Cluster coarsening and luminescence emission intensity of Ge nanoclusters in SiO/sub 2/ layers

SiO2 layers 180 nm thick are implanted with 120 keV Ge+ ions at a fluence of 1.2x1016 cm-². The distribution and coarsening evolution of Ge nanoclusters are characterized by Rutherford backscattering spectrometry and transmission electron microscopy and the results are correlated with photoluminescence measurements as a function of the annealing temperatures in the 400°C ≤T≤900°C range. At 400°C we observe a monomodal array of clusters characterized by a mean diameter ‹Ø›=2.2 nm which increases to ‹Ø›=5.6 nm at 900°C. This coarsening evolution occurs concomitantly with a small change of the total cluster–matrix interface area and an increase of the Ge content trapped in observable nanoclusters. However, at 900°C a significant fraction of up to about 20% of the Ge content still remains distributed in the matrix around the nanoparticles. The results are discussed in terms of possible atomic mechanisms involved in the coarsening behavior that lead to the formation of the oxygen deficiency luminescence centers