Why It Was Almost Impossible to Make the Blue LED

- LEDs do not get their color from their plastic covers. And you can see it because there is a transparent LED here that also glows the same red color. The color of the light comes from the electronics themselves. The housing simply helps us differentiate the different LEDs. In 1962, General Electric engineer Nick Holonyak created the first visible LED. It glowed a faint red. A few years later, Monsanto engineers created a green LED. But for decades, all we had were those two colors. Therefore, LEDs could only be used in things like gauges, calculators, and watches. If only we could

make

blue

, then we could mix red, green and

blue

to

make

white and any other color, unlocking LEDs for every type of lighting in the world, from light bulbs to phones, computers, televisions and billboards.

But blue was

almost

impossible

to make. (dramatic music) Throughout the 1960s, every major electronics company in the world, from IBM to GE to Bell Labs, rushed to create the blue LED. They knew it would be worth billions. Despite the efforts of thousands of researchers, nothing worked. Ten years after Holonyak's original LED became 20, then 30, and the hope of one day using LEDs for lighting faded. According to a Monsanto director, these will never replace the kitchen light. They would only be used on appliances, car dashboards, and stereos to see if the stereo was on. This might still be true today, if it weren't for one engineer who defied the entire industry and made three radical breakthroughs to create the world's first blue LED. (dramatic music) Shūji Nakamura was a researcher at a small Japanese chemical company called Nichia.

They had recently expanded into the production of semiconductors for use in the manufacture of red and green LEDs. But by the late 1980s, the semiconductor division was on its last legs. They were competing against much more established companies in a crowded market and they were losing. Tensions began to rise. Younger employees begged Nakamura to create new products, while older workers called his research a waste of money. And in Nichia money was scarce. Nakamura's laboratory consisted mainly of machinery that he had collected and welded himself. Phosphorus leaks in his laboratory caused so many explosions that his co-workers stopped monitoring him.

In 1988, Nakamura's supervisors were so disillusioned with his investigation that they told him to resign. So, out of desperation, he presented a radical proposal to the company's founder and president, Nobuo Ogawa. (dramatic music) The elusive blue LED, which companies like Sony, Toshiba and Panasonic had failed at. What if Nichia could be the one to create it? After suffering loss after loss in its semiconductors for more than a decade, Ogawa took a chance. He dedicated 500 million yen or $3 million, probably about 15% of the company's annual profits, to Nakamura's Moonshot project. Everyone knew that LEDs have the potential to replace light bulbs, because light bulbs, the universal symbol of a brilliant idea, are actually terrible at producing light.

They work by passing current through a tungsten filament, which gets so hot that it glows. But most of the electromagnetic radiation comes out as infrared heat. Only a negligible fraction is visible light. On the contrary, LED stands for light-emitting diode. It's there in the name. LEDs primarily create light, so they are much more efficient, and a diode is just a device with two electrodes, which only allows current to flow in one direction. This is how an LED works. When you have an isolated atom, each electron in that atom occupies a discrete energy level. You can think of these energy levels as the individual seats in a hockey stadium, and all atoms of the same element, when widely separated from each other, have identical available energy levels.

But when you put several atoms together to form a solid, something interesting happens. The outermost electrons now feel the pole, not only of their own nucleus, but also of all the other nuclei. And as a result, your energy levels change. So instead of being identical, they become a series of closely spaced but separate energy levels. An energy band. The highest energy band with electrons in it is known as the valence band, and the next highest energy band is called the conduction band. You can think of it as the balcony level. In conductors, the valence band is only partially filled.

This means that with a little thermal energy, electrons can jump to nearby empty seats, and if an electric field is applied, they can jump from one empty seat to the next and conduct current through the material. In insulators, the valence band is full and the energy difference between the valence and conduction bands, the bandgap, is large. So when an electric field is applied, no electrons can move. There are no seats available to move in the valence band, and the bandgap is too large for electrons to jump to the conduction band, which brings us to semiconductors. Semiconductors are similar to insulators, except that the bandgap is much smaller.

