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The results of investigations of initial n-4H–SiC structures by various methods are presented. The structures represent a highly doped n+ substrate with epitaxial layers 5 μm thick grown by chemical vapor deposition (CVD). The concentration of uncompensated donors in the epitaxial layer is in the range of Nd – Na = (1–50) × 1014 cm–3. Using the results of X-ray diffraction analysis, it is found that, in order to obtain efficient 4H–SiC ultraviolet photodetectors, it is desirable to have structures of epitaxial layers in which the effect of point-defect gettering, leading to an increase in the lifetime of charge carriers and in the values of quantum efficiency, is observed. The photosensitivity of the investigated samples significantly depends on the degree of imperfection of the CVD epitaxial layer, which results in a change in the lifetime of charge carriers and, as a consequence, in a change in the quantum efficiency of 4H–SiC ultraviolet photodetectors.

The photoluminescence spectra were studied in 3C-SiC / 4H-SiC heterostructures and single crystals of 3C-SiC. It was shown that 3C-SiC epitaxial layers grown on 4H-SiC substrates have significantly less structural perfection than 3C-SiC single crystals. It was found that doping with aluminum leads to the appearance of characteristic photoluminescence (PL) both in the epitaxial layers and in 3C-SiC single crystals. At the same time, the irradiation of the epitaxial layers does not lead to the appearance of “defective PL (DFL), as is observed for single crystals. It was suggested that the twin boundaries existing in 3C-SiC epitaxial layers could serve as getters of radiation defects that are components of donor – acceptor pairs (DAP) responsible for DFL.

The influence exerted by the carrier concentration in the range (1–50) × 1014 cm–3 in n-4H-SiC chemical-vapor deposited (CVD) epitaxial layers on the spectral characteristics of UV photodetectors with Cr Schottky barriers in the range of 200–400 nm is revealed and explained in terms of the photoconductivity theory. Schottky barriers with a Cr film thickness of 20 nm and diameter of 8 mm are formed by thermal evaporation in vacuum through masks. A noticeable effect of the carrier concentration in the CVD epitaxial layers on the spectral characteristics of photodetectors upon heating to 200°C is also observed and accounted for by a difference between the generation-recombination processes. The irradiation of photodetectors with 15-MeV protons at a fluence of 4 × 1012 cm–2 and a temperature of 200°C leads to an increase in the quantum efficiency as compared to samples irradiated in similar modes at 25°C. This is indicative of an increase in the radiation hardness and service life of 4H-SiC devices at elevated temperatures.

Atomic force microscopy, Kelvin-probe microscopy and Raman spectroscopy have been used to examine graphene films grown by thermal decomposition of the Si face of semi-insulating substrates ...

The author elaborates the idea of modern aesthetics that the notion of beautiful is not a fundamental category of modern art and modern philosophy of art. Under the direct influence of science and arts modern philosophy has added to the categories such notions as probability, absurdity, the mundane, the understanding etc. On the other hand a new understanding of society and man prompted the introduction of such categories as lifeworld, fear, solitariness, care, doubt, language games etc. It has become evident that many categories are not only blurred but rather heterogeneous, thus the system of categories is something to be referred to with considerable reservations. The article proposes a preliminary definition and interpretation of the beautiful and the main principles of the analysis of the beautiful. In the most general and tentative terms the beautiful can be defined as something that complies with the idea of beauty accepted in a given society or civilization. Ideas of beauty can vary from culture to culture and from civilization to civilization. This is no to say that certain, albeit few, objects cannot be considered beautiful throughout many historical epochs. Standards of beauty as well as social standards in general, do not refer to any object but only to certain types of objects. Consequently beautiful is always beautiful of a kind. Beauty in general does not exist, there are only beautiful objects of a definite kind. The article maintains that there are at least three reasons why the beautiful cannot be verbally defined. The first is methodological, the second is social and the third is related to the peculiarities of the beautiful itself, primarily it sensual nature. In the first place the degree of clarity of scientific notions depends on the level of the development of science. The scientific study of arts is a never-ending venture. And while it continues, its categories and in particular the category of the beautiful will require clarification.

