Fabrication and characterization of Ge nanocrystalline growth by ion implantation in SiO2 matrix
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Ge nanocrystallites (Ge-nc) have been formed by ion implantation of Ge+74 into SiO2 matrix, thermally grown on p-type Si substrates. The Ge-nc are examined by Raman spectroscopy, photoluminescence (PL) and Fourier transform infrared spectroscopy (FTIR). The samples were prepared with various implantation doses [0.5; 0.8; 1; 2; 3; 4] × 1016 cm−2 with 250 keV energy. After implantation, the samples were annealed at 1,000 °C in forming gas atmosphere for 1 h. Raman intensity variation with implantation doses is observed, particularly for the peak near 304 cm−1. It was found that the sample implanted with a doses of 2 × 1016 cm−2 shows maximum photoluminescence intensity at about 3.2 eV. FTIR analysis shows that the SiO2 film moved off stoichiometry due to Ge+74 ion implantation, and Ge oxides are formed in it. This result is shown as a reduction of GeOx at exactly the doses corresponding to the maximum blue-violet PL emission and the largest Raman emission at 304 cm−1. This intensity reduction can be attributed to a larger portion of broken Ge–O bonds enabling a greater number of Ge atoms to participate in the cluster formation and at the same time increasing the oxygen vacancies. This idea would explain why the FTIR peak decreases at the same implantation doses where the PL intensity increases.