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The fabrication of quasi-phase-matching (QPM) crystals by selective-area growth on the two asymmetrically polar surfaces of GaN is examined. We attempted the fabrication of GaN-QPM crystals by one-time growth using a carbon mask. For GaN double-polarity selective-area growth (DP-SAG), we investigated the effect of varied nitriding times of the Al2O3 templates patterned with the carbon mask. We optimized the nitriding conditions for the DP-SAG process, and evaluated the substrate fabricated by the optimized DP-SAG process. In addition, we examined the interface formation mechanism of DP-GaN fabricated by GaN DP-SAG process. We determined that it is possible to fabricate DP-GaN with a sharp interface by optimizing the growth conditions.

For nonlinear optical applications using gallium nitride (GaN), periodic inversion of crystallographic orientation (polarity) is required for quasi-phase matching. We developed a novel procedure for designing polarity patterns in GaN using metal organic vapor phase epitaxy (MOVPE), and we used this to fabricate periodic polarity-inverted GaN films. By using a carbon mask for the formation of the selective area, substrate nitriding and mask removal of the selective area were carried out in the GaN epitaxial growth process. In this report, double-polarity selective area growth (DP-SAG) was realized by optimizing the nitriding and mask removal conditions. The interface of the Ga-polarity/N-polarity region became sharp by controlling the V/III ratio at 4700.

Calcium-deficient hydroxyapatite (DAp) was synthesized by hydrolysis of -TCP at different pH. Ca/P ratio of DAp increased with increasing pH during the hydrolysis. In addition, DAp which was synthesized at lower pH, showed higher solubility in the simulated body fluid (SBF) and had a more negatively charged surface than that at higher pH. Bone-like crystals were formed on DAp which have been soaked in SBF at 309.5 K in vitro. DAp demonstrated faster formation of a bone-like layer than stoichiometric hydroxyapatite (HAp). Moreover, the formation of the crystals on DAp synthesized at lower pH was much faster than that at higher pH. The adhesion of MC3T3-E1 osteoblast-like cells was also influenced by pH during the synthesis of DAp; the number of adhering cells increased with a decrease in the pH. Therefore, high solubility and negative charge of DAp, especially that synthesized at lower pH resulted in fast formation of bone-like crystals and good cell adhesion.

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