Size-dependent optical properties of Si nanocrystals embedded in amorphous SiO2 measured by spectroscopic ellipsometry

Abstract

Silicon nanocrystals (Si NCs) with average diameters <d _NC >=3 , 5 and 8 nm embedded in amorphous SiO ₂ synthesized by Si ion implantation have been characterized by spectroscopic ellipsometry. The dielectric function of the Si NCs has been extracted from SE data using a Bruggeman effective medium approximation and a Gauss–Lorentz oscillator model, taking into account the size dispersion of the nanoparticles. The dielectric function is found to depend strongly on average NC size. Although electronic critical point transitions of bulk silicon are discernible in NCs down to 3 nm diameter, the E ₁ resonance weakens with decreasing NC size, nearly disappearing for 3 nm diameter, while the dominant E ₂ transition blueshifts. In addition, a non-bulk-Si-like resonance intermediate between E ₁ and E ₂ is observed.