Raman spectra of Ge nanocrystals embedded into SiO2

We start with an analysis of the Raman spectra of Ge nanocrystals obtained in previous studies and demonstrate that in many cases the observed experimental peak attributed to Ge in fact originates from the Si substrate. We further compare various experimental ways to separate the Ge signal from that of the substrate and suggest optimum conditions for such measurements. Finally, we demonstrate that upon the annealing of an amorphous Ge-Si-O film, Ge nanocrystals are formed. The nanocrystals are randomly oriented and Ge-Si mixing takes place only at the interface with the Si substrate. (C) 2000 American Institute of Physics. [S0021-8979(00)09919-9].