Growth Of SiC Research Articles

Carbon solubility in liquid silicon: A computational analysis across empirical potentials.

The nucleation and growth of SiC precipitates in liquid silicon is important in the crystallization of silicon used for the photovoltaic industry. These processes depend strongly on the carbon concentration as well as the equilibrium solubility relative to the precipitate phase. Here, using a suite of statistical thermodynamic techniques, we calculate the solubility of carbon atoms in liquid silicon relative to the β-SiC phase. We employ several available empirical potentials to assess whether these potentials may reasonably be used to computationally analyze SiC precipitation. We find that some of the Tersoff-type potentials provide an excellent picture for carbon solubility in liquid silicon but, because of their severe silicon melting point overestimation, are limited to high temperatures where the carbon solubility is several percent, a value that is irrelevant for typical solidification conditions. Based on chemical potential calculations for pure silicon, we suggest that this well-known issue is confined to the description of the liquid phase and demonstrate that some recent potential models for silicon might address this weakness while preserving the excellent description of the carbon-silicon interaction found in the existing models.

Structural characterization of the grown crystal/seed interface of physical vapor transport grown 4H-SiC crystals using Raman microscopy and x-ray topography

The defect structure at and near the grown crystal/seed interface of 4H-SiC single crystals grown by the physical vapor transport (PVT) growth method has been investigated using Raman microscopy and x-ray topography. To examine the detailed distribution of crystallographic defects across the interface, 4H-SiC wafers containing a beveled growth interface were prepared from nitrogen-doped 4H-SiC single crystal boules; the beveled interface allows more spatially resolved observations of the defect structure near the interface compared to the interface on vertically sliced [e.g., (112¯0) and (11¯00)] wafers. Raman microscopy imaging using the longitudinal optical phonon-plasmon coupled (LOPC) mode determined the position of the growth interface and revealed several characteristic features of the interface through the analyses of the scattering intensity, peak position, and width of the LOPC mode peak. X-ray topography revealed that there existed networks of basal plane dislocations at the growth interface, and they extended deep inside the seed crystal. Based on these observations, we discussed the defect formation process at the initial stage of PVT growth and suggested an important role of vacancy injection during PVT growth of SiC.

Effects of aluminum, boron and carbon additives on microstructure of porous silicon carbide ceramics and their properties

Abstract Porous SiC ceramics with in-situ plate-like grain growth were fabricated by pressureless-sintering using Al, B and C additives, and the effects of Al, B and C additives on the microstructure of porous SiC ceramics and their properties were investigated. Whereas the porous SiC ceramics sintered with B-C additives mostly consisted of fine SiC grains without grain growth, Al additives with B-C system enhanced plate-like grain growth of SiC in the porous SiC ceramics. Notably, the porous SiC ceramics sintered with 0.1 wt% Al and B-C additives consisted of plate-like SiC grains of around 10-20 μm, and the plate-like SiC grains stuck out of the walls of pores and the sintered surface in the porous SiC ceramics. XRD results suggested that the plate-like SiC grains formed in the porous SiC ceramics sintered with Al-B-C additives mainly consisted from 6H (α-SiC) phase. Compressive strength and thermal conductivity of the porous SiC ceramics sintered with 0.1 wt% Al and B-C additives at room temperature were 50 MPa and 10 W/m·K, respectively. From these results, it is concluded that high performance porous SiC ceramics with unique morphology of entangled large plate-like SiC grains were successfully achieved based on in-situ grain growth.

Thermal expansion coefficient of Diamond/SiC composites prepared by silicon vapor infiltration in vacuum

Diamond/SiC composites were fabricated by Si-vapor reactive infiltration where graphite was used to generate SiC via an SiC reaction. The composites exhibited an inward growth of SiC and cracks within the diamond. In the strong interfacial bonding, Si diffusion occurred on the surface of the diamond. The thermal expansion coefficient (CTE) and thermal residual stress at different infiltration temperatures were simultaneously investigated. It was found that the CTE values increased from 1.2 to 4.5 × 10−6 K−1 in the measured temperature range, while the presence of large-sized crushed diamond, high SiC content and high infiltration temperature enhanced the CTE values. In the low-temperature range, the measured CTEs agreed with those predicted by the Turner model; while in the high-temperature range they agreed with those predicted by the lower-bound Schapery model. Additionally, based on the Raman spectra, the thermal residual stresses were found to be 0.85, 1.76, 2.15 and 2.67 GPa at the infiltration temperatures of 1550, 1600, 1650, and 1700 °C, respectively.

