The Influence of Process Parameters on the Microstructural Properties of Spray-Pyrolyzed β-Ga 2 O 3 .

In this work, the deposition of β-Ga 2 O 3 microstructures and thin films was performed with Ga(NO 3 ) 3 solutions by ultrasonic nebulization and spray coating as low-cost techniques. By changing the deposition parameters, the shape of β-Ga 2 O 3 microstructures was controlled. Micro-spheres were obtained by ultrasonic nebulization. Micro-flakes and vortices were fabricated by spray coating aqueous concentrated and diluted precursor solutions, respectively. Roundish flakes were achieved from water-ethanol mixtures, which were rolled up into tubes by increasing the number of deposition cycles. Increasing the ethanol-to-water ratio allows continuous thin films at an optimal Ga(NO 3 ) 3 concentration of 0.15 M and a substrate temperature of 190 °C to be formed. The monoclinic β-Ga 2 O 3 phase was achieved by thermal annealing at 1000 °C in an ambient atmosphere. Scanning electronic microscopy (SEM), X-ray diffraction (XRD), and UV-Raman spectroscopy were employed to characterize these microstructures. In the XRD study, in addition to the phase information, the residual stress values were determined using the sin 2 (ψ) method. Raman spectroscopy confirms that the β-Ga 2 O 3 phase and relative shifts of the Raman modes of the different microstructures can partially be assigned to residual stress. The high-frequency Raman modes proved to be more sensitive to shifting and broadening than the low-frequency Raman modes.