135 research outputs found
Carrier transport properties of the Group-IV ferromagnetic semiconductor Ge1-xFex with and without boron doping
We have investigated the transport and magnetic properties of group-IV
ferromagnetic semiconductor Ge1-xFex 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 Ge1-xFex 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 Ge1-xFex 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 Ge1-xFex from
~1018 cm-3 to ~1020 cm-3 (x = 1.0%) and to ~1019 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
Surface Circular Photogalvanic Effect in Tl-Pb Monolayer Alloys on Si(111) with Giant Rashba Splitting
We have found that surface superstructures made of "monolayer alloys" of Tl
and Pb on Si(111), having giant Rashba effect, produce non-reciprocal
spin-polarized photocurrent via circular photogalvanic effect (CPGE) by
obliquely shining circularly polarized near-infrared (IR) light. CPGE is here
caused by injection of in-plane spin into spin-split surface-state bands, which
is observed only on Tl-Pb alloy layers, but not on single-element Tl nor Pb
layers. In the Tl-Pb monolayer alloys, despite their monatomic thickness, the
magnitude of CPGE is comparable to or even larger than the cases of many other
spin-split thin-film materials. The data analysis has provided the relative
permittivity of the monolayer alloys to be 1.0, which
is because the monolayer exists at a transition region between the vacuum and
the substrate. The present result opens the possibility that we can optically
manipulate spins of electrons even on monolayer materials
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