“It was really unexpected,” said Hiroshi Amano . In fact, he was so surprised that at first he thought it must be a joke or a mistake.
On 7 October 2014, Hiroshi Amano had one of the surreal experiences of his life. He arrived in Frankfurt, Germany, on a flight from Japan and quickly checked his emails before boarding another flight to Lyon, France. “I had many e-mails entitled ‘Congratulations’ or ‘Omedetou (in Japanese)’ but I did not have time to check the contents,” he explains. “I thought they were spam mails.” Upon arriving in France, he stepped out of the airport arrivals hall into a crowd of excited journalists. One of whom informed Amano that he had been jointly awarded the Nobel prize in physics with his former supervisor Isamu Akasaki and another Japanese scientist Shuji Nakamura. “It was really unexpected,” he says. In fact, he was so surprised that at first he thought it must be a joke or a mistake.
The second and the third volumes of the Handbook of Crystal Growth (2nd Edition), describes Amano’s and others’ recent work to improve our fundamental understanding of the growth of nitrides by MOCVD and MOVPE for a range of nitride-based devices.
The Nobel committee had awarded the prize to these three researchers for the invention of efficient blue light-emitting diodes (LEDs) which has enabled bright and energy-saving white light sources. Today, white LEDs are the most energy efficient and longest lasting bulbs on the market, and can be found lighting our homes and business and inside our TVs, computers and mobile phones. In 2012, more than 210 billion LEDs packages were reportedly produced worldwide – this is approximately 30 for each person on Earth.
Hiroshi Amano holding his Nobel medal (Credit: Nobel Media AB 2014/Alexander Mahmoud).To create white light, LEDs that produce all three of the primary colours of light are needed. By the end of the 1960s, red and green LEDs had been successfully made but LEDs that produced blue light were to prove elusive. Akasaki had identified that gallium nitride was the most likely candidate, but his group were struggling to grow crystals of the material of a high enough quality. Additionally, while n-type gallium nitride semiconductors were rather easy to grow, the p-type counterpart was extremely difficult. Amano overcame both these hurdles whilst working under Akasaki’s supervision in the mid 1980s. “My contribution was showing that the high quality GaN can be grown on a sapphire substrate by depositing low temperature AlN buffer layer before the growth of GaN and also that p-type GaN can be made by Mg doping followed by low energy electron beam irradiation treatment,” he explains.
Since 2010, Amano has gone on to set up his own successful research team currently based at Nagoya University – which is also where Akasaki and he performed their Nobel prize-worthy research in the 1980s. His team works broadly on growing novel crystals of semiconducting group 3 nitrides with the aim of enabling the development of other sustainable devices. These crystals are grown either by MOCVD (metalorganic chemical vapor deposition) or the related technique MOVPE (metalorganic vapour phase epitaxy).
In keeping with tradition, Hiroshi Amano autographs a chair at Bistro Nobel in the Nobel Museum, Stockholm (Credit: Janerik Henriksson/TT).The design of LEDs that produce deep UV light has been one of Amano’s team’s most significant recent developments. Photons of deep UV light interact with a huge variety of different chemical and biological molecules and these types of LEDs are expected to find use in applications ranging from sensing to cleaning up pollutants. “The most exciting research carried out in my group recently was realizing high efficiency deep UV LEDs by a high pressure MOVPE growth method,” Amano says. The team are also working on designing improved nitrides for powering more energy-efficient heterojunction field-effect transistors and laser diodes.
To achieve the atomic-level control needed to grow nitrides suitable for these applications; Amano’s team spend much of their time studying how the growth processes occur. They are currently developing a method to observe the growth of InGaN and related semiconductors in almost real-time inside an x-ray diffractometer. “A fundamental understanding of the growth process is essential for realizing new types of devices,” he says.
Since winning the Nobel prize, Amano says he has been inundated with invitations to give talks. “By the end of this year, I will have given more than 200 lectures since the prize was announced. Of course it is busy, but I am enjoying these unexpected encounters with researchers in the different fields to my own,” he says. “I learn a lot through discussions with researchers with different specialties.” It is also talking with others that he credits for his success so far: “I have got many of my inspirations though discussions with my colleagues.”
The second and the third volumes of the Handbook of Crystal Growth (2nd Edition), published by Elsevier and available on ScienceDirect, describes Amano’s and others’ recent work to improve our fundamental understanding of the growth of nitrides by MOCVD and MOVPE for a range of nitride-based devices.