Electrical spin injection from Fe into Al$_{x}$Ga$_{1-x}$As quantum well spin-LEDs

We have studied Fe spin LEDs in which electron-hole recombination takes place either in GaAs or in Al$_{x}$Ga$_{1-x}$As quantum wells (QW). The dependence of the electroluminescence circular polarization P on temperature T in these two types of devices at fixed magnetic field is compared. The polarization in the Al$_{x}$Ga$_{1-x}$As QW LEDs decreases much more slowly with temperature compared with the GaAs QW LEDs; the polarization of the former persists up to room temperature. The improved high temperature performance of the Al$_{x}$Ga$_{1-x}$As spin LEDs is tentatively attributed to the localization of the recombining electron-hole pairs by potential fluctuations in the QW. These sites have zero-dimensional character suppressing the Dyakonov-Perel spin scattering mechanism.