Title: Impurity band conduction in group-IV ferromagnetic semiconductor Ge1-xFex with nanoscale fluctuations in Fe concentration,
Abstract: We study the carrier transport and magnetic properties of group-IV-based
ferromagnetic semiconductor Ge1-xFex thin films (Fe concentration x = 2.3 - 14
%) with and without boron (B) doping, by measuring their transport
characteristics; the temperature dependence of resistivity, hole concentration,
mobility, and the relation between the anomalous Hall conductivity versus
conductivity. At relatively low x (= 2.3 %), the transport in the undoped
Ge1-xFex film is dominated by hole hopping between Fe-rich hopping sites in the
Fe impurity band, whereas that in the B-doped Ge1-xFex film is dominated by the
holes in the valence band in the degenerated Fe-poor regions. As x increases (x
= 2.3 - 14 %), the transport in the both undoped and B-doped Ge1-xFex films is
dominated by hole hopping between the Fe-rich hopping sites of the impurity
band. The magnetic properties of the Ge1-xFex films are studied by various
methods including magnetic circular dichroism, magnetization and anomalous Hall
resistance, and are not influenced by B-doping. We show band profile models of
both undoped and B-doped Ge1-xFex films, which can explain the transport and
the magnetic properties of the Ge1-xFex films.