This means that at room temperature, a few electrons will have enough energy to jump into the conduction band and will now be able to easily access nearby empty seats and conduct current. Not only that, the empty seats they left in the valence band can also be moved. Well, actually, it's the nearby electrons jumping into those empty seats. But if you look at it from afar, it is as if the empty seat or hole is moving as a positive charge in the opposite direction to the electrons in the conduction band. (soft music) On their own, pure semiconductors aren't that useful.

To make them much more functional, impurity atoms must be added to the network. This is known as doping. For example, a small amount of phosphorus atoms can be added to silicon. Phosphorus is similar to silicon, so it fits easily into the lattice, but brings with it an extra valence electron. This electron exists at a donor level just below the conduction band. So, with a little thermal energy, all these electrons can jump into the conduction band and conduct current. Since most of the charges that can move in this type of semiconductor are electrons, which are negative, this type of semiconductor is called n-type, n means negative, but I should note that the semiconductor itself is still neutral.

It's just that most mobile charging operators are negative. They are electrons. There is also another type of semiconductor in which most of the mobile charge carriers are positive and is called p-type. To produce p-type silicon, a small number of atoms of, say, boron are added. Boron fits into the lattice, but brings with it one less valence electron than silicon. Therefore, it creates an empty acceptor level just above the valence band. And with a little thermal energy, electrons can jump out of the valence band, leaving behind holes. It is these positive holes that are primarily responsible for carrying current in the p-type semiconductor.

Again, the material is generally not charged, it's just that most mobile charging stands have positive holes. Where things get interesting is when you put a p-type and n-type piece together. Without even connecting this to a circuit, some electrons will diffuse from n to p and fall into the p-type holes. This makes the p type a little negatively charged and the n type a little positively charged. So now there is an electric field inside a piece of inert material. The electrons continue to diffuse until the electric field becomes so large that it prevents them from crossing. And now we have established the depletion region, an area where mobile charging operators have been depleted.

There are no electrons in the conduction band and no holes in the valence band. If you connect a battery incorrectly to this diode, it will simply expand the depletion region until its electric field perfectly opposes that of the battery and no current flows. But if the polarity of the battery is reversed, then the depletion region is reduced, the electric field decreases, and electrons can flow from n to p. When an electron falls from the conduction band to a hole in the valence band, that bandgap energy can be emitted as a photon. The electron's energy change is emitted as light, and this is how a light-emitting diode works.

The size of the bandgap determines the color of the light emitted. In pure silicon, the band gap is only 1.1 electron volts. So the released photon is not visible, it is infrared light. These LEDs are actually used in your TV remotes and you can capture them on camera. Moving up the spectrum, you can see why the first visible light LEDs were red and then green, and why blue was so difficult. A blue light photon requires more energy and therefore a larger bandgap. By the 1980s, after spending hundreds of millions of dollars searching for the right material, every electronics company had come up empty-handed.

But the researchers had at least discovered the first critical requirement: high-quality glass. No matter what material you used for the blue LED, it required a nearly perfect crystal structure. Any defect in the crystal lattice disrupts the flow of electrons. So instead of emitting its energy as visible light, it is dissipated as heat. So the first step in Nakamura's proposal to Ogawa was to disappear to Florida. He knew an old colleague whose lab was beginning to use a new crystal-making technology called Metal Organic Chemical Vapor Deposition, or MOCVD. A MOCVD reactor, essentially a giant furnace, was and remains the best way to mass produce clean glass.

It works by injecting vapor molecules from your crystal into a heated chamber where they react with a base material called a substrate to form layers. It is important that the lattice of the substrate matches the crystal lattice built on top of it to create a stable and smooth crystal. This is a precise art. Crystal layers often need to be as thin as a couple of atoms. Nakamura joined the lab for a year to master MOCVD. But his stay there was miserable. He was not allowed to use the MOCVD in operation, so he spent 10 of his 12 months assembling a new system,

almost

from scratch.

