  The effect of realistic metal electronic structure on the lower limit of
resistivity in [100] oriented n-Si is investigated using full band Density
Functional Theory and Semi-Empirical Tight Binding (TB) calculations. Using
simulation unit cells guided by the interface chemistry of epitaxial CoSi2 on
[100] oriented Si observed experimentally, it is shown that the 'ideal metal'
assumption fails in some situations and consequently underestimates the lower
limit of contact resistivity in n-Si by at least an order of magnitude at high
doping concentrations. The mismatch in transverse momentum space in the metal
and the semiconductor, the so-called 'valley filtering effect', is shown to be
dependent on the interface chemistry simulated. The results emphasize the need
for explicit inclusion of the metal atomic and electronic structure in the
atomistic modeling of transport across metal-semiconductor contacts
