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Schottky defects arise when some lattice points in a crystal, such as those in NaCl, remain unoccupied, creating lattice vacancies without disturbing the overall electrical neutrality of the crystal. This defect is common in ionic crystals where the positive and negative ions are similar in size, as seen in sodium chloride and cesium chloride. The presence of Schottky defects enables the crystal to conduct electricity to a small extent through an ionic mechanism. Electric fields cause nearby...
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Non-stoichiometric defects refer to a type of defect in the crystal structure of a compound where the ratio of its constituent elements deviates from the ideal stoichiometric ratio. There are two main types of non-stoichiometric defects: metal excess defects and metal deficiency defects.Metal excess defects occur when there is a slight surplus of metal ions than what is required by the stoichiometric ratio of the compound. For example, heating a sodium chloride crystal in sodium vapor results...
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Evidence for Defect-Mediated Tunneling in Hexagonal Boron Nitride-Based Junctions.

U Chandni1, K Watanabe2, T Taniguchi2

  • 1Institute for Quantum Information and Matter, Department of Physics, California Institute of Technology , 1200 East California Boulevard, Pasadena, California 91125, United States.

Nano Letters
|October 29, 2015
PubMed
Summary

Electron tunneling through hexagonal boron nitride (hBN) barriers shows defects causing Coulomb blockade. Annealing these metal-hBN-metal junctions removes defects, improving electron transport.

Keywords:
Tunnelingannealingcoulomb blockadegraphitehBN defectshexagonal boron nitride (hBN)

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Area of Science:

  • Condensed Matter Physics
  • Materials Science
  • Nanotechnology

Background:

  • Atomically thin hexagonal boron nitride (hBN) is a promising material for electronic devices due to its insulating properties.
  • Understanding electron transport mechanisms through hBN barriers is crucial for developing novel electronic components.

Purpose of the Study:

  • To investigate electron tunneling phenomena through hexagonal boron nitride (hBN) barriers of varying thicknesses.
  • To identify and characterize factors influencing electron transport, such as defects and their impact on device performance.

Main Methods:

  • Fabrication of metal (Cr/Au) and semimetal (graphite) counter-electrode junctions with atomically thin hBN barriers.
  • Measurement of electron tunneling current as a function of applied bias voltage.
  • Analysis of tunneling resistance, Coulomb blockade signatures, and the effect of annealing treatments.

Main Results:

  • Tunneling resistance increases exponentially with hBN barrier thickness, as predicted by theory.
  • Thicker hBN junctions exhibit Coulomb blockade, indicated by current suppression near zero bias and step-like features.
  • Defects within the hBN layer are identified as the cause of Coulomb blockade, with annealing effectively removing these defects and blockade signatures.

Conclusions:

  • Electron tunneling through hBN is significantly influenced by intrinsic defects.
  • Coulomb blockade observed in hBN junctions is attributed to single-electron charging of nanometer-scale defects.
  • Annealing is an effective post-fabrication method to mitigate defect-induced scattering and improve electron tunneling characteristics in hBN-based devices.