The work of this year’s winners of the Nobel Prize in Physics cannot be understated. As the Nobel Foundation said when they awarded the prize to Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura—the three inventors for the blue light-emitting diode—“Incandescent light bulbs lit the 20th century; the 21st century will be lit by LED lamps.”
But there’s more to this story. “The background is kind of being swept under the rug,” says Benjamin Gross, a research fellow at the Chemical Heritage Foundation in Philadelphia. “All three of these gentlemen deserve their prize, but there is a prehistory to the LED.” In fact, almost two decades before the Japanese scientists had finished the work that would lead to their Nobel Prize, a young twenty-something materials researcher at RCA named Herbert Paul Maruska had already turned on an LED that glowed blue.
In the 1950s and 60s, RCA was a television giant. David Sarnoff, founder and CEO of the company, was pushing for a technological replacement for the bulky picture tube in color TVs. An LED TV was naturally seen as the next step.
At the time, the company was exploring the electronic properties of compound semiconductors, as opposed to elemental ones. “These had new, unexplored electrical and potentially optical properties,” says Gross. Work on gallium arsenic (GaAs) and gallium phosphide (GaP) had already led to red and green LEDs, respectively. “Blue was the final piece of the puzzle” says Gross.
In May 1968, Maruska was a young scientist working in RCA’s central research lab in Princeton, New Jersey. “I had already been growing GaAs and GaP.” James Tietjen, the director of the lab, marched up to Maruska’s desk and told him, “I got an idea. I think I know how we can make a blue LED. Why don’t you figure out how to grow gallium nitride (GaN)? Then we can make a TV that we can hang on the wall.”
Tietjen knew enough about these semiconductor compounds to know GaN was promising, Gross explains. Based on where gallium and nitrogen fall on the periodic table, it was thought an LED made of that substance would emit blue.
To grow these semiconductors, Tietjen and his lab used a technique called Halide Vapor Phase Epitaxy, an approach where hydrogen chloride is reacted at elevated temperatures with metal to produce gaseous metal chlorides, which are then reacted with ammonia to produce a metal compound that collects on a substrate as a thin layer.
“At this time,” Maruska fondly remembers, “RCA had so much money that we didn’t have to look at a budget or anything—we just went to work on it. It was wonderful time to work on this.” Without financial barriers, Maruska used sapphire as the substrate to grow GaN.
According to Maruska, “we tried for about a year to get something to grow. All I would get was powders and junk. One day I simply thought ‘Oh what the hell, why don’t I just turn up the temperatures to GaAs temperatures—900 degrees?’”
When Maruska pulled out the sapphire substrate, he saw nothing at first. A little closer, he noticed something transparent actually had grown—GaN. By November 1969, Maruska and Tietjen published a paper outlying how to grow GaN crystals. “It caused a stir among the semiconductor industry,” says Gross. “Other companies like Bell and Philips started to try to make their own GaN.”
Maruska went on to earn his Ph.D at Stanford University, but remained an employee of RCA and continued to work on the project. Other famed materials researchers like Jacques Pankove and Edward Miller joined the RCA lab to help with project’s biggest obstacle: the scientists were able to easily grow n-type GaN, but not p-type, which was necessary for developing a PN junction. In 1971, without a solution, Tietjen and the lab set aside the PN architecture in favor of an approach that didn’t need a p-type dopant.
This was the metal insulator semiconductor (MIS) arrangement. It’s essentially a sandwich that, in this case, consisted of a n-type GaN semiconductor in the middle, a top layer of zinc-doped GaN, and a transparent layer of indium on the bottom. Pankove and Miller were able to make a green LED through this layering, albeit at a lower efficiency than a PN-architecture.
In order to generate a blue LED, Maruska changed the dopant from zinc to magnesium. In 1972, after some tinkering, he successfully created a blue LED.
“It lit up and I came back and shined the blue light at everybody,” Maruska says. “Everybody was very impressed.”
Unfortunately, as Maruska recalls, “RCA was collapsing internally.” Sarnoff had died, and his son, Robert, had just taken over. Among many poor decisions, Robert pursued an ill-fated endeavor to make RCA a leader in computers. Unfortunately, RCA was unable to compete with the king company of computers: IBM.
Every branch of RCA had their budgets slashed, and the blue LED project was officially dead by 1974. By that time, Maruska had already been let go. “I’m sure it wouldn’t have been long before I would have gotten a bright blue LED right on the track,” he says. “But once I got kicked out, I couldn’t find another job doing that.”
Meanwhile, Akasaki and Amano worked tirelessly to solve the problem that stumped Maruska and his colleagues: growing a p-type GaN that could lead to an efficient blue LED. “They wouldn’t give up,” says Maruska. “They found out what the problems were and they overcame them.”
“One day,” Maruska recalls, “I was in a hotel in 1990, and there’s a knock on the door, and Akasaki is outside the door. He looks in, and he shines this blue LED in my eyes and says, ‘look at this!’ I say, ‘holy shit! It’s actually a bright blue LED!’ He says, ‘yes, it is.’ And he just disappears down the hall.” Nakamura, working independently, would figure out how to scale the whole process for efficient manufacturing.
Maruska is happy to see his story getting a fresh look again, and there’s no hard feelings on who the Nobel Prize went to. “These three guys really deserve the credit,” he says. “It’s like I say to people: they had been working on the steam engine for 100 years, but they never could make one that really worked, until James Watt showed up. It’s the guy who makes it really work who deserves the Nobel Prize. They certainly deserve it.”