For the first time, comprehensive comparative investigations of ultraviolet photodetectors with Cr Schottky barriers formed on 4H-SiC epitaxial layers are carried out by the X-ray and optical methods before and after irradiation with 15-MeV protons with fluences in the range of (1–4) × 1012 cm–2. When increasing the fluence of proton irradiation, the formation of localized regions with negative deformation is observed along with the unperturbed silicon-carbide matrix. Agreement between the X-ray and optical studies is obtained, which makes it possible to explain the features of the spectral changes in the photosensitivity of detectors in the range of 200–400 nm with an increase in the fluence of proton irradiation. The ultraviolet Cr/4H-SiC photodetectors withstand irradiation by 15-MeV protons with a fluence of 4 × 1012 cm–2 virtually without any changes in the photosensitivity due to the gettering of simple defects by cluster and amorphous formations, which lead to partial structural improvement of the irradiated material.

In this paper, modal analysis is proposed to building simulation models of thermal processes in machine tools. The technique of building simulation models in Simulink in three ways is described. The first way of modeling uses an analytical solution of the thermal conductivity equation. The second way of modeling uses built-in tools for solving differential equations. The third way of modeling uses the apparatus of transfer functions. An analysis of the structures of the generated simulation models was carried out to solve two typical tasks: building the thermal characteristics of the machine tool under zero and nonzero initial conditions. The first way to build simulation models, based on the use of analytical solutions of the thermal conductivity equation, allows you to build the most compact simulation models of the running machine tools. A feature of building invariant S-models is the formation of modeling parameters in Matlab M-file. For multimodal thermal characteristics of machine tools based on experimental modal analysis, a new algorithm for building them under nonzero initial conditions is proposed. It is based on the redistribution between several modes of the thermal displacement level formed in a previous section of the machine diagrammatic work. From full-scale and computational experiments, it was shown that this uniquely made it possible to increase the accuracy of prediction.

The aim of the study was to develop a methodology for measuring the structural and geometric parameters of a straight bull-nose cutter. To test the effectiveness of the developed methodology for measuring the structural and geometric parameters of the cutter, a full-scale experiment was conducted. During the experiment, all the structural and geometric parameters of the straight bull-nose cutter were measured using handheld measuring tools and a coordinate measuring machine Wenzel XOrbit 55 (Germany). A comparative analysis of the results of measurements using a universal handheld measuring tool and coordinate measuring machine showed: all the geometrical parameters of the cutter can only be measured using a coordinate measuring machine; the results of measuring geometric parameters using a universal handheld measuring tool do not allow making unambiguous organizational decisions on the further operation of the cutting tool, since the measurement error is comparable with the current size tolerances; however, for such design parameters as length, height, width of the cutter due to large tolerances, the use of a universal handheld tool is sufficient. The practice of measurements using a coordinate measuring machine has shown that, when conducting critical measurements, the use of coordinate measuring machines is not only accurate, but also more productive in comparison with the use of handheld measuring tools.

Results of the studies of the properties of single-crystalline bulk β-Ga2O3 grown from the melt are presented. High chemical purity and phase uniformity of the grown material are demonstrated. Raman spectroscopy studies confirmed low energies of optical phonons in β-Ga2O3, which makes it a promising material for laser optics applications.

Photoluminescence (PL) spectra have been studied in 3C-SiC/4H-SiC heterostructures and 3C‑SiC single crystals. It was shown that epitaxial 3C-SiC layers grown on 4H-SiC substrates have a markedly poorer crystal perfection than do 3C-SiC single crystals. It was found that doping with aluminum gives rise to a characteristic PL both in epitaxial layers and in 3C-SiC single crystals. At the same time, the electron irradiation of epitaxial layers does not give rise to defect-related PL, in contrast to what is observed for single crystals. An assumption is made that the twin boundaries existing in epitaxial 3C-SiC layers can serve as getters of radiation defects that are components of donor–acceptor pairs responsible for the “defect-related” PL.

Effects of proton irradiation in n-3C-SiC grown by sublimation on a 4H-SiC substrate have been studied by the Hall effect and photoluminescence methods. It was found that the carrier removal rate (Vd) reaches a value of ~110 cm-1. The full compensation of samples with an initial concentration of (1-2) x 1018 cm -3 was estimated to occur at doses of about 6 x 1015 cm -2. Compared with 4H and 6H silicon carbide, no significant increase in the intensity of so-called "defective" photoluminescence was observed in 3C-SiC.

