Effect of metal electrode on Seebeck coefficient of p- and n-type Si thermoelectrics

The measurements of thermoelectric powers and current–voltage characteristics were made on the p- and n-type Si specimens which were doped with 0.1 at. % of Al and P, respectively. The apparent Seebeck coefficients Sa of these specimens were measured using various kinds of metal electrodes at cold end and the brass at hot end. The Sa was plotted as a function of work function of metal electrodes at cold end. The Sa changes significantly with the kind of metal electrodes and has a maximum at a work function of 4.65 eV of Cu for the p-type specimen and 4.33 eV of Zn for the n-type one. These maximum Sa agreed quantitatively well with the Seebeck coefficients S measured by the conventional technique using two alumel–chromel thermocouples as an electrode. There was a negative correlation between Sa and R where the electrical resistance R is the sum of the contact resistance and the resistance of the specimen itself, so that an increase in the Sa leads directly to an enhancement in the thermoelectric power factor Sa2/R. When the p- and n-type thermoelectric materials are connected as a metal–semiconductor junction, it was thus found that it is necessary to select the metal electrode fitted to the thermoelectric material, to make the thermoelectric conversion efficiency as high as possible.