The effect of Ge implantation dose on the optical properties of Ge nanocrystals in SiO₂

Ge nanocrystallites (Ge-nc) embedded in a SiO(2) matrix are investigated using Raman spectroscopy, photoluminescence and Fourier transform infrared spectroscopy. The samples were prepared by ion implantation with different implantation doses (0.5, 0.8, 1, 2, 3 and 4) × 10(16) cm(-2) using 250 keV energy. After implantation, the samples were annealed at 1000 °C in a forming gas atmosphere for 1 h. All samples show a broad Raman spectrum centred at w≈304 cm(-1) with a slight shift depending on the implantation doses. The Raman intensity also depends on the Ge(74+) dose. A maximum photoluminescence intensity is observed for the sample implanted at room temperature with a dose of 2 × 10(16) cm(-2) at 3.2 eV. Infrared spectroscopy shows that the SiO(2) films moved off stoichiometry due to Ge(74+) ion implantation, and Ge oxides are formed in it. This result is shown as a reduction of GeO(x) at exactly the dose corresponding to the maximum blue-violet PL emission and the largest Raman emission at 304 cm(-1). Finally, the Raman spectra were fitted with a theoretical expression to evaluate the average size, full-width at half-maximum (FWHM) and dispersion of Ge-nc size.