InAs/(GaIn)Sb superlattices (SL) grown by solid-source molecular-beam epitaxy were studied by spectroscopic ellipsometry. The pseudodielectric function of InAs/GaSb SLs could be fitted using modified bulk dielectric functions of InAs and GaSb with pronounced energy shifts and broadening of critical-point resonances. These changes in the dielectric functions of the constituent layers can be explained only in part by pseudomorphic strains, therefore providing evidence for thin-layer critical-point broadening and quantum confinement effects. For InAs/(GaIn)Sb SLs, the extremum in the pseudodielectric function derived from theE1critical point of (GaIn)Sb was found to shift to lower energies with increasing In content, and thus can be used as a probe for the composition of the (GaIn)Sb SL layers. ©1997 American Institute of Physics.