Low-temperature annealing (450-700°C) of a-Ge/Sn/c-Ge stacked-structures is examined to achieve high-quality GeSn singlecrystals on Ge substrates. Abnormal phenomena, where a GeSn-layer travels toward the surface during annealing, were found. In-depth analyses of Sn distribution together with epitaxial-growth clarify the mechanisms, i.e., diffusion of Ge atoms from a-Ge into molten-Sn, and subsequent release of GeSn atoms into c-Ge substrates cause the traveling-zone-melting-growth in self-organizingmanner. Transmission- electron-microscopy observation reveals the defect-free GeSn layers on Ge substrates. High thermal-stability of non-equilibrium Sn concentration in GeSn is guaranteed by post-annealing (~600°C) experiments. This method provides the unique tool to achieve multi-functional-devices based on GeSn-related hetero-structures.
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