High-Q integrated photonic microresonators on 3C-SiC-on-insulator (SiCOI) platform.

We report a high-quality 3C-silicon carbide (SiC)-on-insulator (SiCOI) integrated photonic material platform formed by wafer bonding of crystalline 3C-SiC to a silicon oxide (SiO2)-on-silicon (Si) substrate. This material platform enables to develop integrated photonic devices in SiC without the need for undercutting the Si substrate, in contrast to the structures formed on conventional 3C-SiC-on-Si platforms. In addition, we show a unique process in the SiCOI platform for minimizing the effect of lattice mismatch during the growth of SiC on Si through polishing after bonding. This results in a high-quality SiCOI platform that enables record high Qs of 142,000 in 40 µm radius SiC microring resonators. The resulting SiCOI platform has a great potential for a wide range of applications in integrated optics, including nonlinear optical devices, quantum optical devices, and high-power optical devices.

Synthesis of bamboo-like 3C-SiC nanowires with good luminescent property via nano-ZrO2 catalyzed chemical vapor deposition technique

This work provides a novel chemical vapor deposition technique to synthesize bamboo-like 3C-SiC nanowires (NWs) at low temperature (1200 °C) in absence of Ar gas by Si and phenolic resin powders, and catalyzed by trace nano-ZrO2 particles. The obtained bamboo-like 3C-SiC NWs were dozens of microns in length and composed of two alternating structure units with periodical fluctuating diameter, and the diameters of nodes and stems were 50–70 nm and 40–50 nm, respectively. Nano ZrO2 catalyst was key factor for SiC NWs formation and growth because ZrO2 triggered reactions to generate more SiO(g) and CO(g), and activated SiO (g) and CO (g) by weakening Si–O and C–O bond strength. The reciprocal formation of ZrC and ZrO2 occurred repeatedly led to SiC growing into bamboo-like NWs. The bamboo-like SiC NWs have good violent-blue luminescent property.

Stability of multiple Shockley type basal plane stacking faults in heavily nitrogen-doped 4H-SiC crystals

The stability of various types of multiple Shockley type basal plane stacking fault in heavily nitrogen-doped 4H-SiC crystals was theoretically investigated on the basis of the quantum well action (QWA) mechanism. The energy levels of confined electrons within multiple Shockley stacking faults (SSFs) were calculated using the simple quantum well model and compared to the experimental values estimated from photoluminescence measurements. The formation energies of the stacking faults were also calculated on the basis of the axial next nearest neighbor Ising (ANNNI) model for SiC polytypes. Based on these physical and electronic parameters, the stability of multiple SSFs in heavily nitrogen-doped 4H-SiC crystals was discussed, and it was revealed that the stacking sequence of multiple SSFs largely affects their stability; SSFs having a cubic stacking sequence of medium thickness (five to six Si-C bilayer thickness) are stable in heavily nitrogen-doped 4H-SiC crystals at the typical growth and device processing temperatures of SiC, i.e., 1500–2600 K.

Effect of free carbon on micro-mechanical properties of a chemically vapor deposited SiC coating

SiC coatings with different content of free carbon were deposited on polycrystalline silicon substrate by chemical vapor deposition (CVD) by using CH3SiCl3-H2-Ar reactive system. The composition, microstructure and micro-mechanical properties of coatings were investigated. The results show that, when H2/MTS is 10, there is no free carbon in coatings. However, at the ratio of H2/MTS of 8.89, 7.97 and 7.32, the content of free carbon is falling in the range of 0.025–0.065, 0.100–0.800 and 0.005–0.035 respectively. The supersaturation of [H] is a key factor to control the generation of free C and the nucleation and growth of SiC coating. As to mechanical properties of SiC coatings, there may be a critical value of the content of free carbon in the coating. When the content of carbon is less than the critical value, the free carbon can enhance the mechanical properties of the coating; otherwise, the free carbon weakens the mechanical properties.

