Giant enhancement of spin detection sensitivity in (Ga,Mn)As/GaAs Esaki diodes

Shiogai, Junichi; Ciorga, Mariusz; Utz, Martin; Schuh, Dieter; Kohda, Makoto; Bougeard, Dominique; Nojima, Tsutomu; Nitta, Junsaku; Weiss, Dieter

doi:10.1103/physrevb.89.081307

Cited by 23 publications

(32 citation statements)

References 39 publications

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“…Direct tunneling between the (Ga,Mn)As VB and the n-GaAs conduction band (CB), dominating for negative and low positive bias, is suppressed as the overlap of the bands is lifted. It was demonstrated in experiments on bulk samples that tunneling between 3D electron states and the gap states does not enhance the NLSV signal in bulk channels [35]. We can assume that this also holds here and that this transport mechanism, marked by the upper arrow in Fig.…”

supporting

confidence: 61%

Electrical Spin Injection into High Mobility 2D Systems

et al. 2014

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We report on spin injection into a high mobility 2D electron system confined at an ðAl; GaÞAs=GaAs interface, using (Ga,Mn)As Esaki diode contacts as spin aligners. We measured a clear nonlocal spin valve signal, which varies nonmonotonically with the applied bias voltage. The magnitude of the signal cannot be described by the standard spin drift-diffusion model, because at maximum this would require the spin polarization of the injected current to be much larger than 100%, which is unphysical. A strong correlation of the spin signal with contact width and electron mean free path suggests that ballistic transport in the 2D region below ferromagnetic contacts should be taken into account to fully describe the results. DOI: 10.1103/PhysRevLett.113.236602 PACS numbers: 72.25.Dc, 72.25.Hg, 72.25.Mk, 73.40.Kp All-electrical spin injection and detection, one of the key ingredients for functional spintronics devices, has been successfully realized in bulk semiconductors like GaAs [1,2] and Si [3,4]. To implement the spin-transistor functionality, proposed by Datta and Das [5], one needs the capacity to controllably rotate the spin of electrons on the way from source to drain. It has been suggested [5] to employ Rashba spin-orbit interaction, due to which the k vector of an electron in a two-dimensional electron gas (2DEG) is connected to an effective magnetic field, which is in turn tunable by an electric field. Thus, the precession angle in a sufficiently narrow channel can be coherently controlled by a gate voltage, provided transport between source and drain is ballistic. Hence, high mobility 2D systems are needed for these experiments. Although spin injection into graphene, a truly 2D system, has already been realized [6,7], no experiments exist in the ballistic regime where the injector or detector widths or their separation is significantly smaller than the electron mean free path l mf . Spin injection into semiconductor-based 2DEGs turns out to be difficult and only a few reports are available [8][9][10][11]. The analysis of experiments is also complicated by the lack of a corresponding ballistic theory. Although different aspects of ballistic spin injection and spin transport have been discussed theoretically [12][13][14][15][16][17], there is no comprehensive theory that would allow us to describe the experimental outcome in this regime in a way in which the spin drift-diffusion theory describes experiments on devices with bulk 3D channels [1,2].In this Letter we provide clear evidence of spin injection into a high mobility 2DEG confined in an inverted ðAl; GaÞAs=GaAs heterojunction, employing the ferromagnetic (FM) semiconductor (Ga,Mn)As in an Esaki diode configuration [18-21] as a spin aligner. We observed a dramatically enhanced nonlocal spin valve (NLSV) signal at negatively biased Esaki junctions when electrons can tunnel directly from (Ga,Mn)As into 2DEG states. At maximum the amplitude of the signal is much larger than predicted by the standard spin drift-diffusion model. The signal is especially l...

