Papers by Keyword: Solution Growth

Abstract: In the solution growth method for silicon carbide (SiC) single-crystal fabrication, in-situ observations were performed inside the furnace to monitor the meniscus at the seed–solution interface. A meniscus formed at the contact between the seed crystal and the solution, and variations in the reflections on the solution surface enabled optical monitoring and control of this interface. The observed surface images were also dependent on the frequency of the induction heating. Computational fluid dynamics (CFD) simulations indicated that lowering the heating frequency causes an upward displacement of the solution surface at its central region, producing a locally elevated contact position between the seed crystal and the solution. These findings demonstrate that in-situ observation constitutes an effective approach for precise control of meniscus shape during solution growth of SiC single crystals.

Abstract: We have studied the microstructure of the growth surface of the 4H-SiC grown by the m-face solution growth. Atomic Force Microscopy (AFM) revealed the micro-striped morphology with the asperity of several nm in the band-like morphology region. The cross-sectional Transmission Electron Microscopy (XTEM) showed that the growth surface consisted of a bunch of nanofacets and vicinal surface. This peculiar morphology is totally different from that of conventional spiral growth on c-face, which can be closely related with the growth mechanism of the m-face solution growth.

Abstract: We measure the temperature-dependent resistivity (ρ(T)) for thick heavily Al- and Ncodoped p-type 4H-SiC samples grown by chemical vapor deposition (CVD), physical vapor transport (PVT), and solution growth (SG), and investigate their conduction mechanisms. For samples with an Al concentration (CAl) of 3.5×10¹⁹ to 1×10²⁰ cm^-3 grown by CVD, PVT, and SG, the conduction mechanisms at high and low temperatures are band and nearest-neighbor hopping (NNH) conduction, respectively. In the range C_Al of 1×10¹⁹ to 3.5×10¹⁹ cm^-3, on the other hand, an anomalous conduction, referred to as X conduction here, is observed between the band and NNH conduction regions for the samples grown by CVD and PVT, but not those grown by SG. One of the differences between the samples grown by CVD and PVT and those grown by SG is the off-orientation toward [11-20] of the (0001) 4H-SiC substrate. We discuss the reason for the appearance of X conduction, which appears to be consistent with dopant-concentration inhomogeneity model.

Abstract: A 4H-SiC 4° off-wafer fabricated from a bulk crystal grown using the solution method has high quality with extremely low-density threading screw (TSD) and basal plane (BPD) dislocations. For application to electronic devices, we formed an epitaxial layer on the solution-method-prepared wafer via chemical vapor deposition and evaluated the BPD in the epitaxial layer using synchrotron X-ray topography and molten KOH etching. The BPD density of the epitaxial layer formed on the solution-grown crystals was extremely low. Bulk crystals fabricated as wafers by the solution method are expected to be applied to high-voltage bipolar devices that do not suffer from degradation of forward characteristics.

Abstract: We investigated the effect of a melt-back process on the quality of the grown crystal in 4H-SiC solution growth. In our experiments, the crystal was grown by top-seeded solution growth (TSSG) method with and without melt-back, following which the quality of the obtained crystals was compared. When solution growth was carried out without melt-back, solvent inclusions and a different polytype were observed. When molten KOH etching was conducted, the dislocation density in the crystals at the early stage of growth became much higher than that in a seed crystal. Solvent inclusions, a different polytype, and an increase in dislocations were suppressed when solution growth was performed with melt-back. It was confirmed that melt-back is necessary to prevent the deterioration of crystal quality at the early stage of solution growth.

Abstract: We grew large diameter and long size 4H-SiC crystals by the solution growth method using Si-Cr based solvent. To optimize the crystal growth conditions, we applied two-dimensional axisymmetric steady-state analysis to conduct a comprehensive heat transfer analysis that calculates the magnetic field, heat transfer, and liquid flow. In particular, by optimizing the solution surface temperature environment and the seed shaft structure, we suppressed parasitic undesirable crystal formations and promoted single crystal growth at the same time. Consequently, we obtained a 2-inch bulk crystal with a thickness of 20 mm and a 4-inch bulk crystal with a thickness of 15 mm.

Abstract: We have developed the bulk growth technique to reduce threading screw dislocations (TSDs) by combining solution growth and PVT growth methods. More than 80 % of TSDs in original seed crystals were successfully converted to Frank defects on basal planes by the solution growth on 4° off C-face with Si-5at.% Ti solvent. After PVT growth on the as-grown surface of the conversion layer, TSDs in the original seed were successfully reduced. The presence of micrometer-size macrosteps in the initial stage of PVT growth is important to continue to propagate the converted Frank defects on basal planes during PVT bulk growth.

Abstract: A novel heterocyclic compound, 1-(4-methoxy phenyl)-2-((5-(1-(naphthalen-1-yloxy) ethyl) -[1,3,4]-oxadiazol-2-yl) sulfanyl) ethanone was synthesized using standard method and chemical structure of the synthesized compound was identified using FTIR spectrum. Needle shaped single crystals have been grown using solution growth technique. The grown crystals were characterized using single crystal XRD, UV-visible and Thermal analysis. The crystal structure study shows that the compound crystallizes in Monoclinic crystal system with a space group of P21/a and cell parameters are determined. UV-Visible study shows that the crystal is transparent in the entire visible region. The thermal stability of the material was determined by TG and DTA analysis.

Abstract: A novel NLO compound (E)-1-(5-chlorothiophene-2-yl)-3-(4-dimethylamino) phenyl) prop-2-en-1-one has been synthesized by adopting claisen schmidt condensation reaction method and the single crystals are grown using slow solvent evaporation technique. The FT-IR spectrum confirms the various functional groups present in the compound. The crystal structure was studied by XRD method, which reveals that the compound crystallizes in Monoclinic crystal system with a space group P21/n and the corresponding lattice parameters are a = 7.595 (2) Å, b = 17.441 (4) Å, c = 10.917 (3) Å, α = 90^o, β = 102.500 (12)^o, γ = 90^o. UV-Visible spectrum shows that the crystal is transparent in the entire visible region. Refractive index of the crystal was determined using Brewster’s angle method. Thermal stability of the material was determined from TG/DTA test. The Second harmonic generation efficiency of the crystal was estimated using NLO test and the efficiency was found to be 0.84 times that of UREA.

Abstract: The modified crucible in the top seeded solution growth (TSSG) method was proposed to get the stable growth condition and the enhanced growth rate. The temperature gradient and the distribution of dissolved carbon in the solvent were obtained by numerical approaches. Compared simulation results and experiment, we investigated the region where is the most of dissolved carbon and it is supplied to the seed through what path. The cross-sectional samples of crucibles and grown SiC crystals were systematically analyzed to investigate the effect of the crucible modification on SiC crystal growth.