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Incoming links: New Phenomenon in Narrow Germanium Junctions by Leo Esaki
Leo Esaki Created 2026-10-18 Updated 2026-11-05
Leo Esaki observed a distinctive tunnelling response in heavily doped germanium junctions. A narrow barrier allows carriers to tunnel between occupied and empty electronic states on opposite sides. Increasing the voltage can reduce the overlap of available states and hence reduce the current, producing negative differential resistance. The effect turns quantum tunnelling into a useful device characteristic: a falling current-versus-voltage slope is a local differential property, not a requirement that current and voltage have opposite signs.[ref]
New Phenomenon in Narrow Germanium Junctions by Leo Esaki. Physical Review 109, 603 (1958), narrow-junction tunnelling response
Portrait of Leo Esaki
. Unknown photographer (Asahi Shinbun / The Asahi Shimbun). Public domain under Japanese copyright law (as stated on Commons File page). Source usage terms, via Wikimedia Commons. Source.
Quantum tunnelling is supported by transport and decay through barriers that classical particles of the same energy cannot traverse. Three complementary examples are:
- In alpha decay, an alpha cluster escapes the attractive nuclear region through a Coulomb barrier. The barrier penetration factor depends exponentially on a forbidden-region action, helping explain the strong dependence of lifetimes on emitted alpha energy. This is evidence from systematic decay rates, rather than direct imaging of an alpha inside the barrier.
- A scanning tunnelling microscope measures current across a narrow vacuum gap between a conducting tip and sample. At small bias an approximate dependence is with . The strong gap-distance sensitivity enables atomic-scale imaging and local spectroscopy. Electronic density of states and barrier height also affect the current, so constant-current contrast is not an unqualified geometric atom map.[ref]Surface Studies by Scanning Tunneling Microscopy by Gerd Binnig and others. Vacuum-tunnelling measurement and surface imaging
- A heavily doped Tunnel diode has a narrow p-n barrier. Bias changes the overlap of occupied and empty states across it; interband tunnelling produces a characteristic peak and Negative differential resistance interval in its current-voltage curve. The measured voltage dependence agrees with the changing band overlap, providing a solid-state transport example.[ref]New Phenomenon in Narrow Germanium Junctions by Leo Esaki. Germanium-junction tunnelling characteristic
Together these test barrier penetration in nuclear decay, vacuum-gap transport and semiconductor transport. Their detailed currents depend on state supply and matching as well as the barrier transmission probability.