B93501044, B93505007 ??? - PowerPoint PPT Presentation
Title: 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
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