Highly n-doped silicon: Deactivating defects of donors

We report insight into the deactivation mechanisms of group V donors in heavily doped silicon. Based on our ab initio calculations, we suggest a three step model for the donor deactivation. In highly n-type Si grown at low temperatures, in the absence of excess native point defects, the intrinsic limit to n_e seems to rise in part by means of donor deactivating distortions of the silicon lattice in the proximity of two or more donor atoms that share close sites. Also, donor dimers play an important part in the deactivation at high doping concentrations. While the dimers constitute a stable or metastable inactive donor configuration, the lattice distortions lower the donor levels gradually below the impurity band in degenerate silicon. On the other hand, we find that, in general, none of the earlier proposed deactivating donor pair defects is stable at any position of the Fermi level. The lattice distortions may be viewed as a precursor to Frenkel pair generation and donor-vacancy clustering process (step 2) that account for deactivation at elevated temperature and longer annealing times. Ultimately, and most prominently in the case of the large Sb atoms, precipitation of the donor atoms may set in as the last step of the deactivation process chain.