algan uv leds(ann-kathrin nemann) - fh-muenster.de · sources 20 prof. t. jüstel, lecture script...
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Ann-Christine Nemann
AlGaN UV-LEDs
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Overview
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LEDs
UV-radiation and UV-LEDs
AlGaN
comparison of AlGaN UV-LEDs and mercury lamps
Ann-Christine Nemann 26.06.2016
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LED-light emitting diodes
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inorganic and organic LEDs
nowadays more efficient than incandescent and fluorescentlamps
Development of LED-light sources
Ann-Christine Nemann 26.06.2016
1936 indirect
EL
1961 direct EL
1962 Ga(As,P)
1990 PLED
1993 blue LED
1999 red LED
2010 white LED
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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
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LED-light emitting diodes
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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
Ann-Christine Nemann 26.06.2016
Working Principle
http://en.wikipedia.org/wiki/File:PnJunction-LED-E.svg
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LED-light emitting diodesDifferent Types
6 Ann-Christine Nemann 26.06.2016
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
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UV (ultraviolet)-radiation
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from 100-400 nmVUV, UVA, UVB, UVCused for desinfection etc
Ann-Christine Nemann 26.06.2016
http://www.uvlp.ca
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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)
Ann-Christine Nemann 26.06.2016
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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
Ann-Christine Nemann 26.06.2016
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AlGaNStructure
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wurtzite-structurehexagonalsimilar lattice constants
Ann-Christine Nemann 26.06.2016
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr201008sf2.html
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AlGaN
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Structure:
substrate
buffer layer by MOCVD
layers of n-AlGaN
multiple quantum well region
layers of p-AlGaN
Ann-Christine Nemann 26.06.2016
Schematics of a DUV-LED
J.Zhang et al.,Jpn.J. Appl. Phys.,44.2005
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AlGaNSubstrates
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properties:suitable crystal structuresimiliar lattice constanthigh purity
suggestions:AlNGaNsaphireSiGaAs
Ann-Christine Nemann 26.06.2016
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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
Ann-Christine Nemann 26.06.2016
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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
Ann-Christine Nemann 26.06.2016
Band gap engineering
Razeghi, Journal of Crystal Growth 311 (2009) 3067-3074
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AlGaN
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NH3, TMGa, TMAlCp2-Mg, silane970-1080°C50-500 Torr
Ann-Christine Nemann 26.06.2016
Preparation by MOCVD
http://www.tms.org/pubs/journals/jom/9709/steigerwald-9709.html
http://www.emrl.de/imagesArticles/Chemical_Fig2.jpg
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AlGaN
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Ga, Al, N2
400-850°CHochvakuum
Ann-Christine Nemann 26.06.2016
Preparation by MBE
http://newenergyandfuel.com/http:/newenergyandfuel/com/2010/09/13/on-the-path-to-full-spectrum-photovoltaic-solar-cells/
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AlGaNApplications
17 Ann-Christine Nemann 26.06.2016
https://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr201008sf2.html
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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
Ann-Christine Nemann 26.06.2016
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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
Ann-Christine Nemann 26.06.2016
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Sources
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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)
Ann-Christine Nemann 26.06.2016