Characterization of Si nanocrystals grown by annealing SiO2 films with uniform concentrations of implanted Si

We have performed physical and optical characterization of Si nanocrystals grown by ion implantation of Si+ ions at multiple energies with varying doses into thermally grown SiO2 films. The purpose of multiple implants was to achieve uniform composition of the added Si profile throughout the SiO2 film to produce Si particles with a narrow size distribution upon annealing at 1000 degrees C in a nitrogen atmosphere. The depth distribution of the composition and sizes of the Si particles in SiO2 films before and after the anneal were determined using Rutherford backscattering (RBS), forward recoil spectroscopy, small-angle x-ray diffraction (SXRD), and high-resolution transmission electron microscopy (HRTEM). From RBS we concluded that the amount of free silicon was reduced by annealing, presumably due to oxidation in the annealing process. The mean cluster sizes of the annealed samples were determined by SXRD. HRTEM was also employed to determine the average size of Si particles. Photoluminescence spectra (PL) from these samples were broad and the peak positions of the PL spectra were blue-shifted with decreasing cluster size. The line shapes of the PL spectra were calculated with a quantum confinement model assuming a log-normal size distribution of Si nanoparticles and (1/D)(1.25) dependence of the band gap energy as a function of particle size D. The band gap energy and the average particle size obtained from the calculated line shape spectra agree well with the quantum confinement model. (C) 2000 American Institute of Physics. [S0021-8979(00)04020-2].