Leo Esaki
active c. 1925, Osaka, Japan
Japanese physicist who discovered electron tunneling in semiconductor junctions and invented the Esaki tunnel diode.
Working at Sony's precursor Tokyo Tsushin Kogyo in 1957, Esaki studied heavily doped germanium p–n junctions and found a backward current that quantum tunneling alone could explain — leading to the tunnel diode, the first semiconductor device based purely on a quantum effect. At IBM he later pioneered the semiconductor superlattice, an artificial periodic structure that made band engineering possible.
Nobel-winning work
Esaki shared the 1973 Nobel Prize for 'experimental discoveries regarding tunneling phenomena in semiconductors'. In a germanium p–n junction doped so heavily that the band edges overlap, he found that electrons can tunnel through the depletion region, producing a current that first rises then falls with voltage — a region of negative differential resistance.
The resulting Esaki diode, announced in 1957–58, switched at unprecedented speed and became a workhorse of early microwave and computer circuits, while directly demonstrating that tunneling is a practical, controllable transport mechanism in solids.
Workplaces: Sony Corporation (Tokyo Tsushin Kogyo), IBM Thomas J. Watson Research Center
Japan