OXIDE Corp.

Tb₃Ga₅O₁₂ (TGG) single crystals have excellent optical isolator characteristics.However, TGG single crystals grown by the Czochralski method sometimes contain radial stripes along the growth direction, which degrade their optical isolator characteristics.These radial stripes may be caused by a composition mismatch between the melt and crystals.In this study, we grew 25 mmϕ TGG single crystals from Tb-rich melts and precisely measured their lattice constantsThe relationship between the composition and lattice constants was determined using sintered polycrystalline TGG.Based on these experiments, the congruent-melting composition was found to be 37.9 mol% Tb₂O₃.High-quality, 50-mmϕ TGG single crystals without radial stripes were grown using a starting material composition of 37.8 mol% Tb₂O₃, considering the evaporation of Ga₂O₃ from the melt during crystal growth.We repeatedly grew TGG single crystals by adding the TGG starting material to the residue in the crucible used for growth to complete four addnl. growth processes.The fluctuation of in the lattice constant of the TGG boules for the first and fifth growths was within 0.0002 Å, which corresponds to a Tb₂O₃ composition uniformity of 0.01 mol% Tb₂O₃.Therefore, we have succeeded in growing uniform TGG single crystals industrially with composition fluctuations within only 0.01 mol% by optimizing the composition of the TGG starting material to 37.8 mol% Tb₂O₃.

Tb₃Ga₅O₁₂ (TGG) single crystals, which are used as optical isolators, are grown by the Czochralski (Cz) method.Radial stripes are sometimes observed inside the TGG-grown single crystals.Polarized light microscopy, chem. etching, and X-ray topog. results suggest that helical dislocations are present in crystals with radial stripes.Therefore, the radial stripes are considered to be caused by light scattering due to the strain resulting from helical dislocation.

GaN layers are grown on Al-pretreated ScAlMgO₄ (0001) substrates by metal-organic vapor-phase epitaxy (MOVPE) without using low-temperature (LT) buffer layers.The Al pretreatment is performed under a H₂ and N₂ gas mixture and results in the nucleation of AlN on the ScAlMgO₄.High-resolution transmission electron microscopy reveals that the ScAlMgO₄ (0001) surface is terminated with the rocksalt phase ScO (111).Because of the chem. nature of the ScO layer, the AlN nuclei are N-polar.However, subsequent GaN MOVPE inverts the polarity to metal-polar in the vicinity of the boundary between the interfacial AlN nucleation layer and GaN layer, which is attributed to the GaN surface during MOVPE being more stable when it is metal-polar.The grown GaN layers exhibit better crystalline quality compared with GaN grown on ScAlMgO₄ or sapphire (0001) substrates using conventional LT-buffer technol., thereby demonstrating the promise of the method to produce high-quality GaN epilayers on ScAlMgO₄.