  GeSn epitaxial heterostructures are emerging as prominent candidates for the
monolithic integration of light sources on Si substrates. Here we propose a
judicious explanation for their temperature-dependent photoluminescence (PL)
that is based upon the so far disregarded optical activity of dislocations. By
working at the onset of plastic relaxation, which occurs whenever the epilayer
releases the strain accumulated during growth on the lattice mismatched
substrate, we demonstrate that dislocation nucleation can be explicitly seen in
the PL data. Notably, our findings point out that a monotonous thermal PL
quenching can be observed in coherent films, in spite of the indirect nature of
the GeSn bandgap. Our investigation, therefore, contributes to a deeper
understanding of the recombination dynamics in this intriguing group IV alloy
and offers insights into crucial phenomena shaping the light emission
efficiency.
