  An efficient electrical spin injection into an InGaAs/GaAs quantum well light
emitting diode is demonstrated thanks to a CoFeB/MgO spin injector. The
textured MgO tunnel barrier is fabricated by two different techniques:
sputtering and molecular beam epitaxy (MBE). The maximal spin injection
efficiency is comparable for both methods. Additionally, the effect of
annealing is also investigated for the two types of samples. Both samples show
the same trend: an increase of the electroluminescence circular polarization
(Pc) with the increase of annealing temperature, followed by a saturation of Pc
beyond 350{\deg}C annealing. Since the increase of Pc starts well below the
crystallization temperature of the full CoFeB bulk layer, this trend could be
mainly due to an improvement of chemical structure at the top CoFeB/MgO
interface. This study reveals that the control of CoFeB/MgO interface is
essential important for an optimal spin injection into semiconductor.
