Spin lifetimes of electrons injected into GaAs and GaN

Krishnamurthy, Srinivasan; Schilfgaarde, Mark van; Newman, Nathan

doi:10.1063/1.1606873

Cited by 114 publications

(75 citation statements)

References 12 publications

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“…Theoretical studies focusing on spin dephasing in III-V and II-VI systems include those of Wu and Metiu (2000); Lau et al (2001);Wu (2001); Bronold et al (2002); Lau and Flatté (2002); Wu and KuwataGonokami (2002); Krishnamurthy et al (2003); Puller et al (2003). Spin relaxation due to D'yakonov-Perel' mechanism with bulk inversion asymmetry term in the important case of GaAs/AlGaAs rectangular quantum wells was investigated by Monte Carlo simulations at room temperature, including interface roughness scattering.…”

Section: Low-dimensional Semiconductor Structuresmentioning

confidence: 99%

Spintronics: Fundamentals and applications

2004

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Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics. CONTENTS

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Section: Low-dimensional Semiconductor Structuresmentioning

confidence: 99%

Spintronics: Fundamentals and applications

2004

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“…2, a long electron spin coherence of up to 20 ns was observed in Si-doped GaN by using time-resolved Faraday rotation measurements, while short ͑subpicosecond͒ excitonic-spin relaxation times were observed in a GaN epilayer by using spin-dependent transient reflectivity change measurements. 3 Although theoretical work has suggested a significant influence of the sample quality on the spin dynamics in semiconductors, 7 the mechanism that causes the difference between these two results is still unclear.…”

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confidence: 99%

“…[6][7][8][9] A noteworthy issue is the significant variation in the spin relaxation time obtained in previous experiments; in Ref. 2, a long electron spin coherence of up to 20 ns was observed in Si-doped GaN by using time-resolved Faraday rotation measurements, while short ͑subpicosecond͒ excitonic-spin relaxation times were observed in a GaN epilayer by using spin-dependent transient reflectivity change measurements.…”

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confidence: 99%

Exciton spin relaxation in GaN observed by spin grating experiment

Ishiguro

Toda

Adachi

2007

Applied Physics Letters

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The authors studied the exciton spin relaxation of bulk GaN by creating spin polarization gratings using degenerate four-wave mixing spectroscopy. The spectrally resolved analysis achieved with this technique facilitated the direct evaluation of spin polarizations in the individual excitons ͑A and B excitons͒. The spin polarizations for each exciton decay very quickly ͑ s ϳ 1 ps͒ at low temperatures. Moreover the s is faster than the dephasing time T 2 throughout the measured temperature range, suggesting the existence of fast intrinsic spin relaxation processes, which can be attributed to a large exchange constant characterized in GaN. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2430402͔Because of the technological importance of spin-based electronics, so-called spintronics, 1 considerable effort has recently been devoted to understanding the optically induced spin polarization in GaN and related alloys, both experimentally 2-5 and theoretically. 6-9 A noteworthy issue is the significant variation in the spin relaxation time obtained in previous experiments; in Ref. 2, a long electron spin coherence of up to 20 ns was observed in Si-doped GaN by using time-resolved Faraday rotation measurements, while short ͑subpicosecond͒ excitonic-spin relaxation times were observed in a GaN epilayer by using spin-dependent transient reflectivity change measurements. 3 Although theoretical work has suggested a significant influence of the sample quality on the spin dynamics in semiconductors, 7 the mechanism that causes the difference between these two results is still unclear.In this work, we studied exciton spin relaxation in bulk GaN by using spectrally resolved four-wave mixing ͑SR-FWM͒ measurements. Strikingly fast spin relaxations, which were even faster than the dephasing times T 2 , were observed for each exciton resonance at low temperatures. The relaxation time in an A exciton ͑X A ͒ decreases with increasing temperature, and then reaches the experimental resolution limit above 100 K. The results can be understood in terms of an excitonic effect in GaN. Figure 1͑a͒ is a schematic illustration of the experiment. In order to evaluate the spin lifetime in the spectral domain, we employed a three-pulse FWM measurement. 10-12 A frequency doubled, mode-locked Ti:sapphire laser which produced a pulse width of ϳ200 fs ͑spectral width of ϳ13 meV͒ at a repetition rate of 76 MHz was employed as an excitation light source. Two simultaneous excitation pulses and one probe pulse with a controlled time delay were focused at the same point on the sample surface using a lens ͑f = 200 mm͒. These three pulses have almost the same power of about 0.3 mW. The pump pair consisting of crosslinear ͑colinear͒ polarizations of wave vectors k 1 and k 2 forms an exciton spin polarization ͑population͒ grating ͓Fig. 1͑b͔͒ which mainly decays via the exciton spin relaxation ͑recombination͒ process. 13 A third probe pulse of wave vector k 3 diffracts off this grating to produce the FWM signal in the k 4 = k 3 ϯ k 2 ± k 1 direction, which ...

