  We demonstrate a large electrical spin injection into GaAs at zero magnetic
field thanks to an ultrathin perpendicularly magnetized CoFeB contact of a few
atomic planes (1.2 nm). The spin-polarization of electrons injected into GaAs
was examined by the circular polarization of electroluminescence from a Spin
Light Emitting Diode with embedded InGaAs/GaAs quantum wells. The
electroluminescence polarization as a function of the magnetic field closely
traces the out-of-plane magnetization of the CoFeB/MgO injector. A circular
polarization degree of the emitted light as large as 20% at 25 K is achieved at
zero magnetic field. Moreover the electroluminescence circular polarization is
still about 8% at room temperature.
