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For the nondestructive characterization of SiC wafers for power device application, birefringence imaging is one of the promising methods. In the present study, it is demonstrated that birefringence image contrast variation in off-axis SiC wafers corresponds to the in-plane shear stress under conditions slightly deviating from crossed Nicols according to both theoretical consideration and experimental observation. The current results indicate that the characterization of defects in SiC wafers is possible to achieve by birefringence imaging.

We achieved the growth of extremely-high quality SiC crystal with two-step solution method with specially-designed seed crystals. The two-step growth consists of 1st step growth on Si-face for the reduction of threading dislocations and 2nd step growth on C-face for the reduction of basal plane dislocations and thickening. In this method, we can make the dislocation density extremely low, while the polytype easily changes during growth due to the absence of spiral hillocks originating from threading screw dislocation (TSD). In this study, we prepared specially designed seed crystals for both 1st and 2nd growth steps to provide steps continuously. In the seeds, a few TSDs exist at the upper-side of the step structure. Consequently, we demonstrated the suppression of the polytype transformation during the C-face growth with extremely low-dislocation-density crystal. Accordingly, we successfully obtained extremely low-dislocation density 4H-SiC with TSD, TED and BPD density of 11, 385 and 28 cm-2.

We propose a two-step silicon carbide (SiC) solution growth method for dislocation reduction to produce the high-quality silicon carbide SiC crystals. The two-step growth consists of the growth on a Si face and a C face. Firstly, seed crystal with low threading dislocation density was prepared by the growth on a Si face utilizing the threading dislocation conversion. Secondly, the growth on the C face was conducted on the prepared seed crystal with low threading dislocation density to reduce the density of basal plane dislocations and keep smooth growth surface. We demonstrate that the two-step growth leads to the reduction of the density for all types of dislocations by two orders of magnitude compared to the initial density of the seed crystal.

In order to design a solvent for high-purity SiC solution growth, the impurity incorporation and the carbon solubility of various solvent materials have been investigated. Among the transition metal elements, the impurity elements of Cr, Ti, V and Hf are more readily incorporate during the solution growth than the other transition metal elements. The thermodynamic calculation revealed that the Y-Si solvent has relatively large carbon solubility, which is comparable to the Cr-Si and Ti-Si solvents often used in the solution growth of bulk SiC crystals. From these results, the Y-Si solvent is expected to be a suitable solvent for the high-purity SiC solution growth. Furthermore, we have demonstrated that the Y-Si solvent can achieve lower incorporation of metal impurity in the grown crystal than the Cr-Si solvent maintaining the growth rate.

In order to achieve a high-quality SiC crystal in solution growth, one of the most difficult issues is to grow a thick layer on Si face avoiding polytype transformation. In this case, two-dimensional nucleation, which leads to the polytype transformation, is frequently induced because a density of threading screw dislocations acting as a source of spiral step decreases and wide terraces form by step bunching as growth proceeds. Therefore, it is very difficult to stabilize the polytype of crystals grown with extremely low density of threading screw dislocations. In this study, we tried to overcome these problems by using specially designed seed crystal and optimizing growth temperature and temperature distribution. We successfully grew thick low-threading-dislocation density SiC crystal without polytype transformation under the condition of high growth temperature and homogeneous temperature distribution.

The relationship between surface morphology and spatial distribution of basal plane dislocations in 4H-SiC crystal grown by top-seeded solution growth on the C face was investigated by the differential interference microscopy as well as X-ray topography. Basal plane dislocations were generated at the boundaries of the domains with the different macrosteps advance directions. On the other hand, at the position where macrosteps advance to the same direction, BPDs were hardly observed. This results suggest that BPD density can be decreased by the suppression of the collision of macrosteps during the solution growth on the C face controlling the surface morphology.

Birefringence imaging is one of the powerful methods for non-destructive characterization of defects in the semiconductor crystals. However, due to the complicated and unclear contrasts of dislocations in the birefringence image, it was considered to be difficult to automatically detect the position of the dislocation contrasts by the conventional image processing. In the present study, we designed the automatic detection algorithm for the dislocation contrasts taking into account the characteristic feature of the dislocation contrasts, which were always pair of black and white contrasts. To detect the large change in the contrast level near the dislocation contrast, the automatic detection algorithm was constructed by using a variance filter. Finally, we succeeded in detecting the position of the dislocation contrasts with relatively high precision and sensitivity.

