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

The thermal conductivity kappa and the thermoelectric properties of Si1-xGe x(x less than or equal to 0.10) samples doped with B or P which were prepar ed 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 amou nt of B or P, have a significantly low kappa value, less than one tenth tha t 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 r ange 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 betw een the electrical resistivities rho of our samples and their alloys is ver y small. The optimum n value giving the largest thermoelectric figures of m erit (ZT=(ST)-T-2/kappa rho) for n- and p-type Si0.97Ge0.03 samples was abo ut 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 val ues for Si0.7Ge0.3 alloys with little segregation. (C) 2000 American Instit ute of Physics. [S0021-8979(00)06913-9].