Characterization of Thermoelectric Properties of Heavily Doped n-Type Polycrystalline Silicon Carbide Thin Films

Abstract

The thermoelectric properties of heavily doped n-type 3C polycrystalline silicon carbide (poly-SiC) films are investigated for microelectromechanical systems (MEMS) applications in harsh environments. Two MEMS structures are designed and fabricated to measure the Seebeck coefficient and the lateral thermal conductivity of poly-SiC thin films. The van der Pauw structure is used to determine electrical resistivity. The obtained Seebeck coefficient is -10μV/K at room temperature, increasing in magnitude to -20 μV/K at 300 °C. The power factor is in the range of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> W·m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ·K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> within the tested temperature range. The measured lateral thermal conductivity of poly-SiC thin film is 64 W·m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ·K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , significantly lower than that of undoped single-crystalline SiC, due to increased phonon-grain-boundary and phonon-impurity scatterings. The decrease in the thermal conductivity of the heavily doped poly-SiC film benefits its thermoelectric figure of merit, which is 4.6 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> .