Bulk SiC Research Articles

Demonstration of SiC-on-Insulator Substrate with Smart Cut™ Technology for Photonic Applications

Silicon-carbide-on-insulator (SiCOI) is a promising platform for photonic integrated circuits. However, the development of this new photonic platform is hindered by the lack of high-quality commercial SiC-on-insulator substrates. In this study, we present a demonstration of the transfer of a single crystalline semi-insulating 4H-SiC thin film on a SiO2 insulated substrate at 150 mm wafer scale using the Smart Cut™ technology. We describe the development of SiCOI substrates and their characterization at each key step of the process. In particular, we provide a detailed study of bow compensation related to the implanted SiC donor substrate. The quality of the transferred SiC layer was investigated as a function of the final annealing temperature applied. The optical indices of the bulk SiC were measured using spectroscopic ellipsometry, and an advanced model has been used to take into account the strong birefringence of the silicon carbide film. Finally, simulations were conducted to design a preliminary set of basic and advanced photonic devices.

Mechanical properties of aluminum /SiC bulk composites fabricated by aggregate accumulative press bonding and stir-casting process

Today, the emergence of composite structures can be considered a huge transformation on an industrial scale, especially in the transportation industry. Among all the structures made by the composite process, aluminum-based composites (AMMCs) are particularly popular both in the scientific and industrial fields. These structures are very light in weight and, at the same time, have significant strength. The ability to work with the machine in these structures is very high, and their plastic deformation is so high that they can be used in different industry sectors. Today, various methods are used to induce plastic deformation in aluminum-based composites (AMMCs). One of these methods is called aggregate accumulative press bonding (APB). The advantage of this method compared to other methods is that this method can create a homogeneous nanocomposite with ultra-fine grains. In the present study, the investigation of mechanical properties (MP's) of AA5083/5%SiC bulk composites fabricated via APB vs. pressing temperature (Temp) was conducted. All primary composite samples were fabricated via the stir-casting process (SCP). APB process was done on composite samples as a supplementary process. Finally, the effect of pressing Temp on the MP and microstructural properties (MSP) was investigated. The pressing Temp was varied between the ambient Temp's up to T = 300 °C. The MP were measured in this study by the Vickers micro-hardness (VMH) test, tensile test, and scanning electron microscopy (SEM). It was realized that the pressing Temp has a prominent effect on the MS and MP of fabricated 400°C. Samples fabricated at the ambient Temp have low ductility and high strength while for samples fabricated at T = 300 °C, the elongation and toughness values were higher than others. The TS of samples after 2 steps of APB at T = 200°C is 1.31 times more than that of fabricated at T = 300°C. Elongation was reduced sharply to 1.8% after the two steps at the ambient Temp, while it was 21% for the annealed AA5083.

Warm Pressing of Organosilicon Polymer Toward Monolithic Ceramics

Warm pressing of organosilicon polymers is often challenging due to the formation of cracks due to release of volatile compounds during the warm pressing process. The focus of the present study is to warm press crosslinked SMP‐10 powders into crack‐free compacts and to pyrolyze them to get bulk SiC monoliths. Crack formation during warm pressing is addressed by optimizing the crosslinking temperature, and the loss of formability of the powders crosslinked at higher temperatures is overcome with the use of uncured polymer as a binder. The crosslinking temperature of the preceramic polymer plays a crucial role in developing crack‐free green bodies. The amount of binder used is varied to study its effect on the bulk density of the pyrolyzed product. The warm pressed green bodies pyrolyzed at 1400 °C result in the formation of bulk silicon carbide ceramics and are characterized using X‐ray diffractometer and FTIR spectroscopy. Warm pressing is performed at a lower temperature than reported in the literature, and this limits the incorporation of oxygen during the warm pressing.

Diameter enlargement of SiC bulk single crystals based on simulation and experiment

This study employs the physical vapor transport method for diameter enlargement of silicon carbide single crystal. Numerical simulations were utilized to investigate the impact of different crucible designs on crystal enlargement. The guiding angle and ratio of seed diameter to crucible inner diameter are thoroughly examined in this study. Simulations demonstrated that under appropriate conditions for crystal growth, there is no deposition of poly-SiC around the periphery of ingot. These findings were well validated through crystal growth experiments. Subsequently, the crucible was optimized based on the simulation results for crystal growth. The final achievement was the successful enlargement of silicon carbide single crystal from 150 mm to 200 mm, with Raman mapping analysis confirming the absence of foreign polytypes around the periphery of ingot.