Worse still, his lab mates rejected him because Nakamura did not have a PhD or any academic work to his name, since Nichia did not allow publishing. His lab colleagues, all doctoral researchers, dismissed him as a humble technician. This experience motivated him. Nakamura wrote: "I feel resentful when people put me down. I developed more fighting spirit. I wouldn't let those people beat me." (inspirational music) He returned to Japan in 1989 with two things on his plate. One, an order for a new MOCVD reactor for Nichia, and two, a fervent desire to earn his Ph.D. At that time, in Japan, he could obtain a doctorate without having to go to university, simply by publishing five articles.

Nakamura had always known that his chances of inventing the blue LED were slim. But now he had a backup plan. Even if he didn't make it, he could at least get his doctorate. But now the question was, with MOCVD under his belt, what material should he research? At that point, scientists had narrowed the options down to two main candidates: zinc selenide and gallium nitride. Both were semiconductors with band gaps, theoretically, in the blue light range. Zinc selenide was the most promising option. When grown in a MOCVD reactor, it had only a 0.3% lattice mismatch with its substrate, gallium arsenide.

Therefore, the zinc selenide crystal had about a thousand defects per square centimeter, within the upper limit for LED operation. The only problem with it was that while scientists had discovered multiple different ways to create n-type zinc selenide, no one knew how to create p-type. Instead, almost everyone had abandoned gallium nitride for three reasons. First, it was much more difficult to make high-quality glass. The best substrate for growing gallium nitride was sapphire, but its lattice mismatch was 16%. This resulted in larger defects, more than 10 billion per square centimeter. The second problem was that, like zinc selenide, scientists had only created n-type gallium nitride using silicon.

Type P was elusive. And third, to be commercially viable, a blue LED would have to have a total light output power of at least a thousand microwatts. That's two orders of magnitude more than any prototype had ever achieved. So between the two candidates, almost all researchers focused on zinc selenide. Nakamura surveyed the crowded field and decided that if he was going to publish five articles on his own, he'd better focusin gallium nitride, where competition was much less fierce. This material's main claim to fame was a development back in 1972, when RCA engineer Herbert Maruska made a small blue gallium nitride LED, but it was dim and inefficient.

Then RCA slashed the project's budget, calling it a dead end. Twenty years later, scientific opinion had not changed. When Nakamura attended the largest applied physics conference in Japan, the talks on zinc selenide had more than 500 attendees. The conversations about gallium nitride had five. (dramatic music) Two of those five attendees were world experts on gallium nitride, Dr. Isamu Akasaki and his former graduate student, Dr. Hiroshi Amano. Unlike Nakamura's academic background, they were researchers at Nagoya University, one of the best in Japan. A few years earlier, they had made a breakthrough on the first problem of high-quality glass.

Instead of growing gallium nitride directly on sapphire, they first grew a buffer layer of aluminum nitride. It has a lattice space between the other two materials, which facilitates the growth of a clean gallium nitride crystal on top. The only problem was that the aluminum caused problems for the MOCVD reactor, making the process difficult to scale. But Nakamura wasn't even close at this stage. Back at Nichia, he couldn't get the gallium nitride to grow normally in his new MOCVD reactor. After six months, desperate for results, he decided to take the machine apart and build a better version himself.

The 10 months he spent setting up the reactor in Florida suddenly proved invaluable. He started following the same routine every day: arriving at the lab at 7:00 a.m. Spend the first half of the day soldering, cutting and rewiring the reactor. Spend the rest of the day experimenting with the modified reactor to see what it can do. At 7:00 p.m. m. Go home, have dinner, wash and sleep. Nakamura repeated this routine every day, with no weekends or holidays, except New Year's Day, Japan's most important holiday. (soft music) After a year and a half of continuous work, he arrived at the laboratory one winter day in late 1990.

