New optical transitions in Si-Ge strained superlattices

Optical transitions in ultrathin Si-Ge strained superlattices are computed by means of a simple tight-binding model. The use of strain and folding arguments gives a clear understanding of the different origin of the transitions previously observed. The experimental dependence of intensities with the number of layers in the supercell is found to be a consequence of the fact that these superlattices are type II.