Nanoscale contacts between carbon nanotubes and metallic pads

It is well-known that the electrical properties and performance of carbon nanotube field-effect transistors (CNTFETs) are largely dominated by their nanotube/metal contacts. Such nanometer-scaled contacts are typically different from traditional bulk semiconductor/metal contacts, as a thin layer of molecules could be unintentionally introduced between the CNTs and metal electrodes through either adsorption of environmental molecules or device fabrication processes. Here, we present a nanocontact model, in which the energy band bending in the CNTs near the contacts is quantitatively characterized through establishment of electrostatic charge balance between the CNTs and metallic pads under the influences of environmental oxygen. The concept of dipole polarization along the CNT channel in the FET geometry is, for the first time, introduced in order to interpret puzzling findings from several CNT Schottky transistors with asymmetric source and drain contacts.