Designed fabrication of lightweight SiC(Hf, rGO) bulk composites derived from Hafnium-modified precursors for hypersonic vehicle components

Demand for SiC-based polymer-derived ceramics (PDCs) employed as hypersonic vehicle components with light weight, high strength, excellent high-temperature/ablation resistance is increasingly urgent. Herein, bulk SiC(Hf, rGO) nanocomposite PDCs were fabricated via re-pyrolyzing ball-milling blends of unique SiC(Hf, rGO)p/polyhafniumcarbosilane-vinyltriethoxysilane-graphene oxide (PHVG). Highly cross-linked PHVG can effectively optimize compact formability and improve ceramic yield. In-situ formed HfO2 embedded in ceramic network toughens microstructure, while interfacial HfOSi increases structure disorder to improve high-temperature properties. As demonstrated, SiC(Hf, rGO) modified by 3 wt.% Hf and re-pyrolyzed at 1300 °C possess good mechanical performances including hardness (5.83 GPa), fracture toughness (4.29 MPa·m1/2), compressive strength (181.83 MPa) and flexural strength (46.55 MPa). More interestingly, self-healing HfO2(HfSiO4)/SiO2 protective layer emerging during 20 min surface ablation test at 1300 °C, timely covers defects and avoids destructive structure, thus retains stable structure and mechanical properties of specimens. Such nanocomposites can promote uses in thermal protection systems (TPS) for hypersonic vehicles against extreme high-temperature environments.

Advances in fast 4H–SiC crystal growth and defect reduction by high-temperature gas-source method

This paper reviews recent progress in the development of high-speed 4H–SiC bulk crystal growth technology using the high-temperature gas-source method (high-temperature chemical vapor deposition). Vertical-type reactors capable of growing SiC bulk crystals of 50–75 and 100–150 mm in diameter have been developed, as have reactor configurations and growth conditions to achieve a high growth rate and material quality. Using the reactors, high growth rates up to or exceeding 3 mm/h have been achieved by employing an H2–SiH4–C3H8 gas system with high partial pressures of source gases and high growth temperature of 2500–2550 °C. It is also confirmed that the dislocation densities decline significantly in the direction of growth under proper growth conditions. Key factors for enhancing growth rate and improving crystal quality in the growth process are discussed.

Deep learning-based data processing method for transient thermoreflectance measurements

Pump–probe thermoreflectance has been commonly applied for characterizing the thermal properties of materials. Generally, a reliable and efficient non-linear fitting process is often implemented to extract unknown thermal parameters during the pump–probe thermoreflectance characterizations. However, when it comes to processing large amounts of data acquired from similar structural samples, non-linear fitting process appears to be very time-consuming and labor-intensive to search for the best fitting for every testing curve. Herein, we propose to apply deep learning (DL) approach to nanosecond transient thermoreflectance technique for high-throughput experimental data processing. We first investigated the effect of training set parameters (density and bounds) on the predictive performance of the DL model, providing a guidance to optimize the DL model. Then, the DL model is further verified in the measurement of the bulk sapphire, SiC, diamond samples, and GaN-based multilayer structures, demonstrating its capability of analyzing the results with high accuracy. Compared to the conventional non-linear fitting method (such as Global Optimization), the computation time of the new model is 1000 times lower. Such a data-driven DL model enables the faster inference and stronger fitting capabilities and is particularly efficient and effective in processing data acquired from wafer-level measurements with similar material structures.

(Invited) Application of 3D in-Situ X-Ray Visualization to Track the Formation of Dislocation Clusters during PVT Growth of SiC

