Interface ordering inSim/Genmonolayer superlattices: A photoluminescence study

Alternate Si and Ge monolayers deposited by molecular-beam epitaxy on ${\mathrm{Si}}_{0.7}$ ${\mathrm{Ge}}_{0.3}$ alloy have been analyzed by means of photoluminescence spectroscopy. We measured well-resolved excitonic transitions located at 0.8 eV, far from the alloy emission with the same stoichiometric composition. We discuss this feature in terms of interface mixing producing an ordered alloy to accommodate the tetragonal strain in the ${\mathrm{Si}}_{\mathit{m}}$/${\mathrm{Ge}}_{\mathit{n}}$ monolayer superlattice with m and n<3. © 1996 The American Physical Society.