Study On Thermoelectric Properties Of Bi₂te₃-based Thin Films

Thermoelectric?TE?materials can convert heat and electricity directly and are commonly used in power generation and cooling.With the progress of nanotechnology and preparation methods,low dimensional TE materials with high ZT values have been reported a lot and set off a research boom of TE materials.Bi₂Te₃-based thin films exhibit potential improvement in ZT values due to a reduction in thermal conductivity and a relatively high power factor because of quantum-confinement effect and interface scattering effect.However,their TE properties at room temperature are mainly studied and only few works have been reported on the ZT of GeTe/Bi₂Te₃ superlattices?SLs?.This paper systematically studied on the preparation method,surface topography,electrical transport and thermal conduction of Bi₂Te₃ thin films and GeTe/Bi₂Te₃ SLs.Thickness and temperature dependence of their TE properties have been analyzed.In this paper,homogeneous Bi₂Te₃ thin films and GeTe/Bi₂Te₃ SLs were prepared by magnetron sputtering.The Seebeck coefficient,electrical conductivity and thermal conductivity of annealed films were measured at different temperatures.By using relevant models and theoretical calculations,the experimental data have been explained and the transmission mechanism of carrier and phonon in the films have been analyzed.The influence of thickness on electrical properties of the Bi₂Te₃ thin films and GeTe/Bi₂Te₃ SLs have been well explained using the classical size effect and quantum size effect,respectively.The transport properties of carriers in a 3D bulk material and a 2D quantum well proposed by Hicks have been used to analyze temperature dependence of the electrical properties of the Bi₂Te₃ thin films and GeTe/Bi₂Te₃ SLs,respectively.Amorphous Bi₂Te₃-based thin films can be turned into crystalline through annealing in this study.The maximum values of Seebeck coefficient and power factor of the crystal Bi₂Te₃ thin films are 475?V/K and 7mW/?mK²?at 170?.The maximum values of Seebeck coefficient and power factor of the crystal GeTe/Bi₂Te₃ SLs are 232?V/K and 1.34mW/?mK²?at temperature near 100?.The thermal conductivity of thin films was measured by the 3?method at different temperatures.The thermal conductivity of GeTe/Bi₂Te₃ SLs is lower than that of Bi₂Te₃ thin films.Thermal conductivity of the GeTe/Bi₂Te₃ SLs can be as low as 0.173W/mK at room temperature.ZT of the Bi₂Te₃ thin films is as high as 1.56 at 170?,which is higher than ZT of bulk materials.The maximum ZT of GeTe/Bi₂Te₃ SLs is only 0.76,mainly due to the low power factor caused by carrier scattering.This study shows that the ZT of Bi₂Te₃-based thin films can be significantly improved by designing optimal film thickness and applicable temperature environment so that the Bi₂Te₃-based thin films can exhibit potential applications in TE devices.