Structural and paramagnetic properties of dilute Ga1-xMnxN

Systematic investigations of the structural and magnetic properties of single crystal (Ga,Mn)N films grown by metal organic vapor phase epitaxy are presented. High resolution transmission electron microscopy, synchrotron x-ray diffraction, and extended x-ray absorption fine structure studies do not reveal any crystallographic phase separation and indicate that Mn occupies Ga-substitutional sites in the Mn concentration range up to 1%. The magnetic properties as a function of temperature, magnetic field and its orientation with respect to the c-axis of the wurtzite structure can be quantitatively described by the paramagnetic theory of an ensemble of non-interacting Mn$^{3+}$ ions in the relevant crystal field, a conclusion consistent with the x-ray absorption near edge structure analysis. A negligible contribution of Mn in the 2+ charge state points to a low concentration of residual donors in the studied films. Studies on modulation doped p-type (Ga,Mn)N/(Ga,Al)N:Mg heterostructures do not reproduce the high temperature robust ferromagnetism reported recently for this system.Comment: 15 pages, 14 figure

MOVPE InP based material for millimeter and submillimeter wave generation and amplification, Journal of Telecommunications and Information Technology, 2002, nr 1

The potential of the MOVPE growth process for millimeter and submillimeter wave generation and amplification is presented. The increase in layer quality, the improved homogeneity and purity, the precision of mono-layers growth and wide spectrum III-V compounds makes MOVPE techniques very attractive for modern device applications. The characterisation results of the heterostructures dedicated for HBV varactors and 2-DEG transistors (HEMT) are described

Paramagnetic GaN:Fe and ferromagnetic (Ga,Fe)N - relation between structural, electronic, and magnetic properties

We report on the metalorganic chemical vapor deposition (MOCVD) of GaN:Fe and (Ga,Fe)N layers on c-sapphire substrates and their thorough characterization via high-resolution x-ray diffraction (HRXRD), transmission electron microscopy (TEM), spatially-resolved energy dispersive X-ray spectroscopy (EDS), secondary-ion mass spectroscopy (SIMS), photoluminescence (PL), Hall-effect, electron-paramagnetic resonance (EPR), and magnetometry employing a superconducting quantum interference device (SQUID). A combination of TEM and EDS reveals the presence of coherent nanocrystals presumably FexN with the composition and lattice parameter imposed by the host. From both TEM and SIMS studies, it is stated that the density of nanocrystals and, thus the Fe concentration increases towards the surface. In layers with iron content x<0.4% the presence of ferromagnetic signatures, such as magnetization hysteresis and spontaneous magnetization, have been detected. We link the presence of ferromagnetic signatures to the formation of Fe-rich nanocrystals, as evidenced by TEM and EDS studies. This interpretation is supported by magnetization measurements after cooling in- and without an external magnetic field, pointing to superparamagnetic properties of the system. It is argued that the high temperature ferromagnetic response due to spinodal decomposition into regions with small and large concentration of the magnetic component is a generic property of diluted magnetic semiconductors and diluted magnetic oxides showing high apparent Curie temperature.Comment: 21 pages, 30 figures, submitted to Phys. Rev.

Effects of MOVPE Growth Conditions on GaN Layers Doped with Germanium

The effect of growth temperature and precursor flow on the doping level and surface morphology of Ge-doped GaN layers was researched. The results show that germanium is more readily incorporated at low temperature, high growth rate and high V/III ratio, thus revealing a similar behavior to what was previously observed for indium. V-pit formation can be blocked at high temperature but also at low V/III ratio, the latter of which however causing step bunching

Improving the Properties of Composite Titanium Nitride Layers on the AZ91D Magnesium Alloy Using Hydrothermal Treatment

Coating magnesium alloys with nitride surface layers is a prospective way of improving their intrinsically poor surface properties; in particular, their tribological and corrosion resistance. These layers are usually produced using PVD methods using magnetron sputtering or arc evaporation. Even though the thus-produced layers significantly increase the wear resistance of the alloys, their effects on corrosion resistance are unsatisfactory because of the poor tightness, characteristic of PVD-produced products. Tightness acquires crucial significance when the substrate is a highly-active magnesium alloy, hence our idea to tighten the layers by subjecting them to a post-deposition chemical-hydrothermal-type treatment. This paper presents the results of our experiments with a new hybrid surface engineering method, using a final tightening pressure hydrothermal gas treatment in overheated steam of the composite titanium nitride layers PVD, produced on AZ91D magnesium alloy. The proposed method resulted in an outstanding improvement of the performance properties, in particular resistance to corrosion and wear, yielding values that exceed those exhibited by commercially anodized alloys and austenitic stainless 316L steel. The developed hybrid method produces new, high-performance corrosion and wear resistant, lightweight magnesium base materials, suitable for heavy duty applications

Effect of Manganese Alloying on Infrared Detectors Made of Pb_1−xMn_xTe/CdTe Multilayer Composite

The properties of Pb1−xMnxTe/CdTe multilayer composite grown by molecular beam epitaxy on a GaAs substrate were studied. The study included morphological characterization by X-ray diffraction, scanning electron microscopy, secondary ion mass spectroscopy, as well as electron transport and optical spectroscopy measurements. The main focus of the study was on the sensing properties of photoresistors made of Pb1−xMnxTe/CdTe in the infrared spectral region. It was shown that the presence of Mn in the Pb1−xMnxTe conductive layers shifted the cut-off wavelength toward blue and weakened the spectral sensitivity of the photoresistors. The first effect was due to an increase in the energy gap of Pb1−xMnxTe with an increase in Mn concentration, and the second was due to a pronounced deterioration in the crystal quality of the multilayers owing to the presence of Mn atoms, as shown by the morphological analysis

CD4, CD20 and PD-L1 as Markers of Recurrence in Non-Muscle-Invasive Bladder Cancer

Introduction: A tumor microenvironment plays an important role in bladder cancer development and in treatment response. Purpose: The aim of the study was to assess how the components of the microenvironment affect tumor recurrence and to find the potential biomarkers for immunotherapy in NMIBC. Methods: The study group consisted of 55 patients with primary NMIBC. Immunohistochemistry was performed on sections of primary papillary urothelial carcinoma of the bladder. Cox proportional hazard multiple regression analysis was performed to characterize tumors with the highest probability of an unfavorable outcome. Results: Multivariate analysis confirmed that the CD4 (p = 0.001), CD20 (p = 0.008) and PD-L1 expressed on tumor cells (p = 0.01) were independently associated with the risk of recurrence of bladder cancer. Patients with weak CD4+ cell infiltration (+ infiltration (>10%) belong to the group with a lower risk of recurrence. The cancer in this group also frequently recurs after 12 months (p = 0.0005). Conclusions: The evaluation of CD4+ and CD20+ cells in the tumor microenvironment, in addition to PD-L1 on tumor cells, facilitates the determination of a group of patients with a low risk of recurrence

Effect of Nitrogen Doping on the Growth of 4H Polytype on the 6H-SiC Seed by PVT Method

score: 0collation: 29-3