Light Emitting Diode. POSTECH Dept. of Electronic & Electrical Eng.

Transcription

1 Light Emitting Diode

2 Contents 1. History of Lighting 2. What is a Light Emitting Diode (LED) 3. Properties of LED 4. Application of LED 5. PQR

3 1. History of Lighting

4 History of lighting B.C 1000 the first candle gas lighting 1784 Agrand the first lamp relied on research (Lavoisier) Limelight - the first solid-state lighting device (by Thomas Drummond) First paper of LED (1907)

5 History of LED

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7 2. What is a light Emitting Diode (LED)

8 LED (Light Emitting Diode) Impurity doping provides p- and n-type region At forward bias, injected electrons and holes recombine Energy may be released as radiative (light) or non-radiative (heat)

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10 LED fabrication Bulk Substrate Crystal Growth & Machining Epitaxial Deposition Of LED Wafer Fabrication Die Fabrication Final Product Assembly

11 LED materials 현재상용화된 LED 는대부분화합물반도체 대부분 3-5 족,3-3-5 족, 족, 족결합 적색 :AlGaAs, InGaAlP 녹색 : InGaN 청색 : InGaN UV : GaN, InAlGaN IR : GaAs, InGaAs

12 LED materials(blue-green-uv)

13 LED materials(red)

14 External Quantum Efficiency External Quantum efficiency=internal Quantum efficiency x Extraction Efficiency

15 Internal Quantum efficiency : 발광다이오드 (LED) 를통과하는각각의전자에대하여얼마나많은광자가만들어지는가에대한특성값 LED 의 Internal Quantum Efficiency 은반도체물질의품질과활성영역에대한디자인에의해결정 Extraction Efficiency : 이렇게생성된광자가반도체칩밖으로빠져나오는양에대한비율을의미. 반도체와주변물질사이의높은굴절률의차이로인해생성된많은광자들은내부적으로여러번반사를겪게되는데, 이과정을통해다시흡수되기도함. External Quantum Efficiency: Internal Quantum efficiency * Extraction Efficiency

16 Conventional LED Limitation : Very high thermal resistance (>200K/W) Epoxy limited to T~120 Input power limited to <0.1W

17 epoxy All LED, with exception of communication LEDs, are encapsulated with an opticcally transparent Epoxy Refractive index : 1.5 Refractive index contrast between the semiconductor and air is reduced by epoxy Shape of epoxy dome : Hemisphere (angle of incident is always normal) Cylindrical, Rectangular (viewing angle is planar surface normal) Additional function : protection against mechanical and chemical shock (LED dies, bonding wire, two metal leads)

18 LED Structure & Species 1. LED structure 2. Flip chip bonding

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20 Low resistance & high transparancy electrode Transparancy electrode

21 High Power LED Nichia s early high-power LED package has been flip-chip bonding type. High reflective p-electrode by Ag Decrease of absorption of emission light by InGaN layer High heat conductivity with CuW FWHM λ= 10nm, PO= 400 mw, ηext= 24% VF= 4V

22 Lumileds High flux packaging -Temperature increase = red shift, Intensity decrease Reduced LED number Higher brightness Heat problem Low thermal Resistance Silicon encapsulent Good reliability, color uniformity

23 Development trend

24 RCLED RCLED: resonant-cavity light-emitting diode - a light emitting region inside an optical cavity - The resonance wavelength of the cavity coincides or in resonance with the emission wavelength of the light-emitting active region of the LED. - The RCLED is the first practical device making use of spontaneous emission enhancement occurring in microcavities -The light intensity emitted from the RCLED along the axis of the cavity is higher compared with conventional LEDs. ( enhancement factor: 2 ~ 10 )

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26 White LED Method to make White LED : Lighting, backlight unit, medical light 1. R+G+B 2. Blue LED + Yellow Phosphor 3. UV LED + RGB Phosphor

27 3. Properties of LED

28 Photometric 1. Luminous flux: A monochromatic light source emitting an optical power of (1/683) Watt at 555 nm has a luminous intensity of 1 lm :The photometric quantities are related to the corresponding radiometric quantities by the C.l.E. Standard Luminosity Function Km = 683 lm/w X e,λ = radiometric quantity X v = photometric quantity

29 2. Luminous intensity : Cd (lm/sr) : Isotropic dw : solid angle df: Luminance flux anisotropic Luminous efficiency= lm/w(iv), Luminous efficacy= lm/w(radiometric power)

30 3.View angle View Angle describes the spatial intensity distribution and is the difference between the angles corresponding to 50% of the maximum intensity.

