  Concurrent natural time scales related to relaxation, recombination,
trapping, and drifting processes rule the semiconductor heterostructures'
response to external drives when charge carrier fluxes are induced. This paper
highlights the role of stoichiometry not only for the quantitative tuning of
the electron-hole dynamics but also for significant qualitative contrasts of
time-resolved optical responses during the operation of resonant tunneling
devices. Therefore, similar device architectures and different compositions
have been compared to elucidate the correlation among structural parameters,
radiative recombination processes, and electron-hole pair and minority carrier
relaxation mechanisms. When these ingredients intermix with the electronic
structure in Sb-based tunneling devices, it is proven possible to assess
various time scales according to the intensity of the current flux, contrary to
what has been observed in As-based tunneling devices with similar design and
transport characteristics. These time scales are strongly affected not only by
the filling process in the $\Gamma$ and L states in Sb-based double-barrier
quantum wells but also by the small separation between these states, compared
to similar heterostructures based on As.
