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4H Silicon carbide (SiC) is widely recognized as one of the most advanced wide bandgap semiconductors used in the production of high-efficiency power electronic devices. Impurities play a crucial role in achieving the desired electrical properties in 4H-SiC, yet the understanding of impurities in this material remains limited. In this study, first-principles formation-energy calculations were employed to establish a comprehensive database of formation-energy diagrams for impurities in 4H-SiC. This database includes valuable information on site preference, lattice distortion, solubility, and charge transition levels (CTLs) of the impurities. The site preference for each impurity is closely related to factors such as the Fermi energy, chemical potential, and the impurity species itself. To assess the lattice distortion caused by each impurity, a comparison was made between the volume changes before and after doping. Moreover, the solubility of each impurity was determined using the detailed balance theory, thereby enabling a direct measure of the maximum impurity concentration achievable in the material. Based on the CTLs, the impurities in 4H-SiC were classified into four categories: n-type impurities, p-type impurities, amphoteric impurities, and non-electroactive impurities. This comprehensive property database for impurities in 4H-SiC provides valuable insights for tailoring the material properties through controlled doping, thereby ultimately leading to enhanced performance of power electronic devices. [ABSTRACT FROM AUTHOR]

We investigate the crack-healing mechanism of 4H silicon carbide (4H-SiC) and reveal the effect of dopants on the crack-healing behavior of 4H-SiC. Vickers indentation tests and thermal annealing are utilized to generate cracks and heal cracks in 4H-SiC, respectively. High-temperature thermal annealing in the air atmosphere is found to be capable of effectively healing indentation-induced cracks and releasing indentation-induced stress in undoped 4H-SiC by the formation and viscous flow of glass phase SiO2. Nitrogen (N) doping is found to assist the atomic diffusion of 4H-SiC. The crack healing of N-doped 4H-SiC is realized by the synergy of host solid diffusion and the padding of glassy SiO2. In contrast, vanadium (V) doping hinders the viscous flow of SiO2 and results in the incomplete healing of cracks in V-doped 4H-SiC. Although the generation of cracks lowers the bending strength of 4H-SiC, the healing of cracks by the padding of glassy SiO2 is found to effectively recover the bending strength of indented 4H-SiC samples. Our work opens a pathway to design thermal processing technologies to heal the cracks and enhance the mechanical properties of 4H-SiC wafers. [ABSTRACT FROM AUTHOR]

High-purity semi-insulating (HPSI) 4H silicon carbide (4H-SiC) single crystals are critical semiconductor materials for fabricating GaN-based high-frequency devices. One of the major challenges for the growth of HPSI 4H-SiC single crystals is the unintentional doping of nitrogen (N) and boron (B). The addition of hydrogen has been supposed to mitigate unintentional doping. However, the underlying mechanism has not been well understood. In this work, the role of hydrogen in the growth of HPSI 4H-SiC single crystals is investigated by first-principles formation-energy calculations. We find that the addition of hydrogen significantly mitigates N doping while hardly affecting B doping. Once hydrogen is added, hydrogen may adsorb at the growing surface of 4H-SiC, leading to surface passivation. Since N can react with hydrogen to form stable NH3 (g), the chemical potential of N is reduced, so that the formation energy of N in 4H-SiC increases. Hence, the critical partial pressure of nitrogen required for the growth of HPSI 4H-SiC single crystals increases by two orders of magnitude. Moreover, we reveal that the adjustment of relative B and N doping concentrations has a substantial impact on the Fermi energy of HPSI 4H-SiC. When the doping concentration of N is higher than that of B, N interacts with carbon vacancies (VC) to pin the Fermi energy at Z1/2. When the doping concentration of B is higher than that of N, the Fermi energy is pinned at EH6/7. This explains that the resistivity of unintentionally doped HPSI 4H-SiC may vary. [ABSTRACT FROM AUTHOR]