Excessive body weight and obesity in childhood and adolescence are becoming more and more important unfavorable factors that entail extremely adverse consequences and require close attention of physicians of any specialty. Along with the high prevalence of obesity and metabolic syndrome in pediatric patients, children and adolescents in the majority of countries are diagnosed with vitamin D deficiency. Among the non-calcaemic effects of vitamin D, a significant role is played by its impact on the hormonal regulation of glucose metabolism and the synthesis of adipokines by fat tissue. The review presents literature data indicative of a close pathogenic relationship between vitamin D insufficiency and impaired tissue insulin sensitivity. It demonstrates the role of vitamin D insufficiency in immune reactions resulting in development of subclinical inflammation in fat tissue infiltrated with macrophages and lymphocytes. It also shows the role of adipokines, immune system cells and pro-inflammatory cytokines produced by them in the pathogenesis of obesity, as well as the function of vitamin D as an endocrine and paracrine regulator of the process of inflammation in adipose tissue. The relationships between the principal adipokines (leptin, adiponectin, resistin) are revealed in the presence of normal vitamin D content and in vitamin D deficiency. The carbohydrate and lipid metabolism parameters in overweight children and adolescents with vitamin D insufficiency are analyzed. A high prevalence of vitamin D insufficiency in overweight and obese children and adolescents (increasing along with the severity of obesity) is demonstrated. The review also presents the current recommendations for the correction of vitamin D insufficiency and underlines the need for higher cholecalciferol doses to achieve serum calcifediol targets in overweight and obese children and adolescents.

Here we report on the growth and characterization of β-Ga2O3 bulk crystals and polycrystalline layer on different substrates. Bulk β-Ga2O3 crystals were produced by free crystallisation of gallium oxide melt in sapphire crucible. Transparent single crystals measuring up to 8 mm across were obtained. Good structural quality was confirmed by x-ray diffraction rocking curve FWHM values of ~46″. Young’s modulus, shear modulus and hardness of the β-Ga2O3 crystals were measured by nanoindentation and Vickers microindentation techniques. Polycrystalline β-Ga2O3 films were deposited on silicon and sapphire substrates by sublimation method. It was found that structure and morphology of the films were greatly influenced by the material and orientation of the substrates. The best results were achieved on a-plane sapphire substrates where predominantly (111) oriented films were obtained.

The method of chloride epitaxy is employed to grow β-Ga2O3 epitaxial layers on a c-sapphire substrate. Purified dry air is used as the source of oxygen. The layers are studied using the methods of X-ray diffraction, optical microscopy, scanning electron microscopy, transmission electron microscopy, and micro-Raman spectroscopy. It is found that the growth plane of the layers is (\(\bar 2\)01), parallel to the substrate surface. The layers consist of separate large crystalline grains of three different in-plane orientations rotated relative to each other in the growth plane by 60°. Misorientation can be caused by the different symmetry of the substrate and the epitaxial layer.

We report on Ga 2 O 3 deposition on c-plane sapphire substrates by hydride vapour phase epitaxy using metallic gallium, hydrogen chloride and dry air as precursors. High deposition rate up to 250 µm/h has been realized. As confirmed by X-ray diffraction and micro-Raman measurements, produced films consisted of pure monoclinic β-Ga 2 O 3 phase and were (−201) oriented. The full width at half maximum (FWHM) for (−201) rocking curve was decreasing with increasing GaCl flow. The narrowest FWHM of 20 arcmin has been detected.

The main problem of the epitaxial growth of thick AlN layers on a Si substrate consists in the formation of cracks, which complicates the application of structures of this kind in the fabrication of semiconductor devices. The possibility of obtaining crack-free AlN layers with a thickness exceeding 1 μm and a mirror- smooth surface by hydride vapor-phase epitaxy is demonstrated. The properties of the layers are studied by X-diffraction analysis, optical and scanning electron microscopy, and Raman spectroscopy.

The effects of 8-MeV proton irradiation on n-3C-SiC epitaxial layers grown by sublimation on semi-insulating 4H-SiC substrates are studied. Changes in the sample parameters were recorded by the Hall-effect method and judged from photoluminescence spectra. The Hall method was employed to distinguish between the effects of irradiation on the charge-carrier concentration and mobility. It is found that the charge-carrier removal rate (V d ) is ~110 cm–1. Full compensation of the samples with an initial charge-carrier concentration of ~6.5 × 1017 cm–3 is observed at irradiation doses of ~6 × 1015 cm–2. It is found that the mobility at these doses decreased by only a factor of 2.5. Compared with 4H and 6H silicon carbide, no significant increase in the intensity of so-called defect-related photoluminescence is observed.

Results of an epitaxial growth of 3C-SiC epilayers on hexagonal 6H-SiC, 4H-SiC substrates are described. The study of the obtained epitaxial layers grown on 6H substrates was made by photoluminescence and optical microscopy. Also, an image analysis of the interface of 3C-SiC epitaxial layers with 6H, 4H, and 15R substrates obtained by Transmission Electron Microscopy (TEM) are presented. Difference between the layers on the Si and C faces are discussed.

