  Fe$_{3}$Si/Ge(Fe,Si)/Fe$_{3}$Si thin film stacks were grown by a combination
of molecular beam epitaxy and solid phase epitaxy (Ge on Fe$_{3}$Si). The
stacks were analyzed using electron microscopy, electron diffraction, and
synchrotron X-ray diffraction. The Ge(Fe,Si) films crystallize in the well
oriented, layered tetragonal structure FeGe$_{2}$ with space group P4mm. This
kind of structure does not exist as a bulk material and is stabilized by solid
phase epitaxy of Ge on Fe$_{3}$Si. We interpret this as an ordering phenomenon
induced by minimization of the elastic energy of the epitaxial film.
