Electronic Structure of Ge-Si Monolayer Strained-Layer Superlattices.

We report the results of a study of Ge-Si strained-layer superlattices grown on Si substrates. These results allow us to study the transition between superlattice-like and bulk-like states. We have examined samples whose superlattice period lies between 3angstroms and 15angstroms, similar to the lattice parameter of the crystalline unit cell. All of the samples in this study are ordered superlattices with an average composition of Ge sub (0.5) Si sub (0.5). Intentional ordering on a monolayer scale was achieved by molecular beam epitaxy (MBE). The optical energy level spectra of these structures at critical points in the Brillouin zone were measured by Schottky-barrier electro- reflectance in the energy range 0.6 eV to 4 eV.