On the two- and three-dimensional character of the absorption spectra of Si/Ge superlattices

Abstract

The optical properties of some strained symmetrized Si n /Ge n superlattices were studied. In particular the contribution of each direct transition to the absorption spectra and their two- or three-dimensional character is investigated. To achieve this we decomposed each contribution into the density of available superlattice states and the transition probability. It is found that the transition probability is as important is determining the absorption spectra as the density of available states. Furthermore, the signature of direct transitions from the Z point of the superlattice Brillouin zone is predicted to be presented by a structure in the absorption spectra at energies higher than about 0.3 eV above the absorption onset for the case of the Si 5/Ge 5 strained symmetrized superlattice. The possibility arises that transitions from the Z point of the superlattice Brillouin zone can be detected experimentally.