The interfacial electronic states associated with Al and Ga overlayers on cleaved GaAs (110) surfaces are studied by ultraviolet photoemission spectroscopy (UPS) and low energy electron diffraction (LEED). Deposition of Al or Ga can produce valence-band spectra nearly devoid of new structure. Sb produces quite significant changes in the surface valence band and is shown as a contrasting example. Pseudopotential calculations from the literature for Al- and Ga-ordered overlayers are found to be in somewhat better agreement with the data than the corresponding tight-binding calculations, particularly in the adatom states which lie above the GaAs valence-band maximum (VBM), although neither calculation gives a good description of the observed overlayer states. It is shown that Al and Ga most likely form two-dimensional clusters or rafts on the surface at submonolayer coverage which are not in registry with the GaAs surface lattice. A comparison is made with results by other workers for Al, Ga, and In on GaAs and Si.
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Skeath et al. (1980) studied this question.