The physical vapor transport (PVT) method has been widely used in the growth of silicon carbide single crystals. In designing the growth system, effective thermal management is crucial, particularly regarding the temperature of the growth surface and the horizontal and vertical temperature gradients. In this paper, an inner rod positioned along the central axis of the crucible to optimize thermal field through numerical simulations. The results show that the introduction of the inner rod reduces the horizontal temperature difference of the growth surface from nearly 80 °C to less than 10 °C, significantly minimizing the bulging of the growth crystals. Additionally, simulations were performed to examine the effects of varying the radius and height of the inner rod, as well as the radius of the bottom graphite holder, with findings discussed in detail. This study provides a theoretical method for the growth of high-quality, low-stress 4H-SiC crystals with smooth surfaces. It also provides a reference for the growth of 3C-SiC from small distance of material source to seed by sublimation epitaxy.

Silicon carbide (SiC) single-crystal substrates, as core materials for wide-band-gap semiconductor devices, exhibit critical optical and mechanical stability under high-temperature environments, which decisively influences the reliability of aerospace, deep-space exploration, and high-temperature sensor systems. This study systematically investigates the evolution of optical properties and key mechanical parameters (elastic modulus and linear thermal expansion coefficient) of high-purity 4H–SiC single-crystal substrates within a temperature range of 25–1600 °C, elucidating the impact of extreme thermal conditions on the material’s intrinsic characteristics. High-temperature treatments were conducted in an air atmosphere at 600–1600 °C, and the effects on optical performance (transmittance) and surface morphology were analyzed using ultraviolet–visible–near-infrared spectrophotometry (UV–Vis–NIR) and scanning electron microscopy (SEM). Experimental results reveal that: (1) at temperatures ≤ 600 °C, the average transmittance of SiC in the 350–2000 nm spectral range (below 65

Substrate TSDs propagate into an epilayer and cause breakdown holes.

The research and commercialization of SiC based power device have been burgeoning over the last decade worldwide, which is bringing about an increasing demand on lost-cost and low-defect SiC wafers. To meet this challenge, we have been continuously making efforts on improving the crystal growth and wafer processing techniques. Now, the mass-production of high quality 4-inch, 6-inch n-type and semi-insulating SiC wafers has been realized. Statistically, the micropipe density is lower than 0.5 cm-2. The resistivity of the wafers is lower than 0.02 Ω·cm and up to 108 Ω·cm for n-type and semi-insulating SiC single crystals, respectively. A state of the art processing technique has been developed to control wafer deformation and thickness within the desired values for subsequent epitaxy. The total defect number of the epitaxial layers grown on the "epi-ready" 4-inch SiC wafer is 63, and the usable area is 97.6%, indicating the high quality of our SiC substrates.

The morphology and causes of stacking faults (SF) in homoepitaxial layers of 4H-SiC were studied. According to characteristics of PL images and morphology images of 4H-SiC five kinds of SFs have been defined. In the PL images, the morphologies of SF I and SF II-V are trapezoidal and triangular, respectively. SF II lays inside the area of SF I. In the morphology images, SF I and IV are not seen, SF II-III are carrot shaped and SF V is triangular respectively. The results show that SF I is a kind of base plane SF which originates from the base plane dislocation (BPD) lines of the substrate, parallel to < 1 (1) over bar 00 > direction and moving along < 11 (2) over bar0 > direction during epitaxial growing. SF II and most of SF III-IV originate from BPDs in substrate. One BPD converts into threading dislocation during epitaxial growing and propagates to the surface along < 0001 > direction, while other BPDs or partial dislocations originating from threading dislocation propagate in (0001) plane to form triangular base plane SFs. The rest of SF III-IV and SF V originate from threading edge dislocation or other defects in substrate. SF II-III display carrots morphology because a prism SF plane perpendicular to the (0001) plane is formed to intersect with surface during epitaxial growing process. SF IV is not seen in the morphology image because no prism SF plane is formed to intersect with surface. All results demonstrated that reducing BPDs of the substrate is especially important for reducing SFs in the epitaxial layers.

