High Thermoelectric Performance of Non-Stoichiometric and Oriented GeTe Thin Films

The increasing demand for micro-thermoelectric coolers and generators promotes the research on thermoelectric (TE) thin films. As a promising medium-temperature TE material, GeTe has attracted wide attention recently. However, the thermoelectric performance of thin-film GeTe remains inferior. Herein, oriented GeTe films with excessive Ge are obtained by magnetron co-sputtering technique, which can not only reduce the carrier concentration but also increase the carrier mobility, maintaining the high electrical conductivity of GeTe. Furthermore, higher structural symmetry and grain boundary scattering enhance the Seebeck coefficient of oriented GeTe films. As a result, the power factor (PF) value can reach as high as 2848 µW m^-1 K^-2 at room temperature and increase to 5263 µW m^-1 K^-2 at 600 K. Furthermore, a TE device with the Ge-rich GeTe thin film is fabricated and the maximum output power density (power per unit area) reaches 0.3 W cm^-2 at ΔT = 250 K. This work demonstrates that the stoichiometry and orientation modulations are effective strategies to improve the thermoelectric performance of GeTe thin films.