Nobel Prize 2014: Akasaki, Amano & Nakamura

Nature Physics advance online publication, 7 October 2014 doi:10.1038/nphys3147 Research Highlight Nobel Prize 2014: Akasaki, Amano & Nakamura Joerg Heber The 2014 Nobel Prize in Physics has been awarded to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura “for the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources.” For those old enough to remember, in the 1970s and 1980s the world of light-emitting diodes (LEDs) had only a limited range of colours at its disposal. There were green, yellow and red LEDs fabricated from widely studied semiconductor compounds such as gallium arsenide, which, following pioneering work by Nick Holonyak Jr at General Electric as well as others, has been used to make red LEDs since the early 1960s. Although these LEDs decorated many consumer electronic devices, one colour was missing: blue. The higher energy of blue light meant that new semiconductor materials with greater electronic transition energies had to be used. One of the most favourable candidates for this purpose was gallium nitride. Yet, producing working LEDs from gallium nitride proved to be exceptionally difficult. All early fabricated materials were full of imperfections and defects that made light-emission very inefficient. A first breakthrough came in 1986, when Isamu Akasaki and Hiroshi Amano from Nagoya University in Japan developed a suitable growth method and device structure based on a chemical vapour deposition technique. However, one issue remained. To fabricate an LED, additional dopants need to be incorporated into the semiconductor to deliver the positive and negative electrical charges to the active region, where they combine and emit light. For gallium nitride, growing the p-type layer was problematic. The dopants added into the material, usually zinc or magnesium, were neutralized, hampering the efficiency of the LEDs. While Akasaki and Amano were working on improving their p-type layers, Shuji Nakamura from the Nichia Corporation worked independently on the problem. Noting that the Nagoya researchers observed an improvement in the brightness of their LEDs when they were irradiated with electrons in a scanning electron microscope, he worked on more practical techniques to improve the efficiency, and in 1993 developed a thermal annealing technique to remove the detrimental hydrogen that deactivated the p-type dopants. A first high-efficiency blue LED was presented in 1994. Since then, we have experienced a technological revolution, especially when the blue LEDs are combined with fluorescent materials to realize white light. These white LEDs have become so efficient that they are used in applications as diverse as smartphones, light bulbs, car headlights and many more. This year’s prize in physics is therefore certainly in the spirit of Alfred Nobel’s will, rewarding an invention that has been of great benefit to mankind. It follows recent awards for the development of

© 2014 Macmillan Publishers Limited. All rights reserved

efficient semiconductor lasers in 2000 and for optical fibres and CCD cameras in 2009. Together with last year’s prize, awarded to Englert and Higgs for their work on the Higgs boson, it is encouraging to see the physics prize covering the full, rich spectrum of physics and related research, from the very fundamentals of our universe to the technologies that brighten up our daily life. FURTHER READING The Nobel Prize in Physics 2014 From Nature Physics: News and Views Symphony of lights Iulia Georgescu Nature Phys. 8, 639 (2012). doi:10.1038/nphys2416 From Nature: Nitride-‐based semiconductors for blue and green light-‐emitting devices F. A. Ponce & D. P. Bour Nature 386, 351–359 (1997). doi:10.1038/386351a0 Nitride semiconductors free of electrostatic fields for efficient white light-‐emitting diodes P. Waltereit et al. Nature 406, 865–868 (2000). doi:10.1038/35022529 An aluminium nitride light-‐emitting diode with a wavelength of 210 nanometres Yoshitaka Taniyasu, Makoto Kasu & Toshiki Makimoto Nature 441, 325–328 (2006). doi:10.1038/nature04760 From Nature Materials: Editorial Raising the stakes in Japan Nature Mater. 3, 127 (2004). doi:10.1038/nmat1087 Surface-‐plasmon-‐enhanced light emitters based on InGaN quantum wells Koichi Okamoto et al. Nature Mater. 3, 601–605 (2004). doi:10.1038/nmat1198 Repeated temperature modulation epitaxy for p-‐type doping and light-‐emitting diode based on ZnO Atsushi Tsukazaki et al. Nature Mater. 4, 42–46 (2005). doi:10.1038/nmat1284 Origin of defect-‐insensitive emission probability in In-‐containing (Al,In,Ga)N alloy semiconductors Shigefusa F. Chichibu et al. Nature Mater. 5, 810–816 (2006). doi:10.1038/nmat1726 From Nature Photonics: A surface-‐emitting laser incorporating a high-‐index-‐contrast subwavelength grating Michael C.Y. Huang, Y. Zhou & Connie J. Chang-‐Hasnain Nature Photon. 1, 119–122 (2007). doi:10.1038/nphoton.2006.80 Nearly single-‐crystalline GaN light-‐emitting diodes on amorphous glass substrates Jun Hee Choi et al. Nature Photon. 5, 763–769 (2011). doi:10.1038/nphoton.2011.253 Stable and efficient quantum-‐dot light-‐emitting diodes based on solution-‐processed multilayer structures Lei Qian, Ying Zheng, Jiangeng Xue & Paul H. Holloway Nature Photon. 5, 543–548 (2011). doi:10.1038/nphoton.2011.171 Commentary


Prospects for LED lighting Siddha Pimputkar, James S. Speck, Steven P. DenBaars & Shuji Nakamura Nature Photon. 3, 180–182 (2009). doi:10.1038/nphoton.2009.32 Business News Meeting the demand for blue–violet devices, Coherent invests in diode technology, and more Nature Photon. 1, 390 (2007). doi:10.1038/nphoton.2007.113 News and Views Solid-‐state lighting on glass Nicolas Grandjean & Raphaël Butté Nature Photon. 5, 714–715 (2011). doi:10.1038/nphoton.2011.298 From Nature Nanotechnology: Emissive ZnO–graphene quantum dots for white-‐light-‐emitting diodes Dong Ick Son et al. Nature Nanotech. 7, 465–471 (2012). doi:10.1038/nnano.2012.71 From Nature Communications: A novel phosphor for glareless white light-‐emitting diodes Hisayoshi Daicho et al. Nature Commun. 3, 1132 (2012). doi:10.1038/ncomms2138 Improved heat dissipation in gallium nitride light-‐emitting diodes with embedded graphene oxide pattern Nam Han et al. Nature Commun. 4, 1452 (2013). doi:10.1038/ncomms2448 Efficient and tunable white-‐light emission of metal–organic frameworks by iridium-‐complex encapsulation Chun-‐Yi Sun et al. Nature Commun. 4, 2717 (2013). doi:10.1038/ncomms3717


Documents

Nobel Prize 2014: Akasaki, Amano & Nakamura