Abstract
During aggregation, an assembly of oxygen atoms in silicon produces an electrically active site. The center is an effective mass, helium-like center (double donor) with a wave function of C2v symmetry. The formation reactions of the assembly reveal details of the invisible early stages of aggregation. The donor character of the center controls the aggregation process in heavily doped material. The atomic structure and the source of the electrical activity of the center remain unresolved.