Nanocrystal Formation in Annealed a-SiO0.17N0.07:H Films

Silicon nanocrystals have been fabricated by annealing amorphous hydrogenated silicon-rich oxynitride (SRON) films in vacuum for 4 h over the temperature range 850-1150°C. X-ray photoelectron spectroscopy confirmed the composition of the film to be SiO_0.17N_0.07. Glancing angle x-ray diffraction results revealed consistent silicon crystallite sizes of ∼5 nm for films annealed at temperatures < 1050°C, increasing to ∼12 nm for films annealed at 1150°C. The room temperature photoluminescence spectra of the samples annealed at 850 and 950 °C comprised luminescent peaks from silicon nanocrystals and luminescence from the defects in Si-O system. However, only peaks from defects in Si-O system were present in the luminescence spectra from samples annealed at temperatures greater than 950 °C. For the samples annealed at 850 and 950 °C, the presence of strong Si-N bonds prevented the coalescence of smaller silicon crystallites into larger crystallites. Larger, non-luminescent silicon crystallites were only formed in films annealed at temperatures greater than 950 °C, where the energetics of coalescing particles overcame the strong Si-N bonding in SRON films. High-resolution transmission electron microscopy analysis confirmed the presence of silicon nanocrystallites. A proposed growth mechanism of silicon nanocrystals is discussed.