Evolution of phases and their thermal stability in Ge-Sn nanofilms: a comprehensive in situ TEM investigation

The group IV Ge–Sn system is a promising candidate for a variety of electronic and photonic applications due to its tunable bandgap and compatibility with Si-based technology. However, the peculiarities of the components interaction, phases evolution and, especially, their thermal stability are still far from a brimming comprehension. In the course of in situ TEM heating experiments, we demonstrate the high potential of using nanosized, layered Sn/amorphous-Ge films for the synthesis of Ge–Sn solid solutions with an enhanced Sn content. Particularly, we observe the formation of highly uniform, diamond structured Ge1-xSnx solid solution with Sn content of 33 at% by metal-induced crystallization (MIC) at 90 °C. The Ge0.67Sn0.33 alloy is stable in the range of 20–150 °C, whereat additional heating leads to partial Sn segregation and subsequent melting of the Sn-rich phase. The formation of the metastable and stable Sn-rich liquid phases, which was observed at 90 and 150–190 °C, respectively, has a key role in the system thermal stability. The temperatures and the observed complex interphase interactions are discussed in the frame of the size effects in nanoscaled structures.