Found in smartphones, computer screens and energy-efficient bulbs, blue light-emitting diodes (LEDs) are everywhere. That they have now earned three Japanese-born inventors the 2014 Nobel Prize in Physics is a rare example of the award being given for a practical invention.
LEDs are devices that emit light when subjected to an electric current. Green and red versions have been around since the 1950s, but creating blue-emitters was a technical challenge that stumped industry efforts for decades.
It was not until the 1990s that engineers Isamu Akasaki and Hiroshi Amano, both at Japan’s Nagoya University, in parallel with electrical engineer Shuji Nakamura, then working at Japanese chemicals firm Nichia, succeeded in creating a blue LED.
LEDs are sandwiches of semiconductor materials. The layers are ‘doped’ with other elements, which provides some layers with extra electrons and others with a surplus of ‘holes’, where missing electrons leave behind a positive charge. When an electrical current is applied, the electrons and holes combine at the junctions between the layers and emit light as a result.
From the 1980s, physicists focused their efforts on the material gallium nitride as a target for making high-power blue LEDs, but they were faced with several technological hurdles. One was creating thin, high-quality crystals of the material, which are notoriously difficult to grow. Another was doping gallium nitride such that it emitted light efficiently.
Akasaki, Amano and Nakamura persisted with gallium nitride long after their competitors had moved on to other materials, says Wolfgang Schnick, a materials chemist at the Ludwig Maximilian University of Munich in Germany.
Their success in overcoming those hurdles has opened the door to white LEDs, which can have efficiencies nearly 20 times those of conventional bulbs.
Almost all white LED-based lights consist of a blue LED chip combined with one or more luminescent materials, which convert part of the blue light to longer wavelengths. “This has led to a revolution in the lighting industry, and will have more and more impact on the way people are lighting their homes,” says Dirk Poelman, a materials scientist at Ghent University in Belgium.
Schnick says that the development “cannot be estimated too highly”. “This will help to save up to 20% of the global electricity consumption,” he says.
Schnick added that in future, blue LEDs are likely to find uses in portable devices that can disinfect or sterilize water, and perhaps in computer memories that use light instead of electricity to store data. Blue lasers — also invented by Akasaki and Amano, and separately by Nakamura — are already used in Blu-ray Disc technology.
The story is not without twists. Nakamura, who left Japan in 2000 to join the University of California, Santa Barbara, sued Nichia in 2001 over the scant compensation he received for inventing the blue LED technology while he worked there. The case was settled in January 2005, when Nakamura accepted ¥840 million (US$8.1 million at the time). “Nakamura was quite determined to show that gallium nitride could be an effective LED technology. He pushed it very hard — it was something they were not initially concentrating on,” says Martin Dawson, a photonics researcher at the University of Strathclyde in Glasgow, UK.
Speaking on a crackling telephone line to journalists in Sweden on 7 October, Nakamura said that the feeling of winning the prize was “unbelievable”. Staffan Normark, permanent secretary of the Royal Swedish Academy of Sciences, told journalists that the trio had not been expecting the prize. “They had not been waiting all day and all night for this call,” he said.
Announcing the prize, Per Delsing, chairman of the academy’s Nobel Committee for Physics, said that the award cherished the tradition of its founder, the engineer and inventor Alfred Nobel. “I really think that Alfred Nobel would have been happy about this prize,” he said.
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- Additional reporting by Richard Van Noorden
- This story appeared in print under the headline ‘Blue LED wins physics Nobel’