Caractérisations optiques et électrochimiques de films electrodéposés de type Bi2Te3

Abstract : Optical and electrochemical characterizations of electroplated films of bismuth telluride compounds. This work concerns the characterization of electroplated films of bismuth telluride (-0.2 x 0.2) which is a semiconductor compound with narrow band-gap generally used for thermoelectric applications. Transport parameters were determined using Spectroscopic Ellipsometry, Electrochemical Impedance Spectroscopy (Mott-Schottky plot) and additional measurements (Hall & Seebeck effects) which required to optimize the synthesis conditions to improve surface quality of electroplated layers. Mueller Matrix analysis showed the optically isotropic behavior. The dielectric functions of the films were determined in the energy range of 0.03 to 3.10 eV. In the infrared range, Tauc Lorentz combined with Drude dispersion relations were successfully used. The energy band gap Eg was found to be about 0.11 eV independent of x. This analysis was successfully extended to Bi2(Te0.9Se0.1)3 films. All results showed that the films are described as n-type semiconductor independently of x. Carrier concentration of the order of 1020 cm-3, resistivity of 15-50 .m and mobility of 4-14 cm2/(V.s) were explained by polycrystalline material features. An original experimental setup was carried out including simultaneously electrochemical quartz crystal microbalance data, electrochemical data and real time ellipsometer analysis in the visible range. The electrochemical system was found to be fully reversible and the apparent volumic mass of the film is equal to 7.34 g/cm3. The analysis of the layer growth revealed a first period around 30 seconds where the gold substrate is progressively covered by the crystallites of Bi2Te3. A minimum of 35 nm-thick film is necessary to obtain morphological and optical characteristics quite similar to thick samples
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Alexandre Zimmer. Caractérisations optiques et électrochimiques de films electrodéposés de type Bi2Te3. Autre. Université Paul Verlaine - Metz, 2006. Français. ⟨NNT : 2006METZ006S⟩. ⟨tel-01752921⟩

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