Growth of Cadmium-Zinc Telluride Crystals by Controlled Seeding Contactless Physical Vapor Transport

Bulk crystals of cadmium-zinc telluride, 23 mm in diameter and up to 45 grams in weight were grown. Controlled seed formation procedure was used to limit the number of grains in the crystal. Most uniform distribution of ZnTe in the crystals was obtained using excess (Cd + Zn) pressure in the ampoule

Characterization of Cadmium-Zinc Telluride Crystals Grown by 'Contactless' PVT Using Synchrotron White Beam Topography

Crystals of Cd(1-x)Zn(x)Te grown by Physical Vapor Transport (PVT) using self-seeding 'contactless' techniques were characterized using synchrotron radiation (reflection, transmission, and Laue back-reflection X-ray topography). Crystals of low (x = 0.04) and high (up to x approx. = 0.4) ZnTe content were investigated. Twins and defects such as dislocations, precipitates, and slip bands were identified. Extensive inhomogeneous strains present in some samples were found to be generated by interaction (sticking) with the pedestal and by composition gradients in the crystals. Large (up to about 5 mm) oval strain fields were observed around some Te precipitates. Low angle grain boundaries were found only in higher ZnTe content (x greater than or equal to 0.2) samples

Fermi level dependence of magnetism and magnetotransport in the magnetic topological insulators Bi2_{2}Te3_{3} and BiSbTe3_{3} containing self-organized MnBi2_{2}Te4_{4} septuple layers

The magnetic coupling mechanisms underlying ferromagnetism and magnetotransport phenomena in magnetically doped topological insulators have been a central issue to gain controlled access to the magneto-topological phenomena such as quantum anomalous Hall effect and topological axion insulating state. Here, we focus on the role of bulk carriers in magnetism of the family of magnetic topological insulators, in which the host material is either Bi$_{2}$Te$_{3}$ or BiSbTe$_{3}$, containing Mn self-organized in MnBi$_{2}$Te$_{4}$ septuple layers. We tune the Fermi level using the electron irradiation technique and study how magnetic properties vary only through the change in carrier density. Ferromagnetic resonance spectroscopy excludes bulk magnetism based on a carrier-mediated process. Furthermore, the magnetotransport measurements show that the anomalous Hall effect is dominated by the intrinsic and dissipationless Berry-phase driven mechanism, with the Hall resistivity enhanced near the bottom/top of the conduction/valence band, due to the Berry curvature which is concentrated near the avoided band crossings. These results demonstrate that the anomalous Hall effect can be effectively managed, maximized, or turned off, by adjusting the Fermi level.Comment: 11 pages, 7 figure

Coexistence of Anomalous Hall Effect and Weak Net Magnetization in Collinear Antiferromagnet MnTe

Anomalous Hall effect (AHE) plays important role in the rapidly developing field of antiferromagnetic spintronics. It has been recently discussed that it can be a feature of not only uncompensated magnetic systems but also in altermagnetic materials. Hexagonal MnTe belongs to this appealing group of compounds exhibiting AHE and is commonly perceived as magnetically compensated. Here, we demonstrate that bulk form of MnTe exhibits small but detectable magnetic moment correlating with hysteretic behaviour of the AHE. We formulate a phenomenological model which explains how this feature allows to create a disbalance between states with opposite N\'eel vector and prevent the AHE signal from averaging out to zero. Moreover, we show how the dependence of AHE on the N\'eel vector arises on microscopical level and highlight the differences in Berry curvature between magnetically compensated and uncompensated systems

Substrates Grown from the Vapor for ZnO Homoepitaxy

The novel method of preparation of epi-ready ZnO substrates is demonstrated. The substrates were made of unique ZnO crystals grown by chemical vapor transport method using hydrogen as the transport agent. The effect of low-level doping (Mn, Co, Cu, and V) on the structural quality of the crystals was investigated. Atomic layer deposition was used to verify usability of the substrates for homoepitaxy. The thermal annealing prior to the atomic layer deposition process and effect of thermal annealing of the epitaxial layers was studied. The X-ray diffraction and atomic force microscopy methods were applied to study the structural quality of the ZnO layers. Detection of the dopants in the substrates by secondary ion mass spectroscopy made possible the measurement of the thickness of the layers. The obtained root mean square roughness for both the substrates and layers ranged between 0.2 nm and 5 nm, and was dependent on the sample crystallographic orientation and sequence of polishing and annealing procedures. The optimal recipe for the epi-ready substrate preparation was formulated

15R-SiC inclusions in 4H- and 6H-SiC crystals grown by the physical vapour transport method

W pracy zaprezentowano wyniki eksperymentów, mających na celu określenie warunków wzrostu kryształów 4H- oraz 6H-SiC wolnych od wtrąceń politypu 15R-SiC. Kryształy SiC otrzymane w procesie krystalizacji metodą transportu fizycznego z fazy gazowej (PVT) zostały zbadane przy użyciu metod badawczych takich jak: dyfrakcja rentgenowska (XRD), dyfrakcja elektronów wstecznie rozproszonych (EBSD), mikroskopia optyczna oraz trawienie chemiczne, pod kątem występowania wtrąceń politypu 15R w strukturach krystalicznych 4H- oraz 6H-SiC. Otrzymane wyniki badań zostały odniesione do parametrów wzrostu tj.: temperatury, ciśnienia, rodzaju materiału wsadowego, oraz jakości i orientacji monokrystalicznego zarodka SiC. Przeprowadzona została dyskusja na temat wpływu warunków wzrostu na powstawanie politypu 15R, z której jednoznacznie wynika, że tworzenie się wtrąceń politypowych 15R w strukturach 4H i 6H wiąże się ze znacznym spadkiem jakości strukturalnej otrzymanych kryształów. Z przeprowadzonych badań wynika, że otrzymanie jednorodnych kryształów politypu 6H i 4H bez wtrąceń 15R-SiC metodą PVT jest trudne ze względu na bardzo szeroki zakres warunków, w których polityp 15R występuje.In this paper the main problems which have to be resolved to obtain 4H- and 6H-SiC crystals free from 15R-SiC inclusions by the physical vapour transport method (PVT) are presented. The resultant SiC crystals have been investigated using various experimental methods such as X-ray diffraction (XRD), electron backscatter diffraction (EBSD), optical microscopy and KOH etching in order to check the quality of the crystal structure and the amount of the 15R-SiC inclusions. The obtained results have been analysed with reference to the following growth conditions: temperature, pressure, type of the SiC source material and the quality of the crystal seed. The investigations have showed that a serious deterioration of the structural quality is unavoidable when the 15R-SiC polytype occurs in hexagonal polytypes such as 4H- and 6H-SiC. Obtaining homogenious 4H-SiC and 6H-SiC crystals without any 15R-SiC inclusions by the PVT method is difficult due to there being a very wide range of conditions in which the 15R-SiC polytype appears

Single-ion anisotropy in Mn-doped diluted magnetic semiconductors

International audienceMotivated by recent developments in spintronics, we propose an explanation of the single-ion anisotropy of Mn-doped diluted magnetic semiconductors using as an example high-quality ZnO:Mn thin films for which X-band electron-paramagnetic-resonance studies were performed. We derive an analytic formula for the axial parameter D and we prove its validity by the exact diagonalization method. We demonstrate a quantitative agreement between the experimental data and our model. These results bring insights into a long-standing problem of single-ion anisotropy in magnetic solids