Structural and magnetic properties of epitaxially grown Ge1−xFex thin films: Fe concentration dependence

Shuto, Yusuke; Tanaka, Masaaki; Sugahara, Satoshi

doi:10.1063/1.2718270

Cited by 32 publications

(33 citation statements)

References 23 publications

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“…This difference in the lattice constant may be attributed to the difference in the density of the stacking-fault defects along the (111) plane observed in the GeFe films. 5,6 In face-centered cubic crystals, the (004) diffraction peak shifts to the higher angle side with an increase in the density of the stacking-fault defects along the (111) plane. 28,29,30 We observe many stacking-fault defects especially in the locally high-Fe-concentration regions.…”

Section: Discussionmentioning

confidence: 99%

“…28,29,30 We observe many stacking-fault defects especially in the locally high-Fe-concentration regions. 5 We think that the higher the T S is, the larger the non-uniformity of the Fe concentration becomes, which results in the increase in the density of the stacking-fault defects. Thus, the difference in the lattice constant may reflect the difference in the non-uniformity of the Fe concentration, which is thought to be the origin of the difference in the M S and T C values in the GeFe films.…”

Section: Discussionmentioning

confidence: 99%

“…3,4,5,6 In this paper, we present the growth temperature (T S ) dependence of T C and the lattice constant of GeFe, that are investigated by magnetic circular dichroism (MCD) and the X-ray diffraction (XRD) measurements.…”

Section: Introductionmentioning

confidence: 99%

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Important role of the non-uniform Fe distribution for the ferromagnetism in group-IV-based ferromagnetic semiconductor GeFe

Wakabayashi

Ohya

Ban

et al. 2014

Journal of Applied Physics

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We investigate the growth-temperature dependence of the properties of the group-IV-based ferromagnetic semiconductor Ge1−xFex films (x = 6.5% and 10.5%), and reveal the correlation of the magnetic properties with the lattice constant, Curie temperature (TC), non-uniformity of Fe atoms, stacking-fault defects, and Fe-atom locations. While TC strongly depends on the growth temperature, we find a universal relationship between TC and the lattice constant, which does not depend on the Fe content x. By using the spatially resolved transmission-electron diffractions combined with the energy-dispersive X-ray spectroscopy, we find that the density of the stacking-fault defects and the non-uniformity of the Fe concentration are correlated with TC. Meanwhile, by using the channeling Rutherford backscattering and particle-induced X-ray emission measurements, we clarify that about 15% of the Fe atoms exist on the tetrahedral interstitial sites in the Ge0.935Fe0.065 lattice and that the substitutional Fe concentration is not correlated with TC. Considering these results, we conclude that the non-uniformity of the Fe concentration plays an important role in determining the ferromagnetic properties of GeFe.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Important role of the non-uniform Fe distribution for the ferromagnetism in group-IV-based ferromagnetic semiconductor GeFe

Wakabayashi

Ohya

Ban

et al. 2014

Journal of Applied Physics

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“…Group-IV FMSs are particularly important because they are compatible with mature Si-based technology. Ge 1−x Fe x (Ge:Fe) is a promising material [9][10][11][12], and indeed can be grown epitaxially on Ge and Si substrates by the low-temperature molecular beam epitaxy (LT-MBE) method without the formation of intermetallic precipitates [13]. It shows p-type conduction, but the carrier concentration of ∼10 18 cm −3 [13] is orders of magnitude smaller than that of doped Fe atoms (∼10 21 cm −3 ).…”

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Origin of robust nanoscale ferromagnetism in Fe-doped Ge revealed by angle-resolved photoemission spectroscopy and first-principles calculation

et al. 2017

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Ge 1−x Fe x (Ge:Fe) shows ferromagnetic behavior up to a relatively high temperature of 210 K, and hence is a promising material for spintronic applications compatible with Si technology. We have studied its electronic structure by soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) measurements in order to elucidate the mechanism of the ferromagnetism. We observed finite Fe 3d components in the states at the Fermi level (E F ) in a wide region in momentum space and E F was located above the valenceband maximum (VBM). First-principles supercell calculation also suggested that the E F is located above the VBM, within the narrow spin-down d(e) band and within the spin-up impurity band of the deep acceptor-level origin derived from the strong p-d(t 2 ) hybridization. We conclude that the narrow d(e) band is responsible for the ferromagnetic coupling between Fe atoms while the acceptor-level-originated band is responsible for the transport properties of Ge:Fe. 1Ferromagnetic semiconductors (FMSs) such as (Ga,Mn)As [1, 2] have attracted much attention both from scientific and technological points of view [3][4][5][6][7][8]. Group-IV FMSs are particularly important because they are compatible with mature Si-based technology. Ge 1−x Fe x (Ge:Fe) is a promising material [9][10][11][12], and indeed can be grown epitaxially on Ge and Si substrates by the low-temperature molecular beam epitaxy (LT-MBE) method without the formation of intermetallic precipitates [13]. It shows p-type conduction, but the carrier concentration of ∼10 18 cm −3 [13] is orders of magnitude smaller than that of doped Fe atoms (∼10 21 cm −3 ). The Curie temperature (T C ) increases with the Fe content and with the inhomogeneity of Fe atom distribution [11,12], and reaches ∼210 K at highest by post-growth annealing [11], which is above the highest T C of (Ga,Mn)As, ∼200 K [14]. Unlike (Ga,Mn)As, the T C does not depend on carrier concentration [13]. Recent x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements [15] have revealed the valence of Fe substituting Ge to be 2+, which indicates that each Fe atoms would provide two holes. It was also found that nanoscale ferromagnetic domains exist even above the T C , the origin of which was attributed to the inhomogeneous distribution of Fe atoms on the nanoscale.In order to explain the origin of the ferromagnetism in (Ga,Mn)As and related FMSs, two models have been proposed so far [5,16,17], namely, the valence-band model [18,19] and the impurity-band model [20][21][22][23]. In the valence-band model, acceptor levels derived from the magnetic impurities are merged into the valence band and itinerant holes occupying states around the valence-band maximum (VBM) mediate ferromagnetism through Zener's p-d exchange mechanism.In the case of the impurity-band model, on the other hand, impurity levels are detached from the VBM and lies within the band gap of the host semiconductor and hence ferromagnetism is stabilized through a double-exchange-like mec...

