Hiroshi Amano (2016) - Lighting the Earth by LEDs

Good morning everyone. I am so honoured to get this opportunity, so I’d like to thank the members of the Council of Lindau Nobel Laureate Meetings. First of all, I’d like to mention that I am not a physicist. I belong to the engineering department. Today I’d like to emphasise the importance of not only the science but also the engineering, that’s one point. And the second point is, maybe my field is not the major one in this meeting. I’d like to mention that the importance of the minority research is very important. So I’d like to point out 2 things in this presentation. According to the Nobel Foundation, the LED lamp holds great promise for increasing the quality of life for over 1.5 billion people around the world. So first, I’d like to start by saying how I encountered the blue LEDs. From primary school to high school I was not a good student. My impression at that time was, that studying in Japan was only to enter a good high school or a good university. But I couldn’t understand the reason why I should study so hard only to enter high school or only to enter university. But when I entered university, in the first class introduction to engineering the old professor explained the meaning of the Japanese, or Chinese, Kanji character, we call it Kô. Kô is engineering, this character means 'the people'. So this character meaning the engineering is connecting people to people, meaning engineers should support the people. Then, suddenly, I understood why I should study. (Laughter) For me studying is for the people, not to enter university. Then I was able change my mind and study hard, very hard, at university. This here summarises the overview of the development of LEDs. The first commercial LED were the red LEDs, composed of gallium arsenide or gallium arsenide phosphide compound materials, which was invented by Professor Holonyak’s group at the University of Illinois, in 1962. In 1974, George Craford, the Hewlett Packard engineer, developed gallium-phosphide-based green LEDs. At that time the many researchers, not only the researchers, but the person who studied the periodic table of elements, all the people could imagine what’s next. Next should be the gallium-nitride-based blue LEDs. This material, gallium nitride, the seed of the gallium nitride came from this country. The German physicist Professor Grimmeiss found the importance of this material as the blue light emitting diodes in 1960, 56 years earlier. So in the 1970s, many, many researchers around the world tried to commercialise the blue LEDs based on gallium nitride. For example, Stanford University and RCA, in the United States, Philips. Or in Japan Oki Electric, Hitachi or Matsushita, now Panasonic. But unfortunately, all the efforts in the 1970s failed. So it was a too early try, no good crystal, no p-type or no indium gallium nitride. So many, many researchers abandoned these materials and started the new material research such as zinc selenide. But only one person could not abandon this material: my supervisor Professor Isamu Akasaki. He couldn’t abandon this material. But unfortunately, his company decided to quit the project. So he had to move from the company to Nagoya University in 1981. And I joined his group as an undergraduate student in 1982. When I saw the subject of the research for the nitride based blue LEDs, I was so excited. The reason was, from the first year to the third year as a university student, I was interested in the microcomputer system, now PC, personal computer system. Because 1975, Bill Gates and Paul Allen developed Microsoft. And one year later Apple one was realised by Steve Jobs and Steve Wozniak. From this success, the development of personalisation of microcomputer systems was so enormous. I wanted to contribute to the further development of the microcomputer system. And the display was one of them. At that time, in all the displays the Braun tube was used which was so big and energy consuming. So if I could achieve the blue LED, I could change the world. That was the reason why I started to devote myself on gallium nitride research. When Professor Akasaki moved from the company to the university, a very big or very important decision was made. That is the change of the crystal growth method from the conventional hydride vapour phase, HVP, to metalorganic or organometallic vapour phase epitaxy (MOVPE). The reason is the HVP was very, very complicated. And the beginning student like me could not control the growth system. But MOVPE was a new growth system which was rather easy to control. Then Professor Akasaki decided to use the metalorganic vapour phase epitaxy, MOVPE in short. That was a very good decision. But the problem was, if we wanted to buy the MOVPE system we needed at least €1 million. The research fund at that time in Japan, at the university, was €25,000. So we couldn’t buy it. So we students decided to develop our own crystal growth system by ourselves. Now this is "the only one", our original MOVPE reactor for €25,000. The beer bottle - the beer bottle is very important to fabricate the rf coil. By heating it and winding it around the beer bottle we could fabricate a very good rf coil. In such a way we have developed our original MOVPE reactor. and could start to do the experiments for crystal growth of the gallium nitride on a sapphire substrate. That’s the good old days. In the laboratory nobody