Thermoelectric properties of polycrystalline Si1-xGex grown by die-casting vertical Bridgman growth technique

Abstract

ABSTRACTThe die-casting growth process combined with an advanced version of the Bridgman method was employed for manufacturing the multicrystalline bulk crystal of Si1−xGex. This process provides a form of phase transformation which is completely different from that predicted by the Si-Ge phase diagram. By combining this growth with subsequent heat treatment of the precipitated sample, the variation in the germanium content obtained was within ± 4 % for Si0.65Ge0.35 sample with a carrier concentration in the mid-1018 cm−3. The power factor obtained exhibited a quite flat characteristic over the temperature range of room temperature to 800 K. However, there was a drop in the Seebeck coefficient at about 800 K, which corresponded to a rise in the electrical conductivity. The value of the thermal conductivity was about 0.04 W/cmK at temperatures ranging from 600 to 900 K. The maximum value of the figure of merit obtained for the grown Si0.65Ge0.35 sample was 0.19 at 773 K.