Structural changes in amorphous Ge sub(x)SiO sub(y) on the way to nanocrystal formation

Temperature induced changes of the local chemical structure of bulk amorphous Ge sub(x)SiO sub(y) are studied by Ge K-edge x-ray absorption near-edge spectroscopy and Si L sub(2/3)-edge x-ray Raman scattering spectroscopy. Different processes are revealed which lead to formation of Ge regions embedded in a Si oxide matrix due to different initial structures of as-prepared samples, depending on their Ge/Si/O ratio and temperature treatment, eventually resulting in the occurrence of nanocrystals. Here, disproportionation of GeO sub(x) and SiO sub(x) regions and/or reduction of Ge oxides by pure Si or by a surrounding Si sub-oxide matrix can be employed to tune the size of Ge nanocrystals along with the chemical composition of the embedding matrix. This is important for the optimization of the electronic and luminescent properties of the material.