Full-zone optical spin injection in Al x Ga 1−x As alloys

Full-zone optical spin injection in Al x Ga 1− x As alloys is investigated by analyzing the degree of circular polarization (DCP) of luminescence in a quantum well architecture. Aluminium content in AlGaAs barrier layers is varied to explore both the direct- and indirect-bandgap regimes. For all the samples, experimental data are compared with a 30-band k . p model addressing the band structure of the alloy and the optical spin injection over the entire Brillouin zone. We observe circularly polarized luminescence arising from the spin generation either around Γ or the L valley. We interpret the specific shape of the DCP within a framework accounting for smaller electron spin relaxation at the higher k points of the X valley of the AlGaAs barrier layer. Moreover, it is found that the presence of strain plays a vital role in governing the magnitude and shape of the DCP spectra for near band-edge excitation while exciting spin-polarized carriers in the direct-bandgap AlGaAs. We believe that these findings are important for the realization of AlGaAs-based spin-photonic devices aiming at possible applications in quantum technology.