Leo Esaki

Leo Esaki (/ɪˈsɑːki/ ih-SAH-kee; Japanese: 江崎 玲於奈, romanized: Esaki Reona; born March 12, 1925) is a Japanese solid-state physicist who shared the 1973 Nobel Prize in Physics with Ivar Giaever and Brian Josephson for his work on tunneling in semiconductors, which led to his invention of the tunnel diode that exploits this phenomenon. His research was done when he was with Sony. He has also contributed in being a pioneer of semiconductor superlattices.

Leo Esaki was born on March 12, 1925, in Osaka, Japan, and grew up in Kyoto, where he attended the Third Higher School. He then went on to study physics at Tokyo Imperial University (now the University of Tokyo), graduating with a B.S. in 1947.

In 1956, Esaki became chief physicist at Tokyo Tsushin Kogyo (now Sony).

In 1958, Esaki recognized that when the p–n junction width of germanium is thinned, the current–voltage characteristic is dominated by the influence of the tunnel effect—and, as a result, he discovered that as the voltage is increased, the current decreases inversely—indicating negative resistance. This discovery was the first demonstration of solid tunneling effects in physics, and it was the birth of a new electronic device called the tunnel diode (or Esaki diode), the first quantum electronic device in history. He received a Ph.D. from Tokyo Imperial University due to this breakthrough invention in 1959.

In 1973, Esaki was awarded the Nobel Prize in Physics for this work. He became the first Nobel laureate to receive the Prize from King Carl XVI Gustaf of Sweden.

In 1960, Esaki moved to the United States and joined IBM's Thomas J. Watson Research Center, where he was appointed an IBM Fellow in 1967.

In 1970, Esaki predicted that semiconductor superlattices will be formed to induce a differential negative-resistance effect via an artificially one-dimensional periodic structural changes in semiconductor crystals. His unique "molecular beam epitaxy" thin-film crystal growth method can be regulated quite precisely in ultrahigh vacuum. A 1987 comment by Esaki regarding the original paper notes:

"The original version of the paper was rejected for publication by Physical Review on the referee's unimaginative assertion that it was 'too speculative' and involved 'no new physics.' However, this proposal was quickly accepted by the Army Research Office..."