| 1. |
- Guziewicz, E., et al.
(författare)
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Synchrotron photoemission study of (Zn,Co)O films with uniform Co distribution
- 2011
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X. ; 80:10, s. 1046-1050
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Konferensbidrag (refereegranskat)abstract
- We present results of a resonant photoemission study of (Zn,Co)O films with Co content between 2% and 7%. The films were grown by Atomic Layer Deposition (ALD) at low temperature of 160 degrees C and show fully paramagnetic behavior. The Co ions are uniformly distributed in the ZnO matrix and are free of foreign phases and metal accumulations as indicated by TEM data. The electronic structure of (Zn,Co)O films was studied by Resonant Photoemission Spectroscopy across the Co3p-Co3d photoionization threshold. We have observed that the resonant enhancement of the photoemission intensity from the Co3d shell is not the same for samples with different cobalt content. We suggest that the Co3d contribution to the valence band depends on both Co and H content. (C) 2011 Elsevier Ltd. All rights reserved.
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| 2. |
- Racka, K., et al.
(författare)
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Growth of SiC by PVT method in the presence of cerium dopant
- 2013
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 377, s. 88-95
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the presence of CeO2 in the source material on the properties of SiC crystals grown by Physical Vapor Transport (PVT) method is investigated. The doping efficiency and, indirectly, the presence of the cerium vapour in the growth atmosphere were examined by study of structural, electrical and optical properties of the crystals. X-ray photoelectron spectroscopy shows that Ce2O3 and CeO2 coexist on the SiC post-growth surfaces. A detectable Ce incorporation is observed only in the last grown part of the crystal.
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| 3. |
- 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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| 4. |
- Lawniczak-Jablonska, K., et al.
(författare)
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The ratio of interstitial to substitutional site occupation by Mn atoms in GaAs estimated by EXAFS
- 2009
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X. ; 78, s. 80-85
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Konferensbidrag (refereegranskat)abstract
- The location of Mn atoms in the MBE-grown layers of Ga1-xMnxAs is correlated with all important physical properties of the final material, therefore, it is the subject of many studies. It is known that in the as-grown MBE samples the Mn atoms occupy substitutional and interstitial positions but the proportion between these sites is not easy to find. A powerful tool for this kind of study is XAS as it probes the local atomic order and the electronic structure. The EXAFS data analysis was performed considering superposition of possible Mn locations. This allowed for determination of the distribution of Mn between those two lattice sites. (C) 2009 Elsevier Ltd. All rights reserved.
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| 5. |
- Levchenko, K., et al.
(författare)
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Evidence for the homogeneous ferromagnetic phase in (Ga, Mn) (Bi, As) epitaxial layers from muon spin relaxation spectroscopy
- 2019
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 9, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- Ferromagnetic semiconductor thin layers of the quaternary (Ga,Mn)(Bi,As) and reference, ternary (Ga, Mn) As compounds, epitaxially grown under either compressive or tensile strain, have been characterized from a perspective of structural and magnetization homogeneity. The quality and composition of the layers have been confirmed by secondary-ion mass spectrometry (SIMS). A thorough evaluation of the magnetic properties as a function of temperature and applied magnetic field has been performed by means of SQUID magnetometry and low-energy muon spin relaxation (mu SR) spectroscopy, which enables studying local (on the nanometer scale) magnetic properties of the layers. The results testify that the ferromagnetic order builds up almost homogeneously below the Curie temperature in the full volume fraction of both the (Ga, Mn) As and (Ga, Mn)(Bi, As) layers. Incorporation of a small amount of heavy Bi atoms into (Ga, Mn) As, which distinctly enhances the strength of spin-orbit coupling in the quaternary (Ga, Mn)(Bi, As) layers, does not deteriorate noticeably their magnetic properties.
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| 6. |
- Polley, C. M., et al.
(författare)
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Observation of surface states on heavily indium-doped SnTe(111), a superconducting topological crystalline insulator
- 2016
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 93:7
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Tidskriftsartikel (refereegranskat)abstract
- The topological crystalline insulator tin telluride is known to host superconductivity when doped with indium (Sn1-xInxTe), and for low indium content (x=0.04) it is known that the topological surface states are preserved. Here we present the growth, characterization, and angle resolved photoemission spectroscopy analysis of samples with much heavier In doping (up to x≈0.4), a regime where the superconducting temperature is increased nearly fourfold. We demonstrate that despite strong p-type doping, Dirac-like surface states persist.
