Electrical spin injection in GaAs/AlGaAs quantum-well LEDs

We have studied the electroluminescence spectra resulting from spin injecti on in several ZnMnSe/AlGaAs(n)/GaAs/AlGaAs(p) light-emitting diodes(LEDs) a s a function of magnetic field and temperature in the Faraday geometry. The top ZnMnSe layer through which electrons are injected into the GaAs well a cts as a spin aligner due to its large conduction band spin splitting. Elec trons leave the ZnMnSe layer predominantly in the m(s) = -1/2 spin state; t he heavy holes which participate in the elh, transition are injected into t he GaAs well from the substrate with equal numbers in the m(s) = +3/2 and m (s) = -3/2 spin states. As a result, the emitted electroluminescence associ ated with the e(1)h(1) exciton is strongly circularly polarized. The maximu m value of the optical polarization P at T = 4.2 K is 0.5 which corresponds to 75% of the injected electrons in the m(s) = -1/2 state.