Coordinate measuring machines make it possible to measure the geometric parameters of precision parts, the measuring of which is not feasible with a universal hand tool. The purpose of the study was to develop a methodology for measuring the design and geometric parameters of a straight bull-nose turning tool. To test the effectiveness of the developed methodology for measuring the design and geometric parameters of the cutting tool, a full-scale experiment was conducted. During the experiment, the measurement of all the structural and geometric parameters of the cutting was carried out using hand-held measuring tools and the Wenzel XOrbit 55 coordinate measuring machine. A comparative analysis of the results of the measurements showed the folowing: all the geometric parameters of the cutting can only be measured using a coordinate measuring machine; geometric parameters measurements using a universal hand tool do not allow you to make unambiguous organizational decisions on the further operation of the cutting tool, since the measurement error is comparable to the current size tolerances, however, for such design parameters as length, height, and width of the cutting, due to the large tolerances, it is sufficient to use a universal hand measuring tool. The measurement practice using a coordinate measuring machine has shown that when performing critical measurements, the use of coordinate measuring machines, in manual mode, is not only accurate, but also more productive in comparison with a universal hand measuring tools.

The paper presents the original design of a special tap for cutting precise threads. Distinctive design features of the tap are: the presence of the rear threaded guide, which together with the copier threaded sleeve of appliance perceives the axial forces and provides the tap axial feed strictly corresponding to the step of the thread being cut, excluding its breaking under the action of axial forces; the presence of a smooth front guide part with the direction on the cut hole, to reduce the influence of radial forces that lead to an increase in the diameter of the thread due to the radial vibrations of the tap; the presence of the chamfer that implements the most technological cutting scheme such as flank infeed. A prototype of a special tap made on a turning and milling machine tool is presented, confirming the manufacturability of the proposed tool design. Research conducted in the field of engineering analysis with the CAE-system Ansys showed a significant increase in structural rigidity, as well as a significant increase in natural frequencies.

The article presents new technical solutions aimed at improving the performance of the installation for the molding of wood-concrete slabs. Calculation and design of rotary wheel racks which provide movement of installation in two mutually perpendicular directions is made; the proportioning bunker; conveyor that distributes and discharges the ready mortar into the formwork with two pneumatic cylinders; frames of plate forming installation. The study of the frames of plate forming installation, proportioning bunker and conveyor. Engineering analysis was carried out in CAE system ANSYS. Engineering analysis included five types of calculations: calculation of stiffness with rigid and elastic grip conditions, modal analysis, dynamic calculation, thermal and thermal-deformation calculations. The obtained results of the engineering analysis allowed us to conclude that the deformation of the frames is insignificant, that is, their rigidity provides the required accuracy of the manufacture of plates and the accuracy of the position of the proportioning bunker relative to the conveyors. The carried out measures on modernization of plate forming installation provided increase in productivity approximately in 2 times.

The work considers the methodology of experimental studies of double-sided face grinding machines on the criterion of heat stability. The proposed methodology includes: procedure of grinding process simulation; procedure of temperature measurement; procedure of determining the mutual angular position of the grinding wheels due to thermal deformations; procedure of machining error measurement. The described techniques allow you to fine-tune the machine under production conditions. Preliminary full-scale test of a double-sided face grinding machine showed that excess temperatures were distributed nonuniform over the elements of the load-bearing structure of the machine tool when grinding an industrial batch of cylindrical rollers. When idling the end face of the spindle headstocks and bed had the highest excess temperature. When grinding the surface of the machine units, located in the immediate vicinity of the grinding zone, had the highest temperature. The experiments carried out confirmed the coordination of the nature of the change in excess temperatures at characteristic points and cutting coolant when simulating the grinding process on a machine with the corresponding experimental data obtained on a working machine.

Recent progress in the field of silicon carbide sensor technology, such as wireless communications and sensors, has demonstrated the need for a resilient energy supply as an alternative to conventional batteries. Previous work has shown that silicon carbide is an effective energy harvester of UV light in high temperature and hostile environments. Until now however, there has been little work undertaken to assess the long-term effects of elevated temperature on such devices. Although it is understood that silicon carbide is unaffected by long-term temperature exposure below 400 °C, there has been little research into the overall device response and how changes in contact metallisation affect the photovoltaic behaviour.

