Raman spectroscopy of Si nanocrystals in nanocrystalline Si superlattices: Size, shape and crystallographic orientation

We use Raman spectroscopy to study the size, shape and crystallographic orientation of silicon nanocrystals formed by solid phase crystallization of amorphous Si/SiO₂ superlattices (SLs) grown by radio-frequency sputtering. The first and second Raman peaks broadening, their relative positions and intensities indicate the presence of nanoscale Si objects with a degree of disorder (grain boundaries) and strain (Si/SiO₂ interfaces). Shapes of Si nanocrystals sandwiched between SiO₂ layers strongly influence the Si/SiO₂ interface roughness, which is inferred from the intensities of folded acoustic phonon scattering. The averaged crystallographic orientation of Si nanocrystals is determined by polarized Raman analysis. The laterally elongated nanocrystals exhibit 〈111〉 preferred crystallographic orientation along the SL axis due to orientation-dependent crystallization rates. These results demonstrate that control over Si nanocrystals structural parameters has been achieved and that solid phase crystallization of nanometer-thick amorphous Si films remains one of the most promising techniques for Si-based nanoelectronic device fabrication.