Ion beam synthesis of Si and Ge nanocrystals in an SiO2 Matrix is
performed by precipitation from supersaturated solid solutions created by
ion implantation. Films of SiO2 on (100) Si substrates are
implanted with Si and Ge at doses 1 × 1016/cm2 - 5 ×
1016/cm2. IMplanted samples are subsequently
annealed to induce precipitation of Si and Ge nanocrystals. Raman
spectroscopy and high-resolution transmission electron microscopy indicate a
correlation between visible room-temperature photoluminescence and the
formation of diamond cubic nanocrystals approximately 2–5 nm in diameter in
annealed samples. As-implanted but unannealed samples do not exhibit
luminescence. Rutherford backscattering spectra indicate a steepening of
implanted Ge profiles upon annealing. Photoluminescence spectra are
correlated with annealing temperatures, and compared with theoretical
predictions for various possible luminescence Mechanisms, such as radiative
recombination of quantum-confined excitons, as well as possible localized
state luminescence related to structural defects in SiO2
Potential optoelectronic device applications are also discussed.