Rodlike GaOOH particles and films were successfully prepared in a large scale from a simple aqueous gallium nitrate solution. First, a hydrothermal treatment of the solution at 150°C led to the formation of GaOOH rods, and their subsequent heat-treatments at 700°C promoted transformation into β-Ga2O3 having the similar particle morphology. Second, using the same aqueous solutions, strongly c-axis-oriented GaOOH films consisting of rodlike particles could be deposited on substrates through chemical solution processes. It was found that heterogeneous nucleation of GaOOH was enhanced by coating thin metal oxide (SnO2, rutile TiO 2, anatase TiO2, and MgO) underlayers on quartz glass substrates, thereby resulting in the formation of uniform films. Transparent β-Ga2O3 films were obtained by heat-treatments at higher temperatures. Upon excitation by ultraviolet light (250 nm), the β-Ga2O3 films exhibited visible green luminescence.
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