Optimization of the luminescence emission of Si nanocrystals synthesized from non-stoichiometric Si oxides using a Central Composite Design of the deposition process

Si oxide films with a controlled excess of Si were deposited on Si wafers by LPCVD using Si2H6 and O2, thermally annealed to 1100 °C for 1 h to form Si nanocrystals embedded in SiO2 and subsequently annealed at 450 °C in forming gas. The samples were characterized by Fourier transform infrared spectroscopy, spectroscopic ellipsometry and cathodoluminescence spectroscopy. The excess of Si in the as-deposited samples, ranging from 0 to 70% in volume, was obtained from the ellipsometry data analysis. After annealing at 1100 °C, the samples show a luminescence band (peaking at 665 nm) at 80 K and at room temperature which is associated to the presence of Si nanocrystals. The growth rate, the excess of Si incorporated to the films and the intensity of the luminescence band were modelled using a Face-Centered Central Composite Design as a function of the main deposition variables (pressure, 185–300 mTorr; temperature, 250–400 °C; Si2H6/O2 flow ratio, 2–5) aiming to control the growth process and the incorporation of Si in excess as well as to determine the experimental conditions that yield the samples with the maximum intensity of the luminescence emission.