| The coincidence Doppler broadening of positron annihilation radiation instrument and the mono-energetic slow positron beam instrument have been used to measure the Doppler broadening spectra for the SiO2 and samples ofCz-Si with an initial oxygen content (1.1×1018 cm-3 ), thermally treated at several temperatures and pressures. The following experimental results have been obtained:(1) In the single crystal of SiO2, the momenta of 2p electrons of O atom is higher than that of 3p electrons of Si atom. There is a relatively high peak at 11.85×10-3moc on the ratio curve of SiO2,it is due to positron annihilation with high momentum electron of O atom. And it can be used to characterize the behavior of O atom in Si-based semiconductor.(2) In samples of single crystals of Si annealed at 480°C/15h or 600 °C/15h, the ratio curves show the presence of vacancy-like defects but in this case these defects are not clearly associated with oxygen. There is no oxygen precipitates (SiOx) occurring in these samples.
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