Chemical vapour deposition and characterization of gallium oxide thin films

Gallium oxide thin films were deposited on alumina and TiO2 substrates by metal organic chemical vapour deposition using gallium tris-hexafluoroacetylacetonate (Ga(hfac)3) as precursor in the presence of oxygen. The depositions were carried out at 470 °C and 2.6 kPa leading to a growth rate of 0.7 ?mh-1. As-grown films appeared black, smooth and well adherent to the substrates. X-Ray photoelectron spectroscopy (XPS) analysis revealed stoichiometric Ga2O3 with a low carbon content (less than 5%) and almost undetectable fluorine. As-deposited Ga2O3 films were X-ray amorphous, but the onset of a crystallization process was evident after annealing in dry air at 700°C. Moreover, after thermal treatment, the films became carbon free and transparent in the visible range. The effect of annealing at different temperatures on the film structure was investigated by X-ray diffraction. A phase modification from amorphous to polycrystalline Ga2O3 was observed after thermal treatment at temperatures from 600 to 1000°C. As shown by secondary ion mass spectrometry (SIMS) studies, Al diffusion into Ga2O3 films was detected after annealing at 1000°C when pure Al2O3 was used as substrate; this diffusion was completely inhibited using a TiO2 film as buffer layer with a thickness of at least 4 ?m