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 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: 

Review  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

Letters to Nature  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

Letter  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

Letter  Surface-plasmon-enhanced light emitters based on InGaN quantum wells  Koichi Okamoto et al. Nature Mater. 3, 601–605 (2004). doi:10.1038/nmat1198

Letter  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

Article  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:

Letter  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

Article  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

Article  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:

Article  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:

Article  A novel phosphor for glareless white light-emitting diodes  Hisayoshi Daicho et al. Nature Commun. 3, 1132 (2012). doi:10.1038/ncomms2138

Article  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

Article  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