We report Raman scattering and low temperature photoluminescence measurements performed on a series of Molecular-Beam-Epitaxy-grown Si/Ge-n/Si quantum wells with n varying from 3 to 6. Our results are consistent with a gradual evolution of the Si/Ge interface which starts with Ge segregation and formation of terraces for low Ge coverage, to smooth 2-dimensional Ge layers, bounded by interfacial alloy layers, for coverages superior to 4-monolayers. (C) 1998 Elsevier Science Ltd. All rights reserved.1077359362