Patterned Few Layers Graphene (FLG) films were grown by local solid phase epitaxy from nickel silicide supersaturated with carbon. The process was realised by annealing of thin Ni films deposited on the carbon-terminated surface of 6H-SiC semi-insulating wafer followed by wet processing to remove the resulting nickel silicide. Raman spectroscopy was used to investigate both the formation and subsequent removal of nickel silicide during processing. Characterisation of the resulting FLG films was carried out by Raman spectroscopy and Atomic Force Microscopy (AFM). The thickness of the final FLG film estimated from the Raman spectra varied from 1 to 3 monolayers for initial Ni layers varying from 3 to 20 nm thick. AFM observations revealed process-induced surface roughening in FLG films, however, electrical conductivity measurements by Transmission Line Model (TLM) structures confirmed that roughness does not compromise the film sheet resistance.

Trenched implanted vertical JFETs (TI-VJFETs) with self-aligned gate and source contacts were fabricated on commercial 4H-SiC epitaxial wafers. Gate regions were formed by aluminium implantation through the same silicon oxide mask which was used for etching mesa-structures. Self-aligned nickel silicide source and gate contacts were formed using a silicon oxide spacer formed on mesa-structure sidewalls by anisotropic thermal oxidation of silicon carbide followed by anisotropic reactive ion etching of oxide. Fabricated normally-on 4H-SiC TI-VJFETs demonstrated low gate leakage currents and blocking voltages exceeding 200 V.

3.3 kV rated 4H-SiC diodes with nickel monosilicide Schottky contacts and 2-zone JTE regions were fabricated on commercial epitaxial wafers having a 34 m thick blocking layer with donor concentration of 2.2×1015 cm-3. The diodes were fabricated with and without additional field stop rings to investigate the impact of practically realizable stopper rings on the diode blocking characteristics. The field stop ring was formed by reactive ion etching of heavily doped epitaxial capping layer. The diodes with field stop rings demonstrated significantly higher yield and reduction of reverse leakage current. The diodes demonstrated blocking voltages in excess of 4.0 kV and very low change of leakage current at ambient temperatures up to 200 °C.

Few Layers Graphene (FLG) films were grown on the carbon-terminated surface of 4H-SiC from nickel silicide supersaturated with carbon. The process was realised by annealing of thin Ni films deposited on silicon carbide followed by wet processing to remove the nickel silicide. To identify and characterize the fabricated FLG films, micro-Raman scattering spectroscopy, AFM and optical microscopy have been used. The films grown on samples with initially deposited nickel thinner than 20 nm show clear graphene footprints in micro-Raman scattering spectra, namely a single component, Lorentzian shape 2D band with FWHM remarkably lower than that of the 2D peak of graphite.

Free standing AlN wafers were grown on pre-patterned and in situ patterned 4H-SiC substrates by a physical vapor transport method. It is based on the coalescence of AlN microrods, which evolve from the apex of SiC pyramids grown on the SiC substrate during a temperature ramp up for in situ patterned substrate and SiC pyramids formed by reactive ion etching (RIE). This process yields stress-free (according XRD and Raman results) AlN single crystals with a thickness up to 400 µm and low dislocation density.

4H-SiC diodes with 0.60 mm2 nickel silicide Schottky contacts were fabricated on commercial epitaxial layers. At room temperature, the diodes have specific on-resistances (RON-SP) down to 10.5 mΩcm2 and blocking voltages (VBL) up to 4.6 kV, which is equal to 93 % of the calculated parallel plane breakdown voltage for used epitaxial structure. The corresponding figure-of-merit, defined as (VBL)2/RON-SP, is equal to 2015 MW/cm2 and is among the highest FOM values reported to date. The diodes demonstrated stable operation at forward current of 1 A and VBL value in excess of 3.3 kV at ambient temperatures up to 200 °C.

Buried gate static induction transistors (BGSITs) were fabricated on commercial 4H-SiC wafer with 20 m thick n-type epilayer having a net donor density of 0.71015 cm-3. Buried gate regions were formed by the selective implantation of high energy (up to 2 MeV) aluminium performed at 600 °C. Nitrogen was implanted at temperature of 400 °C to form a heavily doped blanket source region. Post-implantation annealing was carried out at the atmospheric pressure in argon using a graphite capping layer. Fabricated normally-on devices with source contact diameter of 0.2 mm were tested at temperatures up to 500 °C and current densities up to 270 A/cm2. The specific on-resistance of a completely open 4H-SiC BGSIT was 34 mcm2 and showed a thermally activated behaviour at temperatures up to 500 °C.

