A Spin Esaki Diode

Kohda, Makoto; Ohno, Y.; Takamura, Koji; Matsukura, F.; Ohno, Hideo

doi:10.1143/jjap.40.l1274

Cited by 131 publications

(108 citation statements)

References 14 publications

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“…n þ GaAs transition layer (n þ ¼ 5 Â 10 18 cm À3 ), 8 nm n þ -GaAs, and 2.2 nm low-temperature (LT)-grown Al 0:36 Ga 0:64 As, serving as a diffusion barrier, followed by LT-grown Ga 0:95 Mn 0:05 As, the thickness of which was chosen between 5 and 20 nm. The highly doped ðGa; MnÞAs=GaAs pn junction forms an Esaki diode [13,14]. In a next step the wafers were transferred, without breaking vacuum, into an attached metal-MBE chamber, where 2 nm of Fe, corresponding to 14 monolayers (MLs), were epitaxially grown at RT, and finally covered by 4 nm (20 MLs) of Au.…”

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confidence: 99%

Proximity Induced Enhancement of the Curie Temperature in Hybrid Spin Injection Devices

et al. 2011

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We investigate the increase of the Curie temperature T C in a lateral spin injection geometry where the ferromagnetic (Ga,Mn)As injector and detector contacts are capped by a thin iron film. Because of interlayer coupling between Fe and (Ga,Mn)As T C gets enhanced by nearly 100% for the thinnest (Ga,Mn)As films. The use of the proximity effect might pave the way for practical implementation of spintronic devices. DOI: 10.1103/PhysRevLett.107.056601 PACS numbers: 72.25.Àb, 75.30.Et, 75.50.Pp, 85.75.Àd The diluted magnetic semiconductor (DMS) (Ga,Mn)As [1] stands out as a seminal spintronic material due to its high spin polarization [2,3] and superior interfacing properties with nonmagnetic semiconductors. This opens a way to semiconducting spintronic devices with functionalities such as nonvolatility and the additional spin degree of freedom [4]. However, the persistently low Curie temperature of DMS has been an obstacle for the integration of DMS into electronic devices. It has been recently shown that the presence of a thin layer of Fe couples the magnetic moments of Fe and Mn in Fe=ðGa; MnÞAs bilayers up to room temperature (RT), thus well exceeding the T C of (Ga,Mn)As [5][6][7]. This proximity polarization leads to an antiparallel coupling of the Fe and Mn moments within an interfacial region of a few nm thickness in the (Ga,Mn)As film. In addition, exchange bias has been observed in the Fe=ðGa; MnÞAs bilayer system at lower temperatures T [7]. Similar exchange bias has been obtained in MnAs= ðGa; MnÞAs bilayers [8][9][10]. Differently, NiFe=ðGa; MnÞAs bilayers switch their magnetization independently [11] and also MnTe=ðGa; MnÞAs heterojunctions did not show exchange bias [12]. Here we use the interlayer coupling between Fe and (Ga,Mn)As to explore its impact on the operation temperature of (Ga,Mn)As based spin injector or detector contacts in a lateral transistorlike geometry.The experiments described below demonstrate enhanced spin injection temperatures measured in an all-electrical fashion.The heterojunctions were grown by molecular-beamepitaxy (MBE) on (001) GaAs substrates and consist of a 1000 nm thick n-type transport channel, doped with 4 Â 10 16 cm À3 Si, a 15 nm thin n ! n þ GaAs transition layer (n þ ¼ 5 Â 10 18 cm À3 ), 8 nm n þ -GaAs, and 2.2 nm low-temperature (LT)-grown Al 0:36 Ga 0:64 As, serving as a diffusion barrier, followed by LT-grown Ga 0:95 Mn 0:05 As, the thickness of which was chosen between 5 and 20 nm. The highly doped ðGa; MnÞAs=GaAs pn junction forms an Esaki diode [13,14]. In a next step the wafers were transferred, without breaking vacuum, into an attached metal-MBE chamber, where 2 nm of Fe, corresponding to 14 monolayers (MLs), were epitaxially grown at RT, and finally covered by 4 nm (20 MLs) of Au. The lateral channel of the devices was made by standard lithographic techniques. Electron beam lithography was used to pattern the Fe=ðGa; MnÞAs injector and detector contacts, oriented along the [110] direction, i.e., the easy axis of Fe. A schematic of the sample layout ...

