We report about the formation of twinning-superlattice regions in Si epitaxial layers grown by molecular beam epitaxy on Si(1 1 1)(root 3 x root 3)R30 degrees B surfaces. Twinning-superlattice regions were formed by periodical arrangement of 180 degrees rotation twin boundaries along [1 1 1]-direction and are only separated by a few nanometers. The preparation method consists of repeating several growth, boron-deposition and annealing cycles on boron-predeposited undoped Si substrates. It is shown that the amount of subsurface boron and the growth mode influence the formation of twin boundaries. Only the nucleation of Si on the Si(1 1 1)(root 3 x root 3)R30 degrees-surface covered by at least 1/3 ML boron results in the formation of 180 degrees rotation twins. The size of superlattice regions is restricted by surface morphology. However, the presented technology should also be suitable to prepare a new type of semiconductor heterostructure based on Si polytypes. (c) 2006 Elsevier B.V. All rights reserved.