16. Semiconductor Photon Sources Electroluminescence devices Light-emitting diode Laser diode Semiconductor (LED) (LD) optical amplifier (SOA) Evolution of Lighting to LEDs LUX (lx)?, LUMEN (lm)?, CANDELA (cd)? RadiometryTable 19-1 and Photometry radiometry photometry Radiant flux : watt (W) lumen (lm) : Luminous flux IdiIrradiance : W/m2 l(l)lux (lx) : illuminance Radiant intensity : W/sr candela (cd): luminous intensity Radiance : W/(sr.m2) Cd/m2 : luminance CIE (International Commission on Illumination) Luminous Efficiency curve Radiant flux 555 nm of 1 Watt at 555 nm is the luminous flux of 685 lm (lumen) Luminous efficiency V(λ) Radiant flux 610 nm of 1 Watt at 610 nm is the lum inous fl ux of 342.5 lm (lumen) Photometric unit = 685 x V(λ)x) x radiometric unit Ex) 100 lm/W means, At Green ~ 100/680 ~ 15 % At Blue/Red ~ 100/340 ~ 30% (If QE ~ 100%) Semiconductor Light for Visualization Osram SID 2004 Semiconductor Light for Illumination Osram SID 2004 LED Roadmap for Automotive Osram SID 2004 LED characteristics + - Forward voltage for LEDs 증명! Exercise 17. 1-3 LED characteristics Internal efficiency Extraction efficiency External efficiency Power-conversion efficiency (or, wall-plug efficiency) Phν ηηην== ≈ []for h ≈ eV powerIV ext eV ext Luminous efficiency (lm/W) Phν η =×={}685VV (λη ){} 685 × ( λ ) lm/ WIV ext eV Extraction efficiency θc A = 2sπφφ(rrinφφ) d ∫0 2 =−2(1cos)πθr c A η = extract 4π r 2 1 = (1− cosθ ) 2 c 1 =−−(1 1 1 /n2 ) 2 1 ≈ 4n2 ηextract ≈=1.9 % for n 3.6 (GaAs) ≈=4 % for n 2.5 (GaN) Extraction efficiency Spatial pattern of emitted light Extraction efficiency Photonic Crystal-LEDs Limited by surface recombination Baba Good scheme!!! 100 um device size achievable. Several layer of PC for extraction. Lumiled Good internal quantum efficiency Ndd(90%)Needed (>90%). Multiple pass limits device size (~10um). Small volume needed. Not so good for lighting. Surface recombination limited Surface recombination limited. Noda OLED (Organic Light Emitting Diode) OLED는 유기물(단분자/저분자 또는 고분자) 박막에 양극과 음극을 통하여 주입된 전자와 정공이 재결합하 여 여기자를 형성하고, 형성된 여기자로 부터의 에너지에 의해 특정한 파장의 빛이 발생하는 현상을 이용한 자체 발광형 디스플레이 소자. • 자체 발광형. (어두운 곳이나 외부의 빛이 들어 올 때도 시인성이 좋은 특성을 갖음.) • 넓은 시야각. (일반 브라운관 같이 바로 옆에서 보아도 화질이 변하지 않음.) • 빠른 응답속도. 텔레비전 화면 수준의 동화상 재생에도 자연스러운 영상을 표현. (LCD의약1,000배 ) • 초박, 저전력. 백라이트라 필요 없기 때문에 저소비전력(약 LCD의 ½ )과 초박형(약 LCD의 1/3 )이가능. OLED Structure • 100 – 500 nanometers thick Organic LEDs (OLEDs) Discovered by Ching Tang and Van Slyke at Eastman Kodak in 1987. OLED 제품 But, OLEDs are … • Life time – blue organics have shorter life time compared to red and green • Manufacturing -expensive • Moisture can damage OLED Resonant-cavity LEDs (RC-LEDs) RCLED spectrum Semiconductor optical amplifiers (SOA) forward-biased heavily doped p-n junction If the intraband relaxation time is much shorter than the interband relaxation time, a steady-state population inversion between the bands may be established. Optical Pumping Electric-Current Pumping Heterostrctures (Double) Injected carrier Heterostructures concentration Narrower active region (l) is important l Microcavity lasers VCSEL Quantum Cascade Lasers QCL QCL QCL QCL.