Si-SiO2 layers with high excess Si content prepared by magnetron co-sputtering of Si and SiO2 and subsequently annealed were studied by electron paramagnetic resonance and photoluminescence methods. It was shown that adding oxygen during the deposition run or aging in air of as-deposited films influences the characteristics of the oxide layer surrounding the silicon crystallites. It was found that for layers with more than 55 vol.% of excess silicon the silicon crystallites are oriented. After high-temperature annealing not all the excess silicon was in crystalline form but part of it was in the amorphous phase. The depth distribution of the crystallites was found to be homogeneous while the distribution of amorphous silicon has a maximum around the middle of the layer. (C) 2009 Elsevier B.V. All rights reserved.