Abstract
Bismuth telluride-based compound is currently widely used in commercial thermoelectric module due to its excellent thermoelectric performances around room temperature regime. Previous study showed that anti-site defects can be much more effectively eliminated after electric current assisted thermal treatment within a short period of time for sputtered Bi0.5Sb1.5Te3 thin films. Enormous enhancement in carrier mobility compensates the reduction in carrier concentration and results in a reasonable electrical resistivity. Thermoelectric power factor of Bi0.5Sb1.5Te3 thin films has been markedly improved by this post-deposition treatment In this study, Bi0.5Sb1.5Te3 thin films were sputtered on SiO2/Si substrate. Electrical transport properties were measured and compared for films with thermal annealing and electric current stressing treatment. Bi0.5Sb1.5Te3 films after electric current stressing treatment has much higher carrier mobility and moderately lower carrier concentration than those thermally annealed at the same temperature. From theoretical calculation and Hall measurement at different temperatures, we confirm that the carrier transport properties is dominated by lattice scattering mechanism especially for high-temperature annealed and electric current stressed samples. Then we apply the conventional 3ω thermal conductivities measurement for samples annealed at different temperatures. Using Lorentz number acquired from theoretical calculation, electronic and lattice thermal conductivities were separated from the measured intrinsic thermal conductivities. Compared with thermal annealing samples, the lattice thermal conductivities of electric current stressed Bi0.5Sb1.5Te3 films were found to be higher than that of thermally annealed samples. According to the variation of lattice thermal conductivity with annealing temperature, there is no obvious grain growth for Bi0.5Sb1.5Te3 films with such short thermal treatments. Elimination of a large number of anti-site defects in Bi0.5Sb1.5Te3 films may be the main cause of higher lattice thermal conductivities in electrical stressed samples. The crystal orientation investigated by XRD analysis indicated no (00l) preferred orientation for processed films. So the ZT values of Bi0.5Sb1.5Te3 films can be further calculated with the value measured by the 3ω thermal conductivities measurement. The experimental results showed that the Bi0.5Sb1.5Te3 films after electrical stressed for 5minutes has a Seebeck coefficient of 201.9(μV/K), a lower electrical resistivity of 4.65(mΩ-cm) and a thermal conductivity of 0.7(W/mK) which brought about a highest thermoelectric power factor of 8.76(μW/K2cm) and a ZT value of 0.38.