| 1. |
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| 2. |
- Bak-Misiuk, J., et al.
(author)
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Creation of MnAs nanoclusters during processing of GaMnAs
- 2009
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In: Radiation Physics And Chemistry. - : Elsevier BV. - 0969-806X. ; 78, s. 116-119
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Conference paper (peer-reviewed)abstract
- GaMnAs layers on (0 0 1)-oriented GaAs substrates were grown by the molecular beam epitaxy (MBE) method. Structural properties of samples processed at up to 920 K under hydrostatic Ar pressure up to 1.1 GPa were investigated by X-ray, secondary ion mass spectroscopy and atomic force microscopy methods. The sign of strain (compressive or tensile) of the GaMnAs layers, related to a creation of MnAs nanoclusters, is found to be dependent on processing conditions and on primary structure defects, whereas it was independent of Mn concentration. An influence of the defects structure in as-grown samples on the strain state of processed GaMnAs layers is discussed. (C) 2009 Elsevier Ltd. All rights reserved.
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| 3. |
- Dynowska, E., et al.
(author)
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Structural and magnetic properties of GaSb:MnSb granular layers
- 2011
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In: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X. ; 80:10, s. 1051-1057
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Conference paper (peer-reviewed)abstract
- The results of structural and magnetic characterization of GaMnSb layers grown on GaSb(0 0 1) and GaAs(1 1 1) substrates are presented. The presence of hexagonal, highly oriented MnSb inclusions embedded in GaSb matrix has been demonstrated. The lattice parameters of these inclusions were the same as those for bulk MnSb for the layers grown on GaSb(1 0 0) substrate while for the layers grown on GaAs(1 1 1) the MnSb inclusions were strained. The influence of a presence of MnSb clusters on the lattice parameter of GaSb matrix has been demonstrated. It was confirmed that in all cases the MnSb clusters exhibit a ferromagnetic: behavior at room temperature. (C) 2011 Elsevier Ltd. All rights reserved.
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| 4. |
- Gluba, L., et al.
(author)
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Band structure evolution and the origin of magnetism in (Ga,Mn) As : From paramagnetic through superparamagnetic to ferromagnetic phase
- 2018
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 97:11
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Journal article (peer-reviewed)abstract
- The high-spectral-resolution optical studies of the energy gap evolution, supplemented with electronic, magnetic, and structural characterization, show that the modification of the GaAs valence band caused by Mn incorporation occurs already for a very low Mn content, much lower than that required to support ferromagnetic spin-spin coupling in (Ga,Mn) As. Only for n-type (Ga,Mn) As with the Mn content below about 0.3% the Mn-related extended states are visible as a feature detached from the valence-band edge and partly occupied with electrons. The combined magnetic and low-temperature photoreflectance studies presented here indicate that the paramagnetic <-> ferromagnetic transformation in p-type (Ga,Mn) As takes place without imposing changes of the unitary character of the valence band with the Fermi level located therein. The whole process is rooted in the nanoscale fluctuations of the local (hole) density of states and the formation of a superparamagnetic-like state. The Fermi level in (Ga,Mn) As is coarsened by the carrier concentration of the itinerant valence band holes and further fine-tuned by the many-body interactions.
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| 5. |
- Lankinen, A., et al.
(author)
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Crystal Defects and Strain of Epitaxial InP Layers Laterally Overgrown on Si
- 2006
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In: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 6:5, s. 1096-1100
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Journal article (peer-reviewed)abstract
- Defects in epitaxial laterally overgrown (ELO) InP layers are examined by high-resolution X-ray diffraction and synchrotron X-ray back-reflection and transmission topography. X-ray diffraction maps produce information about the overall crystal quality of the epitaxial layers in the InP ELO sample. The topographs show small angle boundaries, and the associated dislocations are located at the boundaries between the crystallites; allowing for their relative tilt, the maximum value for this is 0.06 degrees. No defects inside the crystallites can be seen in the topographs, except for a small bending of 0.04 degrees at most, of the ELO lattice planes. The section topographs show deformed X-ray interference fringes resulting from the large strain of the silicon lattice below the seeding areas.
