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ABSTRACT: Semiconductor spintronics is a promising technology in which the spin states of electrons are utilized as an additional degree of freedom for device operation. One of its prerequisites is the ability to inject spin-polarized electrons into semiconductors. An overview is presented of recent progress in spin injection using an injector based on a crystalline CoFe/MgO(001) tunnel structure. The spin polarization of the electrons that were injected into a GaAs quantum-well light-emitting diode was inferred from electroluminescence polarization from the quantum well. Spin polarizations of 57% at 100 K and 47% at room temperature were obtained. The spin polarization was found to exhibit a strong dependence on bias and temperature, which can be explained on the basis of spin relaxation within the GaAs.
Ibm Journal of Research and Development 02/2006; · 0.72 Impact Factor
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ABSTRACT: The spin polarization of electrons injected into GaAs from a CoFe / MgO (100) tunnel spin injector is inferred from the circular polarization of light emitted from a GaAs-based quantum well (QW) detector. The circular polarization strongly depends on the spin and electron hole recombination lifetimes in the QW. Using time-resolved optical techniques, we show that these lifetimes are highly temperature dependent. A peak in the charge lifetime versus temperature is likely responsible for the previously observed dip in the electroluminescence polarization. Evidence for a temperature-independent spin injection efficiency of ∼70% from 10 K to room temperature is found.
Applied Physics Letters 01/2006; · 3.84 Impact Factor
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ABSTRACT: The spin polarization of current injected into GaAs from a CoFe/MgO(100) tunnel injector is inferred from the electroluminescence polarization from GaAs/AlGaAs quantum well detectors. The polarization reaches 57% at 100 K and 47% at 290 K in a 5 T perpendicular magnetic field. Taking into account the field dependence of the luminescence polarization, the spin injection efficiency is at least 52% at 100 K, and 32% at 290 K. We find a nonmonotonic temperature dependence of the polarization which can be attributed to spin relaxation in the quantum well detectors.
Physical Review Letters 03/2005; 94(5):056601. · 7.37 Impact Factor
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ABSTRACT: Postgrowth thermal annealing of a CoFe/MgO(100) tunnel spin injector grown on aGaAs/AlGaAs quantum well structure results in a significantly increased spin injection efficiency as inferred from the polarization of heavy-hole electroluminescence from a quantum well optical detector. The as-deposited sample displayed an initial polarization at 100 K of 43%, which was increased to 52% after a 1 h anneal at 300 °C, and finally to 55% after a second 1 h anneal at 340 °C. The polarization remained unchanged upon further annealing to temperatures as high as 400 °C. These results show that tunnel spin injectors based on CoFe/MgO are robust with high thermal stability, making them useful for device applications.
Applied Physics Letters 01/2005; 86(5):052901-052901-3. · 3.84 Impact Factor
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ABSTRACT: Injection of spin-polarized hot-electron current from a magnetic tunnel transistor into GaAs is demonstrated by the observation of polarized light emission from a GaAs/In(0.2)Ga(0.8)As multiple quantum well light-emitting diode. Electroluminescence from the quantum wells shows a polarization of approximately 10% after subtraction of a linear background polarization. The polarization shows a strong dependence on the bias voltage across the diode, which may originate from changes in the electron spin relaxation rate in the quantum wells under varying bias conditions.
Physical Review Letters 07/2003; 90(25 Pt 1):256603. · 7.37 Impact Factor
