electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...

spintronics Spintronics (a portmanteau meaning spin transport electronics), also known as spin electronics, is the study of the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, in solid-sta ...

, a tunnel junction is a barrier, such as a thin insulating layer or electric potential, between two electrically conducting materials.

Electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary partic ...

s (or

quasiparticle In physics, quasiparticles and collective excitations are closely related emergent phenomena arising when a microscopically complicated system such as a solid behaves as if it contained different weakly interacting particles in vacuum. For exa ...

s) pass through the barrier by the process of

quantum tunnelling Quantum tunnelling, also known as tunneling ( US) is a quantum mechanical phenomenon whereby a wavefunction can propagate through a potential barrier. The transmission through the barrier can be finite and depends exponentially on the barrier ...

. Classically, the electron has zero probability of passing through the barrier. However, according to

quantum mechanics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, q ...

, the electron has a non-zero wave amplitude in the barrier, and hence it has some probability of passing through the barrier. Tunnel junctions serve a variety of different purposes.

Multijunction photovoltaic cell

In multijunction photovoltaic cells, tunnel junctions form the connections between consecutive p-n junctions. They function as an ohmic electrical contact in the middle of a

semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

device.

Magnetic tunnel junction

In magnetic tunnel junctions, electrons tunnel through a thin insulating barrier from one magnetic material to another. This can serve as a basis for a magnetic detector.

Superconducting tunnel junction

In superconducting tunnel junctions, two

superconducting Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fields are expelled from the material. Any material exhibiting these properties is a superconductor. Unlike ...

electrodes are separated by a non-superconducting barrier. Cooper pairs carry the supercurrent through the barrier by quantum tunneling, a phenomenon known as the

Josephson effect In physics, the Josephson effect is a phenomenon that occurs when two superconductors are placed in proximity, with some barrier or restriction between them. It is an example of a macroscopic quantum phenomenon, where the effects of quantum me ...

. This setup can form the basis for extremely sensitive magnetometers, known as

SQUID True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting ...

s, as well as many other devices.

Tunnel diode

tunnel diode A tunnel diode or Esaki diode is a type of semiconductor diode that has effectively " negative resistance" due to the quantum mechanical effect called tunneling. It was invented in August 1957 by Leo Esaki, Yuriko Kurose, and Takashi Su ...

s, a diode allows the tunneling of electrons for certain voltages. This allows them to be used for generating high-frequency signals.

Scanning tunneling microscope

In scanning tunneling microscopy (STM), the tip/air/substrate ( metal-insulator-metal) can be viewed as a tunnel junction.

References

Quantum electronics Electrodes Mesoscopic physics {{Electrochem-stub