Charge transport in semiconducting single-walled nanotubes (SWNTs) with Schottky-barrier contacts has been studied at high bias. We observe nearly symmetric ambipolar transport with electron and hole currents significantly exceeding $25\mu \mathrm{A}$, the reported current limit in metallic SWNTs due to optical phonon emission. Four simple models for the field-dependent velocity (ballistic, current saturation, velocity saturation, and constant mobility) are studied in the unipolar regime; the high-bias behavior is best explained by a velocity-saturation model with a saturation velocity of $2\times {10}^7\mathrm{cm}/\mathrm{s}$.

• Received 29 June 2004

DOI:https://doi.org/10.1103/PhysRevLett.95.236803