Germanium-based quantum emitters towards a time-reordering entanglement scheme with degenerate exciton and biexciton states

We address the radiative emission of individual germanium extrinsic centers in Al0.3Ga0.7As epilayers grown on germanium substrates. Microphotoluminescence experiments demonstrate the capability of high temperature emission (70 K) and complex exciton configurations (neutral exciton X and biexciton XX, positive X + and negative X− charged excitons) 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 ∼70 meV of the emission energy) with increasing quantum confinement. These light emitters, grown on a silicon substrate, may exhibit energy-degenerate X and XX energy levels. Furthermore, they emit at the highest detection efficiency window of Si-based single-photon detectors. These features render them a promising device platform for the generation of entangled photons in the time-reordering scheme.