Defect versus nanocrystal luminescence emitted from room temperature and hot-implanted SiO₂ layers

Silicon nanocrystals have been synthesized in SiO₂ matrix using Si ion implantation. Si ions were implanted into 300-nm-thick SiO₂ films grown on crystalline Si at energies of 30-55 keV, and with doses of 5 × 10¹⁵, 3 × 10¹⁶, and 1 × 10¹⁷ cm^-2. Implanted samples were subsequently annealed in an N₂ ambient at 500-1100°C during various periods. Photoluminescence 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 and time in intensity, and that weak orange luminescence (600 nm) is observed after annealing at low temperatures of 500°C 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 30keV and a low dose of 5 × 10¹⁵ cm^-2. It vanishes after annealing at 800°C for 30 min. We conclude that this luminescence observed around 600 nm is caused by some radiative defects formed in Si-implanted SiO₂.