Despite numerous advances in the preparation and use of GaN, and many leading-edge applications in lighting technologies, the preparation of high-quality GaN powder remains a challenge. Ammonolytic preparations of polycrystalline GaN have been studied using various precursors, but all were time-consuming and required high temperatures. In this study, an efficient and low-temperature method to synthesize high-purity hexagonal GaN powder is developed using sub-micron Ga2O3 powder as a starting material. The sub-micron Ga2O3 powder was prepared by an ultrasonic spray pyrolysis process. The GaN powder is synthesized from the sub-micron Ga2O3 powder through a nitridation treatment in an NH3 flow at 800℃. The characteristics of the synthesized powder are systematically examined by X-ray diffraction, scanning and transmission electron microscopy, and UV-vis spectrophotometer.

The GaN-powder scrap generated in the manufacturing process of LED contains significant amounts of gallium. This waste can be an important resource for gallium through recycling of scraps. In the present study, the influence of annealing temperatures on the structural properties of GaN powder was investigated when the waste was recycled through the mechanochemical oxidation process. The annealing temperature varied from 200oC to 1100oC and the changes in crystal structure and microstructure were studied. The annealed powder was characterized using various analytical tools such as TGA, XRD, SEM, and XRF. The results indicate that GaN structure was fully changed to Ga2O3 structure when annealed above 900oC for 2 h. And, as the annealing temperature increased, crystallinity and particle size were enhanced. The increase in particle size of gallium oxide was possibly promoted by powder-sintering which merged particles to larger than 50 nm.

In this study, GaN powders were synthesized from gallium oxide-hydroxide (GaOOH) through an ammonification process in an NH3 flow with the variation of B2O3 additives within a temperature range of 300-1050˚C. The additive effect of B2O3 on the hexagonal phase GaN powder synthesis route was examined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transformation infrared transmission (FTIR) spectroscopy. With increasing the mol% of B2O3 additive in the GaOOH precursor powder, the transition temperature and the activation energy for GaN powder formation increased while the GaN synthesis limit-time (tc) shortened. The XPS results showed that Boron compounds of B2O3 and BN coexisted in the synthesized GaN powders. From the FTIR spectra, we were able to confirm that the GaN powder consisted of an amorphous or cubic phase B2O3 due to bond formation between B and O and the amorphous phase BN due to B-N bonds. The GaN powder synthesized from GaOOH and B2O3 mixed powder by an ammonification route through β-Ga2O3 intermediate state. During the ammonification process, boron compounds of B2O3 and BN coated β-Ga2O3 and GaN particles limited further nitridation processes.