The conversion of threading screw dislocations (TSDs) to defects on the basal plane during SiC solution growth caused by macrostep advance is a key factor to improve crystal quality. We realized the TSD conversion in 4H-SiC C face solution growth by modification of the surface morphology including macrosteps by addition of 5 atom % Ti into pure Si solvent. Synchrotron X-ray topography revealed that the possibility of TSD conversion increased to about 10% with the addition of 5 atom % Ti. In addition, the TSD conversion ratio depends on the shape of the macrostep edge. The gentle slope hardly made TSD conversion. The elastic energy of dislocations in anisotropy crystals was postulated as an explanation for the influence of step shape on TSD conversion behavior.

Defects generated during 4H-SiC (0001) solution growth have been investigated by synchrotron X-ray topography and transmission electron microscopy (TEM). The defects unidentified before are recognized as V-shaped contrast features in the X-ray topographic images. The detailed analysis combining TEM results revealed that the newly generated defects are identified as a pair of dislocations on a basal plane with opposite Burgers vectors parallel to the [1120] direction. It is found that no defects in the substrate are directly associated with the formation of the V-shaped defects. Geometric analysis of the size and shape of the V-shaped defects indicates that they nucleate in pairs intermittently during the growth process. On the basis of the observed morphology of these defect configurations, a mechanism of two-dimensional nucleation during solution growth is postulated for the generation of the V-shaped defects.

We investigated the spatial distribution of carrier concentration in n-type 4H-SiC grown by the solution method from the peak frequency of the longitudinal optical phonon-plasmon coupled (LOPC) mode of the Raman spectra on the surface. The carrier concentration at the position of the smooth terrace was higher than the carrier concentration at the position where the macrosteps were formed. This indicates the nitrogen incorporation efficiently occurs on the smooth surface where the density of macrosteps is relatively low. The different incorporation of nitrogen depending on the surface morphology can be understood from the view point of the adsorption time of impurity on the terrace. The present result implies that the uniform surface morphology is necessary to achieve uniform doping concentration in SiC crystal.

We demonstrate that a statistically-significant chiral bias in NaClO3 chiral crystallization can be provoked by inducing nucleation via the optical trapping of Ag nano-aggregates using a continuous wave visible circularly polarized laser (λ = 532 nm). The laser was focused at the interface between air and an unsaturated NaClO3 aqueous solution containing Ag nanoparticles. The “dominant” enantiomorph was switchable by changing the handedness of the incident circularly polarized laser, indicating that the chiral bias is enantioselective. Moreover, it has been found that the resulting crystal enantiomeric excess (CEE) reached approximately 25%. The CEE is much higher than the typical enantiomeric excess (EE) in the asymmetric photosynthesis of organic compounds ranging from 0.5 to 2%. The efficient induction of the nucleation and the large chiral bias imply the contribution of localized surface plasmon resonance of the Ag nanoaggregates to chiral nucleation. Our method has potential to offer the benefit for studies on the spatiotemporal nucleation control, optical resolution of chiral compounds and biohomochirality.

Surface morphology of the SiC crystal grown on the C face of the 4H-SiC seed crystal by TSSG method using pure Si, Si-1at%Ti-C, Si-5at%Ti-C and Si-20at%Ti-C solvents was investigated. The surface morphology of the crystal grown from pure Si solvent was smooth. By the addition of Ti to the solvent, the surface morphology became rougher. The RMS value is not proportional to the concentration of Ti. The formation of macrosteps with several micrometers was observed when the addition of Ti increased to 5at% indicating the possibility of the threading screw dislocation conversion on the C face of the 4H-SiC crystal.

Solution growth of SiC has attracted significant attention due to its potential for the production of high-quality SiC wafers. We have recently investigated the dislocation propagation behavior during SiC solution growth with the aim of reducing the dislocation density. Threading dislocations were found to be converted to defects on the basal planes during solution growth. Utilizing this dislocation conversion phenomenon, we have proposed a dislocation reduction process during solution growth and achieved high-quality 4H-SiC crystal growth. Here we confirm the potential of SiC solution growth for the production of high-quality SiC wafers.

We achieved the convex growth interface shape in top-seeded solution growth of SiC applying non-axisymmetric solution convection induced by non-axisymmetric temperature distribution. The detailed solution flow, temperature distribution and carbon concentration distribution were calculated by 3-dimensional numerical analysis. In the present case, the solution flow below the crystal was unidirectional and the supersaturation was increased along the solution flow direction. By the rotation of the crystal in the unidirectional flow and the temperature distribution, we successfully obtained the crystal with the convex growth interface shape.