Numerical investigation of the effect of static magnetic field on the TSSG growth of SiC

A set of numerical simulations were conducted to investigate the effect of applied static magnetic field on the convective flows and carbon concentration in the Top-Seeded Solution Growth (TSSG) process of SiC. The applied magnetic field is considered as vertical and cusp in an axisymmetric configuration. Seed rotation was also included in the simulations. The numerical results show that the applications of VMF (vertical magnetic field) and weak CMF (cusp magnetic field) are effective in suppressing Marangoni convection. The application of VMF slows down growth rate but reduces the variation of growth rate towards a more constant rate. Seed rotation appears to be not beneficial in the presence of CMF alone. However, the combined effect of seed rotation with VMF enhances growth and makes the growth rate variation smaller.

Effect of the Growth Conditions on the Crystal Quality in Solution Growth of SiC Using Cr Solvent without Molten Si

We have succeeded in solution growth of SiC from Cr solvent without Si using ceramic SiC as the SiC source. The effect of the growth conditions, such as the liquid height in the crucible, on the crystal quality in solution growth of SiC from Cr solvent was investigated. For a liquid height in the crucible of up to 10 mm, the growth rate increases with increasing liquid height and the SiC crystals are a single polytype, while the growth rate decreases and the crystals are polycrystalline for a liquid height above 10 mm. In the former case, the balance between dissolution and transportation of the solute are comparable. The latter case is expected to be transportation limited because transportation of free C and Si atoms is inhibited by excrescent crystals in solution and the increase in the distance for solute transportation. In addition, a higher growth temperature leads to growth of only 4H-SiC.

Experimental Determination of Carbon Solubility in Si<sub>0.56</sub>Cr<sub>0.4</sub>M<sub>0.04</sub> (M = Transition Metal) Solvents for Solution Growth of SiC

Si0.56Cr0.4M0.04 (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Rh, and Pd) solvents were investigated to identify new multi-component materials in which carbon is highly soluble, because solubility is a key parameter in solution growth of SiC. The solubility of carbon in Si0.56Cr0.4Co0.04 was 8.37 at%, the highest value among the tested multi-component materials. This is about 2.5 times the solubility of carbon in Si0.6Cr0.4. These results show that addition of a small amount of a transition metal enhanced the solubility of carbon in Si0.6Cr0.4. This technique for determining carbon solubility is effective for investigating crystal growth using solvents with several components, for which complex thermodynamic calculations are necessary.

Solution Growth of SiC from the Crucible Bottom with Dipping under Unsaturation State of Carbon in Solvent

SiC crystals are grown using a Si-Cr-based solvent by a top-seeded solution growth (TSSG) method by changing the dipping time after when the growth temperature is reached. Step-flow-like curve morphologies were observed for a dipping time after 15 min, while polycrystallization occurred at the periphery for that after 120 min, which corresponded to the dipping under unsaturated and supersaturated carbon in the solvent, respectively. Furthermore, the solution growth of SiC with dipping under unsaturated carbon was easily realized by the growth from the crucible bottom, step-flow-like growth was achieved. Using this technique, dominant polytypes of SiC in various growth conditions after stable seed dipping under the unsaturation in the solvent can be demonstrated.

Understanding the Chemistry in Silicon Carbide Chemical Vapor Deposition

Understanding the chemistry in CVD of SiC is important to be able to control, improve and scale up the process to become industrially competitive. A thorough understanding have so far been difficult to achieve due to the complex nature of the process. Through modeling tools, and a systematic approach when constructing the chemical models, new insights to the SiC CVD chemistry can be obtained. Using a general model that is independent on the choice of precursors and reactor configuration, and by coupling modeling results to experimental findings, we here show that SiCl2 and SiH2 previously suggested as the main silicon bearing growth species in the chlorinated and standard chemistries, respectively, does not contribute significantly to the SiC growth, and that the main active species are C2H2, CH3, Si, and SiCl.

