Impurity band conduction in group-IV ferromagnetic semiconductor Ge1-xFex with nanoscale fluctuations in Fe concentration

TL;DR

This study investigates how impurity band conduction influences carrier transport and magnetic properties in Ge1-xFex ferromagnetic semiconductors with nanoscale Fe concentration fluctuations, revealing impurity band dominance at higher Fe levels.

Contribution

It provides a detailed analysis of impurity band conduction mechanisms in Ge1-xFex films and how they relate to magnetic properties, including effects of boron doping.

Findings

Transport is dominated by hole hopping in Fe-rich impurity bands at higher Fe concentrations.

Boron doping does not significantly alter magnetic properties.

Band profile models explain the observed transport and magnetic behaviors.

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.