As usual, in the morning he played around, grew a sample of gallium nitride in the afternoon and tested it . But this time, the electron mobility was four times greater than that of any gallium nitride ever grown directly on sapphire. Nakamura called it the most exciting day of his life. His trick was to add a second nozzle to the MOCVD reactor. The gallium nitride reactive gases had been rising in the hot chamber, mixing with the air to form a powdery residue. But the second nozzle released a downward stream of inert gas, pinning the first stream to the substrate to form a uniform crystal.

For years, scientists had avoided adding a second current to the MOCVD because they thought it would only introduce more turbulence. But Nakamura used a special nozzle so that even when the currents combined, they remained laminar. He called his invention a two-flow reactor. Now, he was ready to take on Akazaki and Amano, but instead of copying their aluminum nitride buffer layer, his two-stream design allowed him to make the gallium nitride so soft and stable that it could be used as a buffer layer over the sapphire substrate. . This, in turn, produced an even cleaner gallium nitride crystal on top, without the problems of aluminum.

Nakamura now had the highest quality gallium nitride crystals ever made. But just as he started, things took a wrong turn. (dramatic music) While in Florida, Nobuo Ogawa had left Nichia to become president. In his time, Nobuo had been a risk-taking scientist and designed the company's first products. That's why he supported Nakamura's noble plans all this time. But in his place, his son-in-law, Eji Ogawa, became CEO of the company, and the younger Ogawa had a much stricter outlook. A customer of Nichia said: "He has a mind of steel and remembers everything." In 1990, an executive from Matsushita, an LED manufacturer and Nichia's largest customer, visited the company to give a talk on blue LEDs.

In it, he claimed that zinc selenide was the way to go and declared that "gallium nitride has no future." That same day, Nakamura received a note from Eji, immediately stopping the gallium nitride work. Eji had never supported the investigation and wanted to put an end to what he considered a colossal waste. But Nakamura crumpled up the note and threw it away, and did so again and again, when a succession of similar notes and phone calls arrived from company management. Out of spite, he published his work on the two-stream reactor without Nichia's knowledge. It was his first article by him.

One down, four to go. With crystal formation resolved, he turned to the second hurdle, creating p-type gallium nitride. Here Akazaki and Amano had once again defeated him. They had created a magnesium-doped gallium nitride sample, but at first it didn't work as p-type as they expected. However, after exposing it to an electron beam, it behaved like a p-type, the world's first p-type gallium nitride, after 20 years of trying. The problem was that no one knew why it worked. And the process of irradiating each crystal with electrons was too slow for commercial production. At first, Nakamura copied Akazaki and Amano's approach, but he suspected that the electron beam was excessive.

Perhaps all the crystal needed was energy. So he tried heating magnesium-doped gallium nitride to 400 degrees Celsius in a process known as annealing. The result, a completely p-type sample. This worked even better than the shallow electron beam, which only made the sample surfaces p-type, and simply heating things up was a fast and scalable process. His work also revealed why type p had been so difficult. To produce gallium nitride with MOCVD, nitrogen is supplied from ammonia, but ammonia also contains hydrogen. Where there should have been holes in the magnesium-doped gallium nitride, these hydrogen atoms sneaked in and bonded to the magnesium, plugging all the holes.

Adding energy to the system released hydrogen from the material, freeing the holes again. (dramatic music) By now, Nakamura had all the ingredients to make a blue LED prototype, and he presented it at a workshop in St. Louis in 1992 to a standing ovation. He was beginning to make a name for himself, but although he had created the best prototype to date, it was more of a violet-blue color and still extremely inefficient, with a light output power of only 42 microwatts, well below 1000 microwatts. . threshold for practical use. At Nichia, the new CEO had run out of patience. Eji sent written orders to Nakamura to stop tinkering and turn everything he had into a product.

