Enhanced Phonon-Drag Thermopower of Ballistic Semiconducting Single-Walled Carbon Nanotubes Near the Second Subband Edge

The phonon-drag thermopower, S-g, of semiconducting single-walled carbon nanotubes is calculated in the ballistic transport regime when two energy subbands become populated. Previous theoretical studies of S-g in these systems are restricted to the quantum limit (only the ground 1D subband was occupied). The carrier transport is described within the Landauer-Buttiker formalism while phonons are treated semiclassically. Numerical simulations of S-g as a function of Fermi level and temperature are presented. It is found that strong peaks of S-g, of the order of mV K-1, occur when the Fermi level approaches the edge of the second subband. Quite remarkably these peaks persist at temperatures as high as 300 K.