Spin injection into semiconductors

Oestreich, M.; Hübner, Jens; Hägele, D.; Klar, Peter J.; Heimbrodt, W.; Rühle, W. W.; Ashenford, D.E.; Lunn, B.

doi:10.1063/1.123515

Cited by 222 publications

(110 citation statements)

References 11 publications

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“…Take a p-doped sample. Then pϷp 0 , nӷn 0 , and ␣ϭ␣ 0 /(1ϩ /T 1 ), with electron lifetime ϭ1/wp 0 , expresses spin orientation: 4 if ӶT 1 , which is usually the case, ␣Ϸ␣ 0 and electron spins are effectively oriented throughout the sample. In an n-doped sample wpϷG/n 0 , and the spin polarization is ␣ 0 /(1 ϩn 0 /GT 1 ).…”

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confidence: 99%

“…3͒. Optical injection of spin-polarized carriers ͑both minority 4,5 and majority 4,6 ͒ has been known for some time. In addition, the relatively long spin diffusion lengths, 6,7 coherent spin transport across semiconductor interfaces, a successful fabrication of a magnetic/nonmagnetic p-n junction 8 based on the ͑Ga,Mn͒As material, 9 and the recent demonstration of a gatevoltage control of magnetization in ͑In,Mn͒As, 10 make semiconductors promising materials for spintronic applications.…”

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confidence: 99%

“…In addition to the approximations used in deriving the usual ͑unpolarized͒ equations, 13 we assume that all the dopants are fully ionized, the carrier populations nondegenerate and varying only in one ͑x͒ direction. Further, we assume the spin polarization to be carried solely by conduction electrons ͑that is, consider holes unpolarized͒, as is the case of III-V semiconductors like GaAs, 4 best candidates for photospintronics.…”

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confidence: 99%

“…1͒. The left surface of the sample, xϭ0, is illuminated by circularly polarized light which creates electrons and holes with photodensities ␦nϭ␦pϭ3ϫ10 14 cm Ϫ3 , and induces electronic spin polarization ␣ 0 ϭ0.5 ͑the value given by the band-structure symmetry 4 ͒ at the surface. Since holes lose their spin orientation faster than they gain it ͑also a band structure effect, 4 ͒ their polarization is effectively zero and need not be considered.…”

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Spin injection through the depletion layer: A theory of spin-polarizedp-njunctions and solar cells

2001

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A drift-diffusion model for spin-charge transport in spin-polarized p-n junctions is developed and solved numerically for a realistic set of material parameters based on GaAs. It is demonstrated that spin polarization can be injected through the depletion layer by both minority and majority carriers, making all semiconductor devices such as spin-polarized solar cells and bipolar transistors feasible. Spin-polarized p-n junctions allow for spin-polarized current generation, spin amplification, voltage control of spin polarization, and a significant extension of spin diffusion range. DOI: 10.1103/PhysRevB.64.121201 PACS number͑s͒: 72.25.Dc, 72.25.Fe, 85.75.Ϫd Spintronics 1,2 has played an important role in defining applications that are either not feasible or ineffective with traditional semiconductor electronics. Spintronic devices have found their niche in industries for magnetic read heads and nonvolatile memory cells. Here we propose and demonstrate a scheme for spintronics, a spin-polarized p-n junction, 2 which amplifies spin density, significantly extends the range of spin diffusion, electronically tailors spin polarization, and, in combination with light as a spin-polarized solar cell, generates spin-polarized currents with tunable spin polarization. We prove these concepts by solving drift-diffusion equations for a realistic device model based on GaAs, which demonstrates that spin polarization can be injected through the depletion layer. Possibility of injecting spin polarization through a transistor is also discussed.The electrical injection of spin-polarized carriers within all-semiconductor structures ͑from a magnetic into a nonmagnetic semiconductor͒ was recently realized experimentally 2 ͑the scheme proposed in Ref. 3͒. Optical injection of spin-polarized carriers ͑both minority 4,5 and majority 4,6 ͒ has been known for some time. In addition, the relatively long spin diffusion lengths, 6,7 coherent spin transport across semiconductor interfaces, a successful fabrication of a magnetic/nonmagnetic p-n junction 8 based on the ͑Ga,Mn͒As material, 9 and the recent demonstration of a gatevoltage control of magnetization in ͑In,Mn͒As, 10 make semiconductors promising materials for spintronic applications. 2 In this paper we investigate the spin-charge transport in semiconductors under the conditions of inhomogeneous bipolar doping ͑there also exist theoretical proposals for semiconductor unipolar transistors and diodes 12 -a very different case from ours͒; we are not concerned with spin injection per se. Our model device is a spin-polarized p-n junction with spin polarization induced ͑either optically-in which case we get a spin-polarized solar cell-or electronically͒ to minority or majority carriers. By studying spin-charge transport numerically across the depletion layer, we observe phenomena, all resulting from the fact that spin polarization is transferred ͑what we call injected͒ through the depletion layer.We introduce a drift-diffusion model for spin-charge transport in an inhomogeneously-doped s...

