  In this paper we investigate the structural and optical properties of few
strain-unbalanced multiple Ge/GeSi quantum wells pseudomorphically grown on
GeSi reverse-graded substrates. The obtained high epitaxial quality
demonstrates that strain symmetrization is not a mandatory requirement for few
quantum-well repetitions. Photoluminescence data, supported by a thorough
theoretical modeling, allow us to unambiguously disentangle the spectral
features of the quantum wells from those originating in the virtual substrate
and to evaluate the impact on the optical properties of key parameters, such as
quantum confinement, layer compositions, excess carrier density, and lattice
strain. This detailed understanding of the radiative recombination processes is
of paramount importance for the development of Ge/GeSi-based optical devices.