SiC has become the key player among wide bandgap semiconductors for power electronic applications. Since the first description of the physical vapour transport (PVT) growth process of SiC by Tairov and Tsvetkov (J. Crystal Growth, 43, 209(1978)), there has been steady progress in SiC-based crystal growth, epitaxy and device processing. The success of SiC compared to Si is related to its superior material properties such as extremely high electrical breakdown field and high thermal conductivity compared to the standard silicon counterpart. In addition, SiC device processing utilises much of the standard Si processing equipment. A major reason for the success of SiC in power electronic applications compared to other wide bandgap counterparts such as GaN, Ga2O3 and diamond is related to the availability of large diameter SiC wafer materials (150mm = standard, 200mm = developped). Bulk SiC growth is now a very well developed process with comparatively high yields. The extraordinary physical properties also include obstacles related to the strong chemical bonding and complex phase diagram of the material, which pose challenges to the growth process. Therefore, there are still a number of open questions related to the nucleation, progression and termination of the bulk growth process that require fundamental research in materials science and technology.The aim of this presentation is (i) to give an overview of the state-of-the-art PVT growth process and (ii) to discuss a current research topic dealing with the early stage of the growth process and the defect formation that can occur during the initial nucleation of SiC. We have applied 3D in-situ visualisation of the growth process using X-ray computed tomography to visualise island formation on the large seeding area. These data are related to growth process instabilities such as temperature variations during the seeding process and axial doping level changes from the seed to the newly grown crystal. Both process instabilities induce mechanical stress on the SiC lattice and act as sources for dislocation generation and multiplication. We will show a series of growth processes with varying growth parameters that shed light on the initial growth stage of SiC.As the crystal diameter of SiC increases from 150 mm to 200 mm, the results of this study become increasingly important.

A MEMS All‐SiC Accelerometer and its Application in Vibration Test of Aero‐Engine†

This paper reports a MEMS accelerometer based on bulk SiC. The fabrication and packaging scheme were designed, an efficient signal processing circuit was built, and the output performance of the sensor was tested. The test results show that the resistivity of the piezoresistive material is 194.40 Ω μm, the sensor's output sensitivity is 0.21 mV/g, the linearity is 99.8%, and the resonance frequency is 1636 Hz. Finally, the accelerometer was applied to the two ground vibration tests of aero‐engine, and the vibration signal of the turbine components and the test bed was successfully extracted. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Evaluation of Crystal Quality and Dopant Activation of Smart Cut<sup>TM</sup> - Transferred 4H-SiC Thin Film

The Smart CutTM process offers an advantageous opportunity to provide a large number of performance-improved SiC substrates for power electronics. The crystalline quality and the electrical activation of the 4H-SiC transferred layer are then at stake when it comes to the power device reliability. In this study, we find that the H+ ion implantation used for the Smart CutTM process leads to electrical deactivation of dopants and partially disorders the material. The transferred layer fully recovers its initial crystalline quality after a 1300°C anneal, with no further evolution beyond this temperature. At this point however, the n-type dopants are still inactive. The dopant reactivation occurs in the same temperature range than that of implanted nitrogen: between 1400°C and 1700°C. After 1700°C, the initial doping level of bulk SiC is recovered.

Stress simulation of 6-inch SiC single crystal

With the size of SiC boule increasing, the problem of crystal creaking becomes more and more serious. In this work, residual stress in SiC boule is calculated by conducting stress simulation based on COMSOL and STR-VR software. A direct diagram comparing on crystal stress distribution is given. Besides, we provide relevant indications for the complete realization of large size SiC bulk with low stress for growing mainstream 6-inch SiC bulk with competitive thickness (40–50 mm) and low residual stress. And a 6-inch stress-free SiC bulk with improved quality was successfully fabricated based on our theoretical investigations.

Solution Processed Schottky Diodes Enabled by Silicon Carbide Nanowires for Harsh Environment Applications.

Silicon carbide nanowires (SiC NWs) exhibit promising features to allow solution-processable electronics to be deployed in harsh environments. By utilizing a nanoscale form of SiC, we were able to disperse the material into liquid solvents, while maintaining the resilience of bulk SiC. This letter reports the fabrication of SiC NW Schottky diodes. Each diode consisted of just one nanowire with an approximate diameter of 160 nm. In addition to analyzing the diode performance, the effects of elevated temperatures and proton irradiation on the current-voltage characteristics of SiC NW Schottky diodes were also examined. The device could maintain similar values for ideality factor, barrier height, and effective Richardson constant upon proton irradiation with a fluence of 1016 ion/cm2 at 873 K. As a result, these metrics have clearly demonstrated the high-temperature tolerance and irradiation resistance of SiC NWs, ultimately indicating that they may provide utility in allowing solution-processable electronics in harsh environments.

