Interface engineering for high-efficiency spin injection and polarized emission in GaN-based devices

Abstract Efficient spin injection is crucial for developing high-performance spintronic and optoelectronic devices. To address the issue of low spin injection efficiency caused by lattice mismatch and interface defects in traditional CoFeB/MgO tunnel junctions, this work proposes a strategy of using graphene as an insertion layer to optimize interface quality and enhance the spin injection efficiency of tunnel junctions. By systematically investigating three types of tunnel junction structures, namely CoFeB/MgO, CoFeB/graphene/MgO, and CoFeB/MgO/graphene, we demonstrate that the graphene insertion layer can effectively release interface stress, reduce defects and distortions induced by lattice mismatch, and thereby suppress spin scattering. Meanwhile, it alleviates resistance mismatch while preserving high spin polarization. Ultimately, the spin injection polarization is increased from 10.6% to 16.2%, representing an enhancement of approximately 53%. Additionally, the optimized CoFeB/MgO/graphene tunnel junction was integrated into GaN-based spin light-emitting diodes, resulting in an increased circular polarization of electroluminescence from 8.4% to 17.3%. This work provides an interface engineering strategy for achieving efficient spin injection and advancing the development of spin-optoelectronic devices.