Co₂FeSi/GaAs/(Al,Ga)As spin light-emitting diodes: Competition between spin injection and ultrafast spin alignment

Electrical injection from the Heusler alloy Co₂FeSi into (Al,Ga)As is investigated for different growth temperatures T_G of the injector layer. Depending on T_G, the spin polarization of injected electrons in the semiconductor is determined by two competing mechanisms: actual spin injection at the Co₂FeSi/(Al,Ga)As interface and ultrafast spin alignment in the (Al,Ga)As layer. This layer is strongly affected by the thermally activated diffusion of Co, Fe, and Si during the growth of the Co₂FeSi layers. Despite the electrical compensation and magnetic transformation in the underlying semiconductor structure, a spin-injection efficiency of at least 50% is achieved as deduced from the analysis of electroluminescence and time-resolved photoluminescence data.