Core-level photoelectron spectroscopy study on the buffer-layer formed in approximately atmospheric pressure argon on n-type and semi-insulating SiC(0001)

Using core-level photoelectron spectroscopy, we studied the surface of SiC(0001)-6√3 × 6√3R30° (buffer layer surface) formed on n-type and semi-insulating substrates via the approximately-atmospheric-pressure graphitization method. When the surface was exposed to air after buffer layer formation, hydrocarbons were adsorbed and oxygen atoms were chemically bonded to the carbon atoms comprising the buffer layer. Subsequently, annealing in ultra-high vacuum and an ethylene ambient allowed the removal of these oxygen atoms and hydrocarbons, and a clean buffer layer surface was obtained. Furthermore, using the peak position of Si 2p, band bending of the buffer layer on the n-type and semi-insulating substrates was estimated. A reasonable value of −0.05 eV was obtained for the n-type substrate. However, for the semi-insulating substrate, the Fermi level (Ef) was located at 0.05 eV below the conduction band minimum (CBM) on the surface. This is anomalous if we interpret the change in the CBM position over Ef from the bulk to the surface to be solely induced by band bending. To interpret this situation, we propose a mechanism in which the n-type region appears near the surface of the SiC bulk under the buffer layer.

Electrical deterioration of 4H-SiC MOS capacitors due to bulk and interface traps induced by proton irradiation

In this study, the displacement damage dose (DDD) effects of proton irradiation on bulk crystal and interfacial properties of 4H-SiC MOS capacitors (MOSCs) were investigated. The Monte Carlo calculation code named SRIM (Stopping and Range of Ions in Matter) was first used to predict the depth profiles and damage distributions of protons. The 4H-SiC MOSCs were irradiated with 60, 100, 150 keV protons to fluences ranging from 5 × 1011 to 5 × 1013 cm−2. Capacitance-voltage (C-V) curves of the MOSCs were then measured to characterize the variation of the electrically active defects in 4H-SiC MOSCs. The results revealed that the non-ionization energy loss of incident protons leads to the accumulation of the primary defects in bulk SiC crystal as well as the increase of the interface traps between SiO2 and SiC crystal. A distinctive bump phenomenon was found in the weak inversion region of the C-V curve and it became more prominent with the increase of proton fluence, providing evidence for the existence of bulk traps. Furthermore, the incident proton energy is also a crucial factor in interface deterioration, suggesting that more interface traps would be formed when the proton damage peak is closer to the SiO2/SiC interface.

Vertical structure of Sb-intercalated quasifreestanding graphene on SiC(0001)

Using the normal incidence x-ray standing wave technique as well as low energy electron microscopy we have investigated the structure of quasi-freestanding monolayer graphene (QFMLG) obtained by intercalation of antimony under the $\left(6\sqrt{3}\times6\sqrt{3}\right)R30^\circ$ reconstructed graphitized 6H-SiC(0001) surface, also known as zeroth-layer graphene. We found that Sb intercalation decouples the QFMLG well from the substrate. The distance from the QFMLG to the Sb layer almost equals the expected van der Waals bonding distance of C and Sb. The Sb intercalation layer itself is mono-atomic, flat, and located much closer to the substrate, at almost the distance of a covalent Sb-Si bond length. All data is consistent with Sb located on top of the uppermost Si atoms of the SiC bulk.

Robust and fast response solar-blind UV photodetectors based on the transferable 4H-SiC free-standing nanowire arrays

Wide band gap semiconductor 4 H -SiC has been considered as the most promising candidate for developing solar blind ultraviolet (UV) photodetectors (PDs). However, the absence of PDs constructed by the desired 4 H -SiC nanostructures greatly limits their performance and practical application. In this study, the free-standing 4 H -SiC bamboo-like nanowire arrays with an even diameter/height of 30 nm/35 µm prepared by the anodic oxidation of 4 H -SiC bulk single crystal in a top-down manner are used to develop the solar-blind PDs. Experiment results reveal that the developed PDs can have an excellent solar-blind detection performance such as high sensitivity to 275 and 365 nm UV light, a considerable light-dark ratio (∼44.3), remarkably low dark current, fast response (47.3 ms), excellent repeatability and stability. Additionally, the unencapsulated PDs can have an excellent high-temperature stability up to 300 ºC. It is expected that the 4 H -SiC nanowire arrays-based PDs can have more potential than their counterpart bulk material for the future optoelectronic device applications. • The MSM solar-blind UV photodetectors based on bamboo-like 4 H -SiC nanowire arrays have been successfully fabricated. • The developed photodetectors can have a large light-dark ratio, high photoresponsivity, and remarkably low dark current. • The resulting photodetectors can achieve the fast response and an excellent high-temperature stability up to 300 ºC.

