Minority carrier lifetime of p-type silicon containing oxygen precipitates: influence of injection level and precipitate size/density

The behaviour of minority carrier lifetime in p-type Czochralski silicon containing various concentrations of oxygen precipitates has been investigated in relationship to precipitate size, which is estimated by means of the reduction of interstitial oxygen concentration and injection level. The latter is varied in a wide range by comparing surface photovoltage technique, which operates at low injection, and microwave probed photoconductive decay technique, which operates at high injection. It is shown that at high injection level, the experimentally observed lifetime dependence on precipitate density and size can be explained, assuming that the recombination process takes place via silicon–precipitate interface states. However, at low injection, it is necessary to also take into account the effect of a fixed positive charge at the silicon–precipitate interface, which creates a depletion region around the precipitate, thus increasing its ‘effective capture size’. A model is presented, based on these mechanisms, which is in good agreement with the experimental data.