We report the effects of potassium doping on the conductance of individual semiconducting single-walled carbon nanotube ropes. We are able to control the level of doping by reversibly intercalating and de-intercalating potassium. Potassium doping changes the carriers in the ropes from holes to electrons. Typical values for the carrier density are found to be $\sim 100$–1000 electrons/$\mu \mathrm{m}.$ The effective mobility for the electrons is ${\mu }_{\mathrm{eff}}\sim 20$–60 ${\mathrm{cm}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1},$ a value similar to that reported for the hole effective mobility in nanotubes [R. Martel et al., Appl. Phys. Lett. 73, 2447 (1998)].

• Received 1 November 1999

DOI:https://doi.org/10.1103/PhysRevB.61.R10606