Observation of thermopower oscillations in the Coulomb blockade regime in a semiconducting carbon nanotube

We have measured the thermoelectric power (TEP) and Coulomb charging characteristics of an individual p-type semiconducting single-wall carbon nanotube (SWNT) in the quantum dot regime. The TEP measured as a function of gate voltage oscillates around a baseline value that is first positive and becomes more negative as the SWNT is depleted. When the device behaves as a single quantum dot, the TEP oscillation period and amplitude agree with theory. We ascribe the positive baseline level to p-type Schottky barriers at the SWNT-metal contacts, and the negative baseline to n-type barrier regions that cause multidot behavior as carriers are removed from the system. Near depletion, large TEP oscillations are observed even though Coulomb oscillations of the conductance are immeasurably small.