Impact of the film thickness and substrate on the thermopower measurement of thermoelectric films by the potential-Seebeck microprobe (PSM)

Thermopower is a key parameter for thermoelectric (TE) materials. Compared to bulk materials, thermopower determination for TE films is challenging especially for those grown on electrically conductive substrates. This work demonstrates the feasibility of the on-substrate thermopower measurement for TE films by the unique potential-Seebeck microprobe (PSM). Thermopower measurements were conducted on the electroplated Bi2Te3 films with different thicknesses prepared on Au-coated Si and quartz substrates in order to reveal the impact of the film thickness and substrate on the measurement accuracy. It is found that the thermopower (Sm) measured on the Bi2Te3 film grown on Si/Au substrates tends to deviate significantly from the real value if the thickness is smaller than 12 μm. Above 12 μm, no thickness dependence was observed and reliable Sm can be obtained for the Bi2Te3 films. Results on quartz/Au substrates show similar thickness dependence for Sm, but the derived values are much lower than those obtained on Si/Au substrates. Finite element method (FEM) simulations are performed to interpret the measurement discrepancy as well as the impact of the film thickness and substrate on the thermopower measurement by investigating the detailed temperature and potential profiles in the samples.