Shunta Harada 교수

The thermoelectric properties of Magnèli phase titanium oxides TinO2n−1 (n=2,3,…) have been investigated, paying special attention to how the thermoelectric performance can be altered by changing the microstructure. Dense polycrystalline specimens with nominal composition of TiO2−x (x=0.05, 0.10, 0.15, and 0.20) prepared by conventional hot-pressing are all identified to be one of the Magnèli phases, in which crystallographic shear planes are regularly introduced according to the oxygen deficien

We report a marked reduction in the dislocation density of a 4H-SiC crystal using a high-efficiency dislocation conversion phenomenon. During the solution growth, threading dislocations were efficiently converted to basal plane defects by the step flow of macrosteps. Utilizing this dislocation conversion phenomenon, we achieved the marked reduction of threading dislocation density. Consequently, the threading screw dislocation density was only 30 cm−2, which was two orders of magnitude lower tha

Evolution of threading screw dislocation (TSD) conversion during the solution growth of 4H-SiC on a vicinal crystal of 4H-SiC(0001) was investigated by synchrotron X-ray topography. Selecting appropriate X-ray wavelength and g vector, we can change the penetration of X-ray, and the dislocation behaviors with the different depth were successfully observed. Evidently TSDs parallel to the c-axis having c-component Burgers vector were changed into defects on the (0001) basal planes with the same Bur

SiC bipolar degradation, which is caused by stacking fault expansion from basal plane dislocations in a SiC epitaxial layer or near the interface between the epitaxial layer and the substrate, is one of the critical problems inhibiting widespread usage of high-voltage SiC bipolar devices. In the present study, we investigated the stacking fault expansion behavior under UV illumination in a 4H-SiC epitaxial layer subjected to proton irradiation. X-ray topography observations revealed that proton

Polytype transformations on the 4H-SiC(0001) Si face during top-seeded solution growth have been investigated by transmission electron microscopy and micro-Raman spectroscopy. 4H-, 15R-, and 6H-SiC were grown on the 4H-SiC(0001) Si face via spiral growth. Once a polytype transformation from 4H-SiC to 15R- or 6H-SiC occurs, the polytype rarely returns to 4H-SiC. Just before the polytype transformation, a disturbance in the stacking sequence involving the introduction of stacking faults was observ

Reduction of threading screw dislocation without polytype transformation from 4H-SiC was performed by the combination of step-flow growth and spiral growth. On a vicinal 4H-SiC seed crystal, threading screw dislocations are converted to Frank-type stacking faults by step-flow during solution growth. As the growth proceeds, the defects are excluded to the crystal. Thus utilizing the conversion, high quality SiC crystal growth without threading screw dislocations is expected to achieve. However, a

Abstract 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 c

Abstract Bipolar degradation in SiC bipolar devices, in which stacking faults (SFs) expand to accommodate the movement of partial dislocations during forward bias application, is one of the critical problems impeding the widespread implementation of SiC power devices. Here we clearly demonstrate that the movement of partial dislocations can be suppressed by proton implantation, which has good compatibility with semiconductor processing, through investigation of the contraction behavior of SFs in

Abstract Silicon carbide (SiC) is widely used in power semiconductor devices; however, basal plane dislocations (BPDs) degrade device performance, through a mechanism called bipolar degradation. Recently, we proposed that proton implantation could suppress BPD expansion by reducing BPD mobility. We considered three potential mechanisms: the hydrogen presence around BPDs, point defects induced by implantation, and carrier lifetime reduction. In this study, we discuss the mechanisms of proton impl

Surface morphology and threading dislocation conversion behavior during solution growth of 4H-SiC using pure Si and Al-Si solvents was investigated. The growth surfaces on the C face were smoother than the Si face. By the addition of Al to the solvent, the growth surface became smooth on the C face and rough on the Si face. Threading screw dislocation conversion took place only in the grown crystals on the Si face and threading edge dislocation conversion occurs both on the Si face and the C fac

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

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 an

Abstract The macroscopic distribution of fluid flows, which affect the quality of final products for various kinds of materials, is often difficult to describe in mathematical formulae and hinders the implementation of empirical knowledge in scaling up. In the present study, the characteristics of the flow distribution in silicon carbide (SiC) solution growth are described by using the position of the saddle point and the solution growth conditions are optimized by computational fluid dynamics s

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 solvent