The development of silicon carbide technologies has allowed for the development of sensors and electronics to measure the changes in a variety of hostile environments. A problem has been identified with reliable and efficient ways to power such sensors in these hostile environments. It is likely to be impractical to run power cables to these sensors and battery power has a finite lifetime. Recent research has demonstrated many energy scavenging techniques but to date none have been developed with a view of operation in hostile environments. To investigate the power density achievable from a SiC based energy scavenging device a SiC pin diode was exposed to both broad spectrum light form a tungsten halogen bulb and a 255 nm UV source. IV and CV measurements were used to determine the structural properties and photovoltaic response of the device, dark saturation current, induced photo current and the fill factor. We present the characteristics and maximum power density of these devices at temperatures between 300 K and 600 K. We demonstrate that the maximum power density achievable decreases with temperature. This is mostly due to the reduction in the built in potential from the pn junction, and the reduction of the generated photocurrent.

Nickel silicide Schottky contacts were formed on 4H-SiC by consecutive deposition of a titanium adhesion layer, 4 nm thick, and nickel, 100 nm thick, followed by annealing at temperatures from 600 to 750 °C. It was found that contacts with barrier heights of 1.45 eV, consisting mainly of NiSi phase, formed in the 600-660 °C temperature range, while annealing at around 750 °C led to the formation of Ni2Si phase with barrier heights of 1.1 eV. Annealing at intermediate temperatures resulted in the nucleation of Ni2Si grains embedded in the NiSi film which were directly observed by micro-Raman mapping. It was concluded that the thermodynamically unfavourable NiSi phase appeared in the 600-660 °C temperature range due to the fact that the solid state chemical reaction between Ni and SiC at these temperatures is controlled by nickel diffusion through the titanium barrier.

Trenched and implanted vertical JFETs (TI-VJFETs) with blocking voltages of 700 V were fabricated on commercial 4H-SiC epitaxial wafers. Vertical p+-n junctions were formed by aluminium implantation in sidewalls of strip-like mesa structures. Normally-on 4H-SiC TI-VJFETs had specific on-state resistance (RO-S ) of 8 mW×cm2 measured at room temperature. These devices operated reversibly at a current density of 100 A/cm2 whilst placed on a hot stage at temperature of 500 °C and without any protective atmosphere. The change of RO-S with temperature rising from 20 to 500 °C followed a power law (~ T 2.4) which is close to the temperature dependence of electron mobility in 4H-SiC.

High voltage 4H-SiC Schottky diodes with single-zone junction termination extension (JTE) have been fabricated and characterised. Commercial 4H-SiC epitaxial wafers with 10, 20 and 45 +m thick n layers (with donor concentrations of 3×1015, 8×1014 and 8×1014 cm-3, respectively) were used. Boron implants annealed under argon flow at 1500°C for 30 minutes, without any additional protection of the SiC surface, were used to form JTE’s. After annealing, the total charge in the JTE was tuned by reactive ion etching. Diodes with molybdenum Schottky contacts exhibited maximum reverse voltages of 1.45, 3.3 and 6.7 kV, representing more than 80% of the ideal avalanche breakdown voltages and corresponding to a maximum parallel-plane electric field of 1.8 MV/cm. Diodes with a contact size of 1×1 mm were formed on 10 +m thick layers (production grade) using the same device processing. Characterisation of the diodes across a quarter of a 2-inch wafer gave an average value of 1.21 eV for barrier heights and 1.18 for ideality factors. The diodes exhibited blocking voltages (defined as the maximum voltage at which reverse current does not exceed 0.1 mA) higher than 1 kV with a yield of 21 %.

Zener diodes are widely used in electrical barriers to protect equipment operating in a potentially explosive atmosphere. Although normally not conducting, the zeners must have a high power rating so that their junction temperature meets safety factors when shunting the maximum fuse current. This often requires two or three lower voltage commercial zeners connected in series. Silicon carbide diodes have much higher thermal conductivity and maximum allowed junction temperature, so it should be possible to use one SiC zener in the place of two or three commercial diodes and/or allow use of higher fuse ratings. Low voltage SiC Zener diodes were fabricated and tested to evaluate potential benefits of their application as a component of intrinsically safe barriers. The diodes demonstrated mixed avalanche-tunnel breakdown at reverse bias voltages of 23 V with positive temperature coefficients of breakdown voltages of about 0.4 mV/°C. The diodes with mesa area of 4×10-4cm2 had maximum DC Zener current of 1.2 A and were capable of operating at ambient temperatures up to 500°C.