Semiconducting silicon carbide (4H-SiC) exhibits characteristics of high hardness, notable brittleness, and excellent chemical stability. The commonly employed technique for achieving an ultra-smooth and flat surface is chemical mechanical polishing (CMP), which is utilized to process the 4H-SiC surface. Wet oxidation, as an important process of chemical-mechanical polishing of single-crystal 4H-SiC, directly affects the rate and surface quality of CMP. This paper provides a comprehensive overview of the current research status of wet oxidation of single-crystal 4H-SiC. It discusses the oxidants used in the wet oxidation of 4H-SiC, such as KMnO4, H2O2, K2S2O8. Based on this, it further summarizes commonly employed oxidation-enhancement methods, including photocatalytic-assisted oxidation, electrochemical oxidation, and Fenton reaction. The mechanism of wet oxidation of single-crystal 4H-SiC is analyzed from the aspect of theoretical calculation, and the future research direction of wet oxidation of 4H-SiC is proposed. [ABSTRACT FROM AUTHOR]

4H silicon carbide (4H-SiC) substrate wafers without surface / subsurface damages and low surface roughness are ideal substrates for the development of power electronics and radio frequency (RF) microwave devices, which hold great promise in applications of new energy, rail transportation, smart grid and 5G communication. The processing of 4H-SiC substrate wafers includes slicing, grinding, lapping, polishing and cleaning. However, the surface damages ( SDs) and subsurface damages (SSDs) introduced during the processing of 4H-SiC substrates affects the properties of 4H-SiC substrates and epitaxial layers, and thus the performance and reliability of devices based on 4H-SiC. This paper focuses on the formation and removal mechanisms of SDs / SSDs during the processing of 4H-SiC substrate wafers. Based on the detection method of SDs / SSDs, the morphologies and characterization approaches of SDs / SSDs are reviewed. Finally, three commonly used technologies for the removal SDs / SSDs, along with their technical advantages, development challenges and trends, are briefly discussed. [ABSTRACT FROM AUTHOR]

The widespread use of 4H silicon carbide (4H-SiC) is just around the corner since high-power electronics based on 4H-SiC are increasingly fabricated to enable the low-carbon development of the world. Quantum technologies are also intensively explored by scrutinizing 4H-SiC as a platform for wafer-scale integration of semiconductor and quantum technologies. Given the importance of impurities and defects for any semiconductor, comprehensive and insightful understanding of impurities and defects in 4H-SiC is imperative. In this Perspective, we summarize recent experimental and theoretical advances in researches on impurities and defects in 4H-SiC after briefly reviewing the history of 4H-SiC. Impurity engineering and defect engineering for the realization of the full potential of 4H-SiC are also discussed. Challenges for the study on impurities and defects in 4H-SiC are finally outlined. [ABSTRACT FROM AUTHOR]

4H silicon carbide (4H‐SiC) holds great promise for high‐power and high‐frequency electronics, in which high‐quality 4H‐SiC wafers with both global and local planarization are cornerstones. Chemical–mechanical polishing (CMP) is the key processing technology in the planarization of 4H‐SiC wafers. Enhancing the performance of CMP is critical to improving the surface quality and reducing the processing cost of 4H‐SiC wafers. In this review, the superior properties of 4H‐SiC and the processing of 4H‐SiC wafers are introduced. The development of CMP with chemical, mechanical, and chemical–mechanical synergistic approaches to improve the performance of CMP is systematically reviewed. The basic principle and processing system of each improvement approach are presented. By comparing the material removal rate of CMP and the surface roughness of CMP‐treated 4H‐SiC wafers, the prospect on the chemical, mechanical, and chemical–mechanical synergistic improvement approaches is finally provided. [ABSTRACT FROM AUTHOR]

Owing to the superior properties of the wide bandgap, high carrier mobility, high thermal conductivity and high stability, 4H silicon carbide (4H-SiC) holds great promise for applications in electrical vehicles, 5G communications, and new-energy systems. Although the industrialization of 150 mm 4H-SiC substrates and epitaxial layers has been successfully achieved, the existence of a high density of dislocations is one of the most severe bottlenecks for advancing the performance and reliability of 4H-SiC based high-power and high-frequency electronics. In this topical review, the classification and basic properties of dislocations in 4H-SiC are introduced. The generation, evolution, and annihilation of dislocations during the single-crystal growth of 4H-SiC boules, the processing of 4H-SiC wafers, as well as the homoepitaxy of 4H-SiC layers are systematically reviewed. The characterization and discrimination of dislocations in 4H-SiC are presented. The effect of dislocations on the electronic and optical properties of 4H-SiC wafers and epitaxial layers, as well as the role of dislocations on the performance and reliability of 4H-SiC based power devices are finally presented. This topical review provides insight into the fundamentals and evolution of dislocations in 4H-SiC, and is expected to provide inspiration for further control of dislocations in 4H-SiC. [ABSTRACT FROM AUTHOR]

