Defect vs. nanocrystal luminescence emitted in Si-implanted SiO₂ layers

Visible photoluminescence is observed from thin Si-implanted SiO₂ films. Si ions were implanted into 300-nm-thick SiO₂ films grown on crystalline Si at energies of 30 and 55 keV, and with doses of 5 × 10¹⁵ and 1 × 10¹⁷ cm^-2. Implanted samples were subsequently annealed in N₂ ambient at 500-1100°C. PL spectra for the sample implanted with 1 × 10¹⁷ cm^-2 at 55 keV show that red luminescence (750 nm) related to Si-nanocrystals clearly increases with annealing temperature in intensity, and that a weak orange luminescence (600 nm) is observed after annealing at low temperatures of 500 and 800°C. The luminescence around 600 nm becomes very intense when a thin SiO₂ sample is implanted at a substrate temperature of 400°C with an energy of 30 keV and a dose of 5 × 10¹⁵ cm^-2. After annealing the sample in forming gas the PL intensity remarkably decreases. It indicates that defects are passivated by hydrogen. We conclude that this luminescence observed around 600 nm is caused by some radiative defects formed in Si-implanted SiO₂.