Size and density control of Si-nanocrystals realized by SiOx/SiO2 superlattice

A process which allows the preparation of size and density-controlled Si nanocrystals (Si-NCs) with a crystal diameter down to 2 nm and a nanocrystal density up to 1019/cm3 has been developed. The process is based on the growth of amorphous SiOx/SiO2 superlattice, and produces Si-NCs due to the thermally induced phase separation of SiOx layers within the films and the crystallization of the resulting Si-nanoclusters. Amorphous SiOx films with adjustable oxygen content have been deposited on Si wafers by reactive evaporation of SiO powder in different O2 atmospheres. The oxygen content of the deposited films can be controlled by changing the oxygen pressure during evaporation. Photoluminescence spectra and transmission electron microscopy images of the superlattice samples indicate that the size of Si-NCs is determined by the initial SiOx layer thickness and, the density of Si-NCs within the layer varies with the stoichiometry of the SiOx layer in the superlattice. In this way, the size and density of Si-NCs within a layer can be controlled separately.