Thermoelectric properties of Mg2Si thin films prepared by thermal evaporation of Mg and face-to-face annealing

Mg2Si thin films were prepared by thermal evaporation of Mg and face-to-face annealing (FTFA) on a crystalline Si substrate and on a P-doped hydrogenated amorphous Si thin films deposited on a quartz substrate. FTFA suppressed the evaporation of Mg, the oxidation of Mg2Si, and the decomposition of Mg2Si. The polycrystalline Mg2Si thin film with a large grain size was obtained. The effects of annealing temperature (TA) during FTFA on crystal structure and thermoelectric properties of Mg2Si thin films were investigated. Raman scattering spectra revealed that Mg2Si was formed by FTFA in the range of TA = 623–923 K, and lower TA led to lower strain and higher crystallinity. From the thermoelectric properties of the sample prepared at TA = 623 K, a relatively high ZT of 0.68 was obtained at 712 K. This ZT was achieved by a drastic increase in electrical conductivity, a relatively high Seebeck coefficient of −235 μV･K−1, and a very low thermal conductivity of 1.4–1.7 W･m−1･K−1.