4H-SiC diodes with nickel silicide (Ni2Si) and molybdenum (Mo) Schottky contacts have been fabricated and characterised at temperature up to 400°C. Room temperature boron implantation has been used to form a single zone junction termination extension. Both Ni2Si and Mo diodes revealed unchanging ideality factors and barrier heights (1.45 and 1.3 eV, respectively) at temperatures up to 400°C. Soft recoverable breakdowns were observed both in Ni2Si and Mo Schottky diodes at voltages above 1450 V and 3400 V depending on the epitaxial structure used. These values are about 76% and 94% of the ideal avalanche breakdown voltages. The Ni2Si diodes revealed positive temperature coefficients of breakdown voltage at temperature up to 240°C.

Although Silicon Carbide has become the material of choice for high power applications in a range of extreme environments, the interest in creating active chemical sensors requires the development of transistors for additional control circuits to operate in these environments. Despite the recent advances in the quality of oxide layers on SiC, the mobility of inversion layers is still low and this will affect the maximum frequency of the operation for these devices. We present simulation results which indicate that a delta channel, in both n-channel and p-channel structures, is suitable for transistors used with these low level signals. By varying the doping levels of the device we have shown that the optimum delta doping for this application is 1.43x1019 cm-3 for both n and p channel devices. We then show the effects of high temperatures on the delta FET devices and make comparisons with standard SiC MOSFET devices.

Structural properties of Ni/Ti films deposited on 4H-SiC and annealed at temperatures from 800 to 1040°C have been studied. Films with three different metal deposition sequences were investigated by X-ray diffraction and Auger electron spectroscopy: (A) Ti(100 nm)/Ni(50 nm); (B) Ti(4 nm)/Ni(50 nm)/Ti(100 nm); and (C) Ti(4 nm)/Ni(150 nm). A distinct spatial separation of nickel silicide and titanium carbide layers was observed in all samples. It was discovered that the distribution of the products of the solid state chemical reaction in samples (A) and (B) was independent on the deposition sequence of Ti and Ni layers. The titanium carbide layer located on the interface and covered by the clearly separated nickel silicide layer was detected in both samples after heat treatments.

The composition and microstructure of compound contacts to 4H-SiC containing both titanium and nickel were investigated. Samples were prepared by metal evaporation on commercial 4H-SiC wafers followed by rapid thermal annealing (RTA). Contact structures with three different metal deposition sequences were investigated: (A) SiC/Ti(4 nm)/Ni(150 nm); (B) SiC/Ti(100 nm)/Ni(50 nm) and (C) SiC/Ti(4 nm)/Ni(50 nm)/Ti(100 nm). RTA was performed in a vacuum at 800, 925 and 1040 °C for a period of 800 s. X-ray diffraction, Auger electron spectroscopy and transmission electron microscopy were used for the characterization. A distinct spatial separation of nickel silicide and titanium carbide layers was observed in all samples. It was discovered that the final distribution of solid-state reaction products in B- and C-samples was independent of the order of the deposition of the initial metal films. In both samples, a two-phase TiC+C layer was found to be adjacent to the SiC substrate. Factors controlling phase formation and segregation are discussed. A two-stage reaction model is proposed to explain the reaction zone structure formed in the Ni–Ti–SiC system after high-temperature treatment.

The implementation of control over self-separation of thick GaN flayers grown by Hydride Vapor-Phase Epitaxy (HVPE) on Metal-Organic Chemical Vapor Deposition (MOCVD)-grown templates with patterned nano-column interlayer is reported. Both numerical simulation and experimental data show that separation of thick HVPE layers is provided by non-uniform redistribution of the growth stress. It is shown that the geometrical parameters of the nano-column structure such as fill factor and shape of the columns are most critical for self-separation effect. By adjusting the nano-column pattern, successful self-separation of thick HVPE layers from 2-inch structured MOCVD GaN/sapphire substrate was demonstrated. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

New results are presented of a surface trench defect observed during anneal of room temperature Al implants. The size of the surface defect is proportional to anneal temperature and occurs predominantly in the implanted zone. Signs of lattice strain are observed outside the implanted zone as well.

A graphite capping layer has been evaluated to protect the surface of patterned and selectively implanted 4H–SiC epitaxial wafers during post-implantation annealing. AZ-5214E photoresist was spun and baked in vacuum at temperatures ranging from 750 to 850 °C to form a continuous coating on both planar and mesa-etched SiC surfaces with features up to 2 µm in height. Complete conversion of the hydrogenated polymer-like film into nanocrystalline graphite layer was verified by Raman spectroscopy. The graphite capping layer remained undamaged and protected both planar and mesa-etched SiC surfaces during subsequent annealing in argon ambient at temperatures up to 1650 °C for 30 min. It effectively suppressed step bunching and dopant out-diffusion in implanted regions and simultaneously ensured that the un-implanted surface of the 4H–SiC epitaxial wafer remained free of contamination. Schottky barrier diodes formed on the un-implanted annealed surfaces displayed almost ideal characteristics.

