We are reporting a new ion beam vapor deposition technique for epitaxial growth of Si-Ge alloys on [100] Si substrates at temperatures as low as 285 degrees C. The growth of Si films involves beam assisted dissociation of SiH4 gas while the incorporation of Ge is achieved through thermal evaporation of elemental Ge. We have used transmission electron microscopy, electron diffraction analysis and Rutherford backscattering to study the quality of the grown films. The results of this study show that a beam energy of 40 to 50 eV yields optimum growth.