Blue LEDs win Nobel Prize in physics

The invention of blue light-emitting diodes that are central to the energy-efficient lights illuminating homes, offices and electronic displays has earned three scientists the 2014 Nobel Prize in physics. Isamu Akasaki of Meijo University and Nagoya University in Japan, Hiroshi Amano of Nagoya University and Shuji Nakamura of the University of California, Santa Barbara will split the roughly $1.1 million prize.

“If we look at the landscape of technology, there’s the transistor and the integrated circuit, and then there’s the blue LED,” says Fred Schubert, an electrical engineer at the Rensselaer Polytechnic Institute in Troy, N.Y.

The blue LED is the crucial ingredient for white LED lamps, which are rapidly replacing incandescent bulbs. Edison’s classic invention uses a filament that emits light in a range of colors that together look white. But a lot of electricity gets wasted heating the filament rather than generating light.

LEDs are far more energy efficient because they use electrons to generate photons. LEDs are made out of layers of semiconductors, materials similar to the ones in computer chips. Some layers have an excess of electrons; others have a deficit, leading to the emergence of positively charged holes where electrons should be (SN: 10/18/14, p. 22). Combine the electrons and holes in a concentrated area and they emit light.

In 1962, Nick Holonyak at General Electric serendipitously discovered the first semiconductor diode to emit visible light when he turned off the lights in his lab and noticed a sample of gallium arsenide phosphide glowing red. From there, scientists rapidly developed LEDs that emitted red and green light. But attaining blue, which is essential for creating a variety of other colors including white, remained a major challenge. Blue light is at the high-energy end of the visible spectrum, and there aren’t many materials that can coax electrons to emit such high-energy light.

In the late 1980s, Akasaki and his then-student Amano were studying a semiconductor called gallium nitride in search of that elusive blue glow. On paper, gallium nitride doped with other chemicals had the capacity to produce blue light. But dozens of engineers had tried and failed to grow high-quality gallium nitride crystals that had a robust electron-deficient layer. In 1986, Akasaki and Amano used a sapphire base to grow gallium nitride on. And then, like Holonyak, they had a big break that came by accident: As they studied the material under an electron microscope to figure out why it was so difficult to produce an electron-deficient layer, they noticed a layer emerging right before their eyes.

Nakamura, working at the same time at Nichia Chemicals, a chemical engineering company in Tokushima, developed his own method for creating high-quality gallium nitride. He also discovered the mechanism behind Akasaki and Amano’s surprise microscope observation. By the early 1990s, he developed a method to simply and cheaply produce blue LEDs.

Nakamura’s discovery caused acrimony. Nichia initially paid Nakamura about $200 for his invention even though the company had told him not to pursue blue LEDs; he had come into the lab late at night to perform the research, according to fellow materials scientist Colin Humphreys of the University of Cambridge. Nakamura sued Nichia, and in 2005 the company settled with him for about $8.1 million.

The researchers’ discovery arrived during the golden age of CDs and just before the advent of DVDs, Schubert says, so the first application was the development of blue lasers (SN: 12/13/97, p. 374), which soon enabled high-capacity Blu-ray discs and more precise laser printers. In 1996, Nichia engineer Yoshinori Shimizu combined blue LEDs with a yellowish coating called a phosphor to create a device that emits white light. Now white LED bulbs last up to 100,000 hours, compared with 1,000 hours for an incandescent bulb.

Technology based on blue LEDs is ubiquitous today, to the tune of a $15 billion industry. Besides illuminating homes, streets and offices, LEDs serve as the backlight for many electronic displays, resulting in energy-efficient televisions and longer battery life for laptops and smartphones.

The Nobel committee at the Royal Swedish Academy of Sciences often presents awards for theories or for observing new fundamental physics phenomena, but this time around, the judges clearly thought of the big-picture impact of the research. Alfred Nobel “wanted his prize to be given to inventors for the benefit of mankind,” said committee member Olle Inganäs, a physicist at Linköping University in Sweden, at a press conference. “What we emphasize today is the usefulness of this thing.”

The committee noted that energy-sipping LEDs can help provide light to the roughly 1.5 billion people worldwide with no access to electrical grids. And Humphreys points out that lighting accounts for about 20 percent of the world’s electricity usage. “If we replace existing lighting with LEDs, we could save half of that electricity,” he says, eliminating the need for about 500 large power plants.