knew about the new growth process, MOVPE. So even a beginning student like me could very, very freely discuss with the professor, the associate professor, with no hierarchical relationship. So the student could independently proceed with the experiments. Then the students tend to feel the responsibility for their research results. So I enjoyed very much to do the experiments but, of course, it was very, very difficult to grow high-quality gallium nitride crystals. So 3 years passed without any improvement. But just at the end of the master courses, I decided to change the growth procedure and to use the buffer layer. The idea came from the discussion with a young professor, Professor Sawaki. He always mentioned, that in case of BP - BP is boron phosphide, boron phosphide on silicon substrate – the predisposition of the buffer that is phosphorus improves the lateral crystal growth of boron phosphide. Then high-quality boron phosphide could be grown on silicon substrate. Then I imagined, if I used the aluminium nitride, the different materials as a buffer layer, maybe I could improve the quality. Then, suddenly, I succeeded in growing the world’s highest quality gallium nitride on a sapphire substrate, using the low temperature buffer. So I wrote the paper and submitted to the Applied Physics Letters. But this paper did not take notice of other researchers. The age changed from the nitride to the zinc selenide. There was zinc selenide booming all over the world. So, young researchers, I’d like to ask you, which would you choose as the research task? The majority field: Many researchers, hot competition. You can write many, many journal papers. High possibility to get the academic position. The minority: Very limited researchers, moderate competition. It may be difficult to write the journal papers. Few possibilities to get the academic position. In my case I chose the minority. Also I tried to write a patent – a patent in engineering field is very important. So I investigated the previous papers. I found 2 important papers: the gallium arsenide on silicone and the gallium nitride on the sapphire. In the case of the gallium arsenide, low temperature gallium arsenide was used, which is the same material. So in my case, I used aluminium nitride - it’s different, ok. And in the case of gallium nitride on sapphire. It was grown by molecular beam epitaxy and the single crystalline gallium nitride was used. In my case I used not a single crystalline but amorphous aluminium nitride or polycrystalline aluminium nitride. So that was also different. So I focused on claiming only the low temperature aluminium nitride, and submitted the patent in 1985. But 6 years later, in 1991, one of the Japanese companies - maybe you know Nichia Corporation, led by professor Nakamura. His team submitted a patent claiming that low temperature gallium aluminium nitride, except only for aluminium nitride. You understand what this meant? I couldn’t believe it. But this patent was accepted - so I learned a lot about the patent. Anyway, for us the next target was, of course, the p-type gallium nitride. So during my doctor courses, for 3 years, I concentrated on growing p-type gallium nitride - but without any success. But I found some interesting phenomenon. I visited NTT as an internship and found that the blue luminescence of zinc-doped gallium nitride was irreversibly enhanced by electron beam irradiation. So I was so excited and tried to write the journal papers to get the PhD. But when I went back to the Nagoya University and investigated the previous papers, I found, that Moscow University, Doctor Saparin, already found just the same phenomenon as I found in 1983 - 4 years before my findings. So I was so depressed and abandoned to get the PhD. But I was very lucky that I could continue research on seeking p-type gallium nitride as a research associate under the support of Professor Akasaki. One year after the graduation of PhD post I found this graph. This graph really shows what Phillips mentioned in "Bonds and Bands in Semiconductors" that in the case of gallium phosphide magnesium is much, much better than zinc in terms of the activation. So I found my mistake. I should use the magnesium. Then, in combination with the electron beam treatment, we realised the p-type gallium nitride, the p-n junction LED, for the first time in the world in 1989. And as for the mechanism of a p-type convergent, the first impression is it should be related to the thermal effect. But for me the thermal effect was not so exciting, it was very, very easy. So I tried to find another mechanism. I searched for the laser beam irradiation or microwave irradiation, any other kind of irradiation. But all the efforts failed. that p-type convergent could be realised only by thermal annealing. In this case also I studied a lot about physics. Then, next target is the true blue luminescence, indium gallium nitride. Of course, we started at the very initial stage, in 1986. But in our case, we only realised the indium amount of 6% which is insufficient for the blue luminescence. For the blue luminescence we need at least 15%. The reason is very simple: we used hydrogen as the carrier gas. But in 1989, NTT group, Professor Matsuoka, succeeded in growing high-indium-content indium gallium nitride. The reason why they succeeded is they used nitrogen as the carrier gas – the only difference is hydrogen or nitrogen. In 1993 was the