  We demonstrate that kinetics play an important role in the epitaxial growth
of Fe$_3$GeTe$_2$ (FGT) van der Waals (vdW) ferromagnetic films by molecular
beam epitaxy. By varying the deposition rate, we control the formation or
suppression of an initial tellurium-deficient non-van der Waals phase
(Fe$_3$Ge$_2$) prior to realizing epitaxial growth of the vdW FGT phase. Using
cross-sectional scanning transmission electron microscopy and scanning
tunneling microscopy, we optimize the FGT films to have atomically smooth
surfaces and abrupt interfaces with the Ge(111) substrate. The magnetic
properties of our high quality material are confirmed through magneto-optic,
magnetotransport, and spin-polarized STM studies. Importantly, this
demonstrates how the interplay of energetics and kinetics can help tune the
re-evaporation rate of chalcogen atoms and interdiffusion from the underlayer,
which paves the way for future studies of van der Waals epitaxy.
