Raman scattering and x-ray absorption studies of Ge-Si nanocrystallization

We have studied the local structure of GeSi nanocrystals embedded in SiO2 prepared by co-sputtering of Ge, Si, and SiO2 targets onto a Si(100) substrate. From Raman scattering, we conclude that the formation of the isotropic crystalline Ge phase starts at about 800 degreesC followed by the formation of a GeSi phase at higher temperatures. The formed nanocrystals, whose size depends on the annealing temperature, are randomly oriented. The local structure of the nanocrystals has been studied by x-ray absorption fine structure spectroscopy. They are found to consist of a relaxed Ge core with a typical diameter of similar to4 nm and the Ge-Ge bond length of 2.45 Angstrom and of a GeSi outer shell, the Ge-Si bond length being 2.39 Angstrom. The average composition of the grown nanocrystals is estimated to be Ge0.75Si0.25. (C) 2002 American Institute of Physics.