We study the optical and theoretical properties of (In,Ga)(As,Sb)/GaAs
quantum dots (QDs) embedded in a GaP (100) matrix, which are overgrown by a
thin GaSb capping layer with variable thickness. QD samples are studied by
temperature-dependent photoluminescence, and the results analyzed with the help
of theoretical simulations by eight-band~\textbf{k⋅p}, with multiparticle
corrections using the configuration interaction. We reveal a type-I to type-II
band alignment switching when QDs are overgrown by a GaSb layer with a
thickness larger than one monolayer. Moreover, we observe a temperature driven
blueshift of the quantum dot luminescence, which is explained by decomposing
the spectra into sum of Gaussians. Our analysis reveals that the GaSb overlayer
causes switching of the intensity between Γ- and L-transitions, making
the k-indirect electron-hole transition in type-II regime to be
optically more radiant than the Γ-direct one. Finally, we provide
theoretical expectations for the storage time for (In,Ga)(As,Sb)/GaAs/GaP QDs
overgrown by the GaSb layer with an AlP barrier underneath, to be embedded in a
nanomemory device. We find that by increasing the thickness of the GaSb layer
from 0 to 1.5~monolayers (MLs) leads to an increase in the storage time of four
orders of magnitude, from 1 hour to up almost a year, rendering such QDs very
promising candidates as storage units for nanomemory devices