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Register a new userThe formation of epitaxial p-i-n structures on the basis of (In,Fe)Sb and (Ga,Fe)Sb layers
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Multilayer structures on the basis of n-type (In,Fe)Sb and p-type (Ga,Fe)Sb diluted magnetic semiconductors (DMS) along with separate (In,Fe)Sb and (Ga,Fe)Sb layers were fabricated on GaAs substrates by pulsed laser sputtering of InSb, GaAs, GaSb, Sb and Fe targets in a vacuum. Transmission electron microscopy and energy-dispersive x-ray spectroscopy reveal a strong dependence of the phase composition of the (In,Fe)Sb compound on the growth temperature. An increase of the latter from 220C to 300C leads to a coalescence of Fe atoms and formation of a secondary crystalline phase in the (In,Fe)Sb layer with a total Fe content of ca. 10 at. %. At the same time, the Ga0.8Fe0.2Sb layers obtained at 220C and 300C are single-phase. The separate In0.8Fe0.2Sb and Ga0.8Fe0.2Sb layers grown on i-GaAs at 220C are DMS with Curie temperatures of ca. 190 K and 170 K, respectively. The three-layer p-i-n diode (In,Fe)Sb/GaAs/(Ga,Fe)Sb structure grown on a GaAs substrate at 220C with a Fe content of ca. 10 at. % in the single-phase (In,Fe)Sb and (Ga,Fe)Sb layers has a rather high crystalline quality and can be considered as a prototype of a bipolar spintronic device based on Fe-doped III-V semiconductors.
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(Ga,Fe)Sb is a promising ferromagnetic semiconductor for practical spintronic device applications because its Curie temperature ($T_{rm C}$) is above room temperature. However, the origin of ferromagnetism with high $T_{rm C}$ remains to be elucidated. Here, we use soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) to investigate the valence-band (VB) structure of (Ga$_{0.95}$,Fe$_{0.05}$)Sb including the Fe-3$d$ impurity band (IB), to unveil the mechanism of ferromagnetism in (Ga,Fe)Sb. We find that the VB dispersion in (Ga$_{0.95}$,Fe$_{0.05}$)Sb observed by SX-ARPES is similar to that of GaSb, indicating that the doped Fe atoms hardly affect the band dispersion. The Fe-3$d$ resonant ARPES spectra demonstrate that the Fe-3$d$ IB crosses the Fermi level ($E_{rm F}$) and hybridizes with the VB of GaSb. These observations indicate that the VB structure of (Ga$_{0.95}$,Fe$_{0.05}$)Sb is consistent with that of the IB model which is based on double-exchange interaction between the localized 3$d$ electrons of the magnetic impurities. The results indicate that the ferromagnetism in (Ga,Fe)Sb is formed by the hybridization of the Fe-3$d$ IB with the ligand $p$ band of GaSb.
Magnetooptical properties of (Ga,Mn)N layers containing various concentrations of Fe-rich nanocrystals embedded in paramagnetic (Ga,Fe)N layers are reported. Previous studies of such samples demonstrated that magnetization consists of a paramagnetic contribution due to substitutional diluted Fe ions as well as of ferromagnetic and antiferromagnetic components originating from Fe-rich nanocrystals, whose relative abundance can be controlled by the grow conditions. The nanocrystals are found to broaden and to reduce the magnitude of the excitonic features. However, the ferromagnetic contribution, clearly seen in SQUID magnetometry, is not revealed by magnetic circular dichroism (MCD). Possible reasons for differences in magnetic response determined by MCD and SQUID measurements are discussed.
(Ga$_{1-x}$,Fe$_x$)Sb is one of the promising ferromagnetic semiconductors for spintronic device applications because its Curie temperature ($T_{rm C}$) is above 300 K when the Fe concentration $x$ is equal to or higher than ~0.20. However, the origin of the high $T_{rm C}$ in (Ga,Fe)Sb remains to be elucidated. To address this issue, we use resonant photoemission spectroscopy (RPES) and first-principles calculations to investigate the $x$ dependence of the Fe 3$d$ states in (Ga$_{1-x}$,Fe$_x$)Sb ($x$ = 0.05, 0.15, and 0.25) thin films. The observed Fe 2$p$-3$d$ RPES spectra reveal that the Fe-3$d$ impurity band (IB) crossing the Fermi level becomes broader with increasing $x$, which is qualitatively consistent with the picture of double-exchange interaction. Comparison between the obtained Fe-3$d$ partial density of states and the first-principles calculations suggests that the Fe-3$d$ IB originates from the minority-spin ($downarrow$) $e$ states. The results indicate that enhancement of the interaction between $e_downarrow$ electrons with increasing $x$ is the origin of the high $T_{rm C}$ in (Ga,Fe)Sb.
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).
We present high-temperature ferromagnetism and large magnetic anisotropy in heavily Fe-doped n-type ferromagnetic semiconductor (In1-x,Fex)Sb (x = 20 - 35%) thin films grown by low-temperature molecular beam epitaxy. The (In1-x,Fex)Sb thin films with x = 20 - 35% maintain the zinc-blende crystal and band structure with single-phase ferromagnetism. The Curie temperature (TC) of (In1-x,Fex)Sb reaches 390 K at x = 35%, which is significantly higher than room temperature and the highest value so far reported in III-V based ferromagnetic semiconductors. Moreover, large coercive force (HC = 160 Oe) and large remanent magnetization (Mr/MS = 71%) have been observed for a (In1-x,Fex)Sb thin film with x = 35%. Our results indicate that the n-type ferromagnetic semiconductor (In1-x,Fex)Sb is very promising for spintronics devices operating at room temperature.
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