β-Ga₂O₃ is an ultra-wide bandgap semiconductor promising for high-power electronic applications; however, heteroepitaxial growth on sapphire is challenging lattice and symmetry mismatch. In this study, β-Ga₂O₃ thin films were grown on C-plane sapphire substrates with various off-axis angles (0–12°) using mist-CVD, and the influence of substrate miscut on structural and optical properties was investigated. All films grown at 900°C exhibited (-201) oriented β phase. The crystal quality was strongly dependent on the off-axis angle, with intermediate off-axis angles (Δ_a = 6–8°) showing the narrowest rocking curve width. Off-axis substrates promoted step-aligned growth behavior compared to on-axis growth. Optical measurements revealed enhanced transmittance and wider bandgap values (4.92–4.95 eV) for off-axis samples compared to the on-axis film (4.69 eV). The findings provide practical guidelines for optimizing heteroepitaxial β-Ga₂O₃ growth on low-cost sapphire substrates for high-performance device applications.

κ-phase Ga₂O₃ is a wide-bandgap semiconductor that has attracted attention for power and optoelectronic device applications. However, its crystal quality and optical properties are highly dependent on the growth temperature, which motivates the need for a systematic study. In this work, κ-Ga₂O₃ thin films were grown on AlN/sapphire templates using mist-CVD at different temperatures. At lower temperatures (400℃), films exhibited incomplete crystallization and partial opacity, whereas higher growth temperatures (500-700℃) produced transparent films with improved properties. The bandgap was found to increase with temperature, consistent with reported values for 600-700℃, and XRD/XRC analysis confirmed that crystal quality improved with higher growth temperature. AFM analysis further revealed reductions in surface roughness and grain size variation at elevated temperatures. These findings indicate that an optimal growth window of 600-700℃ enables high-quality κ-Ga₂O₃ films, with potential implications for integrating this material on other hexagonal substrates such as SiC and GaN.

In this study, the heteroepitaxial thin film growth of β-Ga₂O₃ was studied according to the position of the susceptor in mist-CVD. The position of the susceptor and substrate was moved step by step from the center of the hot zone to the inlet of mist in the range of 0~50 mm. It was confirmed that the average thickness increased to 292 nm (D1), 521 nm (D2), and 580 nm (D3) as the position of the susceptor moved away from the center of the hot zone region. The thickness of the lower region of the substrate is increased compared to the upper region. The surface roughness of the lower region of the substrate also increased because the nucleation density increased due to the increase in the lifetime of the mist droplets and the increased mist density. Therefore, thin film growth of β-Ga₂O₃ in mist-CVD is performed by appropriately adjusting the position of the susceptor (or substrate) in consideration of the mist velocity, evaporation amount, and temperature difference with the substrate, thereby determining the crystallinity of the thin film, the thickness distribution, and the thickness of the thin film. Therefore, these results can provide insights for optimizing the mist-CVD process and producing high-quality β-Ga₂O₃ thin films for various optical and electronic applications.

Calcium fluoride (CaF₂) single crystal is applied to numerous industrial applications, especially for optical uses. To have excellent optical transmission properties, however, CaF₂ crystals should be carefully fabricated through liquid-phase crystal growth techniques. In this study, as one of the early stage research activities to grow CaF₂ crystals with a good transmittance at the ultraviolet wavelength range, computational thermodynamic models were provided to deepen the understanding of the crystal growing processes of CaF₂ under various conditions. To remove point defects and oxygen impurities in the grown CaF₂ crystals, the system was thermodynamically evaluated to get optimal process conditions. From the reviews of previous experimental studies, computational thermodynamic approaches were found to be an effective and powerful tool to understand the meaning of the crystal growth processes and to obtain optimal process conditions.

Gallium oxide (Ga₂O₃) thin films were grown on c-, a-, m-, r-plane sapphire substrates using a mist chemical vapor deposition system. Various growth temperature range of 400~600℃ was applied for Ga₂O₃ thin film deposition. Then, several structural properties were characterized such as film thickness, crystal phase, lattice orientation, surface roughness, and optical bandgap. Under the certain growth temperature of 500℃, all grown Ga₂O₃ featured rhombohedral crystal structures and well-aligned preferred orientation to sapphire substrate. The films grown on c-and r-plane sapphire substrates, showed low surface roughness and large optical bandgap compared to those on a-and m-plane substrates. Therefore, various sapphire orientation can be potentially applicable for future Ga₂O₃-based electronics applications.

