Observation of optical spin injection into Ge-based structures at room temperature

Non-zero spin polarization induced by optical orientation was clearly observed at room temperature in a Ge/Ge0.8Si0.2 quantum well grown on Ge and a Ge layer grown on Si by molecular beam epitaxy, whereas it was absent in bulk Ge. This occurred because indirect-gap photoluminescence (PL), which can obscure the spin-polarization information carried by the direct-gap PL, was quenched by unintentional growth-related defects in the epitaxial layers. Such interpretation was confirmed by applying time gating that effectively removed the indirect-gap PL characterized by a slower rise time, which allowed us to demonstrate the existence of room-temperature spin polarization in bulk Ge.