Fe-Si melt is a candidate for use as an alloy solvent for rapid liquid phase growth of SiC because of the high solubility of carbon in molten iron. In this work, the equilibrium phase relationship between SiC and the liquid phase of the Fe-Si-C system was studied to determine the optimal composition of a high SiC content solvent. The solubility of carbon in molten silicon was examined and the thermodynamic properties of the liquid phase in the Si-C system were reassessed. The phase relationship between SiC and Fe-Si melt was investigated by the equilibration technique at 1523-1723 K. It was found that Fe-36 mol% Si alloy equilibrates with SiC at the corresponding temperatures. The equilibrium phase relationship between SiC and various compositions of Fe-Si melts was studied by using thermodynamic calculations. The results indicated that SiC is far more soluble in iron-rich Fe-Si melt than in silicon-rich melt. The Fe-Si melt of Fe-36 mol% Si composition possessing high SiC solubility should be a suitable solvent for rapid liquid phase growth of SiC.

We report the growth of large Cl-doped and Brdoped SnS single crystals from a molten Sn-based flux. Compared with the small and lamellar undoped SnS crystals, the addition of SnCl 2 or SnBr 2 halogen sources in the flux substantially enhanced lateral growth along the (100)-plane and vertical growth. The maximum size of the obtained single crystals reached a diameter and thickness of 16 mm and 0.7 mm for the Cl-doped SnS and 24 mm and 1.0 mm for the Br-doped SnS, respectively. The X-ray rocking curves and the X-ray back-reflection Laue patterns indicated a high crystal quality. The obtained crystals were further characterized via electrical measurements, including electrical conductivity and Hall measurements, optical absorption spectroscopy, and X-ray and ultraviolet photoelectron spectroscopies. Both the Cl-doped and Br-doped SnS single crystals exhibited degenerate n-type conductivity with a high electrical conductivity of 11.1 S cm −1 for Cl-doped SnS and 18.9 S cm −1 for Br-doped SnS along the (100)-plane at 300 K. Furthermore, the photoelectron spectroscopy results also indicated n-type conductivity. The large single crystals of n-type SnS obtained in this work would enable the fabrication of p-n homojunction SnS solar cells via the deposition of p-type SnS thin films.

Si-Cr alloy is one of the predominant solvents for rapid solution growth of 4H-SiC crystals. The solubilities of carbon in Si-40 mol%Cr alloy at SiC saturation at 1773-2273 K and in Si-Cr alloys of various chromium contents at 2073 K were measured by equilibrating the Si-Cr alloy with a 4H-SiC single crystal. Carbon solubility in Si-40 mol%Cr alloy increased with temperature from 0.22 mol% at 1773 K to 3.59 mol% at 2273 K. At 2073 K, carbon solubility at SiC saturation increased with the chromium content in the liquid from 0.18 mol% in Si-20 mol%Cr to 16.4 mol% in Si-80 mol%Cr. A thermodynamic analysis of the Si-Cr-C alloy was also conducted. Although the sub-regular solution model is often adopted to estimate phase relations in solution systems, this predicted a carbon solubility in Si-40 mol%Cr at SiC saturation more than two times higher than the measured value. In contrast, a quasi-chemical model that considered the competition between substitutional Si and Cr atoms bonding to interstitial carbon atoms reproduced the activity coef cient of carbon in Si-Cr alloys of 60-100 mol%Si composition, in which the carbon solubility at SiC saturation was less than 1.5 mol%, fairly well. This quasi-chemical model enabled the precise phase relation to be evaluated when designing the solution growth of SiC using a Si-Cr solvent.

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Density functional theory calculations with a correction of the long-range dispersion force, namely the van der Waals (vdW) force, are performed for SiC polytypes. The lattice parameters are in good agreement with those obtained from experiments.Furthermore, the stability of the polytypes in the experiments, which show 3C-SiC as the most stable, are reproduced by the present calculations. The effect of the vdW force on the electronic structure and the stability of polytypes are discussed. We observe that the vdW interaction is more sensitive to the cubic site than the hexagonal site. Thus, the influence of the vdW force increases with decreasing the hexagonality of the polytype, which results in the confirmation that the most stable polytype is 3C-SiC. † Present address: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan. 2Silicon carbide (SiC) has attracted great interest as a promising widegap material for use in power devices with low on-resistance because of its high breakdown field. SiC is also well known as a material with polytypism, such as 3C-, 2H-, 4H-, 6H-, 15R-SiC and so forth. Among the SiC polytypes, 4H-SiC has been desired for application in power devices because of its wide band gap and relatively isotropic electron mobility.Although the supply of 4H-SiC wafers with 6 inch size has begun, a large problem remains regarding the difficulty in selective growth of 4H-SiC. So far, many investigations have been performed for understanding the stability of the SiC polytypes experimentally 1,2) and theoretically. 3-7) However, the experimentally observed stability of the SiC polytypes, 1) which show 3C-SiC is more stable at less than 1873 K compared with 4H-, 6H-and 15R-SiC, has never been reproduced by a first principles density functional theory (DFT) calculation. In the DFT calculation, 4H-, 6H-or 15R-SiC is estimated to be the most stable among the typical polytypes. [4][5][6] The discrepancy has been proposed to arise from the entropic term and crystal growth conditions owing to the estimated total energy difference between 3C-and 4H-SiC, which denotes that the internal energy difference at 0 K is within a few meV. 4) However, the long-range dispersion force, that is, the van der Waals (vdW) force, has never been included in the 3 previous DFT calculations for SiC polytypes despite the observation that vdW often affects the electronic structure of covalent materials. 8) Recently, including the vdW force in DFT calculations, namely the DFT-D calculation, has been performed to describe the accurate electronic structure of two-dimensional layered structures and molecular crystals. [8][9][10][11][12] Although SiC is a highly covalent material, the effect of the vdW interaction on the stability of SiC polytypes has not been discussed so far. Herein, the stability of SiC polytypes are evaluated by the DFT-D calculation. The lattice parameters of the typical SiC polytypes are determined, and the effect of the ...