Carrier transport properties of the Group-IV ferromagnetic semiconductor Ge1-xFex with and without boron doping

Abstract

We have investigated the transport and magnetic properties of group-IV ferromagnetic semiconductor Ge 1-x Fe x films (x = 1.0 and 2.3 %) with and without boron doping grown by molecular beam epitaxy (MBE). In order to accurately measure the transport properties of 100-nm-thick Ge 1-x Fe x films, (001)-oriented silicon-on-insulator (SOI) wafers with an ultra-thin Si body layer (~5 nm) were used as substrates. Owing to the low Fe content, the hole concentration and mobility in the Ge 1-x Fe x films were exactly estimated by Hall measurements because the anomalous Hall effect in these films was found to be negligibly small. By boron doping, we increased the hole concentration in Ge 1-x Fe x from ~10 18 cm -3 to ~10 20 cm -3 (x = 1.0%) and to ~10 19 cm -3 (x = 2.3%), but no correlation was observed between the hole concentration and magnetic properties. This result presents a contrast to the hole-induced ferromagnetism in III-V ferromagnetic semiconductors.

Room-temperature local ferromagnetism and its nanoscale expansion in the ferromagnetic semiconductor Ge1–xFex

“…Unlike GaMnAs, in GeFe, interstitial Fe atoms do not lead to a decrease in T C 6 , and T C can be easily increased to above 200 K by thermal annealing 7 . Furthermore, T C does not depend on the carrier concentration, and thus T C and resistivity can be controlled separately 8 , which is a unique feature that is only observed in GeFe and is a considerable advantage in overcoming the conductivity mismatch problem between ferromagnetic metals and semiconductors in spin-injection devices. Despite these attractive features, a detailed microscopic understanding of the ferromagnetism in GeFe, which is vitally important for room-temperature applications, is lacking.…”

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

“…1 One of the important characteristics of Ge 1-x Fe x is that the conductivity can be controlled by boron (B) doping independently of the Fe concentration x. 2 Therefore, when a spin current is injected from GeFe to a nonmagnetic semiconductor, we can avoid the conductivity mismatch problem and suppress the spin flip scattering at the interfaces.…”

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

“…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 ).…”

“…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].…”

“…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.…”