Effect of droplet size on wetting behavior on laser textured SiC surface was studied in this work. The micro-square-convex surface was processed on smooth surface with intrisinc contact angle 101°. Then contact angles were measured on both smooth and textured surface by sessile drop method using deionized water with different droplet volume. It was found that there was significant droplet size effect on wetting behaviors for the textured SiC surface. Contact angles on smooth surface kept stable for different water droplet volume with a variation amplitude 13°. However, contact angles increased significantly from 42.25° to 131.25° with increasing droplet volume from 0.001 μL to 1 μL, then remained unchanged when the droplet volume exceeds 1 μL. The correlation analysis shows that contact angles increase with the increasing ratio of base diameter and groove width, then keep stable when the ratio exceeds 25, which explains the wetting behavior for different droplet volume. [ABSTRACT FROM AUTHOR]

Surface wettability on laser micro-circle-dimpled SiC surfaces was discussed. The morphology on the substrate was measured by the white-light interfering 3D profile meter, and the chemical composition of the substrate was tested by the Energy Dispersive Spectrometer (EDS). Water contact angles measured on the dimpled SiC surfaces and the correlation between the dimple parameters and the contact angles were analyzed. The results show that the circle-dimpled texture enhances hydrophobicity of the SiC surfaces, and the diameter of the circle dimples has more obvious influence on the contact angles than other dimple parameters. [ABSTRACT FROM AUTHOR]

Wettability control of laser textured SiC ceramic surfaces through the addition of pure elements was studied in this work. A correlation analysis between the elements C/O/Si/B/Al/Fe and the contact angle demonstrates that elements C/O/Si/B are all highly correlated with the wettability. The correlation of elements Fe/Al with the contact angle is relatively lower. Because elements C/Si are inherent elements in a SiC material, element O is derived from oxidation, and element B is added along with the additives during the sintering process. A more hydrophilic SiC surface was obtained by controlling the addition of element B. [ABSTRACT FROM AUTHOR]

Abstract: Halide chemical vapor deposition emerges as a potent technique for growing silicon carbide epitaxial layers with a high deposition rate in the range of 50–300μm/h. Experimental studies suggest that the gas composition in the reactor has profound influence on the deposition rate, the quality, and the properties of the as-deposited films. In this study, a comprehensive model was developed for halide chemical vapor deposition process including gas dynamics, heat and mass transfer, gas phase and surface chemistry, and radio-frequency induction heating. Numerical simulations of the deposition process in a horizontal hot-wall reactor using silicon tetrachloride, propane, and hydrogen as precursors were performed over a wide range of operational parameters to quantify the effects of deposition temperature, precursor flow rate, and reactor configuration. Special attention was directed to the etching of silicon carbide films by hydrogen chloride and its impact on the film deposition rate at different processing conditions. Improved gas delivery method was proposed for controlling the formation of hydrogen chloride and the associated etching effect. [Copyright &y& Elsevier]

Silicon carbide (SiC) precursor was obtained by sol–gel used tetraethoxysilane as silicon source and saccharose as carbon source, and then the precursor was used to prepare SiC by carbothermal reduction under dynamic vacuum condition. The samples were characterized by X-ray diffraction, scanning electron microscope, and low-temperature nitrogen adsorption–desorption measurement. The results showed that the carbothermal temperature for synthesizing SiC needed to be at 1,100 °C under dynamic vacuum. At this temperature, the obtained sample is composed of agglomerated regular grains with size ranging from 20 to 40 nm and has a high surface area of 167 m2/g and the main pore size center at 5.3 nm. [ABSTRACT FROM AUTHOR]

