Charge transfer to oxygen chemisorbed on cleaved GaAs(110) surfaces

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Abstract
The change of the work function of cleaved GaAs(110) surfaces due to the chemisorption of oxygen was measured at room temperature by using the Kelvin method. With increasing exposure to oxygen the contact potential first increases and then decreases. Using the dependence of the band bending on the oxygen doses as determined by Spicer and coworkers the change of the ionization energy was calculated. The experimental data show that the ionization energy linearly increases by ?0.4 eV up to a coverage of ϑ?0.6 and then decreases; i.e., the chemisorbed oxgen is charged negatively. The initial slope of the ΔI-vs-ϑ curve amounts to 0.65 eV per monolayer and gives μn/εs=0.04 eo Å. This result is explained in a simple model of localized bonds between surface arsenic and chemisorbed oxygen and then results in a charge transfer of approximately –0.28 eo to the chemisorbed oxygen.

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