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Low-resistance spin injection into silicon using graphene tunnel barriers

Abstract

Spin manipulation in a semiconductor offers a new paradigm for device operation beyond Moore's law. Ferromagnetic metals are ideal contacts for spin injection and detection, but the intervening tunnel barrier required to accommodate the large difference in conductivity introduces defects, trapped charge and material interdiffusion, which severely compromise performance. Here, we show that single-layer graphene successfully circumvents the classic issue of conductivity mismatch between a metal and a semiconductor for electrical spin injection and detection, providing a highly uniform, chemically inert and thermally robust tunnel barrier. We demonstrate electrical generation and detection of spin accumulation in silicon above room temperature, and show that the contact resistance–area products are two to three orders of magnitude lower than those achieved with oxide tunnel barriers on silicon substrates with identical doping levels. Our results identify a new route to low resistance–area product spin-polarized contacts, a key requirement for semiconductor spintronic devices that rely on two-terminal magnetoresistance, including spin-based transistors, logic and memory.

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Figure 1: Schematic and cross-section of the samples.
Figure 2: Electrical characteristics of the NiFe/graphene/Si contacts.
Figure 3: Hanle spin precession measurements.
Figure 4: Bias dependence of spin lifetime/diffusion length and spin-voltage at 4 K.
Figure 5: Temperature dependence of spin diffusion length and voltage.
Figure 6: Resistance–area product window for local magnetoresistance.

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Acknowledgements

This work was supported by core programmes at NRL and the Office of Naval Research. E.C. and A.L.F. acknowledge support from the NRL Karles Fellow programme. The authors acknowledge use of facilities in the NRL Nanoscience Institute, and thank D. Zapotok and D. St. Amand for continual technical support.

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Contributions

O.M.J.v.E. and B.T.J. conceived the experiment. O.M.J.v.E., A.L.F., E.C. and C.H.L. fabricated the samples. J.T.R. grew the CVD graphene and transferred layers to the device structures. O.M.J.v.E. and C.H.L. acquired and analysed the transport data. All authors contributed to the interpretation of the data. O.M.J.v.E. and B.T.J. wrote the paper.

Corresponding authors

Correspondence to O. M. J. van 't Erve or B. T. Jonker.

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The authors declare no competing financial interests.

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van 't Erve, O., Friedman, A., Cobas, E. et al. Low-resistance spin injection into silicon using graphene tunnel barriers. Nature Nanotech 7, 737–742 (2012). https://doi.org/10.1038/nnano.2012.161

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