In order to measure the Seebeck coefficient of nanometer-scale thermoelectric materials, we propose a new technique in which the thermoelectric-motive force (TEMF) is evaluated by Kelvin-probe force microscopy (KFM). In this study, we measured the Seebeck coefficient of an n-type Si wafer. The surface-potential difference between the high- and low-temperature regions on the Si wafer increases with increasing temperature difference. This indicates that the TEMF can be measured by KFM. The Seebeck coefficient evaluated from the surface-potential difference is 0.71š0.08 mV/K, which is close to that obtained by the conventional method.
We measured the Seebeck coefficient of P-doped ultrathin silicon-on-insulator (SOI) layers with thicknesses of 6-100 nm. The dependence of the coefficient on the impurity concentration was investigated, and was shown to be in good agreement with that of bulk Si. In addition, it was found to decrease with increasing impurity concentration, as is usual in semiconductor materials. However, for doping levels above 3.5x1019 cm-3, the Seebeck coefficient was observed to increase. This is likely to be due to the influence of an impurity band.