Evolution of Surface-Assisted Oxidation of GaAs (100) by Gas-Phase N2O, NO, and O2 under Near-Ambient Pressure Conditions

An in situ near-ambient pressure X-ray photoelectron spectroscopy (NAP XPS) study of the interfacial chemistry between GaAs (100) and three oxidants, N2O, NO, and O-2, was conducted at a wide range of pressures and temperatures. The enhancement of surface oxidation was achieved mainly by the formation of Ga2O and Ga2O3, both under elevated pressure and/or temperature conditions. Based on changes in the photoelectron spectra, the extent of surface oxidation due to the dissociative adsorption of oxidants was greatest when NO was introduced, followed by O-2 and then N2O, that is, NO > O-2 > N2O, at elevated pressures and room temperature. A similar order in the extent of oxidation also was observed at higher temperatures; however, when the temperature was above 673 K, O-2 produced the most efficient surface oxidation, followed by NO and then N2O, that is, O-2 = NO > N2O. The distinctive chemical behaviors of the three oxidants depend on surface interaction energetics and bond dissociation kinetics, involving primarily factors such as bond dissociation energies of the oxidants and their electronic configurations and properties. The electronic configuration of the oxidant mainly determines the nature of its adsorption onto the GaAs surface (the bonding strength) and is an important prerequisite for the subsequent dissociation and oxidation processes of the GaAs (100) surface. Once the oxidant properties required for absorption are fulfilled, the bond dissociation energy generally is influenced by surface temperature, and it becomes a controlling parameter for the oxidation of GaAs surfaces. A comparison between the results of our study, which was performed under near-ambient pressure conditions, and previous studies performed under vacuum conditions showed significant differences in the extent of oxidation on the GaAs surface, particularly at elevated temperatures. It also allowed the detection of intermediate species, which were converted later to the final products of the oxidation event. Our results may contribute to a better understanding of oxidation mechanisms and to the technological improvement of surface-passivated GaAs-based, semiconductor devices.