16. Semiconductor Photon Sources

Electroluminescence devices

Light-emitting diode Semiconductor Laser diode(LED) Semiconductor

optical amplifier(SOA)

(LD)

Evolution of Lighting to LEDs

LUX (lx)?, LUMEN (lm)?, CANDELA (cd)?

Table 19-1Radiometry and Photometryradiometry photometry

watt (W)W/ 2

lumen (lm) l (l )

Radiant flux :I di

: Luminous fluxW/m2

W/srW/(sr.m2)

lux (lx)candela (cd)Cd/m2

Irradiance :Radiant intensity :

Radiance :

: illuminance : luminous intensity: luminance

CIE (International Commission on Illumination)Luminous Efficiency curve555 nm Radiant flux

of 1 Watt at 555 nm is the luminous flux

Luminous Efficiency curve

the luminous fluxof 685 lm (lumen)

Radiant flux of 1 Watt at 610 nm is

th l i fl610 nm

Luminous efficiency V(λ)

the luminous fluxof 342.5 lm (lumen)

610 nm

Photometric unit=

685 x V(λ) x radiometric unit685 x V(λ) 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 1-3Exercise 17.1-3

LED characteristics

Internal efficiencyInternal efficiency

Extraction efficiency

External efficiency

Power-conversion efficiency (or, wall-plug efficiency)

[ ] power ext extP h for h eVIV eV

νη η η ν= = ≈ ≈

Luminous efficiency (lm/W)

{ } { }/ 685 ( ) 685 ( )lm W extP hV VIV eV

νη λ η λ= × = ×

Luminous efficiency (lm/W)

Extraction efficiency

( )ic dθ

φ φ∫ ( )0

2

2 sin

2 (1 cos )

c

c

A r rd

r

π φ φ

π θ

=

= −

∫

241

extractAr

ηπ

=

2

1 (1 cos )21 (1 1 1/ )

c

n

θ= −

= − −

2

(1 1 1/ )21

4

n

n

= − −

≈

1.9 % for 3.6 (GaAs)extract nη ≈ =

4n

4 % for 2.5 (GaN)extract

n≈ =

Extraction efficiency

Spatial pattern of emitted light

Extraction efficiency

Photonic Crystal-LEDs

Baba

Limited by surface recombination

Good scheme!!!

Limited by surface recombination

Good scheme!!!

Lumiled

100 um device size achievable.Several layer of PC for extraction.

Good internal quantum efficiency N d d ( 90%)

100 um device size achievable.Several layer of PC for extraction.

Good internal quantum efficiency N d d ( 90%)Needed (>90%).

Multiple pass limits device size (~10um).

Small volume needed.Not so good for lighting

Needed (>90%).Multiple pass limits device size (~10um).

Small volume needed.Not so good for lightingNot so good for lighting.

Surface recombination limited

Surface recombination limited.

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 재결합하여 여기자를 형성하고, 형성된 여기자로 부터의 에너지에 의해 특정한 파장의 빛이 발생하는 현상을 이용한자체 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 )• 넓은 시야각. (일반 브라운관 같이 바로 옆에서 보아도 화질이 변하지 않음.)

• 빠른 응답속도. 텔레비전 화면 수준의 동화상 재생에도 자연스러운 영상을 표현. (LCD의 약 1,000배 )

• 초박, 저전력. 백라이트라 필요 없기 때문에 저소비전력(약 LCD의 ½ )과 초박형(약 LCD의 1/3 )이 가능.

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 - expensiveg p• Moisture can damage OLED

Resonant-cavity LEDs (RC-LEDs)

RCLED spectrum

Semiconductor optical amplifiers (SOA)

forward-biasedheavily dopedp-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 Injected carrierconcentration Narrower

active region (l)

(Double)Heterostructures

active region (l)is important

l

Microcavity lasers

VCSEL

Quantum Cascade Lasers

QCL

QCL

QCL

QCL