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| 6. |
- Lawniczak-Jablonska, K., et al.
(author)
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Structural and magnetic properties of GaAs:(Mn,Ga)As granular layers
- 2011
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In: Physica Status Solidi. B: Basic Research. - : Wiley. - 0370-1972. ; 248:7, s. 1609-1614
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Journal article (peer-reviewed)abstract
- Granular GaAs:(Mn,Ga)As films were prepared by annealing the Ga0.92Mn0.08As/GaAs layer grown by the MBE method at low temperature. The annealing was performed at 500 or 600 degrees C. It is commonly accepted that this processing should result in formation of cubic zinc blende or hexagonal MnAs inclusions depending on the temperature. We demonstrate that such a priory assumption is not justified. The kind of formed inclusions depends not only on the annealing temperature but also on the number of defects and Mn atoms in the substitutional and interstitial positions in as grown sample. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 7. |
- Lawniczak-Jablonska, K., et al.
(author)
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Structural and magnetic properties of nanoclusters in GaMnAs granular layers
- 2011
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In: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596. ; 184:6, s. 1530-1539
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Journal article (peer-reviewed)abstract
- Structural and magnetic properties of GaAs thin films with embedded nanoclusters were investigated as a function of the annealing temperature and Mn content. Surprisingly, the presence of two kinds of nanoclusters with different structure was detected in most of the samples independently of the thermal processing or Mn content. This proved that the presence of a given type of clusters cannot be assumed a priori as is reported in many papers. The fraction of Mn atoms in each kind of cluster was estimated from the extended X-ray absorption fine structure analysis. This analysis ruled out the possibility of the existence of nanoclusters containing a hypothetic MnAs cubic compound-only (Ga,Mn)As cubic and hexagonal MnAs clusters were detected. Moreover the bimodal distribution of Mn magnetic moments was found, which scales with the estimated fraction of Mn atoms in the cubic and hexagonal clusters. (C) 2011 Elsevier Inc. All rights reserved.
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| 8. |
- Levchenko, K., et al.
(author)
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Effect of misfit strain in (Ga,Mn)(Bi,As) epitaxial layers on their magnetic and magneto-transport properties
- 2016
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In: Acta Physica Polonica. Series A: General Physics, Physics of Condensed Matter, Optics and Quantum Electronics, Atomic and Molecular Physics, Applied Physics. - 0587-4246. ; 129:1, s. 90-93
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Journal article (peer-reviewed)abstract
- Effect of misfit strain in the layers of (Ga,Mn)(Bi,As) quaternary diluted magnetic semiconductor, epitaxially grown on either GaAs substrate or (In,Ga)As buffer, on their magnetic and magneto-transport properties has been investigated. High-resolution X-ray diffraction, applied to characterize the structural quality and misfit strain in the layers, proved that the layers were fully strained to the GaAs substrate or (In,Ga)As buffer under compressive or tensile strain, respectively. Ferromagnetic Curie temperature and magneto-crystalline anisotropy of the layers have been examined by using magneto-optical Kerr effect magnetometry and low-temperature magneto-transport measurements. Post-growth annealing treatment of the layers has been shown to enhance the hole concentration and the Curie temperature in the layers.
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| 9. |
- Levchenko, K., et al.
(author)
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Impact of bismuth incorporation into (Ga,Mn)As thin films on their structural and magnetic properties
- 2015
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In: Physica Status Solidi C. - : Wiley. - 1610-1642 .- 1862-6351. ; 12:8, s. 1152-1155
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Conference paper (peer-reviewed)abstract
- Structural and magnetic properties of thin films of the (Ga,Mn)(Bi,As) quaternary diluted magnetic semiconductor grown by the low-temperature molecular-beam epitaxy technique on GaAs substrates have been investigated. High-resolution X-ray diffraction has been applied to characterize the structural quality and misfit strain in the films. Ferromagnetic Curie temperature and magnetocrystalline anisotropy of the films have been examined by using SQUID magnetometry and low-temperature magneto-transport measurements. Post-growth annealing treatment of the films has been shown to reduce the strain in the films and to enhance their Curie temperature. Significant increase in the magnitude of magneto-transport effects caused by incorporation of a small amount of Bi into the films is interpreted as a result of enhanced spinorbit coupling in the (Ga, Mn)(Bi, As) films. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 10. |
- Levchenko, K., et al.
