Germanium nanoparticles formed in silicon dioxide layer by multi-energy implantation and oxidation state of Ge atoms

Ge nanoparticles (NPs) embedded silicon oxide is expected to be promising light emission source, especially, UV – blue light region. We have tried to form Ge NPs in a 100- nm-thick SiO2 layer on Si substrate by multi-energy implantation of Ge negative ions with energies of 50, 20 and 10 keV and doses of 1.4 × 1016, 3.2 × 1015 and 2.2 × 1015 ions/cm2, respectively. Samples were annealed for 1 h at a temperature less than 900oC. By this implantation, Formations of Ge nanoparticles in a surface 50-nm depth region were expected. The depth distribution of implanted Ge atoms in the oxide was measured by XPS (Ge 2p, O 1s, Si 2p) with monochromatic Al K.. and Ar etching at 4 keV. The depth profiles were well agreed with the cross-sectional TEM image. But some extent of Ge atoms diffused to the SiO2/Si interface at 900 oC. The chemical sifted spectra of Ge 2p3/2 showed about 60 % of the oxidation of Ge atom around the end of the range (EOR) even in the as-implanted sample. This oxidation was considered to be due to the excess oxygen atoms near EOR by forward of sputtered oxygen atoms from SiO2 layer. Raman spectra supported this oxidation. In a preliminary investigation of cathode luminescence, the Ge-implanted sample with annealing at 600oC showed CL peak at 3.12 eV (397 nm in wavelength) in UV-blue region at room temperature. This means the Ge-implanted sample has a possibility for light emission in the UV-blue region.