Float-zone crystals of O-doped and N-doped material were investigated. It was shown that inactivation of N-enhanced D-defect suppression was not the result of a reduction in the N-pair concentration due to N-O interactions. It was instead suggested that the diffusivity of vacancies, Si interstitials and N was reduced by interaction with O. This led to a considerable decrease in N-enhanced recombination between vacancies and interstitials. This had previously been proposed in order to explain the simultaneous suppression of vacancies and interstitials by N doping. A radial O precipitation behavior was explained by applying a formula for the critical radius of O precipitates which accounted for the effect of vacancies and self-interstitials. A qualitative picture of the radial variations in vacancy and interstitial concentrations was derived by assuming that D-defect formation occurred before the onset of O precipitation.

W.Von Ammon, P.Dreier, W.Hensel, U.Lambert, L.Koester: Materials Science and Engineering B, 1996, 36[1-3], 33-41