Cobra Effect · Everyday machines
Why a bright blue light took thirty years
How two teams made the bright blue LED that white LED lighting depends on.
7 cards, read aloud in 2:54, with a test and sources.
By the early 1960s, engineers could make tiny lamps from crystals that glowed red.
In a light emitting diode, electrons meet gaps called holes inside a crystal, and give off their extra energy as light. The colour depends on the material, because the material sets how much energy each bit of light carries. Other colours followed, but for about three decades nobody could make a bright blue.
Blue light carries more energy, so it needs a material with a wider gap.
Gallium nitride was a promising choice, but good crystals of it were extremely hard to grow. Making the positive, p type layer that a diode needs seemed hopeless too. Most research groups gave up on it and tried other materials.
At Nagoya University, Isamu Akasaki and his student Hiroshi Amano kept going.
In the mid 1980s, they grew high quality gallium nitride by first laying a thin buffer layer on sapphire. In 1989, they made the first p type gallium nitride, and a diode that gave off ultraviolet and blue light. A clue had come from noticing that the material glowed more brightly after an electron beam passed over it.
At Nichia, a small company in Japan, Shuji Nakamura found another way.
He grew high quality crystals by his own method, and worked out that hydrogen had been spoiling the p type layer. In 1992, he showed that simple heating could drive the hydrogen out. In 1993, Nichia began selling the first bright blue LEDs.
Blue was the missing piece for white LED lighting.
Most white LEDs are blue LEDs under a coating that turns part of the blue light yellow. Together, the blue and the yellow look white to the eye. LED lamps use far less electricity than old bulbs, and last far longer.
In 2014, Akasaki, Amano and Nakamura shared the Nobel Prize in Physics.
The two teams had worked separately, and each solved crucial parts of the problem. Nakamura later took Nichia to court over his pay for the invention, and the case was settled in 2005. The same work also led to blue lasers, used in players for high capacity discs.
So when everyone has given up on an approach, ask what it would take to make it work.
Gallium nitride was the material most groups had abandoned. Patient work on specific obstacles, along the unpopular route, turned out to be the answer. Much of the world’s lighting now runs on it.
Sources
- Blue LEDs, filling the world with new light, The Nobel Prize. The popular background to the 2014 prize.
- Learn about LED lighting, ENERGY STAR, US Environmental Protection Agency. How LED bulbs make white light, and why they save energy.
- Shuji Nakamura, Wikipedia. His methods, commercial production and the dispute with Nichia.
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