Preparation Of Bi₂Te₃ Thermoelectric Thin Films And Study On The Properties

Thermoelectric materials which interconvert between heat and electricity directly can be widely used in the field of the solid state cooling and power generation.As the best thermoelectric materials at room temperature,Bi2Te3-based compounds have caused great attention.But the thermoelectric figure of merits ZT of Bi₂Te₃ materials is still about 1 for decades,which resulted in the lower energy conversion efficiency,compared with traditional systems of power generation and refrigeration.In recent years,with the rise of nanotechnology,low-dimensional thermoelectric materials can improve the performance by increasing power factor due to quantum confinement effect and decreasing thermal conductivity owing to phonon scattering at boundaries and interfaces.Therefore,low-dimensional materials have more space to improve thermoelectric properties.In this paper,Bi₂Te₃ thin films were prepared under different condition by magnetron sputtering,and the micstructure,surface morphology and thermoelectric properties were investigated systematically.Firstly,Bi₂Te₃ thin films were prepared on the quartz glasses.And the effects of deposition temperature,Te content and Ar flux on the performances were investigated respectively.The results show that the deposition temperature has an effect on surface morphology and grains orientation,and Seebeck coefficient improved with increase of deposition temperature.The highest values of Seeebeck coefficient,electrical conductivity and power factor are 83.96 ?V/K,1.89�10⁴ S/m and 6.79 ?W/cmK² when the films were deposited at 400 ?.Furthermore,some excess Te distributed in the structure of thin films is favorable to improvement of Seeebeck coefficient and power factor when Bi₂Te₃ thin films were fabricated by co-sputtering of Te target and Bi₂Te₃ alloy target.The Bi₂Te₃ thin films prepared by co-sputtering had higher Seebeck coefficient,and the optimum was 92.42 ?V/K at 400 ?.Besides,the variation of Ar fix had few influences on structure and morphology of Bi₂Te₃ thin films by control the same pressure under the different Ar flux.But too high or too low Ar flux can make the efficiency of sputtering films decrease.Then,the effects of preferred orientation structure and Te content on structure and thermoelectric properties of Bi₂Te₃ thin films were expolored respectively.Here,highly?00l?-oriented Bi₂Te₃ thin films were prepared on the MgO substrates at 400 ? by co-sputtering of Te target and Bi₂Te₃ alloy target,and the optimum of Seebeck coefficient is 103.6 ?V/K,higher than the Seebeck coefficient of the films prepared on quartz glass under the same condition.In addition,confirming the optimum of Te is vital to the improvement of thermoelectrical performance considering the effect of Te content.Bi₂Te₃ thin films with different Te content were deposited by regulating power of Te target,and the structure and thermoelectric properties of films were explored respectively.It was proved that the Seebeck coefficient and electrical conductivity increased and then decreased as the power of Te target increased,and the optimum values of Seebck coefficient,electrical conductivity and power factor are 157.7 ?V/K,9.68�10⁴ S/m and 24.6 ?W/cmK² respectively when Bi₂Te₃ thin films were prepared under the 8 W of Te target power.However,the power factors were 3.95 ?W/cmK² and 5.24 ?W/cmK² respectively when the films were deposited under the 5 W and 12 W of Te target.Lastly,Bi₂Te₃ thin films with the highly?00l?-oriented structure and high power factor,have prepared on the basis of the optimum technological parameter.The Seebeck coefficient,electrical conductivity and power factor were 145.6 ?V/K,9.68�10⁴ S/m and 39.1 ?W/cmK² respectively.