Rate-equation model of spin dynamics and polarized light emission for spin light-emitting diodes

We measure the circular polarization of the electroluminescence of Co(2)FeSi/(Al,Ga)As/GaAs spin light-emitting diodes in magnetic fields up to 14 T. The observed polarization dependence varies greatly from sample to sample and often eludes an intuitive physical interpretation. We analyze our experimental data by a rate-equation model which explicitly takes into account the transport of carriers from the spin injector to the quantum well and their recombination therein. We show that our experimental data can be understood as an interplay of electron spin injection by the ferromagnetic overlayer and spin alignment in the layers the electrons are traversing before recombining in the quantum well. The main parameter controlling the electron spin polarization is identified to be the ratio of the transit time through these layers to the spin-scattering time in them.