No metal has a Seebeck coefficient larger than 100 ^V/K. The great majority has coefficients much smaller than 10 ^V/K, as can be seen from Table 5.4. Some semiconductors have coefficients of some 300 ^V/K at usable temperatures. Since the figure of merit depends on the square of the Seebeck coefficient, one can see that some semiconductors have an order of magnitude (or more) advantage over metals.
The data in Table 5.4 were taken from the CRC Handbook of Thermo-electronics, which, in turn, obtained the values from different sources. All elements in the table are metals. The Seebeck coefficient for semiconductors depends critically on the doping level. The polarity of the Seebeck effect depends on whether the semiconductor is of the p or n type. Intrinsic semiconductors have zero Seebeck coefficients. For small doping concentrations, the Seebeck effect grows rapidly, with the doping level reaching a peak and then decreasing again as depicted in Figure 5.12.
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