The early stage of the growth of Ge planar films on a Si(001) surface is investigated in real-time by using the spectroscopic ellipsometric technique. We demonstrate the possibility to measure the deposition rate and follow its evolution during the growth. The use of spectroscopic ellipsometry in combination with atomic force microscopy and X-ray photoelectron spectroscopy demonstrates that the deposition rate evolution is related to the stress status of the growing film through the variation of its complex dielectric constant.