(author)
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Magnetic and Magneto-Transport Characterization of (Ga,Mn)(Bi,As) Epitaxial Layers
- 2014
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In: Acta Physica Polonica. Series A: General Physics, Physics of Condensed Matter, Optics and Quantum Electronics, Atomic and Molecular Physics, Applied Physics. - 0587-4246. ; 126:5, s. 1121-1124
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Journal article (peer-reviewed)abstract
- High-quality layers of the (Ga,Mn)(Bi,As) quaternary compound semiconductor have been grown by the low-temperature molecular-beam epitaxy technique. An effect of Si incorporation into the (Ga,Mn)As ferromagnetic semiconductor and the post-growth annealing treatment of the layers have been investigated through examination of their magnetic and magneto-transport properties. Significant enhancement of the planar Hall effect magnitude upon addition of Si into the layers is interpreted as a result of increased spin orbit coupling in the (Ga,Mn)(Bi,As) layers.
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| 11. |
- Levchenko, K., et al.
(author)
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Novel Quaternary Dilute Magnetic Semiconductor (Ga,Mn)(Bi,As) : Magnetic and Magneto-Transport Investigations
- 2017
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In: Journal of Superconductivity and Novel Magnetism. - : Springer Science and Business Media LLC. - 1557-1939 .- 1557-1947. ; 30:3, s. 825-829
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Journal article (peer-reviewed)abstract
- Magnetic and magneto-transport properties of thin layers of the (Ga,Mn)(Bi,As) quaternary dilute magnetic semiconductor grown by the low-temperature molecular-beam epitaxy technique on GaAs substrates have been investigated. Ferromagnetic Curie temperature and magneto-crystalline anisotropy of the layers have been examined by using magneto-optical Kerr effect magnetometry and low-temperature magneto-transport measurements. Post-growth annealing treatment of the layers has been shown to enhance the hole concentration and Curie temperature in the layers. A significant increase in the magnitude of magneto-transport effects caused by incorporation of a small amount of Bi into the (Ga,Mn)As layers, revealed in the planar Hall effect (PHE) measurements, is interpreted as a result of enhanced spin-orbit coupling in the (Ga,Mn)(Bi,As) layers. A two-state behaviour of the planar Hall resistance at zero magnetic field provides its usefulness for applications in non-volatile memory devices.
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| 12. |
- Polley, Craig, et al.
(author)
-
Observation of topological crystalline insulator surface states on (111)-oriented Pb1-xSnxSe films
- 2014
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:7, s. 075317-
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Journal article (peer-reviewed)abstract
- We present angle-resolved photoemission spectroscopy measurements of the surface states on in-situ grown (111) oriented films of Pb1-xSnxSe, a three-dimensional topological crystalline insulator. We observe surface states with Dirac-like dispersion at (Gamma) over bar and (M) over bar in the surface Brillouin zone, supporting recent theoretical predictions for this family of materials. We study the parallel dispersion isotropy and Dirac-point binding energy of the surface states, and perform tight-binding calculations to support our findings. The relative simplicity of the growth technique is encouraging, and suggests a clear path for future investigations into the role of strain, vicinality, and alternative surface orientations in (Pb,Sn)Se solid solutions.
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| 13. |
- Romanowski, P., et al.
(author)
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Defect Structure of High-Temperature-Grown GaMnSb/GaSb
- 2010
-
In: Acta Physica Polonica A. - 0587-4246. ; 117:2, s. 341-343
-
Conference paper (peer-reviewed)abstract
- GaMnSb/GaSb(100) layers with embedded MnSb inclusions have been grown at 720 K using MBE technique. This paper presents the investigation of the defect structure of Ga1-xMnxSb layers with different content of manganese (up to x = 0.07). X-ray diffraction method using conventional and synchrotron radiation was applied. Dimensions and shapes of inclusions were detected by scanning electron microscopy. Depth profiles of elements were measured using secondary ion mass spectroscopy technique.
