Growth and crystallization processes of fully epitaxial Fe/MgO/light-emitting diodes for spin injections

The Fe/MgO/light-emitting diode (LED) structure was prepared by a molecular beam epitaxy. The in situ observations using a reflective high-energy electron diffraction showed that the structure was fully epitaxial. However, the X-ray diffraction (XRD) and transmission electron microscopy results showed the existence of structural defects. The circular polarization degrees of electroluminescence, which deduce the spin polarizations of the current injected from the Fe electrode into the LED, were 0.2% at 4.2 K and 0.4% at 100 K in a 0.5 T magnetic field. The small spin-injection efficiencies are considered due to the degradation of the tunneling injector resulted from the structural defects and an As segregation.