ON THE DECAPPING OF AS4-CAPPED GAAS(111) SURFACES - AN ANGLE-RESOLVE CORE-LEVEL PHOTOEMISSION-STUDY

Angle-resolved core-level photoemission measurements have been performed using synchrotron radiation on GaAs(111BAR) surfaces prepared by thermal decapping of As4-capped samples grown by molecular-beam epitaxy. Using a least-squares fitting routine with strict parameter conditions, the Ga3d and As3d core-level spectra have been decomposed. No surface component is needed for the fitting for the Ga3d spectra, whereas at least two surface components, the intensities of which vary with polar emission angle with respect to that of the bulk component, are required for the As3d spectra. A layer model has been constructed to explain these results, which requires the presence of an As overlayer on the surface. The number of As atoms of the overlayer depends on the heating process and two variants, corresponding to 0.8 and 0.4 of a monolayer respectively, have been obtained in the present study. These results are discussed in relation to literature models of the surface structure.