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Berlin 2018 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 39: Group IV (other than C): Si/Ge/SiC

HL 39.7: Talk

Thursday, March 15, 2018, 12:30–12:45, EW 015

Phase separation in metastable Ge1−xSnx epilayers induced by free running Sn precipitates — •Heiko Groiss1,2,3, Martin Glaser2, Magdalena Schatzl2, Moritz Brehm2, Dagmar Gerthsen3, and Friedrich Schäffler21Center of Surface and Nanoanalytics, Johannes Kepler University Linz, Austria — 2Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Austria — 3Laboratory for Electron Microscopy, Karlsruhe Institute of Technology, Germany

Recently, optical gain was demonstrated in Ge1−xSnx alloys [1], which are the only known group-IV materials that assume a direct band gap. However, Ge and Sn are immiscible over 98% of the composition range, which renders these epilayers inherently metastable. We investigated the temperature stability of pseudomorphic Ge0.9Sn0.1 films grown by MBE [2]. We observed that decomposition of the epilayers sets in above  230C, the melting point of Sn. Videos taken during annealing in a scanning electron microscope reveal the crucial role of liquid Sn precipitates. Driven by a gradient of the chemical potential, the Sn droplets move on the surface and behave like microscopic liquid-phase epitaxy reactors: The strained and metastable GeSn film on the one side acts as a feeding medium for the supersaturation of the Sn melt with Ge. From this Sn melt Ge precipitates epitaxially in a trail region, where it develops low energy facets. Overall, the free-running Sn droplets make phase separation of metastable GeSn layers particularly efficient at rather low temperatures. [1] S. Wirths et al., Nat. Photonics 9, 88-92 (2015). [2] H. Groiss et al., Scientific Reports 7, 16114 (2017).

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