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| 7. |
- Romanowski, P., et al.
(författare)
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Defect Structure of High-Temperature-Grown GaMnSb/GaSb
- 2010
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Ingår i: Acta Physica Polonica A. - 0587-4246. ; 117:2, s. 341-343
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Konferensbidrag (refereegranskat)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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| 8. |
- Sawicki, M., et al.
(författare)
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Homogeneous and heterogeneous magnetism in (Zn,Co)O : From a random antiferromagnet to a dipolar superferromagnet by changing the growth temperature
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:8
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Tidskriftsartikel (refereegranskat)abstract
- A series of (Zn,Co)O layers with Co contents x up to 40% grown by atomic layer deposition have been investigated. All structures deposited at 160 degrees C show magnetic properties specific to II-VI dilute magnetic semiconductors with localized spins S = 3/2 coupled by strong but short-range antiferromagnetic interactions resulting in low-temperature spin-glass freezing for x = 0.16 and 0.4. At higher growth temperature (200 degrees C) metallic Co nanocrystals precipitate in two locations giving rise to two different magnetic responses: (i) a superparamagnetic contribution coming from volume disperse nanocrystals; (ii) a ferromagneticlike behavior brought about by nanocrystals residing at the (Zn,Co)O/substrate interface. It is shown that the dipolar coupling within the interfacial two-dimensional dense dispersion of nanocrystals is responsible for the ferromagneticlike behavior.
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| 9. |
- Strupinski, W., et al.
(författare)
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MOVPE strain layers - growth and application
- 2000
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Ingår i: Journal of Crystal Growth. ; 221, s. 20-25
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Tidskriftsartikel (refereegranskat)abstract
- The critical thickness, characteristic for the lattice-mismatch parameter, plays a key role in the growth of strain layers. The driving force for the 2D-3D transition can be minimized by slowing the relaxation of misfit strain. As a result the relatively smooth layer is deposited at lower temperature for the optimal growth rate. The quality of the InGaAs- and AlAs-strained layers deposited on InP substrate have been examined by the XRD, AFM and SIMS methods. Atomic force microscopy allows to observe 3D growth mode even for very thin layers. Relatively strong relaxation effects are recognized by surface roughness. Two-dimensional di!raction measurement is a much more sensitive tool for the estimation of relaxation degree. The observations results were applied in the heterostructure barrier varactor (HBV) diode. In order to minimize the conduction current through HBV two materials with different design of the barriers were studied: one heterostructure with three homogeneous lattice matched barriers consisting of 20nm Al0.48In0.52As and another one with strained step-like barriers consisting of 5 nm Al0.48In0.52As, 3 nm AlAs and 5 nm Al0.48In0.52As. We found that the use of strained step-like barriers results in a much lower conduction current. For current density
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| 10. |
- Wolska, A., et al.
(författare)
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XANES studies of Mn K and L-3,L-2 edges in the (Ga,Mn) As layers modified by high temperature annealing
- 2008
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Ingår i: Acta Physica Polonica. A. - 0587-4246 .- 1898-794X. ; 114:2, s. 357-366
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Tidskriftsartikel (refereegranskat)abstract
- Ga1-xMnx As is commonly considered as a promising material for microelectronic applications utilizing the electron spin. One of the ways that allow increasing the Curie temperature above room temperature is to produce second phase inclusions. In this paper Gal-,Mn.As samples containing precipitations of ferromagnetic MnAs are under consideration. We focus on the atomic and electronic structure around the Mn atoms relating to the cluster formation. The changes in the electronic structure of the Mn, Ga and As atoms in the (Ga,Mn)As layers after high temperature annealing were determined by X-ray absorption near edge spectroscopy. The experimental spectra were compared with the predictions of ab initio full multiple scattering theory using the FEFF 8.4 code. The nominal concentration of the Mn atoms in the investigated samples was 6% and 8%. We do not observe changes in the electronic structure of Ca and As introduced by the presence of the Mn atoms. We find, in contrast, considerable changes in the electronic structure around the Mn atoms. Moreover, for the first time it was possible to indicate the preferred interstitial positions of the Mn atoms.
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