Recently small silicon nanocrystals (Si-nc) dispersed in a dielectric a-SiO2 matrix have drawn an elevated attention as a prospective composite material for the optical interconnect technology. Being the basis of the conventional microelectronics industry, silicon may be expected to integrate both optical and electronic functionalities, leading to optics on silicon chips. Nevertheless, Si has never been used to the light amplification purposes due to long radiative lifetimes. Other phenomena, such as the recombination electron-hole mechanism and free carrier absorption in silicon also limit the use of this material for laser applications.
However, it has been found that Si can be used for light emitters and amplifiers in the Si nanocrystal approach, whereas a maximization of free carrier confinement, an improved radiative probability by quantum confinement, and a shift of the the emission wavelength to the visible range have been achieved. It also gives a possibility to control the emission wavelength by the Si-nc dimension and the light extraction efficiency by the thickness of the dielectric layer between the Si-nc and air. Many experimental evidences demonstrate the intrinsic nature of the luminescence broadening, which needs better understanding. Thus, a deeper comprehension of the phenomena in the interface region between Si-nc and the surrounding silica may help in the optimization of the optical properties of these structures.
By means of molecular dynamics, we have constructed an atomistic model of Si-nc's implanted into an amorphous a-SiO2 structure. The model is based on the silica structure prepared starting from a randomized space distribution of Si and O atoms (1:2) simulated with the Watabe potential. Small Si nanoclusters have been placed inside the amorphous SiO2 structure. A series of annealing runs have been carried out to obtain a low-energy interface structure between the Si-nc and the silica bulk. The structure and defects at the Si-SiO2 interface are discussed.
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