title: Atomic imaging of nucleation of trimethylaluminum on clean and H2O functionalized Ge(100) surfaces.
abstract: The direct reaction of trimethylaluminum (TMA) on a Ge(100) surface and the effects of monolayer H(2)O pre-dosing were investigated using ultrahigh vacuum techniques, such as scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). At room temperature (RT), a saturation TMA dose produced 0.8 monolayers (ML) of semi-ordered species on a Ge(100) surface due to the dissociative chemisorption of TMA. STS confirmed the chemisorption of TMA passivated the bandgap states due to dangling bonds. By annealing the TMA-dosed Ge surface, the STM observed coverage of TMA sites decreased to 0.4 ML at 250 °C, and to 0.15 ML at 450 °C. XPS analysis showed that only carbon content was reduced during annealing, while the Al coverage was maintained at 0.15 ML, consistent with the desorption of methyl (-CH(3)) groups from the TMA adsorbates. Conversely, saturation TMA dosing at RT on the monolayer H(2)O pre-dosed Ge(100) surface followed by annealing at 200 °C formed a layer of Ge-O-Al bonds with an Al coverage a factor of two greater than the TMA only dosed Ge(100), consistent with Ge-OH activation of TMA chemisorption and Ge-H blocking of CH(3) chemisorption. The DFT shows that the reaction of TMA has lower activation energy and is more exothermic on Ge-OH than Ge-H sites. It is proposed that the H(2)O pre-dosing enhances the concentration of adsorbed Al and forms thermally stable Ge-O-Al bonds along the Ge dimer row which could serve as a nearly ideal atomic layer deposition nucleation layer on Ge(100) surface.
authors.affiliation: Materials Science and Engineering Program, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: Joon Sung
authors.initials: JS
authors.lastname: Lee
authors.forename: Tobin
authors.initials: T
authors.lastname: Kaufman-Osborn
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Melitz
authors.forename: Sangyeob
authors.initials: S
authors.lastname: Lee
authors.forename: Annelies
authors.initials: A
authors.lastname: Delabie
authors.forename: Sonja
authors.initials: S
authors.lastname: Sioncke
authors.forename: Matty
authors.initials: M
authors.lastname: Caymax
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Pourtois
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Kummel