Raman studies of silicon layers formed by cluster beam deposition

Raman studies of Si layers prepared on c-Si and Al 2 O 3 substrates at 300 K by well defined cluster beams have been carried out to establish correlation between the cluster species and the layer composition. The Si clusters were generated by a carbon-dioxide-laser-induced decomposition of SiH 4 in a flow reactor and were transferred to a free molecular flow by introducing a skimmer into the reaction zone. A mass spectroscopic analysis shows that this source emits two qualitatively different types of clusters: small clusters consisting of up to 12 atoms and large species of nearly 10 3 atoms. To produce the Si layers the substrate was placed perpendicular to the cluster beam. The Raman spectra of the deposited clusters show a broad amorphous-like band and a relatively sharp peak at 518.1 cm -1 . Analysis of the Raman shift and line width of this peak based on phonon confinement models allows us to conclude that this peak corresponds to nanocrystals with a size of about 3 nm. This size corresponds to the number of atoms in the large clusters of the cluster beam. It means that the layers conserve the specific properties of the large incident free clusters.