Thenitrogen doped and unintentional nitrogen doped 4H-SiC single crystals were grown by PVT method on the C-terminated 4H seeds offcut by 4 degrees from the c-face towards the <11<(2)overbar>0> axis, respectively. Optical microscope was used to investigate the characteristic of stacking fault defects and the effects of nitrogen doped onstacking fault defects in 4H-SiC single crystals etched by molten KOH etching The result shows that the lines of the basal plane dislocation defect of the 4H-SiC wafer surface are corresponding to stacking fault defects in 4H-SiC single crystals, and the direction of the lines is parallel to <1<(1)overbar>00>. There are more stacking fault defects in 4H-SiC single crystals doped with nitrogen than that of unintentional nitrogen doped 4H-SiC single crystals. This phenomenon is consistent with published literatures in which high concentrations of nitrogen caused the formation of stacking fault defects in 4H-SiC single crystals. However, there is no stacking fault defect in the facet area for nitrogen doped 4H-SiC single crystals, although the nitrogen concentration in the facet area is higher than that in the other area, which is presumably due to specific crystal growth habit in the facet area of 4H-SiC single crystal.

Colloidal silica slurry was used for chemical mechanical polishing (CMP) 4H-type conductive SiC surface to explore the key parameters affecting the surface quality of SiC substrates and obtain higher material removal rate and defect-free surface.The results indicate that SiC surface interact with both hydrogen peroxide (H2O2) and hydroxyl ion (OH-) to form softer oxidations.The removal rate of SiC increase firstly and then remain unchange when the content of H2O2 or OH-is increase under a certain pressure.The removal rate of SiC increase further when the content of OH-is increase under a higher pressure.By optimizing the polishing parameters, the polishing removal rate of SiC is increased to 142 nm/h.The results show that keeping the balance of chemical and mechanical influence is a key factor to obtain the high removal rate and defect free SiC surface.The results of optical surface analyzer (Candela) and atomic force microscope(AFM) show that the wafer surface has no scratch and the surface roughness is 0.06 nm.The densities of defects are less than 1 /cm2 and the surface roughness is 0.16 nm after epitaxial growing a film of SiC.

本文回顾了碳化硅单晶材料的发展历程和研究现状.主要讨论了物理气相传输法、高温化学气相沉积法(HTCVD)、液相法等SiC晶体生长方法,针对每种生长方法,阐述了其生长原理及研究现状.

The present invention discloses a method for peeling off silicon carbide seeds from a seed holder. According to the characteristic that an oxidizing acid with high concentration may react with a seed adhesive which is sugar or organic substances such as an organic adhesive at a certain temperature while silicon carbide seeds do not react with the oxidizing acid with high concentration, the silicon carbide seeds can be peeled off from the seed holder by the method, and the seed peeled off can be used for crystal growth after being washed, dried and re-polished.

Threading edge dislocations (TEDs), threading screw dislocations (TSDs), basal plane dislocations (BPDs) are common line dislocations occurring in silicon carbide crystals. Complex dislocations are a combination of two types or more of individual dislocations and have been less studied. Here, we report the characterization and the formation mechanism of a complex dislocation consisting of one BPD and two TEDs in 6H-SiC single crystals. Our experimental results show that this type of complex dislocations can occur frequently in single crystals as in epitaxial films. We reveal that it originates from an interaction of a TED and a BPD. This interaction is likely to induce the emergence of a new TED.

4H-SiC crystals containing polytype defects are investigated by optical microscopy, atomic force microscopy, and Raman scattering, aiming at understanding the mechanism of polytype transformation during growth processes. It is observed that the crystal surfaces around the facet are uneven and contain many macroscopic triangular domains, consisting of wide triangular terraces and giant macrosteps. Nucleation and growth on the wide terraces are demonstrated to be responsible for the polytype transformation. A possible polytype transformation mechanism is put forward, which can explain the stabilizing effect of nitrogen on 4H-SiC growth.

