Studies On GaAs Surface Properties And Surface Oxidation Excited By UV Light

Gallium Arsenide (GaAs) is one of the most important compound semiconductor materials for national defense and satellites communication due to its high electron mobility and direct band gap. However, the development of GaAs devices is limited by its undesirable surface properties. In this thesis, a series of modern surface analytical techniques were used to study the surface properties of GaAs, and surface oxidation reaction of GaAs excited by UV light. The reaction kinetic mechanism was set up. The new surface treatment method was applied in GaAs MESFET (metal-semiconductor field-effect transistor) fabrication. Following significant results were obtained:1. A measurement method for accurately determining the surface composition and the thickness of oxide layer on GaAs surface with X-ray photoelectron spectroscopy (XPS) was established. The results shows that the native oxide layer on GaAs surface is composed of Ga2O3,As2O5,As2O3 and elemental As; and the Ga/As atomic ratio is drifted off the stoichiometry far away. The thickness of oxide layer on GaAs surface is increased with the Ga/As atomic ratio. 2. Some organic solvents were firstly used as sulfur passivation medium for Na2S and (NH4)2S to treat the GaAs surface. With the decrease of solution dielectric constant, the thickness of the sulfide layer grown on GaAs surface increases. The Soft-Hard Acid-Base Theory was used to interpret the experimental results for the first time, the softness of sulfur, which was a Lewis base, was changed by solvents, and the reactivity of sulfur atom was changed. 3. The oxidation process of GaAs surface induced by ultraviolet light was systemically investigated for the first time. The effects of the reaction atmosphere, the UV intensity, the distance between sample and UV source, and supplementary ozone enhance apparatus on GaAs surface oxidation were quantitatively investigated. The result shows that the oxide layer was grown on GaAs surface, the polluted carbon was removed after UV/ozone treated. The oxide on GaAs surface is made up of Ga2O3 and As2O3 and the Ga /As atomic ratio close to unity after UV/ozone exposing within 30 minute. The thickness of oxide layer can be controlled by the exposing time. A effective passivation layer on GaAs was obtained by this method.The reaction process of GaAs oxidation induced by UV/ozone has two different stages. A new reaction mechanism was set forth, in which not only the oxygen molecular could be excited but also the valence electrons of the GaAs, and then reacted each other. 4. The new GaAs surface preparing method with the UV/ozone technique was successively applied in GaAs MESFET fabrication for the first time. The GaAs MESFET performances are obviously modified, the output power and the static endurance are enhanced.