The formation of amorphous interlayers (a‐interlayers) by solid‐state diffusion in ultrahigh‐vacuum‐deposited polycrystalline Ti thin film on germanium and epitaxial Si1-xGex (x=0.3, 0.4, and 0.7) alloys grown on (001)Si has been investigated by transmission electron microscopy and Auger electron spectroscopy. Amorphous interlayers, less than 2 nm in thickness, were observed to form in all as‐deposited samples. The growth of the a‐interlayers was found to vary nonmonotonically with the composition of Si–Ge alloys in annealed samples. On the other hand, the formation temperature of crystalline phase was found to decrease with the Ge content. The results are compared with those of the Ti/Si system. © 1995 American Institute of Physics.