Nonlinear behavior in the thermopower of doped carbon nanotubes due to strong, localized states

The temperature dependent thermoelectric power (TEP) of boron- and nitrogen-doped multiwalled carbon nanotube mats has been measured showing that such dopants can be used to modify the majority conduction from p-type to n-type. The TEP of boron-doped nanotubes is positive, indicating hole-like carriers. In contrast, the nitrogen doped material exhibits negative TEP over the same temperature range, suggesting electron-like conduction. Therefore, the TEP distinct nonlinearities are primarily due to the formation of donor and acceptor states in the B- and N-doped materials. The sharply varying density of states used in our model can be directly correlated to the scanning tunneling spectroscopy studies of these materials.