Permanent recovery of electron lifetime in pre-annealed silicon samples: A model based on Ostwald ripening

The permanent deactivation of the boron-oxygen-related recombination centre in crystalline silicon was previously found to slow down after pre-annealing at 450 degrees C. In this study, the impact of pre-annealing at 450 degrees C and 475 degrees C on the permanent deactivation process is studied in more detail, revealing that the rate constant is fundamentally reduced. We explain this finding by ascribing the deactivation effect to sinking of interstitial boron atoms (B-i) to boron nano-precipitates. A pre-anneal will result in Ostwald ripening of nano-precipitates and hence to an essential reduction in their sinking efficiency RpNp, where N-p is the density and R-p is the average radius. By simulations it was found that (RpNp)(-3/2) is a linear function of the annealing time-insensitive to the starting size distribution. This linear law well corresponds to the measured variation in the rate constant. In addition, it was concluded that the major traps for B-i (under illumination) are defect complexes BsO2-of substitutional boron and oxygen. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4768688]