Germanium nanoparticles formation in silicon dioxide layer by multi-energy implantation of Ge negative ions and their photo-luminescence

Ge− ions were implanted into SiO2 layer three times by changing the energy of 50, 20 and 10 keV in this order to form germanium nanoparticles at a relatively wide-depth region. Then, the sample was annealed at 600-900 °C for 1 h. Although Ge nanoparticles formation was confirmed by cross-sectional TEM observation, XPS analysis showed about 30-60% of the Ge atoms in SiO2 on average were oxidized. In cathode and photo-luminescence measurement, the emissions of around 400 nm in wavelength from the samples were observed. The photo-luminescence peak position was independent of implanting Ge fluence, annealing temperature intensity and intensity of excitation light. These results suggest that the luminescence mechanism is not quantum confinement effect of Ge nanoparticles but oxygen defect center of oxidized germanium. The luminescence intensity changed dramatically with varying implanting Ge fluence.