High dose oxygen ion implantation into silicon is an established method to form buried insulating layers. The material produced by standard processing techniques typically exhibits buried layers which are a few hundred nanome ers thick with a threading dislocation defect density on the order of 108/cm2. Unusual structures can be obtained by using repetitive cycles of partial doses of ions followed by annealing and possibly epitaxial growth. Both low and high doses may be used, the former intended to provide decreased defect density and the latter to increase the thickness of the buried layer above the theoretical maximum for higher voltage isolation. The material properties resulting from several variations of this technique are described and characterized.