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“…However, the inverse of the magnetic susceptibility  -1 = H/M (at H = 50 Oe, T > 100 K, green open circles in Fig. 4(c) 14,23,24 . In local Fe-rich domains, Fe atoms can sit in the second-nearest-neighbor sites and interact with each other through mechanisms such as superexchange interaction which is effective even at low carrier density.…”

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Growth and characterization of insulating ferromagnetic semiconductor (Al,Fe)Sb

Anh

Kaneko

Hai

et al. 2015

Applied Physics Letters

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We investigate the crystal structure, transport and magnetic properties of Fe-doped ferromagnetic semiconductor (Al1-x,Fex)Sb thin films up to x = 14% grown by molecular beam epitaxy. All the samples show p-type conduction at room temperature and insulating behavior at low temperature. The (Al1-x,Fex)Sb thin films with x ≤ 10% maintain the zinc blende crystal structure of the host material AlSb. The (Al1-x,Fex)Sb thin film with x = 10%shows intrinsic ferromagnetism with a Curie temperature (TC) of 40 K. In the (Al1-x,Fex)Sb thin film with x = 14%, a sudden drop of mobility and TC was observed, which may be due to microscopic phase separation. The observation of ferromagnetism in (Al,Fe)Sb paves the way to realize a spin-filtering tunnel barrier that is compatible with well-established III-V semiconductor devices. a Electronic mail: anh@cryst.t.u-tokyo.ac.jp b Electronic mail: masaaki@ee.t.u-tokyo.ac.jp 2 Injection of highly-spin-polarized carriers into semiconductors is essential to realize spin-based electronic devices, which are expected to lead to next-generation electronics with low-power consumption. A promising way of spin injection to semiconductors is to use a ferromagnetic insulator as a tunneling barrier, in which the spin-split band structure gives different barrier heights for up-spin and down-spin carriers. Since the tunneling current exponentially decreases with increasing the barrier height, one type of spin is effectively filtered out, leading to a highly-spin-polarized current (the "spin-filtering effect"). The tunneling process is not affected by the conduction mismatch, which is usually a serious problem when directly injecting a spin-polarized current from a ferromagnetic metallic electrode into a semiconductor. So far, however, most of the potential ferromagnetic materials for spin-filtering are Europium chalcogenides (EuO 1 , EuS 2 , EuSe 3 ) or complex oxides (CoFe2O4 4 , NiFe2O4 5 , NiMn2O4 6 , BiMnO3 7 , CoCrO4 8 and MnCr2O4 9 ), which are not compatible with mainstream semiconductors. Thus, an insulating ferromagnetic material that is compatible with well-established semiconductors is highly needed.In this paper, we report on the growth and properties of such a material, insulating ferromagnetic semiconductor (FMS) (Al,Fe)Sb. In FMSs, magnetic impurities are doped in conventional semiconductors at a level of several percentages, inducing ferromagnetism while preserving the crystal structure and other important properties of the host semiconductors. Because FMSs are compatible with conventional semiconductors, there 3 were some efforts to realize a FMS-based ferromagnetic tunnel barrier. After the success of Mn-based III-V FMSs such as (Ga,Mn)As and (In,Mn)As, some works have been reported on Mn doped AlAs 10,11 and AlSb 11 . As these materials would work as lattice-matched tunnel barriers in III-V semiconductor heterostructures, spin-filters based on Al-V (V is As or Sb) would significantly broaden the potential of III-V based spin devices such as spin hot-carrier transistors 12 , and t...

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Structural and magnetic properties of epitaxially grown Ge1−xFex thin films: Fe concentration dependence

Cited by 32 publications

References 23 publications

Important role of the non-uniform Fe distribution for the ferromagnetism in group-IV-based ferromagnetic semiconductor GeFe

Important role of the non-uniform Fe distribution for the ferromagnetism in group-IV-based ferromagnetic semiconductor GeFe

Origin of robust nanoscale ferromagnetism in Fe-doped Ge revealed by angle-resolved photoemission spectroscopy and first-principles calculation

Growth and characterization of insulating ferromagnetic semiconductor (Al,Fe)Sb

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