  At semiconductor-metal junctions, the Schottky barrier height is generally
fixed by "Fermi-level pinning". We find that when a semiconducting carbon
nanotube is end-contacted to a metal (the optinal geometry for nanodevices),
the behavior is radically different. Even when the Fermi level is fully
"pinned" at the interface, the turn-on voltage is that expected for the
unpinned junction. Thus the threshold may be adjusted for optimal device
performance, which is not possible in planar contacts. Similar behavior is
expected at heterojunctions between nanotubes and semiconductors.
