Binary information encoded within the spin of carriers can be transferred into corresponding right or left-handed circularly polarized photons which emitted from an active semiconductor medium via carrier-photon angular momentum conversion. In order to attain maximized spin-injection at out-of-plane magnetic remanence, a number of material systems have been explored as possible solid-state spin injectors. However the electroluminescence circular polarization (PC) of emitted light was still limited at 3-4% at remanence. 

In this talk, he presented this recent advancement of CoFeB/MgO as in-plane and out-of-plane spin injector on GaAs quantum well based on spin light emitting diodes (spin-LED). For the in-plane injector, two different growth techniques (sputtering and MBE) were introduced to grow the MgO tunnel barrier. It is interesting to find that the maximal spin injection efficiency was comparable, however the behavior of bias dependent Pc is quite different. Their studies reveal that the control of CoFeB/MgO interface is essential important for an optimal spin injection into semiconductor. 

For out-of-plane injector, they have reduced the thickness of CoFeB down to 1.2nm on MgO tunnel barrier (2.5nm) to obtain a strong perpendicular magnetization anisotropy (PMA). The maximum value of Pc measured at zero field is as large as 20% at 25K and still 8% at 300K, which is almost five times higher than any other types of PMA injectors. The results show that this type of ultrathin perpendicular spin-injectors are of great interest to realize the electrical switching of the magnetization of the injector layer owing to the advanced spin-transfer torque properties of CoFeB layer and to be directly embedded in optical cavities for spin lasers due to their very low optical absorption loss. 

LU Yuan is a research staff working in CNRS since 2008. He received his B.S. degree from Tsinghua University (China) in 1999, and his Ph.D degree in material science from Institute of Semiconductor (Chinese Academic of Science) in 2004. Then he worked as a post-doc fellow in University of Rennes and Unite Mixté CNRS/THALES in France from 2004 to 2007 before obtaining his permanent position in CNRS in 2007. In 2010, he worked as a visiting researcher in University of Maryland (USA). The research aeras of Dr. Lu focus on magnetic tunnel junctions and spin-injection and detection in semiconductors. He has more than 50 publications in international journals (1 Adv. Mat., 3 Phys. Rev. Lett., 13 Appl. Phys. Lett., 4 Phys. Rev. B) and served as referee for journals of Adv. Mat., Appl. Phys. Letts, J. Appl. Phys., Phys. Status Solidi and Surface and Coating Technology. 

                                                 (Information Source: Suzhou Institute of Nano-Tech and Nano-Bionics, CAS)