Structural and optical properties of Al2O3 with Si and Ge nanocrystals

Si and Ge nanocrystals were formed in Al₂O₃ matrix by ion implantation and subsequent annealing. The phase separation of the Si nanocrystals was observed using X-ray photoelectron spectroscopy by monitoring Si 2p electrons. During nanocrystal formation with a high temperature annealing Si⁴⁺ signals corresponding to Si nanoclusters increase while Si ⁴⁺ signals related to a-SiO₂ disappear from the spectrum. The transition from amorphous to nanocrystalline phase for both Si and Ge nanoclusters and the compressive stress exerted on the formed nanocrystals were also studied by Raman spectroscopy. Photoluminescence spectra of the Al ₂O₃ containing nanocrystals were discussed by means of Ti and Cr impurities, as well as F centers. The existence of the amorphous Ge nanoclusters in Al₂O₃ matrix significantly enhances the light emission of Ti³⁺ impurities.