Optimal Thermoelectric Power Factor Of Narrow-Gap Semiconducting Carbon Nanotubes With Randomly Substituted Impurities

We have theoretically investigated thermoelectric (TE) effects of narrow-gap single-walled carbon nanotubes (SWCNTs) with randomly substituted nitrogen (N) impurities, i.e., N-substituted (20, 0) SWCNTs with a band gap of 0.497 eV. For such a narrow-gap system, the thermal excitation from the valence band to the conduction band contributes to its TE properties even at the room temperature. In this study, the N-impurity bands are treated with both conduction and valence bands taken into account self-consistently. We found the optimal N concentration per unit cell, c(opt), which gives the maximum power factor (PF) for various temperatures, e.g., PF = 0.30 W/K(2)m with c(opt) = 3.1 x 10(-5) at 300K. In addition, the electronic thermal conductivity has been estimated, which turn out to be much smaller than the phonon thermal conductivity, leading to the figure of merit as ZT similar to 0.1 for N-substituted (20, 0) SWCNTs with = c(opt) = 3.1 x 10(-5) at 300K.