Formation of Ge-nanocrystals in SiO2 matrix by magnetron sputtering and post-deposition thermal treatment

Germanium Quantum Dots (Ge QDs) were formed in SiO2 by RT magnetron sputtering co-deposition of Ge and SiO2 and subsequent annealing. Films were deposited in the form of alternating (Ge + SiO2) layers (40:60 molar ratio) and pure SiO2 layers, serving as spacers. Grazing incidence small angle x-ray scattering (GISAXS) was applied for structural characterization of the QDs synthesized in the SiO2 amorphous matrix. The chemical composition and phase of the QDs were determined by Raman spectroscopy, and the spatial distribution and concentration of the Ge atoms by Rutherford Backscattering. The 2D GISAXS pattems, besides giving information on the layered structure, were used to reveal the onset of the synthesis of Ge QDs in SiO2 and to determine the average size and shape of QDs. It has been shown that the insertion of spacer SiO2 layers between (Ge + SiO2) layers transforms the 3D growth of Ge QDs into a preferentially 2D growth, within each 7 nm thick (Ge + SiO2) layer. This resulted in a considerably smaller average size of Ge QDs in the layered films. The synthesis of well crystallized, moderately sized, spherical Ge QDs was achieved by post-deposition annealing in the 700-800 degrees C range. (C) 2008 Elsevier Ltd. All rights reserved.