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The electrical creation and detection of spin accumulation in p-type Ge were successfully demonstrated at room temperature by spin-polarized tunneling in epitaxial Fe/MgO contacts on Ge with a hole concentration of 8×1018 cm-3. In Hanle measurements, the spin accumulation produces a spin signal of about 40 µV per mA of tunnel current. The extracted spin lifetime of holes is 13 ps, which is much longer than the momentum relaxation time. The corresponding spin-diffusion length is 80 nm, suggesting that communication of spin information in p-type Ge is possible over the typical channel length of a field-effect transistor.

Anomalous scaling of spin accumulation in ferromagnetic tunnel devices with silicon and germanium Sharma, S.; Spiesser, A.; Dash, S.P.; Iba, S.; Watanabe, S.; Wees, B.J. van; Saito, H.; Yuasa, S.; Jansen, R. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. The magnitude of spin accumulation created in semiconductors by electrical injection of spin-polarized electrons from a ferromagnetic tunnel contact is investigated, focusing on how the spin signal detected in a Hanle measurement varies with the thickness of the tunnel oxide. An extensive set of spin-transport data for Si and Ge magnetic tunnel devices reveals a scaling with the tunnel resistance that violates the core feature of available theories, namely, the linear proportionality of the spin voltage to the injected spin current density. Instead, an anomalous scaling of the spin signal with the tunnel resistance is observed, following a power law with an exponent between 0.75 and 1 over 6 decades. The scaling extends to tunnel resistance values larger than 10 9 μm 2 , far beyond the regime where the classical impedance mismatch or back flow into the ferromagnet play a role. This scaling is incompatible with existing theory for direct tunnel injection of spins into the semiconductor. It also demonstrates conclusively that the large spin signal does not originate from two-step tunneling via localized states near the oxide/semiconductor interface. Control experiments show that spin accumulation in localized states within the tunnel barrier or artifacts are also not responsible. Altogether, the scaling results suggest that, contrary to all existing descriptions, the spin signal is proportional to the applied bias voltage, rather than the (spin) current.