Ellipsometric studies of annealing of SiO2 layers during the formation of light-emitting Si nanocrystals in them

Abstract

Annealing of SiO2 layers with excessive Si leading to the formation of silicon nanocrystals capable of fluorescing in the visible region owing to quantum-dimensional limitations is studied by the ellipsometry method. Excessive Si was introduced in SiO2 layers by ion implantation with an energy of 25 keV and a dose of 5× 1016 cm−2. Isochronous (103 s) annealings were carried out in a temperature interval of 200–1150°C with a step of 100°C. An LEF-2 ellipsometer with a 70° angle of incidence at a wavelength of 632.8 nm was used for the measurements. Fluorescence excited by a nitrogen laser was monitored concurrently. It is found that variations in optical constants of the layers at each step of annealing over the entire temperature range studied are clearly detected by ellipsometry. Variations in optical parameters of excessive Si are calculated in the Bruggeman approximation. They are found to correspond to individual stages of the formation of nanoprecipitates revealed earlier by other techniques. Nanocrystals proper producing intense visible photoluminescence are formed at annealing temperatures of 1000°C and higher.