Influence of Ge to the formation of defects in epitaxial Mg2Sn1−x Ge x thermoelectric thin films

Abstract

Defect formation in epitaxial Mg2Sn1–x Ge x thermoelectric (TE) thin films grown via MBE was studied. We examined the defect formations and structures using cross-sectional transmission electron microscopy and positron annihilation spectroscopy. The defect formation tends to be influenced by Ge incorporation into the Mg2Sn matrix phase of epitaxial thin films. Mg vacancies (V Mg) were identified as point defects, primarily concentrated in the film’s mid-layer. In films with higher Ge composition, stacking faults were observed. The concentration of vacancy-type point defects decreased as the Ge concentration increased. This implies that the vacancy atoms, which would have otherwise been created by increasing chemical pressure due to the higher Ge content, might have played a role in the formation of stacking faults. The high concentration of vacancy-type defects resulted in the lowest thermal conductivity, demonstrating their significance as effective phonon scattering centers in epitaxial TE films.