Inkohärente Lichtquellen Sommersemester 2010 Uli Engelhardt und Kai Kruse Outline 1. 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 History 1907: H. J. Round of Marconi Labs discovered that some inorganic substances glow if a electric voltage is impress on them.

1927: The russian Oleg Vladimirovich Losev independently reported on the creation of an LED, but no practical use was made of the discovery.

1961: Bob Biardand and Gary Pittman (Texas Instruments) find out that arsenide (GaAs) give off infrared radiation when electric current is applied. They receive a patent for this diode. 1. Introduction: Light Emitting Diodes History 1962: First visible red GaAsP-LEDs was developed by Nick Holonyak ("father of the light-emitting diode”) at General Electric Company. 1971: The first blue LEDs (GaN) were made by Jacques Pankove at RCA Laboratories. Too little light output to be 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 energy. 1. Introduction: Light Emitting Diodes Principle Color Wavelength (nm) 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 < 400 e.g.: AlN AlGaN 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/ Disadvantages  Efficiency High initial price  Direct colour generation Temperature dependence  Small size Current-regulated power supplys  Fast switch time Colour rendering  Frequent on-off cycling  Easy dimming  Cool light without IR  Long lifetime  Shock resistance  Parallel ray emission  No mercury needed 2. UV - LEDs Different Types Blue-LEDs, λ 400 - 500 nm UV-LEDs, λ < 400 nm

• Zinc selenide (ZnSe) • Diamond (235 nm) • gallium (InGaN) • Boron nitride (215 nm) Group III- • Indium (InGaN) • AlN (210 nm) • AlGaN • AlGaInN (210 nm) 2. UV - LEDs Applications  Adhesive hardening  Lacquer hardening (ink-jet-printer)

 Quality control scratch-resistant coating of a diffusion disc

bank note control Ink-jet-printer 2. UV - LEDs Applications  Sterilisation/ Disinfection (water, air, …)  Medical technology (dermatology, light therapy)  Organic analytics (fluorescence microscopy)

Drinking water sterilisation Bottle cap 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 Details • Electron movement confined: 3D -> 2D • Sandwich layers of Well (AlGaN) & Barrier (AlN) • Wavelength tunable by semicond. composition and layer thickness (2-10 nm)

„Blue shift“ of emission 3. AlGaN UV - LEDs Development/ outlook

 Heat sinking: Output and lifetime limit

 DUV-LED → DUV : 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 Realized Using 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 emitting diodes, M. Khizar et al, Semicond. Sci. Technol. 22 (2007) 1081-1085