31 4. Color matching diagram & CIE Chromaticity diagram Color mathing diagram

32 Color purity = a/(a+b) : color mixing etc CIE Diagram

33 Temperature dependent

34 Spectrum of LED

35 4. Applications of LED

36 Market of LED Mobile appliance : 58% total : $2.1 billion

37 Display & Sign Ex) LED display 성공사례장소 : 뉴옥맨하탄타임스퀘어가든브로드웨이 44 번가 LED 의지향각이 10deg down 된제품사용건너편아래길에서볼수있게함. Wide angle 사용. Color mixing 이잘되도록함

38 Color mixing

39 Color Rendering Index Ra= (1/8) Ri (i :1~8 : test sample) = 100 (ideal illuminant)

40 LED BLU Merit High color rendering index environment No blurring (high response speed) No color filter High contrast ratio Demerit Heat High cost color control

41 Luminous flex per package and lamp price per lumen

42 * 15 급이상 LCD backlight unit 용으로 RGB Multi-chip 채용 * 2004 년다수기업에서시제품제작 - 소니, 삼성, LG * 고연색성필요로하는모니터에우선채용 - 의료용, 그래픽아트용. - CCFL 대비 color gamut 40% 넓음 * 문제점 - 방열기술, 가격, 색상조절

43 ETC.. Traffic light : low electric power consumption.(~80% of lamp) long lifetime (10 times) High brightness (3 times) Major activity in china Saturation in USA 지나친가격경쟁 lamp :

44 Car : high speed response high lifetime freedom of design Mobile : Keypad (Blue,White) Camera flash 소형 LCD BLU

45 Technical Issue 제품의소형화, 슬림화가능 : 칩사이즈0.3 ~ 2 mm 고속응답 : ~ 10-8 초on-off 스위칭 ( 백열등 = 0.15초 ) 장수명 : 5만 ~ 100만시간 (@30% degradation) 고효율 : Up to 55% 외부양자효율 변조가능 : Up to 500 Mbps (w/ GI nm) 온도에따른광특성변화 ( 주로적색LED) 저전력소자 : 백열등대비15% 소비전력 Cold light : No Infrared radiation

46 5. PQR

47 Emission of red (670 nm) PQR laser Emission images and spectrum of the red PQR laser (670nm) PQR emission Intensity (a.u) φ = 15 μm PQR I = 300 μa Intensity (a.u.) 4 2 φ =10μm Wavelength (nm) Δλ nm LED emission Red PQR array wavelength (nm) - The PQR lasing region is brighter than the LED emission region, which means very high emission efficiency of the PQR laser.

48 Red PQR 8x8 array (30 um) emission 5 ua 10 ua 15 ua 20 ua

49 φ = 30 μm I = 0mA (0 μa/cell) φ = 48 μm I = 0mA (0 μa/cell)

50 φ = 30 μm I = 1.5 ma (23 μa/cell) φ = 48 μm I = 1.5 ma (23 μa/cell)

51 φ = 30 μm I = 2 ma (30 μa/cell) φ = 48 μm I = 2 ma (30 μa/cell)

52 Luminous Intensity angle dependent (View angle)- Setup Angle 의변화 50 cm Goniometer ( Neo Light 3000 ) Photometer

53 φ = 48μm, I = 100 ma 0.8 Luminance Intensity (normalized cd) View angle= θ R θ L 0.5 = 130

54 View angle of Red PQR array (φ= 48 μm, 8x8 array) Luminance Intensity (normalized cd) φ = 48μm, I = 200 ma View angle= θ R θ L 0.5 = 118

55 CIE diagram nm 550 nm CIE diagram Red PQR 30 μm 0.6 y nm White 600 nm nm 670 nm 450 nm a a + b ( x x Color purity : = 1 ( x d x ref ref ) ) 2 2 x + ( y + ( y d y ref y ) ref 2 ) 2

56 Luminance Intensity ( Cd ) Photometer Red PQR array ( 8x8 ) 100mm CIE Standard Condition B Circular aperture of area : 100mm2 Distance : 100 mm Equivalent plane angle : 6.5 deg (0.01sr)

57 Result Sample φ= 30 μm S=4.52x10-8 m 2 φ= 48 μm S=1.15x10-7 m 2 20 ma 2.94 mcd 4.73 mcd 100 ma 23.4 mcd 34.8 mcd 200 ma 43.9 mcd 69.6 mcd

58 Total luminance flux ( lm ) Integrating Sphere (NeoLight PL5000) PQR array Photometer 2 m

59 Result Luminance flux φ= 30 μm φ= 48 μm 0.045m m ma 18.3 mlm 83.4 mlm 200 ma 90.5 mlm 798 mlm Luminance efficiency 100 ma 0.1 lm/w 0.44 lm/w 200 ma 0.23 lm/w lm/w

60 Conventional red LED : 약 620 nm, PQR : 670nm : 시각도에서차이 - Conventional LED 와단순비교어려움 Φ lum = 683 lm W λ V ( λ) P( λ) dλ