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

Abstract

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.

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

“…The value of ∼0.2 eV is smaller than the experimental value of 0.35 eV. This is probably due to the existence of ∼15% of interstitial Fe atoms [12], which provide two electrons per Fe atom to the sp orbitals and partially compensates holes. Figure 3(b) shows the spin-averaged PDOS of Fe 3d(t 2 ) and 3d(e) orbitals in comparison with the experimentally obtained PDOS.…”

“…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 ).…”

“…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].…”

“…The experimental lattice constant of a = 5.648Å for Ge 0.935 Fe 0.065 [12] was used and spin-orbit interaction was included for both calculations. [29].)…”

Spinodal nanodecomposition in semiconductors doped with transition metals

“…In either case, the magnitude of T (app) C correlates with the nonuniformity of the Fe distribution and the stacking fault density (Wakabayashi et al, 2014a,b). Meanwhile, channeling Rutherford backscattering and particle-induced x-ray emission measurements revealed that about 15% of the Fe atoms reside in the tetrahedral interstitial sites and that the substitutional Fe concentration, in agreement with the decomposition scenario, is barely correlated with the magnitude of T (app) C (Wakabayashi et al, 2014b). At the same time, all the (Ge,Fe) films show a weak spin-glasslike behavior in a low-temperature region (below ∼ 26 K), which is insensitive to the annealing temperature.…”