Electrical Spin Injection from Ferromagnetic Metals into GaAs

The spin injection into GaAs has been studied for the ferromagnetic metals MnAs and Fe. Evidence for preferential minority spin injection is obtained by analyzing the electroluminescence signal of GaAs/(In,Ga)As light emitting diodes. The injection behavior for epitaxial Fe and MnAs layers is found to be very similar with respect to the efficiency and preferential spin orientation. Spin injection efficiencies of about 5–6% are estimated on the basis of spin relaxation times extracted from time-resolved photoluminescence measurements. For the Fe/GaAs interface, spin injection at room temperature is demonstrated. In the case of MnAs, the results do not depend on the azimuthal orientation of the epitaxial injection layer. The underlying injection mechanism can be explained in terms of a tunneling process.