (3,600lm@37.5lm/W) Dreams Come True 100W LED 400W Mercury 100W LED Road Test on NTU Campus (3,600lm@37.5lm/W)

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