Notable Alumni

Leo Esaki (Nobel Prize in Physics 1973)

Written by Tohru Okamoto (Associate Professor, Department of Physics)
Leo Esaki

© The Science and Technology Promotion Foundation of Ibaraki

Dr. Leo Esaki graduated from the Department of Physics, Faculty of Science in 1947 and earned a PhD in physics from the Graduate School of Science in 1959. Over many years, Dr. Esaki has realized outstanding achievements in the field of semiconductor physics. The following are the two highly significant accomplishments he has made.

1. Discovering Tunneling Phenomena in Semiconductors

By adding impurity in semiconductors, it is possible to make an n-type region where electrons are the majority charge carriers as well as a p-type region where holes are the majority charge carriers. In a semiconductor crystal, the interface between the p-type and n-type regions is called a p-n junction, which is the fundamental building block of diodes and transistors.

While Dr. Esaki was involved in the development of a transistor with advanced high-frequency performance at Tokyo Telecommunications Engineering Corporation (currently Sony Corporation) in 1957, he discovered a phenomenon called a negative resistance: electric current decreases with the increase of voltage in a p-n junction for which a large amount of impurity is added. He proved that the phenomenon occurs by the jump of electrons from an n-type region to a p-type region, which is caused by a quantum-mechanical tunneling effect. The element developed by this phenomenon is called the Esaki-Diode and is applied to the microwave oscillation circuit. Furthermore, this research became the pioneering study of a new research field called Tunneling Spectroscopy and it made a huge contribution to the development of research on metals and superconductors. For these achievements, Dr. Esaki received the Nobel Prize in physics in 1973 and the Order of Culture in 1974.

2. Proposal on and Realization of the Concept of Semiconductor Superlattice

In 1969, while working at the IBM Watson Research Center in the U.S., Dr. Esaki proposed an artificial material called semiconductor superlattice that has a periodic structure of layered semiconductors with different compositions. With this proposal, he predicted several effects that cannot be observed in ordinary materials. Moreover, he materialized superlattice consisting of group III-V compound semiconductors based on the development of thin film growth technology — this is called molecular beam epitaxy — that can control component fractions on an atomic scale. As he had predicted, he discovered negative resistance (in 1972) and resonant tunneling (in 1973).

The concept of artificial superlattice proposed by Dr. Esaki opened up a new field in solid-state physics and made a major impact on the subsequent study. Moreover, many technologies based on Dr. Esaki's research can be found in devices all around us. These include semiconductor devices such as the quantum-well laser and high-electron-mobility transistor as well as the readout head of hard discs with artificial superlattice composed of ferromagnetic metal and nonmagnetic metal. These achievements led him to the Japan Prize in 1998.

Up to the present date, Dr. Esaki has held a number of important posts and has contributed widely to the activation of scientific research at Japanese universities. During this period, he won many awards.

See also: http://nobelprize.org/nobel_prizes/physics/laureates/1973/

Profile

Current position

  • President, Yokohama College of Pharmacy
  • Director, The Science and Technology Promotion Foundation of Ibaraki

Academic history and professional highlights

1925 Born on March 12 in Osaka
1947 Bachelor in physics, Faculty of Science, the University of Tokyo
1959 PhD in physics, the University of Tokyo
1947 Kobe Kogyo Company
1956 Tokyo Tsushin Kogyo Co., Ltd. (presently SONY)
1960 Watson Research Center, IBM, USA
1967 IMB Fellow
1976 Part-time board member of Japan IBM as additional post
1992 President, University of Tsukuba
1998 - Present Director, The Science and Technology Promotion Foundation of Ibaraki
2000 President, Shibaura Institute of Technology
2006 - Present President, Yokohama College of Pharmacy

Honors & Awards

1965 The Japan Academy Award
1973 The Nobel Prize in Physics (for experimental discoveries regarding tunneling phenomena in semiconductors)
1974 The Order of Culture from the Japanese Government
1985 The American Physical Society
1991 International Prize for New Materials for his pioneering work in artificial semiconductor superlattices, the IEEE Medal of Honor
1998 Japan Prize
1998 Grand Cordon of the Order of the Rising Sun

Achievements

Dr. Esaki has realized outstanding achievements in the field of semiconductor physics over many years. In 1957, he proved the tunneling effect of quantum mechanics with the Esaki Diode, which is an extremely important discovery in physics. He was awarded the Nobel Prize and the Order of Culture for his “experimental discoveries regarding the tunneling phenomena in semiconductors.” His proposal on artificial superlattice in 1969 contributed to open up a new field in solid physics; he received the Japan Prize for this achievement. Dr. Esaki's research is not only important in the field of physics, butit has also significantly contributed to the development and improvement of electronics elements. Dr. Esaki has been outspoken about both Japanese and American society and culture, which has enhanced international understanding.

Dr. Esaki has held posts as president of the University of Tsukuba and president of Shibaura Institute of Technology; he has contributed not only to reforms of the two universities but also to the vitalization of Japanese universities and scientific research as a member of the university council. Since June 1999, he has been active in creating ventures as the chairperson of JANBO (Japan Association of New Business Incubation Organizations). In March 2000, he worked on education issuesas the chairperson of the “National Assembly for Education Reform,” a private advisory body to the prime minister. Since April 2002, Dr. Esaki has been deeply committed to the promotion of creating the world's best universities with global competitiveness as the chairperson of the 21st Century COE program.