The effects of the addition of germanium tetrafluoride, GeF4, are demonstrated on the growth of films of hydrogenated microcrystalline silicon, mu c-Si:H, from SiH4 and H-2 by r.f. plasma-enhanced chemical vapor deposition (r.f. PECVD). The structural and optoelectrical properties of the mu c-Si(Ge):H(F) film are examined as a function of the how rates of GeF4 and H-2 The addition of GeF4 enhances the deposition rate and the crystallinity of the Si network, when the flow rate ratio, r = Fr(GeF4)/Fr(SiH4) is below 10%. On the other hand, under conditions, r > 0.1, the formation of a SiGex crystalline phase is promoted. The combination of the flow rates of GeF4 and H-2 greatly affects the enhancement of crystallinity along with an increase in surface roughness.