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Spin injection through the depletion layer: A theory of spin-polarizedp-njunctions and solar cells

2001

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“…For these applications, a basic requirement is to produce, and sustain, high spin-polarized currents in semiconductors for sufficient long times. Several schemes have been proposed to produce spin injection in semiconductors, such as electrons injected from a ferromagnetic metal into a semiconductor [5][6][7], but the change in device resistance for parallel and antiparallel magnetization is very small. Diluted magnetic semiconductors (DMS) provides us with a new system in which spin dependent optical and transport properties are expected.…”

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Oscillating magnetoresistance in diluted magnetic semiconductor barrier structures

2002

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Ballistic spin polarized transport through diluted magnetic semiconductor (DMS) single and double barrier structures is investigated theoretically using a two-component model. The tunneling magnetoresistance (TMR) of the system exhibits oscillating behavior when the magnetic field are varied. An interesting beat pattern in the TMR and spin polarization is found for different NMS/DMS double barrier structures which arises from an interplay between the spin-up and spindown electron channels which are splitted by the s-d exchange interaction.75.50. Pp, 72.90.+y, Spin polarized transport in solid-state systems has generated intense interest as it is the crucial ingredient for spintronics [1,2] and several quantum computation scheme [3,4]. For these applications, a basic requirement is to produce, and sustain, high spin-polarized currents in semiconductors for sufficient long times. Several schemes have been proposed to produce spin injection in semiconductors, such as electrons injected from a ferromagnetic metal into a semiconductor [5][6][7], but the change in device resistance for parallel and antiparallel magnetization is very small. Diluted magnetic semiconductors (DMS) provides us with a new system in which spin dependent optical and transport properties are expected. The spindependent transport and optical properties in DMS systems arise from the s-d exchange interaction between the conduction electron and the localized 3d 5 electrons of the Mn ions which lifts the degeneracy of the spin-up and spin-down electron and hole states. [8] Spin dependent optical properties in a DMS spin superlattice was proposed [9] and realized [10]. Spin-dependent tunneling through a DMS junction was also studied theoretically within a mean-field approximation [11][12][13]. Very recently, experiments have demonstrated that a robust spin injection through a diluted magnetic semiconductor (DMS) junction Be x Mn y Zn 1−x−y Se [14], and a Mn doped p-type GaAs spin aligner was possible in which holes were injected into GaAs in the presence of an in-plane magnetic field [15]. Spin polarization of the injected carriers was detected by the emitted circular polarized light from the holes which recombined with the electrons in the nonmagnetic semiconductor (NMS) quantum wells. Spin coherence can be maintained in semiconductors over large distances (≥ 100µm) and for long time (up to nanoseconds) [16].In this work, we report an interesting oscillating tunneling magnetoresistance (TMR) and spin polarization (SP) through NMS/DMS structures. The DMS structure is similar to the sample used in the magneto-optical study of Ref. [10]. We find theoretically that the TMR for the double barrier structure oscillates with increasing magnetic field and exhibits a peculiar beat pattern. The underlying physics of the phenomena arises from the interplay of the spin-up and the spin-down channels which are split by the s-d exchange interaction. Note that bandstructure effects and spin-orbit interaction are not very efficient spin-flip processes for electrons....

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Exciton Spin Injection in CdTe/Cd1-xMnxTe Double Quantum Wells

Kayanuma

Debnath

Souma

et al. 2002

phys. stat. sol. (b)

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Spin injection processes of excitons were studied by time-resolved photoluminescence in double quantum wells consisting of Cd 0.95 Mn 0.05 Te and CdTe layers. Selective excitation of the magnetic and non-magnetic wells confirms the dominant spin injection process from the magnetic well to the non-magnetic well. The exciton spin injection from the magnetic quantum well of Cd 0.95 Mn 0.05 Te arises with an injection time of 10 ps and induces a transient spin polarization with the degree of 0.20 in the non-magnetic well of CdTe. The exciton spin relaxation time in the CdTe well was found to be sufficiently longer than the exciton lifetime of 38 ps.

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Spin injection into semiconductors

Cited by 222 publications

References 11 publications

Spin injection through the depletion layer: A theory of spin-polarizedp-njunctions and solar cells

Spin injection through the depletion layer: A theory of spin-polarizedp-njunctions and solar cells

Oscillating magnetoresistance in diluted magnetic semiconductor barrier structures

Exciton Spin Injection in CdTe/Cd1-xMnxTe Double Quantum Wells

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