Abstract: Halide chemical vapor deposition (HCVD) emerges as a promising method for growing thick silicon carbide (SiC) epilayers, due to its ability to deposit SiC film at a high growth rate. In this paper, we develop a comprehensive model for HCVD of SiC film using silicon tetrachloride and propane as precursors. The model includes gas flow, heat and mass transfer, gas-phase reaction, and surface chemistry. Specifically, the gas-phase reactions and surface kinetics in the Si–C–Cl–H system are integrated into a transport process model to predict the composition of the gas mixture in the reactor and the deposition rate. The etching of graphite susceptor and SiC expitaxial layer are considered in the reaction mechanism. Simulations are performed in a horizontal hot wall reactor to provide information on the velocity, temperature, and concentration distributions of chemical species. The predicted deposition rates agree with experimental measurement documented in the literature. The graphite etching by hydrogen is shown to supply a substantial carbon source for the deposition, and is therefore of significant importance in determining the composition and chemical stoichiometry within the gas mixture. The modeling of surface kinetics identifies etching of the SiC layer by HCl as the leading process responsible for the reduced deposition rate at higher temperatures. The model developed can be further used for optimizing the system design and better controlling the SiC deposition process. [Copyright &y& Elsevier]

This work proposes an effective etching method for highly doped n-type 4H–SiC by combining electrochemical reactions and molten alkali etching. By employing our developed method, threading mixed dislocation (TMDs) and threading screw dislocations (TSDs) can be distinctly visualized as hexagonal etching pits of varying sizes. The slightly smaller threading edge dislocations (TEDs) appear as roughly circular etching pits, while basal plane dislocations (BPDs) are revealed as characteristic seashell-shaped pits. Additionally, we provide a reaction equation that elucidates the mechanism of the electrochemical etching process, thus sparking a new investigation into the discrimination of dislocations under molten alkali conditions. By applying a positive voltage to the wafer, we ensure a continuous supply of holes crucial for the reaction, thereby maintaining both the etching rate and the selectivity towards defects. This approach not only enhances the efficiency of the etching process but also provides a more accurate and reliable method for characterizing and understanding the dislocation properties of highly doped n-type 4H–SiC wafers. [ABSTRACT FROM AUTHOR]

Specimens of silicon carbide (6H-SiC) were irradiated with 5 MeV Kr ions (84Kr19+) for three fluences of 5x1013, 2 x1014 and 1x 1015 ions/cm2, and subsequently annealed at room temperature, 500degC, 700degC and 1000degC, respectively. The strain of the specimens was investigated with high resolution XRD and different defect evolution processes are revealed. An interpretation of the defect evolution and migration is given to explain the strain variation. The mechanical properties of the specimens were studied by using a nano-indentation technique in continuous stiffness measurement (GSM) mode with a diamond Berkovich indenter. For specimens irradiated with fluences of 5x1013 or 2x1014 ions/cm2, hardness values exceed that of un-implanted SiC. However, hardness sharply degrades for specimens irradiated with the highest fluence of 1x1015 ions/cm2. The specimens with fluences of 5x1013 and 2x1014 ions/cm2 and subsequently annealed at 700degC and 500degC, respectively, show the maximum hardness value. [ABSTRACT FROM AUTHOR]

In view of technical difficulties in preparing ceramics with complex shapes, gel casting combined with 3D printing was here adopted to prepare silicon carbide ceramic green body, and gaseous silicon infiltration sintering was used to prepare 3D lattice-structured ceramics. The preparation of the slurry, gel curing, and ceramic molding was investigated. Results demonstrate that the ratio of components affects the fluidity and stability of slurry. However, when volume fraction of the solid phase of the slurry reaches 56%, the viscosity of slurry is only 300 mPa s, and drying shrinkage rate of green body is 6.6%; these characteristics make slurry suitable for 3D complex model injection molding. Furthermore, both the temperature and the initiator affect gel curing speed. As the temperature and initiator content increase, the induction and gel time are rapidly shortened. When demolding at 300 °C and when gaseous silicon infiltration sintering is carried out at 1550 °C, a 3D lattice-structured ceramic with relative density of 87% and average compressive strength of 433 MPa can be obtained. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we combined the traditional vacuum furnace with a sur-high accuracy vacuum gauge for measuring the change of gas pressure in the furnace as a function of temperature. The modified vacuum furnace was used for preparing silicon carbide (SiC), and the recorded data named thermobarogram were applied to detect the reaction temperature for synthesis of SiC, which, in particular, changes as catalysts are used. The results showed that the carbothermal reduction temperature for synthesizing SiC, under dynamic vacuum condition, would decrease to 850°C when the mole ratio of Fe/Si=0.06 was employed in the SiC precursor. [Copyright &y& Elsevier]

