  The observed performances of carbon nanotube field effect transistors are
examined using first-principles quantum transport calculations. We focus on the
nature and role of the electrical contact of Au and Pd electrodes to open-ended
semiconducting nanotubes, allowing the chemical contact at the surface to fully
develop through large-scale relaxation of the contacting atomic configuration.
We present the first direct numerical evidence of Pd contacts exhibiting
perfect transparency for hole injection as opposed to that of Au contacts.
Their respective Schottky barrier heights, on the other hand, turn out to be
fairly similar for realistic contact models. These findings are in general
agreement with experimental data reported to date, and show that a Schottky
contact is not merely a passive ohmic contact but actively influences the
device I-V behavior.