His job was at stake, but in Nakamura's own words: "I continued to ignore his order. I was successful because I didn't listen to the company's orders and trusted my own judgment." At this point, he only had the third hurdle left: getting his blue LED to reach a light output power of one thousand microwatts. (soft music) A known trick to increasing the efficiency of LEDs was to create a well, a thin layer of material at the pn junction called the active layer that reduces the bandgap a bit. This stimulates more electrons to fall from the final-type conduction band into holes in the p-type valence band.

It was already known that the best active layer for gallium nitride was indium gallium nitride, which would not only make the bandgap easier to cross, but would also reduce it by just the right amount to reduce its blue gap. violet to true blue. This time, Akasaki and Amano did not take Nakamura. First, they got stuck trying to grow indium gallium nitride. Amano recalled: "It was generally said that gallium nitride and indium nitride did not mix, like water and oil." But Nakamura had one advantage: his ability to customize his MOCVD reactor. This allowed him to use brute force, adjusting the reactor to pump as much indium as he could onto the gallium nitride, hoping that at least some would stay.

To his surprise, the technique worked and he gave her a clean indium gallium nitride crystal. He quickly incorporated this active layer into his LED, but the well worked too well and overflowed with electrons, returning them to the gallium nitride layers. Undeterred, within a few months, Nakamura also fixed this by creating the opposite of a well, a hill. He returned to his reactor once again to produce gallium aluminum nitride, a compound with a larger bandgap that could prevent electrons from escaping the well once inside. (dramatic music) The structure of the blue LED had become much more complex than anyone could have imagined, but it was complete.

In 1992, Shūji Nakamura had this. - And I showed it to the president and said, "Please, president, come to my office." I showed him the blue LED and he said, "ohh, this is cool, isn't it?" I became so happy. I just left my office, yeah. - After 30 years of searching by countless scientists, Nakamura had achieved it. He had created a gloriously bright blue LED that could be seen even in daylight. It had a light output power of 1,500 microwatts and emitted a perfect blue at exactly 450 nanometers. It was more than 100 times brighter than previous pseudo-blue LEDs on the market.

Nakamura wrote: "I felt like I had reached the top of Mount Fuji." Nichia called a press conference in Tokyo to announce the world's first true blue LED. The electronics industry was stunned. A Toshiba researcher commented: "Everyone was caught with their pants down." The effect on Nichia's fortunes was immediate and explosive. Orders poured in and, by the end of 1994, they were manufacturing 1 million blue LEDs a month. Within three years, the company's revenue had nearly doubled. In 1996, they made the leap from blue to white by placing a yellow phosphor on the LED. This chemical absorbs blue photons and re-radiates them in a broad spectrum throughout the visible range.

Soon, Nichia was selling the world's first white LED. Finally, unlocking the last frontiers that many had doubted: LED lighting. Over the next four years, its sales doubled again. In 2001, its revenue was approaching $700 million a year. More than 60% came from blue LED products. Today, Nichia is one of the largest LED manufacturers in the world with annual revenues in the billions. As for Nakamura, to whom did Nichia owe the quadrupling of his fortune? (dramatic music) - I increased my salary, $60,000. After duplicating, yes. - I heard you only received a $170 bonus. - Each patent. - So you got a bonus of $170 for the patent. - Yes Yes. - All of this was while Blue LED was generating hundreds of millions of dollars in sales.

Eji Ogawa had always seen Nakamura's stubborn individuality as a liability, not a strength. The message was clear. In 2000, after more than 20 years at Nichia, Nakamura left the company to go to the United States, where job offers had been coming in. But his problems with Nichia were not over. He began consulting for Cree, another LED company. Nichia became enraged and sued him for leaking company secrets. Nakamura responded by countersuing Nichia for never adequately compensating him for his invention, seeking $20 million. In 2001, Japanese courts ruled in Nakamura's favor and ordered Nichia to pay him 10 times his initial demand. But Nichia appealed and the case was eventually settled with a payout of $8 million.