A diffusion-modified HfC/HfC SiC bilayer system was innovatively designed and synthesized onto cemented carbide (WC-Co) substrate by reactive double glow plasma surface alloying (DGPSA) technique for adherent diamond deposition. The microstructure, phase composition and adhesion of the bilayer system were investigated, as well as its effect on the diamond coating system. The results showed that the bilayer system was made up of a 1.0-μm-thick nanostructured HfC-dominant inner layer and a 0.7-μm-thick HfC SiC mixed outer layer. As the gradient element distributions existed at the bilayer/substrate interface, the bilayer system displayed a superior adherence to the substrate. And the surface microhardness improved from 1802 HV 0.1 to 2857 HV 0.1 after the reactive DGPSA treatment. Subsequently, a uniform and dense nanocrystalline diamond coating with thickness of 4.0 μm was successfully deposited onto the HfC/HfC SiC interlayered substrate. Benefit from the effective suppression of Co diffusion by the interlayer and the reasonable design in its hardness and thermal expansion coefficient (TEC), the obtained diamond coating possessed an excellent adhesion. Therefore, the diffusion-modified HfC/HfC SiC bilayer systems synthesized via reactive DGPSA technique can be considered as a novel interlayer option for depositing adherent diamond coatings on WC–Co substrates. [ABSTRACT FROM AUTHOR]

• 100 mm 4H-SiC crystal is grown by tiling four seed-crystal pieces. • The tiling method may help speed up the increase of the diameter of SiC crystals. • The polytype of the obtained crystal at the gaps are not affected by tiling. • The possible reason of dislocation distribution in different crystal orientation is discussed. Increasing the diameter and reducing the dislocation density of 4H silicon carbide (4H-SiC) single crystals are the development tendency of 4H-SiC single-crystal substrate to reduce the cost of 4H-SiC based devices. In this work, we use the growth of a 100 mm 4H-SiC single crystal as an example to demonstrate that the tiling approach is attractive to enlarge the diameter of physical-vapor-transport (PVT)-grown 4H-SiC single crystals by a single growth period. By titling four pieces of 4H-SiC seed crystals, a 100 mm 4H-SiC boule without crystal deterioration is obtained by the PVT growth method. The shape of the growth interface is convex and complete after the PVT growth, indicating the tiling gaps between neighboring seed-crystal pieces are healed after the PVT growth of 25-mm thick 4H-SiC. Wafers are obtained after sequential slicing, lapping, and chemical mechanical polishing (CMP). The high-resolution X-ray diffraction (HRXRD) rocking curve measurements of the wafer at the latest growth stage indicate that the 4H-SiC crystal is basically healed, with mesoscopic boundaries being created at the central area of the wafer. Raman spectra indicate that the healing polymorph across the tiling gaps is 4H-SiC. We find that threading edge dislocations (TEDs) dominate the dislocation types in the 4H-SiC substrate wafers at the initial, middle, and latest growth stages. As the PVT growth proceeds, the density of dislocations in 4H-SiC wafers significantly decreases, as a result of the crystalline healing. Our work opens a pathway to enlarge the size of 4H-SiC single crystals in a single PVT growth period, which paves the way for the high-efficiency growth of large-size 4H-SiC single-crystals. [ABSTRACT FROM AUTHOR]

Abstract: A series of C/SiC composites was successfully synthesized via the carbothermal reduction of carbonaceous silicon xerogel, which was prepared from the sol gel method by using tetraethoxysilane TEOS and saccharose as the raw materials The obtained samples were characterized by X ray powder diffraction XRD and N2 physical adsorption The specific surface areas of the as prepared C/SiC composites varied from 329 to 849m2/g The average pore diameters and the total pore volumes were in the range of 4.5–7.6nm and 0.53–1.12cm3/g, respectively The as prepared C/SiC composites were proved to be effective supports for Ru catalysts for ammonia synthesis At 435°C, 10.0MPa and a N2/H2 (1/3) flow rate of 10000h−1, the optimum activity of 15.9% ammonia in the effluent was reached when C/SiC-5 (C/TEOS molar ratio=5) was used as the catalyst support. [Copyright &y& Elsevier]