first commercialisation of indium-gallium-nitride-based blue LEDs, that has been achieved by Professor Nakamura’s team of Nichia Corporation. So I’d like to emphasise, how blue LED changed our lives - or your lives. The reason why you can enjoy the Game Boys, smart phone, cell phone with the full colour display is because of the emergence of blue LED. But some people complain about the increase of smart phone addiction. But when I was a student I considered the application, only I imagined the displays. But one of the engineers in Nichia Corporation, Doctor Bandoh, found that this mechanism – this is the blue LED and by adding this yellow film we can easyly realise white LED. Then the applications of blue LEDs have been expanded - not only to the display but also the general lighting system. So I can say that this is a good example that new technology leads to new applications. Today the efficiency of the LED lighting is 8 times higher than that of the incandescent one. And 2 times higher than that of the fluorescent one. Then we can expect a decrease of the electricity consumption by using, or by replacing, the conventional lighting system with LED lighting system. So this graph shows the electricity generation and the CO2 emission in Japan. Before the year 2011, about 30% of the electricity was generated by nuclear power plants. But in Japan we have to stop the nuclear power plants. So the ratio of thermal power increases drastically, almost 90%. So CO2 emission increase drastically. The government target by the year 2030 is this level. Maybe the reduction of economy activity leads to it much faster, but anyway. In Japan, by the year 2020, we can reduce the total electricity consumption by about 7%, by replacing our lighting system with LED lamps - which corresponds to 1 trillion Japanese Yen. More importantly, this LED lighting system not only changes our life, but it also keeps our traditional life, for example in Mongolia. For Mongolia people, the nomad life is the traditional life. But because of the insufficient lighting in the night, the young people want to move to the urban areas, and they want to get fixed housing. But with the emergence of LEDs the young people go back to the nomad life. And I visited this man in the Ger and found that the LED lamp is really used in the Ger house. So I was so pleased to see. Next is the Deep UV LEDs for water purification. UNICEF reported that still more than 600 million people lack access to improved drinking water. And 2.4 million people do not use an improved sanitation facility. And global warming causes increase of bacterium in drinking water, even in the northern part. So water purification is very important. So we developped our new original crystal growth system. And, with the support of the government, we succeeded in fabricating the Deep UV LEDs. This is one example. It’s not so bright, but it can excite the blue phosphor. This is an example of the sterilisation of bacterium. And the water purification system has been already commercialised. And this is also used for steriliser, resin cure, printing, paper money discrimination, photolithography, and also in medicine, in dermatology. So our next target is the power device. For example, the solar cell is DC, but we use AC in our house. The electric vehicle, the battery is DC, but the motor is AC. So we have to change from DC to AC, and the inverter is used. In a conventional inverter system the efficiency is 95% on average. But by replacing it to the new materials, we can further reduce the efficiency to over 99%. So by using this system, we can realise a carbon neutral society in the very near future, like COP 21. Finally, I’d like to emphasise, once again, to the young generation. I do believe that the engineer can solve the global issues. For example, there is a relationship between terrorism and the Gini coefficient, in the difference of rich and poor. It's an important critical point in 1980. And also there is the relationship between the hunger map and the population growth rate. This is the example of the global issues, and I believe that in future you will solve these problems. Finally, I’d like to mention: young researchers, you are very lucky, because we are facing many, many global issues to resolve. And I am praying for all of your success in the future. Thank you so much for you’re kind attention.

Hiroshi Amano (2016)

Lighting the Earth by LEDs

Hiroshi Amano (2016)

Lighting the Earth by LEDs

Abstract

I would like to emphasize how materials science and engineering have played a key role in realizing innovation in displays and artificial lighting, using blue LEDs as an example. Portable game machines and cellular/smart phones are very familiar items, especially to young people. It should be stressed that the younger generation can now enjoy full-color portable games and cellular/smart phones because of the emergence of blue LEDs based on nitrides. Today, the applications of blue LEDs are not limited to displays. In combination with phosphors, blue LEDs can act as a white light source and are also used in general lighting. In this presentation, I will describe how these material systems were developed and what the researchers who first developed these systems were aiming for. In addition, I will discuss what the next generation of researchers should be doing to achieve future innovations.

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