The Influence of Process Parameters on the Microstructural Properties of Spray-Pyrolyzed β-Ga2O3

Abstract

In this work, the deposition of β-Ga2O3 microstructures and thin films was performed with Ga(NO3)3 solutions by ultrasonic nebulization and spray coating as low-cost techniques. By changing the deposition parameters, the shape of β-Ga2O3 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(NO3)3 concentration of 0.15 M and a substrate temperature of 190 °C to be formed. The monoclinic β-Ga2O3 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 sin2(ψ) method. Raman spectroscopy confirms that the β-Ga2O3 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.