High-field Current-carrying Capacity of Semiconducting Carbon Nanotubes
  It is shown that current saturation in semiconducting carbon nanotubes is indistinguishable from metallic nanotubes if the carrier density is above a critical value determined by the bandgap and the LO phonon energy. This feature stems from the higher number of current-carrying states in the semiconducting tubes due to the van-Hove singularity at the band-edge. Above this critical carrier density, the ensemble saturation velocity at high-fields is found to be independent of the bandgap, but strongly dependent on the carrier density, explaining recent observations. 
Debdeep Jena