Out of the blue: Shuji Nakamura's solo ascent to the Nobel Prize

When Shuji Nakamura got a job doing R&D for the obscure Japanese company Nichia Chemical Industries, he couldn’t have known it would end up being a defining career move. He was desperate to find a job within commuting distance of his young family’s rural home, and Nichia was the only option.

In the late 1970s, Nichia Chemical’s main product was phosphor for use in televisions, fluorescent lamps, and red LEDs, but when Nakamura was hired, business wasn’t good. According to Brilliant!, a biography of Nakamura by Bob Johnstone, the Nichia president feared that the company would go bankrupt at any moment. This might not seem like a fortuitous start to a career, but for Nakamura it proved providential. Because the company’s research budget was tight, he would have to be self-reliant and handy—traits that would lead him, along with Isamu Akasaki and Hiroshi Amano, to the 2014 Nobel Prize in Physics for invention of the blue LED.

Nakamura was born in 1954 in Omu, a fishing village in the Ehime Prefecture of Japan. He dreamed of becoming a theoretical physicist or mathematician, but his grades weren’t good enough for prestigious schools like the University of Tokyo. Instead, he was admitted to Tokushima University, a regional school that offered electrical engineering as the closest discipline to physics. Because the laboratory was poorly funded, he would learn to cobble together equipment and gain the bootstrapping skills needed to blaze a trail as one of the 20th Century’s most remarkable engineers.

An LED consists of two layers of the same material—a homojunction—doped to make one side positively charged and the other negatively charged. The negative side (n-type) contains an excess of electrons, and the positive side (p-type) contains “holes.” You can picture two pieces of wholegrain bread, full of seeds, stacked atop one another; the negative side has lots of extra seeds, and on the positive side, the seeds have been picked out. When electric current is applied, the excess electrons from the n-type material combine (somewhat violently) with the holes on the p-type side and release photons at the interface of those layers, emitting light.

Nick Holonyak figured out red LEDs in the 1960s while working for General Electric, and the devices found a niche market, particularly as on/off indicators for switches. White LEDs were the holy grail of solid-state lighting for their potential applications in lamps and displays, but you can’t make white light without blue light. And progress on blue LEDs was 20 years behind.

There are two wide-bandgap materials with the required properties to efficiently emit in the blue wavelength: zinc selenide (ZnSe) and gallium nitride (GaN). Gallium nitride was considered a dead end. The hard material had to be layered onto a sapphire substrate, which left defects in the crystal lattice. Billions of defects. Because defects impede the motion of electrons, that was a problem.

Zinc selenide is a softer material with six orders of magnitude fewer defects, so it’s not surprising that all the big companies thought they’d find success creating blue light with it.

At the 1992 meeting of the Japanese Society on Applied Physics, Nakamura observed that sessions about ZnSe drew hundreds of people, while the session on GaN had just four: the speaker, the session chair, “and two people in the audience, including me!” Nakamura later recounted at a plenary talk at SPIE Optics + Photonics in 2015.

Nakamura chose the underdog GaN for two reasons: First, Johnstone says, all major electronics companies (IBM, 3M, Sony, Toshiba, etc.) were investing in ZnSe, and a small company like Nichia Chemical wouldn’t be able to compete commercially, even with a successful product. With no other companies working on GaN, Nichia would have sole possession of the market—if Nakamura succeeded.

Second, Nakamura, who in 1990 did not yet have a PhD, needed to author five publications to earn a doctoral degree in Japan. He had a better chance of publishing if he tackled GaN. “I never expected I could invent blue LEDs,” he said during his 2015 plenary. “My dream was just publishing five scientific papers!”

Those publications came quickly. In the early 1990s, Nakamura made one advance after another towards the development of a commercially viable blue LED. This solo researcher, with no PhD, from a small company, quickly made a name for himself with the following three Nobel prize-worthy contributions:

1991: The crystals that make up GaN films were successfully produced via metal organic chemical vapor deposition (MOCVD). This technique was the only viable way to grow the crystals, but for months, Nakamura’s attempts failed, and the crystals came out black rather than clear. He used his DIY skills to modify the MOCVD apparatus, which finally resulted in GaN crystals with far fewer defects—in fact, better quality crystal than grown anywhere else in the world.

1992: Akasaki and Amano had already succeeded in creating the first p-type GaN in 1989, a contribution recognized by the Nobel Prize they share with Nakamura. But the p-type material they produced with low-intensity electron beams had too few holes, and their method was too slow and expensive. Nakamura thought that perhaps the secret sauce to hole creation wasn’t the e-beam, rather the heat it creates. He tried thermally annealing magnesium-doped GaN films, which effectively boiled off hydrogen atoms (hydrogen passivation), activating the hole-donating magnesium. This simple, cheap method was perfect for the production line, and it also produced p-type GaN with a higher concentration of holes.

1992: Nakamura’s first blue LED, which glowed for a record-setting 1,000 hours, was too violet. It needed an indium alloy to produce light of a longer, bluer wavelength. The alloyed layer needed to be sandwiched between the n-GaN and p-GaN layers, like a very thin spread of mayonnaise, to create a heterojunction. This sandwiched, or emitting layer, would functionally trap the electrons and holes and increase the likelihood that they would combine to create light. But indium gallium nitride, or InGaN, was tricky to produce, and no one could figure out how to do it. Except, of course, Nakamura. In just five months, he figured out how to create a double heterostructure blue LED—an InGaN sandwich.

In just a few years in the early 1990s, Nakamura went from a solitary engineer doing R&D for a company in rural Japan, to science famous. His breakthroughs brought invitations to give plenary talks at numerous conferences, where, according to Johnstone, it became clear that his work on blue LEDs was miles ahead of competitors.

The commercial uses for a standalone blue LED were somewhat limited. But, by coating a blue LED’s casing with a yellow phosphor, Nichia was able to produce white light. Phosphor-coated LEDs make up the majority of household LED bulbs on the market today due to the ability to tune the light to create a range of color temperatures. Moreover, LEDs are more efficient than incandescent lamps, resulting in massive energy savings.

Although the Nobel Prize recognized Nakamura’s research contributions for the blue LED, he did not stop there. He developed a green LED, and then a blue laser, which would find its first commercial use in Blu-Ray optical data storage in the early 2000s. Nakamura did ultimately earn a PhD in 1994, though by that time he had authored dozens of papers and was well known at physics conferences worldwide.

As Johnstone wrote, Nakamura did all his remarkable early work “in almost total isolation—personal, professional, and geographical.” His solo ascent to the top of light-emitting science was, truly, out of the blue.

Gwen Weerts is Editor-in-Chief of Photonics Focus.