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“…5 As the electronelectron Coulomb scattering does not contribute to the momentum relaxation time τ p , it has long been widely believed that the electron-electron Coulomb scattering is irrelevant in the spin relaxation. 5,6,7,8,9,10,11 However, it was first pointed out by Wu and Ning 12 that in the presence of inhomogeneous broadening, any scattering, including the spin conserving electron-electron Coulomb scattering, can cause an irreversible spin relaxation and dephasing. This inhomogeneous broadening can be the energy-dependent g-factor, 12 the DP term, 13,14 and even the k-dependent spin diffusion along a spacial gradient.…”

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Effect of electron-electron scattering on spin dephasing in a high-mobility low-density two-dimensional electron gas

Ruan

Luo

et al. 2008

Phys. Rev. B

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Utilizing time-resolved Kerr rotation techniques, we have investigated the spin dynamics of a high mobility, low density two dimensional electron gas in a GaAs/Al 0.35 Ga 0.65 As heterostructure in dependence on temperature from 1.5 K to 30 K. It is found that the spin relaxation/dephasing time under a magnetic field of 0.5 T exhibits a maximum of 3.12 ns around 14 K, superimposed on an increasing background with rising temperature. The appearance of the maximum is ascribed to that at the temperature where the crossover from the degenerate to the nondegenerate regime takes place, electron-electron Coulomb scattering becomes strongest, and thus inhomogeneous precession broadening due to D'yakonov-Perel' (DP) mechanism becomes weakest. These results agree with the recent theoretical predictions [Zhou et al., PRB 75, 045305 (2007)], verifying the importance of electron-electron Coulomb scattering to electron spin relaxation/dephasing. PACS numbers: 72.25.Rb, 71.70.Ej, 78.47.jc In recent years, spin dynamics in semiconductors has attracted considerable attention because of its potential application in the spin-based devices. 1 The operation of these devices requires spin lifetime long enough to achieve storage, transport and processing of information. Therefore, a comprehensive understanding of spin relaxation mechanism is a key factor for the realization of these devices. It is generally accepted that the D'yakonov-Perel' (DP) mechanism is the leading spin relaxation/dephasing (R/D) mechanism in n-type zincblende semiconductors. 2 This is caused by an wavevector kdependent effective magnetic field Ω(k) from the bulk inversion asymmetry, 3 i.e., the Dresselhaus term, and/or the structure inversion asymmetry, 4 i.e., the Rashba term. The spin relaxation rate can be determined by τ −1 = Ω(k) 2 τ P (k), where τ P (k) is the momentum relaxation time. 5 As the electronelectron Coulomb scattering does not contribute to the momentum relaxation time τ p , it has long been widely believed that the electron-electron Coulomb scattering is irrelevant in the spin relaxation. 5,6,7,8,9,10,11 However, it was first pointed out by Wu and Ning 12 that in the presence of inhomogeneous broadening, any scattering, including the spin conserving electron-electron Coulomb scattering, can cause an irreversible spin relaxation and dephasing. This inhomogeneous broadening can be the energy-dependent g-factor, 12 the DP term, 13,14 and even the k-dependent spin diffusion along a spacial gradient. 15 In n-type GaAs quantum well, the importance of the electron-electron scattering to the spin relaxation was proved by Glazov and Ivchenko 16 by using perturbation theory and Weng and Wu 14 from a fully microscopic many-body approach. In a temperature-dependent experimental study of the spin relaxation in n-type (001) quantum wells, Harleyet al. indirectly verified the effects of the electron-electron scattering on spin relaxation. 17,18 Nevertheless, the importance of the Coulomb scattering to the spin relaxation/dephasing (R/D)has not yet been ...

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Spin lifetimes of electrons injected into GaAs and GaN

Cited by 114 publications

References 12 publications

Spintronics: Fundamentals and applications

Spintronics: Fundamentals and applications

Exciton spin relaxation in GaN observed by spin grating experiment

Effect of electron-electron scattering on spin dephasing in a high-mobility low-density two-dimensional electron gas

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