The effects of the substrate temperature on the composition and microstructure of Bi-Sb-Te-Se thin films are discussed and related to the Seebeck coefficient and resistivity. The films were prepared on silica substrates by argon ion beam sputtering. The effect of subsequent heat treatment is also discussed. The composition becomes stoichiometric at the substrate temperature around 500 K at which the Seebeck coefficient has a maximum and the resistivity has a minimum. The Seebeck coefficient changes its sign at the substrate temperature around 340 K. The crystal structure of the films deposited at room temperature is identified as the rock-salt type, and the change of the thermoelectric properties as a function of the substrate temperature can be mainly attributed to the volume fraction of the Bi2Te3 and rock-salt structures. The subsequent heat treatment is effective in improving the power factor of the stoichiometric thin films.
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Noro et al. (1993) studied this question.