Thermoelectric properties of Bi/sub 2/Te/sub 3//Sb/sub 2/Te/sub 3/ superlattice structure

Recently, it has been proposed that the use of superlattice structure is effective for reduction of lattice thermal conductivity in the direction perpendicular to superlattice interfaces which can lead to improvement of figure of merit. In this work, we have evaluated the thermal conductivity of Bi/sub 2/Te/sub 3/ and Sb/sub 2/Te/sub 3/ superlattice structure films. Pulsed laser deposition (PLD) has been employed as film formation method because it can easily make superlattice structure by ablating targets alternately. Bi/sub 2/Te/sub 3/ and Sb/sub 2/Te/sub 3/ films were grown respectively and effects of substrate temperature and laser power density on crystallinity, morphology and composition were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Bi/sub 2/Te/sub 3//Sb/sub 2/Te/sub 3/ superlattice structure films were grown with superlattice periods of 10 nm, 20 nm and 80 nm. Thermal conductivities were measured in the direction perpendicular to superlattice interfaces by a novel method specially developed by our group. We compared the thermal conductivities of Bi/sub 2/Te/sub 3//Sb/sub 2/Te/sub 3/ superlattice structure films with that of Bi/sub 2/Te/sub 3/ single film. The results indicates that the involvement of superlattice structure into thermoelectric film is effective for the reduction of thermal conductivity and moreover, thermal conductivity becomes smaller as superlattice-period becomes shorter as predicted.