Mechanism of Replicating 4H-SiC Polytype during Solution Growth on Concave Surface

To determine the mechanism of 4H-SiC replication during solution growth on a concave surface, SiC growth on a 2-in.-diameter 4H-SiC (0001̅) seed and on 0.5-in. square seeds of different planes was carried out at 2273 K using Si–40 mol % Cr-based solvent with and without Al addition. Grown crystal that replicated 4H-SiC possessed (11̅02̅) facets at the periphery of the growth interface, with its growth tips located at both edges of the facet. Al addition to the solvent enlarged such facets on the growth interface and increased the probability of 4H-SiC replication. Furthermore, Al addition to the solvent improved the stability of crystal grown on the (11̅02̅) seed, as evaluated from surface roughness analysis. According to the surface stability, we propose a mechanism for 4H-SiC replication and the effect of Al addition into the solvent during solution growth on a concave surface.

In Situ Interface Observation of 3C-SiC Nucleation on Basal Planes of 4H-SiC During Solution Growth of SiC from Molten Fe-Si Alloy

Solution growth is a promising process to obtain high-quality 4H-SiC crystal for application in high-voltage-power devices. Polytype transition from 4H-SiC into 6H-, 15R-, or 3C-SiC is one of the major issues to be solved to achieve rapid growth of large-diameter 4H-SiC crystals. In this study, the mechanism for the polytype transition to 3C-SiC during the solution growth process was determined from in situ interface observation of SiC growth on basal planes of 4H-SiC from Fe-36 mol.%Si alloy at 1680–1885 K. The nucleation behavior of 3C-SiC on 4H-SiC was discussed in terms of classical nucleation theory.

Molecular dynamics simulation of interfacial growth of SiC from Si–C solution on different growth planes

A critical issue in solution growth of 4H–SiC crystal is to control the morphology at the growth interface. We conducted a molecular dynamics simulation of interfacial growth of SiC from Si–C solution to understand the atomic-scale growth behavior on the different growth planes of 3C–SiC, 4H–SiC and 6H–SiC. The growth rates on the basal plane were smaller than those on the other planes. To understand the growth modes on the growth planes, calculations of growth behavior on the 4H–SiC {0001}, {101¯0} and {101¯2} were performed with larger cells. The growth interface of 4H–SiC {101¯0} and {101¯2} tended to become rough, whereas 4H–SiC {0001} maintained a flat interface. Possible growth modes were estimated from a correlation between the growth rate and the crystal structure.

Electrical and Material Properties Analysis of 5kV 4H-SiC Schottky Barrier Diodes

Silicon carbide is an attractive material for next-generation power devices, it has wide band gap and high thermal conductivity. SiC power devices can operate at higher temperatures and voltages compared to silicon devices. But, electrical characteristics of the SiC power devices can be deteriorated by SiC defects. The killer defects such as micropipes and stacking faults have been reduced through the development of SiC growth technique. But still the threading dislocations (TDs) and basal plane dislocations (BPDs) lowered the breakdown voltage and increased the leakage current during device operation [1]. In this study, we fabricated the 5 kV 4H-SiC Schottky barrier diode (SBD) to study the effect of SiC defect on electrical properties of SiC SBDs. The thickness of epitaxial layer was 50 um and the doping concentration is 1E15 cm-3. The device was fabricated with various length of junction termination extension (JTE). Ion implantation was performed to form p surge (Al, 500 °C, 5E19 cm-3) and JTE (B, 500 °C, 2E18 cm-3) regions. Activation annealing was performed at 1700 °C for 60 m. 100 and 30-nm-thick Ni were deposited as the cathode and front-side ohmic metal respectively, and then annealed at 950 °C for 90 s in RTA system. Finally, 100-nm-thick Ni was sputtered on front-side as a Schottky contact metal. We investigated the forward, reverse characteristics, and reverse breakdown voltage of the fabricated 4H-SiC SBDs. The diode characteristics, ideality factor (IF) and Schottky barrier height (SBH) were obtained from the forward electrical characteristics, about the 1.23 and 1.3 eV, respectively. The relative highly ideality factor may be due to rough surface of thick epitaxial layer. The breakdown voltage was obtained above 5 kV with JTE length longer than 60 um. During reverse characteristics the electrically weak points were observed using electroluminescence (EL). The EL spot was mainly aroused from electrically leaky points, it mostly observed at the edge of JTE. Some EL spots were observed inside the JTE or active region. The defects of the fabricated 4H-SiC 5 kV SBDs were analyzed using non-destructive analysis method, X-ray topography (XRT) and electron beam induced current (EBIC). We tried to determine the correlation between the electrical characteristics of the device and the crystal defects in the device. [1] H. Fujiwara, H. Naruoka, M. Konishi, K. Hamada, T. Katsuno, T. Ishikawa, Y. Watanabe, and T. Endo, Appl. Phys. Lett. 100, 242102 (2012). Figure 1

