The (In,Fe)Sb layers with the Fe content up to 13 at. % have been grown on
(001) GaAs substrates using the pulsed laser deposition. The TEM investigations
show that the (In,Fe)Sb layers are epitaxial and free of the inclusions of a
second phase. The observation of the hysteretic magnetoresistance curves at
temperatures up to 300 K reveals that the Curie point is above room
temperature. The resonant character of magnetic circular dichroism confirms the
intrinsic ferromagnetism in the (In,Fe)Sb layers. We suggest that the
ferromagnetism of the (In,Fe)Sb matrix is not carrier-mediated and apparently
is determined by the mechanism of superexchange interaction between Fe atoms
(This work was presented at the XXI Symposium Nanophysics and Nanoelectronics,
Nizhny Novgorod, March, 13-16, 2017 (book of proceedings v.1, p. 195),
http://nanosymp.ru/UserFiles/Symp/2017_v1.pdf)
The layers of a high-temperature novel GaAs:Fe diluted magnetic semiconductor (DMS) with an average Fe content up to 20 at. % were grown on (001) i-GaAs substrates using a pulsed laser deposition in a vacuum. The transmission electron microscopy (TEM) and energy-dispersive x-ray spectroscopy investigations revealed that the conductive layers obtained at 180 and 200 ºC are epitaxial, do not contain any second-phase inclusions, but contain the Fe-enriched columnar regions of overlapped microtwins. The TEM investigations of the non-conductive layer obtained at 250 ºC revealed the embedded coherent Fe-rich clusters of GaAs:Fe DMS. The x-ray photoelectron spectroscopy investigations showed that Fe atoms form chemical bonds with Ga and As atoms with almost equal probability and thus the comparable number of Fe atoms substitute on Ga and As sites. The n-type conductivity of the obtained conductive GaAs:Fe layers is apparently associated with electron transport in a Fe acceptor impurity band within the GaAs band gap. A hysteretic negative magnetoresistance (MR) was observed in the conductive layers up to room temperature (RT). MR measurements point to the out-of-plane magnetic anisotropy of the conductive GaAs:Fe layers related to the presence of the columnar regions. The studies of the magnetic circular dichroism confirm that the layers obtained at 180, 200 and 250 ºC are intrinsic ferromagnetic semiconductors and the Curie point can reach up to at least RT in case of the conductive layer obtained at 200 ºC. It was suggested that in heavily Fe-doped GaAs layers the ferromagnetism is related to the Zener double exchange between Fe atoms with different valence states via an intermediate As and Ga atom.
The influence of He + ion irradiation on the transport and magnetic properties of epitaxial layers of a diluted magnetic semiconductor (DMS) (In,Fe)Sb, a two-phase (In,Fe)Sb composite and a nominally undoped InSb semiconductor has been investigated. In all layers, a conductivity type conversion from the initial n-type to the ptype has been found. The ion fluence at which the conversion occurs depends on the Fe concentration in the InSb matrix. Magnetotransport properties of the two-phase (In,Fe)Sb layer are strongly affected by ferromagnetic Fe inclusions. An influence of the number of electrically active radiation defects on the magnetic properties of the single-phase In 0.75 Fe 0.25 Sb DMS has been found. At the same time, the results show that the magnetic properties of the In 0.75 Fe 0.25 Sb DMS are quite resistant to significant changes of the charge carrier concentration and the Fermi level position. The results confirm a weak interrelation between the ferromagnetism and the charge carrier concentration in (In,Fe)Sb.
A new method for creating nanomaterials based on gallium oxide by ion-beam synthesis of nanocrystals of this compound in a SiO2/Si dielectric matrix has been proposed. The influence of the order of irradiation with ions of phase-forming elements (gallium and oxygen) on the chemical composition of implanted layers is reported. The separation of gallium profiles in the elemental and oxidized states is shown, even in the absence of post-implantation annealing. As a result of annealing, blue photoluminescence, associated with the recombination of donor–acceptor pairs (DAP) in Ga2O3 nanocrystals, appears in the spectrum. The structural characterization by transmission electron microscopy confirms the formation of β-Ga2O3 nanocrystals. The obtained results open up the possibility of using nanocrystalline gallium oxide inclusions in traditional CMOS technology.
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