POSITRON IMPLANTATION STUDIES OF OXYGEN IN P+-SILICON EPILAYERS

The Doppler broadening of radiation from the annihilation of positrons in p+-silicon epilayers 1 and 0.4 mu m thick epitaxially grown at different temperatures has been measured. The signal from positrons decaying within the epilayers is enhanced at the expense of any significant contribution from surface annihilation, enabling direct measurement of the Doppler lineshape parameter S characteristic of the epilayers. The epilayer S-value is observed to decrease for samples grown at temperatures below 700 degrees C, for which the expected concentration of oxygen defects increases. The correlation between S and oxygen concentration is interpreted in terms of (a) transition-limited trapping by atomic oxygen defects and (b) diffusion-limited trapping by SiO x precipitates. The former is consistent with secondary-ion mass spectrometry measurements if the specific trapping rate is reduced to at least half of the value quoted by earlier researchers; the latter implies that the results are consistent with the formation of SiO1.75 precipitates of mean radius 3.2+or-0.7 nm.