Thermoelectric properties of Si1−xGex(x⩽0.10) with alloy and dopant segregations

The thermal conductivity κ and the thermoelectric properties of Si1−xGex(x⩽0.10) samples doped with B or P which were prepared by arc melting were measured as functions of carrier concentration n and temperature T in the range from 298 to 1273 K. The Si1−xGex(0.03⩽x⩽0.10) samples, doped with a small amount of B or P, have a significantly low κ value, less than one tenth that of pure Si, despite the presence of strong alloy and dopant segregations. The Seebeck coefficients S of the Si0.97Ge0.03 samples over the entire n range from 1018 to 1021 cm−3 were higher than the corresponding values of Si0.7Ge0.3 alloys with little segregation, although the difference between the electrical resistivities ρ of our samples and their alloys is very small. The optimum n value giving the largest thermoelectric figures of merit (ZT=S2T/κρ) for n- and p-type Si0.97Ge0.03 samples was about 2×1020 cm−3, which is almost the same as that for Si0.7Ge0.3 alloys. At n≒2×1020 cm−3 the ZT values of n- and p-type Si0.95Ge0.05 samples with segregation increase linearly with temperature, and become 0.90 and 0.57 at 1073 K, respectively, which corresponds to 92% and 81% of the ZT values for Si0.7Ge0.3 alloys with little segregation.