A 100 mm × 50 mm-sized (100) gallium oxide (Ga₂O₃) single crystal ingot was successfully grown by edge-defined film-fed growth (EFG). The preferred orientation and the quality of grown Ga₂O₃ ingot were compatible with a commercial Ga₂O₃ substrate by showing strong (100) orientation behaviors and 246 arcsec in X-ray rocking curve. Raman characterization was also performed for both samples; thereby providing various Raman-active characteristics of Ga₂O₃ crystals. In particular, we observed A_g(5) and A_g(10) peaks of Raman active mode, directly related to the impurity of the grown Ga₂O₃ crystal. Hence, the comparison of the crystal quality and Raman analysis might be useful for further enhancement of Ga₂O₃ single crystal quality in the future.

Single crystal gallium oxide (Ga₂O₃) has been an emerging material for power semiconductor applications. However, the defect distribution of Ga₂O₃ substrates needs to be carefully characterized to improve crystal quality during crystal growth. We analyzed the type and the distribution of defects on commercial (-201) Ga₂O₃ substrates to get a basic standard prior to growing Ga₂O₃ crystals. Etch pit technique was employed to expose the type of defects on the Ga₂O₃ substrates. Synchrotron white beam X-ray topography was also utilized to observe the defect distribution by a nondestructive manner. We expect that the observation of defect distribution with three-dimensional geometry will also be useful for other crystal planes of Ga₂O₃ single crystals.

In this research, we evaluated the electrical properties of polycrystalline-gallium-oxide (Ga₂O₃) thin films grown by mist-CVD. A 500~800 nm-thick Ga₂O₃ film was used as a channel in a fabricated bottom-gate MOSFET device. The phase stability of the β-phase Ga₂O₃ layer was enhanced by an annealing treatment. A Ti/Al metal stack served as source and drain electrodes. Maximum drain current (I_D) exceeded 1 mA at a drain voltage (VD) of 20 V. Electron mobility of the β-Ga₂O₃ channel was determined from maximum transconductance (gm), as approximately, 1.39 cm²/Vs. Reasonable device characteristics were demonstrated, from measurement of drain current-gate voltage, for mist-CVD-grown Ga₂O³ thin films.

The top seeded solution growth (TSSG) method is an alternative technique to grow high-quality SiC crystals that has been actively studied for the last two decades. However, the TSSG method has different issues that need to be resolved when compared to the commercial SiC crystal growing method, i.e., physical vapor transport (PVT). A particular issue of the TSSG method of results from the presence of liquid droplets on the grown crystal that can remain even after crystal growth; this induces residual stress on the crystal surface. Hence, the residual droplet causes several unwanted effects on the crystal such as the initiation of micro-cracks, micro-pipes, and polytype inclusions. Therefore, this study investigated the formation of the residual droplet through multiphysics simulations and lead to the development of a liquid droplet removal method. As a result, we found that although residual liquid droplets significantly apply residual stress on the grown crystal, these could be vaporized by adopting thermal annealing processes after the relevant crystal growing steps.

In order to fabricate high-quality SiC substrates for power electronic devices, various single crystal growing methods were prepared. These include the physical vapor transport (PVT) and top seeded solution growth (TSSG) methods. All the suggested SiC growth methods generally use induction-heating furnaces. The temperature distribution in this system can be easily adjusted by changing the hot-zone design. Moreover, precise temperature control in the induction-heating furnace is favorably required to grow a high-quality crystal. Therefore, in this study, we analyzed the heat transfer in these furnaces to grow SiC crystals. As the growth temperature of SiC crystals is very high, we evaluated the effect of radiation heat transfer on the temperature distribution in induction-heating furnaces. Based on our simulation results, a heat transfer strategy that controls the radiation heat transfer was suggested to obtain the optimal temperature distribution in the PVT and TSSG methods.

We investigated the growth of Al_xGa_1-x)₂O₃ thin films on c-plane sapphire substrates that were grown by mist chemical vapor deposition (mist CVD). The precursor solution was prepared by mixing and dissolving source materials such as gallium acetylacetonate and aluminum acetylacetonate in deionized water. The [Al]/[Ga] mixing ratio (MR) of the precursor solution was adjusted in the range of 0~4.0. The Al contents of (Al_xGa_1-x)₂O₃ thin films were increased from 8 to 13% with the increase of the MR of Al. As a result, the optical bandgap of the grown thin films changed from 5.18 to 5.38 eV. Therefore, it was determined that the optical bandgap of grown (Al_xGa_1-x)₂O₃ thin films could be effectively engineered by controlling Al content.

Single-crystal diamond obtained by chemical vapor deposition (CVD) exhibits great potential for use in next-generation power devices. Low defect density is required for the use of such power devices in high-power operations; however, plastic deformation and lattice strain increase the dislocation density during diamond growth by CVD. Therefore, characterization of the dislocations in CVD diamond is essential to ensure the growth of high-quality diamond. In this work, we analyze the characteristics of the dislocations in CVD diamond through synchrotron white beam X-ray topography. In estimate, many threading edge dislocations and five mixed dislocations were identified over the whole surface.