Study of Ambipolar Diffusion and Drift of Spatially Separated Charge Carriers

Beck, Markus; Vitzethum, M.; Streb, D.; Kiesel, P.; Metzner, Claus; Malzer, S.; Döhler, G. H.

doi:10.1007/978-3-642-59484-7_420

Springer Proceedings in Physics

2001

DOI: 10.1007/978-3-642-59484-7_420

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Study of Ambipolar Diffusion and Drift of Spatially Separated Charge Carriers

Markus Beck¹,

M. Vitzethum²,

D. Streb³

et al.

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Cited by 4 publications

(4 citation statements)

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“…These strain-induced effective magnetic fields can be used to generate electron spin polarization electrically 6 and coherently manipulate spins using electric fields and in the absence of magnetic fields 5 , but they also contribute to more efficient spin relaxation 7 . In addition, recent steady-state measurements 8,9 have shown that the spatial period of strain-induced spin precession is independent of the applied electric field, which demonstrates the robustness of strain-induced spin precession for applications in functional spin-based devices.…”

mentioning

confidence: 93%

Mechanical control of spin-orbit splitting in GaAs andIn0.04Ga0.96Asepilayers

et al. 2006

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Time-resolved Kerr rotation spectroscopy as a function of pump-probe distance, voltage and magnetic field is used to measure the momentum-dependent spin splitting energies in GaAs and InGaAs epilayers. The strain of the samples can be reproducibly controlled in the cryostat using three-and four-point bending applied with a mechanical vise. We find that the magnitude of the spin splitting increases linearly with applied tension and voltage. A strain-drift-diffusion model is used to relate the magnitude of the measured spin-orbit splitting to the amount of strain in the sample.PACS numbers: 71.70. Ej, 71.70.Fk, 72.25.Dc, 72.25.Rb Potential applications in spintronics 1 and quantum information processing 2 rely upon an understanding of the effect of electric fields and strain on electron spins. Strain reduces the symmetry of a crystal, which introduces momentum k-linear terms to the Dresselhaus 3 and Bychkov-Rashba 4 spin splittings. These strain-induced effective magnetic fields can be used to generate electron spin polarization electrically 6 and coherently manipulate spins using electric fields and in the absence of magnetic fields 5 , but they also contribute to more efficient spin relaxation 7 . In addition, recent steady-state measurements 8,9 have shown that the spatial period of strain-induced spin precession is independent of the applied electric field, which demonstrates the robustness of strain-induced spin precession for applications in functional spin-based devices.Here we employ mechanical three-and four-point bending to tune the tensile strain of GaAs and In-GaAs epilayers while performing low-temperature timeresolved magneto-optical spectroscopy to determine the magnitude of the strain-induced spin splitting. The samples are contacted so that an in-plane electric field can be applied to impart an average drift velocity to the optically-excited electron spins.Kerr rotation measurements as a function of magnetic field and pump-probe distance are performed for different applied electric fields, and we observe that the spin splitting increases with increasing drift velocity and tensile strain. Unlike previous measurements that introduced strain through heterostructure engineering and latticemismatched growth 5 , these measurements are able to map out the strain dependence in a single sample and without the complications of strain relaxation. The vise geometry allows for repeatable tensioning of samples and precise control over the strain level.The samples are grown using molecular beam epitaxy on semi-insulating (001) GaAs substrates. We examine both n-doped GaAs and InGaAs epilayers. The GaAs samples are comprised of 100 nm undoped GaAs buffer layer, 400 nm Al 0.7 Ga 0.3 As, and a 500 nm Si-doped GaAs epilayer. Samples with carrier densities of 2 × 10 16 cm −3 and 4 × 10 16 cm −3 were measured, but since they exhibit qualitatively similar behavior, we show only data for the 2 × 10 16 cm −3 n-GaAs sample in this paper. The InGaAs sample is composed of 300 nm of growth-interrupted GaAs buffer layer, 50...

