Optical properties of Si clusters and Si nanocrystallites in high-temperature annealed SiOx films

Abstract

Structure, optical absorption and photoluminescence (PL) properties of SiOx films subjected to thermal annealing at 750–1100 °C are investigated. Si crystallites with a few nanometers in size are observed in the SiO1.3 and SiO1.65 films annealed at 1100 °C. Threshold energies in optical absorption of the Si nanocrystallites are higher than that for bulk Si, suggesting a contribution from quantum confinement effects. The PL spectrum shows a remarkable increase in intensity after annealing at temperatures above 1000 °C. This PL behavior is closely related to the formation of Si nanocrystallites by the annealing. The PL peak energy of the annealed films shifts to higher energy with decreasing crystallite size but does not follow the blueshift for the absorption threshold energy. These results suggest that a localized state contributes to the PL mechanism. The SiO1.8 film annealed at 1100 °C, which contains no Si crystallites, exhibits an intense PL similar to the annealed SiO1.3 and SiO1.65 films. It is implied that noncrystalline Si nanoparticles are formed in the SiO1.8 film under high-temperature annealing.

Silicon Oxide (SiOx, 0&ltx&lt2): a Challenging Material for Optoelectronics

“…As a result of the phase separation, islands of nano-crystalline silicon (Si-nc) embedded in a SiO 2 matrix are obtained. Such a structure is shown in figure 31, using a TEM spectrum (Inokuma et al, 1998). As it was proved in this section, this new material can be obtained from silicon sub-oxides SiO x (0<x<2) as predecessors, and special post-deposition treatments.…”

“…This is revealed in figure 35 where the peak maximum of the photoluminescence is plotted against the mean crystal size according. The data are from literature (Inokuma et al, 1998;Kahler and Hofmeister, 2002) and reveal the photoluminescence (PL) spectra in SiO x films subjected to thermal annealing between 750 0 C and 1100 0 C. This study shows that there is a remarkable increase in the PL intensity after annealing at temperature above 1000 0 C. Both, the composition of the as-deposited SiO x and the annealing temperature value play an important role in the dimension of the crystals and, from here on the photoluminescence spectrum. Depending on the deposition method for the SiO x precursor thin film and on the post-deposition treatment in order to obtain the phase www.intechopen.com separation, the silicon nanocrystals result in different sizes.…”

“…This new material was obtained from SiO 1.3 annealed at 1100 C. The dimension and the concentrations of these nano crystals are very important for applications in optoelectronics. Reprinted with permission from Inokuma et al, 1998;copyright 1998, American Institute of Physics. www.intechopen.com…”

Combining Rare Events Techniques: Phase Change in Si Nanoparticles

“…Results from Energy Filtered Transmission Electron Microscopy (EFTEM) and Dark-Field Transmission Electron Microscopy (DFTEM) on Si-rich SiO x show that Si nanoparticles start to form at 1000 • C [28,29,24,25,30,27]. At this temperature they are all amorphous, while at 1100 • C about one third become crystalline.…”

“…The rationale for the upper limit of the Q 6 range is that the value of the bond-orientational order parameter for an ideal Si crystal is Q 6 = 0.63 and, since from experiments and previous calculations it is known that Si crystalline nanoparticles assume a structure with a (distorted) diamond-like core and a disordered periphery [23,24,25,26], we expect the Q 6 of crystalline nanoparticles be lower than this limit. The samples created according to the protocol described in Sec.…”