Abstract
In order to elucidate the passivating effects of the chalcogenide solution treatment on GaAs surfaces, we have performed first-principles Pseudopotential calculations of the GaAs(001) surfaces adsorbed with a monolayer of chalcogen atoms. It is shown that chalcogen atoms adsorb in the bridge site on both the Ga-terminated and the As-terminated GaAs surfaces and form covalent bonds with Ga or As atoms. The chalcogen-Ga bond is found to be stronger than the chalcogen-As bond. We have shown that the chalcogen-Ga bond remarkably reduces the surface state density in the GaAs mid-gap region, while the chalcogen-As bond does not. It is suggested that the chalcogen-Ga bonds are dominant on the chalcogen-treated GaAs surface and are responsible for the passivation of the surface. In addition, we infer that Se atoms can passivate GaAs(001) surfaces as effectively as S atoms, but that the passivating effect of Te atoms is weak in comparison with S and Se atoms.
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