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| 14. |
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| 15. |
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| 16. |
- Sadowski, J., et al.
(author)
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Structural and magnetic properties of molecular beam epitaxy grown GaMnAs layers
- 2000
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In: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 18:3, s. 1697-1700
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Journal article (peer-reviewed)abstract
- GaMnAs layers with Mn contents from 0.05% to 7% were grown by low temperature molecular beam epitaxy. At substrate temperatures lower than 300 degrees C and in this composition range a uniform ternary GaMnAs compound can be grown without MnAs precipitation. Reflection high energy electron diffraction intensity oscillations recorded during GaMnAs growth were used to calibrate the composition of the GaMnAs films with high accuracy (better than 0.1%). Films containing more than 1% Mn exhibit a ferromagnetic phase transition with Curie temperatures from a few up to 70 K depending on the composition and other growth parameters. In contrast to previous reports we have observed this transition also in the case of layers grown at very low substrate temperatures (below 300 degrees C).
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| 17. |
- Sawicki, M., et al.
(author)
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Cubic anisotropy in (Ga,Mn) As layers : Experiment and theory
- 2018
-
In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 97:18
-
Journal article (peer-reviewed)abstract
- Historically, comprehensive studies of dilute ferromagnetic semiconductors, e.g., p-type (Cd,Mn) Te and (Ga,Mn) As, paved the way for a quantitative theoretical description of effects associated with spin-orbit interactions in solids, such as crystalline magnetic anisotropy. In particular, the theory was successful in explaining uniaxial magnetic anisotropies associated with biaxial strain and nonrandom formation of magnetic dimers in epitaxial (Ga,Mn) As layers. However, the situation appears much less settled in the case of the cubic term: the theory predicts switchings of the easy axis between in-plane < 100 > and < 110 > directions as a function of the hole concentration, whereas only the < 100 > orientation has been found experimentally. Here, we report on the observation of such switchings by magnetization and ferromagnetic resonance studies on a series of high-crystalline quality (Ga,Mn) As films. We describe our findings by themean-field p-d Zener model augmented with three new ingredients. The first one is a scattering broadening of the hole density of states, which reduces significantly the amplitude of the alternating carrier-induced contribution. This opens the way for the two other ingredients, namely the so-far disregarded single-ion magnetic anisotropy and disorder-driven nonuniformities of the carrier density, both favoring the < 100 > direction of the apparent easy axis. However, according to our results, when the disorder gets reduced, a switching to the < 110 > orientation is possible in a certain temperature and hole concentration range.
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| 18. |
- Yastrubchak, O., et al.
(author)
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Effect of low-temperature annealing on the electronic- and band-structures of (Ga,Mn) As epitaxial layers
- 2014
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In: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 115:1
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Journal article (peer-reviewed)abstract
- The effect of outdiffusion of Mn interstitials from (Ga,Mn) As epitaxial layers, caused by post-growth low-temperature annealing, on their electronic- and band-structure properties has been investigated by modulation photoreflectance (PR) spectroscopy. The annealing-induced changes in structural and magnetic properties of the layers were examined with high-resolution X-ray diffractometry and superconducting quantum interference device magnetometry, respectively. They confirmed an outdiffusion of Mn interstitials from the layers and an enhancement in their hole concentration, which were more efficient for the layer covered with a Sb cap acting as a sink for diffusing Mn interstitials. The PR results demonstrating a decrease in the band-gap-transition energy in the as-grown (Ga,Mn) As layers, with respect to that in the reference GaAs one, are interpreted by assuming a merging of the Mn-related impurity band with the GaAs valence band. Whereas an increase in the band-gap-transition energy caused by the annealing treatment of the (Ga,Mn) As layers is interpreted as a result of annealing-induced enhancement of the free-hole concentration and the Fermi level location within the valence band. The experimental results are consistent with the valence-band origin of itinerant holes mediating ferromagnetic ordering in (Ga,Mn) As, in agreement with the Zener model for ferromagnetic semiconductors. (C) 2014 AIP Publishing LLC.
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| 19. |
- Yastrubchak, O., et al.
