Electrical and thermal transport properties of electrically stressed Bi-Sb-Te nanocrystalline thin films

Abstract

Nanoscale size effect is beneficial for enhancing thermoelectric figure-of-merit of Bi-Sb-Te compounds due to the decrease of thermal conductivity. Bi-Sb-Te nanocrystalline thin films prepared by sputtering at room temperature, in general, require a post-deposition treatment to improve their electrical transport properties by eliminating residual crystal defects. In this study we present an electric current stressing treatment to effectively eliminate crystal defects in sputtered Bi-Sb-Te films at low temperature. By maintaining a low thermal conductivity of 0.6-0.7 W/mK, the electrically stressed Bi-Sb-Te nanocrystalline films possess highly enhanced Hall mobility and moderately reduced carrier concentration as compared to the films thermally treated at the same temperature. Carrier concentration, mobility and Seebeck measurement results suggest that the change of electrical transport properties involves the elimination of SbTe antisite defects as supported by the observation of some Sb-rich precipitates in the thermally/electrically treated Bi-Sb-Te films. Besides, crystal defects are also suggested to be preferentially removed in the (00l)-oriented grains due to anisotropic diffusion and electrical transport properties in the electrically stressed Bi-Sb-Te films. © 2011 Elsevier B.V.