In this contribution, we report the generation of 17-μJ mid-infrared (MIR) pulses with duration of 70 fs and bandwidth of 550 nm centered at 3.75 μm at 1-kHz repetition rate, by a two-stage femtosecond optical parametric amplifier utilizing 4H-silicon carbide crystal as the nonlinear medium. The crystal is selected as it processes orders of magnitude higher damage threshold than traditional MIR nonlinear crystals, and it supports extreme broad parametric bandwidth. With its distinguished features such as MIR central wavelength, ultra-broad bandwidth, self-stable carrier-envelope phase, and potential for energy scaling, this kind of MIR source holds promise for new approaches to extreme short isolated attosecond pulse generation as well as MIR spectroscopy applications.

A femtosecond mid-infrared OPA system based on 4H-SiC, which exhibits ultra-high threshold is established. Broadband 17- μJ pulses have been generated at 3.75- μm, which proves 4H-SiC an ideal nonlinear crystal for intense few-cycle mid-infrared pulse generation.

We report experimental studies on the formation of Type 2 micropipe defects in 4H-SiC crystals grown by a physical vapor transport method. Compared with Type 1 micropipes, Type 2 micropipes exhibit new features allowing them to lie at an oblique angle about 12 degrees to the [0001] crystal axis and are smaller in size than Type 1 micropipes. By changing the growth conditions, we find that a smaller axial temperature gradient and a larger grain size in the SiC source are beneficial to eliminate the Type 2 micropipes. We think that the liquid silicon is responsible for the formation of Type 2 micropipes. A possible formation mechanism for Type 2 micropipes is put forward.

Nonlinear optical (NLO) frequency conversion is commonly used for generating midinfrared (MIR) lasers that offer light sources for a variety of applications. However, the low laser damage thresholds of NLO crystals used so far seriously limit the output power of MIR lasers. Here, a new nonlinear material 4H‐SiC is demonstrated for producing MIR laser. Broadband MIR radiation ranging from 3.90 to 5.60 μm is generated in 4H‐SiC by phase‐matched difference‐frequency generation for the first time. The results may open a door to practically utilize wide‐bandgap semiconductors with high laser damage thresholds as NLO materials for high power output of MIR lasers.

Growth and processing of SiC single crystals was introdeced in order to enlarge the crystal size and obtain quality SiC wafers. Considerable progresses have been made in these aspects, resulting in the first spring-off in China that is devoted to mass production quality 4H-SiC and 6H-SiC wafers. Up to 2011, for most SiC wafers, the micropipe density is lower than 1 cm-2 and the average full width at half maxima of X-ray rocking curves for the (0004) reflection is lower than 20″. N-type and semi-insulating SiC single crystals with homogeneous resistivity lower than 0.02 Ω·cm and up to 108 Ω·cm have been stably grown, respectively. The epi-ready processing was developed and applied to wafers inducing quite low roughness, bow and warp and obtaining quality epitaxial layer. In the meantime, a series progresses have been achieved in the investigation of basic properties of SiC and the fabrication of epitaxial graphene on SiC substrates. Both experimentally and theoretically showed that the intentionally created defects dominated by divacancies are responsible for the magnetism, the first evidence of its kind in SiC single crystals irradiated by neutron. Large area of quality graphene has been fabricated by pulsed electron irradiation and physical vapour transport methods.

OBJECTIVE To study the risk factors of renal failure in the early post-liver transplantation period. METHODS 92 consecutive liver transplantation cases were reviewed and a multi-factor analysis of presumed risk factors of early post-transplantation period renal failure was conducted. The factors analyzed were total bilirubin level, prothrombin activity, onset of structural renal disease, onset of gastrointestinal hemorrhage, whether the patient underwent large-volume paracentesis, or underwent plasmapheresis therapy, needed renal replacement therapy, the operation method used, the bleeding volume during operation and the immunosuppressive agents used. RESULTS Of the 92 patients, 29 (31.5%) developed acute renal failure (ARF) in the early postoperative period. Multi-factor analysis revealed a high pre-transplantation serum creatinine level and low prothrombin activity as risk factors for development of ARF. CONCLUSION ARF is a frequent medical complication after liver transplantation. A high pre-transplantation serum creatinine level and low prothrombin activity are risk factors of its development.