By using magnetic circular dichroism (MCD) spectroscopy with photon energy in both visible (1.5–5 eV) and infrared light regions (0.6–1.7 eV), we systematically investigate the band structure of p-type ferromagnetic semiconductor (Ga1−x,Fex)Sb with various Fe concentrations x = 2%–20% grown by low-temperature molecular beam epitaxy. We observed two peaks in the infrared MCD spectra that can be explained by the optical transitions related to the Fermi level (EF) located in an Fe-related impurity band (IB) in the bandgap. As x increases, the energy shifts of the two peaks suggest that the Fe-related IB extends into the bandgap and EF rises correspondingly. Furthermore, the mobility of hole carriers in these (Ga,Fe)Sb thin films estimated by Hall measurements is very low (0.2–2 cm2/Vs), which is consistent with our conclusion that the hole carriers and EF reside in the IB rather than in the valence band. Our results provide insights into the band structure of p-type ferromagnetic semiconductors (Ga,Fe)Sb with high Curie temperature, which is promising for the realization of spintronic devices operating at room temperature.

We study the growth and properties of the quaternary-alloy ferromagnetic semiconductor (In0.94−x,Gax,Fe0.06)Sb (x = 5%–30%; the Fe concentration is fixed at 6%) grown by low-temperature molecular beam epitaxy. Reflection high-energy electron diffraction patterns, scanning transmission electron microscopy lattice images, and x-ray diffraction spectra indicate that the (In0.94−x,Gax,Fe0.06)Sb layers have a zinc blende crystal structure without any other second phase. The lattice constant of the (In0.94−x,Gax,Fe0.06)Sb films changes linearly with the Ga concentration x, indicating that Ga atoms substitute In atoms in the zinc-blende structure. We found that the carrier type of (In0.94−x,Gax,Fe0.06)Sb can be systematically controlled by varying x, being n-type when x ≤ 10% and p-type when x ≥ 20%. Characterization studies using magnetic circular dichroism spectroscopy indicate that the (In0.94−x,Gax,Fe0.06)Sb layers have intrinsic ferromagnetism with relatively high Curie temperatures (TC = 40–120 K). The ability to widely control the fundamental material properties (lattice constant, bandgap, carrier type, and magnetic property) of (In0.94−x,Gax,Fe0.06)Sb demonstrated in this work is essential for spintronic device applications.

We study the quantum size effect (QSE) in the spin-dependent electronic structure at the conduction band (CB) bottom (Γ point) of an n-type ferromagnetic semiconductor (In0.92,Fe0.08)As ultrathin films (thickness t = 8–14 nm), by performing magnetic circular dichroism (MCD) spectroscopy in an infra-red photon energy range (E = 0.62–1.8 eV). The t-dependence of MCD peaks are well explained by the optical transitions from the valence band top to the quantized levels at the CB bottom of (In,Fe)As obtained from self-consistent calculations. These findings provide new possibilities of spin-device applications utilizing QSE in nm-scale (In,Fe)As thin films.

We report the structural and magnetic properties of the Fe-doped GaSb quantum dots (QDs) (nominal Fe concentration x = 4.7%–16.6%) grown on GaAs (001) substrates by molecular beam epitaxy. The QDs with nanometer-scale dimensions consist of two areas with different crystal structures, a zinc-blende GaAsSb wetting layer and a new phase of FeGaSb alloy that has a simple cubic lattice. The size and distribution of the QDs depend on the Fe concentration, as revealed by atomic force microscopy. Magnetic force microscopy measurements at zero applied magnetic field show the presence of ferromagnetism in the QDs at room temperature with an easy axis in the 1¯10 direction, which is consistent with magnetometry measurements. The Curie temperature in these QDs is very high (>400 K), which is promising for spintronic applications at room temperature.

We report the structural and magnetic properties of Fe-doped InAs quantum dots (QDs) grown on GaAs (001) substrates by molecular beam epitaxy. The size and distribution of the QDs are revealed by atomic force microscopy and characterized by scanning tunnelling electron microscopy, which confirms zinc-blende crystal structure. Magnetometry measurements show the presence of ferromagnetism in the QDs and a very high Curie temperature (>300 K). Magnetic circular dichroism spectra of these QDs exhibit a single peak at 900–1000 nm. These results suggest that the Fe-doped InAs QDs are promising for spintronics device applications such as spin-light emitting diodes operating at room temparture.