Quantifying Mn diffusion through transferred versus directly-grown graphene barriers

Abstract

We quantify the mechanisms for manganese (Mn) diffusion through graphene in Mn/graphene/Ge (001) and Mn/graphene/GaAs (001) heterostructures, for samples prepared by graphene layer transfer versus graphene growth directly on the semiconductor substrate. These heterostructures are important for applications in spintronics; however, challenges in synthesizing graphene directly on technologically important substrates such as GaAs necessitate layer transfer steps, which can introduce defects into the graphene. In-situ photoemission spectroscopy measurements reveal that Mn diffusion through graphene grown directly on a Ge (001) substrate is 1000 times lower than Mn diffusion into samples without graphene (D gr,direct ∼ 4 × 10 −18 cm 2 /s, Dno−gr ∼ 5 × 10 −15 cm 2 /s at 500 • C). Transferred graphene on Ge suppresses the Mn in Ge diffusion by a factor of 10 compared to no graphene (D gr,transf er ∼ 4 × 10 −16 cm 2 /s). For both transferred and directly-grown graphene, the low activation energy (Ea ∼ 0.1 − 0.5 eV) suggests that Mn diffusion through graphene occurs primarily at graphene defects. The diffusivity prefactor D0 scales with the defect density. Similar diffusion barrier performance is found on GaAs substrates; however, it is not currently possible to grow graphene directly on GaAs. Our results highlight the importance of developing graphene growth directly on functional substrates, to avoid the damage induced by layer transfer.