Electronic Structure of the Ferromagnetic Semiconductor Fe-doped Ge Revealed by Soft X-ray Angle-Resolved Photoemission Spectroscopy

TL;DR

This study investigates the electronic structure of Fe-doped Ge using SX-ARPES and first-principles calculations, revealing the role of Fe 3d states and impurity bands in its ferromagnetism and transport properties, relevant for spintronics.

Contribution

The paper provides the first detailed SX-ARPES analysis of Fe-doped Ge, clarifying the electronic states responsible for its ferromagnetism and transport behavior.

Findings

Fe 3d states are present at the Fermi level in momentum space.

Fermi level is above the valence-band maximum.

The narrow d(e) band drives ferromagnetic coupling.

Abstract

Ge$_{1-x}$Fe$_{x}$ (Ge:Fe) shows ferromagnetic behavior up to a relatively high temperature of 210 K, and hence is a promising material for spintronic applications compatible with Si technology. We have studied its electronic structure by soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) measurements in order to elucidate the mechanism of the ferromagnetism. We observed finite Fe 3$d$ components in the states at the Fermi level ($E_{F}$) in a wide region in momentum space and $E_{F}$ was located above the valence-band maximum (VBM). First-principles supercell calculation also suggested that the $E_{F}$ is located above the VBM, within the narrow spin-down $d$($e$) band and within the spin-up impurity band of the deep acceptor-level origin derived from the strong $p$-$d$($t_{2}$) hybridization. We conclude that the narrow $d$($e$) band is responsible for the ferromagnetic coupling between Fe atoms while the acceptor-level-originated band is responsible for the transport properties of Ge:Fe.