Abstract
Bimuth telluride-based compound has been considered as promising candidates for thin-film thermoelectric cooling devices due to its superior thermoelectric properties at room temperature regime. Our previous study showed that an electric current assisted annealing can effectively eliminate crystal defects, thus enhance the carrier mobility of sputtered Bi-Sb-Te thin films in short time. However, a reduced carrier density associated with the electrical annealing causes the deviation of optimized composition of Bi-Sb-Te compound. Thus, Bi-Sb-Te thin films need to be adjusted in composition in order to obtain their optimized thermoelectric properties. In stead of changing the composition of sputter target, we prepared Bi0.5Sb1.5Te3/Sb multilayer films on polyimide/Si substrate at room temperature by consecutively sputtering Bi0.5Sb1.5Te3 and Sb layers alternatively. The overall film composition is modulated by controlling the Sb insertion layer thickness. During the electric current stressing process, the Sb element would diffuse into Bi0.5Sb1.5Te3 layers to compensate the reduced carrier concentration followed by thermal and electrical treatment. The electrically stressed Bi0.5Sb1.5Te3/Sb multilayer film demonstrates high carrier concentration and enhanced Hall mobility, which improves thermoelectric properties. We proposed that the additional Sb supply suppresses electromigration-induced Sb depletion in crystal lattices, which can sustain p-type SbTe antisite defects in Bi0.5Sb1.5Te3 crystal lattice. Thus, Bi0.5Sb1.5Te3 can maintain their high carrier concentration and enhanced Hall mobility after electrical annealing treatment. It not only improves thermoelectric properties of the Bi0.5Sb1.5Te3 films but also decreases the formation of micro voids caused by Te evaporation. In this study,the Bi0.5Sb1.5Te3/Sb multilayer film with the best thermoelectric properties were obtained for the composite films after electrically stressed at 330 °C for 5 minutes. It has Seebeck coefficient of 187.5 μV/K and the lowest electrical resistivity of 2.6 mΩ□cm, leading to the highest power factor of 1.36×10-3 W/m□K2, As compared to the original Bi0.5Sb1.5Te3 thin films, the Sb-insertion multilayer sputtering approach provides a simple means to modulate the composition and improve thermoelectric properties of Bi–Sb–Te films after electrical annealing treatment.