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confidence: 61%

Electrical Spin Injection into High Mobility 2D Systems

et al. 2014

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“…We have recently found that, in general, one cannot describe the effect of the nonlinearity on the spin signal by this simple multiplication [60]. Explicit theoretical evaluation [60] of spin signals for thermally activated transport across a Schottky barrier shows that the ratio of differential resistance and resistance does not appear in the expression for the spin signal, even though the transport is highly nonlinear and rectifying [note that for a Schottky diode under forward bias, (dV /dI )/(V /I ) < 1, which according to previous papers [58,59] would produce a reduction of the spin signal due to the nonlinearity]. Secondly, it was found [60] that a nonlinearity, characterized by a nonzero d 2 I/dV 2 , changes the magnitude of the detected spin signal if the magnitude μ of the induced spin accumulation is sufficiently large compared to the characteristic energy scale E 0 that describes the degree of nonlinearity.…”

Section: Nonlinearity Of the I-v Characteristicsmentioning

confidence: 85%

“…It has recently been pointed out that the magnitude of the spin signals can be modified if the transport across the contact is nonlinear [58,59]. It is relevant to discuss this possibility, since the Schottky contacts we studied here are highly rectifying and exhibit strongly nonlinear I -V characteristics.…”

Section: Nonlinearity Of the I-v Characteristicsmentioning

confidence: 91%

“…Let us first comment on how the nonlinearity affects the spin signal. In previous papers [58,59], it was argued that, when transport is nonlinear, the spin signal is enhanced by a factor (dV /dI )/(V /I ) representing the ratio of the differential resistance and the resistance of the contact. We have recently found that, in general, one cannot describe the effect of the nonlinearity on the spin signal by this simple multiplication [60].…”

Section: Nonlinearity Of the I-v Characteristicsmentioning

confidence: 99%

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Large spin accumulation voltages in epitaxialMn5Ge3contacts on Ge without an oxide tunnel barrier

et al. 2014

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Spin injection in high-quality epitaxial Mn 5 Ge 3 Schottky contacts on n-type Ge has been investigated using a three-terminal Hanle effect measurement. Clear Hanle and inverted Hanle signals with features characteristic of spin accumulation and spin precession are observed up to 200 K. Strikingly, the observed spin voltage is several orders of magnitude larger than predicted by the theory of spin injection and diffusive spin transport. Since the devices have no oxide tunnel barrier, the discrepancy between theory and experiments cannot be explained by the often-invoked spin accumulation in localized states associated with the oxide or oxide/semiconductor interface. The observed spin voltages therefore must originate from the Ge itself, either from spins in the Ge bulk bands or its depletion region.

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“…For instance, such an enhancement is commonly attributed to spin accumulation in interface states or to transport via double step tunneling. 8,21 However, the former is only possible when these states are decoupled from the semiconductor bulk by a large enough barrier resistance. 8,22 Further, the obtained spin lifetime is considerably lower than the recently reported value of $80-100 ps for 0.7 wt.…”

mentioning

confidence: 99%

Electric field effects on spin accumulation in Nb-doped SrTiO3 using tunable spin injection contacts at room temperature

Kamerbeek

Vries

Dankert

et al. 2014

Applied Physics Letters

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We report on features in charge transport and spin injection in an oxide semiconductor, Nb-doped SrTiO 3. This is demonstrated using electrically tunable spin injection contacts which exploit the large electric field at the interface and its interplay with the relative permittivity of the semiconductor. We realize spin accumulation in Nb-doped SrTiO 3 which displays a unique dependence of the spin lifetime with bias polarity. These findings suggest a strong influence of the interface electric field on the charge transport as well as on spin accumulation unlike in conventional semiconductors and opens up promising avenues in oxide spintronics.

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Giant enhancement of spin detection sensitivity in (Ga,Mn)As/GaAs Esaki diodes

Cited by 23 publications

References 39 publications

Electrical Spin Injection into High Mobility 2D Systems

Electrical Spin Injection into High Mobility 2D Systems

Large spin accumulation voltages in epitaxialMn5Ge3contacts on Ge without an oxide tunnel barrier

Electric field effects on spin accumulation in Nb-doped SrTiO3 using tunable spin injection contacts at room temperature

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