We report on the molecular beam epitaxial growth of Ge0.93Sn0.07 alloys on Ge (100). A strained planar Ge0.93Sn0.07 film forms at the initial stages, as observed and confirmed by AFM and X-ray analysis. Continued deposition leads to formation of 3D Sn islands, which initiates phase-separation in the strained GeSn thin film through a kinetic pathway that leaves behind a pattern of nanoscale trenches and wires that run along [100]directions. This morphological transition only happens in a certain range of temperature, thickness and composition. The morphological features observed in Ge0.93Sn0.07 films potentially offer a unique pathway for fabrication of nanostructures,