algan uv leds(ann-kathrin nemann) - fh-muenster.de · sources 20 prof. t. jüstel, lecture script...

Ann-Christine Nemann

AlGaN UV-LEDs

Overview

2

LEDs

UV-radiation and UV-LEDs

AlGaN

comparison of AlGaN UV-LEDs and mercury lamps

Ann-Christine Nemann 26.06.2016

LED-light emitting diodes

3

inorganic and organic LEDs

nowadays more efficient than incandescent and fluorescentlamps

Development of LED-light sources


1936 indirect

EL

1961 direct EL

1962 Ga(As,P)

1990 PLED

1993 blue LED

1999 red LED

2010 white LED

LED-light emitting diodesStructures

4 Ann-Christine Nemann 26.06.2016

http://electronics.howstuffworks.com/led3.htm

http://en.wikipedia.org/wiki/File:LED_bulbs.jpg

http://magazin.merck.de/de/Life_and_Quality/LEDs/isiphor1.html

LED-light emitting diodes

5

semiconducting material with a p-n junctioncurrent flow from anode to cathoderecombination of holes and electrons in the junction arealight emissionwavelength of the emitted light depends on the band gap


Working Principle

http://en.wikipedia.org/wiki/File:PnJunction-LED-E.svg

LED-light emitting diodesDifferent Types


colour wavelength (nm) semiconductor material

infrared > 760 GaAs, AlGaAs

red 610 - 760 AlGaAs, AlGaInPorange 590 - 610 GaAsP, GaPyellow 570 - 590 GaAsP, GaPgreen 500 - 570 InGaN, GaNblue 450 - 500 InGaN, ZnSe

ultraviolet < 400 AlN, AlGaN, AlGaInN

UV (ultraviolet)-radiation

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from 100-400 nmVUV, UVA, UVB, UVCused for desinfection etc


http://www.uvlp.ca

UV-LEDs

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emitt light in the UV-range several advantages over mercury lamps

materials:Diamond (235 nm)

Aluminium gallium nitride (AlGaN) (220 nm)

Boron nitride (BN) (215 nm)

Aluminium nitride (AlN) (210 nm)

Aluminium gallium indium nitride (AlGaInN) (210 nm)


AlGaNIntroduction

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only semiconductor with large direct band gap

efficient UV emission from quantum well

wavelength under 300 nm are available

possibility of p and n-doping

rigid devices with long lifetime

freedom from environmental pollutants


AlGaNStructure

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wurtzite-structurehexagonalsimilar lattice constants


https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr201008sf2.html

AlGaN

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Structure:

substrate

buffer layer by MOCVD

layers of n-AlGaN

multiple quantum well region

layers of p-AlGaN


Schematics of a DUV-LED

J.Zhang et al.,Jpn.J. Appl. Phys.,44.2005

AlGaNSubstrates

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properties:suitable crystal structuresimiliar lattice constanthigh purity

suggestions:AlNGaNsaphireSiGaAs


AlGaNDoping

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doping efficiencies are lower than in GaN

doping ability decreases with increasing Al content

n and p-doping

p-doping is difficultN-vacancies act as compensating centerlow hole concentrationionization energy of Mg increases with increasing Al content


AlGaN

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variation of the band gap wavelength depends on amount of Alhigh amount of Al needed to achieve short wavelengthsall 3 regions of the UV electromagnetic spectrum can be covered


Band gap engineering

Razeghi, Journal of Crystal Growth 311 (2009) 3067-3074

AlGaN

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NH3, TMGa, TMAlCp2-Mg, silane970-1080°C50-500 Torr


Preparation by MOCVD

http://www.tms.org/pubs/journals/jom/9709/steigerwald-9709.html

http://www.emrl.de/imagesArticles/Chemical_Fig2.jpg

AlGaN

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Ga, Al, N2

400-850°CHochvakuum


Preparation by MBE

http://newenergyandfuel.com/http:/newenergyandfuel/com/2010/09/13/on-the-path-to-full-spectrum-photovoltaic-solar-cells/

AlGaNApplications


https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr201008sf2.html

AlGaN UV-LED vs. mercury lamps

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AlGaN UV-LEDefficiency: 5-15 %

lifetime: 15000 h

output power: 30 mW

no environmental pollution by UV-LEDUV-LED need no time to warm upwide range of wavelength available

Hg low pressure lampefficiency: 40 %

lifetime: 16000 h

output power: 4 W


AlGaNConclusion

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growth of AlGaN is challengingcracking and defects

poor doping efficiencies = poor carrier injection

poor electrical conductivity

light emission is weakstill research necessary to improve efficiency

ButUV- LEDs are the future for several applications and will replacemercury lamps


Sources

20

Prof. T. Jüstel, lecture script „Incoherent light sources“Razeghi, Journal of Crystal Growth 311 (2009) 3067-3074Hirayama, Electronics and Communications in Japan, 93 (2010) 24-33http://en.wikipedia.org/wiki/Light-emitting_diodeZhang, Japanese Journal of Applied Physics, 44 (2005) 7250-7253Van de Walle et al., MRS Internet J. Nitride Semicond. Res 4S1, G10.4 (1999)


algan uv leds(ann-kathrin nemann) - fh-muenster.de · sources 20 prof. t. jüstel, lecture script...

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