  The optical response of (InGa)(AsSb)/GaAs quantum dots (QDs) grown on GaP
(001) substrates is studied by means of excitation and temperature-dependent
photoluminescence (PL), and it is related to their complex electronic
structure. Such QDs exhibit concurrently direct and indirect transitions, which
allows the swapping of $\Gamma$ and $L$ quantum confined states in energy,
depending on details of their stoichiometry. Based on realistic data on QD
structure and composition, derived from high-resolution transmission electron
microscopy (HRTEM) measurements, simulations by means of $\mathbf{k\cdot p}$
theory are performed. The theoretical prediction of both momentum direct and
indirect type-I optical transitions are confirmed by the experiments presented
here. Additional investigations by a combination of Raman and photoreflectance
spectroscopy show modifications of the hydrostatic strain in the QD layer,
depending on the sequential addition of QDs and capping layer. A variation of
the excitation density across four orders of magnitude reveals a 50 meV energy
blueshift of the QD emission. Our findings suggest that the assignment of the
type of transition, based solely by the observation of a blueshift with
increased pumping, is insufficient. We propose therefore a more consistent
approach based on the analysis of the character of the blueshift evolution with
optical pumping, which employs a numerical model based on a
semi-self-consistent configuration interaction method.
