| 1. |
- Medjanik, K., et al.
(författare)
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Site-specific atomic order and band structure tailoring in the diluted magnetic semiconductor (In,Ga,Mn)As
- 2021
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 103:7
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Tidskriftsartikel (refereegranskat)abstract
- Diluted ferromagnetic semiconductors combining ferromagnetic and semiconducting properties in one material provide numerous new functionalities, attractive for basic studies and potentially useful for novel device applications. The tailoring of the electronic structure in analogy to conventional semiconductors has yet to be explored. Here, we demonstrate the conservation of broken inversion symmetry and band structure tailoring for high-quality molecular-beam-epitaxy-grown (In,Ga,Mn)As films with 3% In plus 2.5% or 5.6% Mn using hard-x-ray photoelectron diffraction (hXPD) and momentum microscopy. Photon energies of 3-5 keV ensure that the results are not corrupted by surface effects, which are known to be strong in semiconductors. The missing inversion center of the GaAs host lattice leads to fingerprint-like hXPD signatures of As and Ga sites. For both concentrations, Mn predominantly occupies Ga substitutional sites. Momentum microscopy reveals a shift of the chemical potential with increasing Mn doping and a highly dispersing band, crossing the Fermi level for high Mn concentration. The Mn doping induces a pronounced modification of the spin-orbit split-off band.
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| 2. |
- Gluba, L., et al.
(författare)
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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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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 97:11
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Gluba, L., et al.
(författare)
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On the nature of the Mn-related states in the band structure of (Ga,Mn)As alloys via probing the E-1 and E-1 + Delta(1) optical transitions
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:3
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Tidskriftsartikel (refereegranskat)abstract
- The dilute (Ga,Mn)As became a model ferromagnetic semiconductor, however there is still a disagreement on the source of its magnetism. In this paper, we verify the ellipsometric results and compare them with more precise photoreflectance method, which gives an important insight into the interaction of the Mn-related states with the ones of GaAs valence band. No spectral shifts observed for the E-1 and E-1 + Delta(1) interband transitions in highly doped and annealed (Ga,Mn)As epitaxial layers indicate that the coupling between a detached Mn impurity band and the valence band does not occur. Our findings are supported by the characterizations of the (Ga,Mn)As epitaxial layers with the high resolution transmission electron microscopy and magnetization measurements. (c) 2014 AIP Publishing LLC.
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| 4. |
- Yastrubchak, O., et al.
(författare)
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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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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 115:1
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Yastrubchak, O., et al.
(författare)
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Ferromagnetism and the electronic band structure in (Ga,Mn)(Bi,As) epitaxial layers
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:7
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Yastrubchak, O., et al.
(författare)
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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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Ingår i: ACTA PHYSICA POLONICA A. - 0587-4246. ; 114:5, s. 1445-1450
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Konferensbidrag (refereegranskat)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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| 7. |
- Yastrubchak, O., et al.
(författare)
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Ion-Implantation Control of Ferromagnetism in (Ga,Mn)As Epitaxial Layers
- 2010
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Ingår i: Journal Of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 39:6, s. 794-798
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Konferensbidrag (refereegranskat)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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| 8. |
- Yastrubchak, O., et al.
(författare)
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Photoreflectance study of the fundamental optical properties of (Ga,Mn) As epitaxial films
- 2011
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 83:24
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Tidskriftsartikel (refereegranskat)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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