X-RAY PHOTOEMISSION SPECTROSCOPY STUDIES OF CESIUM AND OXYGEN ON GAAS(100)

We have studied the interface formation of Cs on an As rich GaAs(100) surface and the subsequent oxidation of the cesiated surface using x-ray photoemission spectroscopy at room temperature. Several aspects of this interface are in sharp contrast to the nonreacting Cs/GaAs (110) interface. We found that Cs disrupted the GaAs (100) surface and caused As to segregate. Unlike the one monolayer (ML) saturation coverage for Cs/GaAs(110) at room temperature, no saturation coverage for Cs/GaAs (100) could be found. Further exposure to oxygen seemed to resurface the Cs atoms originally buried under the segregated As. The work function reduction was found to be 3.1 eV at Cs coverage of 3.0 ML, and the work function increased by 0.45 eV after 100 L oxygen, unlike the work function decrease found on cesiated GaAs(110). A feature of the conduction band electronic states of GaAs, which is below the vacuum level for a clean surface, was observed to appear in the secondary electron spectrum during the process of cesiation.