Thermoelectric Performance of Ge-Doped Mg2Si0.35Sn0.65 Thin Films

The p-type Ge-doped (0, 1, 4 and 7 at.%) Mg2Si0.35Sn0.65 thin films were deposited by magnetron sputtering. The effect of Ge atomic concentration on morphology and crystal structure of the Mg2Si0.35Sn0.65 thin films was investigated. The stable face-centered cubic structure was only observed for all films. The thermoelectric properties of the films were discussed in the range of temperatures: 30-200 degrees C and carrier concentration and mobility were measured to explain the film electronic transport behaviors. Electrical conductivity and Seebeck coefficient both enhanced which led to an improvement in thermoelectric performance of Ge-doped thin films. The dominated carrier scattering mechanism was determined by the Hall mobility dependence forms as a function of the temperature for all films. The influence of carrier scattering mechanism on thermal conductivity was discussed. Results showed that lower thermal conductivity could be expected, while the acoustical phonon scattering mechanism is dominated. The film with 4 at.% Ge displayed the greatest ZT values till 180 degrees C compared to other films, while at 200 degrees C, the highest ZT = 0.21 was obtained for both films with 4 and 7 at.% Ge. The limit of the film structural stability was determined by annealing treatments under vacuum at different temperatures (up to 600 degrees C).