Local Hanle-effect studies of spin drift and diffusion in n:GaAs epilayers and spin-transport devices

Furis, Madalina; Smith, D. L.; Kos, Šimon; Garlid, E. S.; Reddy, K. Sai Madhukar; Palmstrøm, C. J.; Crowell, P. A.; Crooker, S. A.

doi:10.1088/1367-2630/9/9/347

Cited by 55 publications

(62 citation statements)

References 32 publications

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“…The technique is applied to the submicrosecond electron spin dynamics in bulk n-type GaAs. The spin dephasing time T * 2 measured thereby from the dynamics of spin precession at low magnetic fields is in agreement with data recorded from the Hanle effect [9,10], RSA [6] and spin noise spectroscopy [11,12]. However, at increased magnetic fields the spin precession decay becomes nonexponential, a behaviour hardly accessible in detail by other methods.…”

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confidence: 86%

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Extended pump-probe Faraday rotation spectroscopy of the submicrosecond electron spin dynamics in n -type GaAs

Belykh¹,

Evers²,

Yakovlev³

et al. 2016

Phys. Rev. B

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We develop an extended pump-probe Faraday rotation technique to study submicrosecond electron spin dynamics with picosecond time resolution in a wide range of magnetic fields. The electron spin dephasing time T * 2 and the longitudinal spin relaxation time T1, both approaching 250 ns in weak fields, are measured thereby in n-type bulk GaAs. By tailoring the pump pulse train through increasing the contained number of pulses, the buildup of resonant spin amplification is demonstrated for the electron spin polarization. The spin precession amplitude in high magnetic fields applied in the Voigt geometry shows a non-monotonic dynamics deviating strongly from a mono-exponential decay and revealing slow beatings. The beatings indicate a two spin component behavior with a g-factor difference of ∆g ∼ 4 × 10 −4 , much smaller than the ∆g expected for free and donor-bound electrons. This g-factor variation indicates efficient, but incomplete spin exchange averaging.doi:10.1103/PhysRevB.94.241202Initialized electron spins in semiconductors undergo a complex dynamics depending on external magnetic field, interaction with other charge carriers and nuclei, spinorbit interaction, etc. Knowledge of the resulting spin dynamics provides information on these interactions and related spin properties such as g factors and relaxation times which are important for basic research and application in information technologies. Commonly, information on spin properties is mostly obtained from resonance techniques like electron paramagnetic resonance, optically-detected magnetic resonance, spin-flip Raman scattering, or polarized photoluminescence (Hanle effect). The development of pump-probe Faraday/Kerr rotation spectroscopy has facilitated exploration of the coherent spin dynamics, in particular the Larmor spin precession around a magnetic field, with picosecond temporal resolution and opened new ways for spin control and manipulation [1][2][3][4][5].The main limitation imposed on the standard pumpprobe technique is the restricted time range that can be monitored. This restriction comes from the finite length of mechanical delay lines for the pump-probe delay limiting this time range to a few nanoseconds, which can be too short to address the carrier spin dynamics in semiconductors. To evaluate longer spin dephasing times the resonant spin amplification (RSA) technique [6,7] can be used, which, however, does not provide detailed insight into complex spin dynamics such as a nonexponential decay of spin polarization. Also, the longitudinal spin relaxation characterized by the T 1 time typically exceeds the nanosecond range, so that indirect optical techniques like the spin inertia method [8] have to be used, again with limited access to nontrivial spin dynamics.Here we extend the standard pump-probe Faraday rotation (PPFR) technique to address a much longer time range by employing a tailored pump pulse sequence, while maintaining picosecond time resolution. The technique is applied to the submicrosecond electron spin dynamics in bulk n-type ...

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confidence: 86%

“…Note that the separation between the pump pulse trains is 80T R ≈ 1.05 µs ≫ T * 2 . The measured T * 2 is close to the values obtained from RSA [6], Hanle [9,10], and spin noise [11,12] experiments at B ≈ 0.…”

supporting

confidence: 83%

Extended pump-probe Faraday rotation spectroscopy of the submicrosecond electron spin dynamics in n -type GaAs

Belykh¹,

Evers²,

Yakovlev³

et al. 2016

Phys. Rev. B

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“…Due to the suppression of the DP mechanism, other spin dephasing mechanisms can be studied, yet the measurement of the lifetimes by optical techniques remains challenging due to spin dephasing induced via optically generated holes. A number of optical studies on spin diffusion using two-beam Hanle experiments were performed on n-bulk GaAs samples [23][24][25][26][27], which show spin diffusion lengths well above 10 μm. The mobility in these systems, however, is very low due to the direct doping, and they do not allow for easy manipulation of the carrier density and the Rashba spin-orbit interaction by external gate voltages.…”

