(Al,Ga)N UV LEDs JENNIFER HÖLSCHER

Transcription

1 (Al,Ga)N UV LEDs JENNIFER HÖLSCHER

2 Agenda History of LEDs Functional principle of LEDs UV LED materials (Al,Ga)N Band gap engineering Comparison UV LED/Hg lamp Application Future economical development Manufacturers Conclusion JENNIFER HÖLSCHER - (AL,GA)N UV LEDS 2

3 History of LEDs 1907: Henry Joseph Round finds out that some inorganic materials light up if electric current is applied : Oleg Lossow describes the so-called Round-effect in greater detail 1935: Georges Destriau discovers light emission in ZnS, today credited as inventor of electroluminescence 1951: invention of transistor possibility to explain observed light emission 1961: Biard and Pittman invent first LED (emission in IR range) JENNIFER HÖLSCHER - (AL,GA)N UV LEDS 3

4 History of LEDs 1962: first red LED ((Ga,As)P) invented by Nick Holonyak enters market 1971: LEDs available in more colors, improved performance and effectiveness 1993: Shuji Nakamura develops (In,Ga)N blue LED 1995: first white LED is presented 2014: Nobel Prize in physics is awarded to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura for the development of the blue LED JENNIFER HÖLSCHER - (AL,GA)N UV LEDS 4

5 UV range JENNIFER HÖLSCHER - (AL,GA)N UV LEDS 5

6 Functional Principle LED consists out of a semiconductor chip with a p-doped part (holes) and an n-doped part (electrons) Electrons flow into the n-type material At the barrier layer, recombination with holes from the p-doped material takes place, emission of radiation Wavelength of radiation dependent of the band gap JENNIFER HÖLSCHER - (AL,GA)N UV LEDS 6

7 Set-up JENNIFER HÖLSCHER - (AL,GA)N UV LEDS 7

8 Other UV-LED materials Diamant (225 nm) Boron nitride BN (215 nm) Aluminiumnitride AlN (205 nm) (In,Ga)N (Al,Ga,In)N JENNIFER HÖLSCHER - (AL,GA)N UV LEDS 8

9 Al x Ga 1-x N III-V-compound semiconductor used for LEDs in the range of blue to UV (limit: ʎ >205 nm) Higher resistancy with Al inside lower quality of the (Al,Ga)N layers lower conductivity doping with Mg (p-type) or Si (n-type) Band gap [ev] Emission [nm] lower mobility of the charge carriers especially at high dopant concentration defects caused during the deposition on sapphire lead to high n-background doping For high Al contents, growth most easy on AlN (more expensive than sapphire wavers, smaller sizes) AlN GaN 6,2 3, JENNIFER HÖLSCHER - (AL,GA)N UV LEDS 9

10 Band Gap Engineering change of materials and their percentage composition lead to changes of band gap energy important for mixing materials: crystal structure, thermal properties, lattice constants and layer sequence high Al-weight fraction difficult growth and doping of the material JENNIFER HÖLSCHER - (AL,GA)N UV LEDS 10

11 Comparison to UV Hg lamp Other important factors: Lower purchase cost of Hg UV lamps Life time depending on UV-lamp type, improvement of UV LED life time possible by improved quality and thermal management JENNIFER HÖLSCHER - (AL,GA)N UV LEDS 11

12 Applications JENNIFER HÖLSCHER - (AL,GA)N UV LEDS 12

13 Further development VUV LEDs: limit of emission wavelength: 205 nm (emission of pure AlN) heat dissipation increase efficiency improve quality mass production JENNIFER HÖLSCHER - (AL,GA)N UV LEDS 13

14 Future economical development market size of UV LEDs: $ 30 million (2012) expected: more than $ 300 million in 2018 limiting factors cost break existing industry dynamics JENNIFER HÖLSCHER - (AL,GA)N UV LEDS 14

15 Manufacturers of UV LEDs Sensor Electronic Technology, Inc. and Seoul Optodevice Co. Ltd. (Seoul, Korea) Nichia Corp. (Tokushima, Japan) DOWA Electronics Materials Co., Ltd. (Tokyo, Japan) Crystal IS (Green Island, NY, USA) SemiLEDs (Hsinchu, Taiwan) JENNIFER HÖLSCHER - (AL,GA)N UV LEDS 15

16 Conclusion band gap of (Al,Ga)N can be varied between about nm higher amount of Al leads to more demanding deposition process better properties than Hg UV lamps (except for cost) problems to be solved: development of VUV LEDs, heat dissipation, mass production manufacturers mainly located in Asia JENNIFER HÖLSCHER - (AL,GA)N UV LEDS 16

17 Literature and Sources Figures Nakamura S, Fasol G, The Blue Laser Diode: GaN Based Light Emitters and Lasers, Springer, Berlin, Literature Razeghi M, McClintock. J Cryst Growth. 2009; 311: Fuhrmann, Daniel: Limitierende Mechanismen für (Ga,Al,In)N-basierte LED-Strukturen im grünen und ultravioletten Spektralbereich, Cuvillier Verlag, JENNIFER HÖLSCHER - (AL,GA)N UV LEDS 17

18 JENNIFER HÖLSCHER - (AL,GA)N UV LEDS 18