The two-dimensional (2D) distributions of surface supersaturation of sodium chlorate crystals with and without solutal convection have been measured by means of a multidirectional interferometry (MDI) technique coupled with the principles of three-dimensional (3D) computer tomography. When solutal convection was present over a top face, the supersaturation at the center of the face was depleted by a factor of >0.9 with reference to the value at the edges of the crystal. When the convection was suppressed using an upside-down geometry, the depletion of supersaturation at the center of the face was much smaller

An in-situ X-ray topography system using monochromatic synchrotron radiation for the observation of the stacking faults in 4H-SiC during a high-temperature annealing process was developed. We demonstrated that the stacking faults in nitrogen-doped 4H-SiC not only expand but also shrink at high temperatures. Furthermore, it was confirmed that the types of the core structure of partial dislocations enclosing the stacking fault can be determined at high temperatures.An in-situ X-ray topography system using monochromatic synchrotron radiation for the observation of the stacking faults in 4H-SiC during a high-temperature annealing process was developed. We demonstrated that the stacking faults in nitrogen-doped 4H-SiC not only expand but also shrink at high temperatures. Furthermore, it was confirmed that the types of the core structure of partial dislocations enclosing the stacking fault can be determined at high temperatures.

The present work is concerned with the three-dimensional reconstruction of concentration field around a crystal growing from its aqueous solution using Fourier analysis based phase shift interferometric tomography. Projection data of convective field around a growing NaClO 3 crystal have been recorded using a Mach–Zehnder interferometer. A new numerical method based on the concept of real time phase shift interferometry has been employed for the analysis of the interferograms. By interpreting the interferograms as projection data, the 3-D distribution of salt concentration has been determined using principles of tomography. Study shows that the Fourier analysis-based phase shift method is a novel approach for crystal growth studies as it requires only one interferometric image for the determination of full phase information as opposed to the conventional real time phase shift interferometry wherein at least three or more phase-shifted interferograms are needed. Results have been presented in the form of interferograms, path-integrated concentration contours and three-dimensional concentration profiles over select horizontal planes above the growing crystal. Based on the reconstruction results, distribution of salt concentration in the crystal vicinity is determined and an appropriate mechanism of buoyancy-induced fluid movement in the growth chamber is discussed.

The normal growth rates of the {110} faces of tetragonal hen egg-white lysozyme crystals, R, were measured as a function of the supersaturation σ parameter using a reflection type interferometer under μG at the International Space Station (NanoStep Project). Since water slightly evaporated from in situ observation cells during a long-term space station experiment for several months, equilibrium temperature T(e) changed, and the actual σ, however, significantly increased mainly due to the increase in salt concentration C(s). To correct σ, the actual C(s) and protein concentration C(p), which correctly represent the measured T(e) value in space, were first calculated. Second, a new solubility curve with the corrected C(s) was plotted. Finally, the revised σ was obtained from the new solubility curve. This correction method successfully revealed that the 2.8% water was evaporated from the solution, leading to 2.8% increase in the C(s) and C(p) of the solution.

The growth rate vs. supersaturation of a lysozyme crystal was successfully measured in situ together with the crystal surface observation and the concentration measurements onboard the International Space Station. A Michelson-type interferometer and a Mach-Zehnder interferometer were, respectively, employed for real-time growth rate measurements and concentration field measurements. The hardware development, sample preparation, operation, and analysis methods are described.

We report on the relationship between grown polytypes and the activity ratio of silicon to carbon during SiC solution growth using multicomponent solvents. From the thermodynamic calculation as well as crystallization experiments, we revealed that a high activity ratio (a Si/a C) in the solution leads to the growth of low-hexagonality polytypes, and low a Si/a C results in the growth of high-hexagonality polytypes. 4H-SiC is stable when a Si/a C is relatively low (∼101 > a Si/a C), 3C-SiC is stable when a Si/a C is relatively high (∼104 < a Si/a C), and 6H-SiC is stable in the intermediate a Si/a C range (∼102 < a Si/a C < ∼103). From these results, the Cr–Si solvent at high temperatures is expected to be suitable for 4H-SiC growth, and Sc–Si and Fe–Si solvents at relatively low temperatures are expected to be suitable for 3C-SiC growth.