AlN epitaxial layers were grown on 6H-SiC on-axis substrates by HVPE. The deposition was performed directly on (0001)Si face of the substrates without any buffer layer. Growth temperature was varied from 700 to 1200 °C. Thickness of AlN layers ranged from 0.1 to 1 μm. AlN surface morphology was studied by atomic force microscopy (AFM). The minimum value of Ra roughness was obtained for 0.1 μm thick layer and was less than 1 nm. Structural properties were investigated using X-ray diffraction (XRD). XRD rocking curves (RC) were obtained in ω-scan mode at (0002) reflection. The minimum value of RC FWHM measured in ω-scan (0002) mode was about 60 arcsec. This value indicates that the layers have high crystalline quality. Specific resistivity of AlN was measured in the temperature range from 300 to 700 K. The values of the specific resistivity for AlN were found to be exceed 4 × 1013 and 1 × 109 Ω cm at 300 and 700 K, respectively.

Photoelectrical properties of AlxGa1–xN epitaxial layers grown by Hydride Vapor Phase Epitaxy (HVPE) have been studied. The layers were grown on 6H-SiC and sapphire (Al2O3) substrates. Composition of AlxGa1–xN layers ranged from 0 mol.% up to 45 mol.% of AlN. The dependence of the energy band gap on the Al content has been studied. According to capacitance–voltage (CV) measurements, the concentration of uncompensated donors increased with the AlN mole fraction. The spectral response of the semitransparent Schottky barriers formed by evaporation of Ni on a Al0.06Ga0.94N HVPE layer demonstrated sharp cut-off with the peak value of 210 mA/W and UV/visible contrast about 104.

AlN/SiC epitaxial wafers were fabricated using hydride vapor phase epitaxy. The thickness of AlN layer was varied from 0.1 to 0.5 μm. Surface of AlN layers was characterized by high-energy electron diffraction and atomic force microscopy. The crystal structure of AlN layers was studied using X-ray diffraction. The minimum value of the full width at half maximum of ω-scan (0002) reflection rocking curve was about 120 arcsec. The specific resistivity of AlN was measured in the temperature range from 300 to 700 K.

The n-type doping of GaN by hydride vapor phase epitaxy (HVPE) using undoped single crystalline Si as a dopant source has been demonstrated. The doping has been realized in a wide range of Si atomic concentration (from

GaN bulk crystals up to 2.5-inch diameter were grown from melt-solution. Properties of these crystals were investigated using Auger electron spectroscopy, X-ray diffraction and photoluminescence.

GaN/SiC heterojunctions can improve the performance considerably for BJTs and FETs. In this work, heterojunction diodes have been manufactured and characterized. The fabricated diodes have a GaN n-type cathode region on top of a 4H-SiC p-type epi layer. The GaN layer was grown with HVPE directly on off-axis SIC without a buffer layer. Mesa structures were formed and a Ti metallization was used as cathode contact to GaN, and the anode contact was deposited on the backside using sputtered Al. Both current-voltage (I-V) and capacitance-voltage (C-V) measurements were performed on the diode structures. The ideality factor of the measured diodes was 1.1 and was constant with temperature. A built in potential of 2.06 V was extracted from I-V measurements and agrees well with the built in potential from C-V measurements. The conduction band offset was extracted to 1.1 eV and the heterojunction was of type II. The turn on voltage for the diodes is about 1 V lower than expected and a suggested mechanism for this effect is discussed.

Ohmic contacts to the top p-type layers of 4H-SiC p + –n–n + epitaxial structures having an acceptor concentration lower than 1×10 19 cm −3 were fabricated by the rapid thermal anneal of multilayer Al/Ti/Pt/Ni metal composition. The rapid thermal anneal of multilayer A1/Ti/Pt/Ni metal composition led to the formation of duplex cermet composition containing Ni 2 Si and TiC phases. The decomposition of the SiC under the contact was found to be down to a depth of about 100 nm. The contacts exhibited a contact resistivity R c of 9×10 −5 Ω cm −2 at 21°C, decreasing to 3.1×10 −5 Ω cm −2 at 186°C. It was found that thermionic emission through the barrier having a height of 0.097 eV is the predominant current transport mechanism in the fabricated contacts.