Experimental and theoretical investigation of chemisorbed ga on si(111)

Abstract

Study of the lattice location of Ga adsorbed from weakly acidic methanol solution on chemically cleaned Si(111) surfaces has been carried out by an x-ray standing wave (XSW) technique using a conventional Mo Ka x-ray source. XSW is a very sensitive and precise technique to determine impurity atom locations normal to the diffraction planes. In addition to measurements of adatom locations normal to the crystal surface plane, the atom locations relative to planes inclined to the surface were measured. Self-consistent field Hartree-Fock cluster investigations were carried out for Ga on Si(111) surfaces for different high-symmetry adsorption sites such as substitutional, atop, threefold open, and threefold eclipsed to determine the minimum energy positions. The effect of lattice relaxation was studied for the eclipsed site alone. Analyzing the XSW results together with the bond lengths and binding energies derived from cluster calculations indicates that Ga coadsorbs at the atop and threefold relaxed eclipse sites. Also it is shown that the ultraviolet photoemission spectra for these two sites obtained from cluster calculation explain satisfactorily the observed spectrum for Ga adsorbed on Si(111).