The gap states at a given energy are characterized
using a real-space Green function to determine the energy where the
states convert from valence to conduction character . Using the
Bloch's theorem and the lattice vector R instead of wave
Further G can be decomposed into Gv and
Gc, each are contributions from the valence and conduction
band. As you go to higher energy in the gap the conduction band
contribution to G dominates and vice versa. Then there would be an
energy where , which is likely where the Fermi level
will pin (Refer to Figure 4).
Defect Model vs MIGS Theory
In the Defect Model, the intrinsic states are absent
from the bandgap from surface reconstruction. As metal or oxygen
submonolayers are deposited, local defects are formed to pin the Fermi
level. The model asserts that pinning by intrinsic states could be ruled
out. J. Tersoff in  expressed that the current experimental
techniques cannot directly observe the small number of states that are
required to pin the Fermi level. An adsorbate will cause local
disruptions in the reconstructed surface, inevitably pulling interface
states due to dangling bonds back into the gap. The mechanism of defects
pinning EF at the bare surface may not be applicable to an MS
interface. Unlike in a bare surface where roughly 1012
cm-2 defects can pin the EF, a MS interface
requires 1014 cm-2 since there is screening from
the metal. However, this large number of defects was not detected by
spectroscopic techniques. Later in 1993, W. Spicer  says that the
original assumption of two pinning positions for metallized overlayers
caused him to rule out MIGS which predicts only one position. This
clearly turned out to be a mistake. Since the metal overlayers were not
metallic with only a submonolayer coverage. When cooled down, the
overlayer becomes metallic and the two pinning positions merge to one.
On the other hand, whether or not it's elemental or III-V, specifying
the structure and chemistry of the interface is critical in determining
the transport properties, which is just as important as the barrier
© 2007 Saeroonter Oh. The author grants
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other rights, including commercial rights, are reserved to the
 W. Spicer, et al., "New and Unified Model for
Schottky Barrier and III-V Insulator Interface States Formation,"
J. Vac. Sci. Tech. 16, 5 (1979).
 W. Spicer et al., "The Advanced Unified Defect
Model for Schottky Barrier Formation," J. Vac. Sci. Tech. B 6, 4
 J. Tersoff, "Recent Models of Schottky Barrier
Formation," J. Vac. Sci. Tech. B 3, 4 (1985).
 J. Tersoff, "Calculations of Schottky
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168, 275 (1986).
 W. Spicer and A. Green, "Reaching Consensus and
Closure on Key Questions, a History of Success, and Failure of GaAs
Surfaces and Interfaces," J. Vac. Sci. Technol. B 11, 4 (1993).