We have studied InAs/GaSb superlattices (SL´s) grown with either InSb-like or GaAs-like interfaces (IF´s) on top of a GaSb buffer layer on GaAs substrates. The InAs layer thickness was varied from 4 to 14 monolayers (ML) while the GaSb layer thickness was kept fixed at 10 ML. The type of IF bonds realized was verified by Raman scattering from mechanical IF modes. High-resolution x-ray diffraction using one- and two-dimensional mapping of symmetric and asymmetric reflections allowed us to determine independently the lattice parameters parallel and perpendicular to the growth direction. The GaSb buffer layer was found to be fully relaxed whereas the SL’s with InSb-like IF’s were coherently strained to the in-plane lattice parameter of the GaSb buffer for InAs layer thicknesses exceeding 6 ML. The strain distribution within the SL’s with GaAs-like IF’s was obtained from simulations of the x-ray reflection profiles. The SL’s were found to be coherently strained close to the GaSb buffer and showed increasing strain relaxation with increasing distance from the buffer layer. In addition, these simulations provide an accurate determination of the SL periods. Well-resolved Raman spectra of backfolded longitudinal acoustic ~LA! phonons were observed showing for SL’s with InSb-like IF’s folded LA phonon lines up to the seventh order. The spectrum of quasiconfined optical SL phonons was examined by Raman spectroscopy and by IR reflection. A detailed analysis of the IR reflection spectra allowed an independent determination of the individual layer widths within the SL stack, including the spatial extent of the GaAs-like IF mode.