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

Ge nanocrystallites (Ge-nc) embedded in a SiO2 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) X 10(16) cm(-2) using 250 keV energy. After implantation, the samples were annealed at 1000 degrees C in a forming gas atmosphere for I h. All samples show a broad Raman spectrum centred at omega approximate to 304 cm(-1) with a slight shift depending on the implantation doses. The Raman intensity also depends on the Ge74+ dose. A maximum photoluminescence intensity is observed for the sample implanted at room temperature with a dose of 2 x 10(16) cm(-2) at 3.2 eV. Infrared spectroscopy shows that the SiO2 films moved off stoichiometry due to Ge74+ ion implantation, and Ge oxides are formed in it. This result is shown as a reduction of GeOx, 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.