Effect of Si nanoparticles embedded in SiOx on optical properties of the films studied by spectroscopic ellipsometry and photoluminescence spectroscopy

The optical properties of silicon oxide (SiOx) films, vacuum evaporated and thermally annealed in argon atmosphere at 700 °C and 1000 °C, have been studied by spectral ellipsometry and photoluminescence (PL) measurements. The thickness, complex refractive index values and composition of the films, as well as the size of the formed Si nanocrystallites have been elucidated from the spectral ellipsometric measurements performed in the range of 280-820 nm. The ellipsometric data was analysed by the Bruggeman effective-medium approximation. It has been shown that annealing at 700 °C leads to coagulation of Si atoms into amorphous clusters, while at 1000 °C the Si clusters start to crystallize and form nanocrystallites with average size of 2.2 nm. The PL emission from the films annealed at 700 °C is blue-shifted and 5-10 times more intense in comparison with the films annealed at 1000 °C. This behaviour is correlated with the films structure, i.e., amorphous Si nanoclusters formed in the oxide matrix at 700 °C yield higher PL intensity than Si nanoclusters crystallized at 1000 °C.