Nonlinear behavior in the Thermopower of Doped Carbon Nanotubes Due to Strong, Localized States

TL;DR

This study investigates how doping carbon nanotubes with boron or nitrogen affects their thermoelectric power, revealing nonlinear behaviors linked to localized states and changes in conduction type.

Contribution

It demonstrates the impact of dopants on the thermopower and conduction type of carbon nanotubes, supported by a model correlating density of states with spectroscopy data.

Findings

Boron doping induces p-type, positive thermopower.

Nitrogen doping induces n-type, negative thermopower.

Nonlinear thermopower behavior is due to localized donor and acceptor states.

Abstract

The temperature dependent thermoelectric power (TEP) of boron and nitrogen doped multi-walled 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 nonlinearites 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.