Inkohärente Lichtquellen Sommersemester 2010 Uli ... · 3. AlGaN UV - LEDs Technical Details ......
Transcript of Inkohärente Lichtquellen Sommersemester 2010 Uli ... · 3. AlGaN UV - LEDs Technical Details ......
Inkohärente Lichtquellen
Sommersemester 2010
Uli Engelhardt und Kai Kruse
Outline1. Introduction: Light Emitting Diodes History
Principle/ assembly
Applications
2. UV - LEDs Different types
Applications
3. AlGaN UV - LEDs Technical Details
Development/outlook
1. Introduction: Light Emitting Diodes
History1907: H. J. Round of Marconi Labs discovered that some
inorganic substances glow if a electric voltage isimpress on them.
1927: The russian Oleg Vladimirovich Losev independentlyreported on the creation of an LED, but no practical usewas made of the discovery.
1961: Bob Biardand and Gary Pittman (Texas Instruments) findout that gallium arsenide (GaAs) give off infraredradiation when electric current is applied. Theyreceive a patent for this diode.
1. Introduction: Light Emitting Diodes
History1962: First visible red GaAsP-LEDs was developed by Nick
Holonyak ("father of the light-emitting diode”) at GeneralElectric Company.
1971: The first blue LEDs (GaN) were made by JacquesPankove at RCA Laboratories. Too little light output tobe of much practical use.
1993: Shuji Nakamura (Nichia Corporation) demonstrates the first high-brightness blue LED based on InGaN.
Blaue LEDs aus InGaN
1. Introduction: Light Emitting Diodes
Principle LED consists of a chip of
semiconducting material with a p-n junction.
As in other diodes, current flows easily from the p-side (anode) to the n-side (cathode), but not in the reverse direction.
At the barrier layer electrons and holes recombinat and energy in the form of a photon is emitting.
The wavelength of the light, depends on the band gap energy.
1. Introduction: Light Emitting Diodes
Principle
Color Wavelength (nm) Semiconductor Material
Infrared > 760 e.g.: GaAs, AlGaAs
Red 610 - 760 e.g.: AlGaAs, AlGaInP
Orange 590 - 610 e.g.: GaAsP, GaP
Yellow 570 - 590 e.g.: GaAsP, GaP
Green 500 - 570 e.g.: InGaN, GaN
Blue 450 - 500 e.g.: ZnSe, InGaN
Ultraviolet < 400 e.g.: AlNAlGaN
AlGaInN
1. Introduction: Light Emitting Diodes
Assembly
different LED types
1. Introduction: Light Emitting Diodes
Applications
Illumination with high brightness
Visual signal application
Automotive lighting
Optical measurement systems
Flashlights
LCD Backlit Screens
Grow lights
1. Introduction: Light Emitting Diodes
Advantages/ DisadvantagesHigh initial price
Temperature dependence
Current-regulated power supplys
Colour rendering
Efficiency
Direct colour generation
Small size
Fast switch time
Frequent on-off cycling
Easy dimming
Cool light without IR
Long lifetime
Shock resistance
Parallel ray emission
No mercury needed
2. UV - LEDs
Different TypesBlue-LEDs, λ 400 - 500 nm
• Zinc selenide (ZnSe)
• Indium gallium nitride (InGaN)
• Indium gallium nitride (InGaN)
UV-LEDs, λ < 400 nm
• Diamond (235 nm)
• Boron nitride (215 nm)
• AlN (210 nm)
• AlGaN
• AlGaInN (210 nm)
Group III-nitrides
2. UV - LEDs
Applications Adhesive hardening
Lacquer hardening (ink-jet-printer)
Quality control
bank note control
Ink-jet-printer
scratch-resistant coating of
a diffusion disc
2. UV - LEDs
Applications Sterilisation/ Disinfection (water, air, …)
Medical technology (dermatology, light therapy)
Organic analytics (fluorescence microscopy)
Bottle cap sterilisationDrinking water sterilisation
2. UV - LEDs
Applications Convert light from a blue or UV LED to
broad-spectrum white light
2. UV - LEDs
Comparison UV-LED and low pressure vapour Hg-Lamp
Efficiency: 5-10 % (LED)
40% (Hg-Lamp)
Life-time: > 10.000 hours (LED)
8.000 hours (Hg-Lamp)
LEDs are environmentally friendly than Hg-Lamps
LEDs need no warm up, they are ideal for use in applications that are subject to frequent on-off cycling
3. AlGaN UV - LEDs
Technical Details
Output power 0.1 to 10 mW range Efficiency of max 10% Sharp spectrum due to qantum well Cw and pulsed operation
3. AlGaN UV - LEDs
Technical Details
Semiconductor compound• Increasing Al concentration decreases wavelength• AlGaInN: more degrees of freedom for bandgap and lattice constant, helps growth, increases radiative efficiency but lowers wavelength
3. AlGaN UV - LEDs
Technical DetailsQuantum well• Electron movement confined: 3D -> 2D• Sandwich layers of Well (AlGaN) & Barrier (AlN)• Wavelength tunable by semicond. compositionand layer thickness (2-10 nm)
„Blue shift“ of emission
3. AlGaN UV - LEDs
Development/ outlook Heat sinking: Output and lifetime limit
DUV-LED → DUV Laser Diode: challenging
Wavelength: Theoretical limit is 205nm
Fabrication: Quality + mass production
Increase efficiency: layer processing,
reduce resistive losses
Multiple chip packing: 11mW @ 280nm
Thank you for your attention!
Sources: www.lightemittingdiodes.org
Wikipedia: Light-emitting Diode (english) http://en.wikipedia.org/wiki/Led#Ultraviolet_and_blue_LEDs
AlGaN Deep-Ultraviolet Light-Emitting Diodes, Jianping ZHANG et al, Japanese Journal of Applied Physics Vol. 44, No. 10, 2005, pp. 7250–7253
227nm AlGaN Light-Emitting Diode with 0.15mW Output Power RealizedUsing a Thin Quantum Well and AlN Buffer with reduced Threading Dislocation Density, Hideki Hirayama et al, Applied Physics Express 1 (2008) 051101
Improved local thermal management of AlGaN-based deep-UV light emittingdiodes, M. Khizar et al, Semicond. Sci. Technol. 22 (2007) 1081-1085