Formation of SiC thin films by chemical vapor deposition with vinylsilane precursor

We have examined the formation of SiC thin films by chemical vapor deposition (CVD) using vinylsilane and investigated the chemical bonding state and crystallinity of the prepared SiC thin films. We achieved the formation of a Si–H–less SiC film at growth temperatures as low as 600 °C. Also, we investigated the in situ doping effect of N by the incorporation of NH3 gas in the SiC growth and demonstrated that the chemical composition of N in SiC thin films was controlled by adjusting the NH3 flow rate. In addition, we examined the growth of SiC thin films on a Cu substrate and achieved the formation of a SiC thin film while avoiding any significant reaction between SiC and Cu at a growth temperature of 700 °C.

Role of boron addition on phase composition, microstructural evolution and mechanical properties of nanocrystalline SiBCN monoliths

Nanocrystalline SiBCN monoliths with the same Si/C/N mole ratio and various boron additions ranged from 0 to 3.0mol were prepared by mechanical alloying plus reactive hot pressing methods. Correction of boron content and microstructural/morphological evolution was investigated in detail by XRD, SEM, TEM and STEM-EDX structure characterization. Except for SiC and BN(C), boron addition contributes to BxC formation. Besides, boron addition promotes the crystallization of SiC, leading to the formation of poor crystallinity of spherical structures in inner SiC. Furthermore, boron addition significantly promotes the grain growth of SiC and BxC and therefore increases the relative volume ratios of BxC/BN(C) and BxC/SiC. Amorphous-like BN(C) changes to belt-like structures as boron addition increases. The new formed BxC effectively contributes to the improvement of Vicker’s hardness while pull-out of BN(C) belt-like structures benefits the fracture toughness.

Sandwich-structured C/C-SiC composites fabricated by electromagnetic-coupling chemical vapor infiltration

Carbon fiber (CF) reinforced carbon-silicon carbide (C/C-SiC) composites are one of the most promising lightweight materials for re-entry thermal protection, rocket nozzles and brake discs applications. In this paper, a novel sandwich-structured C/C-SiC composite, containing two exterior C/SiC layers, two gradient C/C-SiC layers and a C/C core, has been designed and fabricated by two-step electromagnetic-coupling chemical vapor infiltration (E-CVI) for a 20-hour deposition time. The cross-section morphologies, interface microstructures and SiC-matrix growth characteristics and compositions of the composites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD), respectively. Microstructure characterization indicates that the SiC growth includes an initial amorphous SiC zone, a gradual crystallization of SiC and grow-up of nano-crystal, and a columnar grain region. The sandwich structure, rapid deposition rate and growth characteristics are attributed to the formation of thermal gradient and the establishment of electromagnetic field in the E-CVI process. The composite possesses low density of 1.84 g/cm3, high flexural strength of 325 MPa, and low linear ablation rate of 0.38 μm/s under exposure to 5-cycle oxyacetylene flame for 1000 s at ~1700 °C.