2024, Vol.34, No.4

Journal of the Korean Crystal Growth and Crystal Technology 2023 KCI Impact Factor : 0.19

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

β-Ga₂O₃ is a representative ultra-wide bandgap (UWBG) semiconductor that has attracted much attention for power device applications due to its wide-bandgap of 4.9 eV and high-breakdown voltage of 8 MV/cm. In addition, because solution growth is possible, it has advantages such as fast growth rate and lower roduction cost compared to SiC and GaN [1-2]. In this study, we have successfully grown Si-doped 10 mm thick Si-doped β-Ga₂O₃ single crystals by the EFG (Edge-defined Film-fed Growth) method. The growth direction and growth principal plane were set to [010] / (010), respectively, and the growth speed was 7~20 mm/h. The as-grown β-Ga₂O₃ single crystal was cut into various crystal planes (001, 100, 201) and off-angles (1°, 3°, 4°), and then surface processed. After processed, the homoepitaxial layer was grown on the epi-ready substrate using the HVPE(Halide vapor phase epitaxy) method. The processed samples and the epi-layer grown samples were analyzed by XRD, AFM, OM, and Etching to compare the surface properties according to the crystal plane and off-angle.

Zinc oxide nanoparticles were synthesized using the polyol method with ethylene glycol containing hydroxyl groups (-OH). It was confirmed that the zinc compounds prepared by the polyol method were a mixture of zinc carbonatehydroxide (Zn₅(OH)₆(CO₃)₂) and zinc oxide (ZnO) crystalline structures. Calcination at 400°C, 600°C and 800°C was performed to examine the effects of calcination temperature on the particle size, morphology and crystallinity of zinc oxide. ZnO powders of calcination at 800°C was evaluated to particle size analysis from ethylene glycol containing precursor solution compared with distilled water based solution. The zinc oxide particles obtained from the former had a particle size of approximately 404 ± 51 nm, whereas those from the latter exhibited a more uniform nanoparticles morphology with aparticle size of approximately 109 ± 29 nm. This demonstrates that the addition of ethylene glycol can control the influence of water molecules, enabling the direct synthesis of zinc oxide in the form of uniform nanoparticles.

Preparation of ferromagnetic powders for the mixture of hematite and pure Mg powders by ball milling has been investigated. Also, consolidation of the ball-milled powders was performed in a spark plasma sintering machine at 800-1,000°C. It is found that a ferromagnetic Fe-MgO composite powders are obtained by ball milling of hematite and pure Mg powders before 1 hour. The magnetization and coercivity of ball-milled samples change at the results of the solid state reaction of hematite by pure Mg during ball milling. The saturation magnetization of ball-milled samples increases with increasing ball milling time and reaches to a maximum value of 93.4 emu/g after 5 hours of ball milling. Shrinkage change after sintering of ball-milled sample for 5 hours was significant above 300°C and gradually increased with increasing temperature up to 800°C. X-ray diffraction result shows that the average grain size of Fe in Fe-MgO bulk sample sintered at 900°C is 50nm. It can be also seen that the coercivity of bulk sample sintered at 900°C is still high value of 90 Oe, indicating that the grain growth of magnetic Fe phase during sintering process tend to be suppressed.