Thermal vaporization and deposition of gallium oxide in hydrogen

The thermodynamics of gallium oxide vaporization and deposition in Ar-6 H-2 at elevated temperatures are described. It is shown that Ga2O3 vaporizes in H-2 as Ga2O(g) at elevated temperatures. During thermal processing the Ga2O(g) moves to cooler zones of the furnace, back reacts with H-2(g) and H2O(g) and condenses out as Ga(1) and Ga2O3(s). Upon removal from the furnace, the exposed Ga forms a ubiquitous surface oxide of Ga2O3. X-ray photoelectron spectroscopy (XPS) was used to examine heat treated Ga2O3 powders and vaporization products deposited onto SiO2 and Cu substrates. In agreement with the thermodynamic predictions, these data demonstrate that the deposition product contained Ga2O3 and metallic Ga. Analysis of the XPS spectra also revealed an intermediate oxidation state for Ga. The precise bonding of this state could not be demonstrated conclusively, but it is suggested that it may be solid Ga2O. For coherent product deposition on Cu the metallic Ga concentration increases and the Ga2O3 concentration decreases with sputtering depth, suggesting the metallic Ga in the outermost layers of the deposit is readily oxidized during air exposure. (C) 1999 Elsevier Science B.V. All rights reserved.