THERMOPOWER MEASUREMENTS OF SEMICONDUCTOR QUANTUM DOTS

We discuss the use of electron-gas heating for measurements of the dif fusion thermopower S of a quantum dot in the regime of single-electron charging. The voltage across a dot in the presence of an electron tem perature gradient oscillates about zero with a period equal to that of the Coulomb blockade (CB) oscillations in electrical conductance G. T he magnitude of S associated with this thermovoltage has been deduced through a detailed investigation of the temperature gradient in the de vice. The magnitude and line shape of the resulting thermopower indica te that transport through the dot is a coherent tunneling process, mea ning that a simple Mott formulation can be used to relate G and S. In addition, a reproducible fine structure on top of the CB oscillations in S has been observed which appears to result from the N-particle exc itation spectrum of the dot. (C) 1998 Elsevier Science B.V. All rights reserved.