Preparation and thermoelectric properties of RF co-sputtered CoSb₃ skutteruddite thin films

Abstract

Various skutterudites have been under investigation because of their potential application in thermoelectric materials and devices. These studies indicate that bulk materials with a skutterudite-type structure show reasonable thermoelectric behaviors at elevated temperatures, which make them suitable for high-temperature thermoelectric applications. The results of thermoelectric-property measurements on skutterudite-phase CoSb₃ thin films are presented in this study in order to extend the bulk material concept to micro-device applications by using thin film deposition technology. Thin films are deposited on oxidized silicon substrates by using the RF co-sputtering method. The film’s composition is found to depend strongly on the deposition conditions. The temperature at which the deposited films transition from an amorphous state to a crystalline state has been reported to be about 153 °C. Therefore, some experiments are performed with the substrate temperature kept at 200 °C to obtain polycrystalline films. The crystal structure of the film is evaluated by using x-ray diffraction (XRD) measurements. Energy dispersive spectroscopy (EDS) is used to determine the film’s composition whereas the surface morphology and the thickness are investigated and measured by using scanning electron microscopy (SEM). Finally, the thermoelectric properties, namely, the electrical resistivity and the Seebeck coefficient, are used to calculate the power factor of the deposited thin films and, their variations with temperature are measured. We report a maximum power factor of 0.41 mW/mK² for the film deposited at a 200 °C substrate temperature.