  We investigate experimentally the transport properties of single-walled
carbon nanotube bundles as a function of temperature and applied current over
broad intervals of these variables. The analysis is performed on arrays of
nanotube bundles whose axes are aligned along the direction of the externally
supplied bias current. The data are found consistent with a charge transport
model governed by the tunnelling between metallic regions occurring through
potential barriers generated by nanotubes contact areas or bundles surfaces.
Based on this model and on experimental data we describe quantitatively the
dependencies of the amplitude of these barriers upon bias current and
temperature.
