| Summary: | We investigated the types of dendrites grown in Si<sub>1−x</sub>Ge<sub>x</sub> (0 < <i>x</i> < 1) melts, and also investigated the initiation of dendrite growth during unidirectional growth of Si<sub>1-x</sub>Ge<sub>x</sub> alloys. Si<sub>1−x</sub>Ge<sub>x</sub> (0 < <i>x</i> < 1) is a semiconductor alloy with a completely miscible-type binary phase diagram. Therefore, Si<sub>1−x</sub>Ge<sub>x</sub> alloys are promising for use as epitaxial substrates for electronic devices owing to the fact that their band gap and lattice constant can be tuned by selecting the proper composition, and also for thermoelectric applications at elevated temperatures. On the other hand, regarding the fundamentals of solidification, some phenomena during the solidification process have not been clarified completely. Dendrite growth is a well-known phenomenon, which appears during the solidification processes of various materials. However, the details of dendrite growth in Si<sub>1−x</sub>Ge<sub>x</sub> (0 < <i>x</i> < 1) melts have not yet been reported. We attempted to observe dendritic growth in Si<sub>1−x</sub>Ge<sub>x</sub> (0 < <i>x</i> < 1) melts over a wide range of composition by an in situ observation technique. It was found that twin-related dendrites appear in Si<sub>1−x</sub>Ge<sub>x</sub> (0 < <i>x</i> < 1) melts. It was also found that faceted dendrites can be grown in directional solidification before instability of the crystal/melt interface occurs, when a growing crystal contains parallel twin boundaries.
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