Section: Introductionmentioning

confidence: 99%

Spin polarization, dephasing, and photoinduced spin diffusion in (110)-grown two-dimensional electron systems

et al. 2014

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We study the optically induced spin polarization, spin dephasing, and diffusion in several high-mobility twodimensional electron systems, which are embedded in GaAs quantum wells grown on (110)-oriented substrates. The experimental techniques comprise a two-beam magneto-optical spectroscopy system and polarizationresolved photoluminescence. Under weak excitation conditions at liquid-helium temperatures, we observe spin lifetimes above 100 ns in one of our samples, which are reduced with increasing excitation density due to additional, hole-mediated, spin dephasing. The spin dynamic is strongly influenced by the carrier density and the ionization of remote donors, which can be controlled by temperature and above-barrier illumination. The absolute value of the average electron spin polarization in the samples is directly observable in the circular polarization of photoluminescence collected under circularly polarized excitation and reaches values of about 5%. Spin diffusion is studied by varying the distance between pump and probe beams in microspectroscopy experiments. We observe diffusion lengths above 100 μm and, at high excitation intensity, a nonmonotonic dependence of the spin polarization on the pump-probe distance.

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“…Finally, we perform Hanle effect measurements (i.e., carrier depolarization by B y ), which have historically played a central role in semiconductor spintronics [24,25] to determine spin lifetimes, nuclear fields, and spin-orbit effects. Figure 3 shows θ K versus B y as the WSe 2 monolayer is tuned from n-to p-type.…”

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confidence: 99%

Gate-Controlled Spin-Valley Locking of Resident Carriers in WSe2 Monolayers

et al. 2017

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Using time-resolved Kerr rotation, we measure the spin/valley dynamics of resident electrons and holes in single charge-tunable monolayers of the archetypal transition-metal dichalcogenide (TMD) semiconductor WSe2. In the n-type regime, we observe long (∼70 ns) polarization relaxation of electrons that is sensitive to in-plane magnetic fields By, indicating spin relaxation. In marked contrast, extraordinarily long (∼2 µs) polarization relaxation of holes is revealed in the p-type regime, that is unaffected by By, directly confirming long-standing expectations of strong spinvalley locking of holes in the valence band of monolayer TMDs. Supported by continuous-wave Kerr spectroscopy and Hanle measurements, these studies provide a unified picture of carrier polarization dynamics in monolayer TMDs, which can guide design principles for future valleytronic devices.Besides their obvious promise for 2D optoelectronics [1][2][3], monolayer transition-metal dichalcogenide (TMD) semiconductors such as MoS 2 and WSe 2 have also revitalized interests in exploiting both the spin and valley pseudospin of electrons and holes for potential applications in (quantum) information processing [4][5][6][7][8][9]. This notion of "valleytronics" arises due to their crystalline asymmetry and strong spin-orbit coupling, which leads to spin-valley locking and valley-specific optical selection rules [7,8]. These rules mandate that the K or K ′ valleys in momentum space can be selectively populated and probed using polarized light, in contrast with most conventional III-V, II-VI, and group-IV semiconductors. Therefore, information may be readily encoded not only by whether an electron (or hole) has spin "up" or "down", but also by whether it resides in the K or K ′ valley -or, indeed, in some quantum-mechanical superposition thereof.The intrinsic timescales of carrier spin and valley dynamics in monolayer TMDs are therefore of considerable interest. However, most studies to date [10][11][12][13][14][15][16] have focused on photogenerated neutral and charged excitons, whose dynamics at low temperatures are inherently limited by their short (3-30 ps) recombination lifetimes [13,17]. An essential but altogether different question, however, concerns the intrinsic spin/valley lifetimes of the resident electrons and holes that exist in n-type and p-type TMD monolayers. In future valleytronic devices, it is likely the properties of these resident carriers that will determine performance -analogous to how the scattering timecales and mobility of resident carriers (not excitons) determines the performance of modernday transistors and interconnects.Several recent time-resolved studies point to encouragingly long polarization dynamics of resident carriers in monolayer TMDs. 3-5 ns polarization decays were observed in CVD-grown MoS 2 and WS 2 monolayers that were unintentionally electron-doped [18,19], while somewhat longer timescales were observed in unintentionally hole-doped CVD-grown WSe 2 [20,21]. However, a significant shortcoming in all these st...

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Local Hanle-effect studies of spin drift and diffusion in n:GaAs epilayers and spin-transport devices

Cited by 55 publications

References 32 publications

Extended pump-probe Faraday rotation spectroscopy of the submicrosecond electron spin dynamics in n -type GaAs

Extended pump-probe Faraday rotation spectroscopy of the submicrosecond electron spin dynamics in n -type GaAs

Spin polarization, dephasing, and photoinduced spin diffusion in (110)-grown two-dimensional electron systems

Gate-Controlled Spin-Valley Locking of Resident Carriers in WSe2 Monolayers

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