Electrical spin injection in GaAs/AlGaAs quantum-well LEDs

We have studied the electroluminescence spectra resulting from spin injection in several ZnMnSe/AlGaAs(n)/GaAs/AlGaAs(p) light-emitting diodes(LEDs) as a function of magnetic field and temperature in the Faraday geometry. The top ZnMnSe layer through which electrons are injected into the GaAs well acts as a spin aligner due to its large conduction band spin splitting. Electrons leave the ZnMnSe layer predominantly in the m_s = -1/2 spin state; the heavy holes which participate in the e₁h₁ transition are injected into the 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 associated with the e₁h₁ exciton is strongly circularly polarized. The maximum 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.