LED History Lesson, Part 2: Expansion of the LED Spectrum
- November 14, 2017
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The Improvement of the Light-Emitting Diode
For almost fifty years after its discovery, the LED was a trifle, an expensive inventor’s novelty with no practical application. Semiconductors glowed when an electrical current passed through, but experimenters had not found a meaningful application for this phenomenon. Then, in a flurry that lasted ten years, engineers unlocked the light-emitting diode’s potential in a series of successive breakthroughs. Despite this progress, LEDs remained prohibitively expensive and unsuitable for everyday illumination. The most important development, one eventually recognized by the Nobel Prize committee, would take another twenty years.
To read the first article in our history of the LED, click here: Part One.
The first visible LED was an accident. A scientist stumbled upon it as engineers at the major American electronics labs raced to create the first semiconductor laser. The first laser, like the first LED, was not very functional. Scientists realized, however, that creating a laser with diodes would enable a more consistent device. In university laboratories and at electronics companies, engineers sprinted to invent the semiconductor laser. General Electric’s Robert Hall was first, discovering his laser in 1962. He was followed almost immediately by researchers at IBM and MIT. Beat to the discovery, another GE scientist thought, “If they can make a laser, I can make a better laser.” A few months later, Nick Holonyak did. With new crystals in the heart of his laser, Holonyak transformed Hall’s infrared laser into a visible red light, inventing the red LED.
Nick Holonyak still sees himself as the founder of the LED revolution. The 88-year-old, who left GE and semiconductor experimentation soon after his discovery, remains vocal about his role in the emergence of the LED. “The LED as you know it,” he told a reporter in 2014, “comes from us.” While Henry Round and Oleg Losev have stronger claims to the crown of the inventor of the LED, Holonyak is not wrong. His eureka moment spawned an outburst of LED innovation, leading the way for the more efficient LEDs now available everywhere.
The LED Rainbow
Holonyak’s discovery opened the door for new LED innovation. His student, George Craford, created the yellow LED. Working for Monsanto, Craford also improved on Holonyak’s red light. By creating a red LED ten times brighter than Holonyak’s, Craford allowed Monsanto to introduce the first mass-produced LEDs to the market. At the same time, researchers at RCA created a green LED and then a dull blue light. While this burst of innovation in the 1960s and 1970s accelerated LED innovation, an LED to replace a common incandescent or fluorescent remained elusive. The red lights were bright enough, but they were red. Yellow lights and blue lights were closer in color, but scientists couldn’t make them bright enough. Starting in the 1970s, LED improved electronics equipment. Until the 1990s, their usefulness ended there.
From the Blue
When they assembled the first bright blue LED, three Japanese scientists made the world, both literally and figuratively, a brighter place. Working for the Japanese Nichia Corporation in the early 1990s, Shuju Nakamura, Isamu Akasaki, and Hiroshi Amano persisted in their experimentation with semiconductors, confident that they were nearing their desired solution. Where other researchers had tried and failed to make a bright blue LED with gallium nitride, the Nichia scientists remained confident that this semiconductor held the solution to the bright blue LED. Gallium nitride was difficult to create and difficult to work with. Nakanura, Akasaki, and Amano were undeterred. In 1994, they found the right combination of ingredients and temperature, uncovering the missing link in the LED rainbow.
The bright blue LED was the breakthrough necessary to create white LEDs. By coating the blue lights with phosphor, engineers altered them to produce white light. Armed with the new understanding from the Nichia team’s research, scientists soon learned how to make white light with both green LEDs and red LEDs. The blue LED was the keystone that enabled the LED revolution, allowing LEDs to replace other light bulbs almost everywhere.
In 2014, the three scientists earned one of the highest recognitions for their research. The Royal Swedish Academy of Scientists awarded the trio the Nobel Prize in Physics “for the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources.” In a press release accompanying the announcement, the Nobel committee explained, “the LED lamp holds great promise for increasing the quality of life for over 1.5 billion people around the world who lack access to electricity grids,” continuing to explain that “due to low power requirements it can be powered by cheap local solar power.” Furthermore, the press release stated, “The invention of the efficient blue LED is just twenty years old, but it has already contributed to create white light in an entirely new manner to the benefit of us all.”
This post originally appeared at Lime Energy's Lime Blog.