  Metal-semiconductor contacts play a key role in electronics. Here we show
that for quasi-one-dimensional structures such as nanotubes and nanowires, side
contact with the metal only leads to weak band re-alignement, in contrast to
bulk metal-semiconductor contacts. Schottky barriers are much reduced compared
with the bulk limit, and should facilitate the formation of good contacts.
However, the conventional strategy of heavily doping the semiconductor to
obtain ohmic contacts breaks down as the nanowire diameter is reduced. The
issue of Fermi level pinning is also discussed, and it is demonstrated that the
unique density of states of quasi-one-dimensional structures makes them less
sensitive to this effect. Our results agree with recent experimental work, and
should apply to a broad range of quasi-one-dimensional materials.
