Si nanoparticle formation in SiO2 by Si ion implantation: Effect of energy and fluence on size distribution and on SiO2 composition

The injection of current in electroluminescent devices based on silicon nanocrystals (Si-nc) embedded in SiO2 matrix is facilitated by the use of very thin SiO2 layer. Therefore, the production of Si-nc by implantation of excess Si ions in the SiO2 substrate has to be performed at lower energy. We have hence studied the effect of the Si ion energy on the Si-nc size distribution as well as on the surrounding SiO2 matrix. Si has been implanted into thermally grown oxide film on Si (100) substrate at 50 and 150 keV with 5 × 1016 to 2.2 × 1017 Si+/cm2. TEM has shown that for low doses (where the photoluminescent signal is at maximum) the Si-nc size is nearly uniform around 3 nm, whereas at high doses there is a size distribution (1.8–20 nm). A good agreement in the Si-nc average size has been found between XRD and TEM characterizations. Measurement by TEM of the implanted SiO2 thickness has revealed that the swelling is more important for low fluence implantation due to the formation of amorphous Si clusters. XPS has shown partial oxygen depletion near the surface as well as a production of non-stoichiometric oxides of varying composition with depth.