200 mm silicon carbide bulk growth optimisation: mass transport controlled by a designed gas deflector

200 mm silicon carbide bulk growth would be the mainstream in industrial production, but the difficulty of multiple physical fields control is increased with the larger diameter. In this study, a resistance heating based physical vapour transport system was established and explored for its appropriate parameters of multiple physical fields (such as thermal, velocity, flux and reaction components fields) by the COMSOL simulation. A combination of pressure at 5 torr and seed temperature of 2340 K was gained by taking the rate and homogeneity of in-plane growth into consideration. Furthermore, a gas deflector was designed to decrease the convection and to improve the homogeneity of mass transport. This gas deflector had the ability to enhance the quality and yield of 200 mm SiC crystal bulk. A high yield of 90.1% was achieved for the 200 mm part within the crystal thanks to this deflector (without the usage of the deflector was 38.5%). This work provides a useful tool and insights into the steps required for the optimisation of 200 mm or larger size SiC bulk growth.

Realizing load bearing-heat insulation integration of lightweight porosity-controlled SiC(rGO) bulk ceramics via precursor route for hypersonic vehicles

Realizing integration of admirable load bearing and outstanding heat insulation characteristics of porosity-controlled ceramics for hypersonic vehicles is a great challenge. Herein, an ingenious strategy based on re-pyrolysis process of ball-milling-induced fillers/precursors(pore-forming agents) blends is proposed to prepare porous SiC(rGO) bulk polymer-derived ceramics (PDCs) for thermal protection. During re-pyrolysis, dense integrated β-SiC/SiOxCy/Cfree(rGO) framework, belonging to SiC(rGO)p tightly tied by SiC(rGO) from polycarbosilane-vinyltriethoxysilane-graphene oxide (PCS-VTES-GO, PVG), can be formed to maintain brilliant mechanical properties of products. Meanwhile, good interfacial compatibility of nanocomposite structure within the framework also contributes to load capacity. A uniquely uniform distribution of dentinal tubules-like pores, originated from polystyrene (PS) in SiC(rGO) region, could relax stress at crack tips and ensure good thermal insulation. Particularly, lightweight porous SiC(rGO) bulk PDCs with 10 wt% PS content possess low thermal conductivity (0.25 W·m−1·K−1), excellent fracture toughness (1.96 MPa·m1/2), outstanding hardness (3.58 GPa), optimal compressive strength (51.80 MPa) and good flexural strength (33.86 MPa). Their large-sized molding ability and good high-temperature oxidation resistance were significantly demonstrated by further exploration. Such well-balanced high load bearing and good heat insulation integration nature can be used to make thermal insulators with complex shapes in a facile and economical manner.

Nanocrystalline Cubic Silicon Carbide: A Route to Superhardness (Small 22/2022)

Superhard Nanocrystalline Cubic Silicon Carbide In article number 2201212, Guoying Gao, Bo Xu, and co-workers successfully synthesize nanocrystalline β-SiC bulks with asymptotic Vickers hardness over the superhard threshold of 40 GPa, broadening the family of superhard materials. The frontispiece emphasizes the superhardness of nanocrystalline SiC bulk by scratching the cBN single crystal.

Electron tomography for sintered ceramic materials by a neural network algebraic reconstruction technique

The missing wedge effect in electron tomography introduces various types of artifacts in the tomograms and lowers the reconstruction resolution and quality. The artifacts produced in tomographic reconstruction of bulk materials can be very severe, particularly for sintered bulk ceramic materials in which there are often nano-pores or pore-like microstructure features. Here, we report a neural network algebraic reconstruction algorithm with no prior knowledge to perform electron tomography for a sintered SiC material with nano carbon zones. The results show that the proposed algorithm has a great suppressive effect on the missing wedge artifacts and a high tolerance for noise. The information in the missing wedge can be partly recovered by this technique. Thus, both the shape of the bulk SiC specimen and its irregular inner pore-like features are correctly retrieved in the obtained 3D image. Our study shows the effectiveness of the neural network algorithm for improving the reconstruction accuracy of electron tomography, in order to reveal sophisticated 3D microstructures generally existing in sintered ceramic materials.