Soft-x-ray photoemission study of Cr-Ge intermixing on crystalline and amorphous Ge surfaces

We have investigated room-temperature interdiffusion and reaction induced by thin Cr films on Ge(111) and on amorphous Ge films of thicknesses between 20 and 120 A{}. Soft-x-ray photoemission results show that Cr and Ge intermix to form several Cr-Ge bonding configurations in the extended interfacial zone. Analysis of Ge 3d core-level shifts shows that the first and the terminal Cr-induced species which form on a-Ge have the same binding energies as those which form on Ge(111). In contrast, for Cr/a-Ge, we also observe an intermediate constituent which does not form on Ge(111). We attribute the differences in reaction products to microstructural differences in a-Ge which influence the diffusion of Ge and Cr. Comparison of the results as a function of substrate thickness shows that the reaction products are always the same but that the width of the interfacial zone varies with the availability of the semiconductor atoms.