A graphene solution to conductivity mismatch: Spin injection from ferromagnetic metal/graphene tunnel contacts into silicon

作者：van 't Erve O M J^*; Friedman A L; Cobas E; Li C H; Hanbicki A T; McCreary K M; Robinson J T; Jonker B T

来源：Journal of Applied Physics, 2013, 113(17): 17C502.

DOI：10.1063/1.4793712

Spin-injection into silicon from a ferromagnetic metal requires a solution to the conductivity mismatch. Oxide tunnel barriers such as MgO, Al2O3, or SiO2 are typically used to solve this problem, but often include defects and must be several monolayers thick to avoid pinholes. At these thicknesses, the overall tunnel-barrier becomes highly resistive, preventing these junctions to be used in devices based on local magnetoresistance. Besides providing a spin dependent interface resistance, these barriers also prevent metal ions from diffusing into silicon, which would severely compromise device performance. Here, we show that we can lower the junction resistance by 2-3 orders of magnitude when using a single layer of graphene as the tunnel barrier rather than SiO2 or Al2O3. Hanle measurements show that the spin lifetime is independent of the tunnel barrier material (graphene, Al2O3, SiO2), demonstrating that the lifetime measured is not dominated by some characteristics of the tunnel barrier. The graphene provides a highly uniform barrier, with well-controlled thickness and minimal defect and trapped charge density, while successfully circumventing the conductivity mismatch between a ferromagnetic metal and Si and preventing metal ion diffusion from the FM contact.

• 出版日期2013-5-7