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Proximity Induced Enhancement of the Curie Temperature in Hybrid Spin Injection Devices

et al. 2011

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“…Therefore, spintronic devices based on (GaMn)As can only operate using hole currents. Regarding the lower mobility of holes in comparison with that of electrons, this necessary condition will limit the operation speed of (Ga,Mn)Asbased devices, unless sophisticated design solutions are applied [29][30][31].…”

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Picosecond Dynamics of the Photoinduced Spin Polarization in Epitaxial (Ga,Mn)As Films

et al. 2004

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Static and time-resolved magneto-optical spectra of the ferromagnetic semiconductor (Ga,Mn)As show that a pulsed photoexcitation with a fluence of 10 J=cm 2 is equivalent to the application of an external magnetic field of about 1 mT, which relaxes with a decay time of 30 ps. This relaxation is attributed to the spin relaxation of electrons in the conduction band and is found to be not affected by interactions with Mn ions.

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“…The nominal widths of the emitter, base, and collector are 2, 1.5, and 2 m, respectively. The dopings are N e ϭ10 17 , N b ϭ10 16 , and N c ϭ10 15 cm Ϫ3 . Electron ͑hole͒ diffusivities at room temperature are taken to be D n ϭ100 and D p ϭ10 cm 2 /s.…”

Section: ͑10͒mentioning

confidence: 99%

Magnetic bipolar transistor

Fabian

Žutić

Sarma

2004

Applied Physics Letters

126

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A magnetic bipolar transistor is a bipolar junction transistor with one or more magnetic regions, and/or with an externally injected nonequilibrium ͑source͒ spin. It is shown that electrical spin injection through the transistor is possible in the forward active regime. It is predicted that the current amplification of the transistor can be tuned by spin. 19 Here we analyze MBTs ͑other types of spin transistors were proposed in Refs. 20-26͒, with a magnetic base and a source spin in the emitter. We predict that spin can accumulate in the collector due to the electrical spin injection, and that the current amplification of MBTs can be controlled by spin.Crucial to MBTs is the use of magnetic semiconductors where the splitting of the carrier bands produces spinpolarized electrons or holes with the spin polarization of 10% or more. The carrier band splitting can be of the Zeeman or the exchange type. The former arises from large g factors ͑for example, in Cd 0.95 Mn 0.05 Se the g factor exceeds 500, 27 while it is as large as 50 in InSb at room temperature͒, and an application of a magnetic field, while the latter comes from the exchange coupling in ferromagnetic semiconductors ͑about 10 meV͒. In addition to the equilibrium spin, a nonequilibrium ͑source͒ spin can be generated in the emitter with external spin injection, electrical or optical. 28Our model is described in Fig. 1. We consider an npn structure doped with N de donors in the emitter, N ab acceptors in the base, and N dc donors in the collectors. There are two depletion layers: one between the emitter and the base, the other between the base and the collector. The transistor is a three terminal device: there is a contact with an external electrode at each region, generating bias V be across the emitter-base and V bc across the base-collector depletion layer. The base is magnetic. For simplicity only electrons are spin polarized. The equilibrium spin polarization in the base is ␣ 0b ϭtanh(q/k B T), 6 where 2q is the conduction band spin splitting ͑assumed to be uniform across the base͒ and a͒ Electronic mail: jaroslav.fabian@uni-graz.at b͒ Electronic mail: igorz@physics.umd. edu FIG. 1. The scheme of an npn transistor with a magnetic base. The top figure shows the bands. The conduction band is separated by the band gap E g from the valence band, and has a spin splitting ͑Zeeman or exchange͒ of 2q, leading to the equilibrium spin polarization ␣ 0b ϭtanh(q/k B T), constant across the base. Holes are unpolarized. The spin is indicated by the shade of the circles ͑dark and light͒. The emitter-base junction is forward biased with voltage V be Ͼ0 lowering the built-in voltage V i and narrowing the depletion layer ͑shaded͒, while the base-collector junction is reverse biased with voltage V bc Ͻ0, widening the depletion layer. Electrons flow easily from the emitter to the base, where some of them recombine ͑dashed lines͒ with holes, the rest being swept by the electric field in the basecollector depletion layer to the collector. Holes, which are the large part...

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A Spin Esaki Diode

Cited by 131 publications

References 14 publications

Proximity Induced Enhancement of the Curie Temperature in Hybrid Spin Injection Devices

Proximity Induced Enhancement of the Curie Temperature in Hybrid Spin Injection Devices

Picosecond Dynamics of the Photoinduced Spin Polarization in Epitaxial (Ga,Mn)As Films

Magnetic bipolar transistor

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