The effect of Ge implantation dose on the optical properties of Ge nanocrystalsin SiO2

Abstract

Ge nanocrystallites (Ge-nc) embedded in aSiO2 matrix are investigated using Raman spectroscopy, photoluminescence andFourier transform infrared spectroscopy. The samples were prepared byion implantation with different implantation doses (0.5, 0.8, 1, 2, 3 and 4) × 1016 cm−2 using 250 keV energy. After implantation, the samples were annealed at1000 °C in a forming gas atmosphere for 1 h. All samples show a broad Raman spectrum centred atw≈304 cm−1 with a slight shift depending on the implantation doses. The Raman intensity also depends on theGe74+ dose.A maximum photoluminescence intensity is observed for the sample implanted at room temperature witha dose of 2 × 1016 cm−2 at 3.2 eV. Infrared spectroscopy shows that theSiO2 films moved offstoichiometry due to Ge74+ ion implantation, and Ge oxides are formed in it. This result is shown as a reduction ofGeOx atexactly the dose corresponding to the maximum blue–violet PL emission and the largest Raman emissionat 304 cm−1. Finally, the Raman spectra were fitted with a theoretical expression to evaluate theaverage size, full-width at half-maximum (FWHM) and dispersion of Ge-nc size.