2025, Vol.35, No.3

Journal of the Korean Crystal Growth and Crystal Technology 2024 KCI Impact Factor : 0.2

pISSN : 1225-1429 / eISSN : 2234-5078
https://journal.kci.go.kr/jkcgct

β-Ga₂O₃, with an ultrawide bandgap of ~4.9 eV, a high critical electric field, and excellent stability, has emerged as a promising candidate material for next-generation power and optoelectronic devices. Wafer technology has rapidly advanced through large-diameter bulk growth using the EFG (Edge-defined Film-Fed Growth) and VB (Vertical Bridgman) methods; however, exploiting the strong anisotropy inherent to its monoclinic crystal structure remains a critical challenge. The electrical and optical properties vary significantly with crystallographic orientation, both out-of-plane and in-plane of β-Ga₂O₃. In particular, the (100) surface has been widely employed for device fabrication but has attracted attention due to its low surface energy and tendency to form twin boundaries. In this study, unintentionally doped (UID) β-Ga₂O₃ single crystals grown by the EFG method were processed into a (100) oriented sample, and its orientation was identified using high-resolution X-ray diffraction (HR-XRD) and Raman spectroscopy. Raman analysis revealed that phonon mode intensities varied markedly among the orientations depending on lattice symmetry. Angle-resolved Raman measurements on the (100) surface further showed that Ag and Bg modes exhibited 2-fold, 4-fold, or complete symmetry, indicating a strong dependence on the interaction between the incident light polarization and the crystallographic orientation of β-Ga₂O₃. These results demonstrate that Raman spectroscopy is an effective, non-destructive technique for probing crystallographic orientation and anisotropy in β-Ga₂O₃ single crystals, providing fundamental insights for device design, optimization of wafer fabrication process, and the evaluation of stress and defects in β-Ga₂O₃ based technologies

Single-phase α-,β-, and γ-MnO₂ nanoparticles with high crystallinity were successfully synthesized by a hydrothermal process using different Mn precursors, such as Mn(OAc)₂, MnSO₄, MnCl₂, and Mn(NO₃)₂. The crystal structure and morphology of the MnO₂ particles could be effectively controlled by changing the Mn source. The use of Mn(OAc)₂ and MnSO₄ as precursors resulted in rod-shaped α- and β-MnO₂ particles, whereas MnCl₂, and Mn(NO₃)₂ yielded aggregated angular nanoparticles of γ-MnO₂. X-ray photoelectron spectroscopic analysis revealed that β-MnO₂ had a high ratio of Mn4+ and Olatt on the particle surface, whereas α- and γ-MnO₂ sample had a lower valence state of Mn, such as Mn3+ and Mn2+, on the surface, and the ratio of Olatt was also relatively low.

The optimization of growth conditions, hot zone design, and insulation structure is crucial for high-quality SiC single crystal growth using Physical Vapor Transport (PVT) techniques. Inadequate growth design can lead to polytype inclusions, crack formation, and increased defect density within the crystal, ultimately deteriorating the quality of the final SiC single crystal. In this study, a new insulation design was developed to enhance the axial and radial temperature gradients at the top of the crucible compared to the conventional graphite insulation structure. Additionally, nitrogen gas was employed during the growth process to ensure polytype stability. Simulations using VR reactor software were conducted to analyze the internal temperature distribution within the crucible and the migration pathways of SiC source chemical species resulting from the enhanced upper insulation. Ingots grown using each design achieved growth rates in the mid-100 µm/hr range. In crystals grown with the conventional Design A, polytype inclusions and cracking were observed throughout the ingot. In contrast, crystals grown with Designs B and C showed significant suppression of polycrystalline formation at the ingot periphery and markedly improved crystallinity. Notably, the application of Design C, which featured enhanced upper crucible insulation and nitrogen gas employed during the growth process, resulted in high-quality 4H-SiC crystals.