Spin injection across a hybrid heterojunction: Theoretical understanding and experimental approach (invited) (original) (raw)
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Electrical Spin Injection in a Ferromagnetic / Tunnel Barrier/ Semiconductor Heterostructure
2001
We demonstrate experimentally the electrical ballistic electron spin injection from a ferromagnetic metal / tunnel barrier contact into a semiconductor III-V heterostructure. We introduce the Oblique Hanle Effect technique for reliable optical measurement of the degree of injected spin polarization. In a CoFe / Al2O3 / GaAs / (Al,Ga)As heterostructure we observed injected spin polarization in excess of 8 % at 80K.
Lateral spin injection and detection through electrodeposited Fe/GaAs contacts
Semiconductor Science and Technology, 2013
Efforts to achieve efficient injection of spin-polarized electrons into a semiconductor, a key prerequisite for developing electronics that exploit the electron's spin degree of freedom, have so far met with limited success. Here we report experimental studies of lateral spin injection and detection through electrodeposited Fe/GaAs tunnel contacts. We demonstrate spin injection efficiencies two orders of magnitude higher than for state-of-the-art contacts fabricated via ultra-high-vacuum methods, including those with MgO or Al 2 O 3 tunnel barriers. To account for this enhancement, we propose that an iron oxide layer that forms at the Fe/GaAs interface during electrodeposition, being magnetic acts as a tunnel barrier with a spin-dependent height, presenting quantum spin transport calculations for such systems. This serendipitous discovery of greatly enhanced efficiency of spin injection into GaAs via electrodeposited contacts introduces a promising new direction for the development of practical semiconductor spintronic devices.
Spin detection and injection using ferromagnetic metal and semiconductor hybrid structure
Proceedings International Conference on MEMS, NANO and Smart Systems, 2003
We investigated spin-dependent transport properties from a viewpoint of spin detection and injection using a ferromagnetic metal / insulator (Al 2 O 3)/ semiconductor tunnel junction with homogeneous and flat interfaces. For spin detection from the semiconductor, spin-polarized electrons were excited in the GaAs layer by circularly polarized light and injected into the permalloy layer. The energy dependence of the observed helicity asymmetry of the photo-induced current shows the absence of the spin-dependent tunneling. The result suggests importance of controlling the electron lifetime to obtain the spin-dependent tunneling. For spin injection into a semiconductor, we prepared Co/ Al 2 O 3 / AlGaAs/ GaAs/ AlGaAs light emitting diode (LED) structure with ferromagnetic electrode. The electro-luminescence from the LED depends on the magnetization direction of the ferromagnetic electrode at room temperature. This fact shows that a spin-injection from the ferromagnetic metal to the semiconductor is achieved. The spin polarization due to the spin-injection current is estimated to be the order of 1 %.
Efficient spin injection and giant magnetoresistance in Fe / MoS 2 / Fe junctions
Physical Review B, 2014
We demonstrate giant magnetoresistance in Fe/MoS2/Fe junctions by means of ab-initio transport calculations. We show that junctions incorporating either a mono-or a bi-layer of MoS2 are metallic and that Fe acts as an efficient spin injector into MoS2 with an efficiency of about 45%. This is the result of the strong coupling between the Fe and S atoms at the interface. For junctions of greater thickness a maximum magnetoresistance of ∼300% is obtained, which remains robust with the applied bias as long as transport is in the tunneling limit. A general recipe for improving the magnetoresistance in spin valves incorporating layered transition metal dichalcogenides is proposed.
Spin injection experiment with multiple NiFe/InAs-2DEG/NiFe junctions
Physica C: Superconductivity, 2001
Ferromagnetic contacts on a high-mobilty two-dimensional electron gas (2DEG) in a narrow gap semiconductor with strong spin±orbit interaction are used to investigate spin-polarized electron transport. We demonstrate the use of magnetized contacts to preferentially inject and detect speci®c spin orientations. Spin dephasing and spin precession eects are studied by temperature and 2DEG channel length dependent measurements.
Journal of Nanoelectronics and Optoelectronics, 2006
Current understanding of spin injection tells us that a metal ferromagnet can inject spin into a semiconductor with 100% efficiency if either the ferromagnet is an ideal half metal with 100% spin polarization, or there exists a suitable tunnel barrier at the interface. In this paper, we show that, at absolute zero temperature, 100% spin injection efficiency from a non-ideal metal ferromagnet into a semiconductor quantum wire can be reached at certain injection energies, without a tunnel barrier, provided there is an axial magnetic field along the direction of current flow as well as a spin orbit interaction in the semiconductor. At these injection energies, spin is injected only from the majority spin band of the ferromagnetic contact, resulting in 100% spin injection efficiency. This happens because of the presence of antiresonances in the transmission coefficient of the minority spins when their incident energies coincide with Zeeman energy states in the quantum wire. At absolute zero and below a critical value of the axial magnetic field, there are two distinct Zeeman energy states and therefore two injection energies at which ideal spin filtering is possible; above the
Electrical detection of spin transport in lateral ferromagnet–semiconductor devices
Nature Physics, 2007
The development of semiconductor spintronics requires a reliable electronic means for writing, processing and reading information using spin-polarized carriers. Here, we demonstrate a fully electrical scheme for achieving spin injection, transport and detection in a single device. Our device consists of a lateral semiconducting channel with two ferromagnetic contacts, one of which serves as a source of spin-polarized electrons and the other as a detector. Spin detection in the device is achieved through a non-local, spinsensitive, Schottky-tunnel-barrier contact whose electrochemical potential depends on the relative magnetizations of the source and detector. We verify the effectiveness of this approach by showing that a transverse magnetic field suppresses the non-local signal at the detection contact by inducing spin precession and dephasing in the channel (the Hanle effect). The sign of the signal varies with the injection current and is correlated with the spin polarization in the channel as determined by optical Kerr rotation measurements.
Towards All Electrical Spin Injection and Detection in GaAs in a Lateral Geometry
Journal of Superconductivity, 2006
We discuss our approach to realizing all-electrical spin injection and detection in GaAs via ferromagnetic metals and oxide tunnel barriers. A critical requirement is suppression of the formed Schottky barrier, which causes conductivity mismatching and prevents detection in reverse bias. However, initial I-V measurements of engineered GaAs/AlO x /CoFe tunnel contacts still show too high resistance area products in comparison to the semiconductor conductance, due to a large Schottky barrier contribution. To this end, optimized doping levels of the tunnel contacts and semiconductor spin transport region are calculated. Secondly, control over the magnetic properties of injector and detector electrode is established by designing both electrodes to have different switching fields, due to different widths.
Spin-Polarized Electron Injection through an Fe/InAs Junction
Japanese Journal of Applied Physics, 2003
We report on the spin-polarized electron injection through an Fe(100)/InAs(100) junction. The circularly polarized electroluminescence of injected electrons from epitaxially grown Fe thin film into InAs(100) in an external magnetic field is measured to investigate the spin injection efficiency. The obtained polarization of the electroluminescence is seen to increase up to about-12 % at the temperature of 6.5 K and the external magnetic field of 10 T. This result suggests that the efficient spin injection is possible through the ferromagnetic metal/semiconductor (FM/SC) interface without a tunneling barrier despite the contradictory arguments based on conductivity mismatch at the FM/SC interface.