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confidence: 93%

Mechanical control of spin-orbit splitting in GaAs andIn0.04Ga0.96Asepilayers

et al. 2006

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“…As a result, the DP mechanism reduces τ s with increasing E x due to the increased average electron energy. For free electrons and a large electrical bias, a detailed calculation of this effect and its influence on τ s was reported by Beck et al [18].…”

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confidence: 99%

Bias-dependent electron spin lifetimes in n-GaAs and the role of donor impact ionization

Furis

Smith

Reno

et al. 2006

Applied Physics Letters

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In bulk n-GaAs epilayers doped near the metal-insulator transition, we study the evolution of electron spin lifetime τs as a function of applied lateral electrical bias Ex. τs is measured via the Hanle effect using magneto-optical Kerr rotation. At low temperatures (T < 10K, where electrons are partially localized and τs > 100 ns at zero bias), a marked collapse of τs is observed when Ex exceeds the donor impact ionization threshold at ∼10 V/cm. A steep increase in the concentration of warm delocalized electrons -subject to Dyakonov-Perel spin relaxation -accounts for the rapid collapse of τs, and strongly influences electron spin transport in this regime. 72.25.Dc, 72.25.Rb, 79.20.Kz The discovery of very long electron spin lifetimes, τ s , in GaAs has helped motivate considerable interest in semiconductor-based spintronic devices [1]. Studies of bulk n-GaAs have established that, in the absence of any applied electric field, long spin lifetimes in the range τ s =100-300 ns are associated with cryogenic temperatures and electron doping in the range of the metalinsulator transition (n MIT ≃ 2 × 10 16 cm −3 ) [2,3,4,5]. Several prototype devices operating at low temperatures have therefore incorporated n-GaAs doped in this range [6,7,8,9,10,11,12]. This is, however, precisely the doping and temperature regime where carrier transport becomes highly nonlinear due to electron localization (freeze-out) and subsequent impact ionization of donorbound electrons at quite modest applied electric fields of order 10 V/cm [13,14]. Since future spin-transport devices may employ electrical biases on (at least) this order, a bias-dependent study of τ s through the threshold of donor impact ionization is important for device design and for the characterization of spin transport in n-type semiconductors in general.Here we measure τ s as a function of temperature and applied electrical bias E x in bulk epilayers of n-GaAs doped near the metal-insulator transition. τ s is obtained from Hanle depolarization measurements using the magneto-optical Kerr effect. At low temperatures, τ s drops dramatically at the threshold of donor impact ionization at E x ≃ 10 V/cm. At this threshold, which coincides with marked nonlinearities in the samples' currentvoltage (I-V ) characteristics, the electron ensemble becomes largely delocalized (and warm) and the DyakonovPerel spin relaxation mechanism dominates.Three silicon-doped bulk n-GaAs epilayers were grown by molecular beam epitaxy on (001)-oriented GaAs substrates. The dopings and thicknesses are: 1 × 10 16 cm −3 (1 µm thick), 5 × 10 16 cm −3 (1 µm thick), and 4 × 10 15 cm −3 (15 µm thick). These samples allow study of the bias-dependent spin lifetime both above and below the metal-insulator transition (MIT). The inset of Figure 1(a) shows the experimental geometry. The samples are mounted, strain-free, on the cold finger of an optical cryostat. Ohmic contacts of annealed indium or AuGeNi permit application of an in-plane electric field, E x . Spinpolarized electrons are optically inject...

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“…As an example we show in the following that spin noise is in principle capable to measure intrinsic electron spin relaxation times at low temperature with less uncertainties than traditional Faraday rotation or Hanle measurements. The intrinsic electron spin relaxation time recently gained new interest, since experiments and calculations by Beck et al at 4 K adumbrate that the electron spin relaxation times in GaAs with an n-doping in the range between 10 15 cm −3 and 10 16 cm −3 might not be limited by the anisotropic exchange interaction [11] but by the Dyakonov-Perel (DP) mechanism [12]. The DP mechanism vanishes for electrons with wave vectors | k| → 0.…”

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confidence: 99%

Spin Noise Spectroscopy in GaAs

et al. 2005

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We observe the noise spectrum of electron spins in bulk GaAs by Faraday-rotation noise spectroscopy. The experimental technique enables the undisturbed measurement of the electron-spin dynamics in semiconductors. We measure exemplarily the electron-spin relaxation time and the electron Landé g factor in -doped GaAs at low temperatures and find good agreement of the measured noise spectrum with a theory based on Poisson distribution probability.

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Study of Ambipolar Diffusion and Drift of Spatially Separated Charge Carriers

Cited by 4 publications

References 3 publications

Mechanical control of spin-orbit splitting in GaAs andIn0.04Ga0.96Asepilayers

Mechanical control of spin-orbit splitting in GaAs andIn0.04Ga0.96Asepilayers

Bias-dependent electron spin lifetimes in n-GaAs and the role of donor impact ionization

Spin Noise Spectroscopy in GaAs

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