Preparation And Thermoelectric Properties Of Bi₂Te₃ Thin Films

Thermoelectric material can achieve direct conversion between heat energy and electric energy, concidered asa type of noiseless, clean, long-life and high stable energy material. The corresponding thermoelectric device, not only to generates power by using temperature difference, but also has unqiue function of the cooling. Especially, the thermoelectric microdevice,prepared fromthermoelectric films, has great application potential in the local heat absorptionand the solid-state refrigeration on the microsystems. Bi2Te3 is one of the best thermoelectric materials at the room temperature, and the 2D Bi2Te3 films areprepared easily withbetter thermoelectric propertiesthanthe Bi2Te3 bulk material, which is a good choice forthermoelectric microdevice preparation. In this paper, the p-type thermoelectric Bi2Te3 films were prepared by electrochemical deposition(ECD)and n-type thermoelectric Bi2Te3 films were preparedby co-sputtering. In addition, the equipment for measuring Seebeck coefficient and the conductivity of the bulkand film materials was designed and set up successfully.These studies laid the solid foundation of the preparation and the measurement of the thermoelectric microdevices.The ECD and the magnetron sputtering both are suitable forthe preparation of film industrialization,because of the advantage of low cost, high efficient. In this paper, the p-type thermoelectric Bi2Te3 films were grown on stainless steelsubstratesby the constant-potential ECD.The effects of deposition potential(-90 mV to 30mV) on morphology,crystal structure and thermoelectric properties of the films were investigated.It is found that the orientation of films can be controlled by deposition potential. The optimum of Seebeck coefficient and power factor was 103.2μV/K and 1.85mW/mK2, respectively, obtained at the deposition potential of-60 mV.The n-type thermoelectric Bi2Te3 films were grown on SiO2/Si substrates by RF magnetron co-sputtering. The effects of the power of Te target on surface morphology, crystal structure and thermoelectric properties of the Bi2Te3 films were investigated. Based on the optimal preparation technology of the stoichiometricBi2Te3, the effects of annealing temperature(150oC to 350oC) on morphology, crystal structure and thermoelectric properties of the Bi2Te3 films were investigated. As increasing the annealing temperature, the crystallization was improved, which contribute to the mobility of charge carriers. It is found that the optimum of Seebeck coefficient and power factor, compared with the unannealedsample, have big improvement that was about-305.0μV/K and 3.78 mW/mK2, respectively, obtained at the annealing temperature of 300 ℃.