Germanium nanoparticle formation in thin oxide films on Si by negative-ion implantation

Abstract Germanium nanoparticles were formed in thin silicon dioxide by using negative-ion implantation, which has the advantage of being almost “charge-up free” even in insulators, resulting in the achievement of precise controls in depth and fluence without any charge compensation. Germanium negative ions were implanted into silica glass and thermally grown SiO 2 on silicon substrates at 10–30 keV with 1 × 10 15 –2 × 10 16  ions/cm 2 . Optical transmission spectra of Ge-implanted silica glass samples showed a clear absorption band in the range 200–280 nm in wavelength after annealing at less than 800 °C. This absorption corresponds well to the low energy tail of the calculated absorption peak at 170–190 nm depending on particle size. Observation by cross-sectional TEM on thin oxide films with Ge implantation at 10 keV and 5 × 10 15  ions/cm 2 into a 25-nm-thick SiO 2 on Si(100) substrate showed Ge nanoparticles with a maximum diameter of 4 nm at around 12 nm in depth. Ge nanoparticles of 2 nm size were formed at a fluence of 1 × 10 15  ions/cm 2 .