Formation of Si twinning-superlattice: First step towards Si polytype growth

We report about the formation of twinning-superlattice regions in Si epitaxial layers grown by multi-step molecular beam epitaxy on Si ( 1   1   1 ) ( 3 × 3 ) R 30 ∘ -B surfaces in which boron acts as a subsurfactant. Twinning-superlattice regions were formed by periodical arrangement of 180° rotation twins along the [1 1 1] direction separated by a few nanometers. The multi-step procedure 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 ) ( 3 × 3 ) R 30 ∘ -surface covered by at least 1/3 ML subsurface boron results in the formation of 180° rotation twins. The presented technology should be suitable to prepare Si polytypes.