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

Annealing of SiO2 layers with excessive Si leading to the formation of sili con nanocrystals capable of fluorescing in the visible region owing to quan tum-dimensional limitations is studied by the ellipsometry method. Excessiv e Si was introduced in SiO2 layers by ion implantation with an energy of 25 keV and a dose of 5 x 10(16) cm(-2). Isochronous (10(3) s) annealings were carried out in a temperature interval of 200-1150 degreesC with a step of 100 degreesC. An LEF-2 ellipsometer with a 70 degrees angle of incidence at a wavelength of 632.8 nm was used for the measurements. Fluorescence excit ed by a nitrogen laser was monitored concurrently. It is found that variati ons in optical constants of the layers at each step of annealing over the e ntire temperature range studied are clearly detected by ellipsometry. Varia tions in optical parameters of excessive Si are calculated in the Bruggeman approximation. They are found to correspond to individual stages of the fo rmation of nanoprecipitates revealed earlier by other techniques. Nanocryst als proper producing intense visible photoluminescence are formed at anneal ing temperatures of 1000 degreesC and higher. (C) 2001 MAIK "Nauka/Interper iodica".