Metal contacts in carbon nanotube field-effect transistors: Beyond the Schottky barrier paradigm

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. As expected from their respective work functions, the Schottky barrier heights for Au and Pd turn out to be fairly similar for realistic contact models. We present, however, direct numerical evidence of Pd contacts exhibiting perfect transparency for hole injection as opposed to that of Au contacts. These findings support experimental data reported to date.