Polarization-resolved Raman spectroscopy reveals the atomic local ordering in silicon germanium tin epitaxial alloys

Ternary SiGeSn alloys have emerged as a promising material system for applications in diverse fields such as photonics, electronics, and thermoelectrics. Its development still requires understanding the alloy properties, where an important role is alleged to be the local arrangement of the Si, Ge, and Sn atoms. Structural properties of SiGeSn epitaxial layers deposited on Ge/Si virtual substrates are investigated here by polarized Raman spectroscopy; in particular, we selected a series of samples with Ge content of similar to 83 at.% and variable Si and Sn content. This technique, which provides access not only to the energy but also to the symmetry of the vibrational modes, makes it possible to observe the effect of composition on the local alloy ordering. By studying how the Raman modes change the energy and the relative intensity variation under different polarization configurations, we could isolate the role of alloy configuration as the composition varies. High Sn content appears to promote local ordering, as Sn atoms tend to repel other Sn and Si atoms. Our results are potentially of great interest in elucidating SiGeSn material properties that are still debated in the literature, e.g., the influence of composition on the bandgap directness of the alloy