Effect of Si implantation on the microstructure of silicon nanocrystals and surrounding SiO2 layer

Si nanocrystals (Si-nc) embedded in a SiO2 layer have been characterized by means of transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). For local Si concentration in excess ⩽ 8 × 1021 Si+/cm3, the size of the Si-nc was found to be ∼3 nm and comparatively homogeneous throughout the whole implanted layer. For local Si concentration in excess of ∼2.4 × 1022 Si+/cm3, the Si-nc diameter ranges from ∼2 to ∼12 nm in the sample, the Si-nc in the middle region of the implanted layer being bigger than those near the surface and the bottom of the layer. Also, Si-nc are visible deeper than the implanted depth. Characterization by XPS shows that a large quantity of oxygen was depleted from the first ∼25 nm in this sample (also visible on TEM image) and most of the SiO2 bonds have been replaced by Si-O bonds. Experimental and simulation results suggest that a local Si concentration in excess of ∼3 × 1021 Si/cm3 is required for the production of Si-nc.