(author)
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Ferromagnetism and the electronic band structure in (Ga,Mn)(Bi,As) epitaxial layers
- 2014
-
In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:7
-
Journal article (peer-reviewed)abstract
- Impact of Bi incorporation into (Ga,Mn)As layers on their electronic-and band-structures as well as their magnetic and structural properties has been studied. Homogenous (Ga,Mn)(Bi,As) layers of high structural perfection have been grown by the low-temperature molecular-beam epitaxy technique. Post-growth annealing treatment of the layers results in an improvement of their structural and magnetic properties and an increase in the hole concentration in the layers. The modulation photoreflectance spectroscopy results are consistent with the valence-band model of hole-mediated ferromagnetism in the layers. This material combines the properties of (Ga,Mn)As and Ga(Bi,As) ternary compounds and offers the possibility of tuning its electrical and magnetic properties by controlling the alloy composition. (C) 2014 AIP Publishing LLC.
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| 20. |
- Yastrubchak, O., et al.
(author)
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Influence of Ion Implantation on Magnetic, Structural and Optical Properties of (Ga,Mn)As Epitaxial Films
- 2008
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In: ACTA PHYSICA POLONICA A. - 0587-4246. ; 114:5, s. 1445-1450
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Conference paper (peer-reviewed)abstract
- We performed implantation experiments; applying both the chemically active oxygen ions and inactive ions of neon noble gas, to thin epitaxial films of (Ga,Mn)As ferromagnetic semiconductor. Inspection of their magnetic properties by means of a superconducting quantum interference device magnetometer revealed that the implantation with a low dose of either O or Ne ions completely suppressed ferromagnetism in the films. Both the high resolution X-ray diffraction technique and the Raman spectroscopy showed significant changes in the structural and optical properties of the films caused by oxygen and neon implantation.
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| 21. |
- Yastrubchak, O., et al.
(author)
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Ion-Implantation Control of Ferromagnetism in (Ga,Mn)As Epitaxial Layers
- 2010
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In: Journal Of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 39:6, s. 794-798
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Conference paper (peer-reviewed)abstract
- Epitaxial layers of (Ga,Mn)As ferromagnetic semiconductor have been subjected to low-energy ion implantation by applying a very low fluence of either chemically active, oxygen ions or inactive ions of neon noble gas. Several complementary characterization techniques have been used with the aim of studying the effect of ion implantation on the layer properties. Investigation of their electrical and magnetic properties revealed that implantation with either O or Ne ions completely suppressed both the conductivity and ferromagnetism in the layers. On the other hand, Raman spectroscopy measurements evidenced that O ion implantation influenced optical properties of the layers noticeably stronger than did Ne ion implantation. Moreover, structural modifications of the layers caused by ion implantation were investigated using high-resolution x-ray diffraction technique. A mechanism responsible for ion-implantation-induced suppression of the conductivity and ferromagnetism in (Ga,Mn)As layers, which could be applied as a method for tailoring nanostructures in the layers, is discussed in terms of defects created in the layers by the two implanted elements.
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| 22. |
- Yastrubchak, O., et al.
(author)
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Photoreflectance study of the fundamental optical properties of (Ga,Mn) As epitaxial films
- 2011
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 83:24
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Journal article (peer-reviewed)abstract
- Fundamental optical properties of thin films of the (Ga,Mn) As diluted ferromagnetic semiconductor with low (1%-2%) and high (4%-6%) Mn content and of a reference GaAs film, grown by low-temperature molecular-beam epitaxy, have been investigated by photoreflectance (PR) spectroscopy. In addition, the films were subjected to complementary characterization by means of superconducting quantum interference device magnetometry, Raman spectroscopy, and high-resolution x-ray diffractometry. Thorough full-line-shape analysis of the PR spectra, which enabled determination of the E-0 electronic transition in (Ga,Mn) As, revealed significant differences between the energy band structures in the vicinity of the Gamma point of the Brillouin zone in the investigated (Ga,Mn) As films. In view of the experimental results obtained, the evolution of the valence band structure in (Ga,Mn) As with increasing Mn content is discussed, pointing to a merging of the Mn-related impurity band with the host GaAs valence band for high Mn content.
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