Electrical spin injection from Fe$_{1-x}$Ga$_{x}$ (001) films into AlGaAs/GaAs(001) LEDs*

Electron spin polarizations of 40-70{\%} have been obtained in GaAs due to electrical injection from Fe or FeCo contacts using surface-emitting spin-LEDs. In such LEDs, since Fe has its magnetization easy axis in the substrate plane, a large magnetic field ($>$2.2 tesla) along the surface normal is required to saturate the magnetization out-of-plane. We have grown epitaxial films of Fe$_{1-x}$Ga$_{x}$ (0 $<$ x $<$ 0.75), a material noted for its high magnetostriction, on AlGaAs/GaAs (001) heterostructures, and summarize the structure, magnetization, spin polarization, and results for electrical spin injection into AlGaAs/GaAs. The out-of-plane saturation field and magnetization decrease rapidly with Ga content, but the point contact spin polarization remains near that of Fe for x $\le $ 0.5. Electrical spin injection from an Fe$_{0.5}$Ga$_{0.5}$ contact produces an electron spin polarization of 30{\%} in the GaAs at 20 K, similar to that obtained from Fe contacts, but with out-of-plane saturation fields as low as 0.4 T. Post-annealing at low temperature increases the electron spin polarization up to 40{\%} and it will be discussed at the meeting.