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