For many years, Si_1−yGe_y alloys have been applied in the semiconductor industry due to the ability to adjust the performance of Si-based nanoelectronic devices. Following this alloying approach of group-IV semiconductors, adding tin (Sn) into the alloy appears as the obvious next step, which leads to additional possibilities for tailoring the material properties. Adding Sn enables effective bandgap and strain engineering and can improve the carrier mobilities, which makes Si_1−x−yGe_ySn_x alloys promising candidates for future opto- and nanoelectronics applications. The bottom-up approach for epitaxial growth of Si_1−x−yGe_ySn_x, e.g., by chemical vapor deposition and molecular beam epitaxy, allows tuning the material properties in the growth direction only; the realization of local material modifications to generate lateral heterostructures with such a bottom-up approach is extremely elaborate, since it would require the use of lithography, etching, and either selective epitaxy or epitaxy and chemical-mechanical polishing, giving rise to interface issues, non-planar substrates, etc. This article shows the possibility of fabricating Si_1−x−yGeySn_x alloys by Sn ion beam implantation into Si_1−yGe_y layers followed by millisecond-range flash lamp annealing (FLA). The materials are investigated by Rutherford backscattering spectrometry, micro-Raman spectroscopy, x-ray diffraction, and transmission electron microscopy. The fabrication approach was adapted to ultra-thin Si_1−yGe_y layers on silicon-on-insulator substrates. The results show the fabrication of single-crystalline Si_1−x−yGeySn_x with up to 2.3 at. % incorporated Sn without any indication of Sn segregation after recrystallization via FLA. Finally, we exhibit the possibility of implanting Sn locally in ultra-thin Si_1−yGe_y films by masking unstructured regions on the chip, thus demonstrating the realization of vertical as well as lateral Si_1−x−yGe_ySn_x heterostructures by Sn ion implantation and flash lamp annealing.