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Electrical Spin Injection from Fe into Silicon
G. Kioseoglou 1,2* , A.T. Hanbicki 1 , C.H. Li 1 , P.E. Thompson 1 , and B.T. Jonker 1
1 Naval Research Laboratory, Washington, DC 20375
2 Materials Science and Technology, University of Crete, Heraklion, Crete
*gnk@materials.uoc.gr
An essential requirement for the success of spintronic devices is efficient electrical injection of spin-polarized carriers
from a contact into a semiconductor. Ferromagnetic metals (such as Fe) are attractive contact materials because they
supply spin-polarized electrons and offer high Curie temperatures. While significant progress has been realized in
GaAs where electron spin polarizations up to 40% have been obtained due to electrical injection from Fe or FeCo
contacts [1,2], little has been made in Si, despite its overwhelming dominance of the semiconductor industry.
Several fundamental properties of Si make it an ideal host for spin-based functionality. Spin orbit effects
producing spin relaxation are much smaller in Si than in GaAs due to the lower atomic mass and the inversion
symmetry of the crystal structure itself. In addition, the dominant naturally occurring isotope, Si 28 , has no nuclear spin,
suppressing hyperfine interactions and therefore relatively long spin lifetimes are expected.
We report successful electrical injection of spin-polarized electrons from an Fe film through an Al 2 O 3 tunnel
barrier into Si (001). Two types of samples were studied: (i) Si samples consisting of n-i-p doped heterostructures
grown by molecular beam epitaxy (MBE) on p-doped Si (001) wafers and (ii) Si epilayers (n-doped, 80 nm thick)
grown on n-Al 0.1 Ga 0.9 As/GaAs/p-Al 0.3 Ga 0.7 As QW structures. The second type enables a quantitative determination of
the electron spin polarization although the crystalline quality of the Si is lower and an additional heterointerface is
introduced (Si/Al 0.1 Ga 0.9 As). The electroluminescence (EL) spectra from an Fe/Al 2 O 3 /Si n-i-p structure are dominated
by transverse acoustic and optical phonon emission in the p+ Si layer, which is 140 nm below the Fe contact. The
circular polarization of the EL resulting from radiative recombination in Si and in GaAs (in Si/AlGaAs/GaAs
structures) tracks the Fe magnetization, confirming that these spin polarized electrons originate from the Fe contact.
The polarization reflects Fe majority spin. We determine a lower bound for the Si electron spin polarization of 10%,
with significant polarization extending to at least 125K.
[1] A.T. Hanbicki et al, Appl. Phys. Lett. 80, 1240 (2002).
[2] X. Jiang et al, Phys. Rev. Lett. 94, 056601 (2005).
This work was supported by ONR and core programs at NRL.
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