Spin polarized photoemission from strained Ge epilayers

Bottegoni, Federico; Isella, Giovanni; Cecchi, Stefano; Ciccacci, Franco

doi:10.1063/1.3599493

Cited by 33 publications

(27 citation statements)

References 23 publications

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“…26,27 Similar to direct band-gap semiconductors, optical orientation is an additional viable tool to investigate spin properties of electrons and holes in Ge. [28][29][30][31][32][33][34] Unlike silicon, optical orientation in Ge is efficient because of the energy proximity between the direct and indirect gaps. Spin-polarized electrons are first photoexcited to the Γ valley and then they relax via ultrafast spin conserving scattering to the conduction band edges in one of the four L valleys (located ∼140 meV below the zone center Γ-valley).…”

Section: -18mentioning

confidence: 99%

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Intrinsic spin lifetime of conduction electrons in germanium

2012

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We investigate the intrinsic spin relaxation of conduction electrons in germanium due to electronphonon scattering. We derive intravalley and intervalley spin-flip matrix elements for a general spin orientation and quantify the resulting anisotropy in spin relaxation. The form of the intravalley spinflip matrix element is derived from the eigenstates of a compact spin-dependent k·p Hamiltonian in the vicinity of the L point (where thermal electrons are populated in Ge). Spin lifetimes from analytical integrations of the intravalley and intervalley matrix elements show excellent agreement with independent results from elaborate numerical methods.

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Section: -18mentioning

confidence: 99%

“…(26c)] does not affect the spinflip amplitude [Eq. (30)] when the spin orientation is along the valley axis (ϑ = 0). This effect will lead to a pronounced anisotropy in the intravalley spin lifetime.…”

Section: 61mentioning

confidence: 99%

Intrinsic spin lifetime of conduction electrons in germanium

2012

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“…In fact, thanks to the inversion symmetry of the crystal and the related absence of the D Yakonov-Perel spin scattering mechanism, Ge presents a longer spin coherence time than the one of GaAs. Spin manipulation [1], spin transport [2], spin optical pumping in the infrared [3][4][5][6][7], and electrical spin injection [8] in Ge have been reported. In our previous works [9,10], we demonstrated the room temperature operation of spin-PDs based on fully epitaxial Fe/MgO/Ge(001) heterostructures, working at 0.95 eV [11,12].…”

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confidence: 99%

Wide-range optical spin orientation in Ge from near-infrared to visible light

et al. 2014

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Ge-based spin-photodiodes have been employed to investigate the spectral dependence of optical spin orientation in germanium, in the range 400-1550 nm. We found the expected maximum in the spin polarization of photocarriers for excitation at the direct gap in (1550 nm) and a second sizable peak due to photogeneration in the L valleys (530 nm). Data suggest distinct spin depolarization mechanisms for excitation at and L, with shorter spin relaxation times whether the X point is involved. These devices can be used as integrated photon-helicity detectors over a wide spectral range. Spin-optoelectronics is a novel branch of semiconductor spintronics, aiming at adding a new degree of freedom to optoelectronics: the photon helicity. Exploiting the interplay between the photon angular momentum and the spin of electrons, integrated emitters (spin-LEDs) and detectors (spin photodiodes) of circularly polarized light have been proposed. Although GaAs is traditionally the material of choice for spin optoelectronics, because of its direct gap allowing for efficient conversion between light and spin polarization, recently Ge has attracted a considerable attention. In fact, thanks to the inversion symmetry of the crystal and the related absence of the D Yakonov-Perel spin scattering mechanism, Ge presents a longer spin coherence time than the one of GaAs. Spin manipulation [1], spin transport [2], spin optical pumping in the infrared [3][4][5][6][7], and electrical spin injection [8] in Ge have been reported. In our previous works [9,10], we demonstrated the room temperature operation of spin-PDs based on fully epitaxial Fe/MgO/Ge(001) heterostructures, working at 0.95 eV [11,12]. However, there is still a poor understanding of electrons and holes optical spin orientation in Ge, especially at photon energies much higher than the direct gap (0.8 eV). The optical spin orientation in Ge over a wide spectral range has been theoretically investigated by Rioux and Sipe [13]. However, no experimental data for excitation far from the point of the Brillouin zone (BZ) have been reported so far. Even for GaAs, only very recently the photon energy dependence of optical spin orientation well above the absorption edge has been reported [14].In this Rapid Communication, we report on the spectral dependence of the optical spin orientation in Ge at room temperature and over a wide spectral range (400-1550 nm, corresponding to 3.1-0.8 eV), via measurements of the helicitydependent photocurrent on Ge-based spin PDs. Surprisingly enough, the maximum sensitivity to photon helicity is observed far away from the direct gap (0.8 eV), where optical pumping is supposed to produce the highest initial spin polarization. Indeed, the helicity-dependent photocurrent variation indicates a first peak around 1500 nm (0.8 eV) and then an absolute maximum of about 10% at ∼530 nm (∼2.3 eV), corresponding to optical pumping in the L valley of the Ge band structure, * christian.rinaldi@polimi.it as shown in Fig. 1(a). Fitting of our data within a simple diffusive m...

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“…The behaviour of ∆V nicely resembles the dependence of the electron spin polarization P as a function of the incident photon energy. 7,8,36 The maximum ISHE signal is obtained for hν = 0.8 eV, i.e. when the photon energy is resonant with the Ge direct gap, which indeed corresponds to the maximum initial electron spin polarization P = 50%.…”

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confidence: 99%

“…In this materials optically-injected electrons can reach spin polarization values up to 50% in bulk semiconductors [4][5][6][7][8] or even larger in semiconductor nanostructures. [8][9][10][11][12][13][14][15][16] In this respect it would be highly desirable to implement the control of the spin degree of freedom in Ge-based heterostructures, which can be integrated on the common Si-based electronics platform. In bulk Ge the energy difference between direct (E d = 0.80 eV) and indirect (E i = 0.66 eV) bandgap is only 140 meV at room temperature.…”

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confidence: 99%

Pure spin currents in Ge probed by inverse spin-Hall effect

et al. 2016

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We perform photoinduced inverse spin-Hall effect (ISHE) measurements on a Pt/Ge(001) junction at room temperature. The spin-oriented electrons are photogenerated at the Γ point of the Ge Brillouin zone using circularly-polarized light. After the ultrafast Γ−L scattering in the Ge conduction band, which partially preserves the spin polarization, electrons diffuse into the Pt layer where spin-dependent scattering with Pt nuclei yields a transverse electromotive field EISHE. The ISHE signal dependence as a function of the incident photon energy is investigated and interpreted in the frame of a one-dimensional spin drift-diffusion model. This allows estimating the electron spin lifetime at the L-valleys to be τs=1 ns.

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Spin polarized photoemission from strained Ge epilayers

Cited by 33 publications

References 23 publications

Intrinsic spin lifetime of conduction electrons in germanium

Intrinsic spin lifetime of conduction electrons in germanium

Wide-range optical spin orientation in Ge from near-infrared to visible light

Pure spin currents in Ge probed by inverse spin-Hall effect

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