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

Abstract

Si oxide films with a controlled excess of Si were deposited on Si wafers by LPCVD using Si 2 H 6 and 0 2 , thermally annealed to 1100°C for 1 h to form Si nanocrystals embedded in Si0 2 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; Si 2 H 6 /0 2 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.

Magnetron sputtered nanocomposite films of SI nanocrystals embedded in SIO2 for electronic and optoelectronic applications.

“…In order to clarify the growth mechanism of the Si nanocrystals, the detailed thermal decomposition process of the Si suboxides should be fully understood. The dependence of the stability on Si oxidation numbers has been theoretically calculated by Barranco et al [19].…”

“…Two main models have been proposed for the growth mechanisms: the diffusion-controlled growth and the phase segregation growth. The diffusion-controlled growth theory believes that the nc-Si are grown by the classical nucleation, thermal diffusion of the excess Si atoms and ripen in the amorphous SiOx matrix [17,18]; while the phase segregation growth theory considers the rapid growth of nc-Si as a result of the segregation of Si suboxides [19].…”

“…The segregation mechanism of Si oxide is proposed based on the observation of the rapid growth of nc-Si during pulse annealing or rapid thermal annealing. Kachurin et al [19] The segregation proceeds as a percolation via "weak points" in the form of "silicon cracks" or "silicon breakdowns" in a-SiO 2 . It does not need long-range diffusion of Si atoms and the process could be fast.…”

“…As for the Si suboxides, since sufficient (almost half of the content) Si atoms are in the forms of Si suboxies, one should not take them to be the interface layer (usually with a thickness of several atomic layers) between Si clusters and SiO 2 matrix. However, they may form a transition layer between the Si clusters and the the Si suboxides has been reported by many researchers, and is widely accepted to the following reaction [19].…”

“…These two reactions take place simultaneously but with different manner. Barranco et al [19] suggested that reaction (1) takes place by the ligand exchanging of oxygen atoms within the Si-(O 2 ,Si 2 ) tetrahedron with a energy barrier at least 54kJ/mol. Reaction (2) takes place by inserting oxygen into a Si 3+ -Si 1+ bond with an activation energy of 125kJ/mol.…”