Stoichiometry-Dependent Microstructural and Transport Evolution in Thermally Aged SnTe Thin Films

Abstract Tin telluride (SnTe) has emerged as a high-performance, lead-free alternative to PbTe for medium-temperature thermoelectric applications, drawing significant interest due to its environmental compatibility and unique band structure. However, while its initial properties are well documented, the Te-volatilization-driven microstructural evolution of SnTe thin films during prolonged thermal exposure remains strongly dependent on the starting Sn:Te stoichiometry because stoichiometric deviations directly affect elemental redistribution, interfacial degradation, and defect evolution during thermal exposure. Therefore, clarifying the role of the initial Sn:Te ratio is essential for understanding the composition-dependent microstructural and transport evolution of SnTe thin films. In this work, SnTe thin films with three initial compositions, Sn55Te45, Sn50Te50, and Sn45Te55, were deposited on SiO2/Si substrates by cosputtering and aged at 300 °C for 30 days. Experimental results revealed that the Te-rich Sn45Te55 film showed the lowest interfacial void fraction and the mildest overall structural deterioration under the present aging condition. Detailed analysis of the Sn45Te55 film indicated progressive Sn redistribution during aging, with relative Sn enrichment near the surface and the SnTe/SiO2 interface driven by Te volatilization and local Sn oxidation. This Sn-rich layer in the Sn45Te55 film further suppressed Te evaporation and facilitated the generation of Sn vacancies in the thin film during prolonged thermal exposure, contributing to p-type conduction with improved carrier concentration and power factor. These findings demonstrate that the initial Sn:Te stoichiometry plays a critical role in governing Te-volatilization-induced microstructural evolution and the corresponding thermoelectric transport properties of sputtered SnTe thin films under prolonged thermal exposure at 300 °C.