Studies of Oxidation on GaAs（100）Surface by XPS

X-ray photoelectron spectroscopy（XPS）was used to study two different oxidation treatments on the GaAs（100）surface———the thermal oxidation in the air，and the ultraviolet-light oxidation in the UV-ozone. A series of properties including the oxide composition，chemical states，the surface Ga/As atomic ratio and the thickness of the oxide layer grown on GaAs surface were compared. The results indicate that the oxide composition，the surface Ga / As atomic ratio and the thickness of the oxide layer oxide on GaAs surface are different for different oxidation methods. The oxides on GaAs surface grown by thermal oxidation in the air are composed of Ga2O3，As2O5，As2O3 and elemental As；and the Ga/As atomic ratio is drifted off the stoichiometry far away. The Ga/As atomic ratio of oxide layer on GaAs surface is increases with the thickness of oxide. However，the oxides on GaAs surface grown by UV-ozone are made up of only Ga2O3 and As2O3，As2O5 and elemental As are not detected，the Ga/As atomic ratio is close to unity. The thickness of oxide layer on GaAs can be controlled by the UV exposing time. The mechanism of oxidation of GaAs is also discussed. The UV-light radiation not only causes the oxygen molecular excited forming atomic oxygen，but also induces the valence electrons of the GaAs excited from the valence band，and then the reactivity of Ga and As atom increase，and they can easily react with the excited atomic oxygen at the same reactive velocity.