In the end, this was only enough to cover Nakamura's legal fees. (soft music) This is all he got for an invention that now comprises an $80 billion industry, from household lights to streetlights. While watching this video on a phone, computer or TV. If you're outside following traffic lights or displays, you'll likely rely on blue LEDs. We may even be getting too many of them. You may have heard warnings to avoid blue light from screens before bed because it can disrupt your circadian rhythm. That all comes from the blue gallium nitride LED. But when it comes to lighting, an LED bulb has practically no drawbacks.

Compared to an incandescent or fluorescent bulb, they are much more efficient. They last much longer, are safer to handle, and are completely customizable. 30 years after the first white LED, high-end light bulbs today allow you to choose between 50,000 different shades of white. Most importantly, its price has been reduced to just a couple of dollars more than other types of bulbs. And thanks to its efficiency, with an average daily use and electricity price, you can recover that cost in just two months and continue saving for years. The result is a revolution in lighting. In 2010, only 1% of residential lighting sales worldwide were LED.

In 2022, it was more than half. TheExperts estimate that in the next 10 years almost all lighting sales will be LED. (soft music) The energy savings will be enormous. Lighting accounts for 5% of all carbon emissions. A complete switch to LED could save approximately 1.4 billion tonnes of CO2, which is equivalent to taking almost half of the world's cars off the road. Currently, Nakamura's research focuses on the next generation of LEDs, micro LEDs and UV LEDs. - So what are they doing there? - LEDs, lasers, power devices. This is one of the best facilities in the US - and this is your fault?

What is the size of a standard LED? - 300 times 200 microns. - Well. - The smallest is five microns. - That's incredibly small. - Basically, you can use it for near-eye displays, like AR and VR. - Could you have a retina screen like up here? - Yes. - A human hair would be that thick. - Yes. - And that's a really small LED. Ultraviolet LEDs could be used to sterilize surfaces such as in hospitals or kitchens. Simply turn on the UV lights and the pathogens will be killed in seconds. - COVID-19, you know, the stock prices of UV LED companies skyrocketed because everyone was hoping to use these UV LEDs.

We can sterilize all COVID-19, right? To emit diodes, we use indium gallium nitride. For UV rays, we use gallium aluminum nitride. Well. - Because the forbidden band is much larger. - Do you think this is what's coming? - Okay, it works, but the problem is the cost. The efficiency is less than 10%. The cost is very high. But if the efficiency exceeds 50%, the cost is almost comparable to that of a mercury lamp. - And you think it will happen, right? Will efficiency increase? - Yes, yes, I think so. - It's just a matter of time. - Yes I think so. - And it's even tackling one of the biggest challenges of our time. - I'm interested in physics. - Me too! - I'm still interested in nuclear fusion.

I recently started the nuclear fusion company. - Actually? - Oh, yes, last year. - No way. - No way, huh. (soft music) - In 2014, Nakamura, Akasaki and Amano received the Nobel Prize in Physics for creating the blue LED. Shortly after, Nakamura publicly thanked Nichia for supporting his work and offered to visit him and make amends, but they rejected his offer and today their relationship remains cold. But perhaps even more important than the Nobel Prize: by the time Nakamura launched Blue LED in 1994, he had published more than 15 papers and eventually received his doctorate in engineering. Today he has published more than 900 articles.

Throughout his entire journey, one thing has never changed. What is your favorite color? - Ah, blue. - Was it always blue? Or only after making the LED? - I was born in a fishing village. Fishing town. In front of the house there is a stunning ocean. Always blue. -As I learned about Nakamura's story, I realized that what set him apart from the thousands of researchers trying to unlock the blue LED was not necessarily his knowledge, but his determination, critical thinking, and problem-solving skills. Where others saw dead ends, he saw potential solutions. So if he's looking for a free and easy way to start developing these skills yourself right now, look no further than today's sponsor, Brilliant.

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