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Silicon dioxide including Ge nanoparticles (NPs) is expected to apply to light emission source. We have investigated luminescence properties of a thin SiO2 layer on Si including Ge NPs formed by negative-ion implantation. We implanted Ge negative ions three times into a 100-nm-thick SiO2 layer at different energies of 50, 20 and 10 keV in this order to make a flat depth profile of Ge in a depth region from 10 to 50 nm. In the multi-energy implantation, we obtained various Ge atomic concentrations less than 6.0 at.% in the SiO2 layer by choosing proper dose amount for each energy. Relation among three doses has a mutual ratio of 100:30:15. The implanted samples were annealed at various temperatures (600-800°C) for 1 h under N2 gas flow. Ge NPs in samples were confirmed by cross-sectional TEM observation. Although XPS analysis showed Ge atoms of about 30-40 % were oxidized, Raman spectrometry proved Ge-Ge bonds in the sample. In cathode-luminescence (CL) measurement, the sample showed CL peak at about 400 nm in wavelength. The CL peak wavelength and FWHM did not change for the various densities of implanted Ge atoms and for the various annealing temperatures. In general, the NP size depends on the implanted atom concentration and annealing temperature, and the size affects the emission wavelength. Therefore, the present luminescence is not caused by the quantum effect of NPs. On the other hand, it was reported that the oxygen defect center (ODC) of twofold-coordinated Ge works as emission center at 2.9-3.2 eV. The CL from Ge-implanted SiO2 well agreed with the above emission center. To check the ODC contribution, we annealed a Ge implanted sample in air. There is no presence of GeO with ODC, in contrast, the GeO2 were presented by XPS analysis, and the sample did not show any luminescence around 400 nm. Therefore, the CL emission at about 400 nm came from Ge-ODC. The stronger luminescence near 400 nm is obtained with the more Ge-ODC. By decreasing Ge concentration from 6 at.% to 0.5 at.%, we have obtained much more stranger 400-nm luminescence after the same annealing at 800°C. As for photoluminescence, we have also obtained PL peak at about 400-nm for Ge-implanted SiO2 samples. Details of the CL and the PL are presented at the conference. |