Silicon carbide (SiC) has a range of useful physical, mechanical and electronic properties that make it a promising material for next-generation electronic devices. Careful consideration of the thermal conditions in which SiC [0001] is grown has resulted in improvements in crystal diameter and quality: the quantity of macroscopic defects such as hollow core dislocations (micropipes), inclusions, small-angle boundaries and long-range lattice warp has been reduced. But some macroscopic defects (about 1-10 cm(-2)) and a large density of elementary dislocations (approximately 10(4) cm(-2)), such as edge, basal plane and screw dislocations, remain within the crystal, and have so far prevented the realization of high-efficiency, reliable electronic devices in SiC (refs 12-16). Here we report a method, inspired by the dislocation structure of SiC grown perpendicular to the c-axis (a-face growth), to reduce the number of dislocations in SiC single crystals by two to three orders of magnitude, rendering them virtually dislocation-free. These substrates will promote the development of high-power SiC devices and reduce energy losses of the resulting electrical systems.

Carrier lifetimes in 4H-SiC epilayers are investigated by differential microwave photoconductivity decay measurements. When the Z 1/2 concentration is higher than 10 13 cm −3 , the Z 1/2 center works as a recombination center. In this case, carrier lifetimes show positive dependence on the injection level ͑number of irradiated photons͒. On the other hand, other recombination processes such as surface recombination limit the lifetime when the Z 1/2 concentration is lower than 10 13 cm −3. In this case, carrier lifetimes have decreased by increasing the injection level. By controlling the Z 1/2 concentration by low-energy electron irradiation, the lifetime control has been achieved.

Two-dimensional (2D) materials combine the collective advantages of individual building blocks and synergistic properties and have spurred great interest as a new paradigm in materials science. For the mass production of these materials, large-scale exfoliations are the main production route; but, recent approaches in the liquid-phase exfoliation are based on empirical trial and error strategies. This study aims to propose a method to determine the suitable solvents for efficiently exfoliating germanane (GeH) and the optimal solvent removal conditions at moderate temperatures using Hansen solubility parameters. We confirm the presence of GeH nanosheets using atomic force microscopy. The proposed method revealed that GeH can be efficiently dispersed in 1,3-dioxolane and can be deposited as individual sheets, which have the thickness of 3−4 nm and the lateral size in the range of a few micrometers.

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The work reported herein demonstrated that nanopipes can be formed via a surfactant effect, in which boron impurities preferentially migrate to semipolar and nonpolar facets. Approximately 3 μm-thick GaN layers were grown using halogen-free vapor phase epitaxy. All layers grown in pyrolytic boron nitride (pBN) crucibles were found to contain a high density of nanopipes in the range of 1010 to 1011 cm−2. The structural properties of these nanopipes were analyzed by X-ray rocking curve measurements, transmission electron microscopy, and three-dimensional atom probe (3DAP) tomography. The resulting 3DAP maps showed nanopipe-sized regions of boron segregation, and these nanopipes were not associated with the presence of dislocations. A mechanism for nanopipe formation was developed based on the role of boron as a surfactant and considering energy minima. A drastic reduction in the nanopipe density was achieved upon replacing the pBN crucibles with tantalum carbide-coated carbon crucibles. Consequently, we have confirmed that nanopipes can be formed solely due to surface energy changes induced by boron impurity surface segregation. For this reason, these results also indicate that nanopipes should be formed by other surfactant impurities such as Mg and Si.

To integrate surface and interfacial properties and phenomena into the Hansen solubility parameter (HSP) framework, we propose an equation for estimating both surface tension/energy for liquids and solids as well as interfacial tension/energy. The contact angles of probe liquids on various polymers estimated using the proposed equation based on bulk HSPs (derived from bulk properties such as solubility or swelling, and not on surface properties) are compared with those measured using the sessile drop method. It is found that their correlations are sufficient for predicting wettability in practical use. All the respective tension and energy correlations are reasonably good, confirming the predictive power of the proposed equation for all values of liquid surface tension, solid surface energy, and interfacial tension. The unification of surface and interfacial properties and phenomena with HSPs (derived from bulk properties) enables us to estimate the surface properties from bulk properties and vice versa. The huge database of HSPs is now applicable to not only bulk phenomena but also surface and interfacial phenomena. Furthermore, complex processes or systems composed of multiple constituents and phases can be understood and designed using the modified HSP framework.

Here, we propose a halogen-free vapor phase epitaxy (HF-VPE) technique to grow bulk GaN single crystals. This technique employs the simplest reaction for GaN synthesis (reaction of Ga vapor with NH3) and can potentially achieve a high growth rate, a prolonged growth duration, a high crystal quality, and a low cost. The analyses of thick HF-VPE-GaN layers grown under optimized growth conditions revealed that high-quality crystals, both in terms of dislocation density and impurity concentration, are obtained at high growth rates of over 100 µm/h.

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