B93501044, B93505007 ???

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Fermi-Level Pinning Schottky Barrier Height
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Schottky Barrier

• Ideal Condition
• Fm The work function of metal (about 2eV6eV)
• FS The work function of n-type semiconductor
• ? The electron affinity (q?Ec vacuum level)
• FB0 Schottkey barrier height (FB0 Fm - ?)

Thermal equilibrium
In Sperated system
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Schottky Barrier (contd)

• Ideal Condition (Contd)
• The work function of metal

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Schottky Barrier (contd)

• Ideal Condition (Contd)
• The deviation of Schottky barrier height
• The interface layer (oxide)
• Image-force lowering
• The presence of interface states

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Schottky Barrier (contd)

• Image-force lowering
• Image-force lowering results the distortion of
  the potential barrier
• The effect is very small since the reduction is
  about 10-20 m-eV

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Fermi-Level Pinning

• Interface States
• Metal / N-type semiconductor
• If the density of bandgap states near is
  very large, then addition or depletion of
  electrons to semiconductor doesnt alter the
  Fermi level position at the surface and Fermi
  level is said to be pinned

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Fermi-Level Pinning (contd)

• The Schottky Barrier Height

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Fermi-Level Pinning (contd)

• The Schottky Barrier Height
• When surface states ? 8
• The Fermi level at the surface is pinned by large
  amount of surface states at the value
  above the valence band, and the barrier height is
  independent of the metal work function and is
  entirely determined by the surface properties of
  the semiconductor. (Bardeen limit)
• When surface states ? 0
• Identical to the ideal condition
• Generally, the number of surface states is hard
  to control, so the barrier height is determined
  by experiment.

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Fermi-Level Pinning (contd)

• The Schottky Barrier Height
• Metal/ n-type Si based semiconductor
• Experimental Result

Reference S. M. Sze, Physics of Semiconductor
Devices, 3rd ed., Wiley, New York 2006, ch.3
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Reference

• Donald A.Neamen, Semiconductor Physics and
  Devices Basic Principles, 3ed ed., McGRAW-HILL,
  2003, ch1
• S. M. Sze, Physics of Semiconductor Devices, 3rd
  ed., Wiley, New York 2006, ch.3
• Jasprit Singh, Semiconductors Devices Basic
  Principle, Wiley, New York 2001, ch.6