Thermoelectric properties of Si1-xGex(x≤0.10) with alloy and dopant segregations

The thermal conductivity kappa and the thermoelectric properties of Si1-xGex(x less than or equal to 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 less than or equal to x less than or equal to 0.10) samples, doped with a small amount of B or P, have a significantly low kappa 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 10(18) to 10(21) cm(-3) were higher than the corresponding values of Si0.7Ge0.3 alloys with little segregation, although the difference between the electrical resistivities rho of our samples and their alloys is very small. The optimum n value giving the largest thermoelectric figures of merit (ZT=(ST)-T-2/kappa rho) for n- and p-type Si0.97Ge0.03 samples was about 2x10(20) cm(-3), which is almost the same as that for Si0.7Ge0.3 alloys. At n = 2x10(20) 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. (C) 2000 American Institute of Physics. [S0021-8979(00)06913-9].