Anisotropic Behavior of the Temperature-Dependent Thermal Conductivity in p-Type Bismuth Antimony Telluride (p-Bi0.5Sb1.5Te3) Thin Films

Abstract

Bismuth antimony telluride (Bi0.5Sb1.5Te3, BST) is the most widely used p-type thermoelectric (TE) material operating near room temperature. Recently, several research groups reported the enhancement of the dimensionless figure of merit, ZT, of Bi0.5Sb1.5Te3 bulk materials, as a result of using various solidification techniques. It is well known that the ZT value can be enhanced in low-dimensional systems, more so than in bulk material, owing to the enhanced phonon scattering present in such systems. Thus, systematic studies should be carried out on a number of TE materials in order to further enhance their ZT value, by reducing their thermal conductivity. In this study, both the in-plane and cross-plane thermal conductivities of p-type BST thin films in the temperature range 100-450 K were investigated using the four-point-probe 3 omega technique. In this temperature range, the average in-plane and cross-plane thermal conductivities of the films were determined to be approximately, similar to 0.60-0.77 W m(-1) K-1, and similar to 0.4-0.53 W m(-1) K-1, respectively. Furthermore, our experimental results were analyzed using modified Sondheimer and Callaway models in order to calculate the anisotropic ratio, and temperature dependence of the lattice and electronic thermal conductivities for the p-BST thin films in both the in-plane and cross-plane directions.