Growth and thermoelectric properties of Bi_2Te_3 films deposited by modified MOCVD

摘要

Bismuth telluride films were prepared by a modified metal organic chemical vapor deposition (MOCVD) on (001) GaAs substrates, and their thermoelectric properties were investigated. In the modified MOCVD system used in this study, metal organic sources of bismuth and tellurium were mixed with hydrogen gas in a graphite mixing room which can be heated by radio frequency induction and transferred to the substrate through a planar gap of mixing room. The effect of deposition parameters such as Te/Bi ratio in the reactor and mixing room temperature on the surface morphologies and the thermoelectric properties of the films was investigated. It was found that the grain size and the growth rate of the films can be controlled by adjusting the mixing room temperatures. Growth rates 2-3 times faster than that of the conventional MOCVD were obtained. A maximum growth rate of 7 μm/h was achieved at the mixing room temperature of 300 ℃. The highest Seebeck coefficient was about -225 μV/K. Reduction of thermal conductivity can be expected when the size of grain can be controlled to nano-scale. The results in this study suggest that the fabrication of Bi2Te3 films with high thermoelectric performance using a high throughput process can be achieved by the modified MOCVD system used in this work.