Papers by Author: Mamoru Imade

Abstract: Seeded growth of gallium nitride (GaN) crystals on a spontaneously nucleated small GaN by the Na flux method was performed. In this study, we attempted to control the growth habit by changing the flux composition (Ga/Na) and by introducing a small amount of additives (Ca and Li). Our experiment clarified that a low Ga composition was preferred to grow high-crystallinity prismatic GaN crystals with a high growth rate. Furthermore, the transparent GaN single crystals with prism shape could be grown by the addition of Ca and Li.

Abstract: The growth of thick 2H-SiC layers in Si-Li solution under a continuous CH₄ flow at atmospheric pressure was investigated. The thickness of the 2H-SiC layer increased linearly with the growth period, reaching as thick as 270-μm with a growth period of 7 hr. The Li concentration in the layers was as low as 1.0 × 10¹⁸ atoms/cm³, which was less than one-hundredth that observed in a previous study.

Abstract: We attempted the vapor–liquid–solid (VLS) growth of SiC film in Si-Li solution using gaseous CH4 as a carbon source at 900 oC. A 100-m-thick liquid-phase epitaxy (LPE) layer was obtained on a 4H-SiC (0001) substrate under CH4 pressure of 0.9 MPa. X-ray diffraction (XRD) and a high-resolution transmission electron microscope (HR-TEM) measurement showed that the LPE layer was single-phase 2H-SiC. We concluded that VLS growth in Si-Li solution using gaseous CH4 as a carbon source is useful for growing single-phase 2H-SiC.

Abstract: We succeeded in growing a GaN single crystal substrate with diameter of about two inches using the Na flux method. Our success is due to the development of a new apparatus for growing large GaN single crystals. The crystal grown in this study has a low dislocation density of 2.3×105 (cm-2), The secondary ion mass spectrometry (SIMS) technique demonstrates that the Na element is difficult to be taken in the crystal in both the + and – c directions, resulting in a Na concentration of 4.2 × 1014 (cm-3) in the crystal. Our success in growing a two-inch GaN substrate with a low impurity content and low dislocation density should pave the way for the Na flux method to become a practical application.

Abstract: We have achieved the first successful growth of 2H-SiC single crystals using the C-Li-Si melt system. Li-Si melt, whose melting point is lower than 1000 oC, was chosen because the 2H-SiC polytype is more stable at lower temperatures than other polytypes such as 3C-, 4H-, and 6H-SiC. Many hexagonal-shaped crystals of approximately 100 m in diameter were observed via a scanning electron microscope (SEM). A high resolution transmission electron microscope (HR-TEM) lattice image of the grown crystals showed a periodical structure with A-B stacking along the <0001> direction. These results indicated that the Li-based flux was useful for growing bulk 2H-SiC single crystals.