Thermal vaporization and deposition of gallium oxide in hydrogen

Abstract The thermodynamics of gallium oxide vaporization and deposition in Ar–6% H 2 at elevated temperatures are described. It is shown that Ga 2 O 3 vaporizes in H 2 as Ga 2 O(g) at elevated temperatures. During thermal processing the Ga 2 O(g) moves to cooler zones of the furnace, back reacts with H 2 (g) and H 2 O(g) and condenses out as Ga(l) and Ga 2 O 3 (s). Upon removal from the furnace, the exposed Ga forms a ubiquitous surface oxide of Ga 2 O 3 . X-ray photoelectron spectroscopy (XPS) was used to examine heat treated Ga 2 O 3 powders and vaporization products deposited onto SiO 2 and Cu substrates. In agreement with the thermodynamic predictions, these data demonstrate that the deposition product contained Ga 2 O 3 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 Ga 2 O. For coherent product deposition on Cu the metallic Ga concentration increases and the Ga 2 O 3 concentration decreases with sputtering depth, suggesting the metallic Ga in the outermost layers of the deposit is readily oxidized during air exposure.