  We address the photoluminescence emission of individual germanium extrinsic
centers in Al_0.3Ga0.7As epilayers grown on germanium substrates. Through a
thorough analysis of micro-photoluminescence experiments we demonstrate the
capability of high temperature emission (70 K) and multiexcitonic features
(neutral exciton X, biexciton XX, positive X+ and negative X- charged exciton)
of these quantum emitters. Finally, we investigate the renormalization of each
energy level showing a large and systematic change of the binding energy of XX
and X+ from positive to negative values (from ~+5 meV up to ~-7 meV covering
about ~ 70 meV of the emission energy) with increasing quantum confinement.
These light emitters exhibiting energy-degenerate X and XX energy levels at
~1.855 eV (680 nm) are a promising resource for the generation of entangled
photons in the time-reordering scheme on a silicon platform.
