All Cross-Plane Thermoelectric Properties of n-Type Bi2Te3 Thin Films in the Temperature Range from 77 to 500 K

Abstract

Among various thermoelectric (TE) materials, Bi2Te3 (BT) materials are widely used n-type TE materials that operate properly near 300 K, with a high anisotropy behavior. Recently, thin film-based BT TE materials have also a great interest for use in solid state cooling and energy harvesting TE devices. The TE properties of the films are highly dependent on the anisotropic properties of the films. However, there have been very few reports of the particular cross-plane figure of merit (ZT), including thermal conductivity, Seebeck coefficient, and electrical conductivity, of the thin films. Thus, information concerning the cross-plane ZT for these promising films should be provided to evaluate the TE properties of the materials. In this study, we present all cross-plane ZT properties of n-type Bi2Te3 thin films prepared by radio frequency (RF) magnetron sputtering at room temperature. The cross-plane thermal conductivity of the 200-nm-thick BT films was determined using the four-point-probe 3-omega method, while a Pt heater-embedded Cu/BT/Cu structure was used to characterize both the cross-plane Seebeck coefficient and electrical conductivity of the films at a temperature range from 77 to 500 K. The annealed n-BT films exhibit good cross-plane TE properties, with a peak ZT of similar to 0.57 at 375 K, which is comparable with that of nanostructured n-BT bulk materials.