Thermoelectric properties of Si-based thermoelectrics

The thermal conductivity κ and the electric properties of Si1-xGex (x≤0.03) samples doped with Group 3B and 5B elements which were prepared by arc melting were measured as functions of carrier (or dopant) concentration n and of temperature in the range from 298K to 1273K. Consequently it was found that the combination of alloying with 3at% Ge and doping with 0.5at% P or 0.3at% B decreases the values of κ to as low as about 12W/m·K at 298K. The electrical resistivities ρ of doped Si and Si0.97Ge0.03 samples decrease linearly with increase of n. However the Seebeck coefficients S of doped Si have a local maximum or a hump at a concentration of about 3×1019cm-3, while no such maxima appeared in doped Si0.97Ge0.03 although its S values are considerably higher than those obtained by Dismukes et al, for Si0.7Ge0.3 alloys over the whole concentration range from 1018cm-3 up to 1021cm-3. At 1073K, the maximum values of the figure of merit ZT were 0.62 for n-type Si0.97Ge0.03 doped to 1.8×1020cm-3 electrons and 0.47 for p-type Si0.97Ge0.03 doped to 1.7×1020cm-3 holes, so that they attained to about 70% of those obtained by Dismukes et al. for Si0.7Ge0.3 alloys.