Spin Accumulation in Nondegenerate and Heavily Doped p-Type Germanium

Iba, Satoshi; Saito, H.; Spiesser, A.; Watanabe, S.; Jansen, R.; Yuasa, Shinji; Ando, Koji

doi:10.1143/apex.5.023003

Cited by 30 publications

(53 citation statements)

References 22 publications

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“…The spin RA product also displays an exponential variation with thickness of the tunnel oxide, and a power law is revealed when the spin RA product is plotted against tunnel resistance [see Figs [20,21], we also find that R tun and the spin RA product vary exponentially with MgO thickness [see Fig. 3(c)], although the data set is too limited to extract an accurate value for the scaling exponent.…”

Section: Scaling With Tunnel Barrier Thicknessmentioning

confidence: 73%

“…Note that for the devices with an Al 2 O 3 tunnel barrier, the line width depends slightly on the oxidation time. The spin lifetime for devices with MgO/Fe contacts is smaller than with Al 2 O 3 /Ni 80 Fe 20 contacts. This can be attributed to broadening of the Hanle curve by inhomogeneous magnetostatic fields, which is more pronounced for Fe owing to its larger magnetization [34].…”

Section: E Two-step Tunneling Via Localized States Within the Tunnelmentioning

confidence: 93%

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Anomalous scaling of spin accumulation in ferromagnetic tunnel devices with silicon and germanium

et al. 2014

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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.

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Section: Scaling With Tunnel Barrier Thicknessmentioning

confidence: 73%

Section: E Two-step Tunneling Via Localized States Within the Tunnelmentioning

confidence: 93%

Anomalous scaling of spin accumulation in ferromagnetic tunnel devices with silicon and germanium

et al. 2014

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“…This is about 3 orders of magnitude smaller that the experimental values. Interestingly, several research groups using three-terminal Hanle measurements have also reported such large values in Si [1][2][3][4][5][6][7]30 , Ge 11,12,[14][15][16][17] , and GaAs 29 , no matter what type of tunnel barrier was used. As it was recently discussed 37,38 , the origin of the discrepancies is not clear yet.…”

Section: Spin Accumulation In P-type Si Using Fe/mgo Contactsmentioning

confidence: 99%

“…Hence, one can expect that MgO is also an effective tunnel barrier for Si-based spintronics devices if a thin MgO(001) layer can be epitaxially grown on Si. Whereas epitaxial growth of FM/MgO(001) for spin injection on Ge [11][12][13][14][15][16][17] and GaAs [18][19][20] has been intensively studied, the way towards epitaxial growth of MgO on Si is still not well established. Therefore, it is important to clarify the growth techniques and conditions for achieving epitaxial FM/MgO(001) layers on Si 4,7,[21][22][23] .…”

Section: Introductionmentioning

confidence: 99%

Electrical spin injection in p-type Si using Fe/MgO contacts

et al. 2012

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We report the successful electrical creation of spin polarization in p-type Si at room temperature by using an epitaxial MgO(001) tunnel barrier and Fe(001) electrode. Reflection high-energy electron diffraction observations revealed that epitaxial Fe/MgO(001) tunnel contacts can be grown on a (2×1) reconstructed Si surface whereas tunnel contacts grown on the (1×1) Si surface were polycrystalline. Transmission electron microscopy images showed a more flat interface for the epitaxial Fe/MgO/Si compared to that of the polycrystalline structure. For the Fe/MgO/p-Si devices, the Hanle and inverted Hanle effects were clearly observed at 300 K by using a three-terminal configuration, proving that spin polarization can be induced in the Si at room temperature. Effective spin lifetimes deduced from the width of the Hanle curve were 95 ± 6 ps and 143 ± 10 ps for the samples with polycrystalline and epitaxial MgO tunnel contacts, respectively. The observed difference can be qualitatively explained by the local magnetic field induced by the larger roughness of the interface of the polycrystalline sample. The sample with epitaxial Fe/MgO tunnel contact showed higher magnitude of the spin accumulation with a nearly symmetric behavior with respect to the bias polarity whereas that of the polycrystalline MgO sample exhibited a quite asymmetric evolution. This might be attributed to the higher degree of spin polarization of the epitaxial Fe/MgO(001) tunnel contact, which acts as a spin filter. Our experimental results suggest that an epitaxial MgO barrier is beneficial for creating spins in Si.

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“…[23][24][25] as well as into Ge through MgO. [26][27][28][29][30][31][32][33][34] Among the latest experiments, the transformation of a spin-polarized electron current into left-or righthanded circularly polarized light in a spin light-emitting diode (spin LED) integrating a III-V semiconductor heterostructure 8,11,[13][14][15][16][17]19,23,34,35 is one of the most striking physical phenomena. The electric dipolar selection rules involved in a quantum well 36 (QW) embedded in a spin LED during electron-hole recombination require spin injection with an out-of-plane magnetization.…”

Section: Introductionmentioning

confidence: 99%

Spin injection at remanence into III-V spin light-emitting diodes using (Co/Pt) ferromagnetic injectors

et al. 2012

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We have studied the perpendicular magnetic anisotropy of Co/Pt multilayers and the electron spin injection efficiency by optical spectroscopy from a [Co(0.6 nm)/Pt(1 nm)] 4 /Fe(0.3 nm)/MgO perpendicular tunnel spin injector grown on AlGaAs/GaAs semiconductor light-emitting diodes. We observe a 2.5% circular polarization at low temperature close to the magnetic remanence when the 0.3 nm Fe film of the ferromagnetic injector is sufficiently thin to maintain the magnetization out of plane. The acquired squared magnetization cycle is explained by the remaining interlayer exchange coupling existing between Fe and the (Co/Pt) multilayer through Pt or possible perpendicular magnetic anisotropy at the MgO/Fe interface. The corresponding spin polarization of the current is then estimated as 7%, measured by photoluminescence techniques, after the necessary uprenormalization, taking into account the electron spin-flip rate in the quantum well. In contrast, no circular polarization is observed when the thin Fe layer is removed and despite the rather high magnetic polarizability of the 5d 9 electronic open shell of Pt at the interface with MgO. This emphasizes the reduced size of tunneling branching of wave functions at the interface, of the order of the atomic plane unit.

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Spin Accumulation in Nondegenerate and Heavily Doped p-Type Germanium

Cited by 30 publications

References 22 publications

Anomalous scaling of spin accumulation in ferromagnetic tunnel devices with silicon and germanium

Anomalous scaling of spin accumulation in ferromagnetic tunnel devices with silicon and germanium

Electrical spin injection in p-type Si using Fe/MgO contacts

Spin injection at remanence into III-V spin light-emitting diodes using (Co/Pt) ferromagnetic injectors

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